BACKGROUND

Field

[0001] Embodiments of the present disclosure generally relate to a method of depositing a film on a flexible substrate conveying a flexible substrate in a processing environment and more particularly to a method of depositing a film on a flexible substrate conveying a flexible substrate past one or more evaporation sources for depositing one or more materials on the substrate.

Description of the Related Art

[0002] A roll-to-roll deposition process is commonly used to form thin film solar cells, batteries and other commercial electronic devices, such as CIGS (copper- indium-gallium-(di)selenide) solar cell devices. During processing, equipment in a deposition system is generally used to unwind a flexible substrate (also referred to as the "web") from a payout roll, guide the flexible substrate through a processing region, and then rewind the flexible substrate on a pickup roll. In one example, a series of evaporation sources are used to deposit the different elements of the CIGS absorber layer of a solar cell in the processing region. Typically, these types of deposition processes are performed within a vacuum chamber.

[0003] The edges of the flexible substrate can be supported by clamps to help transport the flexible substrate past the evaporation sources. Although the clamps help to maintain the flexible substrate at given height above the evaporation sources, the flexible substrate can still sag (e.g., sagging in a vertical direction) between the clamps along the edges and between the edges. This sag can affect the uniformity of the deposited layer(s) on the flexible substrate. Furthermore, this sag can prevent accurate measurements of the composition and thickness of the deposited layer(s) on the flexible substrate. [0004] Therefore, there is a need for a method of depositing a semiconductor film on a flexible substrate and for a deposition system that solve one or more of the problems described above.

SUMMARY

[0005] The problem to be solved by the present invention is to set a up a method of depositing a semiconductor film on a flexible substrate, suited in particular also for the deposition of GICS semiconductor films used in the production of solar cells and/or solar modules, which method is fast, inexpensive, reliable, reproducible, controllable with high accuracy and fast reaction response, wherein the composition and/or physical properties of the deposited film can be measured and controlled in-situ rapidly and reliably with high reproducibility, and can be consequently adapted, changed and/or optimized according to the results of the performed and provided measurements.

[0006] The problem to be solved by the present invention has been solved according to the features of the independent claims. The dependent claims show preferred embodiments of the invention.

[0007] Embodiments of the present disclosure generally relates to a method of depositing a film on a flexible substrate. The method includes conveying the flexible substrate between a payout hub and a pickup hub; applying an initial voltage to a first electrode spaced apart from the flexible substrate in a first direction, wherein the flexible substrate is disposed between a first evaporation source and the first electrode; directing deposition material from the first evaporation source towards the flexible substrate to deposit a first layer onto a first surface of the flexible substrate; and measuring a property of the first layer deposited on the flexible substrate.

[0008] In another embodiment, a deposition system is provided for conveying a flexible substrate in a processing environment and more particularly for a deposition system for conveying a flexible substrate past one or more evaporation sources for depositing one or more materials on the substrate.

[0009] In one embodiment, a deposition system is provided for guiding a flexible substrate along a deposition path. The deposition system includes a payout hub for unwinding the flexible substrate; a pickup hub for winding the flexible substrate; one or more evaporation sources; one or more electrodes spaced apart from the one or more evaporation sources in a first direction; one or more measurement devices; and a controller configured to adjust one or more voltages provided to the one more electrodes.

According to the invention, a method of depositing a semiconductor film on a flexible substrate is provided, the method comprising

conveying the flexible substrate between a payout hub and a pickup hub; applying an initial voltage to a first electrode spaced apart from the flexible substrate in a first direction, wherein the flexible substrate is disposed between a first evaporation source and the first electrode;

directing deposition material from the first evaporation source towards the flexible substrate (450) to deposit a first layer onto a first surface of the flexible substrate; and

measuring a property of the first layer deposited on the flexible substrate.

The deposition material directed from the first evaporation source towards the flexible substrate to deposit a first layer onto a first surface of the flexible substrate may be advantageously Se, Ga, In and/or Cu.

A dielectric base may be advantageously disposed between the electrode and the evaporation source.

The flexible substrate is preferably guided using a plurality of clamps supported by a rail. The initial voltage applied to the first electrode may be advantageously between 50 and 10 000 V DC, preferably between 500 and 4 500 V DC.

According to a preferred embodiment, the method further comprises:

measuring a position of the flexible substrate in the first direction with one or more sensors configured to measure a position of the flexible substrate in the first direction; and

adjusting the voltage applied to the first electrode based on the measured position of the flexible substrate in the first direction with a controller configured to adjust one or more voltages provided to one more electrodes based on the one or more measurements of the one or more sensors.

According to another preferred embodiment, the method further comprises:

adjusting the temperature of the of the flexible substrate with a first heater, wherein the first electrode is disposed between the first heater and the first evaporation source in the first direction.

Measuring the property of the first layer may comprise advantageously measuring a composition of the first layer by detecting x-rays emitted from the first layer with a measurement device comprising an x-ray detector.

According to a preferred embodiment, measuring the property of the first layer may comprise:

- emitting x-ray radiation with an x-ray source of the measurement device towards the first layer to excite the atoms of said first layer;

- measuring the composition of the first layer by detecting the x-rays consequently emitted from the first layer with a x-ray detector of the measurement device; wherein the x-ray detector is positioned to be on a first side of the flexible substrate, and

the x-ray source is positioned to be on a second side of the flexible substrate.

The first electrode may be advantageously disposed directly over the first evaporation source.

The first measurement device may be advantageously disposed directly over the first evaporation source.

According to another preferred embodiment, the method further comprises:

directing deposition material from a second evaporation source towards the flexible substrate to deposit a second layer onto the first surface of the flexible substrate, wherein

the first evaporation source and the second evaporation source are spaced apart in a second direction, and the first electrode is disposed between the first evaporation source and the second evaporation source in the second direction.

