WO2010011200A1

WO2010011200A1 - Edge coating apparatus and methods for non-circular solar cell substrates

Info

Publication number: WO2010011200A1
Application number: PCT/US2008/008863
Authority: WO
Inventors: Neil Kaminar; Michael J. Cudzinovic; Enrique Garcia; Emmanuel Abas; Luca Pavani
Original assignee: Sunpower Corporation
Priority date: 2008-07-21
Filing date: 2008-07-21
Publication date: 2010-01-28
Also published as: AU2008359693A1; JP2011528618A; DE112008003942T5; KR101555081B1; JP5329664B2; KR20110043690A

Abstract

An edge coating apparatus (300) is configured to apply a coating material to an edge of a non-circular solar cell substrate (371). The substrate (371) is placed on a rotatable substrate support in the form of a chuck (303) configured to hold and rotate the substrate (371). A coating material dispenser (308) includes an applicator in the form of a roller (309) having a recessed portion in the form of a groove (310). During the edge coating process, the roller (309) is positioned such that the edge of the substrate (371) is received in the groove (310). Knurled surface of the roller (309) contacts the edge of the substrate (371) to apply the coating material to the edge of the substrate (371). A motor (307) rotates the chuck (303) by way of a transmission belt (306) and a shaft (305-1, 305-2) to rotate the substrate (371) for edge coating.

Description

EDGE COATING APPARATUS AND METHODS FOR NON-CIRCULAR

SOLAR CELL SUBSTRATES

Inventors: Neil Kaminar, Michael Cudzinovic, Enrique Garcia, Emmanuel Abas, and Luca Pavani

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to solar cells, and more particularly but not exclusively to solar cell fabrication processes and tools.

2. Description of the Background Art

Solar cells are well known devices for converting solar radiation to electrical energy. They may be fabricated on a semiconductor wafer using semiconductor processing technology. A solar cell includes P-type and N-type diffusion regions. Solar radiation impinging on the solar cell creates electrons and holes that migrate to the diffusion regions, thereby creating voltage differentials between the diffusion regions. In a backside contact solar cell, both the diffusion regions and the metal contact fingers coupled to them are on the backside of the solar cell. The contact fingers allow an external electrical circuit to be coupled to and be powered by the solar cell.

An edge of a solar cell substrate may be coated with a dielectric for electrical isolation and to prevent metal deposition or growth on the substrate perimeter. The present disclosure pertains to apparatus and methods for edge coating of solar cell substrates suitable for mass production.

SUMMARY An edge coating apparatus is configured to apply a coating material to an edge of a non-circular solar cell substrate. The substrate is placed on a rotatable substrate support in the form of a chuck configured to hold and rotate the substrate. A coating material dispenser includes an applicator in the form of a roller having a recessed portion in the form of a groove. During the edge coating process, the roller is positioned such that the edge of the substrate is received in the groove. Knurled surface of the roller contacts the edge of the substrate to apply the coating material to the edge of the substrate. A motor rotates the chuck by way of a transmission belt and a shaft to rotate the substrate for edge coating.

These and other features of the present invention will be readily apparent to persons of ordinary skill in the art upon reading the entirety of this disclosure, which includes the accompanying drawings and claims.

DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically show a plan view and a side view, respectively, of an edge coating tool in accordance with an embodiment of the present invention. FIG. 2A shows a schematic diagram of an edge coating tool in accordance with another embodiment of the present invention.

FIG. 2B shows a non-circular substrate received in a groove of a roller in the edge coating tool of FIG. 2A. FIG. 3, which comprises FIGS. 3A, 3B, and 3C, shows an edge coating tool for coating an edge of a solar cell substrate in accordance with an embodiment of the present invention.

FIGS. 4A and 4B show a side view and a side cross-sectional view, respectively, of a coating material dispenser in accordance with an embodiment of the present invention.

FIG. 5 shows an exploded view of the coating material dispenser of FIGS. 4A and 4B.

FIGS. 6A and 6B schematically show the principle of operation of a main cylinder for a coating material dispenser in accordance with an embodiment of the present invention.

FIGS. 7A, 7B₁ 7C, and 7D show features of the coating material dispenser of FIG. 5 for controlling the coating width and thickness uniformity of coating material applied on a substrate edge, in accordance with an embodiment of the present invention. The use of the same reference label in different drawings indicates the same or like components. DETAILED DESCRIPTION

In the present disclosure, numerous specific details are provided, such as examples of apparatus, components, and methods, to provide a thorough understanding of embodiments of the invention. Persons of ordinary skill in the art will recognize, however, that the invention can be practiced without one or more of the specific details. In other instances, well-known details are not shown or described to avoid obscuring aspects of the invention.

