The present invention relates to a deposition facility for depositing, on a substrate, coatings formed from metallic and/or non-metallic materials, said facility being more particularly intended for coating steel strips by vacuum deposition, without being limited thereto. This facility is particularly intended for the manufacturing of thin-film solar cells based upon absorbing layers that contain copper, indium, gallium, aluminum and selenium. The present invention also relates to the method for coating a substrate thereof.

Vacuum roll coating has long been used to deposit single and multiple layers of metallic and/or non-metallic materials on flexible substrate strips. Basically, it consists in unwinding a coil at the entrance of a vacuum deposition chamber, depositing the different layers on the moving strip and winding the coil at the end of the vacuum deposition chamber. One particular advantage of vacuum roll coating is in its ability to coat large substrate areas at relatively high speed. That said, when it comes to deposit a succession of sensitive layers such as those constituting a thin-film solar cell, it is essential to avoid damaging or contaminating a freshly deposited layer before the next one is deposited. Practically speaking, it means that the strip side to be coated cannot touch anything and in particular drive rollers and that the deposition sources cannot be located above the strip otherwise dust resulting from the deposition process can fall on the strip and alter the layer.

It is known from JP2017082255 to deposit the multiple layers in a vacuum deposition chamber comprising a roll for transporting the strip along a helical path. Partition walls located along the roll length divide the deposition chamber into a plurality of individual chambers so that the strip, after entering the vacuum deposition chamber and while following the helical path, enters successively each of the individual chambers and is coated with the corresponding metallic and non- metallic materials. Drawbacks of this deposition chamber are that, on one hand, it is difficult to efficiently separate the atmospheres of the individual chambers, which leads to cross-contaminations, and, on the other hand, the number of individual chambers cannot be varied to match the requirements of the coatings that are being produced. A first aim of the present invention is therefore to remedy the drawbacks of the facilities and processes of the prior art by providing a deposition facility that allows one side of the strip to remain untouched while the lay-out of the facility can be easily varied to match the requirements of the coatings that are being produced.

A second aim of the present invention is to provide a vacuum deposition facility that efficiently separates the atmospheres of the individual chambers.

For this purpose, a first subject of the present invention is a deposition facility for continuously depositing coatings, formed from metallic and/or non- metallic materials, on a strip running along a path, the facility comprising a structural envelope, delimiting an inside and an outside, and a succession of individual process chambers mounted on the structural envelope in such a way that the path to be followed by the running strip while going through consecutively each individual process chamber of the succession of process chambers is rendered wound a plurality of turns around an axis of the structural envelope.

The facility according to the invention may also have the optional features listed below, considered individually or in combination:

- the angle between the tangent line at any point of the path and the winding axis is a,

- the structural envelope is a truss structure comprising posts, rafters and struts,

- the winding axis is horizontal,

- the structural envelope comprises four lateral sides parallel to the winding axis,

- the path is helical, the angle a being constant,

- the angle a is constant and comprised between 45° and 85°,

- the angle a varies along the length of the winding axis,

- the angle a is set at a first value in a first portion of the structural envelope and set at a second value in a second portion of the structural envelope. - the succession of individual process chambers is mounted on the outside of the structural envelope,

- the succession of individual process chambers is mounted on the inside of the structural envelope,

- the succession of individual process chambers is made of chambers independent from one another in term of energy supply and, if applicable, pumping devices,

- the succession of individual process chambers comprises deposition chambers and transition chambers,

- the succession of individual process chambers comprises at least partially an alternation of deposition chambers and of transition chambers,

- the path inside each deposition chamber is flat between an entry section and an exit section,

- the deposition chambers are positioned at a first value of angle a and the transition chambers at a second value of angle a,

- the transition chambers are perpendicular to the winding axis,

- the deposition chambers are mounted on vertical portions of the structural envelope,

- the facility is a vacuum deposition facility.