Another aspect of the invention provides a deposition system for guiding a flexible substrate along a deposition path to carry out a method of depositing a semiconductor film on a flexible substrate according to the invention, the deposition system comprising:

a payout hub for unwinding the flexible substrate;

a pickup hub for winding the flexible substrate ;

one or more evaporation sources;

one or more electrodes spaced apart from the one or more evaporation sources in a first direction;

one or more measurement devices ; and a controller configured to adjust one or more voltages provided to the one more electrodes.

A CIGS thin film deposited on a flexible substrate is preferably produced with a method according to the invention and/or with a deposition system according to the invention.

A solar cell and/or a solar module may advantageously comprise a CIGS thin film deposited on a flexible substrate according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0011] Figure 1A is a side cross-sectional view of a deposition system, according to one embodiment.

[0012] Figure 1 B is a side sectional view of the processing section of the deposition assembly of Figure 1A showing additional detail of a first assembly in the processing section, according to one embodiment.

[0013] Figure 1 C is a bottom sectional view of a process set of Figure 1 B, according to one embodiment.

[0014] Figure 1 D is a side sectional view of one of the measurement devices in the process set of Figure 1 C, according to one embodiment. [0015] Figure 1 E is a partial side view of an electrode, a base 504, and a flexible substrate of the deposition system of Figure 1A, according to one embodiment.

[0016] Figure 2A is a partial side view of a deposition system including a first assembly, according to one embodiment.

[0017] Figure 2B is a partial side view of a deposition system including a first assembly, according to one embodiment.

[0018] Figure 3A is a partial side view of the deposition system of Figure 1A when a first biasing voltage is applied to the electrode, according to one embodiment.

[0019] Figure 3B is a partial side view of the deposition system of Figure 1A when a second biasing voltage is applied to the electrode, according to one embodiment.

[0020] Figure 4 is a process flow diagram of a method for depositing a material layer onto the substrate, according to one embodiment.

[0021] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

[0022] In the following, reference is made to embodiments. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the claimed subject matter. Furthermore, although embodiments described herein may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the claimed subject matter. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s).

[0023] Embodiments of the present disclosure generally relate to a deposition system for conveying a flexible substrate and more particularly for a deposition system for conveying a flexible substrate past one or more evaporation sources for depositing one or more materials on the substrate. Embodiments of the disclosure may generally provide one or more electrodes for chucking the flexible substrate towards the one or more electrodes, so that the flexible substrate is located at a uniform and consistent distance from the evaporation sources and from one or more measurement devices used to determine the composition and/or thickness of the layer(s) deposited onto the flexible substrate.

[0024] Figure 1A is a side cross-sectional view of a deposition system 10, according to one embodiment. The deposition system 10 is a roll-to-roll system for depositing material layers onto a flexible substrate 450. In some embodiments, the deposition system 10 can be a vacuum deposition system used to perform depositions on the flexible substrate 450 in a vacuum environment. In other embodiments, the deposition system 10 may also be used to process a substrate 450 at other pressures besides vacuum pressures. Although the remainder of the disclosure is largely described as a deposition system, aspects of the disclosure may also be applied to equipment used to transport, convey, or translate the substrate 450 in the absence of a deposition, such as a substrate transport system that transports and/or processes (e.g., scribes or thermal processes) the substrate 450 as the substrate 450 passes from a payout hub 1 10 to a pickup hub 210. The flexible substrate 450 can be, for example, a web or foil of flexible polyimide or stainless steel material. The deposition system 10 includes a deposition assembly 1 1 , a controller 601 , and an operator station 605. [0025] The controller 601 is generally used to facilitate the control and automation of the components within the equipment included in the deposition assembly 1 1 as well as related equipment connected to or associated with the deposition assembly 1 1. In one embodiment, the deposition assembly 1 1 is a vacuum deposition assembly configured to process the substrate 450 in a vacuum environment. The operator station 605 can provide status of the deposition assembly 1 1 to a user as well as allow the user to control the processes executed with the equipment in the deposition system 10, such as allowing the user to start and stop the transport of the flexible substrate 450 through the deposition assembly 1 1.

[0026] The controller 601 can be, for example, a computer, a programmable logic controller, or an embedded controller. The controller 601 typically includes a central processing unit (CPU) (not shown), memory (not shown), and support circuits for inputs and outputs (I/O) (not shown). The CPU may be one of any form of computer processors that are used in industrial settings for controlling various system functions, substrate movement, chamber processes, and control support hardware (e.g., sensors, motors, evaporation sources, heaters, etc.), and monitor the processes performed in the system (e.g., substrate tension, I/O signals, etc.). The memory is connected to the CPU, and may be one or more of a readily available non-volatile memory, such as random access memory (RAM), flash memory, read only memory (ROM), floppy disk, hard disk, or any other form of digital storage, local or remote. Software instructions and data can be coded and stored within the memory for instructing the CPU. The support circuits are also connected to the CPU for supporting the processor in a conventional manner. The support circuits may include cache, power supplies, clock circuits, input/output circuitry, subsystems, and the like.

[0027] A program (or computer instructions) readable by the controller 601 determines which tasks are performable on the substrate 450 in the deposition assembly 1 1. Preferably, the program is software readable by the controller 601 that includes code to perform tasks relating to monitoring, execution and control of the movement, support, and/or positioning of the substrate 450 along with the various process tasks and various sequences being performed by the controller 601 (e.g., starting up or shutting down the deposition assembly 1 1 ). The operator station 605 may include a wired or wireless computing device that contains various user input devices, such as a touch screen display, keyboard and buttons, and an output device, such as a GUI display, LED lights or other similar device.

