METHOD

TECHNICAL FIELD [0001 ] Embodiments of the present disclosure relate to deposition apparatuses for depositing one or more layers, particularly layers including organic materials therein, on a substrate. In particular, embodiments of the present disclosure relate to evaporation apparatuses for evaporating a material to be evaporated, and evaporation methods, particularly for OLED manufacturing. Specifically, embodiments described herein relate to evaporation apparatuses, evaporation sources, and evaporation methods.

BACKGROUND

[0002] Techniques for depositing a layer on a substrate typically include an evaporation of a material in an evaporation source. For instance, evaporation sources are a tool for the production of organic light-emitting diodes (OLED) and other electronic or optic devices including a stack of deposited materials. OLEDs are a special type of light-emitting diode in which the emissive layer comprises a thin- film of certain organic compounds. Organic light emitting diodes (OLEDs) are used in the manufacture of television screens, computer monitors, mobile phones, other hand-held devices, etc., for displaying information. OLEDs can also be used for general space illumination. The range of colors, brightness, and viewing angles possible with OLED displays is greater than that of traditional LCD displays because OLED pixels directly emit light and do not involve a back light. Therefore, the energy consumption of OLED displays is considerably less than that of traditional LCD displays. Further, the fact that OLEDs can be manufactured onto flexible substrates results in further applications. Evaporation sources can also be used for the deposition of other material layers, e.g. metal layers, on substrates, such as on glass substrates or semiconductor wafers.

[0003] Evaporation sources typically include an evaporation apparatus that is configured to evaporate a source material by heating the source material to a temperature at or above the evaporation temperature of the source material. The evaporated material may be guided into a vapor distribution pipe of the evaporation source that is configured for directing the evaporated material onto a substrate.

[0004] Continuously providing a suitable deposition rate and quality with an evaporation source is challenging. In particular, the deposition rate may change over time due to a non-continuous flow of heat from the evaporation apparatus to the material to be evaporated. Furthermore, the quality of the source material may be affected if the source material is exposed to elevated temperatures over an extended time in the evaporation apparatus.

[0005] Using a foam structure as a heating element for evaporating the source material reduces the amount of source material that is exposed to elevated temperatures at a time, such that material degradation can be reduced and the source material quality can be improved. However, the evaporation rate is typically smaller as compared to evaporation apparatuses with a crucible that is configured for heating up a large material storage volume.

[0006] Accordingly, there is a continuing demand for providing improved evaporation apparatuses, evaporation sources and evaporation methods. Specifically, it would be desirable to provide an evaporation apparatus that can provide a high evaporation rate while reducing or avoiding a degradation of the source material due to extended exposure to elevated temperatures. Further, it would be beneficial to improve the quality of the source material and hence to improve the quality of the material layers deposited on the substrate.

SUMMARY

[0007] In light of the above, an evaporation apparatus, an evaporation source, and an evaporation method according to the independent claims are provided. Further aspects, benefits, and features of the present disclosure are apparent from the claims, the description, and the accompanying drawings.

[0008] According to an aspect of the present disclosure, an evaporation apparatus for evaporating a material to be evaporated is provided. The evaporation apparatus includes a heatable foam structure for supporting the material thereon, a vapor guiding conduit below the heatable foam structure, and a pressure device configured for pressing at least a portion of the material towards the heatable foam structure. [0009] Terms as used herein referring to directions or to the position of features relative to one another, for example “below”, “thereon”, “vertical” or “downward”, can be understood with respect to the direction of a gravitational force. For example, a downward vertical direction is directed along the direction of the gravitational force (exemplarily indicated in Fig. 2, see reference sign (g)). [0010] According to another aspect of the present disclosure, an evaporation source is provided. The evaporation source includes an evaporation apparatus according to any of the embodiments described herein, and a vapor distribution pipe in fluid communication with the vapor guiding conduit of the evaporation apparatus, the vapor distribution pipe comprising a plurality of vapor nozzles for directing the evaporated material toward a substrate.

[0011] According to yet another aspect of the present disclosure, an evaporation method is provided. The evaporation method includes arranging a material to be evaporated in a material reservoir on top of a heatable foam structure, heating the heatable foam structure for evaporating the material supported on the heatable foam structure, and pressing at least a portion of the material downwardly towards the heatable foam structure.

