SUBSTRATE

TECHNICAL FIELD

[0001] Embodiments of the disclosure relate to thin-film deposition apparatuses and methods, particularly to apparatuses and methods for coating flexible substrates with a stack of thin layers, particularly in roll-to-roll (R2R) deposition systems. Some embodiments relate to apparatuses and methods for coating one or both main surfaces of a flexible substrate with a stack of layers, respectively, such as for thin-film solar cell production, thin-film battery production, and flexible display production. Further embodiments relate to methods for aligning thin-film deposition apparatuses.

BACKGROUND [0002] Processing of flexible substrates, such as plastic films or foils, is in high demand in the packaging industry, semiconductor industries and other industries. Processing may consist of coating of a flexible substrate with a material, such as a metal, a semiconductor and a dielectric material, etching and other processing actions conducted on a substrate for the respective applications. Systems performing this task generally include a coating drum, e.g. a cylindrical roller, coupled to a processing system with a roller assembly for transporting the substrate, and on which at least a portion of the substrate is coated. Roll-to-roll (R2R) coating systems can provide a high throughput.

[0003] Therein, a coating process such as a CVD process or a PVD process, particularly a sputter process, can be utilized for depositing thin layers onto flexible substrates. Roll-to-roll deposition systems are understood in that a flexible substrate of a considerable length, such as one kilometre or more, is uncoiled from a storage spool, coated with a stack of thin layers, and recoiled again on a wind-up spool. In the manufacture of thin film batteries as well as in the display industry and the photovoltaic (PV) industry, the demand for roll-to- roll deposition systems is also increasing. For example, touch panel elements, flexible displays, and flexible PV modules result in an increasing demand for depositing suitable layers in R2R-coaters. [0004] In some applications, a layer stack with two or more layers may be deposited on a first main surface of the flexible substrate. Sometimes, a second stack of layers may be deposited on the second main surface of the flexible substrate opposite the first main surface. When a substrate is to be coated on two sides, the coating drums should be carefully designed and operated to avoid damage of a first already coated surface of the substrate during coating of the second main surface.

[0005] In view of the above, a deposition apparatus for coating one or both main surfaces of a flexible substrate with a stack of layers is provided, wherein the layers have a high uniformity and a low number of defects per surface area that overcomes at least some of the problems in the art.

SUMMARY

[0006] In light of the above, a deposition apparatus for coating a flexible substrate, a method of coating a flexible substrate, as well as a method of aligning a deposition apparatus according to the independent claims are provided. Further aspects, advantages, and features are apparent from the dependent claims, the description, and the accompanying drawings.

[0007] According to embodiments described herein, a deposition apparatus for coating a flexible substrate is provided. The deposition apparatus includes: a first spool chamber housing a storage spool for providing the flexible substrate; a deposition chamber arranged downstream from the first spool chamber and including a coating drum for guiding the flexible substrate past a plurality of deposition units; a second spool chamber arranged downstream from the deposition chamber and housing a wind-up spool for winding the flexible substrate thereon after deposition; and a roller assembly configured to transport the flexible substrate along a partially convex and partially concave substrate transportation path from the first spool chamber to the second spool chamber.

[0008] According to a further aspect described herein, a method of coating a flexible substrate with a stack of layers, particularly with a deposition apparatus described herein, is described, wherein the flexible substrate is transported along a partially convex and partially concave substrate transportation path from a first spool chamber to a second spool chamber. The method includes: unwinding the flexible substrate from a storage spool provided in the first spool chamber; depositing at least one first layer of the stack of layers on a first main surface of the flexible substrate, while the flexible substrate is guided by a coating drum provided in a deposition chamber; and winding the flexible substrate on a wind-up spool provided in the second spool chamber after deposition. [0009] According to one embodiment described herein, a method of aligning a deposition apparatus is provided, wherein the deposition apparatus comprises a roller assembly configured to transport a flexible substrate along a partially convex and partially concave substrate transportation path from a first spool chamber to a second spool chamber. In particular, a method of aligning a deposition apparatus according to embodiments described herein is provided. The method includes: defining at least one guiding roller of the roller assembly as reference roller; and aligning the rotation axes of two or more remaining guiding rollers of the roller assembly with respect to a first rotation axis of the reference roller such as to extend parallel to the first rotation axis of the reference roller.

[0010] Embodiments are also directed to apparatuses for carrying out each of the disclosed methods and include apparatus parts for performing each described method feature. The method features may be performed by way of hardware components, a computer programmed by appropriate software, by any combination of the two or in any other manner. Furthermore, embodiments are also directed to methods which the described apparatus operates with or which the described apparatus is manufactured by. The method includes method features for carrying out functions of the apparatus or manufacturing parts of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS [0011] Some of the above indicated and other more detailed aspects of embodiments will be described in the following description and partially illustrated with reference to the figures.

FIG. 1 shows a sectional schematic view of a deposition apparatus according to embodiments described herein; FIG. 2 shows a sectional schematic view of a deposition apparatus according to embodiments described herein;

FIG. 3 shows a sectional schematic view of a deposition apparatus according to embodiments described herein;

FIG. 4 shows a sectional schematic view of a deposition apparatus according to embodiments described herein;

FIG. 5 shows a more detailed sectional view of a deposition apparatus according to embodiments described herein;

FIG. 6 shows a schematic view of a heatable roller that may be used in some of the embodiments described herein; FIG. 7 shows a sectional schematic view of a coating drum that may be used in some of the embodiments described herein;

FIG. 8 shows a sectional schematic view of a coating drum that may be used in some of the embodiments described herein;

FIG. 9 shows an enlarged schematic view of a part of a deposition chamber that may be used in some of the embodiments described herein; FIG. 10 shows a schematic view of an AC sputter source that may be used in some of the embodiments described herein;

FIG. 11 shows a schematic view of a DC sputter source that may be used in some of the embodiments described herein; FIG. 12 shows a schematic view of a double DC planar cathode sputter source that may be used in some of the embodiments described herein;

FIGS. 13A-13C show exemplary schematic layouts of a sequence of deposition units which may be provided around a coating drum in a deposition chamber according to embodiments described herein; FIG. 14 shows a flowchart for illustrating a method of coating of a flexible substrate according to embodiments described herein, and

FIG. 15 shows a flowchart for illustrating a method of aligning a deposition apparatus according to embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS [0012] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in the figures. Within the following description of the drawings, the same reference numbers refer to same components. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation and is not meant as a limitation. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield yet a further embodiment. It is intended that the description includes such modifications and variations.

[0013] It is noted that a flexible substrate as used within the embodiments described herein is typically bendable. The term "flexible substrate" or "substrate" may be synonymously used with the term "foil" or the term "web". In particular, it is to be understood that embodiments of the deposition apparatus described herein can be utilized for coating any kind of flexible substrate, e.g. for manufacturing flat coatings with a uniform thickness, or for manufacturing coating patterns or coating structures in a predetermined shape on the flexible substrate or on top of an underlying coating structure. For example, electronic devices may be formed on the flexible substrate by masking, etching and/or depositing. For example, a flexible substrate as described herein may include materials like PET, HC-PET, PE, PI, PU, TaC, OPP, CPP, one or more metals, paper, combinations thereof, and already coated substrates like Hard Coated PET (e.g. HC-PET, HC-TaC) and the like. In some embodiments, the flexible substrate is a COP substrate provided with an index matched (IM) layer on both sides thereof.

[0014] Embodiments described herein generally relate to apparatuses and methods for coating a flexible substrate with a stack of layers. A "stack of layers" as used herein may be understood as two, three or more layers deposited on top of each other, wherein the two, three or more layers may be composed of the same material or of two, three or more different materials. For example, the stack of layers may include one or more conductive layers, e.g. a metal layer, and/or one or more isolating layers, e. g. a dielectric layer. In some embodiments, the stack of layers may include one or more transparent layers, e.g. a Si0 ₂ layer or an ITO layer. In some embodiments, at least one layer of the stack of layers may be a conductive transparent layer, e.g. an ITO layer. For example, an ITO layer may be beneficial for capacitive touch applications, e.g. for touch panels. In some embodiments, one or more layers may be patterned. In some embodiments, one or more Si0 ₂ layers may be deposited on a first main surface of the substrate, followed by one or more ITO layers, optionally followed by one or more metal layers, e.g. copper layers. In some implementations, also the second main surface of the substrate may be coated, e.g. with the same stack of layers or with a different stack of layers in a deposition apparatus according to embodiments described herein. [0015] According to some embodiments, which can be combined with other embodiments described herein, the deposition apparatus may be configured for a substrate length of 500 m or more, 1000 m or more, or several kilometres. The substrate width can be 300 mm or more, particularly 500 mm or more, more particularly 1 m or more. According to an example, the substrate width is about 1.4 m. For instance, a deposition apparatus configured for a substrate width of about 1.4 m may be configured for depositing one or more layers of ITO, e.g. for capacitive touch applications. According to another example, the substrate width is about 1.7 m. For instance, a deposition apparatus configured for a substrate width of about 1.7 m may be configured for depositing one or more layers on the substrate, e.g. for window film applications. The substrate width can be 3 m or less, particularly 2 m or less. Typically, the substrate thickness can be 20 μιη or more and 1 mm or less, particularly from 50 μιη to 200 μιη.

[0016] According to some embodiments, some chambers or all chambers of the deposition apparatus may be configured as vacuum chambers that can be evacuated. For instance, the deposition apparatus may include components and equipment allowing for the generation of or maintenance of a vacuum in at least a part of the processing system, such as in the spool chambers and in the deposition chambers. The deposition apparatus may include vacuum pumps, evacuation ducts, vacuum seals and the like for generating or maintaining a vacuum at least in parts of the deposition apparatus. For instance, each chamber may have individual corresponding vacuum pumps or pumping stations for evacuating the respective chamber. In some embodiments, two or more turbo-vacuum pumps may be connected to at least one vacuum chamber, particularly to each vacuum chamber of the deposition apparatus. [0017] According to some embodiments, the vacuum chambers of the deposition apparatus are adapted for operating under vacuum conditions form a vacuum tight enclosure, i.e. can be evacuated to a vacuum with the pressure of 10 mbar or less, particularly 1 mbar or less, or even to a pressure between lxl O ⁴ and lxl 0 ² mbar or less during deposition. Different pressure ranges are to be considered specifically for PVD processes such as sputtering, which may be conducted in the 10 ^~3 -mbar range, and CVD processes, which are typically conducted in the mbar-range. Further, the vacuum chambers can be evacuated to a background vacuum with a pressure of lxlO ⁶ mbar or less. Background pressure means the pressure which is reached by evacuation of a chamber without any inlet of any gases. [0018] FIG. 1 illustratively shows a deposition apparatus 100 for coating a flexible substrate 10 with a stack of thin layers. The deposition apparatus 100 includes a plurality of vacuum chambers that can be evacuated to a pressure below atmospheric pressure. The deposition apparatus 100 depicted in FIG. 1 includes a first spool chamber 110, a deposition chamber 120 arranged downstream from the first spool chamber 110, and a second spool chamber 150 arranged downstream from the deposition chamber 120. The first spool chamber 110 may be considered as a vacuum chamber configured for housing a storage spool with a flexible substrate wound thereon, and the second spool chamber 150 may be considered as a vacuum chamber configured for housing a wind-up spool for winding the coated flexible substrate thereon after deposition.

[0019] The deposition apparatus 100 may be configured such that the flexible substrate 10 can be guided from the first spool chamber 110 to the second spool chamber 150 along a substrate transportation path, wherein the substrate transportation path may lead through the deposition chamber 120. The flexible substrate can be coated with the stack of layers in the deposition chamber 120. A roller assembly comprising a plurality of rolls or rollers can be provided for transporting the substrate along the substrate transportation path, wherein two or more rollers, five or more rollers, or ten or more rollers of the roller assembly may be arranged between the storage spool and the wind-up spool. In the present disclosure, the roller assembly may also be referred to as winding system.

[0020] According to some embodiments herein, the substrate transportation path may be partially convex and partially concave. In other words, the substrate transportation path is partially curved to the right and partially curved to the left such that some guiding rollers contact a first main surface of the flexible substrate and some guiding rollers contact a second main surface of the flexible substrate opposite the first main surface. For example, the first guiding roller 107 in FIG. 1 contacts a second main surface of the flexible substrate and the flexible substrate is bent to the left while being guided by the first guiding roller 107 ("convex" section of the substrate transportation path). The second guiding roller 108 in FIG. 1 contacts a first main surface of the flexible substrate and the flexible substrate is bent to the right while being guided by the second guiding roller 108 ("concave" section of the substrate transportation path). A compact deposition apparatus may be provided that may be suitable also for two-side deposition, because the substrate transportation path changes directions several times between the first spool chamber and the second spool chamber in the concave section, i.e. in sections where the first main surface of the substrate contacts a support surface, and in convex sections, i.e. in sections where the second main surface of the substrate contacts a support surface. [0021] The terms "upstream from" and "downstream from" as used herein may refer to the position of the respective chamber or of the respective component with respect to another chamber or component along the substrate transportation path. For example, during operation, the substrate is guided from the first spool chamber 110 through the deposition chamber 120 and subsequently guided to the second spool chamber 150 along the substrate transportation path via the roller assembly. Accordingly, the deposition chamber 120 is arranged downstream from the first spool chamber 110, and the first spool chamber 110 is arranged upstream from the deposition chamber 120. When, during operation, the substrate is first guided by or transported past a first roller or a first component and subsequently guided by or transported past a second roller or a second component, the second roller or second component is arranged downstream from the first roller or first component.

[0022] The first spool chamber 110 is configured to accommodate a storage spool 112, wherein the storage spool 112 may be provided with the flexible substrate 10 wound thereon. During operation, the flexible substrate 10 can be unwound from the storage spool 112 and transported along the substrate transportation path from the first spool chamber toward the deposition chamber. The term "storage spool" as used herein may be understood as a roll on which a flexible substrate to be coated is stored. Accordingly, the term "wind-up spool" as used herein may be understood as a roll adapted for receiving the coated flexible substrate. The term "storage spool" may also be referred to as a "supply roll" herein, and the term "wind-up spool" may also be referred to as a "take-up roll" herein.

[0023] In some embodiments, which may be combined with other embodiments described herein, a storage spool drive may be provided for rotating the storage spool 112 for unwinding the flexible substrate therefrom. In other words, the storage spool 112 may be an actively driven roller.

[0024] The deposition chamber 120 may be arranged directly downstream from the first spool chamber 110, as is schematically depicted in FIG. 1. Alternatively, one or more further vacuum chambers, e.g. a cleaning chamber, may be arranged between the first spool chamber 110 and the deposition chamber 120. In the embodiment shown in FIG. 1, the flexible substrate exiting the first spool chamber 110 through a small passage such as a slit may directly enter the deposition chamber 120.

[0025] The first spool chamber 110 may be configured as a load-lock chamber. In other words, the first spool chamber 110 may be flooded, e.g. for exchanging the storage spool in the first spool chamber with a new storage spool, without impairing the vacuum in the remaining vacuum chambers. A passage or opening in the wall between the first spool chamber 110 and the vacuum chamber arranged downstream from the first spool chamber can be sealed. Accordingly, other vacuum chambers of the deposition apparatus 100, and particularly the deposition chambers, can be maintained in an evacuated state during an exchange of a storage spool in the first spool chamber, e.g. when the flexible substrate has been unwound from the storage spool.

[0026] In some embodiments, which may be combined with other embodiments described herein, the flexible substrate 10 may be guided through openings, e.g. slits, in the walls separating the vacuum chambers from each other, respectively. For example, a slit in the wall between two vacuum chambers may be adapted for guiding the substrate from one vacuum chamber to another vacuum chamber, respectively. In some embodiments, the opening may be provided with a sealing device in order to separate, at least substantially, the pressure conditions of the two vacuum chambers linked by the opening. For instance, if the chambers linked by the opening provide different pressure conditions, the opening in the wall may be designed so as to maintain the respective pressure in the chambers. [0027] According to embodiments described herein, at least one gap sluice or load- lock valve may be provided for separating two adjacent vacuum chambers from each other, e.g. for separating the first spool chamber from the vacuum chamber arranged downstream therefrom. The at least one gap sluice may be configured such that the flexible substrate can move therethrough and the gap sluice can be opened and closed for providing a vacuum seal. Thus, for instance, the first spool chamber 110 can be vented while the deposition chamber 120 can be maintained under technical vacuum.