[0028] The deposition assembly 1 1 includes a deposition chamber 20 (e.g., a vacuum chamber) including one or more walls 12 for enclosing an interior 15 of the deposition chamber 20. Inside the deposition chamber 20, the deposition assembly 1 1 includes a payout section 100 for unwinding the flexible substrate 450 from a payout roll 150, a processing section 400 for performing a deposition on the flexible substrate 450, and a pickup section 200 for rewinding the flexible substrate 450 onto a pickup roll 250 after processing. The processing section 400 includes one or more evaporation sources 300 for depositing one or more materials on the flexible substrate 450 and a first assembly 500. The first assembly 500 includes one or more electrodes (not shown) for chucking the flexible substrate 450 towards the first assembly 500, so that the flexible substrate 450 is located at a uniform and consistent distance from the evaporation sources 300 and from one or more sensors used to determine a property of the layer(s), such as the composition, crystal structure or thickness of the layer(s) deposited on the flexible substrate 450. The first assembly 500 is described in further detail in reference to Figures 1 B and 1 C.

[0029] The deposition system 10 guides the flexible substrate 450 along a deposition path from the payout roll 150 in the payout section 100, through the processing section 400, and to the pickup roll 250 in the pickup section 200. In one example, the payout roll 150 is a roll of the unprocessed flexible substrate 450, such as a roll of polyimide foil or a roll of polyimide foil coated by one or more layers that include one or more metals, such as molybdenum. The payout roll 150 is placed on a payout hub 1 10 before processing of the flexible substrate 450 begins. The payout hub 1 10 can rotate to unwind the flexible substrate 450 from the payout roll 150. The payout roll 150 decreases in diameter as the flexible substrate 450 is unwound from the payout roll 150. The pickup roll 250 is a roll that includes the processed flexible substrate 450, for example, after the one or more evaporation sources 300 have deposited one or more materials on the flexible substrate 450. The pickup roll 250 is formed around a pickup hub 210. The pickup hub 210 can rotate to wind the flexible substrate 450 onto the pickup roll 250. The pickup roll 250 increases in diameter as the flexible substrate 450 is wound onto the pickup roll 250.

[0030] The payout section 100 can include a first payout roller 120 and a second payout roller 130 to assist in guiding the flexible substrate 450 to the processing section 400 by adjustment of their relative positions or orientations to each other and/or to the payout hub 1 10. The relative positions or orientations of the first payout roller 120 and the second payout roller 130 may be accomplished by use of an actuator (not shown) that is coupled to the supporting elements (not shown) of each of these assemblies. The first payout roller 120 is closer to the payout hub 1 10 than the second payout roller 130 is to the payout hub 1 10. The actuators coupled to the first payout roller 120 and the second payout roller 130 can also assist in providing the proper tension to the flexible substrate 450 as the flexible substrate 450 is guided into the processing section 400. One or more payout tension sensors (not shown) can be connected to the controller 601 to monitor the tension of the flexible substrate 450 as the flexible substrate 450 is guided into the processing section 400.

[0031] The processing section 400 can include one or more payout tractors 410, 415 and, optionally, one or more pickup tractors 420, 425 to assist in conveying the flexible substrate 450 through the processing section 400. The payout tractors 410, 415 are positioned closer to the payout section 100 than the pickup tractors 420, 425 are to the payout section 100. The payout tractors 410, 415 include a first payout tractor 410 and, optionally, a second payout tractor 415. The payout tractors 410, 415 can be positioned to engage opposing sides (i.e., the opposing sides in the Y-direction of Figure 1 A) of the flexible substrate 450. For example, the first payout tractor 410 may be positioned to engage the left side of the flexible substrate 450, and the second payout tractor 415 may be positioned to engage the right side of the flexible substrate 450 when looking down (i.e., -Z- direction) on a given length of the flexible substrate 450.

[0032] The pickup tractors 420, 425 are positioned closer to the pickup section 200 than the payout tractors 410, 415 are to the pickup section 200. The pair of pickup tractors 420, 425 include a first pickup tractor 420 and a second pickup tractor 425. The pickup tractors 420, 425 can be positioned to engage opposing sides (i.e., the opposing sides in the Y-direction of Figure 1A) of the flexible substrate 450. For example, the first pickup tractor 420 may be positioned to engage the left side of the flexible substrate 450, and the second pickup tractor 425 may be positioned to engage the right side of the flexible substrate 450 when looking down (i.e., -Z -direction) on a given length of the flexible substrate 450.

[0033] The processing section 400 further includes the one or more evaporation sources 300 and the first assembly 500. In this embodiment, the one or more evaporation sources 300 include five evaporation sources 300i-300 ₅ . These evaporation sources 300 can heat material inside the evaporation sources 300 causing the material to evaporate. The evaporated material can then be directed towards the flexible substrate 450 as the flexible substrate 450 is conveyed past the one or more evaporation sources 300. Evaporation sources that are used to deposit metals (e.g., copper (Cu), indium (In), gallium (Ga), selenium (Se)) and/or dielectric materials are typically operated at temperatures that exceed 1000°C. The heat from the evaporation sources 300 can cause other equipment (e.g., structural supports, sensors, etc.) in the deposition assembly 1 1 and the flexible substrate 450 to heat up and expand. In some cases, this expansion can cause the flexible substrate 450 to become wrinkled due to a created difference in tension across the transfer direction length (X-direction) and/or lateral direction length (i.e., Y-direction). This misalignment and tendency of the flexible substrate 450 to wrinkle can be corrected in the pickup section 200 as described below in reference to Figure 1 C. The one or more electrodes in the first assembly 500 described below can also be used to reduce the occurrence of these wrinkles.

[0034] A front side 450A of the flexible substrate 450 may face the one or more evaporation sources 300. In one embodiment, the one or more evaporation sources 300 include an evaporation source 300 for each one of the elements included in a CIGS layer of a solar cell device. The evaporated material from the one or more evaporation sources 300 can deposit on the front side 450A of the flexible substrate 450. A back side 450B of the flexible substrate 450 may face the first assembly 500.

