WO2012174432A2

WO2012174432A2 - Solar cell process carrier

Info

Publication number: WO2012174432A2
Application number: PCT/US2012/042749
Authority: WO
Inventors: Mark V. Smith; John Burns
Original assignee: Entegris, Inc.
Priority date: 2011-06-15
Filing date: 2012-06-15
Publication date: 2012-12-20
Also published as: TW201305030A; WO2012174432A3

Abstract

A process carrier for solar cells includes a plurality of supports configured as toothed rails extending between a pair of endwalls. Each cell support includes a plurality of teeth arranged in a row extending outwardly therefrom defining a solar cell receiving region with plurality of slots for containing cells. Toothed rails are connected to endwalls with connections having significant strength, high dimensional accuracy and that minimize potential leaks. Rigid structural support members of the rails, such as metal shafts, can be isolated from process fluids and can be totally encapsulated by chemical resistant polymers such as fluoropolymers by overmolding or other isolation means. End caps configured as fittings attach to receiving openings on the endwalls and an uppermost toothed rail can be inserted and removed and rotated to secure batches of cells in place for processing.

Description

SOLAR CELL PROCESS CARRIER

FIELD OF THE INVENTION

The present invention relates to processing substrates. More particularly, the present invention relates to a process carrier suitable for holding wafers, such as silicon wafers, and particularly solar cell wafers during processing baths.

BACKGROUND OF THE INVENTION

As a part of processing silicon wafers into semiconductors the wafers are immersed into various solutions in carriers often known as boats. See prior art Figure la, for example, from U.S. Patent No. 4,872,554 originally assigned to Fluoroware, Inc. a predecessor of Entegris, Inc. the owner of the instant application. Such a substrate process carrier 20 has a pair of endwalls 22, 24 with several tubular rails 30 with integral teeth 32 for engaging the substrates extending between the endwalls. The teeth extend from the tubular rails inwardly toward the substrates 34. Such process boats may utilize polymers, such as fluoropolymers, to resist the caustic process fluids utilized in the processing steps. Stiffening members 36 may be embedded in the elongate tubular rails such as by non contact welding the tubular polymer rail pieces of the carrier to the endwalls.

The specific processing of solar cells conventionally utilize such carriers or boats. It is very advantageous in processing silicon that the entirety of the surfaces of the wafers, particularly including cells, are uniformly processed with the fluids in which the cells are immersed. The substrate carriers, including solar cell process carriers, have contact areas on teeth positioned on the rails for supporting and restraining the substrates. Typically, the tubular rails or rods having the integral teeth for supporting the solar cells or other substrates during processing are directly connected to the endwalls by, for example, ultrasonic welding. While this provides a simple design with minimal parts, leaks are common and it results in poor dimensional accuracy. Leaks can result in the processing fluid contacting metal shafts within the polymer rods, which can contaminate the processing fluid and or degrade the metal shafts. A more robust connection between the supporting rods and endwalls would therefore be desirable.

SUMMARY OF THE INVENTION

A process carrier for solar cells includes a plurality of cell supports configured as toothed rails extending between a pair of endwalls. Each cell support includes a plurality of teeth arranged in a row extending outwardly therefrom defining a solar cell receiving region with plurality of slots for containing cells. Toothed rails are connected to endwalls with connections having significant strength, high dimensional accuracy and that minimize potential leaks. Metal portions of toothed rails can be isolated from process fluids and can be totally encapsulated by chemical resistant polymers such as fiuoropolymers.

A feature and advantage of embodiments of the present invention is isolation of a metal shaft of a toothed rail from the processing fluid. This can be done by overmolding the polymer material of the toothed rail in a way to completely encapsulate the metal shaft, by providing o- rings to provide a seal between the metal components and the process fluid, or both.

A feature and advantage of embodiments of the present invention is use of an overmolded endcap configured as a fastener to connect a toothed rail to each endwall. The fastener endcap can be configured as a male or female threaded connector or an an unthreaded protruding shaft. In one embodiment, a toothed rail end and a cooperating endwall can have cooperating flanges that engage each other and a fastener can be inserted through a receiving aperture in end wall and into an aperture in toothed rail either into a fitting or into a threaded hole in a rigid reinforcing member to releasably lock the toothed rail and endwall together. This allows the endwalls and cell supports to be readily disassembled and also provides a high degree of dimensional accuracy in placement of the components. Sealing elements can also be provided between the endwall and toothed rail and endwall and fastener to prevent leaks.

