WO2012178180A2

WO2012178180A2 - Solar cell process carrier

Info

Publication number: WO2012178180A2
Application number: PCT/US2012/044046
Authority: WO
Inventors: Mark V. Smith; Scott Harder
Original assignee: Entegris, Inc.
Priority date: 2011-06-23
Filing date: 2012-06-25
Publication date: 2012-12-27
Also published as: TW201320222A; WO2012178180A3

Abstract

A process carrier for solar cells includes a pair of parallel spaced apart endwalls with a plurality of cell. Each cell support includes a rail with a plurality of teeth extending outwardly therefrom defining slots for receiving solar cells. Each adjacent pair of teeth on a rail, along with corresponding pairs of teeth on each of the other rails, define a slot. Means for shifting each solar cell can be provided to shift the solar cells in the slots so that they are predominantly towards one side of the slots or are shifted in the slots or are otherwise in a more constrained position. This can create a larger open region for flow of processing fluid on one side of each portion of the solar cell that is within a slot at a particular rod. Fluid flow non-uniformities therefore can be controlled to occur only on one side of each portion within the slot, which reduces the amount of boat marks occurring on the solar cell and can position the remaining boat marks at more preferable locations, for example on a nonactive side of the cell.

Description

SOLAR CELL PROCESS CARRIER

RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/500,529, filed on June 23, 201 1 , the disclosure of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

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

BACKGROUND OF THE INVENTION

As a part of processing of silicon wafers into semiconductors, the wafers are immersed into various solutions in carriers often known as boats. See prior art Figure 1 a, for example, from U.S. Patent No. 4,872,554 originally assigned to Fluoroware, Inc. a corporate 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 welding the tubular polymer rail pieces of the carrier to the endwalls.

The specific processing of solar cells, also known as photovoltaic cells, conventionally utilizes such carriers or boats. The substrate carriers, including solar cell process carriers, have contact areas on the teeth positioned on the rails for supporting and restraining the substrates. The minimization of these contact areas is believed to be beneficial. There are a number of ways in which these contact areas can lead to nonuniformities in fluid action at these areas. The process fluids can attach to the carrier at these areas where the carrier interfaces with the cells after the carrier and substrates are removed from the fluids, extending the contact time of the fluids with the substrates at these areas causing a nonuniformity in fluid action at these areas. In addition, when the carrier and substrates are immersed, the contact areas may also reduce the fluid flow at the substrate surfaces at the contact areas causing further nonuniformities in the processing. Further, the close proximity of the support rails to the teeth can cause fluid flow disruptions and interference at the edges of the substrates, particularly cells, which can affect further nonuniformities in the fluid processing. These nonuniformities can result in processing defects which are often visible along the edges of the solar cells and are termed "boat marks." The teeth on each supporting rail have the same pitch, that is, they are in alignment with corresponding teeth on the other rails. Conventionally the teeth are uniformly shaped amongst all the rails and are symmetrical with respect to each side of each tooth, each side of each tooth defining a portion of a slot for the solar cells. Conventionally, the contact areas, the spacing between the corresponding adjacent tooth pairs are uniform around the solar cell, which results in both sides of the solar cells incurring boat marks at each supporting rod. It is most desirable to reduce the possibility of etching defects such as boat marks, by way of carrier design while complying with informal industry standardizations, particularly the rail positions.

SUMMARY OF THE INVENTION A process carrier for solar cells includes a pair of parallel spaced apart endwalls with a plurality of cell supports configured as rods extending therebetween. Each cell support includes a rail with a plurality of teeth extending outwardly therefrom defining slots for receiving solar cells. Each adjacent pair of teeth on a rod, along with corresponding pairs of teeth on each of the other rods, define a slot. Means for shifting each solar cell can be provided to shift the solar cells in the slots so that they are predominantly towards one side of the slots or are tilted or shifted in the slots or are otherwise in a more constrained position. This can create a larger open region for flow of processing fluid on one side of each portion of the solar cell that is within a slot at a particular rod. Fluid flow non-uniformities therefore can be controlled to occur only on one side of each portion within the slot, which reduces the amount of boat marks occurring on the solar cell and can position the remaining boat marks at more preferable locations, for example on a nonactive side of the cell.