[0035] The pickup section 200 can include a first pickup roller 220 and a second pickup roller 230 to assist in guiding the flexible substrate 450 from the processing section 400 by adjustment of their relative positions or orientations to the pickup hub 210. The relative positions or orientations of the first pickup roller 220 and the second pickup roller 230 may be accomplished by use of an actuator (not shown) that is coupled to the supporting elements (not shown) of each of these assemblies. The first pickup roller 220 is closer to the pickup hub 210 than the second pickup roller 230 is to the pickup hub 210. The actuators coupled to the first pickup roller 220 and the second pickup roller 230 can also assist in providing proper tension to the flexible substrate 450 as the flexible substrate 450 is conveyed to the pickup hub 210. One or more tension sensors (not shown) can be connected to the controller 601 to monitor the tension of the flexible substrate 450 as the flexible substrate 450 is conveyed into the pickup section 200.

[0036] Figure 1 B is a side sectional view of the processing section 400 of the deposition assembly 1 1 showing additional detail of the first assembly 500, according to one embodiment. The first assembly 500 is used to chuck the flexible substrate 450 towards the first assembly 500 to improve the accuracy of the measurements of the composition and thickness of the material layer(s) deposited onto the flexible substrate 450, and in some embodiments to improve the consistency of the material layer(s) deposited onto the flexible substrate 450. The first assembly 500 may also be used to heat the flexible substrate 450 to a desired temperature during processing.

[0037] The first assembly 500 includes a body 501. The body 501 can include one or more walls 502, a top 503, and a base 504. The base 504 can be formed of a dielectric material (e.g., glass or ceramic material) that allows the electric field generated by electrically biasing the electrodes 510 (described below) to attract the flexible substrate 450 toward the first assembly 500. In some embodiments, the electrodes 510 may be embedded in the base 504, so that the electrodes 510 are directly exposed to the flexible substrate 450 without any portion of the base 504 disposed between the electrodes 510 and the flexible substrate 450. In some embodiments, the electric field from the electrodes 510 of the first assembly 500 can electrostatically attract the flexible substrate 450 to the outer surface of the base 504, so that the flexible substrate 450 contacts the base 504 at least at the locations of the electrodes 510. When the flexible substrate 450 is attracted to be against or a desired gap from the outer surface of the base 504, the position of the flexible substrate 450 in the Z-direction can be known with greater certainty, which can improve the accuracy of the measurements performed by the measurement device 550 described below.

[0038] The first assembly 500 is spaced apart from the five evaporation sources 300ι-300δ in the Z-direction (first direction). The first assembly 500 includes five process sets 505i-505s. In some embodiments, as shown in Figure 1 B, each process set 505 is disposed above a corresponding evaporation source 300. In some embodiments, each process set 505 includes an electrode 510, a heater 530, and one or more measurement devices 550. In some embodiments, each process set 505 includes an electrode 510 and a heater 530, as is discussed further below. [0039] Each electrode 510 can be used to electrostatically attract the flexible substrate 450 towards or against the base 504 of the first assembly 500, or in some embodiments directly towards an exposed electrode 510. Each electrode 510 can be placed directly over a corresponding evaporation source 300. Used herein, "directly over" refers to when an object is displaced from another object only in the Z-direction, so that the two objects share coordinates in the X and Y directions. Although the following description focuses on electrostatic chucking of any type of flexible substrate 450 towards or against the base 504, an electrostatic chucking design may also be used when a magnetizable flexible substrate 450 is used, such as flexible substrate 450 including a ferromagnetic material (e.g., 400 series stainless steels). Each electrode 510 can be independently controlled by the controller 601 so that different electrical properties (e.g., voltage) can be applied to the electrodes 510. For example, each electrode 510 can be electrically connected to a different switching device (not shown), such as a relay or contactor, so that a power supply 603 can energize that electrode 510. In some embodiments, the power supply 603 can apply a voltage from about 50 V DC to about 10,000 V DC, such as from about 500 V DC to about 4,500 V DC. Higher voltages can be applied to the electrodes 510 to attract the flexible substrate 450 closer to the base 504 of the first assembly 500 relative to when a lower voltage is applied to the electrodes 510. Furthermore, higher voltages can also be used when the weight, thickness, or stiffness of the flexible substrate 450 is increased by use of different substrate materials or due to the deposition of material on the substrate as it passes through the processing section 400.

[0040] Each heater 530 can be used to heat the flexible substrate 450 as the flexible substrate 450 passes over the respective evaporation source 300. The controller 601 can independently vary the power supplied to each heater 530, so that the heat generated by each heater 530 can be varied as needed. Each heater 530 can be disposed between the electrode 510 of that process set 505 and the top 503 of the first assembly 500. However, in some embodiments, the electrode 510 can be disposed between the heater 530 of that process set 505 and the top 503. Furthermore, in some embodiments, the electrode 510 and the heater 530 of a given process set may be disposed at locations not to overlie each other, for example, as shown in Figures 2A and 2B described below.

[0041] Each measurement device 550 can measure one or more properties, such as the composition and/or thickness of the material layer(s) deposited onto the flexible substrate 450. Although each process set 505 is shown including one measurement device 550 in Figure 1 B, each process set 505 can include multiple measurement devices 550, such as three measurement devices 550 as described below in reference to Figure 1 C. The measurements made by the measurement device 550 of a given process set 505 can be used to control the corresponding evaporation source 300 or heater 530 within that process set 505. For example, if the measured composition of the material deposited onto the flexible substrate 450 from a given evaporation source 300 is below a set point, then the heat applied to that evaporation source 300 can be raised to increase the flux of evaporated material from that evaporation source 300 towards the flexible substrate 450. However, in some embodiments, some process sets 505 in a series of process sets within the process section 400 may not contain a measurement device 550. In one example, as shown in Figure 1 B, the process sets 505i, 505 ₃ and 505 each do not contain a measurement device 550, while the process sets 505 ₂ and 505s each contain a measurement device 550. In this example, the measurement devices 550 in the process sets 505 ₂ and process set 505 ₅ may be used to control the corresponding evaporation source 300 or heater 530 in their process set and also other proximately positioned process sets (e.g., upstream and/or downstream process sets), such as the data collected from the measurement device 550 in process set 505 ₂ may also be used to control the components in the process set 505i and the data collected from the measurement device 550 in process set 505s may also be used to control the components in the process sets 505 ₃ and 505 .

