PULSE PLATING OF A LOW STRESS FILM ON A SOLAR CELL SUBSTRATE

• US 20080092947A1
• Filed: 10/24/2006
• Published: 04/24/2008
• Est. Priority Date: 10/24/2006
• Status: Abandoned Application

• Current Assignee: Applied Materials Incorporated
• Original Assignee: Applied Materials Incorporated
• Inventors: Kovarsky, Nicolay Y., Lopatin, Sergey, Gay, Charles, Eaglesham, David, Dukovic, John O.
• Application Number:
  US11/552,497
• Publication Number:
  US 20080092947A1
• Time in Patent Office: Days
• US Class Current: 136/255
• CPC Class Codes: H01L 31/022425 for solar cells
• CPC Class Codes: H01L 31/02245 for metallisation wrap-through [MWT] type solar cells
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

Embodiments of the invention contemplate the formation of a low cost solar cell metal contact structure that has improved electrical and mechanical properties through the use of an electrochemical plating process. The resistance of interconnects formed in a solar cell device greatly affects the efficiency of the solar cell. It is thus desirable to form a solar cell device that has a low resistance connections that is reliable and cost effective. One or more embodiments of the invention described herein are adapted to form a low cost and reliable interconnecting layer using an electrochemical plating process containing common metal, such as copper. However, generally the electroplated portions of the interconnecting layer may contain a substantially pure metal or a metal alloy layer. Methods are discussed herein that are used to form a solar cell containing conductive metal interconnect layer(s) that have a low intrinsic stress.

Claims

1. A method for forming a metal interconnect in a solar cell substrate, comprising:

providing a substrate that has either an n-type region or a p-type region generally adjacent to a surface of a substrate;

forming a seed layer that is in electrical communication with the n-type region or the p-type region on the surface of the substrate; and

forming a first metal layer over the seed layer by immersing the seed layer and an electrode in a first electrolyte and biasing the seed layer relative to the electrode using one or more waveforms delivered from a power supply.

2. The method of claim 1, wherein the surface is a light-receiving surface or a backside surface.

3. The method of claim 1, wherein the one or more waveforms comprises a first waveform that is adapted to form a first metal layer that has a first grain size and a second waveform that is adapted to form a second metal layer that has a second grain size.

4. The method of claim 1, wherein the first electrolyte contains a copper salt selected from a group consisting of copper sulfate, copper chloride, copper acetate, copper pyrophosphate, and copper fluoroborate.

5. The method of claim 1, wherein first metal layer comprises copper and at least one element selected from a group consisting of silver, nickel, zinc and tin.

6. The method of claim 1, further comprising forming a second metal layer over the first metal layer by immersing the first metal layer and an electrode in a second electrolyte and biasing the first metal layer relative to the electrode using one or more waveforms delivered from a power supply.

7. The method of claim 6, wherein the second electrolyte contains a metal ion selected from a group consisting of tin, silver, copper, gold, lead and ruthenium.

8. The method of claim 1, wherein the waveform comprises a DC component that lasts a first period of time and pulse plating component that lasts for a second period of time, wherein the pulse plating component is a forward pulse or a pulse reverse type pulse.

9. A method for forming a metal interconnect on a solar cell substrate, comprising:

providing an electrolyte container configured to receive and maintain a first electrolyte therein, the electrolyte container having an electrode disposed within the electrolyte container;

providing a head assembly positioned above the electrolyte container, the head assembly including a substrate holder for supporting a substrate and a first electrode, wherein the substrate holder covers the processing surface of the substrate and the substrate holder has a plurality of features formed therein that preferentially allow regions of the processing surface to contact the first electrolyte;

positioning a substrate in contact with the first electrolyte, the substrate holder and the first electrode; and

applying one or more waveforms to the first electrode and a second electrode in an electroplating process.

10. The method of claim 9, wherein the substrate has either an n-type region or a p-type region generally adjacent to a light-receiving surface of a substrate and a seed layer that contacts the n-type region or the p-type region on the light-receiving surface of the substrate.

11. The method of claim 9, wherein the one or more waveforms comprises a first waveform that is adapted to form a first metal layer that has a first grain size and a second waveform that is adapted to form a second metal layer that has a second grain size.

12. The method of claim 9, wherein the first electrolyte contains a copper salt selected from a group consisting of copper sulfate, copper chloride, copper acetate, copper pyrophosphate, and copper fluoroborate.

13. The method of claim 12, wherein first electrolyte comprises copper ion and at least one metal ion selected from a group consisting of silver, nickel, zinc and tin.

14. The method of claim 9, further comprising:

removing the first electrolyte from the electrolyte container;

delivering a second electrolyte to the electrolyte container, wherein the second electrolyte contains a metal ion that is not found in the first electrolyte; and

applying one or more waveforms to the first electrode and the second electrode, wherein the processing surface and the second electrode are in contact with the second electrolyte.

15. The method of claim 14, wherein the second electrolyte contains a metal ion selected from a group consisting of tin, silver, gold, lead and ruthenium.

16. The method of claim 9, wherein the one or more waveforms are a pulse reverse, a forward pulse or a DC waveform.

17. The method of claim 9, wherein the waveform comprises a DC component that lasts a first period of time and pulse plating component that lasts for a second period of time, wherein the pulse plating component is a forward pulse or a pulse reverse type pulse.

18. A metal contact structure for a solar cell comprising:

an n-type region disposed on a substrate;

a p-type region disposed on the substrate and adjacent to the n-type region;

a first metal seed layer that is in electrical communication with the n-type region, wherein the first metal seed layer is deposited using a process selected from a group consisting of an electroless deposition process, a physical vapor deposition process, a chemical vapor deposition process and an atomic layer deposition process;

a first metal layer that is formed over the first metal seed layer using an electrochemical deposition process using a first waveform;

a second metal seed layer that is in electrical communication with the p-type region, wherein the second metal seed layer is deposited using a process selected from a group consisting of an electroless deposition process, a physical vapor deposition process, a chemical vapor deposition process and an atomic layer deposition process; and

a second metal layer that is formed over the second metal seed layer using an electrochemical deposition process using a second waveform.

19. The metal contact structure of claim 18, wherein the first metal seed layer and the second metal seed layer each contain at least one metal selected from a group consisting of nickel (Ni), cobalt (Co), titanium (Ti), titanium nitride (TiN), titanium tungsten (TiW), tantalum (Ta), tantalum nitride (TaN), molybdenum (Mo), tungsten (W), aluminum (Al) and ruthenium (Ru).

20. The metal contact structure of claim 18, wherein the first metal seed layer and the second metal seed layer each comprise:

a first layer that contains at least one metal selected from a group consisting of cobalt, titanium, titanium nitride, tantalum, tantalum nitride, molybdenum, tungsten, and ruthenium; and

a second layer that contains at least one metal selected from a group consisting of copper, silver, ruthenium and nickel.

21. The metal contact structure of claim 18, wherein the first metal layer and the second metal layer each contain at least one metal selected from a group consisting of copper, silver, gold, tin, cobalt, rhenium, ruthenium, iron, nickel, zinc, lead, palladium, and/or aluminum.

22. The metal contact structure of claim 18, further comprises:

a third metal layer that is formed over the first metal layer using an electrochemical deposition process; and

a fourth metal layer that is formed over the second metal layer using an electrochemical deposition process.

23. The metal contact structure of claim 22, wherein the third metal layer and the fourth metal layer each contain at least one metal selected from a group consisting of tin, silver, copper, gold, lead and ruthenium.