A second subject of the present invention is a process for continuously depositing coatings, formed from metallic and/or non-metallic materials, on a strip running along a path, the process comprising the step according to which the strip runs through a succession of individual process chambers wound a plurality of turns around an axis.

Other characteristics and advantages of the invention will be described in greater detail in the following description. The invention will be better understood by reading the following description, which is provided purely for purposes of explanation and is in no way intended to be restrictive, with reference to:

- Figure 1 , which is a view in perspective of a facility according to a first embodiment of the invention,

- Figure 2, which is a side view of the facility illustrated on Figure 1 ,

- Figure 3, which is a cross-section of the facility illustrated on Figure 1 ,

- Figure 4, which is a view in perspective of a strip path according to a second embodiment of the invention,

- Figure 5, which is a side view of the strip path illustrated on Figure 4,

- Figure 6, which is a cross-section of the strip path illustrated on Figure 4,

- Figure 7, which is a view in perspective of a strip path according to a third embodiment of the invention,

- Figure 8, which is a side view of the strip path illustrated on Figure 7, - Figure 9, which is a cross-section of the strip path illustrated on Figure 7.

It should be noted that the terms“bottom”,“top”,“lateral”... as used in this application refer to the positions and orientations of the different constituent elements of the facility when the latter is installed on a deposition line.

Throughout the text, a photovoltaic stack is understood to mean a stack of a plurality of layers which comprises a layer capable of converting solar energy into electricity and protected from the outside by insulating layers. Photovoltaic stacks usually comprise a foil of insulating material called back-sheet, a first layer of encapsulation material, solar cells connected via ribbons, a second layer of encapsulation material and a transparent foil of insulation material called front- sheet.

One aim of the present invention is to deposit, on a substrate, coatings formed from metallic and/or non-metallic materials. The aim is in particular to obtain solar cells. However, the deposition facility is not limited to this purpose.

The solar cells are usually composed of several layers among which a substrate, a back-electrode, a p-n junction comprising an absorber layer and a front electrode. Copper indium diselenide (CulnSe2 or CIS) and its higher band gap variants copper indium gallium diselenide (Cu(ln/Ga)Se2 or CIGS), copper indium aluminum diselenide (Cu(ln/AI)Se2), copper indium gallium aluminum diselenide (Cu(ln/Ga/AI)Se2)and any of these compounds with sulfur replacing some of the selenium represent a group of materials, referred to as CIGS, that have desirable properties for use as the absorber layer in thin-film solar cells. To function as a solar absorber layer these materials must be p-type semiconductors. This is accomplished by establishing a slight deficiency in copper, while maintaining a chalcopyrite crystalline structure.

CIGS thin-film solar cells are normally produced by first depositing a molybdenum-based back electrode onto a substrate such as glass, stainless steel foil, carbon steel foil, or other functional substrate material. It can be done by RF or DC magnetron sputtering. The molybdenum-based back electrode can be made of a layer of molybdenum (Mo) or of molybdenum-sodium (Mo/Na) or of molybdenum-potassium (Mo/K) or made of a plurality of sublayers of Mo and/or Mo/Na and/or Mo/K. Alternatively, a zirconium nitride barrier layer can be added above the back electrode so that diffusion is blocked, thus allowing replacing molybdenum by other metals such as silver, aluminum, copper.

A relatively thick layer of CIGS is then deposited on the molybdenum layer by known techniques. In the precursor technique, the metals (Cu/ln/Ga) are first deposited onto the substrate using a physical vapor deposition (PVD) process (i.e. evaporation or sputtering), chemical bath, or electroplating process. Subsequently, a selenium bearing gas is reacted with the metals layer in a diffusion furnace at temperatures ranging up to about 600° C to form the final CIGS composition. The most commonly used selenium bearing gas is hydrogen selenide, which is extremely toxic to humans and requires great care in its use. A second technique avoids the use of hydrogen selenide gas by co-evaporating all of the CIGS constituents onto a hot substrate from separate thermal evaporation sources. In a third technique, the CIGS layer is deposited by DC magnetron sputtering with planar and/or rotative magnetrons.