[0042] However, when the distance between the flexible substrate 450 and the measurement device 550 of a given process set 505 varies in the Z-direction as the flexible substrate 450 is guided past the measurement device 550, for example due to a sagging flexible substrate 450, then the measurement device 550 can inaccurately measure and/or generate signals that indicate a changing composition and/or thickness even if the composition and/or thickness of deposited material layer is not changing. Thus, the electrode 510 of each process set 505 can be used to attract the flexible substrate 450 to a desired location in the Z- direction, so that the distance in the Z-direction between the measurement device 550 and the flexible substrate 450 remains constant as lengths of the flexible substrate 450 are guided past the measurement device 550 as the substrate 450 passes from the payout hub 1 10 to the pickup hub 210.

[0043] Figure 1 C is a bottom sectional view of the process set 505i of Figure 1 B, according to one embodiment. In this embodiment, the base 504 can be clear material (e.g., glass), so that the process set 505i disposed behind the base 504 is visible in the drawing. In some embodiments, the base 504 can be formed of a graphite window, which can be transparent to the X-rays detected by the measurement devices 550. In general, the base 504 can be formed of a material that is transparent for the detection method used by the measurement devices 550. However, in some embodiments, the measurement devices 550 can extend through a hole of the base 504, so that the base 504 does not interfere with the measurements performed by the measurement devices 550. The process set 505i can be used to heat the flexible substrate 450 and to attract the flexible substrate 450 towards the base 504 of the first assembly 500 in the region directly above the first evaporation source 300i (Figure 1 B). The process set 505i includes an electrode 510i, a heater 530i, three measurement devices 550IA-IC, three position sensors 570IA-I C, and three temperature sensors 580i _A- ic- Although Figure 1 C is described in reference to process set 505i, the description can also be applicable to the process sets 505 _2- 5-

[0044] The electrode 510i can be used to electrostatically attract the flexible substrate 450 towards or against the base 504 of the first assembly 500. In some embodiments, the electrode 510i can be embedded in the base 504, so that the electrode 510i is exposed to the flexible substrate 450. In such embodiments, the electrode 510i may be coated with a ceramic material (e.g., a high temperature- resistant ceramic), so that electrical discharges between the electrode 510i and other objects, such as the flexible substrate 450, may be prevented. Having the electrode 510i exposed to the flexible substrate 450 can allow for the flexible substrate 450 to be more strongly attracted towards the electrode 510i by the electrical field generated when the biasing voltage is applied to the electrode 510-i.

[0045] The electrode 510i can include a terminal 519 through which the biasing voltage is provided to the electrode 510i relative to a ground reference. The electrode 510i further includes a first end 511 , a second end 512, a first leg 513, and a second leg 514. The first leg 513 and the second leg 514 each extend in the Y-direction (third direction) from the first end 51 1 to the second end 512. The first leg 513 and the second leg 514 are spaced apart from each other in the X- direction (second direction), which in Figure 1 C is the direction in which the substrate travels. The first end 51 1 and the second end 512 each form a partial ring around respective measurement devices 550-ic, 550-IA- Furthermore, the first leg 513 includes a curved feature 515, and the second leg 514 includes a curved feature 516. The curved feature 515 and the curved feature 516 are disposed at the same location in the Y-direction to collectively form a partial ring 517 around the measurement device 550-I B- These partial rings formed around each of the measurement devices 550 can ensure that a sufficiently strong electrical field is provided to attract the flexible substrate 450 towards the base 504 at the locations of these measurement devices 550, which can improve the accuracy of the composition and/or thickness measurement performed by these measurement devices 550.

[0046] In some embodiments, the electrode 510i having a shape substantially in the form of a loop between the first end 51 1 and the second end 512 can be replaced with an electrode having a shape of a plate. In some embodiments, the electrode having the shape of a plate can be placed directly on the dielectric base 504, so that an electric field generated by the electrode can pass through a large surface area of the base 504. Furthermore, in some embodiments, the electrode having the shape of a plate can be embedded within the base 504, so that the electrode is exposed to the substrate 450. The electrode having a shape of a plate may still have holes through which the measurement devices 550 may extend to enable the measurement devices 550 to accurately measure the composition and/or thickness of the material layer(s) deposited onto the flexible substrate 450 without any obstruction by the base 504.

[0047] In the embodiment shown in Figure 1 C, a DC voltage can be applied to the electrode 510i, so that the electrode 510i can function as a monopolar electrostatic chucking device. However, in some embodiments, a process set (e.g., process set 505i) may include two or more electrically isolated electrodes to which opposing DC voltages can be applied, so that the two or more electrically isolated electrodes can function as a bipolar electrostatic chucking device. Furthermore, as mentioned above, in some embodiments, an electrode in the process set can form part of a circuit through which current can flow to electromagnetically chuck a magnetizable substrate, such as a substrate including a ferromagnetic material. In some embodiments, in which an electromagnetic chuck is used the current and/or the frequency of an alternating current may be adjusted to modify the chucking force.

[0048] The heater 530i can be used to heat and/or stabilize the temperature of the flexible substrate 450 and measurement environment that the measurement device 550 is exposed to as the flexible substrate 450 passes over the evaporation source 300i (Figure 1 B). The heater 530i can be a resistive heating cable through which electrical current can flow to generate the heat by a resistive heating method. The heater 530i includes a first end 531 and a second 532. The electrical current can, for example, flow from a positive voltage source through the first end 531 and to the second end 532, which can be coupled to an electrical ground. The heater 530i can include a plurality of rings 535. Each ring 535 can surround a corresponding measurement device 550 to ensure that heat is evenly distributed around the respective measurement devices 550 and so that the heat is homogeneously applied to the flexible substrate 450 below the respective measurement device 550.