[0028] For example, a sealing device 105 arranged between the first spool chamber 110 and the deposition chamber 120 is schematically indicated in FIG. 1. However, it is to be understood that further sealing devices providing a corresponding functionality may be provided between other adjacent vacuum chambers, e.g. between the deposition chamber 120 and the second spool chamber 150. Accordingly, beneficially the winding chambers (i.e. the first spool chamber 110 and the second spool chamber 150) may be vented or evacuated independently, in particular independently from the deposition chamber.

[0029] The sealing device 105 may include an inflatable seal configured to press the substrate against a flat sealing surface. Accordingly, the opening in the wall between the first spool chamber 110 and the deposition chamber 120 can be sealed, even when the flexible substrate may be present in the opening. Removal of the flexible substrate may not be necessary for closing or opening the sealing device.

[0030] Yet, also other devices or apparatuses for selectively opening and closing a gap sluice can be utilized, wherein opening and closing, i.e. having an open substrate path and a vacuum seal, can be conducted while the substrate is inserted. The gap sluice for closing the vacuum seal while the substrate is inserted allows for particularly easy exchange of the substrate, as the substrate from the new roll can be attached to the substrate from the previous roll.

[0031] Although the sealing devices, slits, openings or gap sluices are described with respect to guiding the flexible substrate from the first spool chamber to the following vacuum chamber, the sealing devices, slits, openings or gap sluices as described herein may also be used between other chambers or parts of the deposition apparatus.

[0032] The deposition chamber 120 may include a coating drum 122 configured for guiding the flexible substrate 10 past a plurality of deposition units 121. The coating drum 122 may be rotatable around a rotation axis 123. The coating drum may include a curved substrate support surface, e.g. an outer surface of the coating drum 122, on which the flexible surface can be guided past the plurality of deposition units 121. While guiding the flexible substrate past the plurality of deposition units 121, the flexible substrate may be in direct contact with the substrate support surface of the coating drum, which may be cooled. The temperature of the flexible substrate may be reduced during deposition, when the flexible substrate is in direct thermal contact with the coating drum. [0033] The flexible substrate 10 may be coated with one or more thin layers by the plurality of deposition units 121. For example, the deposition units of the plurality of deposition units 121 may be arranged in a circumferential direction around the coating drum 122, as schematically depicted in FIG. 1. The deposition chamber 120 may include two or more deposition units arranged next to each other along the substrate transportation path. A first main surface of the flexible substrate may be coated, while a second main surface of the flexible substrate opposite the first main surface, i.e. the rear surface of the flexible substrate, may be in contact with the curved substrate support surface of the coating drum. [0034] As the coating drum 122 rotates, the flexible substrate is guided past the deposition units which face toward the curved substrate support surface of the coating drum, so that the first main surface of the flexible substrate can be coated while being moved past the deposition units at a predetermined speed.

[0035] In some embodiments, one or more rollers, e.g. guiding rollers, of the roller assembly may be arranged between the storage spool 112 and the coating drum 122 and/or downstream from the coating drum 122. For example, in the embodiment shown in FIG. 1, two guiding rollers are provided between the storage spool 112 and the coating drum 122, wherein at least one guiding roller may be arranged in the first spool chamber and at least one guiding roller may be arranged in the deposition chamber upstream from the coating drum 122. In some embodiments, three, four, five or more, particularly eight or more guiding rollers are provided between the storage spool and the coating drum. The guiding rollers may be active or passive rollers.

[0036] An "active" roller or roll as used herein may be understood as a roller that is provided with a drive or a motor for actively moving or rotating the respective roller. For example, an active roller may be adjusted to provide a predetermined torque or a predetermined rotational speed. Typically, the storage spool 112 and the wind-up spool 152 may be provided as active rollers. In some embodiments, the coating drum may be configured as an active roller. Further, active rollers can be configured as substrate tensioning rollers configured for tensioning the substrate with a predetermined tensioning force during operation. A "passive" roller as used herein may be understood as a roller or roll that is not provided with a drive for actively moving or rotating the passive roller. The passive roller may be rotated by the frictional force of the flexible substrate that may be in direct contact with an outer roller surface during operation. [0037] In the present disclosure, a "roll" or "roller" may be understood as a device which provides a surface with which the flexible substrate or part of the flexible substrate may come in contact during transport of the flexible substrate along the substrate transportation path in the deposition apparatus. At least a part of the roller as referred to herein may include a circular-like shape for contacting the flexible substrate before or after deposition. The substantially cylindrical shape may be formed about a straight longitudinal axis. According to some embodiments, a roller may be a guiding roller adapted to guide a substrate while the substrate is transported, e.g. during a deposition process or while the substrate is present in the deposition apparatus. The roller may be configured as a spreader roller, i.e. an active roller adapted for providing a defined tension for the flexible substrate. A spreader roller may also be referred to as a k-roller. As exemplarily shown in FIG. 5, the spreader roller 117 can be arranged downstream, particularity directly downstream, from the coating drum 122. Further, the roller as described herein may be configured as a processing roller, e.g. a coating drum, for supporting the flexible substrate while being coated, a deflecting roller for deflecting the substrate along the curved substrate transportation path, an adjusting roller, a storage spool, a wind-up spool etc. [0038] In some embodiments, at least one deflecting roller may be configured for deflecting the flexible substrate in a clockwise direction, and at least one deflecting roller may be configured for deflecting the flexible substrate in a counterclockwise direction. For example, in the embodiments shown in FIG. 1, a first guiding roller 107 deflects the flexible substrate in a counterclockwise direction (i.e. the flexible substrate is bent to the left when moved along the substrate transportation path), and a second guiding roller 108 deflects the flexible substrate in a clockwise direction (i.e. the flexible substrate is bent to the right when moved along the substrate transportation path). Therein, the first guiding roller 107 may rotate in a counterclockwise direction, and the second guiding roller 108 may rotate in a clockwise direction. A partially convex and partially concave substrate transportation path can be provided. Guiding rollers rotating in a clockwise direction during transport of the flexible substrate may be referred to herein as "clockwise rotating rollers" and rollers rotating in a counterclockwise direction during transport of the flexible substrate may be referred to herein as "counterclockwise rotating rollers". [0039] In some embodiments, at least one guiding roller, e.g. the first guiding roller 107, contacts the first main surface of the substrate, and at least one guiding roller, e.g. the second guiding roller 108, contacts the second main surface of the substrate, i.e. the surface opposite the first main surface. Accordingly, cleaning of both main surfaces of the flexible substrate may be beneficial, in order to reduce the risk of winding defects.

[0040] According to some implementations, the rollers as described herein may be mounted to low friction roller bearings, particularly with a dual bearing roller architecture. Accordingly, roller parallelism of the transportation arrangement as described herein can be achieved and a transverse substrate "wandering" during substrate transport may be eliminated. Accordingly, beneficially the roller assembly as described herein provides for a high precision winding system with low friction roller bearings.

[0041] In some embodiments, a guiding roller which guides the flexible substrate along the substrate transportation path may also be configured for conducting a tension measurement. According to typical embodiments, at least one tension measurement roller, e.g. a passive roller, may be provided in the deposition apparatus. Beneficially, one, two or more tension measurement rollers on both sides of the coating drum may be provided which allow for tension measurements on the winding side and on the unwinding side of the coating drum. In particular, the tension measurement rollers may be configured for measuring the tension of the flexible substrate. Accordingly, the substrate transport can be better controlled, the pressure of the substrate on the coating drum can be controlled and/or damage to the substrate can be reduced or avoided. [0042] In some embodiments, which can be combined with other embodiments described herein, the plurality of deposition units may be configured for coating the first main surface of the flexible substrate. Accordingly, a stack of layers can be deposited on the first main surface of the flexible substrate by the plurality of deposition units in the deposition chamber. In other words, according to some embodiments, only the first main surface of the flexible substrate may be coated with a stack of layers during transport of the flexible substrate along the substrate transportation path through the deposition apparatus. [0043] For also coating the second main surface of the flexible substrate, the flexible substrate with the coated first main surface may be loaded again into the first spool chamber and transported through the deposition apparatus in an inverted orientation. In the "inverted orientation" as used herein, the second main surface of the substrate, i.e. the other main surface as compared to the first pass of the flexible substrate through the deposition apparatus, is directed toward the plurality of deposition units during transport of the flexible substrate along the substrate transportation path. Accordingly, two-side deposition on the flexible substrate is possible by guiding the same flexible substrate twice through the deposition apparatus. In some embodiments, a first stack of layers is deposited on the first main surface of the flexible substrate on the first pass through the deposition apparatus, and a second stack of layers is deposited on the second main surface of the flexible substrate on the second pass through the deposition apparatus. The first stack of layers and the second stack of layers may have a corresponding thickness and/or a corresponding material sequence. In some embodiments, the flexible substrate with two coated main surfaces may be essentially symmetrical with respect to the central plane of the substrate.

[0044] In some embodiments, which may be combined with other embodiments described herein, the coating drum may be actively driven. In other words, a drive may be provided for rotating the coating drum. [0045] In some embodiments, one or more guiding rollers 113 may be arranged downstream from the coating drum 122 and upstream from the second spool chamber 150. For example, at least one guiding roller may be arranged in the deposition chamber 120 downstream from the coating drum 122 for guiding the flexible substrate 10 toward the vacuum chamber, e.g. the second spool chamber 150, arranged downstream from the deposition chamber 120, or at least one guiding roller may be arranged in the second spool chamber 150 upstream from the coating drum 122 for guiding the flexible roller in a direction essentially tangential to the substrate support surface of the coating drum, in order to smoothly guide the flexible substrate onto the wind-up spool 152. At least one or more of these guiding rollers may have functions that are discussed below in further detail.

[0046] The second spool chamber 150 may be arranged directly downstream from the deposition chamber 120. In other embodiments, one or more vacuum chambers may be arranged between the deposition chamber 120 and the second spool chamber 150. The second spool chamber 150 may be configured for housing a wind-up spool 152 for winding the flexible substrate thereon after deposition. Sealing devices may be provided in the walls between the vacuum chambers, respectively, and particularly in a wall which separates the second spool chamber 150 from the deposition chamber. For example, in the embodiments shown in FIG. 1, a sealing device 105 is provided between the deposition chamber 120 and the second spool chamber 150. The sealing device 105 may include an inflatable seal configured to press the substrate against a sealing surface. Accordingly, the opening in the wall between the deposition chamber 120 and the second spool chamber 150 can be sealed, even when the flexible substrate may be present in the opening. Removal of the flexible substrate may not be necessary for closing or opening the sealing device.

[0047] In some embodiments, which may be combined with other embodiments described herein, a wind-up spool drive may be provided for rotating the wind-up spool 152 for winding the flexible substrate thereon. In other words, the wind-up spool 152 may be an active roller.

[0048] The second spool chamber 150 may be configured as a load-lock chamber. Therein, the second spool chamber may be configured such that the wind-up spool with the coated flexible substrate wound thereon can be unloaded from the second spool chamber, while the second spool chamber 150 may be flooded. For flooding of the second spool chamber 150, a passage between the second spool chamber 150 and the vacuum chamber arranged upstream from the second spool chamber may be sealed, e.g. via the sealing device 105. Accordingly, other vacuum chambers of the deposition apparatus, and particularly the deposition chambers, can be maintained in an evacuated state during an exchange of a wind-up spool with a new wind-up spool. In some embodiments, the second spool chamber 150 may include a gap sluice or load lock valve, e.g. including a sealing device, e.g. for closing and opening a passage or slit between the second deposition chamber and the second spool chamber. The substrate may remain in the opening in a sealed state of the sealing device.

[0049] During the deposition, the deposition chamber 120 may be under medium vacuum or under high vacuum, e.g. at a pressure between lxlO ² mbar and lxlO ⁴ mbar, e.g. when sputter sources are used. The pressure inside the deposition units may be higher than the pressure in a main volume of the deposition chambers, e.g. by an order of magnitude. For example, the pressure inside the sputter deposition units during sputter deposition may be about 5x10 ^{" 3} mbar. The pressure in the first spool chamber 110 and in the second spool chamber 150 may be higher than the pressure in the deposition chambers during deposition, e.g. by one or two orders of magnitude. For example, the background pressure in the first spool chamber and/or in the second spool chamber may be between 10 ¹ mbar and 10 ^~3 mbar. One or more vacuum control units may be provided, e.g. in at least one vacuum chamber and/or in at least one deposition unit. [0050] Before, during and/or after deposition, particles may gather on the flexible substrate, which may lead to dirt and damage on the substrate's surface if not removed. Specifically, the substrate's surface may be scratched or damaged when the flexible substrate with particles formed thereon comes into contact with a support surface of a guiding roller. Those issues may also be called "winding defects". In more detail, such a defect can be a small area of the order of magnitude of 10 microns or less, where the deposited layer or even the complete flexible substrate is locally abraded. Possible sources for these defects are, for instance, particles that are located on the flexible substrate of the storage spool, and also particles that are caused by the coating process and adhere to the substrate.

[0051] Several approaches were made in the attempt to avoid the problem of winding defects. One approach is a system where only one main surface of the flexible substrate, e.g. the surface which is not coated, comes in direct contact with roller surfaces during the deposition process. However, such a design may not be suitable for two-side deposition processes and for thin film deposition processes which make use of an advanced tension control. In particular, in a deposition apparatus including a substrate transportation path with both concave and convex sections, both main surfaces of the flexible substrate may come into direct contact with a roller surface during transport. Accordingly, it may be beneficial to clean one or both main surfaces of the substrate in order to reduce the risk of winding defects.

[0052] In some embodiments, in order to avoid winding defects, the deposition apparatus may include at least one cleaning device configured for cleaning the substrate, particularly before the flexible substrate is wound on a roller or comes in direct contact with a roller surface at a high tension.

[0053] In some embodiments, which may be combined with other embodiments described herein, a first cleaning device may be provided for cleaning a first main surface of the flexible substrate, e.g. the first main surface that is coated with the stack of layers, and/or a second cleaning device may be provided for cleaning a second main surface of the flexible substrate, e.g. the rear surface of the flexible substrate opposite the first main surface.

[0054] FIG. 2 illustratively shows a deposition apparatus 100 for coating a flexible substrate 10 which includes a first cleaning device 171 and a second cleaning device 172. Most features of the deposition apparatus 100 of FIG. 2 correspond to the respective features of the deposition apparatus shown in FIG. 1, so that reference can be made to the above explanations which are not repeated here.

[0055] A first cleaning device 171 may be provided for cleaning the first main surface of the flexible substrate, and a second cleaning device 172 may be provided for cleaning the second main surface of the flexible substrate. The first cleaning device 171 and/or the second cleaning device 172 may be arranged upstream from the plurality of deposition units such that the surfaces of the flexible substrate can be cleaned before deposition in the deposition chamber.

[0056] The first main surface of the substrate may be the substrate surface that is subsequently coated in the deposition chamber, and the second main surface of the substrate may be the substrate surface opposite the first main surface. In some embodiments, the second main surface may be an uncoated substrate surface, whereas, in other embodiments, the second main surface may have been previously coated, e.g. on a first pass through the deposition apparatus. Particles or other types of contamination which may already be present on the first main surface of the flexible substrate may be removed before deposition, such that the coating quality on the first main surface can be improved. Particles or other types of contamination which may already be present on the second main surface of the flexible substrate may be removed before the second main surface (or a coating already provided thereon) comes into contact with a substrate support surface of the coating drum, such that winding defects can be avoided. [0057] In other embodiments, only the first cleaning device or only the second cleaning device may be provided. For example, only the first main surface of the substrate may be cleaned or only the second main surface that comes in contact with the substrate support surface of the coating drum may be cleaned.

[0058] In some embodiments, the first cleaning device 171 and/or the second cleaning device 172 may be arranged in a cleaning chamber 170 which may be provided downstream from the first spool chamber 110 and upstream from the deposition chamber 120, as depicted in FIG. 2. In other embodiments, the first cleaning device 171 and/or the second cleaning device 172 may be provided in the first spool chamber downstream from the storage spool 112 or in the deposition chamber 120 upstream from the coating drum 122. In some embodiments, which may be combined with other embodiments described herein, no separate cleaning chamber may be provided. Providing a cleaning chamber 170 may have the advantage of a better vacuum separation between the first spool chamber 110 which is typically flooded in regular intervals and the deposition chamber. In particular, the cleaning chamber may act as a further gas separation area between the first spool chamber and the deposition chamber. In some embodiments, only a small passage such as a slit for guiding the flexible substrate therethrough may be provided between the cleaning chamber and the deposition chamber. Accommodating the cleaning devices in a cleaning chamber 170 may have the further advantage that components of the cleaning devices can be exchanged more easily and that contaminants generated by the cleaning process may not enter the deposition chamber, but can be pumped from the cleaning chamber.

