WO2018197006A1

WO2018197006A1 - Apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell, solar cell production apparatus, and method for screen printing of a material on a substrate used in the manufacture of a solar cell

Info

Publication number: WO2018197006A1
Application number: PCT/EP2017/060237
Authority: WO
Inventors: Luigi De Santi; Andrea Baccini; Davide Colla
Original assignee: Applied Materials Italia S.R.L.
Priority date: 2017-04-28
Filing date: 2017-04-28
Publication date: 2018-11-01
Also published as: CN109196664A; CN109196664B

Abstract

An apparatus (100) for screen printing of a material on a substrate (10) used in the manufacture of a solar cell is provided. The apparatus (100) includes a process head assembly (110) moveable at least in a first direction and including one or more deposition devices (120) configured for transferring the material from a screen (154) to the substrate (10) and two or more material processing devices (130) for processing of the material on the screen (154).

Description

APPARATUS FOR SCREEN PRINTING OF A MATERIAL ON A SUBSTRATE

USED IN THE MANUFACTURE OF A SOLAR CELL, SOLAR CELL PRODUCTION APPARATUS, AND METHOD FOR SCREEN PRINTING OF A MATERIAL ON A SUBSTRATE USED IN THE MANUFACTURE OF A SOLAR

CELL

FIELD

[0001] Embodiments of the present disclosure relate to an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell, a solar cell production apparatus, and a method for screen printing of a material on a substrate used in the manufacture of a solar cell.

BACKGROUND

[0002] Solar cells are photovoltaic devices that convert sunlight directly into electrical power. Within this field, it is known to produce solar cells on a crystalline silicon base using deposition techniques, particularly printing techniques, achieving on the front surface of the solar cells a structure of selective emitters. A processing cycle can include at least one printing operation during which material is deposited on the substrate by a deposition device, and an optional further material processing operation. A productivity and/or throughput of the apparatus can be limited by a cycle time of the processing cycle.

[0003] In view of the above, new apparatuses for screen printing of a material on a substrate used in the manufacture of a solar cell, solar cell production apparatuses, and methods for screen printing of a material on a substrate used in the manufacture of a solar cell, that overcome at least some of the problems in the art are beneficial. The present disclosure particularly aims at providing an apparatus and method that can reduce a cycle time of a processing cycle to increase at least one of a productivity and throughput. SUMMARY

[0004] In light of the above, an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell, a solar cell production apparatus, and a method for screen printing of a material on a substrate used in the manufacture of a solar cell are provided. Further aspects, benefits, and features of the present disclosure are apparent from the claims, the description, and the accompanying drawings.

[0005] According to an aspect of the present disclosure, an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell is provided. The apparatus includes a process head assembly moveable at least in a first direction. The process head assembly includes one or more deposition devices configured for transferring the material from a screen to the substrate and two or more material processing devices for processing of the material on the screen.

[0006] According to another aspect of the present disclosure, an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell is provided. The apparatus includes a process head assembly moveable at least in a first direction. The process head assembly includes one or more deposition devices configured for transferring the material from a screen to the substrate and one or more material processing devices for the processing of the material on the screen.

[0007] According to yet another aspect of the present disclosure, an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell is provided. The apparatus includes a process head assembly moveable at least in a printing direction. The process head assembly includes one or more material processing devices, wherein at least one material processing device of the one or more material processing devices has a blade configured for processing of the material, and wherein the blade is non-straight in a direction essentially perpendicular to the printing direction.

[0008] According to a further aspect of the present disclosure, a solar cell production apparatus is provided. The solar cell production apparatus includes one or more deposition stations and the apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to the embodiments described herein. [0009] According to another aspect of the present disclosure, a method for screen printing of a material on a substrate used in the manufacture of a solar cell is provided. The method includes moving a process head assembly having one or more deposition devices and two or more material processing devices in a first direction along a substrate support at least from a first position to a second position to transfer the material from a screen to the substrate using at least one deposition device of the one or more deposition devices and to perform processing of the material on the screen using a first material processing device of the two or more material processing devices.

[0010] Embodiments are also directed at apparatuses for carrying out the disclosed method 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. The methods for operating the described apparatus include method aspects for carrying out every function of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] 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:

FIG. 1 shows a schematic view of an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to embodiments described herein;

FIGs. 2A and B show schematic views of a process head assembly moving in the first direction and the second direction, respectively, for printing and material processing according to embodiments described herein; shows a schematic view of an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to further embodiments described herein; show schematic views of process head assemblies of an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to yet further embodiments described herein; shows a schematic view of an arrangement of deposition devices and material processing devices according to embodiments described herein; shows a schematic view of an arrangement of deposition devices and material processing devices during a printing process according to embodiments described herein; shows a schematic view of an arrangement of deposition devices and material processing devices during a printing process according to further embodiments described herein; show schematic views of a process head assembly of an apparatus for the screen printing of a material on a substrate used in the manufacture of a solar cell according to embodiments described herein; shows a schematic view of a material processing device having a blade according to embodiments described herein; shows a schematic view of a solar cell production apparatus according to embodiments described herein; and FIG. 11 shows a flow chart of a method for the screen printing of a material on a substrate used in the manufacture of a solar cell according to further embodiments described herein.

DETAILED DESCRIPTION OF EMBODIMENTS

[0012] Reference will now be made in detail to the various embodiments of the disclosure, 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 of the disclosure and is not meant as a limitation of the disclosure. 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] A processing cycle for forming conductive line patterns on a substrate can include at least one deposition process using a deposition device to deposit material on the substrate and at least one further process using a material processing device. The deposition device and the material processing device are mounted to a process head such that the material deposition on the substrate and the material processing are performed when the process head moves in a certain direction.

[0014] The apparatus for screen printing of a material on a substrate according to the present disclosure uses a moveable process head assembly for screen printing. As an example, a layer of the material can be provided on a screen. The material can be transferred from the screen to the substrate using a deposition device, which can be a squeegee. The material processing device can follow the deposition device and provide another layer of the material on the screen for deposition on e.g. a subsequent substrate. The process head assembly of the present disclosure has two or more material processing devices such that the material processing can be performed in two directions, i.e., bidirectionally. The productivity and/or throughput of the apparatus can be increased, because at least the material processing can be performed in two directions instead of only one direction.