[0049] The measurement devices 550 can be used to measure a property, such as composition and/or thickness, of the material layer(s) deposited onto the flexible substrate 450. For example, the measurement devices 550 can measure the percentage of one or more of the elements found in a CIGS layer that is formed of copper, indium, gallium, and/or selenium. In some embodiments, each measurement device 550 can be an x-ray fluorescence (XRF) measuring device. In other embodiments, the measurement devices 550 can be an optical measuring device. Figure 1 D below describes an exemplary XRF measuring device that can be used in the embodiments described herein. The process set 505i can include three measurement devices 550IA-I C spaced apart from each other in the Y- direction. Although three measurement devices 550IA-I C are shown, other embodiments may include more or less measurement devices 550, and the measurement devices 550 may also be spaced apart in the X-direction as well as the Y-direction. Furthermore, in some embodiments one or more of the measurement devices 550 may be movable in the X-Y plane. The composition and/or thickness of the material layer(s) deposited on the flexible substrate 450 can often vary across the width of the flexible substrate 450 in the Y-direction (i.e., the direction perpendicular to the direction of travel of the substrate). Thus, the measurement devices 550IA-I C that are spaced apart in the Y-direction can be used to measure and correct for any variation in the Y-direction by adjusting the heat provided from heating elements that are distributed in the Y-direction within a corresponding evaporation source 300. For example, in some embodiments, the evaporation source 300i can include heaters that can selectively increase or reduce heat towards the edges of the evaporation source 300i in the Y-direction, so that the deposition rate across the width of the flexible substrate 450 becomes more uniform.

[0050] The position sensors 570 can be used to measure the position of the flexible substrate 450 in the Z-direction. The position sensors 570 were not shown in Figure 1 B in order to not clutter the drawing. The process set 505i can include three position sensors 570IA-I C spaced apart from each other in the Y-direction. Each position sensor 570 can be a non-contact position sensor, such as an optical position sensor, a capacitive position sensor, or an ultrasonic position sensor. In some embodiments, a contact position sensor may be used, such as a force sensor or a tactile sensor. The position of the flexible substrate 450 can often vary in the Z-direction across the width of the flexible substrate 450 in the Y-direction (i.e., the direction perpendicular to the direction of travel of the substrate). For example, a center of the flexible substrate 450 can sag lower in the Z-direction than the outer portions of the flexible substrate 450, which may be supported by clamps (see clamps 470 in Figure 3A) or other supports. Thus, the three position sensors 570IA-I C spaced apart from each other in the Y-direction can measure how the positon in the Z-direction of the flexible substrate 450 varies in the Y-direction. Furthermore, the position of the flexible substrate 450 in the Z-direction can also vary at the same locations in the Y-direction as the flexible substrate 450 is guided past the flexible substrate 450. For example, in some embodiments, the flexible substrate may be supported at the edges in the Y-direction by clamps that are spaced apart in the X-direction. Because the clamps are spaced apart in the X- direction, the flexible substrate 450 can sag lower in the Z-direction at locations further from the clamps than at locations closer to the clamps.

[0051] The controller 601 can use measurements of the position sensors 570 to vary the voltage supplied to the electrode 510i to place the flexible substrate 450 in a consistent position in the Z-direction across the width of the substrate 450 in the Y-direction as the flexible substrate 450 is guided past the evaporation source 300i (Figure 1 B) in the X-direction. By placing the flexible substrate 450 in a consistent position in the Z-direction at the locations of the measurement devices 550, the accuracy of the composition and/or thickness measurements of the measurement devices 550 can be improved. When accurate composition and/or thickness measurements are made by the measurement devices 550, product quality can be improved because the controller 601 can modify outputs (e.g., heat provided to the evaporation source 300i) when modifications are actually needed instead of modifying outputs based on inaccurate measurements. Furthermore, by placing the flexible substrate 450 at a consistent position in the Z-direction at the location in the X-direction above the evaporation source 300i (Figure 1 B), the consistency of the deposition can also be improved. For example, the process conditions (e.g., temperature and flux of evaporated material towards the substrate) in the deposition chamber 20 above the evaporation source 300i can vary in the Z-direction, so any significant variance of the position in the Z-direction of the flexible substrate 450 can produce a corresponding variance of the deposition rate of evaporated material onto the surface of the flexible substrate 450. Thus, the position sensors 570 and the electrode 510i can be used to place the flexible substrate 450 at a consistent position in the Z-direction when the flexible substrate 450 is above the evaporation source 300i, which removes a variable that can result in varying deposition rates on the surface of the flexible substrate 450.

[0052] In one embodiment, the controller 601 can average the three position measurements from the three position sensors 570IA-I C and use the average to adjust the voltage supplied to the electrode 510i . For example, the average of the three position measurements can be the input to a proportional-integral-derivative (PID) control loop formed within software used by the controller 601 , and the voltage can be the output of the PID control loop. In other embodiments, a different process set (i.e., different from the process set 505i described above) may include an electrode for each position sensor 570, so that an individual control loop may be executed to independently control the position in the Z-direction of the flexible substrate 450 across the width of the flexible substrate 450 in the Y-direction. [0053] Each temperature sensor 580i _A- ic can be used to measure the temperature of the flexible substrate 450 as the flexible substrate 450 passes above the evaporation source 300i (Figure 1 B). Each temperature sensor 580 can be a non-contact temperature sensor, such as an infrared thermometer, a thermocouple, or a pyrometer. The temperature sensors 580 can be spaced apart from each other in the Y-direction. The controller 601 can use the measurements from the temperature sensors 580 to modify the power supplied to the heater 530i. In some embodiments, the process set (e.g., the process set 505i) can include a heater for each temperature sensor 570, so that the temperature of the different locations in the Y-direction of the flexible substrate 450 can be independently controlled, for example with an independent PID control loop for each temperature sensor and heater pair.