[0059] In some embodiments, which may be combined with other embodiments described herein, further cleaning devices may additionally or alternatively be provided at other positions along the substrate transportation path. For example, in the embodiment shown in FIG. 2, an after-coating cleaning device 173 may be positioned downstream from the plurality of deposition units 121. The after-coating cleaning device 173 may be configured for cleaning the surface of the coating coated on the first main surface of the flexible substrate by the plurality of deposition units 121.

[0060] Cleaning may be performed directly downstream from the plurality of deposition units 121, such that particles generated on the coating surface during coating can be reliably removed before the coated surface comes into contact with a roller surface. "Directly downstream" as used herein may imply that the flexible substrate is cleaned directly after coating without guiding the substrate to a guiding roller or pulley that could exert a pressure on the freshly coated surface. The generation of winding defects can be reduced or avoided. [0061] The purpose of the cleaning devices may be to collect particles or other types of contamination on the flexible substrate before winding up or deflecting the substrate with a high tension by a guiding roller. For example, the flexible substrate is typically pulled around the coating drum at a high tension in order to improve the thermal contact between the flexible substrate and the coating drum, such that cleaning of the second main surface of the substrate upstream from the coating drum may be beneficial. The generation of winding defects can be reduced or entirely avoided.

[0062] For example, as is depicted in FIG. 2, after deposition and before contacting any guiding roller, the (freshly coated) first main surface of the flexible substrate 10 is cleaned by the after-coating cleaning device 173. The after-coating cleaning device 173 is positioned directly downstream from the plurality of deposition units 121. Not limited to any embodiment, the after- coating cleaning device is typically configured to clean the freshly coated side of the flexible substrate. [0063] In some embodiments, the after-coating cleaning device 173 may be positioned such that the after-coating cleaning device 173 contacts the flexible substrate 10 at a position where the flexible substrate 10 is in contact with the coating drum 122, e.g. downstream from the last deposition unit of the plurality of deposition units 121 in a circumferential direction around the rotation axis 123 of the coating drum 122. At least some of the deposition units, particularly more than half of the plurality of deposition units 121, may be positioned below the rotation axis 123 of the coating drum 122, as depicted in FIG. 2.

[0064] At least some of the cleaning devices may be configured as follows. It is noted that also the after-coating cleaning devices are considered as cleaning devices herein. The functionality of the cleaning devices is explained with respect to the first cleaning device 171. The first cleaning device 171 may include a particle displacement unit and a particle dissipation unit. The particle displacement unit is shown as a first adhesive roll 175 with an adhesive or sticky surface, and the particle dissipation unit is shown as a second adhesive roll 176 with an adhesive or sticky surface. In some embodiments, the stickiness of the second adhesive roll 176 is larger than the stickiness of the first adhesive roll 175 (i.e., the second adhesive roll's capability to make particles adhere to the second adhesive roll is stronger than the first adhesive roll's capability to make particles adhere to the first adhesive roll). [0065] The first cleaning device 171, including the first adhesive roll 175 and the second adhesive roll 176, may operate as follows. The first adhesive roll 175 is positioned to be in direct contact with a main surface of the flexible substrate 10 that is to be cleaned. The first adhesive roll 175 is typically rotating with the identical circumferential speed as the circumferential speed of an oppositely arranged guiding roller that provides a counter-pressure surface. The first adhesive roll 175 may be driven by the flexible substrate with which the first adhesive roll 175 is in frictional contact during operation of the deposition apparatus.

[0066] Due to the sticky surface of the first adhesive roll 175, particles on the flexible substrate are gathered by the sticky surface of the first adhesive roll. The particles thus temporarily adhere to the first adhesive roll and are rotated up, on the first adhesive roll's circumference, to the opposite side of the first adhesive roll. The second adhesive roll 176 is positioned such that the second adhesive roll is in contact with the first adhesive roll 175. Notably, the second adhesive roll 176 is typically not in contact with the flexible substrate. Given the greater stickiness of the second adhesive roll as compared to the stickiness of the first adhesive roll, the particles on the first adhesive roll adhere to the sticky surface of the second adhesive roll.

[0067] Thus, the particles will remain on the surface of the second adhesive roll while the outer surface of the first adhesive roll will rotate back to contact the flexible substrate again. Accordingly, there will not be any particles on the first adhesive roll when the first adhesive roll contacts the flexible substrate, and hence the contact of the first adhesive roll with the flexible substrate will not cause any damage. Instead, the particles are stored on the second adhesive roll. From time to time, the second adhesive roll may be replaced by a new second adhesive roll.

[0068] The second cleaning device 172, the after-coating cleaning device 173, and possible further cleaning devices may have a corresponding setup in some embodiments. For example, the substrate support surface of the coating drum 122 may act as a counter-pressure surface for the first adhesive roll of the after-coating cleaning device 173.

[0069] In some embodiments, which may be combined with other embodiments described herein, at least one coating device may additionally or alternatively include a laser which may be expanded to cover the complete width of the flexible substrate. The expanded laser beam is typically sufficiently energetic to separate particles from the surface of the flexible substrate. Alternatively, the laser may be controlled by an automatic particle localization system that may include a camera and a controller for analyzing the taken pictures. The localization system may be positioned upstream from the respective cleaning device. The particle localization system may localize individual particles on the substrate. The laser may direct the laser beam to the particle localized on the flexible substrate.

[0070] In some embodiments, the laser beam is sufficient for separating the particle from the substrate. A further particle dissipation unit such as a suction device may be provided for permanently taking the particle away from the substrate. The suction device may be positioned downstream from the laser. In embodiments, the laser is controlled and operated such that the particles are dissipated by the laser beam. In this case, a further storage device such as a suction device can be dispensable.

[0071] In some embodiments, a suction device may serve as the cleaning device. Not limited to this embodiment, it is generally possible to provide a further gas separation stage between the last deposition unit and an after- coating cleaning device arranged directly downstream therefrom.

[0072] In some embodiments, which may be combined with other embodiments described herein, an ionized particle beam generated by an ionized particle beam generation unit may additionally or alternatively serve as one of the cleaning devices as described herein. The ionized particle beam may be expanded to cover the complete width of the flexible substrate. For instance, an air blade or an array of nozzles may be provided as an outlet. The flow of ionized particles may serve to separate particles from the surface of the flexible substrate. The beam may include or consist of nitrogen. Alternatively, the ionized particle beam may be controlled by an automatic particle localization system that may include a camera and a controller for analyzing the pictures taken.

[0073] Due to the potentially high temperatures during coating, and due to the positioning of the after-coating cleaning devices close to the deposition process, the after-coating cleaning device may be configured to withstand temperatures of at least 50°C, 70°C, or even 100°C or more. The flexible substrate temperature or the temperature of the coating drum can be from -30°C to +100°C, particularly from -15°C to +30°C during operation, particularly during sputter deposition on the flexible substrate.

[0074] Particularly, in deposition processes that may include highly exothermic reactions, it may be desirable to cool the coating drums. For sputtering, the process heat is mainly related to the condensation energy of the particles on the flexible substrate as well as heat due to ion bombardment. It may be desirable to avoid high temperatures of the flexible substrate. Accordingly, the coating drum as disclosed herein may include a cooling unit (not shown in the figures), for instance, a cooling unit configured to cool down the coating drum to a temperature below 0°C.

[0075] Alternatively or additionally, at least one of the cleaning devices may include a cooling unit. Thus, the cleaning devices can be held at temperatures that allow for keeping the evaporation of unknown or undesired gases from the cleaning devices at an acceptable level. Such a cooling of the cleaning devices is particularly beneficial where the deposition process is performed at high temperatures. [0076] In some embodiments, which may be combined with other embodiments described herein, a pretreatment device 201 may be provided, particularly upstream from the plurality of deposition units 121, as exemplarily shown in FIG. 2. For example, the pretreatment device 201 may be located in the deposition chamber 120 upstream from the plurality of deposition units 121. In some embodiments, the pretreatment device 201 is arranged such that the flexible substrate can be pretreated when the flexible substrate is in contact with the substrate support surface of the coating drum 122. In some embodiments, more than one pretreatment device may be provided. The pretreatment device 201 may be configured to activate the first main surface of the flexible substrate, in order to promote the adhesion of the stack of layers to be deposited. For instance, the pretreatment device may include a DC glow discharge.

[0077] According to one example, the pretreatment device 201 may include a plasma source, e.g. an RF plasma source, configured for pretreating the flexible substrate with plasma. For example, the pretreatment with a plasma can provide for a surface modification of the substrate surface to enhance the adhesion of a film deposited thereon, or can improve the substrate morphology in another manner to improve processing thereof.

[0078] According to another example, the pretreatment device 201 may be an ion source, particularly a linear ion source (LIS). The pretreatment device 201 may be configured for pre-cleaning the first main surface of the flexible substrates directly prior to coating of the first main surface. The pretreatment device 201 may be configured to direct a plasma jet towards the first main surface of the flexible substrate in order to burn off hydrocarbons and in order to activate the surface to promote the adhesion of the layer to be deposited. In some embodiments, argon ions may be used to provide effective plasma cleaning of the flexible substrate. In some embodiments, a combination of gases, e.g. a combination of argon ions and oxygen ions, can be used for providing an effective plasma cleaning. In some embodiments, for example for the pre-treatment of PI based substrates, also N ₂ is a possible gas.

[0079] In some embodiments, at least one discharging assembly for adapting the charge on the flexible substrate may be provided. For example, one discharging assembly may be arranged upstream from the plurality of deposition units, e.g. in the first spool chamber, and optionally a further discharging assembly may be arranged downstream from the plurality of deposition units. Providing a discharging assembly may be beneficial for improving the quality of the processing result since, for instance, positive and/or negative charges may accumulate on the flexible substrate. In particular, the charges may originate whilst the flexible substrate is unwound from the storage spool. The static charges may then remain on the substrate even when the flexible substrate moves into the deposition chamber and, hence, may attract stray particles to the surfaces of the flexible substrate. Thus, by providing a discharging assembly as described herein, ions of opposing polarity may be provided that move to the surfaces of the flexible substrate to neutralize the charges. Accordingly, a clean and discharged surface of the flexible substrate can be provided, such that the quality of the processing of the substrate, e.g. a coating, may be improved.

[0080] In the present disclosure, the term "discharging assembly" is intended to be representative of any device that is capable of ionizing a gas through an electric field. The discharging assembly may either be a passive or active unit or both. Further, the discharge assembly may include one or more neutralizing devices that may be connected to a power supply and control unit. The one or more neutralizing devices may be provided as a neutralizing lance or an ionization lance with one or more spikes. Further, a power supply, particularly a high voltage power supply, may be connected to the neutralizing device in order to provide high voltage to the one or more spikes to enable an electrical breakdown of a processing gas to produce ions that may move in the electric field towards the surfaces of the flexible substrate in order to neutralize the charges thereon. The control unit may initiate commands or execute preprogrammed discharging profiles, such that a flow of negatively or positively charged ions is produced by the neutralization device that will flow to the surface of the substrate such that ions of opposite polarity to the charge on the surface of the substrate may move to the surface of the substrate and neutralize the charge there.

[0081] Accordingly, according to embodiments described herein, the impact of particles on the production yield may be reduced by the use of electrostatic charge mitigation devices, e.g. a discharging assembly as described herein. Particulate material can be prevented from being attracted due to a charging of the substrate caused by the rolls employed for substrate transportation during unwinding. This helps to limit the level of extrinsic contamination at the substrate surface.

[0082] FIG. 3 illustratively shows a deposition apparatus 100 for coating a flexible substrate 10 according to embodiments described herein. Most features of the deposition apparatus 100 of FIG. 3 correspond to the respective features of the deposition apparatus shown in FIG. 1, so that reference can be made to the above explanations which are not repeated here.

[0083] In some embodiments, which may be combined with other embodiments described herein, an annealing unit 114 may be provided upstream from the plurality of deposition units 121. The annealing unit 114 may be configured for heating or annealing the flexible substrate 10 at a position upstream from the plurality of deposition units 121. Heating of the flexible substrate wound from the storage spool 112 may be beneficial, in order to allow for a degassing of the flexible substrate before deposition. Further, flexible substrates, such as substrates comprising synthetics like PET, HC-PET, PE, PI, PU, TaC, COP, may include considerable amounts of moisture. Outgassing of the moisture during the coating process under high vacuum conditions may have a negative influence on the properties of the stack of layers to be deposited, such as layer adhesion, optical uniformity, sheet resistivity and further layer properties. Accordingly, annealing the flexible substrate upstream from the plurality of deposition units 121 may be beneficial.

[0084] An impairment of the vacuum conditions in the deposition chamber by the annealing process can be reduced or avoided by positioning the annealing unit 114 in one of the one or more vacuum chambers upstream from the deposition chamber. For example, the annealing unit 114 may be provided in the first spool chamber 110 downstream from the storage spool 112, or the annealing unit 114 may be provided in an (optional) cleaning chamber positioned between the first spool chamber 110 and the deposition chamber 120.

[0085] In some embodiments, the annealing unit 114 may include at least one of a heatable roller 115 and a radiation heater 116 configured for directing thermal radiation toward the flexible substrate. In some embodiments, an additional heating chamber with heating zones may be provided. In some embodiments, the flexible substrate may be annealed to a temperature of 80°C or more, particularly 100°C or more, or even up to 150°C by the annealing unit 114.

[0086] The heatable roller 115 may be a passive guiding roller adapted to guide the flexible substrate along the substrate transportation path without an own roller drive, or an active roller. In some embodiments, the heatable roller may be a deflecting roller for deflecting the flexible substrate by a predetermined deflection angle. In some embodiments, the heatable roller 115 may be heated by a heat transfer medium, such as oil or water. However, such a roller may need a vacuum tight sealing of the rotary feedthrough for the transfer medium via tubes. [0087] In some embodiments, an electrical heating device may be provided for the heatable roller 115. The heating device may include a first end and a second end, and the heating device may be held at the first end and at the second end. The electrical heating device may be arranged inside the heatable roller. In some embodiments, the heating device may be fixed at the first end and at the second end.

[0088] In some embodiments, the heating device may be an irradiation heating device, such as an infrared heating device, an induction heating device or the like. According to some embodiments, the electrical heating device may be a contactless heating device. The contactless heating device may be able to bring a surface of the heatable roller to a defined temperature without contacting the flexible substrate. In some embodiments, the heating device may have two ends and may be adapted for being supported, held or fixed at both ends. In one embodiment, the heating device may have a substantially cylindrical form, wherein the two ends of the heating device are the two ends of the longitudinal axis of the substantially cylindrical heating device.

[0089] In some embodiments, the deposition apparatus may be provided with a trap, e.g. a cold trap, for collecting an outgassed vapor from the flexible substrate, for example by using a heatable roller. In particular, the trap for collecting an outgassed vapor from the flexible substrate may be arranged at a position opposite the surface of the flexible substrate from which the moisture may evaporate, e.g. during the heating of the flexible substrate by the annealing unit 114.

[0090] FIG. 6 shows a side view of a heatable roller 115, which may be used in a deposition apparatus 100 according to embodiments described herein. For instance, the heatable roller 115 may be used as a deflecting roller directly downstream from the storage spool, as is exemplarily shown in FIG. 3, or as a deflecting roller arranged further downstream along the substrate transportation path. In some embodiments, two or more heatable rollers may be provided in the first spool chamber 110 and/or in other vacuum chambers, e.g. in a cleaning chamber downstream from the first spool chamber. The heatable roller 115 may include a roller surface 210, which is adapted to be in contact with the flexible substrate 10. The roller surface 210 of the heatable roller 115 may be adapted to guide the flexible substrate as a guiding roller. Within the heatable roller 115, an electrical heating device 220 is provided. The electrical heating device 220 may be adapted to be operated under vacuum conditions.

[0091] In FIG. 6, the outer surface of the electrical heating device is denoted with the reference sign 225. The first end 250 and the second end 260 of the electrical heating device 220 can be seen as being located at the front sides of the substantially cylindrical shape of the heating device. The heating device may be held at the first end 250 and at the second end 260. According to some embodiments, the first end 250 is held by a first holding device 271, and the second end 260 is held by a second holding device 272.