[0015] FIG. 1 shows a schematic view of an apparatus 100 for screen printing of a material on a substrate 10 used in the manufacture of a solar cell according to embodiments described herein. The material can be a material suitable to form conductive line patterns, such as fingers and/or busbars, on a surface 12 of the substrate 10. As an example, the material can be a paste, such as a silver paste.

[0016] The apparatus 100 includes a process head assembly 110 that is moveable in a first direction 1, which can be a printing direction. The process head assembly 110 includes one or more deposition devices 120 configured for transferring the material from a screen 154 to the substrate 10 and one (or two) or more material processing devices, such as a first material processing device 130 and a second material processing device 132, for processing of the material on the screen 154. In some implementations, the one or more deposition devices 120 can be one or more printing devices, such as squeegees. The material processing, which can also be referred to as "flood phase", can provide an essentially uniform layer of the material on the screen 154 which is to be transferred e.g. to a subsequent substrate that follows the processed substrate.

[0017] In some implementations, the apparatus 100 further includes a drive device configured for moving the process head assembly 110 or portions of the process head assembly 110, such as process heads thereof, in the first direction 1 along a substrate support 20 for transferring the material from the screen 154 to the substrate 10 and/or for the processing of the material on the screen 154 e.g. during a deposition process. The deposition, such as the printing, and the material processing can be performed during one stroke or cycle. In other words, the deposition and the material processing can be simultaneously performed. The combined flood movement during the deposition process can reduce a process time, such as a critical path time. As an example, the critical path time can be reduced by about one third.

[0018] In the example of FIG. 1, the process head assembly 110 includes a process head 140, e.g., one single process head, wherein at least one deposition device of the one or more deposition devices 120 and at least one material processing device of the one (or two) or more material processing devices are attached to the process head 140. However, the present disclosure is not limited thereto and the process head assembly can include two or more process heads having respective deposition devices and/or material processing devices attached thereto. [0019] In some implementations, the deposition and the material processing are simultaneously performed during at least a part of a duration of the deposition process performed using the one or more deposition devices. As an example, the material processing can be performed during 50% or more, specifically 70% or more, and more specifically 90%> or more of the duration of the deposition process. According to some embodiments, the deposition and the material processing are simultaneously performed during essentially the entire duration of the deposition process, such as 100% of the duration of the deposition process. The deposition process may correspond to one stroke or movement performed by the process head, for example, between a first position A and a second position B. A distance between the first position A and the second position B can be equal to, or larger than, an extension of the substrate 10 or of the conductive line pattern such that the conductive line pattern or a layer thereof can be deposited on the substrate 10 during one stroke.

[0020] The apparatus 100 can include a screen device 150 provided between the substrate support 20 and the process head assembly 1 10. The screen device 150 can include a frame 152 and the screen 154 attached to the frame 152. According to some embodiments, which can be combined with other embodiments described herein, the one or more deposition devices 120 can be one or more printing devices. The one or more printing devices can each include a squeegee. The squeegee can be configured to contact the screen 154 for printing. In some embodiments, a tip of the squeegee contacts the screen 154 and urges material to be printed onto the substrate 10 through the screen 154. The squeegee can be a diamond squeegee or an angled squeegee.

[0021] The screen 154 may include at least one of a net, a printing mask, a sheet, a metal sheet, a plastic sheet, a plate, a metal plate, and a plastic plate. In some embodiments, the screen 154 defines a pattern corresponding to a structure to be printed on the substrate, wherein the pattern may include at least one of holes, slots, incisions or other apertures. The pattern can correspond to the conductive line pattern to be printed on the substrate 10, such as fingers and/or busbars of the solar cell. As an example, the screen 154 can have openings defining the conductive line pattern and a wire mesh provided within the openings. The material to be deposited on the substrate 10 can be provided as an essentially uniform layer on the screen 154 by use of the one or more first material processing devices 130. The material does not flow through the openings due to the presence of the wire mesh. During the deposition process, the deposition device, for example, the squeegee, exerts a force or pressure on the material and urges the material through the openings such that the material is transferred to (i.e., deposited on) the substrate 10. [0022] According to some embodiments, which can be combined with other embodiments described herein, the one (or two) or more material processing devices, such as the first material processing device 130 and the second material processing device 132, are configured for providing the essentially uniform film of the material on the screen 154. In some implementations, the material processing can provide an optimal transfer of the material onto the substrate 10. Optionally or alternatively, the material processing devices are configured for recovery of excess material on the substrate 10 and/or the screen 154. In some implementations, the one (or two) or more material processing devices can be flood bars. The material processing can be referred to as "flooding".

[0023] According to some embodiments, which can be combined with other embodiments described herein, the drive device is configured for moving the process head assembly 110 in the first direction 1 at least from the first position A to the second position B to perform the deposition/transferring and processing, e.g., distributing, of the material on the screen 154 at least during the movement from the first position A to the second position B. A movement from the first position A to the second position B or vice versa can correspond to one stroke performed by the process head assembly 110 or a process head thereof, such as a first stroke and a second stroke, respectively. The first direction 1 can be a horizontal direction 3 perpendicular to a vertical direction 4.

[0024] The first position A and the second position B can be defined as respective positions of the process head assembly 110, e.g., of the process head 140, with respect to at least one of the substrate 10, the substrate support 20 and/or the screen 154. The position of the process head assembly 110 may in turn define respective positions of the one or more deposition devices 120 and the material processing devices with respect to at least one of the substrate 10, the substrate support 20 and/or the screen 154.

[0025] As an example, the first material processing device 130 can be at a position (a) and a deposition device of the one or more deposition devices 120 can be at a position (b) when the process head assembly 110 or the process head 140 is in the first position A and moving in the first direction 1 ("movement direction"). Likewise, the first material processing device 130 can be at a position (c) and the deposition device can be at a position (d) when the process head assembly 110 or the process head 140 is in the second position B and moving in the second direction 2 ("movement direction"). When the process head assembly 110 arrives at the second position B from the first position A, the material processing device moves from position (a) to position (c) and the deposition device moves from position (b) to position (d). In some implementations, the deposition device does not change position if the deposition is equally operated in both directions. As an example, in the case of non-symmetric deposition devices such as angled squeegees, one deposition device is lifted and the other one is lowered.