[0054] Figure 1 D is a side sectional view of one of the measurement devices 550-iA in the process set 505i, according to one embodiment. The measurement device 550-IA includes an x-ray source 551 and an x-ray detector 552 to determine the composition and thickness of the deposited material layer(s) on the flexible substrate 450. The x-ray source 551 may emit monochromatic or broadband x- ray radiation 555. The radiation 555 of the x-ray source 551 is used to excite atoms in all deposited layer(s) and atoms of the flexible substrate 450. The excited atoms relax by emitting fluorescent radiation 556 of discrete wavelengths. The discrete wavelengths emitted by the excited atoms can be analyzed by the measurement device 550-IA to determine the composition and thickness of the deposited layer(s). In some embodiments, the measurement device 550-IA can include two or more x- ray sources 551 for each x-ray detector 552. For example, in one embodiment the measurement device 550-IA can include three x-ray sources 551 (e.g., an x-ray source for copper (Cu), an x-ray source for Gallium (Ga), and an x-ray source for Indium (In)) and a single x-ray detector 552.

[0055] The x-ray source 551 and the x-ray detector 552 can be placed in the same housing 553. The housing 553 is shown extending through the base 504 of the first assembly 500 or in some embodiments through an electrode 510 embedded within the base 504, so that the radiation emitted by x-ray source 551 and received by the x-ray detector 552 are not interfered with by the base 504. In embodiments in which the flexible substrate 450 is chucked against the outer surface of the base 504, the housing 553 may be flush with or recessed relative to the outer surface of the base 504, so that the measurement device 550i does not contact the flexible substrate 450. In other embodiments (see Figure 2B), the x-ray source 551 and the x-ray detector 552 may be placed in different housings. Furthermore, in some embodiments, the x-ray source 551 can be replaced with an electron source. An electron source can also excite atoms to emit fluorescent radiation that can be similarly detected by the x-ray detector 552 to determine the composition and thickness of the deposited layer(s).

[0056] Figure 1 E is a partial side view of the electrode 510-i, the base 504, and the flexible substrate 450 of the deposition system 10 of Figure 1A, according to one embodiment. Figure 1 E illustrates a charge distribution across the electrode 510i and the flexible substrate 450 when the electrode 510i is biased with a positive voltage. The following description of Figure 1 E is also applicable when the electrode 510i is embedded within the base 504, so that the electrode 510i is exposed to the substrate 450. In such instances, the electrical field E created by the biased electrode 510i can more directly attract the substrate 450 relative to when electric filed E polarizes the base 504 to attract the substrate 450 towards the base 504.

[0057] When the controller 601 energizes the electrode 510i with a positive voltage, a positive charge 527 accumulates on the electrode 510-i. When the positive voltage is applied to the electrode 510i, an electric field E develops between the electrode 510i and the flexible substrate 450. It is believed that the base 504 formed of the dielectric material (e.g., glass) may polarize so that a positive charge accumulates on the surface of the base 504 facing the flexible substrate 450. The flexible substrate 450 can also become polarized due to the generated bias, so that an opposing charge can migrate through the flexible substrate 450 in response to the generated electric field E. In this example, the electric field E created by the positive bias of the electrode 51 Oi attracts negative charges 458 to the back side 450B of the flexible substrate 450 while positive charges 457 are repelled by the generated electric field E towards the front side 450A. The accumulation of positive charge 517 at the electrode 51 Oi and negative charge 458 at the back side 450B of the flexible substrate 450 attracts the flexible substrate 450 towards the base 504. The magnitude of the positive voltage applied to the electrode 510i can be increased to attract the flexible substrate 450 closer to the base 504 or to be against the base 504.

[0058] It is generally desirable to assure that a gap G (Figure 1 B) is formed between the back side 450B of the flexible substrate 450 and the lower surface of the base 504, by the substrate 450 guiding elements (e.g., payout tractors 410, 415 and pickup tractors 420, 425). The gap G can be less than about 20 millimeters (mm), such as less than about 10 millimeters (mm). In another example, the gap G can be between about zero millimeters and 20 mm, such as between about 0.1 mm and 10 mm. By assuring that the gap G is within a desirable range of distances one can make sure that the flexible substrate 450 will be "chucked" as the substrate processing and substrate tensioning variables drift over time.

[0059] In some embodiments, the flexible substrate 450 can be electrically coupled to an electrical ground of the circuit which applies the bias voltage to the electrode 510i, so that the flexible substrate 450 is not electrically floating, and is electrically referenced with respect to the electrode 510-i. Furthermore, in some embodiments, a negative voltage may be applied to the electrode 510-i, so that a negative charge accumulates on the electrode 510i and a positive charge accumulates on the back side 450B of the flexible substrate 450 to attract the flexible substrate 450 towards the base 504. [0060] Figure 2A is a partial side view of a deposition system 10A including a first assembly 500A, according to one embodiment. The first assembly 500A is similar to the first assembly 500 described above except that the first assembly 500A includes process sets (e.g., process set 505i _A ) which are different from the process sets (e.g., process set 505i) described above. The process set 505IA shown here includes the electrode 510-i, the heater 530i, and the measurement device 550i like the process set 505i described above and shown in Figure 1 B. However, the electrode 51 Oi and the measurement device 550i are disposed at a location other than directly above the evaporation source 300i. For example, in this embodiment the electrode 510i and the measurement device 550i are disposed at a location in the X-direction after the evaporation source 300i. Thus, the electrode 510i and the measurement device 550i may be disposed between the first evaporation source 300i and the second evaporation source 300 ₂ (see Figure 1 B) in the X- direction. Disposing the electrode 510i and the measurement device 550i at a position in the X-direction after the flexible substrate 450 passes the evaporation source 300i allows the measurement device 550i to measure the composition and/or thickness of a more completed deposition. Furthermore, the electrode 510i can be energized, so that the flexible substrate 450 is in a consistent position in the Z-direction, so that the accuracy of the composition and/or thickness measurement made by the measurement device 550i can be improved. In the embodiment shown, the measurement device 550i and the electrode 510i are disposed on the back side 450B of the flexible substrate 450. However, in other embodiments, one or more of the measurement devices 550i and the electrode 510i can be disposed on the front side 450A of the flexible substrate 450. Furthermore, in some embodiments, the heater 530i may also be disposed on the front side 450A of the flexible substrate 450, so that in some embodiments the components in each process set 505 are all disposed on the front side 450A of the flexible substrate 450.

