Solar Cell Fabrication Using Extruded Dopant-Bearing Materials

• US 20080138456A1
• Filed: 12/12/2006
• Published: 06/12/2008
• Est. Priority Date: 12/12/2006
• Status: Active Grant

• Current Assignee: SolarWorld Industries GmbH
• Original Assignee: Palo Alto Research Center, Inc. (Xerox Holdings Corp.)
• Inventors: Fork, David K., Shrader, Eric J.
• Granted Patent: US 7,928,015 B2
• Time in Patent Office: Days
• US Class Current: 425/113
• CPC Class Codes: H01L 21/2254 from or through or into an applied layer, e.g. photoresist, nitrides
• CPC Class Codes: H01L 21/228 using diffusion into or out of a solid from or into a liquid phase, e.g. alloy diffusion processes H01L21/221 - H01L21/222 take precedence
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/0682 back-junction, i.e. rearside emitter, solar cells, e.g. interdigitated base-emitter regions back-junction cells
• CPC Class Codes: H01L 31/18 Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
• CPC Class Codes: H01L 31/188 Apparatus specially adapted for automatic interconnection of solar cells in a module
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

Wafer-based solar cells are efficiently produced by extruding a dopant bearing material (dopant ink) onto one or more predetermined surface areas of a semiconductor wafer, and then thermally treating the wafer to cause diffusion of dopant from the dopant ink into the wafer to form corresponding doped regions. A multi-plenum extrusion head is used to simultaneously extrude interdigitated dopant ink structures having two different dopant types (e.g., n-type dopant ink and p-type dopant ink) in a self-registered arrangement on the wafer surface. The extrusion head is fabricated by laminating multiple sheets of micro-machined silicon that define one or more ink flow passages. A non-doping or lightly doped ink is co-extruded with heavy doped ink to serve as a spacer or barrier, and optionally forms a cap that entirely covers the heavy doped ink. A hybrid thermal treatment utilizes a gaseous dopant to simultaneously dope exposed portions of the wafer.

Claims

1. A method for fabricating a device on a semiconductor substrate, the method comprising:

extruding a first dopant bearing material on a surface of the semiconductor substrate such that the first dopant bearing material forms a first extruded structure on a first surface area of the semiconductor substrate, the first dopant bearing material including a first dopant of a first dopant type; and

heating the semiconductor substrate such that the first dopant diffuses through the first surface area into the semiconductor substrate, thereby forming a first doped region of the semiconductor substrate.

2. The method according to claim 1, further comprising removing residual portions of the first extrusion structure after said heating.

3. The method according to claim 1, further comprising:

depositing a passivation layer on the surface of the semiconductor substrate over the first doped region,

laser ablating portions of the passivation layer such that a plurality of contact openings are defined through the passivation layer to the surface area,

disposing a conductive contact structure in each of the contact openings, and

disposing at least one metal line structure onto an upper surface of the passivation layer such that said metal line structure contacts said first doped region by way of said conductive contact structure.

4. The method according to claim 1, further comprising:

depositing a passivation layer on the surface of the semiconductor substrate over the first doped region,

removing portions of the passivation layer such that a plurality of contact openings are defined through the passivation layer to the surface area,

depositing a conductive contact structure into each of the contact openings using a direct-write metallization apparatus, and

depositing at least one metal line structure onto an upper surface of the passivation layer such that said metal line structure contacts said first doped region by way of said conductive contact structure.

5. The method according to claim 1,

wherein said extruding further comprises forming a second extruded structure on a second surface area of the semiconductor substrate,

wherein said heating the semiconductor substrate further comprises diffusing said first dopant from said second extruded structure into a second doped region of the semiconductor substrate through the second surface area.

6. The method according to claim 5, wherein the first doped region is separated from the second doped region by a first undoped region of the semiconductor substrate.

7. The method according to claim 5, wherein said extruding comprises simultaneously extruding a third material such that the extruded third material forms a third extruded structure on a third surface area of the semiconductor substrate that is disposed between the first surface area and the second surface area.

8. The method according to claim 7, wherein extruding said third material comprises forming a continuous sheet such that said third extruded structure extends from a side edge of said first extruded structure to a side edge of said second extruded structure.

9. The method according to claim 8, wherein extruding said first dopant bearing material comprises compressing said first material between said third extruded structure and a fourth extruded structure comprising said third material.

10. The method according to claim 7, wherein the third material has a relatively light dopant content relative to the first dopant bearing material.