[0026] According to some embodiments, which can be combined with other embodiments described herein, the drive device is configured for moving the process head assembly 110 in a second direction opposite the first direction 1 to perform deposition and/or material processing during the movement in the second direction. The movement of the process head assembly 110 in the second direction can correspond to a movement of the process head assembly 110 from the second position B to the first position A. The second direction can be a horizontal direction 3 and/or a printing direction.

[0027] In some implementations, the movement of the process head assembly 110 between the first position A and the second position B, such as the first stroke and/or the second stroke, can correspond to a stroke distance of 400 mm or less, specifically 300 mm or less, and more specifically 200 mm or less. As an example, the stroke distance can be in a range of between 150 mm to 300 mm, and can specifically be about 220 mm. The stroke distance can be equal to or larger than the extension of the substrate 10 or of the conductive line pattern. The first position A and the second position B can be defined with respect to a center point between the first position A and the second position B, and particularly as a center point between the position (b) of the deposition device when the process head assembly 110 is in the first position A and the position (d) of the deposition device when the process head assembly 110 is in the second position B. As an example, when the stroke distance between the first position A and the second position B is 220 mm, the position (b) of the deposition device can be -110 mm when the process head assembly 110 is in the first position A, and the position (d) of the deposition device when the process head assembly 110 is in the second position B can be +110 mm. In some embodiments, one or more reference positions are provided. The one or more reference positions can be, for example, a center of the substrate (zero position), a position of the deposition device when the stroke starts (e.g., -110mm), and the final position of the deposition device when the stroke is complete (e.g., +110mm). The roll of paste can be moved back and forth from the -110 mm position to the +110 mm position. Since the processing device can be provided with an offset from the deposition device (e.g., 30 mm), the process head assembly 110 can perform an extra run to return the roll of paste to the exact position.

[0028] According to some embodiments, a distance or spacing can be provided between the one or more deposition devices and the one (or two) or more material processing devices. Specifically, the distance or spacing can be provided between adjacent or neighboring deposition devices and material processing devices. As an example, the distance or spacing between a deposition device and an adjacent material processing device in the first direction 1 can be in the range of between 10 mm to 50 mm and can specifically be about 30 mm. The distance or spacing can provide room for accumulation of material ("paste roll").

[0029] In some embodiments, the apparatus 100 can be configured at least for double printing. As an example, the conductive line pattern, such as the fingers and/or busbars of the solar cell, can include two or more material layers. A first material layer can be printed on the substrate 10 and a second material layer can be printed at least partially on top of the first material layer to form the conductive line pattern. In some implementations, the apparatus 100 can print the first material layer during a first deposition process including the movement or first stroke from the first position A to the second position B. The apparatus 100 can, in some embodiments, print the second material layer during a second deposition process including the movement or second stroke from the second position B to the first position A. However, the present disclosure is not limited thereto and the deposition processes can be performed with the process head assembly 110 moving in the same direction, for example, the first direction 1 or the second direction. In some embodiments, the substrates are printed alternately, e.g. one substrate using the first direction 1, another substrate using the second direction 2, and so on (e.g. for every processing or printing station).

[0030] In some implementations, the first direction 1 and the second direction 2 can be substantially horizontal directions. The term "horizontal direction" is understood to distinguish over "vertical direction". That is, the "horizontal direction" relates to a substantially horizontal movement e.g. of the process head assembly 110, wherein a deviation of a few degrees, e.g. up to 5° or even up to 10°, from an exact horizontal direction is still considered as a "substantially horizontal direction". The vertical direction 4 can be substantially parallel to the force of gravity.

[0031] According to some embodiments, which can be combined with other embodiments described herein, the apparatus 100, and particularly the process head assembly 110, further includes an actuator assembly configured for moving the one or more deposition devices 120 and/or the one (or two) or more material processing devices. As an example, the actuator assembly includes one or more first actuators configured to adjust at least one of a distance between at least one material processing device, such as the first material processing device 130 and/or the second material processing device 132, of the one or more material processing devices and the screen 154 and/or the substrate support 20 and an angle of the at least one material processing device with respect to the screen 154 and/or the substrate support 20. Additionally or alternatively, the actuator assembly includes one or more second actuators configured to adjust at least one of a distance between at least one deposition device of the one or more deposition devices 120 and the screen 154 and/or the substrate support 20 and an angle of the at least one deposition device with respect to the screen 154 and/or the substrate support 20.

[0032] In some implementations, the distance (e.g., in the vertical direction) between the at least one material processing device of the one or more material processing devices and the screen 154 and/or the substrate support 20 can be adjusted or controlled during the movement of the process head assembly 110, e.g., between the first position A and the second position B. As an example, the distance can be adjusted by adjusting a vertical position of the at least one material processing device. The real-time adjustment of the vertical position can ensure that the at least one material processing device does not interfere with the screen 154, particularly when the screen 154 is deformed due to a contact of the screen 154 with the one or more deposition devices 120. According to some embodiments, the distance between the at least one material processing device of the one or more material processing devices and the screen 154 and/or the substrate support 20 can be adjusted to follow a screen profile. In particular, the vertical position of the at least one material processing device can be controlled or adjusted to follow said screen profile. As an example, the distance between the at least one material processing device and the screen 154 and/or the substrate support 20 can be adjusted or controlled during the movement of the process head assembly 110 so as to be essentially constant.

[0033] FIGs. 2A and B show schematic views of a process head assembly 110 moving in the first direction 1 and the second direction 2 for deposition, such as printing, and material processing according to embodiments described herein. [0034] According to some embodiments, which can be combined with other embodiments described herein, the two or more material processing devices include at least the first material processing device 130 and the second material processing device 132. When the process head assembly 110, e.g., the process head 140, is in the first position A, the first material processing device 130 is at position (a), the deposition device is at position (b), and the second material processing device 132 is at a position (a'). When the process head assembly 110 is in the second position B, the first material processing device 130 is at position (c), the deposition device is at position (d), and the second material processing device 132 is at a position (c').

