APPLICATION SPECIFIC IMPLANT SYSTEM AND METHOD FOR USE IN SOLAR CELL FABRICATIONS

• US 20090309039A1
• Filed: 06/11/2009
• Published: 12/17/2009
• Est. Priority Date: 06/11/2008
• Status: Active Grant

• Current Assignee: Intevac
• Original Assignee: Solar Implant Technologies, Inc. (Intevac, Inc.)
• Inventors: Murrer, Edward S., Adibi, Babak
• Granted Patent: US 8,871,619 B2
• Time in Patent Office: Days
• US Class Current: 250/396.R
• 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

Solar cells and other semiconductor devices are fabricated more efficiently and for less cost using an implanted doping fabrication system. A system for implanting a semiconductor substrate includes an ion source (such as a single-species delivery module), an accelerator to generate from the ion source an ion beam having an energy of no more than 150 kV, and a beam director to expose the substrate to the beam. In one embodiment, the ion source is single-species delivery module that includes a single-gas delivery element and a single-ion source. Alternatively, the ion source is a plasma source used to generate a plasma beam. The system is used to fabricate solar cells having lightly doped photo-receptive regions and more highly doped grid lines. This structure reduces the formation of “dead layers” and improves the contact resistance, thereby increasing the efficiency of a solar cell.

Claims

1. A system for implanting a semiconductor substrate comprising:

an ion source;

an accelerator to generate from the ion source a beam having an energy of no more than 150 kV; and

a beam director to expose the substrate to the beam.

2. The system of claim 1, wherein the ion source is a single-species delivery module comprising a single-gas delivery element and a single-ion source.

3. The system of claim 2, wherein the beam director comprises a focusing element, wherein the focusing element comprises magnetic optics, electromagnetic optics, or both to focus the beam onto the substrate.

4. The system of claim 2, wherein the single-ion source has a beam slot length of between 5 and 10 cm and a width of less than 5 mm.

5. The system of claim 1, wherein the beam is a plasma beam.

6. The system of claim 1, wherein the ion source contains an n-type dopant selected from the group consisting of antimony, arsenic, and phosphorous.

7. The system of claim 1, wherein the ion source contains a p-type dopant.

8. The system of claim 1, wherein the beam has a power density of at least 5 kW per square centimeter.

9. The system of claim 1, wherein the ion source, the accelerator, or both are plug-compatible with the system.

10. The system of claim 1, further comprising a scanning element to step the beam across the substrate in orthogonal directions.

11. A method of fabricating a semiconductor device comprising:

doping photo-receptive regions within a substrate to a first concentration;

doping the photo-receptive regions to a second concentration larger than the first concentration to form gridlines, wherein the gridlines extend from topmost surfaces of the photo-receptive regions down into the substrate; and

coupling metal fingers to the gridlines,

wherein the photo-receptive regions and the gridlines are doped using a system comprising a single-species delivery module.

12. The method of claim 11, wherein the substrate is doped separately from other substrates.

13. The method of claim 11, wherein forming the gridlines comprises exposing the substrate through a mask displaced from a surface of the substrate to an ion beam containing a dopant, wherein the mask has openings sized to widths of the gridlines.

14. The method of claim 11, wherein forming the gridlines comprises exposing the substrate through a mask coupled to a surface of the substrate to an ion beam containing a dopant, wherein the mask has openings adjacent to where the gridlines are to be formed.

15. The method of claim 11, wherein forming the gridlines comprises shaping a beam containing dopants to a width of the gridlines and directing the beam onto the photo-receptive regions.

16. The method of claim 15, wherein directing the beam comprises scanning the beam across the photo-receptive regions to sequentially form the gridlines.

17. The method of claim 15, wherein directing the beam comprises generating the beam to simultaneously form the gridlines.

18. The method of claim 11, wherein the first concentration is less than 1E15 per square centimeter.

19. The method of claim 11, wherein the photo-receptive regions have a resistance of at least 100 ohms per square.

20. The method of claim 11, wherein the gridlines have a resistance of about 10 to 30 ohms per square.

21. The method of claim 11, wherein the gridlines are no more than 200 microns wide.

22. The method of claim 11, wherein the gridlines are no more than 5 millimeters apart.

23. The method of claim 11, further comprising annealing the substrate at between 400 and 500 degrees Centigrade.

24. The method of claim 11, further comprising forming a contact on a back surface of the substrate.

25. The method of claim 11, further comprising implanting a seed on each of the gridlines before coupling the gridlines to metallic fingers.

26. A method of fabricating a solar cell comprising:

doping photo-receptive regions within a substrate to a first concentration using an ion beam having an energy of no more than 150 kV;

doping the photo-receptive regions to a second concentration larger than the first concentration using the ion beam to form gridlines, wherein the gridlines extend from topmost surfaces of the photo-receptive regions down into the substrate; and

coupling metal fingers to the gridlines,

wherein the substrate is 156 mm×

156 mm, the photo-receptive regions are doped using a system comprising a single-species delivery module, and a throughput of the system is at least 1,000 wafers per hour.