[0012] Embodiments are also directed at apparatuses for carrying out the disclosed methods and include apparatus parts for performing each described method aspect. These method aspects 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 according to the disclosure are also directed at methods for operating the described apparatus. It includes method aspects for carrying out every function of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments. The accompanying drawings relate to embodiments of the disclosure and are described in the following:

Figs. 1-5 show schematic views of evaporation apparatuses according to embodiments described herein;

Fig. 6 shows a schematic view of an evaporation source according to embodiments described herein; and

Fig. 7 shows a flow chart illustrating an evaporation method according to embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

[0014] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations. [0015] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment can apply to a corresponding part or aspect in another embodiment as well.

[0016] Before various embodiments of the present disclosure are described in more detail, some aspects with respect to some terms and expressions used herein are explained.

[0017] In the present disclosure, an “evaporation apparatus” can be understood as a device configured for evaporating a material, particularly by heating the material to a temperature at or above an evaporation temperature at which the material vaporizes. The evaporation apparatus includes a heatable foam structure for supporting the material thereon.

[0018] In some embodiments, the heatable foam structure is a heatable porous structure. In particular, the heatable foam structure includes openings and/or open pores to allow for the evaporated material to propagate through the heatable foam structure. The porosity or void fraction of the heatable foam structure may be in the range of 50% to 99%, particularly in the range of 70% to 99%, more particularly in a range of 90% to 99%. For example, the heatable foam structure may have a porosity of about 97%. Due to the pores, the heatable foam structure can have a large surface area. For example, the surface area of the heatable foam structure may be in the range of 10 cm ² to 100 cm ² per cubic centimeter of foam volume of the heatable foam structure, e. g. 65 cm ² per cubic centimeter. In some embodiments, the heatable foam structure may have 5 pores or more per inch (ppi) or more, 45 ppi or more, particularly 65 ppi or more, and/or 200 ppi or less, 150 ppi or less, particularly 120 ppi or less. For example, the heatable foam structure may have a pore density in a range of 65 ppi to 120 ppi.

[0019] In some embodiments, the heatable foam structure can include an open cell reticulated structure, in particular a conductive, open-cell reticulated structure. For example, the heatable foam structure includes a carbon foam or a glassy carbon foam. Open-cell vitreous carbon foam, also called reticulated vitreous carbon foam, is a vitreous carbon structure of three-dimensional interconnected polyhedron cells. The carbon material may be a glassy carbon (as opposed to a graphitic carbon). An “open-cell porous structure” as used herein relates to a structure where no film or solid is connected between the ligaments so that there is free communication into and out of a foam cell, and groups of adjoining cells are typically interconnected and form a 3D interconnected structure. A carbon foam is beneficial in view of the foam properties and porosity, at the same time being conductive, such that the carbon foam can be used as a resistive heating element by guiding electric current therethrough. In some embodiments, other porous materials may be used as the heatable foam structure.

[0020] In some embodiments, the heatable foam structure may include a coated surface. For example, the heatable foam structure can include an electrically conductive foam, particularly a carbon foam, and an electrically insulating material layer on the electrically conductive foam. In particular, the heatable foam structure may be an open-cell reticulated structure that is coated with the electrically insulating material. In some embodiments, the electrically insulating material includes a ceramic and/or a polymer, particularly silicon carbide. The electrically insulating material layer may electrically insulate the electrically conductive foam. In particular, the electrically conducting foam may be electrically insulated from an environment by the electrically insulating material layer. The electrically insulating material layer may form the outer surface layer of the heatable foam structure. In other words, the heatable foam structure may have an electrically insulating surface layer covering an electrically conductive inner porous structure.

[0021] The electrically insulating material layer may be a layer with a high thermal conductivity, such that the heat of the electrically conductive foam is conducted to the outer surface of the heatable foam structure where the source material is brought into contact with the heatable foam structure. In other words, the electrically insulating material layer may include an electrically insulating, but thermally conductive material, which may form the outer surface layer of the heatable foam structure. For example, in some embodiments, the electrically insulating material layer may include a thermally conductive ceramic material, e.g. SiC.

[0022] In some embodiments, the heatable foam structure can be heated directly. For example, the heatable foam structure can be electrically conductive and a foam heating device can supply an electric current through the heatable foam structure to heat the heatable foam structure. In some embodiments, the heatable foam structure can be heated indirectly. For example, the heatable foam structure can be heated by a foam heating device including a heat source. In particular, the heatable foam structure can be in thermal contact with the heat source of the foam heating device. For example, the heatable foam structure can be heated by solid-to-solid heat transfer from the heat source to the heatable foam structure.