[0035] In some implementations, at least one deposition device of the one or more deposition devices 120 is positioned between the first material processing device 130 and the second material processing device 132. Although FIGs. 2A and B exemplarily illustrate one deposition device between the first material processing device 130 and the second material processing device 132, the present disclosure is not limited thereto. In particular, more than one deposition device, such as two deposition devices, can be provided between the first material processing device 130 and the second material processing device 132. [0036] In further embodiments, the one or more deposition devices 120 include at least a first deposition device and a second deposition device. At least one material processing device of the one or more material processing devices can be positioned between the first deposition device and the second deposition device. As an example, two material processing devices can be positioned between the first deposition device and the second deposition device.

[0037] According to some embodiments, which can be combined with other embodiments described herein, the first material processing device 130 is positioned behind the one or more deposition devices 120 when the process head assembly 110 moves in the first direction 1. The second material processing device 132 can be positioned behind the one or more deposition device 120 when the process head assembly 110 moves in the second direction 2. In other words, the respective material processing device follows the one or more deposition devices 120 in a moving direction, such as the first direction or the second direction. [0038] As shown in FIG. 2A, the process head assembly 110 uses the first material processing device 130 for material processing during the movement of the process head assembly 110 in the first direction 1. Further, as shown in FIG. 2B, the process head assembly 110 uses the second material processing device 132 for material processing during the movement of the process head assembly 110 in the second direction 2. The material processing device that is used for material processing during the movement of the process head assembly 110 can be positioned close enough to the screen 154 to allow for material processing, such as providing an essentially uniform material layer on the screen 154. As an example, a distance between the material processing device that is used for material processing and the screen 154 (e.g. the first distance dl or the second distance d2 described in the following paragraphs) may be selected according to at least one of a layer thickness of the material deposited on the screen 154, a rheology of the material, e.g. the paste, and a composition of the material.

[0039] According to some embodiments, a first distance dl between the screen 154 and the first material processing device 130 is less than a second distance d2 between the screen 154 and the second material processing device 132 during the movement of the process head assembly 110 in the first direction 1. The second distance d2 between the screen 154 and the second material processing device 132 can be less than the first distance dl between the screen 154 and the first material processing device 130 during the movement of the process head assembly 110 in the second direction 2. The first distance dl and the second distance d2 can be defined in a vertical direction. [0040] In some implementations, the larger distance of the first distance dl and the second distance d2 (i.e., the second distance d2 in FIG. 2A and the first distance dl in FIG. 2B) can be in a range between 0 and 25 mm, specifically in a range between 1 and 15mm, and can more specifically be about 10 mm. The smaller distance of the first distance dl and the second distance d2 (i.e., the first distance dl in FIG. 2A and the second distance d2 in FIG. 2B) can be in a range between 0.01 and 2 mm, specifically in a range between 0.05 and 1.5 mm, and can more specifically be in a range between 0.1 mm and 1 mm.

[0041] In some implementations, the first distance dl and/or the second distance d2 can be adjusted or controlled during the movement between the first position A and the second position B. The real-time adjustment of the first distance dl and/or the second distance d2 can ensure that the at least one material processing device does not interfere with the screen 154. According to some embodiments, the first distance dl and/or the second distance d2 can be adjusted to follow a screen profile. According to some embodiments, only the distance of the material processing device in use is adjusted. The distance of the unused material processing device can be kept constant. As an example, the distance of the material processing device in use can be adjusted to keep the distance between said material processing device and the screen 154, such as the first distance dl or the second distance d2, essentially constant.

[0042] According to some embodiments, which can be combined with other embodiments described herein, the apparatus 100, and particularly the process head assembly 110, e.g., the process head 140, further includes the actuator assembly configured for moving the one or more deposition devices 120 and/or the two or more material processing devices. As an example, the actuator assembly includes the one or more first actuators configured to adjust at least one of a distance (e.g., the first distance dl and/or the second distance d2) between at least one material processing device of the one or more material processing devices and the screen 154 and/or the substrate support 20 and an angle of the at least one material processing device with respect to the screen 154 and/or the substrate support 20. As an example, the one or more first actuators can include a first actuator unit configured to adjust the first distance dl between the first material processing device 130 and the screen 154 and/or the substrate support 20 and a second actuator unit configured to adjust the second distance d2 between the second material processing device 132 and the screen 154 and/or the substrate support 20.

[0043] The actuators of the actuator assembly, such as the one or more first actuators and/or the one or more second actuators, can be selected from the group consisting of stepper motors, linear motors, pneumatic motors, and any combination thereof. [0044] FIG. 3 shows a schematic view of an apparatus for deposition of a material on a substrate used in the manufacture of a solar cell according to further embodiments described herein.

[0045] According to some embodiments, which can be combined with other embodiments described herein, the one or more deposition devices 120 are configured for contacting the screen 154 during the deposition process. The one (or two) or more material processing devices used for material processing during the deposition process can be configured for not contacting the screen 154 during said deposition process. In particular, the two or more material processing devices can be spaced apart from the screen 154, e.g., by the first distance and/or the second distance explained with respect to FIGs. 2A and B. [0046] In some implementations, a distance between the one or more deposition devices 120 and the substrate support 20 can be less than a distance between the two or more material processing devices and the substrate support 20. In the example of FIG. 3, the distance between the one or more deposition devices 120 and the substrate support 20 can essentially correspond to the combined thicknesses of the screen 154 and the substrate 10. The deposition device can apply a force on the screen. The screen is deformed and the force applied by the deposition device less the resistance of the screen is transferred to the substrate.

[0047] In FIG. 3, a difference d is shown between the distance between the one or more deposition devices 120 and the substrate 10 and the distance between the first material processing device 130 and the substrate 10. The difference d can be adjusted by moving the first material processing device 130, as is indicated with the arrow 5. The difference d can be defined with respect to the substrate 10 or alternatively with respect to the substrate support 20, such as a support surface of the substrate support configured for supporting the substrate during the deposition process, and/or a horizontal plane. The horizontal plane can be defined by the support surface. In some implementations, the difference d can correspond to a height difference between the tips of the one or more deposition devices 120 and the tips of the first material processing device 130, for example, in the vertical direction. The difference d can be in a range between 5 and 25 mm, specifically in a range between 10 and 20 mm, and can more specifically be about 15 mm. The same applies to a difference between the distance between the one or more deposition devices 120 and the substrate 10 and the distance between the second material processing device (not shown) and the substrate 10 and is thus to repeated.