The CIGS layer can be made of a plurality of sublayers. In certain embodiments, each sublayer has the same composition. In other embodiments, the compositions of the sublayers differ such that the CIGS layer has a composition that is graded in at least one elemental concentration from at least one sublayer to another sublayer. In some embodiments, each sublayer has the same thickness, while in other embodiments, at least two sublayers have different thicknesses.

The n-type material most often used with CIGS absorbers to form the thin "window" or "buffer" layer is cadmium sulfide (CdS). It is much thinner than the CIGS layer and can be applied by chemical bath deposition (CBD) or by DC sputtering. Because of the toxicity and waste disposal problems associated with cadmium, ZnS can be used as a substitute. It can be made by AC reactive sputtering from elemental zinc targets and injection of hydrogen sulfide.

Finally, the window or buffer layer is covered with a relatively thick transparent electrically conducting oxide, which is also an n-type semiconductor. In the past zinc oxide (ZnO) has been used as an alternative to the traditional, but more expensive, indium tin oxide (ITO). Recently, aluminum-doped ZnO (AZO) has been shown to perform about as well as ITO, and it has become the material of choice in the industry. It can be made by magnetron sputtering.

Optionally, additional conductive layers such as top metallization layer or a passivation layer may be deposited over the buffer layer. Patterning and interconnect steps may also be performed to provide a monolithically integrated device.

The strip can be made of a polymer, such as polyimide or made of metal such as carbon steel, stainless steel, copper, aluminum, titanium. When the strip is metallic, it can be coated with a dielectric layer to isolate the solar cells from the conductive substrate.

In order to deposit, on a strip, coatings formed from metallic and/or non- metallic materials, the strip has to go through a succession of individual process chambers 5 as illustrated on Figure 1.

By“chambers”, it is meant an enclosed space delimited by a casing and whose atmosphere can be separated from the outside. By“individual”, it is meant that each chamber has its own casing. By“go through”, it is meant that the strip moves in one side and out of the other side of each process chamber.

The process chambers are notably chosen among deposition chambers, i.e. process chambers dedicated to deposition, transition chambers, i.e. process chambers making the transition between two deposition chambers, cleaning chambers, etching chambers.

The deposition chambers can be equipped with any device suitable for depositing the desired film layers either at atmospheric pressure or under vacuum. Common devices at atmospheric pressure include, surface preparation devices, roll-coaters and their corresponding curing systems, such as UV curing or Electron-Beam (EB) curing, atmospheric evaporation techniques, chemical vapor deposition (CVD), inkjet devices... Among vacuum technology, common devices include thermal evaporation, electron beam (e-beam) evaporation, sputtering, AC or DC magnetron sputtering, chemical vapor deposition (CVD), polymer multilayer (PML), etc. As some of the layers to be deposited may be relatively thick, a deposition chamber can be equipped with several devices in series. The deposition chambers can also comprise additional equipment such as heater, cooler, measuring device, etc. placed in locations where necessary depending upon process requirements.

The transition chambers can be chambers simply maintained under vacuum with vacuum pumps, or they can comprise additional equipment such as heater, cooler, measuring device, strip edge detection, patterning/marking equipment, atmosphere separation...

Cleaning chambers can be equipped with plasma cleaning system.

Etching chambers can be equipped with subtractive processes, such as plasma etching or ablation, which are used to remove material (polymers, metals, oxides and other inorganic layers, etc.).

Each process chamber n has successively an entry section 6, a central section 7 and an exit section 8 and a given strip path P _n to be followed by the strip between the entry section and the exit section. In order to precisely position the strip path P _n , the process chamber can comprise at least one guide roll, preferably in the entry section and/or in the exit section. Preferably the process chamber doesn’t comprise any guide roll between the ones located in the entry section and/or the exit section. Consequently, the process chamber length is preferably chosen so that the strip remains flat and stable between the guide rolls located in the entry section and the exit section. If the process chamber is too long, the strip starts to curve and/or vibrate which alters the deposition process. Preferably, the strip path in each deposition chamber is flat between the entry section and the exit section so that the coating deposition can be easily performed.