[0023] In some embodiments of the present disclosure, the material that is to be evaporated (also referred to as a “source material” herein) is provided in a solid form, e.g. as a powder or a granulate. The source material can be an organic material, particularly an organic material for the manufacturing of OLED devices. Organic materials may have an evaporation temperature in a range between 200°C and 400°C.

[0024] The source material can be placed on top of the heatable foam structure, such that the source material is supported on the heatable foam structure, and a lowermost portion of the source material is in contact with the heatable foam structure. When the heatable foam structure is heated, the portion of the source material contacting the heatable foam structure evaporates and passes through the heatable foam structure in a downward direction. The evaporated source material can exit the heatable foam structure at a lower side thereof and can enter a vapor guiding conduit that is arranged below the heatable foam structure.

[0025] According to the present disclosure, the source material may evaporate or sublimate from a solid state directly to a vapor state, or the source material may liquefy from a solid state to a liquid state and evaporate from the liquid state to a vapor. In some embodiments, the source material infiltrates the heatable foam structure at least partially. In particular, if the source material liquefies before evaporating, the melting material can move into the heatable foam structure by capillary forces.

[0026] In the present disclosure, an “evaporation source” can be understood as a device or assembly configured for providing an evaporated material to be deposited on a substrate. In particular, an “evaporation source” may be a device or assembly having an evaporation apparatus configured to evaporate the material to be deposited and a vapor distribution pipe configured for directing the evaporated material to the substrate in a deposition direction (see Fig. 6). The vapor distribution pipe can have a plurality of vapor nozzles that can be directed toward a substrate. Accordingly, the evaporated material, for example an organic material, is guided within the vapor distribution pipe and exits the vapor distribution pipe through one or more vapor nozzles.

[0027] In the present disclosure, a “vapor distribution pipe” can be understood as an assembly configured for directing evaporated material, particularly one or more plumes of evaporated material, toward the substrate. For example, the vapor distribution pipe may include a pipe which can be an elongated tube. For instance, a distribution pipe as described herein may provide a line source with a plurality of vapor nozzles, which are arranged in at least one line along the length of the pipe.

[0028] In some embodiments, the vapor distribution pipe can be a linear distribution showerhead. The linear distribution showerhead may extend in an essentially vertical direction, such that an essentially vertically oriented substrate can be coated by the evaporation source. A linear distribution showerhead can have a hollow space or tube in which the evaporated material can be guided, for example from the evaporation apparatus, in particular from a vapor guiding conduit of the evaporation apparatus, to the substrate.

[0029] Fig. 1 shows a schematic view of an evaporation apparatus 100 for evaporating a material 110 to be evaporated. The evaporation apparatus 100 includes a heatable foam structure 105, which supports the material 110. The heatable foam structure can be configured to be heated to or above an evaporation temperature of the material 110, particularly such that material 110 at the interface of the material 110 and the heatable foam structure 105 evaporates. The heatable foam structure 105 is permeable to vapor such that evaporated material can pass through the heatable foam structure 105 into a vapor guiding conduit 115 positioned below the heatable foam structure 105. In some embodiments, the vapor guiding conduit 115 can be heated to or above the evaporation temperature of the material 110. Heating the vapor guiding conduit 115 can reduce or prevent condensation of evaporated material in the vapor guiding conduit 115.

[0030] The evaporation apparatus 100 includes a pressure device 120 configured for pressing at least a portion of the material 110 towards the heatable foam structure 105. In particular, the pressure device 120 is configured to press at least a portion of the material 110 by applying a force on the material 110, wherein at least one component of the force is directed towards the heatable foam structure 105. Particularly, the at least one component of the force can be directed in a downward direction, for example along the direction of a gravitational force. In some embodiments, the pressure device 120 is configured for pressing with a limited force, wherein the limited force is limited such that a material 110, which liquefies before evaporating, is not pressed through the heatable foam structure 105 in a liquid state.

[0031 ] Pressing the material towards the heatable foam structure can be beneficial in providing a stable evaporation rate or deposition rate in an evaporation apparatus. In particular, during the evaporation of the source material that is provided in a solid state (e.g., as a powder) in the evaporation apparatus, voids or bridges between particles can form at the interface between the material and the heatable foam structure. The voids or bridges may inhibit or reduce solid-to-solid heat transfer (i.e., thermal conduction) between the material and the heatable foam structure. The reduction in solid-to-solid heat transfer may reduce the evaporation rate. As a result, the temperature of the heatable foam structure may need to be increased, in order to increase the heat transfer from the heatable foam structure to the material through the voids (i.e., by thermal radiation). However, increasing the temperature of the heatable foam structure can promote decomposition of the material, in particular of organic material. Pressing the material towards the heatable foam structure according to the present disclosure can reduce or inhibit the formation of bridges or voids. Pressing can keep the material and the heatable foam structure in contact, particularly such that heat is transferred from the heatable foam structure to the material by solid-to-solid heat transfer.