[0048] FIGs. 4A to C show schematic views of process head assemblies of an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to further embodiments described herein.

[0049] According to some embodiments, which can be combined with embodiments described herein, the one or more deposition devices are arranged between the two or more material processing devices. As an example, as illustrated in the example of FIG. 4A, the one or more deposition devices include a first deposition device 120 and a second deposition device 122 arranged between the first material processing device 130 and the second material processing device 132. In some implementations, the first material processing device 130 and the first deposition device 120 can be used for material processing and deposition, respectively, when the process head assembly moves in the first direction. Likewise, the second material processing device 132 and the second deposition device 122 can be used for material processing and deposition, respectively, when the process head assembly moves in the second direction.

[0050] Referring to another example illustrated in FIG. 4B, the one or more deposition devices are two or more deposition devices and the one or more material processing devices are arranged between the two or more deposition devices. As an example, the two or more deposition devices include the first deposition device 120 and the second deposition device 122. The first material processing device 130 and the second material processing device 132 can be arranged between the first deposition device 120 and the second deposition device 122. In some implementations, the first deposition device 120 as well as the first material processing device 130 and/or the second material processing device 132 can be used for deposition and material processing, respectively, when the process head assembly moves in the first direction. Likewise, the second deposition device 122 as well as the first material processing device 130 and/or the second material processing device 132 can be used for deposition and material processing, respectively, when the process head assembly moves in the second direction. [0051] As illustrated in FIG. 4C, according to another aspect of the present disclosure, an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell is provided. The apparatus includes a process head assembly moveable at least in a first direction. The process head assembly includes one or more deposition devices configured for transferring the material from a screen to the substrate and one or more material processing devices for the processing of the material on the screen.

[0052] As an example, the one or more deposition devices are two or more deposition devices and the one or more material processing devices are arranged between the two or more deposition devices. As an example, the two or more deposition devices include the first deposition device 120 and the second deposition device 122. The one or more material processing devices, such as the first material processing device 130, can be arranged between the first deposition device 120 and the second deposition device 122.

[0053] In some implementations, the one or more material processing devices can be configured for processing of the material on the screen when the process head assembly moves in the first direction and the second direction. In other words, the one or more material processing devices can be configured for material processing in both directions. As an example, the one or more material processing devices can be essentially symmetrical with respect to the first direction and the second direction to allow for processing in both directions. A compact design of the process head assembly can be achieved. [0054] FIG. 5 shows a schematic view of a process head assembly 520 of an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to further embodiments described herein.

[0055] The process head assembly 520 includes a first process head 522 and a second process head 524. At least one deposition device of the one or more deposition devices and at least one material processing device of the one or more material processing devices are attached to the first process head 522. At least one further deposition device of the one or more deposition devices and at least one further material processing device of the one or more material processing devices are attached to the second process head 524. In the present example, both the deposition device(s) and the material processing device(s) are attached to the respective process head.

[0056] Although one deposition device and one material processing device are shown at each process head, it is to be understood that the present disclosure is not limited thereto and that two or more deposition devices and/or two or more material processing devices can be attached to the first process head 522. Likewise, two or more deposition devices and/or two or more material processing devices can be attached to the second process head 524.

[0057] According to other embodiments, which can be combined with embodiments described herein, the apparatus, and particularly the process head assembly, includes two or more process heads. The two or more process heads can be independently controllable and/or movable from each other. As an example, the process head assembly includes a first process head and a second process head. A first drive device can be configured for moving the first process head and a second drive can be provided for moving the second process head e.g. in the first direction and/or the second direction. At least one deposition device of the one or more deposition devices can be attached to the first process head and at least one material processing device of the one or more material processing devices can be attached to the second process head.

[0058] As an example, the process head assembly includes a first process head and a second process head. At least one deposition device of the one or more deposition devices can be attached to the first process head. At least one material processing device of the one or more material processing devices can be attached to the second process head. In the present example, either the deposition device(s) or the material processing device(s) can be attached to the respective process head. In other words, each process head has either the deposition device(s) or the material processing device(s) attached thereto. [0059] FIG. 6 shows a schematic view of an apparatus 600 for screen printing of a material on a substrate used in the manufacture of a solar cell according to further embodiments described herein.

[0060] According to some embodiments, which can be combined with embodiments described herein, the apparatus, and particularly the process head assembly, includes two or more process heads (also referred to as "groups" or "process groups"). The two or more process heads can be independently controllable and/or movable from each other. As an example, the process head assembly includes a first process head 610 and a second process head 620. A first deposition device 612 of the one or more deposition devices is attached to the first process head 610 and a second deposition device 622 of the one or more deposition devices is attached to the second process head 620. Likewise, a first material processing device 614 of the one or more material processing devices is attached to the first process head 610 and a second material processing device 624 of the one or more material processing devices is attached to the second process head 620.

[0061] The one or more deposition devices can be angled deposition devices, such as angled squeegees or precision squeegees. Each angled deposition device may be configured for printing in only one direction (unlike the previously described diamond squeegee, which is substantially symmetrical and configured for printing in both the forward and the backward direction). In order to be able to perform printing in both directions, the process head assembly includes two angle deposition devices, e.g., the first deposition device 612 and the second deposition device 622 between the material processing devices, e.g., the first material processing device 614 and the second material processing device 624.

[0062] During the deposition process performed in the first direction 1, the second process head 620 having the second deposition device 622 and the second material processing device 624 can be lifted. In other words, the second process head 620 is not used during the deposition process performed in the first direction 1. The first process head 610 is lowered such that the first deposition device 612 contacts the screen 154 for transferring the material 30 onto the substrate (not shown). A distance is provided between the first material processing device 614 and the screen 154 such that the first material processing device 614, which follows the first deposition device 612, provides an essentially uniform film or layer of the material 30 on the screen 154.