11. The method according to claim 1, wherein said heating comprises disposing said semiconductor substrate in an ambient including a gaseous phase dopant.

12. The method according to claim 7, wherein extruding said third material comprises forming a capping structure that entirely covers said first extruded structure.

13. The method according to claim 1,

wherein said extruding further comprises simultaneously extruding a second dopant bearing material such that the extruded second dopant bearing material forms a second extruded structure on a second surface area of the semiconductor substrate, the second dopant bearing material including a second dopant of a second dopant type,

wherein said heating the semiconductor substrate further comprises simultaneously causing said second dopant to diffuse through the second surface area into the semiconductor substrate, thereby forming a second doped region.

14. The method according to claim 13,

wherein the first doped region has a first, relatively heavy doping level,

wherein the second doped region has a second, relatively heavy doping level,

wherein the third region has one of a third, relatively light doping level or an intrinsic state.

15. The method according to claim 14, further comprising removing residual portions of at least one of the first extrusion structure and the second extrusion structure after said heating.

16. The method according to claim 13, further comprising:

depositing a passivation layer on the surface of the semiconductor substrate over the first and second doped regions,

laser ablating portions of the passivation layer such that a plurality of contact openings are defined through the passivation layer to each of the first and second surface areas,

depositing a conductive contact structure into each of the contact openings using a direct-write metallization apparatus, and

depositing metal line structures onto an upper surface of the passivation layer such that each metal line structure contacts a group of said contact structures that are disposed over a corresponding one of said first and second doped regions.

17. The method according to claim 13, wherein said extruding further comprises simultaneously extruding a third material such that the extruded third material forms a third extruded structure on a third surface area of the semiconductor substrate that is disposed between the first surface area and the second surface area.

18. The method according to claim 17, wherein extruding said third material comprises forming a continuous sheet such that said third extruded structure extends from a side edge of said first extruded structure to a side edge of said second extruded structure.

19. A system for fabricating a wafer-based semiconductor device on a substrate, the system comprising:

means for extruding a first dopant bearing material and a second dopant bearing material on a surface of the semiconductor substrate such that the first dopant bearing material forms a first extruded structure on a first surface area of the semiconductor substrate, and such that the second dopant bearing material forms a second extruded structure on a second surface area of the semiconductor substrate, wherein the first and second surface areas are separated by a third surface area, and wherein the first dopant bearing material includes a first dopant of a first dopant type, and the second dopant bearing material includes a second dopant of a second dopant type and

means for heating the semiconductor substrate such that the first dopant diffuses through the first surface area into the semiconductor substrate, thereby forming a first doped region, and such that the second dopant diffuses through the second surface area into the semiconductor substrate, thereby forming a second doped region.

20. The system of claim 19, further comprising means for removing residual portions of at least one of the first extrusion structure and the second extrusion structure after said heating.

21. The system according to claim 19, further comprising:

means for depositing a passivation layer on the surface of the semiconductor substrate over the first and second doped regions,

means for removing portions of the passivation layer such that a plurality of contact openings are defined through the passivation layer to each of the first and second surface areas,

means for disposing a conductive contact structure into each of the contact openings, and

means for disposing metal line structures onto an upper surface of the passivation layer such that each metal line structure contacts a group of said contact structures that are disposed over a corresponding one of said first and second doped regions.

22. The system according to claim 19, wherein said means for extruding comprises an extrusion head that includes a laminated structure comprising a plurality of micro-machined sheets comprising at least one of silicon, glass and polymer materials.

23. The system according to claim 22, wherein the extrusion head comprises a first sheet defining a plurality of nozzle channels, a second sheet defining a first plenum and a first plurality of feed channels operably disposed to pass said first dopant bearing material from the first plenum to a first plurality of the nozzle channels, and a third sheet defining a second plenum and a second plurality of feed channels operably disposed to pass said second dopant bearing material from the second plenum to a second plurality of the nozzle channels.

24. The system according to claim 23, wherein the first sheet is disposed between the second sheet and the third sheet.

25. The system according to claim 23, wherein the second sheet is disposed between the first sheet and the third sheet.

26. The system according to claim 23, further comprising means for passing a third material to a third plurality of the nozzle channels.

27. The system according to claim 26, wherein at least one of said nozzle channels of the third plurality is disposed between a first associated nozzle channel of the first plurality and a second associated nozzle channel of the second plurality.

28. The system according to claim 23, wherein at least one of said nozzle channels of the first plurality comprises tapered nozzle walls.