In the case of a vacuum deposition facility, each chamber has preferably a means of pumping to provide the required vacuum and to handle the flow of process gases during the coating operation. High throughput turbomolecular pumps are preferred for this application.

Optionally, the process chambers are independent from one another in term of energy supply and, if applicable, pumping devices so that they can be very easily dismounted and reassembled together in series in various combinations The number of process chambers may be varied to match the requirements of the coatings that are being produced.

In the case of a vacuum deposition facility, the succession of process chambers 5 is preferably at least partially an alternation of deposition chambers and of transition chambers so that possible process gas escaping a process chamber is vacuumed in the adjacent transition chamber before it reaches the next deposition chamber. In particular, very efficient gas separation between two deposition chambers can be managed through high pressure drops and high differential pumping in the transition chamber. Consequently, pressure variations of several decades can be easily managed between the two deposition chambers while avoiding any cross-contamination of atmospheres. Moreover, as it will be explained latter, such alternation also allows the deposition chambers to be positioned only on vertical portions of the structural envelope.

The deposition facility is preferably equipped with an input chamber and an output chamber separated by the succession of process chambers 5. The input chamber may comprise a decoiler. The output chamber may comprise a recoiler. The input and output chamber can also comprise a tensioner. They can be either at atmospheric pressure or under vacuum.

The strip continuously extends from the input chamber to the output chamber while passing through the plurality of process chambers along path P.

The strip is managed through the facility by rolls. In order to accommodate the specific strip path, the rolls are preferably mounted on pivot axis or cambered rolls. The latter additionally facilitate the processing of strips of various width. The deposition facility 1 comprises a structural envelope 2 delimiting an inside 3 and an outside 4. The structural envelope can be made of any elements that, when combined, form a structure capable of supporting process chambers 5 mounted on it. The shape of the envelope is not particularly limited as long as a succession of process chambers can be mounted on it, either on the inside or on the outside, in such a way that the path P to be followed by the running strip while going consecutively through each individual process chamber of the succession of process chambers is rendered wound a plurality of turns around an axis of the structural envelope. This axis is referred to as the“winding axis”. The structural envelope is preferably in open air so that the operators can easily access the facility and its process chambers, notably for maintenance and repairs.

According to one embodiment, the structural envelope 2 is of regular shape so that the deposition facility is very modular. In the example illustrated on Figures 1 to 3, the structural envelope is a truss structure, that is to say a framework, typically consisting of posts 9, rafters 10 and struts 1 1 , designed for and capable of supporting process chambers. The truss structure extends along a longitudinal axis L and comprises lateral sides parallel to the longitudinal axis L.

In the example illustrated on Figures 1 to 3, the truss structure is of horizontal longitudinal axis L with four lateral sides parallel to the longitudinal axis, a top side 12, a bottom side 13 and two vertical sides 14. The bottom side rests on legs 15 so that there is space between the bottom side and the ground. Preferably, the legs are simply an extension of the posts 9. Depending on the room available to build the facility, the truss structure can also be of vertical longitudinal axis. In that case, the lateral sides are all vertical. The advantages of having vertical lateral sides will be detailed later on.

In the example illustrated on Figures 1 to 3, the truss structure is of constant cross-section, i.e. all the lateral sides are flat, so that the deposition facility is very modular. In that case, the process chambers mounted on the vertical sides 14 can all have the same length and it is easy to move them to reorganize the line lay-out. The cross-section is preferably rectangular. According to one variant, the longitudinal axis L is an axis of symmetry of the truss structure.