[0063] During a subsequent deposition process performed in the second direction opposite the first direction 1, the first process head 610 is lifted and the second process head 620 is lowered. The second deposition device 622 contacts the screen 154 to transfer the material on the screen (i.e., the film or layer previously provided by the first material processing device 614 onto the substrate, which can be the same substrate as before (e.g., if double printing is performed) or another/subsequent substrate.

[0064] Although one deposition device and one material processing device are shown at each process head, it is to be understood that the present disclosure is not limited thereto and that two or more deposition devices and/or two or more material processing devices can be attached to the first process head 610. Likewise, two or more deposition devices and/or two or more material processing devices can be attached to the second process head 620.

[0065] According to some embodiments, the two or more process heads, e.g., the first process head 610 and the second process head 620, can be moved or lifted in the vertical direction. Additionally or alternatively, the two or more process heads can be configured to move the one or more deposition devices and/or the one or more material processing devices as previously described herein.

[0066] FIG. 7 shows a schematic view of an arrangement of deposition devices and material processing devices during a printing process according to further embodiments described herein. The deposition device can be an angled squeegee.

[0067] FIG. 7 illustrates an exemplary process head assembly having one or more material processing devices, such as the first material processing device 712, and one or more deposition devices, such as the first deposition device 720. The one or more deposition devices, and particularly a tip 722 of the one or more deposition devices, can be angled with respect to the substrate support and/or the screen (not shown). An angle a can be defined with respect to a surface of the substrate support and/or a surface 12 of the substrate. As an example, the angle a can be defined between a line of symmetry of the tip 5 722 and the surface of the substrate support and/or the surface 12 of the substrate. In some implementations, the angle a can be in a range between 0° and 90°, specifically in a range between 10° and 80°, specifically in a range between 50° and 80°, and more specifically in a range between 60° and 70°. As an example, the angle can be 60° or 70°.

[0068] In some implementations, the deposition device, such as the first deposition0 device 720, includes the tip 722 and a connection element 724 connecting the tip 722 to the process head assembly 710, e.g., a body 714 of the process head assembly 710. The connection element 724 can be curved such that the tip 722 is angled with respect to e.g. the surface 12 of the substrate. The curved connection element further allows to minimize an extension of the deposition device e.g. in the first direction / second direction such that a5 compact design of the process head assembly 710 can be achieved. In particular, according to some embodiments, a width w of the tip 722 can be minimized to allow for a compact design of the process head assembly. As an example, a distance or spacing (e.g. in the horizontal direction) between the first material processing device 712 and the first deposition device 720 can be 40 mm or less, and specifically 30 mm or less. An extension0 of the tip 722 in the first direction / second direction (e.g. the horizontal direction) can be 30 mm or less, and specifically 20 mm or less, such as 16 mm.

[0069] FIGS. 8 A and B show schematic views of a process head assembly 800 of an apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to embodiments described herein. 5 [0070] The process head assembly 800 includes a process head 810. The process head 810 can be connected to a head support 812. In some implementations, the process head 810 can be rotatably connected to the head support 812. In particular, the head support 812 can provide a rotational axis 801 around which the process head 810 can rotate e.g. to adjust an angle of the process head 810 with respect to the substrate and/or the substrate0 support. The rotational axis 801 can be an essentially horizontal rotational axis. In some embodiments, the rotational axis 801 can be essentially perpendicular to the first direction and the second direction.

[0071] In some implementations, the apparatus includes one or more rotating actuators configured to rotate the process head assembly 800, and particularly the process head 810, around the rotational axis 801. The one or more rotating actuators can be configured to adjust an angle of the process head assembly 800 and/or the process head 810 with respect to the screen 154 and/or the substrate and/or the substrate support. The angle a' between the screen and/or the substrate and/or the substrate support and the process head 810 can be defined with respect to a vertical plane. The process head 810 can have an angle +α', which may correspond to a tilt of the process head 810 in a clockwise direction, when moving in the first direction.

[0072] The process head 810 can have an angle -α', which may correspond to a tilt of the process head 810 in a counter-clockwise direction, when moving in the second direction. The angles +α' and -a' may be 70° or less with respect to the vertical plane or direction, specifically 60° or less, more specifically 40° or less, and even more specifically 20° or less. As an example, the angles +α' and -a' may be in a range between 20° and 70°, and more specifically in a range between 40 to 70°. FIG. 8A illustrates an angle a' of about 0°, and FIG. 8B exemplarily illustrates an angle of +α'.

[0073] The process head assembly 800 includes the one or more deposition devices, such as the first deposition device 820 and the second deposition device 822, and the one (or two) or more material processing devices, such as the first material processing device 830 and the second material processing device 832. The one or more deposition devices and the one or more material processing devices can be configured according to the embodiments described herein. [0074] According to some embodiments, which can be combined with other embodiments described herein, the apparatus, and particularly the process head assembly 800, includes an actuator assembly configured for moving the one or more deposition devices and/or the one or more material processing devices, such as the first material processing device 830 and the second material processing device 832. The one or more deposition devices can be squeegees, such as rectangular squeegees. The squeegee can have a tip, such as a rectangular-like tip. According to some embodiments, which can be combined with embodiments described herein, the one or more deposition devices can be essentially symmetric. For example, the one or more deposition devices can have an essentially symmetric tip such that the same (e.g., one single) deposition device can be used for printing in the first direction and the second direction.

[0075] In some embodiments, the actuator assembly includes one or more first actuators configured to adjust a distance between the two or more material processing devices and the screen 154 and/or the substrate support and optionally an angle of the one or more processing devices with respect to the screen and/or the substrate support. For example, the one or more first actuators can include a first actuator unit configured to adjust at least one of the distance, e.g., the first distance, between the first material processing device 830 and the screen and an angle, such as a first angle, of the first material processing device 830 with respect to the screen 154 and/or the substrate support. The one or more first actuators can include a second actuator unit configured to adjust at least one of the distance, such as the second distance, between the second material processing device 832 and the screen 154 and an angle, such as a third angle, of the second material processing device 832 with respect to the screen 154 and/or the substrate support. In some implementations, the one or more first actuators can only linearly move the processing devices. Another actuator can be provided which is configured to change the angle of the whole process head assembly, e.g., around the rotational axis.