Another feature and advantage of embodiments of the present invention is a toothed rail having an end cap having a threaded connector overmolded with a toothed rail. The threaded connector of the end cap can be inserted into a receiving aperture in an endwall and secured to the endwall with a nut or other fastener. This provides simple assembly and can be readily disassembled, does not require any separate sealing elements, maintains high dimensional accuracy and has a low part count.

A further feature and advantage of embodiments of the present invention is a toothed rail having an end cap configured as a fitting portion overmolded to the toothed rail that has a projection that can be a threaded connector portion or can be welded to an endwall. The projection can be inserted through a receiving aperture in the endwall and then diametrically expanded and/or welded to an exterior surface of the endwall to securely connect the toothed rail and endwall. This provides a strong connection between the toothed rail and the endwall and does not require a separate sealing element, has a low part count and provides high dimensional accuracy. Another feature and advantage of embodiments of the present invention includes a toothed rail having a rotatable end cap. The rotatable end cap can be overmolded with the toothed rail and can be inserted into a slot in the endwall into a receiving aperture in the end wall. After insertion, the end cap can be rotated thereby rotating the toothed rail to rotate an eccentric shaft portion into a locked position with a cooperating slot portion in an end wall. This provides simple assembly and can be readily disassembled, does not require any separate sealing elements, maintains high dimensional accuracy and has a low part count.

A feature and advantage of embodiments of the invention is the absence of washers, bushings, and assembly parts. In particular, a robust carrier can be assembled with two endwalls with receiving openings, a plurality of toothed rails with integral and unitary fittings on the ends, and with threaded fasteners connecting the rails to the endwalls at the openings. Sufficient structural support is provided by four or six such toothed rails.

Although specific embodiments herein are described in the context of a process carrier for solar cells, the configurations herein are also intended for use with other silicon wafer process carriers, and carriers for substrates other than silicon.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure la is a prior art substrate process carrier;

Figure lb is a cross section of a rail base portion and a tooth of the prior art carrier of Figure la;

Figure 2 is a perspective view of a solar cell process carrier according to an embodiment of the present invention in a vertical position.

Figure 3 is a perspective view of a solar cell process carrier according to an embodiment of the present invention in a horizontal position.

Figure 4 is a cut-away perspective view of a solar cell process carrier according to an embodiment of the present invention.

Figure 5a is a perspective view of a rigid elongate shaft member configured as a steel rod of a solar cell process carrier according to an embodiment of the present invention.

Figure 5b is a perspective view of a threaded fitting portion positioned at the end of a steel rod of a solar cell process carrier according to an embodiment of the present invention.

Figure 5c is a perspective view of the fitting portion having a threaded shaft portion and rigid reinforcing member configured as a rod of Figure 5b assembled prior to overmolding a threaded sleeve thereon. Figure 5d is a perspective view of the rigid shaft member and fitting overmolded with the toothed sleeve portion.

Figure 5e is a perspective view of the end portion of the toothed rail of Figure 5d attached to an endwall with a threaded connector— a nut.

Figure 6a is a perspective view of another embodiment of a fitting comprising a heat deformable shaft portion extending through a receiving opening in an endwall.

Figure 6b is a perspective view of the portion of a toothed rail of Figure 6a with the shaft portion deformed and welded to the endwall.

Figure 7a is a perspective view of an alternative embodiment with a manually handle configured as a key with a eccentric shaft at the end of an uppermost toothed rail.

Figure 7b is a perspective view of an end wall with a slot having a cooperating slot portion to interface with eccentric shaft portion of the fitting of Figure 7a according to an embodiment of the present invention.

Figure 7c is a perspective view of the uppermost toothed rail of Figure 7b inserted into the slot in the endwall with the teeth at a rotational position of about 3:00 o'clock according to an embodiment of the present invention.

Figure 7d is a perspective view of the uppermost toothed rail of Figures 7b and 7c rotated about 90 degrees to secure the eccentric portion in the cooperating slot portion and with the teeth at a rotational position of about 6:00 o'clock for an engaging position with the batch of substrates according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figures 2 and 3 depict a process carrier 100 for holding substrates, particularly solar cells 102, during a process bath processing the substrates. The cells may be inserted and withdrawn when the carrier is vertical and with the cells horizontal as shown in Figure 2. When immersed in process fluid, the carrier is horizontal as shown in Figure 3 with the substrates vertical.