FIGS. 1A and 1 B schematically show a plan view and a side view, respectively, of an edge coating tool 100 in accordance with an embodiment of the present invention. In the example of FIGS. 1A and 1 B, the edge coating tool 100 includes a coating material dispenser 110 for applying a coating material on an edge of a non-circular solar cell substrate 101 , which may comprise a semiconductor substrate, held by a rotatable vacuum chuck 102 (FIG. 1B). The dispenser 110 includes a barrel 113 with an ink plunger 114 and a roller 112. The barrel 113 pivots on a spring loaded fulcrum 111 so that it can keep applying pressure on the wafer edges. A production operator manually guides the dispenser 110 to avoid hard collisions with the substrate 101 and manually activates the plunger 114 to deliver ink to the roller 112, which applies the ink to coat an edge of the substrate 101. The substrate 101 is rotated on the chuck 102 to have the entire perimeter edge of the substrate 101 coated with the coatirig material. While the tool

100 is satisfactory, it has several disadvantages including primarily manual operation and inadequate control of application of coating material to the substrate edge.

FIG. 2A shows a schematic diagram of an edge coating tool 200 for coating an edge of a solar cell substrate in accordance with an embodiment of the present invention. In the example of FIG. 2A, the edge coating tool 200 includes a coating material dispenser 308 with an applicator in the form of a roller 309. The roller 309 has a recessed portion in the form of a groove 310, as shown in the side view of the roller 309 in FIG. 2B. FIG. 2B also shows a non-circular substrate 371 received in the groove 310 during the edge coating process and a nozzle 311 for flowing coating material onto the groove 310 for application on the edge of the substrate 371. The substrate 371 may comprise a semiconductor wafer with a pseudo- square shape, for example.

Referring back to FIG. 2A, a coating material supply system 150 includes a cartridge 153 containing the coating material, which may comprise thermal or UV ink. In operation, the plunger 151 is adjusted to force the coating material from the chamber 154 of the cartridge 153 to the nozzle 311 by way of the supply tube 152. From the nozzle 311 , the coating material flows to the groove 310 for application to the edge of the substrate 371 received in the groove 310 (see FIG. 2B). The groove 310 is pushed against the edge of the substrate 371 to receive the edge and apply the coating material thereon. The tool 200 is a "contact" edge coater in that the roller 309 physically contacts the substrate 371 to apply coating material to the edge of the substrate 371. The substrate 371 is on a rotatable substrate support in the form of a chuck 303, which may hold the substrate 371 by vacuum force. The substrate 371 rotates with the chuck 303 to have the coating material applied on the entire perimeter edge of the substrate 371.

FIG. 3, which comprises FIGS. 3A, 3B, and 3C, shows an edge coating tool 300 for coating an edge of a solar cell substrate in accordance with an embodiment of the present invention. The tool 300 is a particular embodiment of the tool 200.

FIG. 3A shows a perspective view of the edge coating tool 300. The tool 300 is configured to receive and apply a coating material on an edge of the non-circular solar cell substrate 371. The tool 300 may include the coating material dispenser 308 with an applicator in the form of the roller 309. As in the tool 200, the roller 309 includes a recessed portion in the form of the groove 310 for receiving and coating the edge of the substrate 371 (see FIG. 2B). A substrate support in the form of the rotatable chuck 303 supports the substrate 371. A vacuum system 304 directly underneath the chuck 303 allows for holding of the substrate 371 by vacuum force.

The substrate 371 may be placed manually or by using an automated handling system (e.g., pick and place robot) on a pre-aligner station 301 , which provides a stop for positioning and aligning the substrate 371 over the chuck 303. A pneumatic slide 302 is configured to lower and raise the station 301. In the raised position, the station 301 keeps the substrate 371 above the chuck 303. The slide 302 may be actuated to lower the station 301 such that the substrate 371 is resting on and supported by the chuck 303 (see FIG. 3B). A shaft 305 (i.e., 305-1 and 305- 2) is concentric with and mechanically coupled to the chuck 303. A transmission belt 306 mechanically couples the shaft 305 to a motor 307.

