PROTECTION LAYER FOR FABRICATING A SOLAR CELL
A method for fabricating a solar cell is described. The method includes first providing, in a process chamber, a substrate having a light-receiving surface. An anti-reflective coating (ARC) layer is then formed, in the process chamber, above the light-receiving surface of the substrate. Finally, without removing the substrate from the process chamber, a protection layer is formed above the ARC layer.
This application is a continuation of U.S. patent application Ser. No. 12/106,561 entitled “PROTECTION LAYER FOR FABRICATING A SOLAR CELL” filed Apr. 21, 2008, which claims the benefit of U.S. Provisional Application No. 60/930,800, filed May 17, 2007, the entire contents of which are hereby incorporated by reference herein.
TECHNICAL FIELDEmbodiments of the present invention are in the field of Semiconductor Fabrication and, in particular, Solar Cell Fabrication.
BACKGROUNDPhotovoltaic cells, commonly known as solar cells, are well known devices for direct conversion of solar radiation into electrical energy. Generally, solar cells are fabricated on a semiconductor wafer or substrate using semiconductor processing techniques to form a p-n junction near a surface of the substrate. Solar radiation impinging on the surface of the substrate creates electron and hole pairs in the bulk of the substrate, which migrate to p-doped and n-doped regions in the substrate, thereby generating a voltage differential between the doped regions. The doped regions are coupled to metal contacts on the solar cell to direct an electrical current from the cell to an external circuit coupled thereto.
Typically, the surface of the solar cell to receive radiation is textured and/or coated with a layer or coating of an anti-reflective material to decrease the reflection of light, thereby increasing the efficiency of the solar cell. The fabrication of such solar cells, in particular the formation of the p-n junction and contacts thereto, involves a number of complicated process steps including the deposition, doping and etching of many different layers of material. These process steps are performed or carried out with low variation tolerances using many different processing tools under controlled environmental conditions.
Accordingly, there is a need for a simplified process for fabricating solar cells that reduces the number of separate steps needed, thereby reducing the time and cost of fabricating solar cells. It is further desirable that the method eliminates entirely the need for one or more processing tools, thereby further reducing the cost of fabricating solar cells.
Methods to fabricate a solar cell are described herein. In the following description, numerous specific details are set forth, such as specific dimensions, in order to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known processing steps, such as patterning steps, are not described in detail in order to not unnecessarily obscure the present invention. Furthermore, it is to be understood that the various embodiments shown in the Figures are illustrative representations and are not necessarily drawn to scale.
Disclosed herein is a method to fabricate a solar cell. A substrate having a light-receiving surface may be provided in a process chamber. In an embodiment, an anti-reflective coating (ARC) layer is then formed, in the process chamber, above the light-receiving surface of the substrate. Finally, without removing the substrate from the process chamber, a protection layer (also known as an etch mask) may then be formed above the ARC layer. In one embodiment, the protection layer comprises amorphous carbon. In another embodiment, the protection layer comprises amorphous silicon.
Formation of a protection layer on an ARC layer may enable preservation of the ARC layer during various process operations in the fabrication of a solar cell. For example, in accordance with an embodiment of the present invention, a protection layer is used to maintain the integrity of an ARC layer disposed on a solar cell substrate during exposure of the solar cell substrate to a buffered oxide etch (BOE). In order to reduce the number of processing steps required to fabricate a completed solar cell, the protection layer may be fabricated in the same process tool as the ARC layer. For example, in accordance with an embodiment of the present invention, an ARC layer is first formed on a solar cell substrate in a process chamber. Then, without removing the substrate from the process chamber, the protection layer is formed on the ARC layer.
A protection layer may be utilized in the fabrication of a solar cell.
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In accordance with an embodiment of the present invention, protection layer 230 is formed directly after the formation of, and in the same process chamber as, ARC layer 220. For example, in an embodiment, ARC layer 220 is first formed in the process chamber and then, without removing substrate 200 from the process chamber, protection layer 230 is formed on ARC layer 220. Thus, in an embodiment of the present invention, at least one complete process step is eliminated from an integration scheme for fabricating a solar cell. In one embodiment, ARC layer 220 and protection layer 230 are formed by the same technique such as, but not limited to, chemical vapor deposition, plasma-enhanced chemical vapor deposition, atmospheric-pressure chemical vapor deposition or physical vapor deposition. In a specific embodiment, ARC layer 220 and protection layer 230 are formed by first flowing, in a process chamber, at least a first process gas and a second process gas to form ARC layer 220 above light-receiving surface 202 of substrate 200. Then, without removing substrate 200 from the process chamber, at least the first process gas, but not the second process gas, is flowed to form protection layer 230 above ARC layer 220. In a particular embodiment, ARC layer 220 is composed of a material such as, but not limited to, silicon nitride, silicon oxy-nitride or carbon-doped silicon oxide, protection layer 230 is composed of amorphous silicon, the first process gas is silane (SiH4) and the second process gas is ammonia (NH3).
Following formation of protection layer 230, dielectric layer 208 may be patterned to form a plurality of contact openings to the plurality of active regions 206 at back surface 204 of substrate 200.