Process carrier 100 includes a pair of parallel spaced endwalls 104 with a plurality of cell supports configured as rods or rails 106 extending therebetween. Endwalls 104 can include a plurality of receiving apertures 108 for receiving and aligning the wafer supports 106. In one embodiment, endwalls 104 can be generally U-shaped in order to provide an open path for the etching fluid to the bottommost and topmost solar cells 102. Toothed rails 106 can include bottom toothed rails 105 on a bottom side of the process carrier 100 (relative to the horizontal position of the carrier during processing), side toothed rails 107 on each side of the carrier 100 and, in some embodiments, a top toothed rail (not pictured) on a top side of the carrier 100. Each cell support 106 is defined by a sleeve 1 13 with a plurality of spaced teeth 1 14 for holding cells 102. In one embodiment, rails include a metal shaft surrounding by a polymeric sheath or sleeve. Process carrier 100 can also include a pair of additional structural supports 118 extending between the endwalls 104 for providing increased structural rigidity to the carrier 100. Generally, structural support may be provided by rigid metal bars or rigid polymers, such as Polyetheretherketone, that is embedded within or encapsulated by polymers resistant to the processing fluids. Fluoropolymers, including PVDF (polyvinylidene fluoride), PFA (perfluoroalkoxy) and PTFE (polytetrafluoroethylene) are appropriate.

In one embodiment, process carrier 100 can include four or six toothed rails 106 arranged around three sides of the endwalls 104 providing an open front or top 120, depending on the carrier orientation, for insertion of solar cells 102. Solar cells 102 can be inserted into process carrier 100 by introducing them through open front 120 into a cell receiving region 121 and into slots 122 defined between the spaced teeth 1 14 of cell supports 106. The cell receiving region 121 can be defined as having the depth and width of a cell to be carried therein and extending from the bottommost slot to the uppermost slot. Cells 102 can be stacked in an axially spaced relationship defined by the teeth 1 14. In some embodiments, a top toothed rail (not pictured) can be inserted across open front 120 following insertion of solar cells 102 to further secure cells within cell receiving region 121. In some embodiments, process carrier 100 can include a colored information plug 124 that identifies the particular solar cells 102 contained in process carrier 100. Various teeth and support alignments and configurations that can be used in embodiments of the present invention are depicted in PCT Application No. PCT/US201 1/026890, which is hereby incorporated by reference in its entirety.

Referring now to Figure 4, there can be seen a connection between an endwall 104 and a toothed rod or rail 106 of a solar cell process carrier 100 according to an embodiment of the present invention. Endwall 104 and rail 106 are connected by way of a fastener 130. In one embodiment, fastener 130 is comprised of a polymer material, for example PVDF with carbon or carbon fiber filler. Rail 106 can have a flange 132 defining an endwall receiving region 134 and a fastener receiving opening 136 and can include a sleeve 113 with rigid elongate shaft 146. In one embodiment, shaft 146 is comprised of stainless steel and surrounding portion of sleeve 1 13 comprises a fluoropolymer material. Endwall 104 can have a flange 138 extending outwardly at receiving aperture 108 defining a support receiving region 140. Endwall may be formed of PVDF without filler, in other embodiments it may be formed of other polymers or will fillers. To connect endwall 104 and toothed rail 106, a fitting portion configured as a flange 132 of rail 106 is inserted onto flange 138 of endwall 104 so that the rail 106 is received in the rail receiving region 140 of the endwall 104 and the endwall flange 138 is received in the endwall receiving region 134 of the rail 106. Fastener 130 is then inserted through receiving aperture 108 in endwall 104 and into fastener receiving aperture in toothed rail 106. A first sealing element 142, such as, for example, an o-ring or gasket, can be positioned between the endwall 104 and the support rod 106 and second sealing element 144 can be inserted between the endwall 104 and the fastener 130 prior to making the connection to prevent process fluid from contacting the shaft 146. This embodiment allows the endwalls 104 and cell supports 106 to be disassembled and also provided a high degree of dimensional accuracy in placement of the components. In one embodiment, outer portion of sleeve 1 13 and flange 132 can be previously joined to each other and can also be joined to shaft 146 by an overmolding or welding process. In an embodiment they may both be simultaneously formed in a mold as a single unit with the steel rod subsequently inserted. In an embodiment the sleeve and fitting 132 may be simultaneously overmolded as a unitary piece on the steel rod.