[0076] In some implementations, the one or more first actuators are configured to adjust the distance between the two or more material processing devices and the screen. As an example, the one or more first actuators can move the one or more material processing devices, such as the first material processing device 830 and the second material processing device 832, essentially parallel with respect to each other. The one or more first actuators can be linear actuators, such as linear motors.

[0077] Additionally or alternatively, the actuator assembly includes one or more second actuators configured to adjust a distance between the one or more deposition devices and the screen 154 and/or the substrate and/or the substrate support and optionally an angle, such as a second angle, of the one or more deposition devices with respect to the screen and/or substrate support. For example, the one or more second actuators can be configured to move the one or more deposition devices, such as the first deposition device 820 and/or the second deposition device 822, towards the screen 154 for making contact with the screen 154. The one or more second actuators can further be configured to adjust the pressure of the one or more deposition devices exerted on the screen. The one or more second actuators can be configured to move the one or more deposition devices in a direction essentially parallel to the movement direction provided by the one or more first actuators. The distance (e.g. "dl" in FIG. 2B) between the tip of the processing device and the screen 154 can be controlled by an interpolation of the one or more first actuators and the one or more second actuators. [0078] The distances between the one or more material processing devices and the one or more deposition devices with respect to the screen 154 and/or the substrate and/or the substrate support can be defined in a vertical or horizontal plane. Likewise, the angles of the respective material processing devices and deposition devices with respect to the screen and /or the substrate support can be defined with respect to the vertical or horizontal plane. [0079] According to some embodiments, which can be combined with other embodiments described herein, the apparatus is configured to adjust one or more processing parameters of at least one material processing device of the one or more material processing devices, for example, before, during and/or after the deposition process. The one or more processing parameters are selected from the group consisting of the distance, such as the first distance and/or the second distance, between the at least one material processing device and the screen and/or the substrate support and the angle of the at least one material processing device with respect to the screen and/or the substrate support.

[0080] According to some embodiments, which can be combined with other embodiments described herein, the apparatus is configured to adjust one or more deposition parameters of the one or more deposition devices, for example, before, during and/or after the deposition process. The one or more deposition parameters can be selected from the group consisting of the distance between at least one deposition device of the one or more deposition devices and the screen and/or substrate support, an angle of at least one deposition device of the one or more deposition devices with respect to the screen and/or the substrate support, a moving speed of the process head assembly, e.g., of the process head, with respect to the screen and/or the substrate support, and a pressure of at least one deposition device of the one or more deposition devices acting for example on the screen used in the deposition process.

[0081] In some implementations, at least one processing parameter of the one or more processing parameters is adjusted during the deposition process, particularly during the material processing. Additionally or alternatively, at least one deposition parameter of the one or more deposition parameters is adjusted during the deposition process. The real-time adjustment of the processing parameter(s) and/or the deposition parameter(s) can improve a quality of the conductive line patterns. According to some embodiments, at least one processing parameter of the one or more processing parameters can be adjusted based on, or according to, the one or more deposition parameters.

[0082] FIG. 9 shows a schematic view of a material processing device 900 having a blade according to embodiments described herein.

[0083] In some implementations, the geometry of the material processing device 900 can be adapted to a screen profile. As an example, the geometry of the material processing device 900 in a direction perpendicular to the printing direction (the first direction and/or the second direction) can be adapted to a deformed screen profile. The geometry can be designed for an optimal value (e.g., 2 or 3 mm) and to fit others.

[0084] According to some embodiments, which can be combined with other embodiments described herein, at least one material processing device of the two or more material processing devices has, or is, a blade configured for the processing of the material on the screen 154. The blade can be non-straight in a direction different from the first direction, e.g., in a direction essentially perpendicular to the printing direction. As an example, the blade can have a contact portion configured to contact the screen 154 to transfer the material to the substrate. The contact portion can be non-straight or non-linear in the direction different from the first direction. The direction can be essentially perpendicular to the first direction, such as the horizontal direction.

[0085] In some implementations, the blade 900 has a first edge section 910, a second edge section 912 and a middle section 920 between the first edge section 910 and the second edge section 912. The first edge section 910 and the second edge section 912 can be slanted with respect to the middle section 920. As an example, the middle section 920 can extend essentially linearly and/or essentially parallel to the surface of the substrate and/or the surface of the substrate support. The first edge section 910 and the second edge section 912 can be slanted upwards from the middle section 920. For instance, the first edge section 910 and the second edge section 912 can be slanted in an essentially vertical direction away from the substrate and/or the substrate support.

[0086] According to some embodiments, a slanting angle of the first edge section 910 and the second edge section 912 with respect to the surface of the substrate and/or the surface of the substrate support (e.g., a horizontal plane) is equal to or larger than a slanting angle (snap-off angle) of the screen 154 with respect to the surface of the substrate and/or the surface of the substrate support (e.g., a horizontal plane). If the slanting angle of the edge sections is larger than the slanting angle of the screen 154, the edge sections do not contact edge portions of the screen 154 and a damaging of the screen 154 can be avoided.

[0087] In some implementations, a snap-off of the screen 154 is defined as a difference between the un-deformed (flat) screen and the lowest point of the deformed screen being in contact with the material processing device 900. According to some embodiments, the slanting angle of the edge sections can be selected for a predetermined snap-off value, such as 2 mm or 3 mm. In particular, the slanting angle of the edge sections can be selected such that the edge sections do not contact the screen 154 for a predetermined range of snap-off values, such as 10 mm or less, specifically 5 mm, and specifically 3 mm or less, and more specifically 2 mm or less.

[0088] FIG. 10 shows a schematic view of a solar cell production apparatus 1000 according to embodiments described herein.