[0092] By supporting the electrical heating device at both ends, the heatable roller 115 including the electrical heating device 220 may be held stably during operation of the deposition apparatus, especially irrespective of the weight of the flexible substrate. According to some embodiments, a higher accuracy of the position of a roller may be desirable for ensuring a reliable operation of the deposition apparatus 100.

[0093] In some embodiments, which may be combined with other embodiments described herein, the annealing unit 114 may additionally or alternatively include a radiation heater 116. The radiation heater may be configured as a heating lamp, e.g. an infrared lamp, in some embodiments. In some embodiments, the radiation heater 116 may be arranged directly upstream from or directly downstream from the heatable roller 115. For example, as is shown in FIG. 3, the annealing unit 114 may include a heatable roller 115 and a radiation heater 116 positioned directly downstream from the heatable roller 115.

[0094] The radiation heater 116 may be configured to direct thermal radiation towards the flexible substrate 10, as the flexible substrate is guided past the radiation heater 116. One, two, or more guiding rollers may be provided for guiding the flexible substrate past the radiation heater 116, for example in one or two passes. The outgassing efficiency may be improved. The flexible substrate can be reliably degassed and pre-annealed before coating, e.g. by heating the flexible substrate to a temperature of 100°C or more, or even up to 150°C.

[0095] As is schematically depicted in FIG. 3, the deposition apparatus 100 may further include a defect inspection device 154 for detecting defects of the flexible substrate after deposition. The defect inspection device 154 may be arranged downstream from the plurality of deposition units 121. For example, as is shown in the embodiment of FIG. 3, a defect inspection device 154 may be provided in the second spool chamber 150. In other embodiments, two or more defect inspection devices may be provided.

[0096] The defect inspection device 154 may be configured for detecting defects such as winding defects or coating defects, e.g. pinholes, cracks or other openings, in the stack of layers deposited on the flexible substrate. The defect inspection device 154 may be operated inline, i.e. for defect detection during transport of the flexible substrate along the substrate transportation path after deposition of the stack of layers. For example, the freshly coated stack of layers may be continuously inspected by the defect inspection device 154. Therein, the defect inspection device 154 may be configured to be operated under vacuum conditions, i.e. for inspecting the substrate during transport of the substrate through a vacuum chamber, .e.g. the second spool chamber.

[0097] For example, defects, e.g. pinholes, cracks or openings in the deposited stack of layers, having a size of 50 μιη or less, particularly 30 μιη or less, more particularly 15 μιη or less, or even 5 μιη or less, may be detected with the defect inspection device 154. The size (e.g. the maximum diameter) of one or more detected defects and/or the number of defects per surface area may be determined.

098] In some implementations, the defect inspection device 154 may be optical defect inspection device, particularly including a light source 155 and a light detector 156, such as a camera. Estimating the number and approximate size of defects in the deposited stack of layers may be beneficial. Inspecting the coated substrate may be reasonable in order to check the coating result. In some embodiments, the number of defects in the outermost layer of the stack of layers which may be a metal layer such as a Cu-layer should be minimized. In some embodiments, a defect with a size (e.g. a maximum diameter) of 10 μιη or more may impair the functionality of the deposited stack of layers. Accordingly, the defect inspection device may be configured for detecting defects with a size of 10 μιη or more, or even smaller defects. [0099] In some embodiments, the deposition apparatus according to embodiments described herein may be configured for depositing a stack of layers on a first main surface of the flexible substrate, particularly wherein the outermost layer of the stack of layers may be a metal layer, e.g. a Cu-layer. The layer quality of the outermost layer may be such that the outermost layer has essentially no defects or pinholes with a size of 30 μιη or more, that the outermost layer has less than 10 defects or pinholes with a size from 15 μιη to 30 μιη per 625 cm ² surface area (A4-sheet area), and/or that the outermost layer has less than 15 defects or pinholes with a size from 5 μιη to 15 μιη per 625 cm ² surface area (A4-sheet area). The defect inspection device 154 may be configured to inspect whether these or similar quality properties of the coated stack of layers are given.

[00100] The defect inspection device 154 may be configured for conducting an optical transmission measurement, particularly when inspecting a non- transparent layer such as a metal layer. For example, the light source 155 may be provided on a first side of the flexible substrate, and the light detector 156 may be provided on the second side of the flexible substrate such that a transmission measurement of the flexible substrate and/or of the layers deposited thereon can be conducted. An increase in transmissivity of the flexible substrate measured by the light detector may mean that the non- transparent layer deposited on the fiexible substrate may have a defect such as a pinhole or an opening. [00101] In some embodiments, which may be combined with other embodiments described herein, the defect inspection device 154 may be installed between a first guiding roller and a second guiding roller, i.e. in a "free span" section of the flexible substrate, where the flexible substrate is not in direct contact with one of the guiding rollers. For example, the light source 155 of the defect inspection device 154 may be mounted on a first side of the flexible substrate such that a light beam generated by the light source 155 may be transmitted through the free span section of the flexible substrate. The light detector 156 of the defect inspection device may be arranged on the other side of the flexible substrate such that the light beam having propagated through the free span section of the flexible substrate may be detected by the light detector 156. In some embodiments, the defect inspection device may be mounted downstream from the deposition units and upstream from the wind-up spool, e.g. between two guiding rolls directly upstream from the wind-up spool. [00102] In some embodiments, a width of the light beam generated by the light source 155 may be adapted to a width of the flexible substrate such that the flexible substrate may be inspected essentially over the full width of the flexible substrate or at least over the full width of the deposited stack of layers. For example, the width of the light beam may be 500 mm or more, particularly l m or more, more particularly between 1.2 m and 1.8 m. In some embodiments, and particularly in cases where the light source is arranged inside a vacuum chamber, the light source may be cooled, e.g. with a cooling fluid, e.g. with water. For example, a water circuit may be provided for cooling the light source 155, particularly when the light source 155 is arranged inside a vacuum chamber. A supply tube for supplying the cooling medium, e.g. water, into the vacuum chamber may be provided, for example including a vacuum feedthrough through the wall of the second spool chamber. Further, in some embodiments, vacuum feedthroughs may be provided for the supply of further media, e.g. electricity, into the vacuum chamber. For example, a control cable and/or a power supply cable for controlling and/or powering the light source and/or the light detector may be guided through a wall of a vacuum chamber via one or more vacuum feedthroughs. [00103] In some embodiments, the light detector 156, which may include one, two, three or more cameras, may be arranged outside the vacuum chamber, e.g. behind one, two, three or more windows provided in a wall of a vacuum chamber. This allows an easy access to the light detector 156 for adjustment, aligning and service. Further, no vacuum feedthroughs may be provided for controlling and powering the light detector when the light detector 156 is arranged outside the vacuum chamber. Even further, it may be difficult to provide the light detector 156 inside the vacuum chamber, as the available space inside the vacuum chamber may be limited. Accordingly, a more compact vacuum chamber may be provided.

[00104] Accordingly, in some embodiments, the light source 155 may be arranged inside the vacuum chamber, e.g. inside the second spool chamber 150, and the light detector 156 may be arranged outside the vacuum chamber, e.g. behind one or more windows in a wall of the second spool chamber 150. Alternatively, at least one of the light source and the light detector may be housed in a vacuum-tight enclosure provided in a vacuum chamber, e.g. in an atmosphere box located in a main volume of the vacuum chamber, e.g. in the second spool chamber 150. For example, two, three or more windows may be provided in a top wall of the second spool chamber 150 or in a wall of a vacuum-tight enclosure, and the light beam having propagated through the flexible substrate may be directed upward through the two or more windows toward two or more cameras of the light detector 156. In some implementations, the light detector 156 may be mounted on an adjustable bar outside the vacuum chamber such that a distance between the light source 155 and the light detector 156 can be adjusted as appropriate.

[00105] For example, it may be reasonable to mount the light detector at a certain distance from the deposited stack of layers, e.g. depending on one or more parameters such as an inspection width, a number of cameras of the light detector, a focal length of the light beam etc. Accordingly, in some embodiments, no vacuum compatible cameras may be necessary. The described inline defect inspection device allows a precise defect detection with a high resolution in a R2R deposition apparatus.

[00106] In other embodiments, both the light source 155 and the light detector 156 may be arranged outside the vacuum chamber, e.g. behind one or more respective windows. For example, a reflector may be provided inside the vacuum chamber for back-reflecting the light beam such that the light source 155 and the light detector 156 may be arranged on the same side of the flexible substrate, e.g. outside the vacuum chamber. In yet further embodiments, the light source 155 and the light detector 156 may be arranged inside the vacuum chamber, as is schematically indicated in FIG. 3. Yet further setups of the defect inspection device are possible, e.g. including a light source being provided outside the vacuum chamber and a light detector being provided inside the vacuum chamber.

[00107] In some embodiments, which may be combined with other embodiments described herein, the deposition apparatus 100 may further include a monitoring device 161 arranged downstream from the plurality of deposition units 121, as exemplarily shown in FIG. 3. In some embodiments, the monitoring device 161 can be an inline monitoring device which may be operable during operation of the deposition apparatus, particularly under vacuum conditions. In particular, the monitoring device 161 may be configured for detecting one or more properties of at least one layer deposited on the flexible substrate. For example, the monitoring device 161 may be configured for detecting or measuring one or more properties of one or more layers deposited by the plurality of deposition units 121. [00108] In some embodiments, which may be combined with other embodiments described herein, the monitoring device 161 may be arranged in the deposition chamber 120 downstream from the coating drum 122. One or more guiding rollers, such as active or passive rollers, may be arranged between the coating drum and the monitoring device. [00109] The monitoring device may be configured for measuring at least one of an electrical property and an optical property of one or more layers deposited on the flexible substrate. For example, an electrical property related to a conductivity of one or more layers deposited on the flexible substrate may be measured. In particular, an electrical sheet resistance of one or more conductive layers deposited on the flexible substrate may be measured. In some embodiments, an electrical property of one or more layers deposited on the substrate may be measured by applying an electrical potential or voltage between two spaced-apart positions of the one or more layers, and by measuring a current which flows through the one or more layers between the two spaced-apart positions.

[00110] In some embodiments, an electrical property such as a sheet resistance of one or more layers deposited on the substrate can be measured by inducing local currents such as Eddy currents in the one or more layers, and by measuring the strength of the induced Eddy currents. Measuring an electrical property of the one or more layers deposited on the flexible substrate by inducing Eddy currents in the one or more layers may have the advantage that a spatially resolved measurement of the electrical property may become possible. For example, the sheet resistance in a side area of the flexible substrate can be measured by inducing and measuring Eddy currents in the side area of the flexible substrate. Likewise, the sheet resistance in a center area of the flexible substrate can be measured by inducing and measuring Eddy currents in the center area of the flexible substrate. Further, Eddy currents may be induced in a contactless way. Accordingly, the risk of damaging the coated substrate may be reduced.

[00111] In some embodiments, the monitoring device 161 may be alternatively or additionally configured for measuring one or more optical properties of one or more layers deposited on the flexible substrate. For example, a transmittivity, a reflectivity and/or a color value of one or more layers may be measured. Coatings on substrates can be characterized by specified spectral reflectance and transmittance values and resulting color values, and a reliable inline measurement of transmission and reflection during the production of the coatings can be an aspect that should be considered for the control of the deposition process. A layer uniformity and/or a layer thickness value may be deduced from measured transmittivity and/or reflectivity values.

[00112] Reflectance measurements can be challenging on a moving flexible substrate, since small deviations in flatness of the substrate can cause geometrical changes in the path of the reflectance beam to the detector, resulting in erroneous measurement results. The reflectance can be measured at positions where the flexible substrate is in mechanical contact with a guiding roller of the deposition apparatus to ensure a flat contact of the substrate with the roller surface. A transmission measurement can be made at a position between a first roller and the second roller. The area between the first roller and a second roller may be referred to as a "free span" section of the flexible substrate.

[00113] In some embodiments, which may be combined with other embodiments described herein, the monitoring device 161 may be configured for measuring one or more optical properties of the flexible substrate or of one or more coating layers. In some embodiments, the monitoring device may include at least one sphere structure. The sphere structure may be an integrating sphere, for example an Ulbricht sphere. The sphere structure may be positioned in a free span area between a first guiding roller and a second guiding roller. The sphere structure may provide a uniform scattering or diffusion of light inside the sphere structure. Light incident on the inner surface of the sphere structure can be distributed equally within the sphere structure. Diffuse light emitted from the sphere structure through a port can be shone onto the flexible substrate for measurement of at least one optical property of the flexible substrate or of one or more coating layers.

[00114] In some embodiments, at least one monitoring device may include a layer measurement system (LMS), such as an optical layer measurement system, for measuring and evaluating a coating result. Accordingly, it is to be understood that embodiments provide a metrology capability, for example for the evaluation of a layer thickness of one or more deposited layers through the use of an optical reflection and/or transmission system, e.g. for use with transparent or semitransparent flexible substrates or coating layers. [00115] In some embodiments, at least one monitoring device may be provided for measuring an absolute thickness and/or a thickness uniformity of one or more coating layers.

[00116] Further, particularly for thin substrates, for example a substrate having a thickness of 200 μιη or below, or 100 μιη or below, or 50 μιη or below, for example about 25 μιη, a wrinkle-free substrate processing and substrate winding is beneficial and challenging. According to some embodiments, a wrinkle-free and tension-controlled substrate winding and/or transport (or a substrate winding and/or transport with a reduced wrinkle generation) may be provided using one or more tensioning rollers and/or one or more tension measurement rollers .

[00117] As is schematically depicted in FIG. 4, according to some embodiments described herein, the deposition apparatus may include one or more tensioning rollers and one or more tension measurement rollers. Accordingly, the roller assembly that is configured for guiding and transporting the flexible substrate along the substrate transportation path may be operated tension controlled. A tensioning roller may be understood as an active roller including a drive for driving the roller, e.g. with an adjustable driving force. A tension measurement roller may be understood as a roller including a sensor for measuring a tension of a portion of the flexible substrate guided over the roller surface. The enlacement angle of the flexible substrate 10 around a tension measurement roller may be 90° or more, particularly 120° or more, or even up to 180°, in order to improve the reliability of the measurement result.

[00118] In some embodiments, at least one or more of the following rollers may be active rollers: the storage spool 112, the coating drum 122, and the wind-up spool 152. Additional active rollers may be provided in some implementations. For example, in the embodiment shown in FIG. 4, a tensioning roller 181 may be provided, e.g. in the deposition chamber. The active rollers are marked with a curved arrow in FIG. 4.

[00119] In some embodiments, a tension measurement roller may be associated to at least one of the active rollers. In some embodiments, two or more active rollers may have an associated tension measurement roller, respectively. In some embodiments, all but one of the active rollers may have an associated tension measurement roller, respectively. The one active roller, which may not have an associated tension measurement roller, may be referred to herein as a "master roller". The transport speed of the flexible substrate along the transportation path, also referred to as the "line speed", may be determined by the rotation speed of the master roller, which may be rotated at a predetermined rotation speed.

[00120] A tension measurement roller may be arranged upstream from or downstream from an active roller that is associated with the tension measurement roller. Typically, no further active rollers are provided between the active roller and the associated tension measurement roller. However, in some cases, one, two or more passive rollers can be provided between an active roller and the associated tension measurement roller. In particular, active rollers and tension measurement rollers may be alternately provided along the substrate transportation path, whereas passive rollers may or may not be arranged therebetween, respectively.

[00121] As an example, in the embodiment shown in FIG. 4, a first tension measurement roller 184 is associated to the storage spool 112, a second tension measurement roller 185 is associated to the tensioning roller 181, and a third tension measurement roller 188 is associated to the wind-up spool 152. The coating drum, which is also an active roller, may be configured as the master roller which determines the transport speed of the flexible substrate and which may not have an associated tension measurement roller. It is to be understood that this arrangement is an exemplary setup. For example, in other embodiments, another active roller may be configured as the master roller. Further, in some embodiments, more or less than three tension measurement rollers may be provided, and/or more or less than one additional tensioning roller may be provided. The setup and the respective locations of the tension measurement rollers and of the tensioning rollers may be different in other embodiments. One of numerous possible setups for tension control of the flexible substrate is shown in FIG. 4 and will be explained in detail.