Figures 5a-5d depict the elements of a toothed rail 106 for connecting with endwalls 104 according to another embodiment of the present invention. Toothed rail 106 includes a cylindrical rigid shaft member 146 and an end cap configured as a fitting 148. In one embodiment, shaft is comprised of stainless steel. Fitting 148 can include an aperture 150 for receiving shaft member 146 and also includes a threaded portion 152. Shaft 146 is inserted into fitting 148 to form a sub-assembly as depicted in Figure 5C. Outer portion of sleeve 113 and teeth 1 14, which can be comprised of a fluoropolymer material, are then overmolded over shaft 146 and end cap 148 to lock them together and encapsulate shaft 146. Toothed rail 106 can then be connected to endwall 104 as shown in Figure 5e, by inserting threaded connector 152 of end cap 148 through receiving aperture 108 in endwall 104 and then threading a fastener, such as a nut 154, onto threaded connector. This embodiment provides simple assembly and can be readily disassembled. It also isolates the shaft 146 without any separate sealing elements, maintains high dimensional accuracy and has a low part count.

Referring now to Figures 6a and 6b, there can be seen a toothed rail 106 and endwall 104 connection according to another embodiment of the present invention. This embodiment can utilize a toothed rail 106 having a rigid shaft member 146 and end cap 148 with an overmolded outer portion, sleeve 1 13, similar to that described in Figures 5a-5e. In this embodiment, the end cap 148 includes a projection 156 that is extended through the receiving aperture or opening 108 in the endwall 104. After insertion into the endwall 104, the projection 156 is melted and diametrically expanded and may also be welded onto an exterior surface 158 of the endwall 104. This results in a strong connection between the toothed rail 106 and the endwall 104. In addition, this embodiment isolates the shaft 146 without a separate sealing element, has a low part count and provides high dimensional accuracy.

Figure 7a depicts an uppermost toothed rail with a manual handle configured as a key on an end cap 160 that can be used with a solar cell process carrier according to another embodiment of the present invention. Rail 106 has a shaft portion 162 and an eccentric or cammed shaft portion or neck 164, a flange 165, and a handle shaped as a key 166. End cap 160 can be overmolded with sleeve 1 13 of toothed rail 106 at end projection 162. In one embodiment, toothed rail 106 includes a stainless steel or other metal shaft 146 that is encapsulated by the overmolding process. Endwall 104 can have a receiving opening or aperture 108 configured as a slot extending downwardly form the top edge 167 that includes a cooperating slot portion 109 extending from an interior side 168 of the endwall 104 to the exterior side 169. To connect toothed rail 106 with endwall 104, the neck 164 of the end cap 160 is first inserted through the slot 109 in the side 168 of the endwall and into the receiving aperture 108 as indicated in Figures 7b and 7c. The key 166 is then rotated, as shown in Figures 7c and 7d, to secure the end cap 160 within the receiving aperture 108. This locks the toothed rail 106 into engagement with the endwall 104. In one embodiment, the end cap 160 and sleeve 1 13 are unitary and thus rotate together so that the teeth 1 14 of the toothed rail 106 come into engagement with the batch of solar cells as the rail 106 is locked in place on the endwalls. In embodiments both endwalls or one endwall may have the cooperating slot portion that engages with the eccentric shaft portion.

In one embodiment, the toothed rail 106 and end wall 104 are interlocked by inserting a narrow portion of an eccentric, oval, or elliptical neck 164 through the slot 109 and into the receiving aperture 108, which is wider than the slot 109, and then rotating the rod 106 within the receiving aperture 108 so that a wider portion of the neck 164 cannot be withdrawn through the slot 109. Generally there will be a tight interference fit for retaining the rail in the locked position. In another embodiment, one or more of the neck 164, key 166, slot 109 or receiving aperture 109 may include cooperating structure that is engaged to lock the toothed rail 106 and endwall 104 together when the key 166 is rotated. In some embodiments, a toothed rail 106 that is rotated to be locked in place can be a top toothed rail that is positioned to engage the solar cells after they have been inserted into the carrier and retain them therein. Although described with reference to a process carrier for immersing solar cells in a process bath, it should be noted that supports as described herein can also be used in transport carriers and any other type of container for supporting solar cells. Similarly, although described with respect to solar cells, the present invention could be used with any other type of substrate, such as semiconductor wafers. The present invention can be assembled by welding molded tubular polymer, such as fluoropolymers, rail portions together and to the endwalls with a rigid insert inserted in the tubing. See U.S. Patent No. 4,872,554, which is incorporated herein by reference, for suitable construction details.