According to one embodiment, the structural envelope is of irregular shape to adapt to the length required by each process chamber to process the strip according to the specifications, for example to deposit the targeted layer thickness. The structural envelope can comprise a first portion of a first cross-section and a second portion of a second cross-section. In the example illustrated on Figures 4 to 6, the truss structure differs from the one illustrated on Figures 1 to 3 in that it is of variable cross-section. In particular, the top side comprises a step, decreasing the cross-section of the end of the truss structure, so that the last process chambers mounted on the vertical sides are shorter.

The individual process chambers 5 are mounted on the structural envelope 2 and positioned one after the other in such a way that the path (P) to be followed by the running strip while going through consecutively each individual process chamber of the succession of process chambers is rendered wound a plurality of turns around an axis of the structural envelope. In other words, the individual process chambers are positioned along a wound path P. In particular, the length of each process chamber is along the wound path P. More particularly, each chamber n has an entry section, an exit section and a given strip path P _n to be followed by the strip between the entry section and the exit section and each of strip paths Pn is congruent with the wound path P inside chamber n.

For the sake of clarity, as the winding of the strip path P is given by the position of the individual process chambers, the path P is not wounded a plurality of turns within each of the individual process chambers. In other words, each of strip paths Pn is not wound a plurality of turns within the individual process chamber n.

The number of turns may be varied depending on the number of process chambers needed to match the requirements of the coatings to be produced on the deposition facility. For a given number of process chambers, the number of turns will be preferably maximized in order to minimize the footprint of the facility. For example, for 20 process chambers, it is preferable to have a facility made of 5 turns around a compact parallelepiped structure than a large facility made of 2 turns around a large structure. Moreover, increasing the number of turns while keeping a compact structure helps maintain a good strip stability and helps avoid strip vibrations or twists. Preferably, the number of turns is preferably 4 or above. Thanks to this winding, the guide rolls guiding the strip along its path are only positioned on one side of the strip so that the other side, where the layers are deposited, remains untouched. Moreover, the process chambers can be easily dismounted and reassembled together in series in various combinations depending on the coatings to be produced on the deposition facility. Moreover, in particular thanks to the plurality of turns, the facility footprint is limited and the process length can be very long while keeping good strip steering thanks to the guide rolls. The strip is also in very close contact with the guide rolls which make it possible to install airlocks with very small tolerances at the level of the guide rolls This efficiently prevents process gases from mixing between chambers.

Preferably the succession of process chambers is wound around the longitudinal axis of the truss structure.

According to one embodiment, the succession of individual process chambers 5 is mounted on the structural envelope 2 in such a way that the path P to be followed by the running strip while going through the succession of individual process chambers is rendered helical around an axis of the structural envelope. By“helical” it is meant that the tangent line at any point of the strip path makes a constant angle with the winding axis.

In the example illustrated on Figures 7 to 9, the succession of process chambers is mounted on the lateral sides of the truss structure in such a way that the path P to be followed by the running strip is helical around the axis L. In other words, the process chambers are positioned along a helical path P. In particular, the length of each process chamber is along the helical path P. More particularly, each chamber n has an entry section, an exit section and a strip path P _n to be followed by the strip between the entry section and the exit section and each of strip paths Pn is congruent with the helical path P inside chamber n.

Thanks to this helical path, the strip tension is homogeneous along the strip width and the strip is not twisted. Consequently, the dimensions of the structural envelope, and in particular of the truss structure, can be more easily adapted since no minimal width of lateral sides is needed to accommodate the strip twist. Moreover, different strip widths can be easily processed on the facility.

The constant angle a between the tangent line at any point of the strip path and winding axis is preferably comprised between 45° and 85°. Above 85°, the gap between two turns is not enough to process strips wide enough unless the truss structure is extremely wide, which is not sought after. Furthermore, above 85°, maintenance operations are made difficult because of the small gap between the process chambers positioned adjacent to one another on one side of the truss structure. Below 45°, the pitch of the helix is so important that the truss structure has to be very long to deposit all the layers, which is not sought after either. The angle is preferably chosen so that the corresponding pitch is slightly larger than the strip path and/or the process chamber width, so that the facility length is limited. More preferably, the constant angle is comprised between 75° and 85°. Thanks to this inclination, for the process chambers positioned on a vertical side, possible dust resulting from the deposition process falls on the bottom part, which corresponds to the vicinity of either the entry section or the exit section of the process chamber, so that cleaning and maintenance are facilitated.