In an embodiment of the invention, the teeth are non-symmetrical such that for each slot at each rod, the confronting relationship between the teeth and opposite sides of each of the solar cells is different, thus providing different process fluid flow characteristics on each side proximate to the rod. A feature and advantage of embodiments of the present invention is a top support rod having a pitch or alignment different than that of the bottom and side support rods. The teeth of the top support rod are therefore offset from the teeth of the other support rods, which results in the solar cells being shifted to one side of the slots. This leads to minimal boat marks on one side of the solar cells.

A feature and advantage of embodiments of the present invention is a top support rod that shifts the top edge of the substrates in a process boat whilst the lower opposite edge of the substrates remains seated.

Another feature and advantage of embodiments of the present invention is support rods having non-uniform teeth, such as a first side of each tooth having a larger angle than the other, including multiple angles or a curved profile, and a second side of each tooth being generally vertical. This serves to shift the alignment of the cells to one side of the slots so there is a larger region for fluid flow on one side of the solar cell, resulting in minimal boat marks on that side.

A further feature and advantage of embodiments of the present invention is a top support rod having a helical cam on an end portion of the support rod that is inserted into the endwalls of the carrier. When the top support rod is inserted into the carrier, it can rotated along the helical cam, which causes the teeth of the top support rod to be offset from the teeth of the other support rods. This causes the solar cells to be shifted or tilted to one side of the respective slots, so that minimal boat marks are formed on one side of the solar cells at particular locations.

Another feature and advantage of embodiments of the present invention is a top support rod having teeth that are rotatable at an angle relative to an end portion of the support rod or an end portion and a rail of the support rod. Rotation of the teeth causes the teeth of the top support rod to be offset from the teeth of the other support rods, thereby shifting the cell to one side of the slots. Minimal boat marks are therefore formed on one side of the solar cell.

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.

Figure 3 is a schematic representation of a solar cell process carrier supporting a solar cell according to an embodiment of the present invention.

Figure 4a is a partial view of a solar cell support rod according to an embodiment of the present invention.

Figure 4b is a partial view of the solar cell support rod of Figure 4a.

Figure 4c is a partial view of a solar cell support rod according to an embodiment of the present invention.

Figure 4d is a partial view of the solar cell support rod of Figure 4a.

Figure 4e is a partial view of a solar cell support rod according to an embodiment of the present invention.

Figure 4f is a partial view of the solar cell support rod of Figure 4a.

Figure 5 a is a partial view of a solar cell support rod according to an embodiment of the present invention.

Figure 5b is a partial view of the solar cell support rod of Figure 5a.

Figure 6a is a side view of a solar cell support rod according to an embodiment of the present invention.

Figure 6b is an opposite side view of the solar cell support rod of Figure 6a.

Figure 6c is an cross sectional view of the solar cell support rod of Figure 6b taken at line 6c-6c.

Figure 7a is a schematic sectional taken at line 7-7 of Figure 2.

Figure 7b is a schematic sectional of Figure 7a with a wafer shift imparted to the wafer by movement of the upper slot. Figure 8 is a perspective view illustrating a handle for rotating toothed rails and a neck that inserts into an endwall according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 2 depicts a process carrier 100 for holding substrates, particularly solar cell substrates 102, during a process bath processing the substrates. Generally, solar cells will be inserted and withdrawn when the carrier is in a vertical position with cells horizontal. When immersed in process fluid, the carrier is in a horizontal position as generally shown in Figure 2.

Process carrier 100 includes a pair of parallel spaced apart endwalls 104 with a plurality of cell supports configured as rails, more particularly rods, extending therebetween. Substrate support rods include bottom support rails or rods 106 on a bottom side of the process carrier 100 (relative to the horizontal position of the carrier during processing), side support rails configured as rails or rods 108 on each side of the carrier 100 and a top support rail configured as a rod 1 10 on a top side of the carrier 100. Endwalls 104 can include a plurality of receiving apertures 1 12 for receiving and aligning the substrate support rods. Each substrate support rail or rod is defined by a rail or rod 1 13 with a plurality of spaced teeth 1 14 defining slots for holding cells or substrates 102.