The present invention may be embodied in other specific forms without departing from the spirit of any of the essential attributes thereof. Therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Claims

1. A method of manufacturing a rigidized wafer process carrier having a pair of spaced endwalls and a plurality of toothed rails extending therebetween, the method comprising:

manufacturing a plurality of toothed rails, each toothed rail manufactured by

overmolding on rigid elongate shaft member a fluoropolymer sleeve with a row of teeth extending from the sleeve, each toothed rail having a row of teeth formed of the fluoropolymer and each tooth rail having fluoropolymers fittings on opposite ends of the toothed rail, each fitting having a securement shaft extending in axial alignment with the rigid elongate shaft member;

installing each securement shaft portion of each of the plurality of toothed rails through a receiving opening in one of the respective endwalls with the toothed rails in perpendicular alignment with each of the pair of endwalls; and

securing the toothed rails to the pair of endwalls by way of the securement shafts.

2. The method of claim 1 wherein each securement shaft is threaded and securing each toothed rail to the respective endwalls comprises attaching threaded connectors to portions of the securement shafts that extend through the respective endwalls.

3. The method of claim 2 wherein each threaded connector has one of a manual flange handle extending axially, the manual flange handle with finger gripping surfaces and a tool accommodating head.

4. The method of claim 1 wherein each securement shaft, when installed in the respective receiving opening, has a protruding portion that extends beyond an outer surface of the endwalls and the method further comprising melting the protruding portion to create a melted portion that has a diametric size larger than the receiving opening.

5. The method of claim 1 further comprising installing a pair of endcaps configured as fittings on each end of the rigid elongate shaft prior to overmolding the fluoropolymer sleeve thereon.

6. The method of claim 1 wherein the receiving opening in each endwall is configured as a slot extending downwardly from a top edge of the respective endwalls and each fitting is sized to be received in a respective slot.

7. The method of claim 6 wherein each fitting has an eccentric shaft portion that engages a cooperatively shaped portion of the respective slots and the method further comprises lowering the fittings of the toothed rail into the slots and then rotating the toothed rail securing the toothed rail into the respective slots.

8. A method of manufacturing a rigidized wafer process carrier having a pair of spaced endwalls and a plurality of toothed rails extending therebetween, the method comprising:

manufacturing a toothed rail by overmolding circumferentially a sleeve with teeth on a rigid elongate reinforcing member;

providing the toothed rail with a pair of fittings on each end;

providing a pair of end walls with cooperating pairs of openings for attachment of a plurality of toothed rails;

securing the toothed rail by using a threaded portion on each end of the toothed rail and a cooperating threaded connector for securing each end of the toothed rail to a respective opening in the pair of end walls.

9. The method of claim 8 wherein the pair of fittings are positioned at each end of the rigid elongate reinforcing member before the sleeve is overmolded onto the reinforcing member and further comprising selecting the material of the fitting to cooperate with the material of the toothed sleeve such that the juncture between the pair of fittings and the overmolded toothed sleeve is imperviously bonded.

10. The method of claim 8 wherein the cooperating threaded connector is one of a threaded screw and a nut.

11. The method of claim 8 further comprising selecting PVDF as the material for the overmolded sleeve.

12. The method of claim 8 further comprising selecting PVDF as the material for fittings.

13. The method of claim 8 further comprising the encapsulating the rigid elongate reinforcing member with PVDF by way of the overmolding process.

14. A rigidized process carrier comprising:

a pair of endwalls, each endwall having a plurality of receiving openings extending through a thickness of the respective endwalls, the receiving openings of one endwall corresponding to the receiving openings of the other endwall; and,

a plurality of toothed rails, each toothed rail comprising a rigid reinforcing member encapsulated by a fluoropolymer and attachable and detachable to the endwalls at the receiving openings by threaded connectors, whereby when attached to the endplates the toothed rails support a plurality of axially aligned substrates for processing in baths.