[0032] In some embodiments, the evaporation apparatus 100 includes a material reservoir 125 above the vapor guiding conduit 115 for housing the material 110 to be evaporated, the heatable foam structure 105 being configured to heat and evaporate the material 110 and to let the evaporated material pass through into the vapor guiding conduit 115. In particular, the material reservoir 125 and the heatable foam structure 105 may enclose the material 110. The pressure device 120 can be positioned at least partially within the material reservoir 125. In some embodiments, the material reservoir may be configured to contain a volume of 1 dm ³ or more of the material, or of 3 dm ³ or more, particularly of 5 dm ³ or more, and/or 30 dm ³ or less, particularly of 20 dm ³ or less.

[0033] According to some embodiments, which can be combined with any other embodiment described herein, the pressure device of the evaporation apparatus may include a stirring element. A stirring element can stir or otherwise move the material and press at least a portion of the material towards a heatable foam structure. In particular, the stirring element can be configured to be positioned within the material. For example, the stirring element can be positioned in the material reservoir 125 at a distance of 40 mm or less, particularly 4 mm or less, above the heatable foam structure.

[0034] In some embodiments, the stirring element includes at least one blade, particularly at least two, three or four blades, rotatable around a rotation axis of the stirring element. For example, the rotation axis may be oriented along a vertical direction or along a horizontal direction. Herein, horizontal or vertical directions are to be understood with respect to a direction of a gravitational force. [0035] In some embodiments, the at least one blade includes a blade surface which is tilted or curved with respect to a plane perpendicular to the rotation axis of the stirring element. The at least one blade can be arranged at a rod of the stirring element, e.g. at a lower end of the rod. The rod can be rotatable around the rotation axis of the stirring element. The rod may be rotated by a motor, in particular by a motor positioned outside a material reservoir.

[0036] In Fig.2, a stirring element of the pressure device 120 exemplarily includes two blades 230 rotatable around a rotation axis (A). The blades 230 are arranged at a rod 233 of the stirring element. The rod 233 of Fig. 2 extends in a vertical direction, i.e. in the direction of the gravitational force (g). The rod 233 may extend through a wall of the material reservoir 125, e.g. through a top wall of the material reservoir. The stirring element can be moved, particularly rotated, by a drive or motor (not shown) that may be positioned outside the material reservoir 125.

[0037] Pressing at least a portion of the material towards the heatable foam structure using a stirring element can prevent or reduce the formation of voids or bridges in the material at an interface between the material and the heatable foam structure. Pressing using a stirring element can be particularly advantageous when a material is evaporated which liquefies before evaporating.

[0038] By moving a stirring element that is positioned close above the heatable foam structure, a defined force can specifically be applied to a portion of the material arranged just above the interface between the material and the heatable foam structure. In other words, a local force can be created inside the material in the direction of the foam structure, pressing a small portion of the material into contact with the foam structure with a defined force just above the foam structure. Void formation can reliably be reduced or prevented, and a thermal conduction from the heatable foam structure to the material can be ensured. Accordingly, the temperature of the heatable foam structure can be maintained at or slightly above the evaporation temperature of the material, reducing or avoiding a thermally caused degradation of the material. [0039] A downwardly directed force can, e.g., be generated by rotating a stirring element with tilted blades, by moving the stirring element in a downward direction, and/or by tilting the stirring element at least partially. For example, the stirring element can be moved downwardly and upwardly in a reciprocating manner, and the stirring element can additionally or alternatively be rotated or otherwise moved or tilted.

[0040] In some embodiments, an evaporation apparatus, in particular a material reservoir of the evaporation apparatus, may include a material feeding system to provide refill material to the material reservoir. In particular, a material feeding system may include a load lock for transferring refill material from an outside region outside the material reservoir into the material reservoir. For example, the outside region may have an outside pressure, e. g. atmospheric pressure, and the material reservoir may have a reservoir pressure, e. g. a vacuum. Pressing at least a portion of the material towards the heatable foam structure using a stirring element can provide the advantage that material can be refilled without interrupting an evaporation process or a deposition process.