FIG. 3B shows a perspective view of the tool 300 with the substrate 371 lowered onto the chuck 303. In FIG. 3B, a pneumatic main cylinder 314 (see FIG. 5) is actuated to move the dispenser 308 in coating position towards the substrate 371 once the substrate 371 is positioned on the chuck 303. The motor 307 drives the shaft 305 by way of the transmission belt 306 to rotate the chuck 303 and thus the substrate 371. The groove 310 receives and contacts the edge of the substrate 371 to apply the coating material thereon. FIG. 3C shows an exploded view of the tool 300. The components shown in

FIG. 3C have been previously described with reference to FIGS. 3A and 3B.

FIGS. 4A and 4B show a side view and a side cross-sectional view, respectively, of the coating material dispenser 308 in accordance with an embodiment of the present invention. A coating material supply system 150 provides the coating material (e.g., thermal ink, or UV ink) to the dispenser 308 by way of the supply tube 152, which is fitted to an inlet 403 of the nozzle 311. The groove 310 may be machined on the surface of the roller 309 to have a specific depth and width for the type of coating material and the substrate to be coated. When coating material is pushed on one side of the roller 309 surface by means of the nozzle 311 , the groove 310 gets completely filled with ink material. A doctor blade (not shown) positioned closely to the roller surface removes excess coating material, leaving the coating material only in the depth of the groove 310. The dispenser 308 includes a tray 312 for collecting excess coating material scraped with the doctor blade. The substrate 371 is positioned on the opposite side of the roller 309 (see FIG. 2B)₁ with the edge of the substrate within the groove 310 touching the surface of the roller 309. Once the substrate 371 spins around the axis of the chuck 303 (see FIG. 3B), the substrate 371 will collect ink on its perimeter edge. A slider mechanism 313 allows the dispenser 308 to be moved towards and away from the substrate 371 along a single axis.

FIG. 5 shows an exploded view of the coating material dispenser 308 in accordance with an embodiment of the present invention. As mentioned, the dispenser 308 is mounted on the slider mechanism 313. The pneumatic main cylinder 314 pushes the dispenser 308 in coating position towards the edge of the substrate 371. To slow down and control the impact force of the roller 309 on edge of the substrate 371 , an auxiliary cylinder may be used to apply an opposite force to the cylinder 314. Also shown in FIG. 5 are the doctor blade 401 and the tray 312. The dispenser 308 is positioned back to its starting position away from the substrate 371 at the end of the edge coating process. Other components shown in FIG. 5 have been previously discussed with reference to FIGS. 4A and 4B.

FIGS. 6A and 6B schematically show the principle of operation of the main cylinder 314 in accordance with an embodiment of the present invention. The cylinder 314 includes a chamber 451 and a portion 452. In the example of FIGS.

6A and 6B, the main cylinder 314 is configured to keep the pressure P1 and thus the force applied to the substrate 371 by the roller 309 relatively constant independent of the profile of the substrate 371. A pressure PO equal to the load pressure P_LOAD is applied to the chamber 451 using an air supply system that includes a small vent 453 with an air leak with corresponding leak pressure P_LE_AK- Because of the air leak, the total pressure applied in the pressurized chamber 451 of the cylinder 341 is PI=PO- P_LEAK- The portion 452 on the other side of the chamber 451 is at atmospheric pressure. Accordingly, no pressure or resistance is applied in the portion 452. The piston 454 is mechanically coupled to the slider mechanism 313 supporting the dispenser 308 (see FIG. 5). When the roller 309 is in contact with the flat edge of the substrate 371 , the cylinder 314 applies an active force on the dispenser 308 pushing the roller 309 towards the edge of the substrate 371. When the roller 309 is in contact with the corner edge of the substrate 371 , the dispenser 308 is pushed out and the cylinder 314 is pressed by a force directly coming from the edge of the substrate 371 as illustrate in FIG. 6B. In the case of FIG. 6B, the air volume in chamber 452 bottom chamber decreases, making pressure P/ tend to increase. At this point some air starts flowing out from the vent 453, keeping the pressure P1 relatively constant.

FIGS. 7A, 7B, 7C, and 7D show features of the coating material dispenser 308 for controlling the coating width and thickness uniformity of coating material applied on the substrate edge, in accordance with an embodiment of the present invention. Generally speaking, there are two major factors that control the coating uniformity: the rotational speed of the substrate and the amount of coating material transferred from the grove 310 to the substrate edge. To control the rotational speed of the substrate, the speed of the motor 307 rotating the chuck 303 (see FIG. 3B) is controlled and small knurls 315 are machined in the groove 310. FIG. 7A shows the knurls 315 on the surface ("contact surface") of the roller 309 contacting the substrate edge during edge coating. The knurls 315 prevent the substrate edge from sliding with respect to the contact surface, increasing the friction at the interface between the contact surface and the substrate in the groove 310.