Figure 3 depicts a top support rod 1 10 and a bottom support rod 106 supporting a solar cell substrate 102. Teeth 1 14 can extend axially along each support rod. Solar cell substrates 102 can be inserted into process carrier into slots 122 defined between the spaced teeth 1 14 of the cell support rods so that they rest on contact surfaces 1 16 of teeth. Substrates 102 can be stacked in an axially spaced relationship defined by teeth 1 14. 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. Also see PCT US2012/042749 and Provisional Application 61/497,371 as illustrating a related invention, including rotatable support rails; said applications incorporated by reference herein and illustrates suitable attachment means of the rails to the endwalls.

Referring again to Figure 3, it can be seen that top support rod 106 and its associated teeth 1 14 can have an off-set pitch from the teeth 114 of the bottom support rods 1 10. Although not pictured, side support rods 108 can have the same pitch as bottom support rods 1 10. This shifts each end of the solar cell substrates 12 towards one side of its respective slot 122 and can create a cant or tilt of the solar cell substrate 102. Alternatively, the solar cell substrate 102 may extend generally vertically and horizontally between support rods. This creates a closer contact between the solar cell substrate 102 and tooth 1 14 in a region 1 18 on one side of the solar cell substrate 102 and a larger, more open region 120 between the tooth 1 14 and solar cell substrate 102 on the other side of the solar cell 102. This results in a relatively large non-uniformity in fluid flow around region 1 18, but provides a minimal non-uniformity around region 120. As such, a boat mark is created on only one side of the solar cell substrate 102 at each of the support rods.

Figures 4a-4f depict various embodiments of the present invention that shift the solar cell substrate 102 alignment within the slots 122 by virtue of the tooth 1 14 design, rather than the pitch of the support rods. Figures 4a and 4b show an embodiment where the teeth 1 14 have different angles on a first side 124 and a second side 126 of the teeth 1 14. This creates a larger region 120 between the solar cell substrate 102 and the first side 124 and a smaller region 1 18 between the solar cell substrate 102 and the second side 126, resulting in the same effect described above wherein the non-uniformity and associated boat mark are minimized on the side adjacent the larger region 120. Figures 4c and 4d depict a further embodiment wherein the larger region 120 for providing minimal boat marks is provided by a first side 124 of a tooth 114 having multiple angles relative to a generally vertical second side 124 that creates a smaller region 1 18. A further embodiment that creates a larger region 120 with a first side 124 of a tooth 1 14 having a curved profile and a smaller region 1 18 with a generally vertical second side 126 is depicted in Figures 4e and 4f. In one embodiment, the teeth 1 14 in each of the bottom support rods 106, side support rods 108 and top support rod 1 10 can have the same tooth profile. In another embodiment, only the teeth 1 14 in the top support 106 have a non- uniform configuration.

Referring now to Figures 5a and 5b, another embodiment of the present invention shifts the alignment of the solar cells with a moveable, in this case rotatable, top support rod or rail 1 10. In one embodiment, support rod 1 10 can use standard symmetrical teeth 1 14. Support rod 1 10 can include a helical cam 132 on one or both end portions 130 of support rod 1 10. When the support rod 1 10 is inserted into receiving apertures 1 12 of the endwalls 104, as shown in Figure 2, it can be rotated within the aperture 1 12 via the cam 132 to offset the alignment of the teeth 1 14 of the support rod 1 10 relative to the other support rods. This allows for the solar cell substrates inserted into the carrier to be shifted to one side of the slots to provide for minimal non-uniformity in fluid flow and resulting boat marks on one side of each solar cell at the support rod as described above.

Figures 6a-6c depict a top support rail or rod 1 10 that can be used with a carrier according to another embodiment of the present invention. Teeth 114 of support rod 110 can be rotated at an angle 134 in order to be offset from the teeth of the other support rods to shift the solar cells so that they are positioned towards one side of the slots 122. In one embodiment, rail or rod 1 13 is rotated with teeth 1 14 relative to end portions 130 of support rod 1 10 that are inserted into receiving apertures 1 12 of endwalls 104 of carrier 100. In another embodiment, only teeth 1 14 are rotated and they rotate relative to both rail or rod 1 13 and end portions 130. Reinforcing member 131 can provide enhanced rigidity to the rail and can provide a base for when the outer sleeve 133 with teeth rotate in particular embodiments without the entire rail rotating.

