FORMATION OF SOLAR CELL-SELECTIVE EMITTER USING IMPLANT AND ANNEAL METHOD

• US 20090308440A1
• Filed: 06/11/2009
• Published: 12/17/2009
• Est. Priority Date: 06/11/2008
• Status: Abandoned Application

• Current Assignee: Intevac
• Original Assignee: Solar Implant Technologies, Inc. (Intevac, Inc.)
• Inventors: Murrer, Edward S., Adibi, Babak
• Application Number:
  US12/483,017
• Publication Number:
  US 20090308440A1
• Time in Patent Office: Days
• US Class Current: 136/255
• CPC Class Codes: H01L 21/26506 in group IV semiconductors
• CPC Class Codes: H01L 21/26513 of electrically active species
• CPC Class Codes: H01L 21/2658 of a molecular ion, e.g. decaborane
• CPC Class Codes: H01L 21/266 using masks H01L21/26586 takes precedence
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/072 the potential barriers being only of the PN heterojunction type
• CPC Class Codes: H01L 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: Y02E 10/547 Monocrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

A method of forming a solar cell, the method comprising: providing a semiconducting wafer having a pre-doped region; performing a first ion implantation of a dopant into the semiconducting wafer to form a first doped region over the pre-doped region, wherein the first ion implantation has a concentration-versus-depth profile; and performing a second ion implantation of a dopant into the semiconducting wafer to form a second doped region over the pre-doped region, wherein the second ion implantation has a concentration-versus-depth profile different from that of the first ion implantation, wherein at least one of the first doped region and the second doped region is configured to generate electron-hole pairs upon receiving light, and wherein the first and second ion implantations are performed independently of one another.

Claims

1. A method of forming a solar cell, the method comprising:

providing a semiconducting wafer having a pre-doped region;

performing a first ion implantation of a dopant into the semiconducting wafer to form a first doped region over the pre-doped region, wherein the first ion implantation has a concentration-versus-depth profile; and

performing a second ion implantation of a dopant into the semiconducting wafer to form a second doped region over the pre-doped region, wherein the second ion implantation has a concentration-versus-depth profile different from that of the first ion implantation,

wherein at least one of the first doped region and the second doped region is configured to generate electron-hole pairs upon receiving light, and

wherein the first and second ion implantations are performed independently of one another.

2. The method of claim 1, wherein a p-n junction is formed between the pre-doped region and the at least one of the first doped region and the second doped region that is configured to generate electron-hole pairs.

3. The method of claim 1, wherein the semiconducting wafer is provided as a silicon substrate.

4. The method of claim 1, wherein the first doped region formed by the first ion implantation has a sheet resistance in a range of approximately 80 Ohms/square to approximately 160 Ohms/square.

5. The method of claim 1, wherein the second doped region formed by the second ion implantation has a sheet resistance in a range of approximately 10 Ohms/square to approximately 40 Ohms/square.

6. The method of claim 1, wherein:

the first doped region formed by the first ion implantation has a sheet resistance in a range of approximately 80 Ohms/square to approximately 160 Ohms/square, and

the second doped region formed by the second ion implantation has a sheet resistance in a range of approximately 10 Ohms/square to approximately 40 Ohms/square.

7. The method of claim 1, further comprising the step of disposing metal contact lines on the surface of the semiconducting wafer, wherein the metal contact lines are configured to conduct electrical charge from at least one of the first and second doped regions.

8. The method of claim 1, wherein the pre-doped region is p-type doped and the first and second doped regions are n-type doped.

9. The method of claim 1, further comprising the step of performing an annealing process on the semiconducting wafer after at least one of the ion implantation steps.

10. A method of forming a solar cell, the method comprising:

providing a semiconducting wafer having a pre-doped region;

forming a homogeneously doped region in the semiconducting wafer over the pre-doped region by performing a first ion implantation of a dopant into the semiconducting wafer, wherein a p-n junction is formed between the pre-doped region and the homogeneously doped region and the homogeneously doped region is configured to generate electron-hole pairs upon receiving light; and

forming a plurality of selectively doped regions in the semiconducting wafer over the homogeneously doped region by performing a second ion implantation of a dopant into the semiconducting wafer,

wherein the first and second ion implantations are performed independently of one another, and

wherein the selectively doped regions have a higher concentration of dopant than the homogeneously doped region.

11. The method of claim 10, wherein the semiconducting wafer is provided as a silicon substrate.

12. The method of claim 10, wherein the homogeneously doped region formed by the first ion implantation has a sheet resistance in a range of approximately 80 Ohms/square to approximately 160 Ohms/square.