[0041] According to some embodiments, a heatable foam structure 105 can be heated by a foam heating device 222 to a temperature at or above the evaporation temperature of the material 110, as shown for example in Fig. 2. [0042] According to some embodiments which can be combined with other embodiments, the vapor guiding conduit of the evaporation apparatus can be heated by a conduit heating device to a temperature at or above the evaporation temperature of the material. The conduit heating device can be arranged at least partially around the vapor guiding conduit. For example, in Fig. 2, a conduit heating device 255 is arranged around and along the length of the vapor guiding conduit 115.

[0043] In some embodiments, an inner radiation shield 245 can be positioned below the heatable foam structure 105. In particular, the inner radiation shield 245 can be positioned in the vapor guiding conduit 115. For example, the inner radiation shield 245 can be configured to shield the heatable foam structure 105 and/or the material 110 above the inner radiation shield 145 from at least a portion of heat radiation from the vapor guiding conduit 115 towards the material reservoir 125. The inner radiation shield 245 may be permeable to vapor. For instance, the inner radiation shield 245 may include a foam structure or a mesh structure. For example, the inner radiation shield 245 may be a carbon foam or a glassy carbon foam.

[0044] In some embodiments, an evaporation apparatus may include a temperature controlling device at least partially provided around the material reservoir. The temperature controlling device may be configured for adjusting a temperature within a main volume of the material reservoir, particularly to a temperature or to a temperature gradient in a temperature range of 80°C or more and/or 120°C or less. The temperature controlling device may be configured for maintaining a temperature of 30°C or more below the evaporation temperature of the material in a main volume of the material reservoir. The “main volume” can be understood as a volume of the material reservoir above a temperature gradient layer directly above the heatable foam structure. In the temperature gradient layer, the temperature of the material decreases from the heatable foam structure, where the material is heated to or above the evaporation temperature of the material, to an upper end of the temperature gradient layer, where the material has a temperature of 120°C or less. For example, the temperature gradient layer can have a vertical thickness of 100 mm or less, particularly of 40 mm or less, more particularly of 4 mm or less. In some embodiments, the temperature controlling device is configured to provide a temperature in a range between 80° and 120° in the main volume of the material reservoir. The main volume may house 80% or more of the material that is arranged in the material reservoir, particularly the upper 80% or more in the vertical direction. Accordingly, a major part of the material housed in the material reservoir can be maintained at a temperature well below the evaporation temperature, further reducing or avoiding material degradation.

[0045] In the exemplary embodiment of Fig. 2, a temperature controlling device 250 is provided around the material reservoir 125. Providing a temperature of a material 110 in the main volume of the material reservoir 125 of 80°C or more and/or 120°C or less may advantageously expel water vapor or contaminant gases from the material 110. In particular, a temperature controlling device 250 may improve a quality of a material layer deposited on a substrate. A temperature of the material of 120°C or less can avoid or reduce decomposition of the material 110, which may occur at higher temperatures.

[0046] According to some embodiments, which can be combined with other embodiments, an evaporation apparatus can include a gas outlet for guiding at least one of water vapor and contaminant gases out of the material reservoir. For example, the gas outlet may guide water vapor and contaminant gases expelled from the material out of the material reservoir. The gas outlet can be an evacuation outlet for evacuating the material reservoir or a separate gas outlet. In Fig. 2, the evaporation apparatus 200 includes a gas outlet 240, which extends through a wall of the material reservoir 125. The gas outlet 240 may be arranged above the material 110.

[0047] According to some embodiments, which can be combined with other embodiments, a pressure device of an evaporation apparatus can include a top pressure unit arranged to apply a pressure to the material from above. In some embodiments, the top pressure unit can include a weight configured to be positioned on top of the material. The weight may press the material downwards toward the heatable foam structure due to gravity. Fig. 3 shows a schematic view of an evaporation apparatus 300 including a weight 335 positioned above a material 110. The weight 335 is positioned within a material reservoir 125 of the evaporation apparatus 300. For example, the weight 335 may provide a pressure to the material from above of 10 g/cm ² or more, of 15 g/cm ² or more, particularly of 20 g/cm ² or more, and/or of 300 g/cm ² or less, of 250 g/cm ² or less, particularly of 200 g/cm ² or less. For example, the weight 335 may provide a pressure in a range of 20 g/cm ² to 200 g/cm ² .