[0089] The solar cell production apparatus 1000 includes one or more deposition stations 1200 and the apparatus 1250 for screen printing of a material on a substrate used in the manufacture of a solar cell according to the embodiments described herein. The apparatus 1250 can be provided in at least one deposition station of the one or more deposition stations 1200. [0090] The solar cell production apparatus 1000 can include one or more further stations upstream and/or downstream of the one or more deposition stations 1200. As an example, the solar cell production apparatus 1000 can include a first inspection station 1100 for inspection of the substrates to be input into the one or more deposition stations 1200. The solar cell production apparatus 1000 can include a drying station 1300 for the drying of the material deposited on the substrates in the one or more deposition stations 1200. In some embodiments, the solar cell production apparatus 1000 can include a second inspection station 1400 for inspection of the conductive line patterns deposited on the substrates in the one or more deposition stations 1200. [0091] The solar cell production apparatus 1000, and particularly the one or more deposition stations 1200 having the apparatus according to the present disclosure can be part of a larger production system for producing solar cells, such as an in-line production system.

[0092] FIG. 11 shows a flowchart of a method 2000 for the screen printing of a material on a substrate used in the manufacture of a solar cell according to embodiments described herein. The method 2000 can be implemented using the apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell according to embodiments described herein.

[0093] The method 2000 includes, in block 2100, a moving of a process head assembly having one or more deposition devices and one (or two) or more material processing devices in a first direction along a substrate support at least from a first position to a second position to transfer the material from a screen to the substrate using at least one deposition device of the one or more deposition devices and to perform the processing of the material on the screen using a first material processing device of the one (or two) or more material processing devices.

[0094] The transferring and the processing of the material can be performed at least during the movement of the process head assembly from the first position to the second position. In some implementations, the method 2000 includes in block 2200 a moving of the process head assembly in a second direction opposite to the first direction to perform transferring, such as printing, and processing of the material on the screen using a second material processing device of the one (or two) or more material processing devices.

[0095] The transferring and the processing of the material can be simultaneously performed during at least a part of a duration of a deposition process, and particularly during essentially the entire duration of the deposition process. The two or more material processing devices can, for example, provide an essentially uniform film or layer of the material on the screen. Optionally, the one or more material processing devices can recover excess material from the screen.

[0096] According to embodiments described herein, the method for screen printing of a material on a substrate used in the manufacture of a solar cell can be conducted using computer programs, software, computer software products and the interrelated controllers, which can have a CPU, a memory, a user interface, and input and output devices being in communication with the corresponding components of the apparatus for deposition of a material on a substrate used in the manufacture of a solar cell. [0097] The apparatus for screen printing of a material on a substrate according to the present disclosure uses a moveable process head assembly for screen printing. For example, a layer of the material can be provided on a screen. The material can be transferred from the screen to the substrate using a deposition device, which can be a squeegee. The material processing device can follow the deposition device and provide another layer of the material on the screen for deposition on e.g. a subsequent substrate. The process head assembly of the present disclosure can have two or more material processing devices such that the material processing can be performed in two directions, i.e., bidirectionally. The productivity and/or throughput of the apparatus can be increased, because at least the material processing can be performed in two directions instead of only in one direction.

[0098] 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.

Claims

1. An apparatus for screen printing of a material on a substrate used in the manufacture of a solar cell, comprising: a process head assembly moveable at least in a first direction, including: one or more deposition devices configured for transferring the material from a screen to the substrate; and two or more material processing devices configured for processing of the material on the screen.

2. The apparatus of claim 1, wherein the one or more deposition devices are arranged between the two or more material processing devices.

3. The apparatus of claim 1, wherein the one or more deposition devices are two or more deposition devices, and wherein the two or more material processing devices are arranged between the two or more deposition devices.

4. The apparatus of any one of claims 1 to 3, wherein at least one material processing device of the two or more material processing devices has a blade configured for processing of the material on the screen, and wherein the blade is non-straight in a direction different from the first direction.

5. The apparatus of claim 4, wherein the direction is essentially perpendicular to the first direction.

6. The apparatus of claim 4 or 5, wherein the blade has a first edge section, a second edge section and a middle section between the first edge section and the second edge section, and wherein the first edge section and the second edge section are slanted with respect to the middle section.

7. The apparatus of any one of claims 1 to 6, further including a driving device configured for moving the process head assembly in the first direction and in a second direction opposite the first direction along a substrate support.

8. The apparatus of any one of claims 1 to 7, wherein the apparatus is configured for processing of the material on the screen using a first material processing device of the two or more material processing devices during a movement of the process head assembly in the first direction, and wherein the apparatus is configured for processing of the material on the screen using a second material processing device of the two or more material processing devices during a movement of the process head assembly in the second direction.

9. The apparatus of any one of claims 1 to 8, further including one or more first actuators configured to adjust a distance between at least one material processing device of the two or more material processing devices and the screen, particularly wherein the one or more first actuators include a first actuator unit configured to adjust a first distance between the first material processing device and the screen and a second actuator unit configured to adjust a second distance between the second material processing device and the screen.

10. The apparatus of any one of claims 1 to 9, wherein the screen is provided between the substrate support and the process head assembly, wherein the one or more deposition devices include a squeegee, and wherein the squeegee is configured to make contact with the screen for printing.

11. The apparatus of any one of claims 1 to 10, wherein the process head assembly includes a first process head and a second process head, wherein at least one material processing device of the two or more material processing devices is attached to the first process head and at least one further material processing device of the two or more material processing devices is attached to the second process head, or wherein the process head assembly includes a process head, wherein the two or more material processing devices are attached to the process head.

12. A solar cell production apparatus, comprising: one or more deposition stations, the apparatus according to one of claims 1 to 11 in at least one deposition station of the one or more deposition stations.

13. A method for screen printing of a material on a substrate used in the manufacture of a solar cell, comprising: moving a process head assembly having one or more deposition devices and two or more material processing devices in a first direction along a substrate support at least from a first position to a second position to transfer the material from a screen to the substrate using at least one deposition device of the one or more deposition devices and to perform processing of the material on the screen using a first material processing device of the two or more material processing devices.

14. The method of claim 13, further including: moving the process head assembly in a second direction opposite to the first direction to perform the transference and the processing of the material on the screen using a second material processing device of the two or more material processing devices.

15. The method of claim 13 or 14, wherein the transferring and the processing of the material are simultaneously performed during at least a part of a duration of a deposition process, and particularly during essentially the entire duration of the deposition process.