13. The method of claim 10, wherein each one of the selectively doped regions formed by the second ion implantation has a sheet resistance in a range of approximately 10 Ohms/square to approximately 40 Ohms/square.

14. The method of claim 10, wherein:

the homogeneously doped region formed by the first ion implantation has a sheet resistance in a range of approximately 80 Ohms/square to approximately 160 Ohms/square, and

each one of the selectively doped regions formed by the second ion implantation has a sheet resistance in a range of approximately 10 Ohms/square to approximately 40 Ohms/square.

15. The method of claim 10, further comprising the step of disposing metal contact lines on the surface of the semiconducting wafer, wherein the metal contact lines are aligned over the plurality of selectively doped regions and are configured to conduct electrical charge from the plurality of selectively doped regions.

16. The method of claim 15, further comprising the step of forming a metallic seed layer near the surface of the semiconducting wafer, wherein the metallic seed layer is configured to act as a transition layer between the selectively doped regions and the metal contact lines.

17. The method of claim 16, wherein the metallic seed layer comprises a silicide.

18. The method of claim 16, wherein the step of forming the metallic seed layer comprises ion implanting at least one material into the semiconducting wafer, wherein the at least one material is chosen from the group consisting of:

Ni, Ta, Ti, W, and Cu.

19. The method of claim 10, wherein the pre-doped region is p-type doped and the homogeneously and selectively doped regions are n-type doped.

20. The method of claim 10, further comprising the step of performing an annealing process on the semiconducting wafer after at least one of the ion implantation steps.

21. The method of claim 10, further comprising the step of forming an anti-reflective coating layer over the homogeneously doped region.

22. The method of claim 10, wherein the selectively doped regions are implanted in the semiconducting wafer at predetermined locations using a mask, wherein the mask comprises openings that are aligned with the predetermined location.

23. The method of claim 22, wherein the mask is a contact mask disposed on the surface of the semiconducting wafer during the second ion implantation.

24. The method of claim 22, wherein the mask is a physical mask disposed a predetermined distance above the surface of the semiconducting wafer during the second ion implantation.

25. The method of claim 10, wherein the selectively doped regions are implanted in the semiconducting wafer at predetermined locations using a shaped ion beam, wherein the shaped ion beam is aligned with the predetermined locations.

26. The method of claim 10, wherein the selectively doped regions are laterally spaced apart from one another a distance in the range of approximately 1 mm to approximately 3 mm.

27. A solar cell comprising:

a semiconducting wafer having a background doped region;

a homogeneously doped region formed in the semiconducting wafer over the background doped region, wherein the homogeneously doped region has a sheet resistance of between approximately 80 Ohms/square and approximately 160 Ohms/square and is formed by ion implanting a dopant into the semiconducting wafer;

a p-n junction formed between the homogeneously doped region and the background doped region;

a plurality of selectively doped regions formed in the semiconducting wafer over the homogeneously doped region, wherein each one of the selectively doped regions has a sheet resistance of between approximately 10 Ohms/square and approximately 40 Ohms/square and is formed by ion implanting a dopant into the semiconducting wafer; and

a plurality of metal contacts disposed on the surface of the semiconducting wafer and aligned over the plurality of selectively doped regions, wherein the plurality of metal contacts is configured to conduct electrical charge from the plurality of selectively doped regions.

28. The solar cell of claim 27, wherein the semiconducting wafer is a silicon substrate.

29. The solar cell of claim 27, wherein the homogeneously doped region formed by the first ion implantation has a sheet resistance of approximately 100 Ohms/square.

30. The solar cell of claim 27, wherein each one of the selectively doped regions formed by the second ion implantation has a sheet resistance of approximately 25 Ohms/square.

31. The solar cell of claim 27, further comprising a metallic seed layer disposed over the selectively doped regions and under the metal contacts.

32. The solar cell of claim 31, wherein the metallic seed layer comprises a silicide.

33. The solar cell of claim 31, wherein the metallic seed layer comprises at least one material chosen from the group consisting of:

Ni, Ta, Ti, W, and Cu.

34. The solar cell of claim 27, wherein the pre-doped region is p-type doped and the homogeneously and selectively doped regions are n-type doped.

35. The solar cell of claim 27, further comprising an anti-reflective coating layer disposed over the homogeneously doped region.

36. The solar cell of claim 27, wherein the selectively doped regions are laterally spaced apart from one another a distance in the range of approximately 1 mm to approximately 3 mm.