[0048] In some embodiments, the evaporation apparatus includes a vapor permeable element, particularly a mesh or foam structure, configured to be positioned between the material and the top pressure unit. The vapor permeable element may be movable in a downward direction inside the material reservoir, e.g. along a vertical axis. Accordingly, the vapor permeable element may move downwardly in accordance with a filling level of the material in the material reservoir. The vapor permeable element can allow water vapor or contaminant gases expelled from the material to pass through the vapor permeable element. For example, the water vapor or contaminant gases can pass through the vapor permeable element and be evacuated from the material reservoir through a gas outlet. In particular, the gas outlet can be positioned above the vapor permeable element. In Fig. 3, a vapor permeable element 360 is positioned between the material 110 and the weight 335. The vapor permeable element may include mesh, a foam, or a sheet element with at least one opening, e.g. a perforated plate. The weight of the top pressure unit can be distributed more evenly across the material, and water vapor and other gases can propagate upwardly from the material through the vapor permeable element, e.g. toward the gas outlet.

[0049] In some embodiments, the evaporation apparatus includes a cooling device configured to be positioned within the material. In particular, the cooling device can include a cooling grid, for example a cooling grid with a thermal conductivity of > 20 W/(m K). The cooling device can be positioned at a distance of 15 mm or less above the heatable foam structure, particularly at a distance of 10 mm or less, or 5 mm or less. The cooling device can be positioned at a distance of 0.1 mm or more above the heatable foam structure, particularly at a distance of 1 mm or more, or 2 mm or more. For example, under vacuum conditions a material, which may be provided as a powder, can support a thermal gradient of approximately 200°C/mm. The cooling device can effectively keep the bulk of the material cooler than the evaporation temperature, for example 30°C or more cooler, particularly 50°C or more cooler.

[0050] In particular, materials which liquefy before evaporating often support only lower thermal gradients, e. g. 20°C/mm or less. In embodiments, which are configured for evaporating a material which liquefies before evaporating, the cooling device can be particularly positioned at a distance of 3 mm or more, or 5 mm or more above the heatable foam structure. For example, the cooling device can be positioned at a distance between 5 mm and 10 mm from the heatable foam structure. Such positioning can prevent liquefied material from coming into contact with the cooling device or from solidifying at the cooling device. In some embodiments, the cooling device can be positioned between at least one blade of a stirring element and the heatable foam structure, or the cooling device can be positioned above at least one blade of a stirring element. In Fig. 3, the evaporation apparatus 300 includes a cooling device 365, exemplarily shown as a cooling grid, positioned within the material 110 between the heatable foam structure 105 and the vapor permeable element 360.

[0051] In some embodiments, the evaporation apparatus may include a powder level sensor configured to determine a filling height of the material within the material reservoir. For example, the powder level sensor may measure the vertical position of an upper surface of the material or of a vapor permeable element and calculate the volume of the material in the material reservoir. In the exemplary embodiment shown in Fig. 3, a powder level sensor 370 is configured to measure the vertical position of the vapor permeable element 360 and to calculate the volume of the material 110 within the material reservoir 125.

[0052] According to embodiments, which can be combined with other embodiments, a top pressure unit of an evaporation apparatus can include a preload element, particularly a spring or bellows, configured to apply a biasing pressure to the material from above. For example, a spring or a bellows may be compressed between a wall of a material reservoir and the material such that the spring or bellows apply the biasing pressure onto the material. In some embodiments, a vapor permeable element may be positioned between the preload element and the material. Fig. 4 shows a schematic view of an evaporation apparatus 400 with a bellows 435, in particular a metal bellows, positioned between a wall of a material reservoir 125 and a vapor permeable element 360 positioned on top of the material 110 within the material reservoir 125. [0053] In some embodiments, a pressure device can include both a top pressure unit and a stirring element. For example, Fig. 5 shows a schematic view of an evaporation apparatus 500, wherein a pressure device includes a weight 335 and a stirring element. The weight 335 may optionally be positioned on top of a vapor permeable element 360, which is arranged on the material 110 in the material reservoir 125. The stirring element is rotatable around a rotation axis (A) and may include blades 230 arranged at a rod 233. A top pressure unit and a stirring element may for example advantageously prevent or reduce void or powder bridge formation and press the material onto the heatable foam structure, thereby affecting e. g. the density of the material or the evaporation rate.