According to another embodiment of the invention, the angle a between the tangent line at any point of the center line of path P and the winding axis varies along the length of the winding axis between a minimum and a maximum, that can be 90°.

According to one variant of this embodiment illustrated on Figures 1 to 6, the strip is twisted in some process chambers, in particular the transition chambers, so that the pitch between process chambers can be reduced. Preferably, angle a at the level of the deposition chambers is constant for all these chambers and is comprised between 45° and 85° whereas angle a at the level of the transition chambers is constant for all these chambers at 90° so that the footprint of the facility is minimized. In other words, the transition chambers are perpendicular to the winding axis L. The angle at the level of the deposition chambers is preferably chosen depending on the yield strength of the strip. On figures 1 to 6, the deposition chambers are on the vertical sides of the truss structures and the transition chambers are on the top side and bottom side of the truss structure. For the sake of clarity, the transition chambers have not been represented on Figures 1 to 3. According to this embodiment, the width of the lateral sides supporting the transition chambers may have to be adjusted so that the strip is not twisted too abruptly. According to another variant of this embodiment, angle a is set at a first value in a first portion of the structural envelope and set at a second value in a second portion of the structural envelope. In other words, the strip is twisted when transitioning from a first portion of the structural envelope to a second portion. For example, in the case of a facility comprising a second portion of smaller cross- section than the first portion, angle a in the second portion is smaller than angle a in the first portion so that, in both portions, the pitch between process chambers is minimized.

The process chambers are preferably mounted on the outside of the structural envelope, in particular on the outer face of the lateral sides of the truss structure. In that case, the strip path is wound a plurality of turns around the structural envelope. The chambers are thus very easily accessible, which facilitates their maintenance, cleaning and moving. In that case, the electrical cabinets, the vacuum pumps or any other machinery can be positioned within the truss structure, which frees up floor space.

Alternatively, the process chambers can be mounted on the inside of the structural envelope, in particular on the inner face of the lateral sides of the truss structure.

Whether the process chambers are mounted on the inside or the outside of the structural envelope, knowing that the process chambers are mounted on the structural envelope and that the path P goes consecutively through each process chambers, it goes without saying that the path P is wound a plurality of turns along the structural envelope, either along its external perimeter or along its internal perimeter, in particular along the outer face of the lateral sides of the truss structure or along the inner face of the lateral sides of the truss structure.

The deposition chambers are preferably mounted on vertical portions of the structural envelope, in particular on the vertical sides of the truss structure. Consequently, parts of the deposition devices, for example the electrodes, can be very easily accessible by the side for replacement and repairs. Moreover, as the strip follows a vertical path, the possible dust resulting from the deposition process doesn’t fall on the running strip, which prevents its pollution. When the deposition chamber includes a vacuum evaporation device, it is preferably positioned on the bottom side of the truss structure so that the vapor efficiently deposits on the strip running above the evaporation crucible, while keeping potential dust away from the strip.

Preferably, to make the facility simple and modular, there is only one deposition chamber per side per turn.

The corresponding process, for continuously depositing coatings, formed from metallic and/or non-metallic materials, on a strip S running along a path P, comprises the step according to which the strip runs through a succession of individual process chambers 5 wound a plurality of turns around an axis L.

The details of the deposition facility described above apply to the process.

The invention has been illustrated with a vacuum deposition facility but it is not limited to this kind of deposition. The deposition facility according to the invention can comprise deposition chambers containing deposition devices working at atmospheric pressure or a combination of vacuum deposition chambers and atmospheric deposition chambers depending on the type of coatings to be applied on the strip.