[00122] In the embodiment shown in FIG. 4, the first tension measuring roller 184 is associated to the storage spool 112. The first tension measurement roller 184 may be located downstream from the storage spool 112, wherein one, two or more passive rollers may be arranged between the storage spool 112 and the first tension measurement roller 184. For example, the first tension measurement roller 184 may be located in the deposition chamber 120 upstream from the coating drum 122 which is the next active roller.

[00123] A set point, i.e. a target value, for a substrate tension at the position of the first tension measurement roller 184 may be preset. If a tension value above the set point is measured by the first tension measurement roller 184, the torque value provided by the storage spool 112 drive may be decreased. If a tension value below the set point is measured by the first tension measurement roller 184, the torque value provided by the storage spool 112 drive may be increased. Accordingly, an appropriate tension of the flexible substrate downstream from the storage spool can be ensured. Damages such as ruptures, cracks, pinholes or winding defects of the flexible substrate caused by an extensive substrate tension may be avoided. Further, wrinkles, undulations, sagging or defects due to an excessive substrate temperature of the substrate caused by a low substrate tension can be avoided.

[00124] In the embodiment of FIG. 4, the coating drum 122 may be the master roller that determines the transport speed of the flexible substrate along the substrate transportation path. The rotation speed of the master roller can be set as appropriate. For example, the transport speed of the flexible substrate may be 1 m/minute or more and 5 m/minute or less, particularly about 2 m/min. The drives of all other active rollers along the substrate transportation path may be tension controlled depending on a measurement value of an associated tension measurement roller.

[00125] As schematically shown in FIG. 4, in some embodiments, the second tension measuring roller 185 may be associated to another active roller such as the tensioning roller 181. The second tension measurement roller 185 may be located directly downstream from the coating drum 122 and directly upstream from the tensioning roller 181. However, in other embodiments, one or more passive rollers may be arranged therebetween, respectively. For example, the second tension measurement roller 185 may be located in the deposition chamber 120 downstream from the coating drum 122. The second tension measurement roller 185 may be configured to measure a substrate tension at a position downstream from the coating drum 122.

[00126] A set point, i.e. a target value, for a substrate tension at the position of the second tension measurement roller 185 may be preset. If a tension value above the set point is measured by the second tension measurement roller 185, the torque value provided by the drive of the tensioning roller 181 may be decreased. If a tension value below the set point is measured by the second tension measurement roller 185, the torque value provided by the drive of the tensioning roller 181 may be increased. Accordingly, an appropriate tension of the flexible substrate around the coating drum can be ensured.

[00127] It is noted that a high substrate tension may increase the risk of winding defects. For example, if the flexible substrate is pressed to a roller surface with a high tension, scratches or other winding defects may be generated. Accordingly, a low substrate tension may be beneficial at positions in which the flexible substrate is in direct contact with a roller surface. On the other hand, a high substrate tension around the coating drum may be beneficial, as the flexible substrate may be cooled more efficiently during deposition, when the flexible substrate is in close contact with the cooled substrate support surface of the coating drum. Accordingly, an exact control of the substrate tension along the substrate transportation path is beneficial. [00128] Therefore, the target value of the second tension measurement roller 185 may be higher than the target value of the first tension measurement roller 184. This is because a low substrate tension between the storage spool 112 and the first tension measurement roller 184 may be beneficial for reducing the risk of winding defects, whereas a higher substrate tension between the coating drum 122 and the tensioning roller 181 may be beneficial for improving the thermal contact between the flexible substrate and the substrate support surface of the coating drum 122. For example, the target value of the second tension measurement roller 185 which may stand for the intended substrate tension around the coating drum 122 may be 100 N or more and 900 N or less, particularly from 200 N to 400 N. In some embodiments, a target value for the substrate tension below 200 N may be beneficial.

[00129] As is schematically depicted in FIG. 4, in some embodiments, the third tension measurement roller 188 may be provided upstream from the wind-up spool 152 and be associated to the wind-up spool 152. The torque generated by the drive of the wind-up spool 152 may be controlled depending on a tension value measured by the third tension measurement roller 188. If a tension value above a set point is measured by the third tension measurement roller 188, the torque value provided by the wind-up spool 152 may be decreased. If a tension value below the set point is measured by the third tension measurement roller 188, the torque value provided by the wind-up spool 152 may be increased. Accordingly, an appropriate tension of the flexible substrate upstream from the wind-up spool can be ensured.

[00130] Providing one or more additional tensioning rollers, e.g. a tensioning roller 181 may be beneficial in order to reduce a substrate tension in a central section between two active rollers with a long distance or with several passive rollers therebetween. For example, in some embodiments, at least one tensioning roller may be arranged between the coating drum and the wind-up spool. Further, providing one or more tensioning rollers may be beneficial in a deposition apparatus providing a partially convex and partially concave substrate transportation path. For example, changes in the substrate direction and large bending angles in different bending directions may increase the substrate tension such that providing further active rollers may be advantageous. Further, providing additional tensioning rollers may have the advantage that the substrate tension may be set to different values in different areas along the substrate transportation path as appropriate in the respective area.

[00131] FIG. 5 shows a schematic sectional view of a deposition apparatus 100 according to embodiments described herein. The deposition apparatus 100 includes a plurality of vacuum chambers including a first spool chamber 110, a cleaning chamber 170 (optional), a deposition chamber 120, and a second spool chamber 150. Further, the deposition apparatus 100 includes a roller assembly configured for transporting the flexible substrate along the substrate transportation path.

[00132] As is schematically depicted in FIG 5, the vacuum chambers may be arranged in an essentially linear setup. In other words, the second chamber along the substrate transportation path, i.e. the cleaning chamber 170, may be arranged on one side, e.g. on the right side, of the first chamber along the substrate transportation path, i.e. the first spool chamber 110. Similarly, the third chamber along the substrate transportation path, i.e. the deposition chamber 120, may be arranged on the one side, i.e. on the right side, of the second vacuum chamber, i.e. the cleaning chamber 170. Similarly, the fourth chamber along the substrate transportation path, i.e. the second spool chamber 150, may be arranged on the one side, i.e. on the right side, of the third vacuum chamber, i.e. the deposition chamber 120. Accordingly, the vacuum chambers may be arranged essentially in a linear setup or in a row which extends from the left to the right in FIG. 5. Accordingly, the overall direction of the substrate transportation path may likewise extend from the left to the right. However, the substrate transportation path may be curved or may change direction several times within the individual vacuum chambers, e.g. downward and upward and/or rightward and leftward, as is indicated in FIG. 5. [00133] For example, in some embodiments, the substrate transportation path may alternately be curved downward and upward. Accordingly, beneficially space requirements may be reduced. In the exemplary embodiment of FIG. 5, the substrate transportation path extends downward from the storage spool 112 to the heatable roller 115 which may be a counterclockwise rotating roller. Then, the substrate transportation path may be curved upward toward the guiding roller 113 which may be a clockwise rotating roller. The guiding roller 113 may turn the flexible substrate downward again toward a deflection roller which may be a counterclockwise rotating roller. The deflection roller may deflect the flexible substrate toward a slit in the wall between the first spool chamber 110 and the cleaning chamber 170. A sealing device 105, e.g. including an inflatable seal, may be provided in the wall between the first spool chamber 110 and the cleaning chamber 170. On the way from the heatable roller 115 toward the guiding roller 113 or downstream from the guiding roller 113, the flexible substrate may be heated by a radiation heater 116.

[00134] Clockwise rotating rollers may come into contact with the first main surface of the flexible substrate which may be the main surface to be coated during the respective pass through the deposition apparatus, and counterclockwise rotating rollers may come into contact with the second main surface of the substrate which is the rear surface of the substrate (which may or may not be an already coated surface). Accordingly, it may be beneficial to provide a first cleaning device 171 configured for cleaning the first main surface, and a second cleaning device 172 configured for cleaning the second main surface. The first cleaning device 171 and the second cleaning device may be arranged in the cleaning chamber 170. The first cleaning device 171 and the second cleaning device 172 may be arranged directly upstream from or downstream from each other. In the embodiment shown in FIG. 5, the roller surface of a counterclockwise rotating roller may act as a counter-pressure surface for the first cleaning device 171, and the roller surface of a clockwise rotating roller may act as a counter-pressure surface for the second cleaning device 172. Said clockwise rotating roller may deflect the flexible substrate downward toward an opening in the wall between the cleaning chamber 170 and the deposition chamber 120. A further sealing device may optionally be arranged in the wall between the cleaning chamber 170 and the deposition chamber 120 in order to improve a gas separation between the cleaning chamber 170 and the deposition chamber 120, and in order to avoid gases released by the cleaning devices to enter the deposition chamber 120.

[00135] In the deposition chamber 120, two or more and five or less, particularly three guiding rollers may be provided upstream from the coating drum 122, and two or more and five or less, particularly three guiding rollers may be provided downstream from the coating drum 122. As explained above in more detail, one of the guiding rollers arranged upstream from the coating drum 122 may be configured as a first tension measurement roller 184 which may be associated to the storage spool 112. The guiding roller arranged directly upstream from the coating drum 122 may be configured as a deflecting roller for smoothly guiding the flexible substrate 10 onto the substrate support surface of the coating drum 122.

[00136] Further, at least one of the guiding rollers arranged downstream from the coating drum 122, particularly the guiding roller arranged directly downstream from the coating drum 122, may be configured as a second tension measurement roller 185. Further, one of the guiding rollers arranged downstream from the second tension measurement roller 185 may be configured as a tensioning roller 181 associated to the second tension measurement roller 185. The concept of tension control has already been explained above in more detail and is not repeated here. As schematically depicted in FIG. 5, the substrate transportation path may change direction several times downstream from the coating drum 122 in the deposition chamber 120. A change in direction of the substrate transportation path may be generated by providing a guiding roller with an enlacement angle of 120° or more, particularly 150° or more, or even about 180° or more. For example, the enlacement angle of the second tension measurement roller 185 may be approximately 180°. The flexible substrate may entirely change direction several times such that a compact overall setup of the deposition apparatus can be provided. In some embodiments, a monitoring device 161 may be provided in the deposition chamber 120 downstream from the coating drum 122.

[00137] Further, in FIG. 5 two alternative winding passes are shown. In particular, the roller assembly may be configured to provide a first winding pass which is shown as the solid line of the flexible substrate guided through the deposition apparatus. Typically, the configuration of the first winding pass as exemplarily shown in FIG. 5 is beneficial for thick film winding. Additionally or alternatively, the roller assembly may be configured to provide a second winding pass 111 indicated by the dotted lines which indicate the difference compared to the first winding pass. Typically, the second winding pass may include more rollers than the first winding pass. A configuration of the second winding pass as exemplarily shown in FIG. 5 may be particularly beneficial for thin film winding.

[00138] The last guiding roller in the deposition chamber 120 may be configured as a deflecting roller for deflecting the flexible substrate toward an opening in the wall between the deposition chamber 120 and the second spool chamber 150. In some embodiments, a sealing device (optional) may be provided in the wall between the deposition chamber 120 and the second spool chamber 150. [00139] In particular, according to some embodiments, the deposition apparatus as described herein may have a modular design. For example, in some embodiments, a second deposition chamber may be provided. In this case, a connection chamber may be provided between a first deposition chamber and the second deposition chamber. Further, the second spool chamber may be connected to the second deposition chamber. For instance, the connection chamber may be arranged downstream from the first deposition chamber, e.g. the deposition chamber 120, and upstream from the second deposition chamber. The connection chamber may include a connection chamber entrance for receiving the flexible substrate from the first deposition chamber, and a connection chamber exit for guiding the flexible substrate into the second deposition chamber. Accordingly, the gas separation between the first deposition chamber and the second deposition chamber can be improved. One or more guiding rollers may be arranged in the connection chamber, in order to deflect the flexible substrate in the direction of the connection chamber exit such that the flexible substrate can smoothly enter the second deposition chamber through a passage, e.g. a small slit, between the connection chamber and the second deposition chamber.

[00140] In other embodiments, it may be reasonable to add a third deposition chamber. In this case, a second connection chamber may be provided instead of the second spool chamber downstream from the second deposition chamber, and the third deposition chamber and the second spool chamber may be connected downstream from the second connection chamber. Accordingly, the deposition apparatus may be provided with flanges or connection bases allowing for expanding the deposition apparatus by connecting further vacuum chambers or by removing some of the vacuum chambers from the deposition apparatus 100 shown in FIG. 5. Accordingly, it is to be understood that further vacuum chambers may be provided for extending the operation range of the deposition apparatus. Accordingly, the modular design of the deposition apparatus as described herein allows for adapting the size in the base shape which fits to the request of the user, e.g. space requirements in a factory.

[00141] According to some embodiments which can be combined with other embodiments described herein, the deposition apparatus may be provided with an interleaf module (not explicitly shown) for example in a case in which the flexible substrate to be processed is provided on the storage spool 112 together with an interleaf. Accordingly, the interleaf can be provided between adjacent layers of the flexible substrate such that direct contact of one layer of the flexible substrate with an adjacent layer of the flexible substrate on the storage spool can be avoided. For instance, the first spool chamber 110 may be equipped with a first interleaf module for taking up an interleaf provided for the protection of the substrate on the storage spool 112. The interleaf module may include some interleaf guiding rolls for guiding the interleaf to an interleaf take-up roll upon unwinding the flexible substrate with the interleaf from the storage spool. Accordingly, the second spool chamber 150 may also include an interleaf module including interleaf guiding rolls for guiding the interleaf supplied from an interleaf supply roll to the wind-up spool 152. Accordingly, the second interleaf module may provide an interleaf, which is wound on the wind-up spool together with the processed substrate for protecting the processed substrate on the wind-up spool. It is to be understood that the first spool chamber 110 and the second spool chamber 150 may be provided with holdings and/or receptions for mounting the interleaf take-up roll and the interleaf supply roll, respectively, as well as holdings and/or receptions for mounting the respective interleaf guiding rolls.

[00142] The basic setup of the second deposition chamber may correspond to the setup of the first deposition chamber, i.e. the deposition chamber 120, so that reference is made to the above explanations which are not repeated here. In particular, the tension of the substrate in the second deposition chamber may be controlled in a way similar to the first deposition chamber. However, in some embodiments, a pretreatment device 201, which may be provided in the first deposition chamber upstream from the first plurality of deposition units, may not be provided in the second deposition chamber. Further, in some embodiments, a monitoring device, e.g. the monitoring device 161 as described herein, may only be provided in the second deposition chamber downstream from a second plurality of deposition units. The second plurality of deposition units may be configured similarly to the first plurality of deposition units, i.e. the plurality deposition units 120 as described herein. For example, in some embodiments, monitoring of the stack of layers downstream from the second plurality of deposition units may be sufficient. Alternatively, a first monitoring device and a second monitoring device may be provided which can be configured as the monitoring device 161 described herein. Further, in some embodiments, the deposition units of the first plurality of deposition units may be different from the deposition units of the second plurality of deposition units. For the rest, the second deposition chamber may have a setup similar or identical to the first deposition chamber, i.e. the deposition chamber 120 as described herein.

[00143] In some embodiments, which may be combined with other embodiments described herein, a further sealing device may be provided in the wall between the second deposition chamber and the second spool chamber. In some embodiments, a defect inspection device 154 as explained above in more detail may be arranged in the second spool chamber upstream from the wind- up spool 152.

[00144] FIG. 7 shows a schematic sectional view of a coating drum 122 according to embodiments described herein. In some embodiments, which may be combined with other embodiments described herein, the coating drum 122 may include a curved substrate support surface 401 for contacting the flexible substrate 10, wherein the curved substrate support surface 401 may be rotatable about a rotation axis 123 and may include a substrate guiding region 403; a group of gas outlets 404 disposed in the curved substrate support surface 401 and adapted for releasing a gas flow; and a gas distribution system 405 for selectively providing the gas flow to a first subgroup of the gas outlets 404 and for selectively preventing the gas from flowing to a second subgroup of the gas outlets 404, wherein the first subgroup of the gas outlets 404 comprises at least one gas outlet in the substrate guiding region 403 and the second subgroup of gas outlets includes at least one gas outlet outside the substrate guiding region 403.