[0054] According to one aspect described herein, an evaporation source is described. Fig. 6 shows a schematic view of an evaporation source 600. The evaporation source 600 includes an evaporation apparatus 601 according to any of the embodiments described herein. In particular, the evaporation apparatus 601 includes a heatable foam structure 105 for supporting a material 110 to be evaporated, a pressure device 120 configured for pressing at least a portion of the material 110 towards the heatable foam structure 105, and a vapor guiding conduit 115 arranged below the heatable foam structure 105. The vapor guiding conduit 115 is in fluid communication with a vapor distribution pipe 680. The vapor distribution pipe 680 includes a plurality of vapor nozzles 685 for directing the evaporated material 690 toward a substrate. In the evaporation source 600, material 110 is evaporated at the heatable foam structure 105. The evaporated material 690 passes through the heatable foam structure 105 into the vapor guiding conduit 115. From the vapor guiding conduit 115, the evaporated material 690 enters the vapor distribution pipe 680 and is directed through the vapor nozzles 685 towards the substrate, in particular for depositing a material layer on the substrate. The vapor guiding conduit 115 and the vapor distribution pipe 680 can be heated to or above the evaporation temperature of the material 110, in particular to avoid or reduce condensation of evaporated material 690 in the vapor guiding conduit 115 and in the vapor distribution pipe 680. [0055] According to one aspect described herein, an evaporation method is described. Fig. 7 shows a flow diagram of an evaporation method 700 according to embodiments described herein. The evaporation method 700 includes arranging (see block 710) a material to be evaporated in a material reservoir on top of a heatable foam structure. In some embodiments, a stirring element can be arranged within the material and/or a top pressure unit, e. g. a weight or a preload element, can be arranged above the material, in particular on a vapor permeable element positioned on the material.

[0056] The evaporation method 700 includes heating (see block 720) the heatable foam structure for evaporating the material supported on the heatable foam structure. Since the material is supported on the heatable foam structure, the lowermost portion of the material that is in contact with the heated foam structure evaporates and propagates through the heatable foam structure into the vapor guiding conduit. In particular, the heating (block 720) can include supplying an electric current through the heatable foam structure or heating a heat source in contact with the heatable foam structure such that heat is transferred from the heat source to the heatable foam structure, for example by solid-to-solid heat transfer.

[0057] In some embodiments, the evaporation method 700 includes cooling at least a part of the material during the heating of the heatable foam structure (block 720). In particular, a part of the material may be cooled, e. g. using a cooling device, at a distance of 15 mm or less above the heatable foam structure, particularly at a distance of 10 mm or less, or 5 mm or less and/or at a distance of 0.1 mm or more above the heatable foam structure, particularly at a distance of 1 mm or more, or 2 mm or more. In particular, cooling may provide a thermal gradient in the material, in particular between the location of the cooling device and the heatable foam structure.

[0058] The evaporation method 700 includes pressing (see block 730) at least a portion of the material downwardly towards the heatable foam structure. Pressing (block 730) may include stirring the material, particularly with a stirring element arranged within the material to be evaporated. Additionally or alternatively, pressing (block 730) may include applying a pressure onto the material from above, particularly with at least one of a weight and a preload element. In particular, pressing may include providing a pressure onto the material towards the heatable foam structure, such that the formation of voids or powder bridges is reduced or inhibited.

[0059] In some embodiments, the evaporation method 700 may further include expelling at least one of water vapor and contaminant gases from the material to be evaporated, particularly by maintaining a main volume of the material reservoir at a temperature of 80°C or more and/or 120°C or less. In particular, expelling may be performed before and/or during the heating of the heatable foam structure (block 720) and/or the pressing (block 730) of the evaporation method 700. In one embodiment, water is expelled from the material before the evaporation is started. In one embodiment, water is expelled from the material during the evaporation. Expelling may include evacuating the material reservoir such that water vapor and contaminant gases are guided out of the material reservoir.

[0060] In some embodiments, the material can be an organic material, in particular an organic material for OLED manufacturing, more particularly an organic powder.

[0061 ] In view of the embodiments described herein, it is to be understood that an improved evaporation apparatus, an improved evaporation source and an improved evaporation method are provided, particularly for OLED manufacturing. In particular, pressing a material towards a heatable foam structure can inhibit or reduce the formation of voids or powder bridges in the material. This can particularly be beneficial to provide a stable evaporation rate, in particular during the start of a deposition process. Further, evaporation of the material can be achieved by solid-to-solid heat transfer instead of by heat transfer via heat radiation. For example, evaporation at a predetermined evaporation rate by solid-to-solid heat transfer can be achieved with a lower temperature of the heatable foam structure than evaporation involving heat transfer by heat radiation. Evaporation with a heatable foam structure having a lower temperature can reduce decomposition of the material to be evaporated. Reduced material decomposition can result in deposited layers of higher quality.