15. The rigidized process carrier of claim 14 wherein each toothed rail further comprises threaded portions that cooperate with the threaded connectors to connect each toothed rail to the end plates.

16. The rigidized process carrier of claim 14 wherein each toothed rail has a male threaded portion that extends through the respective receiving openings and is secured to the respective endwalls by threaded nuts.

17. The rigidized process carrier of claim 14 wherein one of the toothed rails has a nut with a finger graspable plate handle extending and wherein said one of the toothed rails is manually rotatable by way of said finger graspable handle.

18. The rigidized process carrier of claim 14 wherein each toothed rail has a sleeve that is melt bonded to a pair of fittings with threaded portions positioned at each end of the rigid reinforcing member.

19. The rigidized process carrier of claim 14 further comprising a plurality of O-rings positioned between the pair of endwalls and a plurality of the toothed rails.

20. The rigidized process carrier of claim 14 wherein an uppermost rail is receivable in a pair of slots extending downwardly, one from each of the top edges of the two endwalls whereby the uppermost rail may be removed for insertion and removal of bathes of substrates and may be secured in place for retaining substrates during bath processing.

21. The rigidized process carrier of claim 14 wherein the uppermost rail is toothed and may be rotated from an substrate engagement position to a non-engagement position.

22. The rigidized process carrier of claim 21 wherein the uppermost rail has a pair of eccentric shaft portions that cooperate with cooperating slot portions in each of the pair of slots whereby when the teeth are in the substrate engagement position the uppermost rail is secured within the cooperating slot portions.

23. The process carrier of any of the above claims 14 through 22 in combination with a batch of substrates.

24. The process carrier of claim 23 wherein the substrates are solar cell substrates.

25. The process carrier of any of the above claims 14 through 22 wherein each of the toothed rails has an encapsulation comprising polyvinylidene fluoride.

26. The process carrier of claim 25 wherein the encapsulation comprises at least one of carbon powder, carbon nanotubes, and carbon fibers.

27. A method of processing solar cell substrates comprising:

inserting a batch of solar substrates into a substrate carrier having a plurality of toothed rails fixed to a pair of endwalls;

inserting an uppermost toothed rail into a pair of receiving openings at top portions of the endwalls;

positioning the uppermost toothed rail securing the uppermost toothed rail to an engagement position wherein teeth of the toothed rail are positioned intermediate pairs of solar cell substrates of the batch of solar cell substrates;

securing the uppermost toothed rail into said engagement position; and

lowering substrate carrier with the batch therein into a process bath.

28. The method of processing solar cell substrates of claim 27 further comprising securing the uppermost rail into said engagement position by rotating said uppermost rail such that an eccentric portion of a shaft portion of the rail is secured into a cooperating slot portion.

29. The method of claim 27 or 28 further comprising securing each of the plurality of fixed rails to the endwalls utilizing threaded connectors.

30. A solar cell substrate carrier comprising:

four toothed rails attached to a pair of endwalls, the four toothed rails defining a axially aligned set of slots for receiving a batch of solar cell substrates;

a uppermost toothed rail manually securable on and removable from the pair of endwalls for each batch, the uppermost toothed rail when secured on the pair of endwalls positioned to retain the batch of solar substrates within the aligned set of slots.

31. The solar cell substrate carrier of claim 30 wherein the uppermost toothed rail comprises an eccentric portion that cooperates with a cooperating slot portion on one of the endwalls that allows insertion of the uppermost toothed rail into the slot and securement therein by way of rotation of the uppermost toothed rail within the cooperating slot portion.

32. The solar cell substrate carrier of claim 30 or 31 wherein each toothed rail has a central and axially extending rigid reinforcing member that is encapsulated by a fluoropolymer.

33. The solar cell substrate carrier of claim 30 or 31 wherein the four toothed rails defining the axially aligned set of slots each have threaded portions and each of the four toothed rails are secured to the endwalls with cooperating threaded fasteners each threaded fastener comprising a fluoropolymer.

34. The solar cell substrate carrier of claim 30 or 31 wherein the four toothed rails defining the axially aligned set of slots each have a pair of fluoropolymer threaded fittings thereon and said four toothed rails are attached to the endwalls utilizing the fittings with cooperating fittings.

35. The solar cell substrate carrier of claim 30 or 31 comprising an additional two toothed rails attached to the endwalls.