Referring to Figures 7a and 7b, the individual bar slots 140 defining the overall slot 144 are illustrated before and after a shift at the upper most bar slot 146. The dashed lines of Figure 7b represent the original position of the teeth and bar slot before the shift, the intermediate bar teeth 150 schematically shown as arcs. The right side tooth 156 of the intermediate upper rod is in very close confronting engagement, and perhaps contact with the cell. The lower intermediate right side bar tooth 160 is not as close in confronting the cell. The cell is positioned at the left side of the upper rod tooth. In this arrangement, a boat mark would be expected at the right side edge but not the left side edge of the cell for the upper intermediate bar. Also a boat mark might be expected at the upper left side of the upper slot.

Figure 8 depicts an uppermost toothed rail 1 10 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 1 10 has a shaft portion 182 and an eccentric or cammed shaft portion or neck 184, a flange 185, and a handle shaped as a key 186. End cap 180 can be overmolded with sleeve 193 of toothed rail 106 at end projection 182. In one embodiment, toothed rail 1 10 includes a stainless steel or other metal shaft 131 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 187 that includes a cooperating slot portion 109 extending from an interior side 188 of the endwall 104 to the exterior side 189. To connect toothed rail 106 with endwall 104, the neck 184 of the end cap 180 is first inserted through the slot 109 in the side 188 of the endwall and into the receiving aperture 108 as indicated in Figure 8. The rail is rotated such that the neck is oriented to be narrow as it confronts and is inserted into a narrowed portion 109 of the slot. When the neck seats in the slot, the key 186 is then rotated to secure the end cap 180 within the receiving aperture 108, the lower portion also being eccentrically shaped. This locks the toothed rail 1 10 into engagement with the endwall 104. As illustrated, the end cap 180 and sleeve 193 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 other embodiments, the sleeve with teeth may rotate on a nonrotating shaft. In embodiments both endwalls or one endwall may have the cooperating slot portion that engages with the eccentric shaft portion. In other embodiments, the rod may slide axially or substantially axially with respect to the endwalls in order to shift the substrates. For example the axial length of the neck 184 can be slightly longer than the thickness of the endwall.

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 cell substrates. 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 processing substrates and controlling processing marks produced on solar cell substrates during said processing, the method comprising;

insertion of a plurality of solar cell substrates into a substrate boat having a plurality of vertical slots defined by a plurality of toothed rails thereby providing an aligned array of solar cell substrates;

installing a toothed movable rail in the substrate boat with the teeth of said movable rail intermeshed within the aligned array of solar cell substrates,

shifting, by way of the intermeshed teeth of the top rail, all of the solar cell substrates in the array of solar cell substrates in a common direction in their respective slots; and

immersing the substrate boat with the shifted solar cells in a process bath.

2. The method of claim 1, wherein the shifting of all of the solar cell substrates in the array of solar cell substrates is effected by rotation of the moveable rail, the teeth urging each of the solar cell substrates in the common direction.

3. The method of any of the above claims, wherein the shifting of all of the solar cell substrates is effected by camming of the teeth, the teeth having a helically shaped cam surface.

4. The method of any of the above claims, wherein the shifting of all of the solar cell substrates is effected by axial movement of the moveable rail in the common direction.

5. The method of claim 4 wherein the axial movement is effected by engagement of a helical surface as part of an engagement between the moveable rail and an endwall supporting said top rail.

6. A substrate process carrier having a pair of endwalls supporting a plurality of toothed rails, the toothed rails defining a plurality of slots for holding an array of solar cell substrates, each slot of the at least one of the plurality of toothed rails having a first side and a second side, each side being defined by teeth projecting from the toothed rail, the teeth presenting confronting surfaces to the substrates in the slots, and wherein the teeth are configured such that the confronting surfaces are different on each of the first side and the second side of each slot.