[0062] Pressing onto a portion of the material at a position close to the heatable foam structure, e.g. via a stirring element arranged within the material, is particularly beneficial because a more defined force can be applied on the areas of interest which are susceptible to void formation.

[0063] Embodiments as described herein further provide the possibility of expelling water vapor or contaminant gases from the material. In particular, the arrangement of the material above the heatable foam structure and a gas outlet in the material reservoir can reduce water vapor or contaminant gases in the material before or during evaporation and improve the quality of deposited layers.

[0064] Embodiments described herein are configured to reduce the cost of ownership, since wastage of material, particularly expensive organic material, can be reduced, e.g. during calibration of an evaporation apparatus or an evaporation source, for instance by providing more stable evaporation rates or by providing stable evaporation rates more quickly as compared to conventional evaporation sources.

[0065] The term “substrate” as used herein may particularly embrace substantially inflexible substrates, e.g., a wafer, slices of transparent crystal such as sapphire or the like, or a glass plate. However, the present disclosure is not limited thereto, and the term “substrate” may also embrace flexible substrates such as a web or a foil. The term “substantially inflexible” is understood to distinguish over “flexible”. According to embodiments described herein, the substrate may be made of any material suitable for material deposition. For instance, the substrate may be made of a material selected from the group consisting of glass (for instance soda-lime glass, borosilicate glass etc.), metal, semiconductor, polymer, ceramic, compound materials, carbon fiber materials or any other material or combination of materials which can be coated by a deposition process. In some embodiments, the substrate may be a wafer, e.g. a semiconductor wafer. [0066] The term “substrate” as used herein encompasses large area substrates. For instance, a “large area substrate” can have a main surface with an area of 0.5 m ² or larger, particularly of 1 m ² or larger. In some embodiments, a large area substrate can be GEN 4.5, which corresponds to about 0.67 m ² of substrate (0.73m x 0.92m), GEN 5, which corresponds to about E4 m ² of substrate (1.1 m x E3 m), GEN 7.5, which corresponds to about 4.29 m ² of substrate (1.95 m x 2.2 m), GEN 8.5, which corresponds to about 5.7 m ² of substrate (2.2 m x 2.5 m), or even GEN 10, which corresponds to about 8.7 m ² of substrate (2.85 m x 3.05 m). Even larger generations such as GEN 11 and GEN 12 and corresponding substrate areas can similarly be implemented.

[0067] In the present disclosure, at least one of an evaporation apparatus and an evaporation source can be arranged in a vacuum deposition chamber. A “vacuum deposition chamber” is to be understood as a chamber configured for vacuum deposition. The term “vacuum”, as used herein, can be understood in the sense of a technical vacuum having a vacuum pressure of less than, for example, 10 mbar. Typically, the pressure in a vacuum chamber as described herein may be between 10 ⁵ mbar and about 10 ⁸ mbar, more typically between 10 ⁵ mbar and 10 ⁷ mbar, and even more typically between about 10 ⁶ mbar and about 10 ⁷ mbar. According to some embodiments, the pressure in the vacuum chamber may be considered to be either the partial pressure of the evaporated material within the vacuum chamber or the total pressure (which may approximately be the same when only the evaporated material is present as a component to be deposited in the vacuum chamber). In some embodiments, the total pressure in the vacuum chamber may range from about 10 ⁴ mbar to about 10 ⁷ mbar. In some embodiments, a material reservoir may be evacuated, in particular through a gas outlet, such that a reservoir pressure inside the material reservoir is reduced to a vacuum as understood herein.

[0068] A “vapor distribution pipe” as described herein may be configured to provide a line source extending essentially vertically. In the present disclosure, the term “essentially vertically” is understood particularly when referring to the substrate orientation, to allow for a deviation from the vertical direction of 10° or below. This deviation can be provided because a substrate support with some deviation from the vertical orientation might result in a more stable substrate position. Yet, the substrate orientation during deposition of the organic material is considered essentially vertical. The surface of the substrates can be coated by a line source extending in one direction corresponding to one substrate dimension and a translational movement along the other direction corresponding to the other substrate dimension.

[0069] While the foregoing is directed to embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

[0070] In particular, this written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the described subject-matter, including making and using any devices or systems and performing any incorporated methods. While various specific embodiments have been disclosed in the foregoing, mutually non-exclusive features of the embodiments described above may be combined with each other. The patentable scope is defined by the claims, and other examples are intended to be within the scope of the claims if the claims have structural elements that do not differ from the literal language of the claims, or if the claims include equivalent structural elements with insubstantial differences from the literal language of the claims.