The width (see 502) and depth (see 501) of the groove 310 and the position of the groove 310 with respect to the substrate edge control the amount of coating material applied on the edge of the substrate.

By adjusting the position of the roller 309 relative to the substrate, the position of the groove 310 relative to the upper surface of the substrate may be adjusted. In FIG. 7C, the roller 309 is raised to a height H1 (e.g., 32mm) relative to the slider mechanism 313 to position the groove 310 such that the substrate 371 is on the bottom portion of the groove 310. In FIG. 7D, the roller 309 is lowered to a height H2 (e.g., 28.5 mm) relative to the slider mechanism 313 to position the groove 310 such that the substrate 371 is on the upper portion of the groove 310. The roller 309 may be continuously adjusted such that the substrate 371 is between the upper and lower portions of the groove 310. Doing so controls the coating material compression between the upper surface of the substrate 371 and the wall of the groove 310 and thus the width of the coating material on the edge of the substrate 371. The more the coating material is squeezed, the more will overflow out of the groove 310.

As can be appreciated, the aforementioned components of the edge coating tool 300 are particularly suited for automated control. For example, a computer (not shown) with appropriate control software and data acquisition system may control the speed and direction of motor components and actuate pneumatic components.

While specific embodiments of the present invention have been provided, it is to be understood that these embodiments are for illustration purposes and not limiting. Many additional embodiments will be apparent to persons of ordinary skill in the art reading this disclosure.

Claims

CLAIMSWhat is claimed is:

1. An apparatus for coating an edge of a non-circular solar cell substrate, the apparatus comprising:

an applicator having a recessed portion for accepting an edge of a non- circular solar cell substrate, the applicator being configured to be pushed against the edge of the substrate in the recessed portion to apply a coating material on the edge of the substrate; a substrate support configured to support and rotate the substrate; and a slider mechanism configured to support the applicator and move the applicator relative to the substrate.

2. The apparatus of claim 1 wherein the applicator comprises a roller and the recessed portion comprises a groove in the roller.

3. The apparatus of claim 2 wherein the applicator includes a knurled surface in the groove, the knurled surface being configured to increase friction between the edge of the substrate and the roller.

4. The apparatus of claim 1 wherein the slider mechanism is pneumatically driven to move the applicator along a single axis.

5. The apparatus of claim 1 further comprising a pre-aligner station configured to receive the substrate, to lower the substrate onto the substrate support to coat the edge of the substrate with the coating material, and to raise the substrate from the substrate support after the edge of the substrate has been coated with the coating material.

6. The apparatus of claim 1 wherein the substrate support comprises a chuck that holds the substrate by vacuum force.

7. The apparatus of claim 1 wherein the applicator is configured to be raised and lowered relative to the substrate while the substrate is in the recessed portion to control an amount of the coating material applied on the edge of the substrate.

8. The apparatus of claim 1 further comprising a motor configured to rotate the substrate support by means of a transmission belt coupled to a shaft coupled to the substrate support.

9. The apparatus of claim 1 wherein the substrate comprises a semiconductor wafer.

10. A method of coating an edge of a non-circular solar cell substrate, the method comprising: positioning an applicator to receive a non-circular solar cell substrate in a recessed portion of the applicator;

providing a coating material to the applicator;

rotating the substrate, and applying the coating material to an edge of the substrate while the substrate is rotating and in the recessed portion of the applicator.

11. The method of claim 10 wherein the applicator comprises a roller and the recessed portion comprises a groove in the roller.

12. The method of claim 10 further comprising: placing the substrate on a pre-aligner station;

lowering the pre-aligner station to lower the substrate onto a rotatable substrate support where the substrate is rotated to apply the coating material to the edge of the substrate; and raising the pre-aligner station to raise the substrate from the substrate support after the coating material is applied to the edge of the substrate.

13. The method of claim 10 wherein the substrate comprises a semiconductor wafer.

14. The method of claim 10 wherein the substrate is rotated on a substrate support holding the substrate by vacuum force.

15. The method of claim 10 further comprising:

raising and lowering the applicator relative to the substrate to control an amount of the coating material applied to the edge of the substrate.