[00145] Typically, the coating drum 122 is rotatable about the rotation axis 123. In some embodiments, the coating drum 122 includes a stationary part and a part which can be rotated, e.g. about the stationary part. For instance, the coating drum 122 may include a stationary inner part (which may in some embodiments include the gas distribution system or components of the gas distribution system) and a rotary outer part which rotates about the inner stationary part. [00146] According to some embodiments, the coating drum 122 includes a curved substrate support surface 401. The curved substrate support surface of the coating drum 122 may be adapted to be (at least partly) in contact with the flexible substrate during operation of the deposition apparatus 100. According to embodiments which can be combined with any other embodiments described herein, the curved substrate support surface can be a cylindrically symmetric surface. In particular, the curved substrate support surface may be selected from a group consisting of a cylindrical surface, a concave-cylindrical surface, a surface of a cone, and a surface of a truncated cone. [00147] According to some embodiments, the curved substrate support surface 401 may contact the flexible substrate at contact locations during the operation of the deposition apparatus. For instance, due to the surface properties (such as roughness) of the curved substrate support surface of the coating drum, the substrate may be in punctual contact with the curved substrate support surface. The curved substrate support surface having a roughness may mean that the microscopic view of the curved substrate support surface shows "mountains and valleys", wherein the punctual contact between the curved substrate support surface and the substrate is at positions where the roughness of the curved substrate support surface has "mountains." According to some embodiments, which may be combined with other embodiments, the roughness of the curved substrate support surface of the coating drum may typically be in a range between about 0.1 Rz and about 1.5 Rz, more typically between about 0.2 Rz and about 0.8 Rz. According to some embodiments, the contact between the coating drum 122 and the substrate may allow the substrate to be moved when the coating drum 122 rotates.

[00148] During operation, the substrate is guided over the substrate guiding region 403 on the curved substrate support surface 401. In some embodiments, the substrate guiding region 403 may be defined as an angular range of the coating drum 122 in which the substrate is in contact with the curved substrate surface during the operation of the coating drum, and may correspond to the enlacement angle of the coating drum. [00149] In some embodiments, the enlacement angle of the coating drum may be 120° or more, particularly 180° or more, or even 270° or more, as is schematically depicted in FIG. 5. In some embodiments, an uppermost portion of the coating drum may not be in contact with the flexible substrate during operation, wherein the enlacement area of the coating drum may cover at least the entire lower half of the coating drum. In some embodiments, the coating drum may be enlaced in an essentially symmetric way by the flexible substrate.

[00150] The exemplary embodiment of the coating drum shown in FIG. 7 further includes a group of gas outlets 404 disposed in the curved substrate support surface 401. The gas outlets 404 are adapted to release a gas from a gas distribution system 405 of the coating drum 122, in particular in a direction substantially perpendicular to the curved substrate support surface 401, at the position where the respective gas outlet is located. In the example of a coating drum shown in FIG. 7, the gas outlets are distributed over the whole circumference of the coating drum. In some embodiments, the gas outlets 404 may be distributed in a regular manner over the whole circumference of the coating drum.

[00151] According to embodiments which can be combined with any other embodiments described herein, any individual gas outlet, any subgroup of the gas outlets or all gas outlets can be selected from the group consisting of: openings, holes, slits, nozzles, blast pipes, spray valves, duct openings, orifices, jets, outlets provided by a porous material and the like. According to some embodiments, the outlets are recesses in the surface that are typically funnel- shaped or cup-shaped, with the recesses being fed with gas from the bottom of the recesses or sideways. The gas outlets of the coating drum described herein can also be openings of a porous layer. According to some embodiments, the gas outlets as referred to herein may have any suitable shape, such as substantially round, circular, elliptic, triangular, rectangular, quadratic, a polygon, an irregular shape, such as an irregular round shape, an irregular angled shape, a shape being different from one gas outlet to the other, or the like. According to some embodiments, the gas outlets do not protrude out of the surface.

[00152] The coating drum 122 according to some embodiments described herein further includes the gas distribution system 405. According to some embodiments, the gas distribution system 405 includes a gas source 408. The gas distribution system 405 allows for selectively providing a gas flow to a first subgroup of the gas outlets. For instance, the coating drum with the gas outlets 404 and the gas distribution system 405 as exemplarily shown in FIG. 7 provides a gas flow to the gas outlets 404 in the substrate guiding region 403 of the curved substrate support surface. The gas outlets being (temporarily) located in the substrate guiding region 403 may be denoted as a first subgroup of the gas outlets. According to some embodiments described herein, the gas distribution system 405 in the coating drum is adapted to selectively prevent the gas from flowing to gas outlets of the coating drum outside the substrate guiding region 403. The gas outlets being (temporarily) located outside the substrate guiding region 403 may be denoted as a second subgroup of the gas outlets.

[00153] During rotation of the coating drum, any single gas outlet temporarily belongs to the first subgroup and to the second subgroup. In other words, an open gas outlet may be closed at a later time and vice versa. Gas outlets entering the substrate guiding region 403 during the rotation of the curved substrate support surface are opened or connected to the gas source, i.e., the membership is changed to the first subgroup. Gas outlets leaving the substrate guiding region during the rotation of the curved substrate support surface are closed or disconnected from the gas source, i.e., the membership is changed to the second subgroup.

[00154] The gas distribution system 405 of the coating drum may be adapted to selectively provide and prevent gas flow to defined gas outlets. For instance, in the example of FIG. 7, the gas distribution system 405 of the coating drum includes a gas source 408 being arranged in a stationary part 406 of the coating drum 122. The gas source 408 has a size encompassing a section of the circumference of the stationary part of the coating drum. The curved substrate support surface 401 of the coating drum may rotate about the rotation axis 123 of the coating drum and, in particular, about the stationary part of the coating drum (including the gas source). [00155] According to some embodiments described herein, the gas distribution system 405 may include gas channels 407. The gas channels 407 may lead from the gas source 408 to the gas outlets 404 on the curved substrate support surface 401 when the respective gas outlet is in the substrate guiding region 403. The gas channels may lead from the gas source 408 to the first subgroup of the gas outlets 404 on the curved substrate support surface 401. The gas distribution system 405 with a gas source 408 and gas channels 407 may be described as being partially rotary and partially stationary. With the gas channels 407 rotating about the gas source 408, the gas distribution system 405 allows to selectively connect and disconnect the gas channels 407 to/from the gas source 408.

[00156] According to some embodiments, the gas distribution system 405, and in particular the gas source 408 provides a gas flow to the gas outlets 404. In some embodiments, the gas flow provided by the gas distribution system 405 to the gas outlets 404 is a gas flow which still allows the flexible substrate to be in contact with the curved substrate support surface 401. For instance, the gas flow may typically be between about 10 seem and about 400 seem, more typically between about 30 seem and about 300 seem. In some embodiments, the coating drum 122 may be adapted to a flow rate of the gas per area of the curved substrate support surface 401 typically between about 10 sccm/m ² and about 200 seem/ m ² , more typically between about 30sccm m ² and about 120 seem/ m ² . In one example, the coating drum may be adapted to a flow rate of the gas per area of the curved substrate support surface which may typically be about 100 seem/ m ² .

[00157] According to some embodiments, which may be combined with other embodiments described herein, the number of gas outlets may typically be between 20 and 100, more typically between 40 and 100, in particular for a coating drum with gas channels (as exemplarily shown in FIG. 7). According to some embodiments, the curved substrate support surface may be partitioned into gas sections. In some embodiments, each gas section has several gas outlets. In some embodiments, the number of gas outlets in the substrate guiding region is between 5 and 20. The number of gas outlets for a porous layer of the coating drum may typically be at least 5000, more typically at least 6000, and even more typically at least 8000. According to some embodiments, the number of gas outlets is between 20 and 100 or the coating drum includes a porous layer providing the gas outlets. [00158] According to some embodiments, which may be combined with other embodiments described herein, a gas outlet as referred to herein may have a cross sectional size between about 0.1 mm and about 1mm. The cross sectional size may be measured as the minimum cross-section of the gas outlets at the curved substrate support surface. In some embodiments, the fluid conductance of the gas outlets may typically be between about 0.001 liter/sec and about 0.1 liter/sec, more typically between about 0.009 liter/sec and about 0.05 liter/sec. In one embodiment, the fluid conductance of the gas outlets may be about 0.01 liter/sec.

[00159] According to some embodiments, the gas flow provided in the direction toward the substrate during operation of the deposition apparatus may result in a gas bearing, especially a hydrodynamic or thermic gas bearing, between the substrate and the curved substrate support surface 401 of the coating drum. In some embodiments, the gas bearing may also be denoted as a kind of thin or small gas cushion outside the contact locations between the substrate and the curved substrate support surface. It may be understood that the substrate being in contact with the curved substrate support surface of the coating drum and having a gas bearing between the substrate and the curved substrate support surface may be in contact at some contact locations of the curved substrate support surface (e.g. punctual locations provided by the roughness of the curved substrate support surface) and may have gas bearings between the locations of contact. Between the contact locations (such as areas or points of the curved substrate support surface) of the substrate and the curved substrate support surface, gas bearings may be formed by the gas flow released from the gas outlets. According to some embodiments, which may be combined with other embodiments described herein, the pressure in the gas bearing(s) is typically between about 0.1 mbar to about 10 mbar, more typically between about lmbar and 10 mbar during deposition.

[00160] In some embodiments, the gas bearings between the substrate and the curved substrate support surface may fill the voids present due to the roughness of the curved substrate support surface of the coating drum and the substrate, especially outside of contact locations between the substrate and the curved substrate support surface. A thickness of the gas bearing may correspond to the roughness of the curved substrate support surface of the coating drum and the substrate being in contact with each other.

[00161] According to some embodiments, a plurality of gas bearings is formed between the substrate and the curved substrate support surface by the gas flow released from the gas outlets.

[00162] The gas bearing(s) between the substrate and the curved substrate support surface may improve the thermal conductivity between the coating drum and the substrate, e.g. for cooling or heating the substrate during deposition of the stack of layers on the substrate. For instance, the coating drum may include a temperature adjusting system, exemplarily shown as a temperature adjusting system 430, e.g. for cooling or heating the coating drum. The gas bearing(s) provided by a coating drum help to increase the thermal conductivity between the substrate and the coating drum. According to some embodiments described herein, the temperature of the flexible substrate can be kept below a defined upper limit during deposition.

[00163] The coating drum as exemplarily shown in FIG. 7 allows for solving some problems of other systems. For instance, the risk of substrate damage can be reduced because the substrate can be guided over the substrate support surface of the coating drum with a lower substrate tension. In particular, the increased thermal conductivity between the flexible substrate and the coating drum improves the cooling of the substrate, and it may not be necessary to pull the substrate toward the cooled substrate support surface with a high substrate tension, in order to obtain a sufficient cooling efficiency. A higher deposition rate (coating speed) results in a higher heat load towards the substrate. For using a high deposition rate (e.g. for accelerating the coating process), a proper thermal contact between the substrate and the coating drum is useful.

[00164] For example, the exemplary embodiment of the coating drum 122 shown in FIG. 7 may for instance beneficially be used in a two-side deposition process. Therein, a flexible substrate being already coated on a first main surface may be transported by the coating drum for coating also the second side of the substrate. During coating of the second main surface, the already coated first main surface may be in contact with the curved substrate support surface 401 of the coating drum 122. Accordingly, there may be a risk of damaging the already coated first main surface of the flexible substrate, for instance, when the flexible substrate is guided with an excessive tension over the curved substrate support surface of the coating drum or over the surface of another roller. According to some embodiments, the coated film on the first main surface of the flexible substrate has already been degassed prior to coating of the second main surface of the flexible substrate, e.g. via the annealing unit 114. A degassed surface may result in a lower heat transfer. The coating drum according to embodiments described herein allows for increasing the thermal conductivity between the flexible substrate and the curved substrate support surface, compensating the lower heat transfer of the degassed web, particularly in a two-side deposition process.

[00165] The coating drum 122 according to embodiments described herein includes a drive 410 (schematically shown in FIG. 7) for rotating the coating drum during operation and for moving the substrate being in contact with the coating drum. [00166] According to some embodiments, which may be combined with other embodiments described herein, the gas for the gas distribution system 405 may be selected from the group consisting of: inert gases, argon, helium, nitrogen, hydrogen, silane and any mixtures thereof. In some embodiments, the gas emitted from the gas outlets is a gas having a heat conductivity of at least 0.01 W/mK, more typically of at least 0.1 W/m and even more typically of at least 0.15 W/mK.

[00167] The gas bearings being formed while the substrate is in contact with the coating drum may be small enough (i.e. contain an amount of gas that is small enough) to not substantially influence the vacuum environment, or may be small enough to at least not disturb the vacuum environment used for the coating process. For specifically sensitive processes, or if the risk of pollution of the vacuum environment is still to be reduced, some embodiments may have further features for actively preventing the vacuum environment from being polluted.

[00168] For example, in some embodiments, a vacuum generating system (not shown in FIG. 7) may provide suction through the gas channels 407 connected to the vacuum generating system. The vacuum generating system may provide suction in a direction away from the substrate and towards the vacuum generating system. The gas released from the gas source to form the hydrodynamic thermal bearing(s) between the substrate and the coating drum may be removed with the vacuum generating system. For example, the gas may be removed before the substrate leaves the substrate guiding region 403. The vacuum environment of the coating drum is protected by the vacuum generating system.

[00169] FIG. 8 shows a coating drum 122 that may be used in a deposition apparatus according to embodiments described herein. The coating drum 122 of FIG. 8 is similar to the coating drum exemplarily shown in FIG. 7. The features described with respect to FIG. 7 may also be applied to the embodiment of FIG. 8. The embodiment of the coating drum 122 of FIG. 8 further includes a sealing. In some embodiments, the sealing may be made of a plurality of sealing units 413, such as sealing units being made of an at least partially elastic material. According to some embodiments, the sealing units 413 may be lip sealing units. The sealing may prevent or limit the amount of gas of the gas bearing spreading into the vacuum environment of the deposition chamber. In some embodiments, the sealing units 413 reduce or prevent a gas flow toward a main volume of the deposition chamber in which the coating drum 122 may be arranged.

[00170] The sealing units 413 may be arranged in a direction substantially perpendicular to the circumferential direction of the coating drum 122 and substantially perpendicular to the radial direction of the coating drum 122. In some embodiments, the sealing units 413 may be arranged in a width direction of the coating drum 122.

[00171] The sealing units may provide individually pressurized pockets on the second main surface of the substrate that is in contact with the curved substrate support surface 401. In some embodiments, each pocket formed between two sealing units may provide an individual pressure. The pressure in the individual pockets may depend on the rotational position of the pocket.

[00172] In some implementations, the curved substrate support surface may be partitioned in the width direction of the coating drum, e.g. for adapting the coating drum to substrates with different widths. For instance, the coating drum may be adaptable for a substrate width between about 0.5 m to about 2 m, and more typically between about 1.2 m and about 1.8 m. The partitioning segments may provide an adapted distribution of the gas outlets, such as a different number of gas outlets, a different density of gas outlets on the curved substrate support surface, a different size of the gas outlets and the like. In some embodiments, the gas source may be dividable in different sections providing gas for the different segments of the coating drum (in particular in the width direction).

[00173] In some embodiments, which may be combined with other embodiments described herein, the coating drum may have one or more e- chuck devices. In particular, the one or more e-chuck devices may provide an attraction force for holding the substrate in contact with the curved substrate support surface of the coating drum. According to some embodiments, each segment of the curved substrate support surface may include an individual e- chuck tile. The individual e-chuck tile may provide a suitable attraction force to the substrate, e.g. depending on the rotational position of the coating drum. In some embodiments, the individual e-chuck tiles are controlled to be operated depending on the position of the segment in or outside the substrate guiding region. According to some embodiments, the e-chuck tiles may be controlled to be operated dependent on the position of the respective segment with respect to the gas source 408 of the gas distribution system 405. In some embodiments, the coating drum may include sensors and control units for sensing the rotational position of the coating drum, and in particular the rotational position of each segment. The control unit may control the operation of the e-chuck depending on the sensed data.

[00174] According to some embodiments, the coating drum may include a backing structure for supporting a porous layer, wherein the porous layer may form the concave substrate support surface 401 which contacts the substrate. The porous layer may further provide the gas outlets 404 for releasing gas toward the substrate. In some embodiments, the backing structure may include supporting bars and areas for the gas release arranged between the supporting bars. In particular, the supporting bars and the areas for the gas release may be arranged in an alternating manner in a circumference direction.