Thus, a method for fabricating a solar cell has been disclosed. In accordance with an embodiment of the present invention, a substrate having a light-receiving surface is provided in a process chamber. An ARC layer is then formed, in the process chamber, above the light-receiving surface of the substrate. Finally, without removing the substrate from the process chamber, a protection layer is formed above the ARC layer. In one embodiment, the protection layer comprises amorphous carbon. In another embodiment, the protection layer comprises amorphous silicon.
The advantages of the method for fabricating solar cells of the present invention over previous or conventional cells and methods may include: (i) substantial savings in the cost of fabricating solar cells through the elimination of the need for a dedicated tool to form a protection layer for an ARC layer, (ii) significant reduction in the time needed to fabricate solar cells through the combining of the ARC layer and protection layer deposition steps, and (iii) improved yield through the reduced handling of the substrate achieved through the deposition of the protection layer in the same process chamber used to form an ARC layer.
Claims
1. A method for fabricating a solar cell, comprising:
- providing, in a process chamber, a substrate having a light-receiving surface;
- forming, in the process chamber, an anti-reflective coating (ARC) layer above the light-receiving surface of the substrate; and
- depositing, in the process chamber, an etchant-resistive protection layer above the ARC layer.
2. The method of claim 1, wherein the etchant-resistive protection layer comprises amorphous carbon.
3. The method of claim 2, wherein the etchant-resistive protection layer is deposited by vapor deposition using a gas selected from the group consisting of methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4), propylene (C3H6), and liquid toluene (C7H8) transported by a carrier gas selected from the group consisting of argon (Ar), nitrogen (N2), helium (He) and hydrogen (H2).
4. The method of claim 1, wherein the etchant-resistive protection layer comprises amorphous silicon.
5. The method of claim 4, wherein the etchant-resistive protection layer is deposited by vapor deposition using silane (SiH4) gas.
6. The method of claim 1, wherein the etchant-resistive protection layer is deposited to a thickness approximately in the range of 1-30 nanometers.
7. The method of claim 1, wherein both the ARC layer and the etchant-resistive protection layer are formed by a technique selected from the group consisting of chemical vapor deposition, plasma-enhanced chemical vapor deposition, atmospheric-pressure chemical vapor deposition and physical vapor deposition.
8. The method of claim 1, wherein the etchant-resistive protection layer is resistant to a buffered oxide etch (BOE).
9. A method for fabricating a solar cell, comprising:
- providing a substrate having a light-receiving surface and a second surface with a plurality of active regions;
- forming, in a process chamber, an anti-reflective coating (ARC) layer above the light-receiving surface of the substrate; and
- depositing, in the process chamber, an etchant-resistive protection layer above the ARC layer;
- forming, using a buffered oxide etch (BOE), a plurality of contact openings to the plurality of active regions at the second surface of the substrate, wherein the etchant-resistive protection layer protects the ARC layer during the forming of the plurality of contact openings; and
- forming a plurality of contacts in the plurality of contact openings.
10. The method of claim 9, wherein the etchant-resistive protection layer comprises amorphous carbon.
11. The method of claim 10, wherein the etchant-resistive protection layer is deposited by vapor deposition using a gas selected from the group consisting of methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4), propylene (C3H6), and liquid toluene (C7H8) transported by a carrier gas selected from the group consisting of argon (Ar), nitrogen (N2), helium (He) and hydrogen (H2).
12. The method of claim 9, wherein the etchant-resistive protection layer comprises amorphous silicon.
13. The method of claim 12, wherein the etchant-resistive protection layer is deposited by vapor deposition using silane (SiH4) gas.
14. The method of claim 9, wherein the etchant-resistive protection layer is deposited to a thickness approximately in the range of 1-30 nanometers.
15. The method of claim 9, wherein both the ARC layer and the etchant-resistive protection layer are formed by a technique selected from the group consisting of chemical vapor deposition, plasma-enhanced chemical vapor deposition, atmospheric-pressure chemical vapor deposition and physical vapor deposition.
16. A method for fabricating a solar cell, comprising: providing, in a process chamber, a substrate having a light-receiving surface;
- flowing, in the process chamber, at least a first process gas and a second process gas to form an anti-reflective coating (ARC) layer above the light-receiving surface of the substrate; and
- flowing, in the process chamber, at least the first process gas, but not the second process gas, to deposit an etchant-resistive protection layer above the ARC layer.
17. The method of claim 16, wherein the etchant-resistive protection layer comprises amorphous silicon, and wherein the ARC layer comprises a material selected from the group consisting of silicon nitride, silicon oxy-nitride and carbon-doped silicon oxide.
18. The method of claim 17, wherein the first process gas is silane (SiH4) and the second process gas is ammonia (NH3).
19. The method of claim 16, wherein the etchant-resistive protection layer is deposited to a thickness approximately in the range of 1-30 nanometers.
20. The method of claim 16, wherein both the ARC layer and the etchant-resistive protection layer are formed by a technique selected from the group consisting of chemical vapor deposition, plasma-enhanced chemical vapor deposition, atmospheric-pressure chemical vapor deposition and physical vapor deposition.
Type: Application
Filed: Jan 14, 2010
Publication Date: May 27, 2010
Inventors: Hsin-Chiao Luan (Palo Alto, CA), Peter Cousins (Menlo Park, CA)
Application Number: 12/687,810
International Classification: H01L 31/18 (20060101);