Metal contact structure for solar cell and method of manufacture

• US 20040200520A1
• Filed: 04/10/2003
• Published: 10/14/2004
• Est. Priority Date: 04/10/2003
• Status: Active Grant

• Current Assignee: Maxeon Solar Pte Limited
• Original Assignee: Sunpower Corporation (Totalenergies Se)
• Inventors: Smith, David, Pass, Thomas, Mulligan, William P., Swanson, Richard M., Cudzinovic, Michael J.
• Granted Patent: US 7,388,147 B2
• Time in Patent Office: Days
• US Class Current: 136/256
• CPC Class Codes: H01L 31/022441 Electrode arrangements specially adapted for back-contact 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: Y02E 10/547 Monocrystalline silicon PV cells

Abstract

In a solar cell having p doped regions and n doped regions alternately formed in a surface of a semiconductor wafer in offset levels through use of masking and etching techniques, metal contacts are made to the p regions and n regions by first forming a base layer contacting the p doped regions and n doped regions which functions as an antireflection layer, and then forming a barrier layer, such as titanium tungsten or chromium, and a conductive layer such as copper over the barrier layer. Preferably the conductive layer is a plating layer and the thickness thereof can be increased by plating.

Claims

1. In the fabrication of a solar cell in a semiconductor substrate, a method of fabricating metal contacts on a surface of the solar cell comprising the steps of:

a) forming a first thin metal layer in contact with the semiconductor substrate,

b) forming a thin barrier metal layer over the first metal layer, and

c) increasing thickness of the barrier layer by plating.

2. The method as defined by claim 1 wherein the first metal layer functions as an infrared reflector.

3. The method as defined by claim 2 wherein the thin barrier layer comprises a refractory metal and a strike metal that serves as a base to initiate plating.

4. The method as defined by claim 3 and further including before step c) the step of applying a plating resist to limit plating area.

5. The method as defined by claim 4 and including after step c) the steps of removing the plating resist, and removing by etching exposed barrier metal and underlying first metal.

6. The method as defined by claim 5 wherein the first metal layer comprises aluminum, the refractory metal comprises titanium tungsten, and the plating metal comprises copper.

7. The method as defined by claim 2 wherein the first metal comprises aluminum and the barrier layer comprises a metal chosen from chromium and titanium tungsten.

8. The method as defined by claim 7 wherein the barrier layer comprises a plating metal which serves as a strike layer to initiate plating.

9. The method as defined by claim 8 and further including before step c) the step of applying a plating resist to limit plating area.

10. The method as defined by claim 9 and including after step c) the steps of removing the plating resist, and removing by etching exposed barrier metal and underlying base metal.

11. The method as defined by claim 1 and further including before step c) the step of selectively etching the exposed barrier metal layer to limit plating area.

12. The method as defined by claim 1 wherein the barrier layer comprises a metal which functions as a diffusion barrier and as a strike layer to initiate plating.

13. In the fabrication of a solar cell, a method of fabricating metal contacts to doped regions in a surface of a semiconductor wafer comprising the steps of:

a) forming a silicon oxide layer over the surface of the semiconductor wafer,

b) forming a seed metal layer over the silicon oxide layer and contacting the doped regions through the oxide layer,

c) forming a plating resist over the seed metal layer to thereby define the geometry of metal contacts,

d) plating an electrically conductive layer over the seed layer,

e) stripping the plating resist, and

f) selectively etching the seed metal layer that was under the plating resist.

14. The method as defined by claim 13, wherein the seed metal layer comprises a first layer of aluminum which functions as a reflector.

15. The method as defined by claim 14, wherein the seed metal layer includes a diffusion barrier layer of titanium tungsten.

16. The method as defined by claim 15, wherein the seed metal layer includes a conductive layer of copper which functions as a strike layer to initiate plating.

17. The method as defined by claim 13 wherein step a) includes etching holes through the silicon oxide to permit the seed metal layer to contact the doped regions in step b).

18. The method as defined by claim 13 wherein step c) includes defining contacts and a grid pattern.

19. The method as defined by claim 13 and further including after step d) the step of applying a cap layer over the electrically conductive layer.

20. The method as defined by claim 19 wherein the cap layer comprises plated tin.

21. The method as defined by claim 19 wherein the cap layer comprises an electroless plated metal.

32. The method as defined by claim 17 wherein step a) includes applying a chemical paste on the silicon oxide layer where holes through the silicon oxide are to be etched.

33. The method as defined by claim 32 wherein the chemical paste is applied by printing.

22. In the fabrication of a solar cell, a method of fabricating a contact on a surface of a semiconductor wafer comprising the steps of:

a) forming a thin base metal layer on the surface,

b) forming a thin barrier metal layer, including a strike layer, over the base metal layer, and

c) forming a conductive layer over the barrier layer by plating metal on the strike layer.

23. The method as defined by claim 22, wherein the base metal layer comprises aluminum, the barrier layer comprises titanium tungsten, and the strike layer and the conductive layer comprise copper.

24. The method as defined by claim 22 wherein the base metal layer comprises aluminum, and the barrier metal layer comprises chromium.

25. In a semiconductor solar cell, a metal contact structure comprising:

a base metal in contact with a semiconductor substrate of the solar cell, and

a barrier metal overlying the base metal, the barrier metal including a strike metal layer and a metal plated on the strike layer.

26. The metal contact structure as defined by claim 25 wherein the base metal functions as an infrared reflector.

27. The metal contact structure as defined by claim 26 wherein the barrier metal includes a refractory metal and a plating metal on the refractory metal.

28. The metal contact structures as defined by claim 27 wherein the base metal comprises aluminum, the barrier metal comprises titanium tungsten.

29. The metal contact structure as defined by claim 28 wherein the plating metal and strike metal comprise copper.

30. The metal contact structure as defined by claim 27 wherein the base metal comprises aluminum, and the barrier metal comprises chromium.

31. The metal contact structure as defined by claim 30 wherein the plating metal comprises copper.