[00175] According to some embodiments, the porous layer may be made of a porous material providing a plurality of gas outlets by the porosity of the material. The porous material may be suitable for releasing a gas, in particular He, Ar, and/or H ₂ , toward the substrate. For instance, the porous material may have a density typically between about 60% and about 85%, more typically between about 65% and about 75%. In one example, the porous material has a density of about 70%. In some embodiments, the porous material may be a sintered material. For instance, the porous material may be a metal, such as stainless steel, sintered stainless steel, aluminum, chromium, or a metal alloy.

[00176] According to some embodiments, the porous material may be processed, e.g. polished or the like, for influencing the roughness of the porous material and the curved substrate support surface in contact with the flexible substrate during operation. In some embodiments, which may be combined with other embodiments described herein, the porous material may be coated with a layer of a material having a lower roughness than the porous material. For instance, the porous material may be coated with a metal layer, such as a Cr layer. According to some embodiments, the coating layer on the porous layer, or even the porous layer itself, may have additional gas outlets processed into the layer, such as by drilling, laser cutting, or the like.

[00177] According to some embodiments described herein, the coating drum 122 may be a temperature controlled coating drum. The temperature controlled coating drum may allow the substrate to be cooled. For instance, the coating drum may include a temperature adjusting system, such as a temperature adjusting system 430. The temperature adjusting system 430 of the coating drum may include a system of channels disposed in the coating drum for cooling or heating the coating drum. The channels of the temperature adjusting system of the coating drum may be disposed close to the surface. The term "close to" typically relates to a distance of less than 5 cm, more typically less than 2.5 cm, and even more typically less than 1 cm between the surface oriented side of the channels and the curved substrate support surface 401. The channels are typically adapted for receiving a cooling fluid. [00178] According to some embodiments, which may be combined with other embodiments described herein, the coating drum may be controlled to be held at a temperature typically between about -30°C and about +170°C, more typically between about -20°C and about + 150°C, and even more typically between about -20°C and about + 80°C. In particular, for temperatures up to 100°C, even more particularly for temperatures below room temperature, the cooling fluid is typically a water-glycol mixture. In other applications, in particular in those applications where the surface is heated, the cooling fluid is typically a heat transferring oil. The used cooling fluid is suitable for temperatures up to typically 400°C, even more typically up to 300°C. The heat transferring oil that may be used is made on the basis of petroleum such as naphthene or paraffin. Alternatively, the heat transferring oil can be synthetic such as an isomer composite.

[00179] According to some embodiments, which may be combined with other embodiments described herein, the coating drum 122 may typically have a width in the range from 0.1 m to 4 m, more typically from 0.5 to 2 m, e.g. about 1.4 m. The diameter of the coating drum may be more than 1 m, e.g. between 1.5 m and 2.5 m.

[00180] As is schematically depicted in FIG. 5, the plurality of deposition units 121 may include three or more and 12 or less deposition units which may be arranged in a circumferential direction around the coating drum 122. Similarly, in some embodiments including a first deposition chamber and a second deposition chamber, the second plurality of deposition units may include three or more and 12 or less second deposition units which may be arranged in a circumferential direction around the second coating drum. For example, six first deposition units may be arranged in the first deposition chamber, and/or six second deposition units may be arranged in the second deposition chamber.

[00181] In some embodiments, the deposition units may cover the lower half of the respective coating drum, respectively. In other words, the flexible substrate may come into contact with the coating drum in an upper angular region of the curved surface of the coating drum, may be guided downward by the rotating curved surface past the deposition units which may partially or entirely be provided in the lower half of the circumference of the coating drum, and may leave the curved substrate support surface after having been brought upward again to a second upper angular region of the curved substrate support surface. In some implementations, the deposition units may be arranged around the respective coating drum in an essentially symmetric way. In other words, the arrangement of the deposition units around the respective coating drum may be essentially symmetric with respect to a vertical symmetry plane intersecting through the rotation axis of the respective coating drum. For example, three deposition units of a total of six deposition units may be arranged on a first side of the vertical symmetry plane, and the remaining three deposition units may be arranged on the second side of the vertical symmetry plane.

[00182] In some embodiments, which may be combined with other embodiments described herein, gas separation units 510 may be provided between two adjacent deposition units 512 in order to reduce a flow of process gases from one deposition unit to other deposition units, e.g. to an adjacent deposition unit during operation, respectively. Gas separation units 510 between adjacent deposition units 512 are schematically depicted in FIG. 5 and in FIG. 9. [00183] The gas separation units 510 may be configured as gas separation walls which divide the inner volume of the deposition chamber in a plurality of separate compartments, wherein each compartment may include one deposition unit. One deposition unit 512 may be arranged between two neighboring gas separation units 510, respectively. In other words, the deposition units may be separated by the gas separation units 510, respectively. Accordingly, beneficially a high gas separation between neighboring compartments/ deposition units can be provided.

[00184] According to embodiments, which can be combined with other embodiments described herein, each of the compartments which house a respective deposition unit can be evacuated independently from the other compartments housing other deposition units, such that the deposition conditions of the individual deposition units 512 can be set as appropriate. Different materials can be deposited on the flexible substrate by adjacent deposition units which may be separated by gas separation units 510. [00185] According to some embodiments, the gas separation units 510 may include a gas separation wall which prevents or reduces gas from one deposition unit from flowing toward a neighboring deposition unit or from entering a main volume of the deposition chamber. The gas separation units 5 510 may be configured for adjusting a width of a slit 511 between the respective gas separation unit and the respective coating drum. According to some embodiments, the gas separation unit 510 may include an actuator configured for adjusting the width of the slit 511. In order to reduce the gas flow between adjacent deposition units and in order to increase the gas0 separation factor between adjacent deposition units, the width of the slit 511 between the gas separation units and the coating drum may be small, for example 1 cm or less, particularly 5 mm or less, more particularly 2 mm or less. In some embodiments, the lengths of the slits 511 in the circumferential direction, i.e. the length of the respective gas separation passages between two5 adjacent deposition compartments, may be 1 cm or more, particularly 5 cm or more, or even 10 cm or more. In some embodiments, the lengths of the slits may even be about 14 cm, respectively. The gas separation factor between two adjacent deposition units can be improved by increasing the length of the slits 511 between two adjacent deposition units. Gas separation factors of 1/100 or0 better may be provided. The mean free path length for gas molecules during deposition in the deposition units may be in the order of several centimeters. Accordingly, by providing slits 511 having a slit width below 5 mm and a length above 10 cm between adjacent deposition units, hardly any gas molecules will propagate between the deposition units. 5 [00186] In some embodiments, which may be combined with other embodiments described herein, at least one first deposition unit of the plurality of deposition units 121 may be a sputter deposition unit. In some embodiments, each deposition unit of the plurality of deposition units 121 is a sputter deposition unit. Therein, one or more sputter deposition units may be0 configured for DC sputtering, AC sputtering, RF (radio frequency) sputtering, MF (middle frequency) sputtering, pulsed sputtering, pulsed DC sputtering, magnetron sputtering, reactive sputtering or combinations thereof. DC sputter sources may be suitable for coating the flexible substrate with conductive materials, e.g. with metals such as copper. Alternating current (AC) sputter sources, e.g. RF sputter sources or MF sputter sources, may be suitable for coating the flexible substrate with conductive materials or with isolating materials, e.g. with dielectric materials, semiconductors or metals.

[00187] However, the deposition apparatus described herein is not limited to sputter deposition, and other deposition units may be used in some embodiments. For example, in some implementations, CVD deposition units, evaporation deposition units, PECVD deposition units or other deposition units may be utilized. In particular, due to the modular design of the deposition apparatus, it may be possible to replace a first deposition unit with a second deposition unit by radially removing the first deposition unit from the deposition chamber and by loading another deposition unit into the deposition chamber. For that reason, the deposition chamber may be provided with sealed lids which may be opened and closed for replacing one or more deposition units.

[00188] In some embodiments, which can be combined with other embodiments described herein, at least one AC sputter source may be provided, e.g. in the deposition chamber, for depositing a non-conductive material on the flexible substrate. In some embodiments, at least one DC sputter source may be provided in the deposition chamber for depositing a conductive material on the flexible substrate.

[00189] In some embodiments, at least one first deposition unit 301 of the plurality of deposition units 121 may be an AC sputter source. In the embodiment shown in FIG. 9, the first two deposition units of the plurality of deposition units are AC sputter sources, e.g. dual target sputter sources described below in more detail. A dielectric material such as silicon oxide may be deposited on the flexible substrate with the AC sputter sources. For example, two adjacent deposition units, e.g. the first deposition units 301, may be configured to deposit a silicon oxide layer directly on the first main surface of the flexible substrate in a reactive sputter process. The thickness of the resulting silicon oxide layer may be increased, e.g. doubled, by utilizing two or more AC sputter sources next to each other.

[00190] The remaining deposition units of the plurality of deposition units 121 may be DC sputter sources. In the embodiment shown in FIG. 9, at least one second deposition unit 302 of the plurality of deposition units arranged downstream from the at least one first deposition unit 301 may be a DC sputter source, e.g. configured for depositing an ITO layer. In other embodiments, two or more DC sputter sources configured for depositing an ITO layer may be provided. In some embodiments, the ITO layer may be deposited on top of the silicon oxide layer deposited by the at least one first deposition unit 301.

[00191] Further, in some embodiments, at least one third deposition unit 303 (e.g. three third deposition units) arranged downstream from the at least one second deposition unit 302, may be configured as DC sputter units, e.g. for depositing a first metal layer, e.g. a copper layer. Several layers of different metals may be deposited, or one thick layer of a single metal, e.g. Cu, may be deposited by the at least one third deposition unit 303.

[00192] In some embodiments, the first metal layer may be deposited on top of the ITO layer deposited by the at least one second deposition unit 302.

[00193] Accordingly, a stack of layers may be deposited on the first main surface of the flexible substrate in the deposition chamber, e.g. comprising a silicon oxide layer, an ITO layer, and a Cu layer deposited on top of each other.

[00194] In some embodiments including a first deposition chamber and a second deposition chamber, further layers may be deposited afterward in the second deposition chamber. For example, at least one fourth deposition unit of a second plurality of deposition units may be configured as a DC sputter unit, e.g. for depositing a second metal layer, e.g. a second Cu layer, on top of the first metal layer. In some implementations, all deposition units of the second plurality of deposition units may be DC sputter units configured for depositing a metal layer, respectively. Further, in some implementations, the same metal, e.g. copper, may be deposited. Accordingly, a single thick metal layer, e.g. a thick copper layer, may be deposited by the second plurality of deposition units.

[00195] Accordingly, e.g. in the embodiment shown in FIG. 5, a total of 6 deposition units may be provided. The first two deposition units (at least one first deposition unit 301) are configured for depositing a silicon oxide layer, the subsequent deposition unit (at least one second deposition unit 302) is configured for depositing an ITO layer, and the remaining three deposition units (third deposition units 303) may be configured for depositing a thick copper layer. It is to be understood that the described arrangement is only an exemplary arrangement, and modifications of the total number of deposition units, of the types of deposition units, of the order of deposition units, as well as of the materials to be deposited by the deposition units are possible as appropriate.

[00196] A layer stack including a Si0 ₂ -layer, an ITO layer, and a copper layer may be deposited on a flexible substrate. The flexible substrate may be a polymeric substrate having an index matched (IM) layer provided on one main surface thereof or on both main surfaces thereof. For example, the flexible substrate may be a COP substrate with an IM-layer on both main surfaces thereof. [00197] After coating of the first main surface of the flexible substrate with the stack of layers, the one-side coated substrate may be loaded again into the first spool chamber in an inverted orientation. Afterward, also the second main surface of the flexible substrate may be coated with a corresponding stack of layers or with a different stack of layers by transporting the flexible substrate a second time through the deposition apparatus 100 in an inverted orientation. Accordingly, a two-side coated substrate can be manufactured, whereas winding defects can be reduced or entirely avoided.

[00198] In FIG. 9, which shows an enlarged view of part of a deposition chamber, e.g. of the deposition chamber 120, a plurality of deposition units, namely six deposition units, are arranged in the deposition chamber. Gas separation units 510 are provided between adjacent deposition units, respectively. Accordingly, as exemplarily shown in FIG. 9, six compartments for six deposition units may be provided around the coating drum, particularly around the lower half of the coating drum. A flexible substrate may be transported through the slits 511 between the gas separation units 510 and the coating drum 122. The deposition units may be configured such that the heat load provided toward the flexible substrate during deposition may be reduced or minimized.

[00199] At least one first deposition unit 301 may be configured as an AC sputter source 610, at least one second deposition unit 302 may be configured as a DC sputter source 612, and at least one third deposition unit 303 may be configured as a DC sputter source 612.

[00200] FIG. 10 shows the AC sputter source 610 in more detail, and FIG. 11 shows the DC sputter source 612 in more detail. [00201] The AC sputter source 610 shown in FIG. 10 may comprise two sputter devices, i.e. a first sputter device 701 and a second sputter device 702. In the following description, a "sputter device" is to be understood as a device including a target 703 comprising a material to be deposited on the flexible substrate. The target may be made of the material to be deposited or at least of components of the material to be deposited. In some embodiments, a sputter device may include a target 703 configured as a rotatable target having a rotation axis. In some implementations, a sputter device may include a backing tube 704 on which the target 703 may be arranged. In some implementations, a magnet arrangement for generating a magnetic field during the operation of the sputter device may be provided, e.g. inside a rotatable target. In cases where a magnet arrangement is provided in the rotatable target, the sputter device may be referred to as a sputter magnetron. In some implementations, cooling channels may be provided within the sputter device in order to cool the sputter device or parts of the sputter device. [00202] In some implementations, the sputter device may be adapted to be connected to a support of a deposition chamber, e.g. a flange may be provided at an end of the sputter device. According to some embodiments, the sputter device may be operated as a cathode or as an anode. For example, the first sputter device 701 may be operated as a cathode, and the second sputter device

702 may be operated as an anode at one point in time. When an alternating current is applied between the first sputter device 701 and the second sputter device 702, at a later point in time, the first sputter device 701 may act as an anode and the second sputter device 702 may act as a cathode. In some embodiments, the target 703 may include or be made of silicon.

[00203] The term "twin sputter device" refers to a pair of sputter devices, e.g. to the first sputter device 701 and the second sputter device 702. The first sputter device and the second sputter device may form a twin sputter device pair. For instance, both sputter devices of the twin sputter device pair may be simultaneously used in the same deposition process to coat the flexible substrate. Twin sputter devices may be designed in a similar way. For example, twin sputter devices may provide the same coating material, may substantially have the same size and substantially the same shape. The twin sputter devices may be arranged adjacent to each other to form a sputter source which may be arranged in a deposition chamber. According to some embodiments, which may be combined with other embodiments described herein, the two sputter devices of the twin sputter device include targets made of the same material, e.g. silicon.

[00204] As can be seen in FIG. 9 and in FIG. 10, the first sputter device 701 has a first axis, which may be the rotation axis of the first sputter device 701. The second sputter device 702 has a second axis, which may be the rotation axis of the second sputter device 702. The sputter devices provides a material to be deposited on the flexible substrate. For reactive deposition processes, the material finally deposited on the flexible substrate can additionally include compounds of a processing gas. Accordingly, it is to be understood that a target

703 consisting e.g. of silicon or doped silicon includes silicon material, whereas exemplarily oxygen can be added as a processing gas to finally deposit silicon oxide.

[00205] According to the embodiment as exemplarily shown in FIG. 9, the flexible substrate is guided past the twin sputter devices by the coating drum 122. Therein, a coating window is limited by a first position 705 of the flexible substrate on the coating drum 122 and a second position 706 of the flexible substrate on the coating drum 122. The coating window, i.e. the portion of the flexible substrate between the first position 705 and the second position 706, defines the area of the substrate on which material may be deposited. As can be seen in FIG. 9, particles of the deposition material released from the first sputter device 701 and particles of the deposition material released from the second sputter device 702 reach the flexible substrate in the coating window.

[00206] The sputter source 610 may be adapted so as to provide a distance of the first axis of the first sputter device 701 to the second axis of the second sputter device 702 of 300 mm or less, particularly 200 mm or less. Typically, the distance of the first axis of the first sputter device 701 and the second axis of the second sputter device 702 may be between 150 mm and 200 mm, more typically between 170 mm and 185 mm, such as 180 mm.

[00207] According to some embodiments, the outer diameter of the first sputter device and of the second sputter device which may be cylindrical sputter devices may be typically in the range of 90 mm and 120 mm, more typically between about 100 mm and about 110 mm.