7. The substrate process carrier of claim 6 wherein the slots are configured to provide a first position of each substrate in each slot when a plurality of substrates is loaded into the slots and at least one of the toothed rails is movable to impart a shift to each of the substrates in each slot to place each substrate in a second position, shifted from the first position.

8. The substrate process carrier of any of the above claims wherein each toothed rail has a rigid reinforcing member inserted therein.

9. A substrate process carrier having a pair of endwalls supporting a plurality of toothed rails, the toothed rails defining a plurality of slots for holding an array of solar cell substrates, the solar cell process carrier having means for minimizing processing marks caused by the toothed rails.

10. The substrate process carrier of any of the above claims wherein for at least one toothed rail having a plurality of slots, each slot having an apex and one side of the slot presenting a steeper side surface extending from the apex that the side surface of the other side.

1 1. The substrate process carrier of claim 9 wherein the means for minimizing processing marks comprises at least one of the set:

an axially moveable toothed rails for shifting the substrates in the slots;

a rotatable toothed rail with teeth that shift the substrates in the slots when the rotatable toothed rail is rotated;

a rotatable toothed rail with teeth having a helical cam surface to shift the substrates when the rotatable toothed rail is rotated; and

slots defined by tooth portions whereby each slot has a steep side surface extending to an apex and a less steep side surface extending to the apex.

12. A method of loading substrates into a carrier comprising:

shifting, by way of the intermeshed teeth of the top rail, of all of the solar cell substrates in the array of solar cell substrates in a common direction in their respective slots.

13. The method of claim 12 wherein the shifting of all of the solar cell substrates is effected by a rotation of the toothed moveable rail such that a helical cam surface imparts an axial movement to the toothed moveable rail.

14. The method of claim 12 wherein the shifting of all of the solar cell substrates is effected by a rotation of the toothed moveable rail such that a helical cam surface on each tooth urges a respective substrate toward the common direction.

15. A substrate process carrier having a pair of endwalls with a plurality of toothed rails nonmovably fixed thereto and at least one moveable toothed rail attached to said pair of endwalls, the toothed rails defining a plurality of slots for holding an array of solar cell substrates, the moveable toothed rail having teeth that shift the array of solar cell substrates in a common direction when the moveable toothed rail is moved.

16. The substrate process carrier of claim 15 wherein the moveable toothed rail is detachable from the endwalls allowing insertion and removal of substrates to and from the slots.

17. A substrate process carrier having a pair of endwalls with a plurality of rails nonmovably fixed thereto and at least one moveable rail attached to said pair of endwalls, the fixed rails defining a plurality of slots for holding an array of solar cell substrates, the moveable rail engageable with the array of solar cell substrates to shift the substrates in a common direction when the moveable rail is moved.

18. A substrate process carrier having a pair of endwalls with a plurality of rails nonmovably fixed thereto and at least one moveable rail attached to said pair of endwalls, the fixed rails defining a plurality of slots for holding an array of solar cell substrates, the moveable rail engageable with the array of solar cell substrates for moving the substrates between a first position and a second position.

19. The substrate process carrier of claim 17 or 18 wherein the moveable rail is rotatably attached to the pair of endwalls and has a plurality of helical surfaces that engage the substrates and shift the substrates in a common direction when the rail is rotated.

20. The substrate process carrier of claim 17 or 18 wherein the moveable rail is attachable and detachable to and from the endwalls and when attached to the endwalls the moveable rail engages and moves substrates that are in the slots in a common direction.

21. The substrate process carrier of claim 17 or 18 whereby the moveable rail comprises teeth moveable on a rail base, the teeth moveable to shift the substrates in the slots.

22. The substrate process carrier of claim 17 or 18 whereby the moveable rail comprises a shaft that rotates with respect to the endwalls to move teeth of the rail circumferentially with respect to the rail and the teeth having a surface that shifts upper edges of the substrates in a direction parallel to the axis of the rail whilst an opposite edge of the substrates do not move in the axial direction.

23. The substrate process carrier of claim 17 or 18 whereby the moveable rail comprises a shaft that moves axially with respect to the endwalls to move teeth of the rail and accordingly the substrates.