[0061] Figure 2B is a partial side view of a deposition system 10B including a first assembly 500B, according to one embodiment. The first assembly 500B is similar to the first assembly 500A described above except that the first assembly 500B includes process sets (e.g., process set 505I B), which are different from the process sets (e.g., process set 505-i _A ) described above. The process set 505i _B shown here includes the electrode 51 Oi and the heater 530i like the process set 505-iA described above and shown in Figure 2A. However, the process set 505I B includes a measurement device 560i instead of the measurement device 550i. The measurement device 560i places the x-ray source 551 and the x-ray detector 552 on different sides of the flexible substrate 450. Placing the x-ray source 551 and the x-ray detector 552 on different sides of the flexible substrate 450 can help prevent the radiation emitted by the x-ray source 551 from interfering with the radiation received by the x-ray detector 552. In the embodiment shown, the x-ray source 551 is disposed on the back side 450B of the flexible substrate 450 and the x-ray detector 552 is disposed on the front side 450A of the flexible substrate 450. However, in other embodiments, the x-ray source 551 can be disposed on the front side 450A of the flexible substrate 450 and the x-ray detector 552 can be disposed on the back side 450B of the flexible substrate 450.

[0062] Figure 3A is a partial side view of the deposition system 10 when a first biasing voltage is applied to the electrode 510-i , according to one embodiment. The view in Figure 3A shows the flexible substrate 450 being guided past the evaporation source 300i using a plurality of clamps 470 that are supported by a rail 460. The clamps 470 can slide along the rail 460 to provide vertical support for portions of the flexible substrate in the Z-direction. Despite the use of the clamps 470, the flexible substrate 450 will still sag in the Z-direction between the clamps 470 due to its inherent weight. In cases where the electrode 510 is biased with a voltage (e.g., voltage between 0 Volts and V _M Volts) that only produces a biasing force F _B i that is created by the formed electric field that is insufficient to overcome the gravitational force F _G created by the weight of the flexible substrate 450 and inherent mechanical stiffness of the flexible substrate 450, the substrate may not be able to be "chucked" and/or will only be moved to an unknown position relative to the base 504. [0063] Figure 3B is a partial side view of the deposition system 10 when a second biasing voltage (e.g., V _B 2 Volts) is applied to the electrode 510i, according to one embodiment. The second biasing voltage is greater in magnitude than the first biasing voltage (e.g., V _B 2 > V _M ). The second biasing voltage produces a biasing force FB2 that is sufficient to overcome the gravitational force FG to attract the flexible substrate 450 to a position closer to the base 504, such as a position in the Z-direction substantially even with the rail 460. Because the flexible substrate 450 is attracted to a position in the Z-direction that is even with the rail 460, the flexible substrate 450 directly below the measurement device 550i is at a consistent position in the Z-direction, which improves the accuracy of the composition and/or thickness measurements performed by the measurement device 550i. The improved accuracy of the composition and/or thickness measurements can enable the controller 601 to more appropriately respond to changes in composition and/or thickness measurements, which can improve product quality. In some embodiments, the second biasing voltage produces a biasing force FB2 that causes the flexible substrate 450 to be positioned at a distance equal to a desired measurement gap that is measured in the Z-direction relative to the base 504. In some configurations, the measurement gap, which is created by the application of the bias and the positioning of the substrate 450 provided by the substrate guiding elements (e.g., payout tractors and pickup tractors), may be between about zero micrometers and 20 millimeters (mm), such as between about 0.1 μηη and 3 millimeters (mm).

[0064] Figure 4 is a process flow diagram of a method 600 for depositing a material layer onto the substrate 450, according to one embodiment. Referring to Figures 1 B and 1 C, the method 600 is described. At block 602, an initial bias voltage is applied to the electrode 510i. At block 604, the evaporation source 300i is activated to direct a flux of material towards the substrate 450 and the substrate 450 is guided past the evaporation source 300i. At block 606, the position of the flexible substrate 450 in the Z-direction directly above the evaporation source 300i is measured. At block 608, the position of the flexible substrate 450 in the Z- direction is compared to a setpoint for the position of the flexible substrate 450 in the Z-direction. At block 610, if the flexible substrate 450 is located at a position in the Z-direction that corresponds with the setpoint, then the previously applied voltage to the electrode 510i is maintained. At block 612, when there is a difference between the position in the Z-direction of the flexible substrate 450 and the setpoint, then a new voltage is applied to the electrode 510i in order to decrease the difference between the measured position of the flexible substrate in the Z-direction and the setpoint. For example, the magnitude of the voltage applied to the electrode 510i may be increased if the flexible substrate 450 is lower in the Z-direction than a desired position of the flexible substrate 450. After the execution of either block 610 or 612, the process loops around to repeatedly execute blocks 606, 608, and either 610 or 612, so that the voltage applied to the electrode 510i can either be adjusted or maintained in order to adjust the position of the flexible substrate 450 to be closer to or at the set point.

[0065] In some embodiments, the bias voltage that is applied to the electrodes 510 positioned in each of the successive process sets 505, which are serially distributed along the processing section 400, may be increased due to the need to compensate for the increased thickness and stiffness of the substrate as material is deposited on the surface of the substrate 450. In some embodiments, the bias voltage that is applied to the electrodes 510 in each of the process sets 505, which are serially distributed along the processing section 400, may be separately adjusted based on a need to compensate for changes in the stiffness of the substrate 450 due to temperature fluctuations or other material structural related effects seen within or on the substrate 450 within different areas of the processing section 400.

[0066] While the foregoing is directed to embodiments of the present 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.