[00208] In some embodiments, the first sputter device 701 may be equipped with a first magnet arrangement and the second sputter device 702 may be equipped with a second magnet arrangement. The magnet arrangements may be magnet yokes configured for generating a magnetic field to improve the deposition efficiency. According to some embodiments, the magnet arrangements may be tilted towards each other. The magnet arrangements being arranged in a tilted way towards each other may mean in this context that the magnetic fields generated by the magnet arrangements are directed towards each other.

[00209] According to some embodiments, the above described sputter devices may be used to deposit non-conductive and/or conductive materials onto flexible substrates. For example, the sputter source 610 may provide target materials such as silicon, titanium, aluminum. Together with a gas inlet for introducing one or more process gases, materials such as silicon oxide, silicon nitride, titanium oxides, aluminum oxide, or the like, may be deposited on the flexible substrate, e.g. by reactive sputtering processes. In particular, the AC sputter source 610 may be used for a reactive sputter process, such as reactive sputtering of Si0 ₂ . Thus, according to some embodiments, which may be combined with other embodiments described herein, the deposition apparatus may be provided with further equipment such as gas inlets for process gases such as oxygen or nitrogen. [00210] According to some embodiments, the AC sputter source 610 may be used in a process where two sputter devices are operated at middle frequency, such as in the frequency range between about 10 kHz to about 50 kHz. In one embodiment, the AC sputter source 610 may be adapted for using one of the two sputter devices as an anode and the respective other one as a cathode. Generally, the AC sputter source 610 is adapted so that the operation of the sputter devices as anode and cathode may be alternated. That means that the sputter device being formerly used as an anode may be used as a cathode, and the sputter device being formerly used as a cathode may be operated as an anode, corresponding to the frequency of the applied voltage. [00211] According to some embodiments, the AC sputter source 610 may be configured for a reactive deposition process. A closed-loop control for the reactive deposition process may be provided. A reactive deposition process can be used for the deposition of a silicon oxide layer, wherein silicon is sputtered from a sputter device, and a process gas such as oxygen is provided from a gas inlet. In the case of a low process gas flow and a high electric field applied to the sputter devices, the process is conducted in a metallic mode. In the case of a higher process gas flow, the deposition process may turn into an oxygen mode, where a transparent silicon oxide layer can be deposited. Accordingly, a method of controlling the reactive deposition process may control the deposition process to be provided in a transition mode, where a transparent layer, such as silicon oxide, can be deposited at a comparably high rate.

[00212] In some embodiments, the deposition process can be controlled by providing a voltage supply that can keep the sputter device in the transition mode by using a voltage control. Therein, the power supply connected to the sputter devices for powering the sputter devices may be operated voltage controlled, e.g. providing a fixed voltage to the sputter devices. However, when providing a voltage control to the power supply, the voltage supply results in being voltage controlled and the power is not kept constant, because the power supply can only keep one parameter fixed. If a voltage control is used, the power and therefore the deposition rate may be changing with the used process gases and this is not always acceptable.

[00213] Accordingly, in addition to the voltage control of the power supply, a power control can be provided as a closed control loop, wherein the actual power is monitored and the flow rate of the process gas is controlled to keep the power essentially constant. A closed-loop control providing an essentially constant deposition rate can be provided. Accordingly, in some implementations, the reactive deposition process is voltage controlled and establishes an oxygen flow regulation which keeps the sputter power constant.

[00214] In some implementations, the process gas can include at least one of oxygen, argon, nitrogen, hydrogen, H ₂ 0, and N ₂ 0. Typically, oxygen can be provided as a reactive gas for the reactive deposition process. Providing a small amount of nitrogen in the process gas for an oxygen-based reactive process can be beneficial for stabilizing the generated plasma.

[00215] According to typical embodiments, a voltage set point value may be provided to the power supply as an upper limit for the voltage which the power supply can provide to the sputter device. The voltage of the power supply may be fixed by the set point value. The power provided by the power supply may depend on the fiow of reactive gas in the plasma region. For example, for a silicon oxide deposition process, the power can depend on the oxygen fiow while being limited by the voltage set point value. A controller, which provides the closed-loop control, controls the process gas fiow depending on the actual power, which is provided to the sputter device.

[00216] The fiow rate of the process gas introduced into the plasma region may be proportional to the output power of the power supply provided to the sputter device. A controller may control the gas fiow rate such that the actual power value, which may be provided as a signal from the power supply to the controller, is essentially kept constant.

[00217] Accordingly, according to embodiments described herein, the reactive deposition process may be kept in the transition mode, and a highly uniform non-conductive layer such as a silicon oxide layer may be deposited on the flexible substrate by the at least one first deposition unit 301 which may be configured as an AC sputter source 610.

[00218] FIG. 11 shows an enlarged schematic view of a DC sputter source 612 that may be used in some of the embodiments described herein. In some embodiments, the at least one second deposition unit 302 depicted in FIG. 9 is configured as a DC sputter source 612, and/or the at least one third deposition unit 303 is configured as a DC sputter source 612.

[00219] The DC sputter source 612 may include at least one cathode 613 including a target 614 for providing the material to be deposited on the flexible substrate. The at least one cathode 613 may be a rotatable cathode, particularly an essentially cylindrical cathode, which may be rotatable around a rotation axis.

[00220] The target 614 may be made of the material to be deposited. For example, the target 614 may be a metal target, such as a copper or an aluminum target. A magnet assembly 615 for confining the generated plasma may be arranged inside the rotatable cathode. [00221] In some implementations, the DC sputter source 612 may include a single cathode, as exemplarily shown in FIG. 11. In some embodiments, a conductive surface, e.g. a wall surface of the deposition chamber, may act as an anode. In other implementations, a separate anode, such as an anode having the shape of a rod, may be provided next to the cathode such that an electric field may build up between the at least one cathode 613 and the separate anode. A power supply may be provided for applying an electric field between the at least one cathode 613 and the anode. A DC-electric field may be applied which may allow for the deposition of a conductive material, such as a metal. In some implementations, a pulsed DC field is applied to the at least one cathode 613. In some embodiments, the DC sputter source 612 may include more than one cathode, e.g. an array of two or more cathodes.

[00222] According to some embodiments, which may be combined with other embodiments described herein, a deposition unit as described herein may be configured as a double DC planar cathode sputter source 616, as exemplarily shown in FIG. 12. For instance, the double DC planar cathode may include a first planar target 617 and a second planar target 618. The first planar target can include a first sputter material and the second planar target can include a second sputter material which is different from the first sputter material. According to some implementations, a protection shield 619 may be provided between the first planar target 617 and the second planar target 618, as exemplarily shown in FIG. 12. The protection shield may be attached, e.g. clamped, to a cooled part such that cooling of the protection shield can be provided. More specifically, the protection shield may be configured and arranged between the first planar target and the second planar target such that intermixing of the respective material provided from the first planar target and the second planar target can be prevented. Further, as exemplarily shown in FIG. 12, the protection shield can be configured such that a narrow gap G between the protection shield and a substrate on the coating drum 122 is provided. Accordingly, a double DC planar cathode can beneficially be configured for depositing two different materials. Typically, as described herein, a deposition unit including an AC sputter source 610, a DC sputter source 612, or a double DC planar cathode sputter source 616 is provided in a compartment as described herein, i.e. a compartment provided between two gas separation units 510 as described herein.

[00223] According to embodiments, which can be combined with other embodiments described herein, it is to be understood that the deposition units, particularly the cathodes (e.g. the AC sputter source, the DC-rotatable cathode, the twin rotatable cathode, and the double DC planar cathode) are interchangeable. Accordingly, a common compartment design may be provided. Further, the deposition units may be connected to a process controller which is configured to individually control the respective deposition unit. Accordingly, beneficially, a process controller may be provided such that the reactive process can be run fully automated.

[00224] In some embodiments, which may be combined with other embodiments described herein, the deposition apparatus may be used for manufacturing a transparent body for use in a touch panel. A first transparent layer stack may be deposited on a first main surface of the flexible substrate, wherein the first transparent layer stack may include one or more silicon containing layers, e.g. a silicon oxide layer. A transparent conductive film, e.g. an ITO film, may be deposited on top of the first transparent layer stack. The ITO film may be provided in a predetermined pattern. In some embodiments, a monitoring device may be provided for measuring, during deposition, optical properties, e.g. the transmission and/or the reflection, of at least one of the first transparent layer stack and the transparent conductive film. In some embodiments, a metal layer may be deposited on top of the transparent layer stack.

[00225] Afterward, in some embodiments, the same layer stack or a different layer stack may be deposited on the second main surface of the substrate which is the opposite main surface of the flexible substrate. The second main surface of the substrate may be coated by loading the one-side coated surface into the deposition apparatus in an inverted orientation and by transporting the flexible substrate in the inverted orientation past the deposition units provided in the deposition chamber such that the second main surface can be coated with the same layer stack or with a different layer stack.

[00226] A two-side coated flexible substrate can be provided with a low number of defects due to the tension-controlled transport of the flexible substrate along a substrate transportation path which is partially concave and partially convex. Further, a two-side coated flexible substrate with a reduced number of defects can be provided because both main surfaces of the substrate may be cleaned, particularly before deposition and/or after deposition, particularly before the respective main surface of the flexible substrate comes into contact with a roller surface at a high tensioning force.

[00227] FIGS. 13A-13C show exemplary schematic layouts of a sequence of deposition units which may be provided around a coating drum in a deposition chamber according to embodiments described herein. In the following, the sequence of the plurality of deposition units 121 for the different layout examples shown in FIGS. 13A-13C are described from left to right, i.e. the first deposition unit refers to the very left deposition unit and the sixth deposition unit refers to the very right deposition unit in FIGS. 13A-13C. Further, for better understanding, typically the first deposition unit is the first deposition unit along the substrate transportation part, e.g. for depositing a first layer onto the substrate.

[00228] In particular, FIG. 13A shows a first exemplary schematic layout for a plurality of deposition units 121 provided around a coating drum in a deposition chamber as described herein. As exemplarily shown in FIG. 13 A, according to embodiments which can be combined with any other embodiments described herein, the first deposition unit can be a twin rotational deposition unit, particularly an AC sputter source 610 as described herein, configured for Si0 ₂ deposition. The second deposition unit can be a DC rotational deposition unit, particularly a DC sputter source 612 as described herein, configured for NbO _x deposition. The third deposition unit, the fourth deposition unit and the fifth deposition unit can be twin rotational deposition units, particularly AC sputter sources as described herein, configured for Si0 ₂ deposition. The sixth deposition unit can be a DC rotational deposition unit, particularly a DC sputter source 612 as described herein, configured for ITO deposition. Accordingly, with the first exemplary schematic layout as shown in FIG. 13 A, a layer stack with a first layer of Si0 ₂ , a second layer of NbO _x , a third layer of Si02, a fourth layer of Si0 ₂ , a fifth layer of Si0 ₂ , and a sixth layer of ITO can be deposited on a substrate. Such a layer stack can for example be used for providing a hardcoat with an ITO top layer on a substrate, e.g. a PET substrate.

[00229] According to a second exemplary layout for a plurality of deposition units 121 as exemplarily shown in FIG. 13B, the first deposition unit can be a twin rotational deposition unit, particularly an AC sputter source 610 as described herein, configured for Si0 ₂ deposition. Further, also the second deposition unit, the third deposition unit, and the fourth deposition unit can be twin rotational deposition units, particularly AC sputter sources as described herein, configured for Si0 ₂ deposition. The fifth deposition unit and the sixth deposition unit can be DC rotational deposition units, particularly DC sputter sources 612 as described herein, configured for ITO deposition. Accordingly, with the second exemplary schematic layout as shown in FIG. 13B, a layer stack with a first layer of Si0 ₂ , a second layer of Si0 ₂ , a third layer of Si02, a fourth layer of Si0 ₂ , a fifth layer of ITO, and a sixth layer of ITO can be deposited on a substrate. Such a layer stack can for example be used for providing an ITO double top layer on a refractive index matching layer stack with four layers of Si0 ₂ on a substrate.

[00230] According to a third exemplary layout for a plurality of deposition units 121 as exemplarily shown in FIG. 13C, the first deposition unit and the second deposition unit can be twin rotational deposition units, particularly AC sputter sources as described herein, each configured for deposition of a di- electrical layer. The third deposition unit can be a DC rotational deposition unit, particularly a DC sputter source 612 as described herein, configured for depositing a seed layer. The fourth deposition unit can be a double DC planar cathode sputter source 616 as described herein configured for deposition of silver (Ag) and a blocker layer. The fifth deposition unit and the sixth deposition unit can be twin rotational deposition units, particularly AC sputter sources as described herein, each configured for deposition of a di-electrical layer. Accordingly, with the third exemplary schematic layout as shown in 5 FIG. 13C, a layer stack with a first di-electric layer, a second di-electric layer, a third layer being a seed layer, a fourth layer including Ag and a blocker, a fifth di-electric layer, and a sixth di-electric layer can be deposited on a substrate. Such a layer stack can for example be used for providing a low emittance coating also known as low E-coating.

10 [00231] FIG. 14 is a flow diagram illustrating a method 800 of coating a flexible substrate with a stack of layers according to embodiments described herein. The method may be conducted with a deposition apparatus 100 according to any of the embodiments described herein. Therein, the flexible substrate is transported along a partially convex and partially concave substrate

15 transportation path from a storage spool in a first spool chamber to a wind-up spool in a second spool chamber. The method includes, in box 810, unwinding the flexible substrate from the storage spool provided in the first spool chamber; followed by, in box 820, depositing at least one first layer of the stack of layers on a first main surface of the flexible substrate, while the

20 flexible substrate is guided by a coating drum provided in a deposition chamber; followed by, in box 830, winding the flexible substrate on the wind- up spool provided in a second spool chamber after deposition.

[00232] Thereafter, also the second main surface of the flexible substrate may optionally be coated with a second stack of layers by: removing, in box

25 840, the wind-up spool with the flexible substrate wound thereon (which may have a coated first main surface) from the second spool chamber and replacing the storage spool in the first spool chamber with the removed wind-up spool in an inverted orientation; followed by, in box 850, depositing the second stack of layers on the second main surface, while guiding the flexible substrate through

30 the deposition chamber; followed by, in box 860, winding the flexible substrate on a further wind-up spool provided in the second spool chamber. [00233] According to a further aspect described herein, a method 900 of aligning a deposition apparatus for coating a flexible substrate is provided, as exemplarily illustrated by the flowchart as shown in FIG. 15. In particular, a deposition apparatus of any of the embodiments described herein may be aligned before the deposition apparatus is used for depositing a stack of layers on a flexible substrate. The deposition apparatus may include a roller assembly configured to transport the flexible substrate along a partially convex and partially concave substrate transportation path from a storage spool arranged in a first spool chamber to a wind-up spool arranged in a second spool chamber. [00234] The method of aligning may include, in box 910, defining at least one guiding roller of the roller assembly having a first rotation axis as a reference roller; and, in box 920, aligning rotation axes of two or more remaining guiding rollers of the roller assembly with respect to a first rotation axis of the reference roller such as to extend parallel to the first rotation axis of the reference roller. In other word, the rollers of the roller assembly may be referenced against one master roller, i.e. the reference roller.

[00235] When the roller axis of each of the remaining guiding rollers is aligned with respect to the first rotation axis of the reference roller, the roller axes of all guiding rollers are not only parallel with respect to the reference roller, but also with respect to each other. A roller assembly with an excellent roller alignment can be provided, and a diagonal pulling force acting on the flexible substrate can be avoided. In particular, the rollers of the roller assembly can be adjusted to deviation of < 0.1 mm/m length, in particular in a horizontal and/or a vertical direction. [00236] In some embodiments, the roller axes of the guiding rollers may have a length along the rotation axis of 1 m or more and 2 m or less, particularly about 1.5 m or about 1.8 m. The deposition apparatus may have more than 20 guiding rollers and less than 60 guiding rollers, for example about 30 guiding rollers which may be aligned with respect to the reference roller, respectively, in order to be essentially parallel with the reference roller and, thus, with each other. [00237] In view of the embodiments described herein, it is to be understood that compared to conventional deposition systems, an improved deposition apparatus for coating one or both main surfaces of a flexible substrate with a stack of layers is provided, wherein the layers have a high uniformity and a low number of defects per surface area.

[00238] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope is determined by the claims that follow.