Semiconductor etching paste and the use thereof for localized etching of semiconductor substrates

• US 7,196,018 B2
• Filed: 06/27/2003
• Issued: 03/27/2007
• Est. Priority Date: 07/01/2002
• Status: Expired due to Fees

• Current Assignee: Interuniversitair Micro-Electronica Centrum VZW (IMEC International)
• Original Assignee: Interuniversitair Micro-Electronica Centrum VZW (IMEC International)
• Inventors: Allebe, Christophe, Van Kerschaver, Emmanuel, Szlufcik, Jozef
• Primary Examiner(s): Vinh; Lan
• Application Number:
  US10/609,015
• Publication Number:
  US 20040063326A1
• Time in Patent Office: 1,369 Days
• Field of Search: 438/745, 438/750, 252/79.1, 252/79.2, 216/24, 216/83, 216/96
• US Class Current: 438/745
• CPC Class Codes: C09K 13/02 containing an alkali metal hydroxide
• CPC Class Codes: H01L 31/068 the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction 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 31/1804 comprising only elements of Group IV of the Periodic Table
• CPC Class Codes: Y02E 10/546 Polycrystalline silicon PV cells
• 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 etching a semiconductor substrate is described, the method comprising the steps of applying a paste containing an etchant to the substrate, and carrying out a thermal processing step to etch a part or a layer of the substrate where the paste has been applied. The etchant paste is preferably a caustic etching paste. The etchant paste may be applied selectively to a major surface of the substrate to form a pattern of applied paste. For example, the paste may be applied by a printing method, such as screen-printing. The method may be used to produce solar cells.

Claims

1. A method of etching a semiconductor substrate, the method comprising the steps of:

doping a region of a substrate to yield a doped region of the substrate;

applying a caustic etching paste comprising an etchant and a thickener to the doped region of the substrate, wherein the semiconductor substrate is selected from the group consisting of a microcrystalline silicon substrate, a polycrystalline silicon substrate, an amorphous silicon substrate, a doped silicon substrate, a gallium arsenide substrate, a gallium arsenide phosphide substrate, a germanium substrate, and a silicon germanium substrate, and wherein the etchant is a water-based etchant selected from the group consisting of potassium hydroxide, sodium hydroxide, ammonium hydroxide, combinations thereof, and derivatives thereof; and

heating the substrate, such that the part or the layer of the substrate upon which the etching paste has been applied is etched.

2. The method according to claim 1, wherein the etching paste comprises a synthetic etching paste.

3. The method according to claim 1, wherein the etching paste comprises a natural etching paste.

4. The method according to claim 1, wherein the etching paste is applied selectively to a major surface of the substrate to form a pattern of applied paste.

5. The method according to claim 1, wherein the etching paste is applied by a selective deposition method.

6. The method according to claim 5, wherein the selective deposition method comprises screen-printing.

7. The method according to claim 1, wherein the substrate comprises a part of a solar cell, and wherein the doped region comprises an emitter region of the solar cell.

8. The method according to claim 1, wherein the etching paste is applied to at least one edge of the substrate.

9. The method according to claim 1, wherein the etchant comprises potassium hydroxide.

10. The method according to claim 1, wherein the etchant comprises sodium hydroxide.

11. The method according to claim 1, wherein the etchant comprises ammonium hydroxide.

12. The method according to claim 1, wherein the thickener is selected from the group consisting of a metal carboxyalkylcellulose salt, a hydrocolloid-forming cellulose, a starch, a physically modified hydrocolloid-forming cellulose, a chemically modified hydrocolloid forming cellulose, a physically modified starch, a chemically modified starch, a strongly hydrolyzed polyacrylamide gel, combinations thereof, and derivatives thereof.

13. The method according to claim 1, wherein the etching paste comprises:

a solvent; and

wherein the thickener is selected from the group consisting of a metal carboxyalkylcellulose salt, a hydrocolloid-forming cellulose, a starch, a physically modified hydrocolloid-forming cellulose, a chemically modified hydrocolloid forming cellulose, a physically modified starch, a chemically modified starch, a strongly hydrolyzed polyacrylamide gel, combinations thereof, and derivatives thereof.

14. The method according to claim 1, wherein the etching paste comprises an etchant comprising potassium hydroxide, a thickener comprising sodium carboxymethylcellulose, and a solvent comprising water.

15. The method according to claim 1, wherein the etching paste further comprises a solvent.

16. The method according to claim 15, wherein the solvent comprises water.

17. A method of etching a semiconductor substrate, the method comprising the steps of:

forming at least one metal contact on a base region of the substrate;

forming at least one metal contact on an emitter region of the substrate;

applying a caustic etching paste comprising an etchant and a thickener to a part or a layer of the substrate, wherein the semiconductor substrate is selected from the group consisting of a microcrystalline silicon substrate, a polycrystalline silicon substrate, an amorphous silicon substrate, a doped silicon substrate, a gallium arsenide substrate, a gallium arsenide phosphide substrate, a germanium substrate, and a silicon germanium substrate, and wherein the etchant is a water-based etchant selected from the group consisting of potassium hydroxide, sodium hydroxide, ammonium hydroxide, combinations thereof, and derivatives thereof; and

heating the substrate, such that the part or the layer of the substrate upon which the etching paste has been applied is etched.

18. The method according to claim 17, wherein the heating step yields an insulating region, wherein the insulating region is situated between the emitter region and the base region so as to isolate a metal contact from the emitter region.

19. The method according to claim 17, wherein the etching paste comprises a synthetic etching paste.

20. The method according to claim 17, wherein the etching paste comprises a natural etching paste.

21. The method according to claim 17, wherein the etching paste is applied selectively to a major surface of the substrate to form a pattern of applied paste.

22. The method according to claim 17, wherein the etching paste is applied to at least one edge of the substrate.

23. The method according to claim 17, wherein the etchant comprises potassium hydroxide.

24. The method according to claim 17, wherein the etchant comprises sodium hydroxide.

25. The method according to claim 17, wherein the etchant comprises ammonium hydroxide.

26. The method according to claim 17, wherein the thickener is selected from the group consisting of a metal carboxyalkylcellulose salt, a hydrocolloid-forming cellulose, a starch, a physically modified hydrocolloid-forming cellulose, a chemically modified hydrocolloid forming cellulose, a physically modified starch, a chemically modified starch, a strongly hydrolyzed polyacrylamide gel, combinations thereof, and derivatives thereof.

27. The method according to claim 17, wherein the etching paste comprises:

a solvent; and

wherein the thickener is selected from the group consisting of a metal carboxyalkylcellulose salt, a hydrocolloid-forming cellulose, a starch, a physically modified hydrocolloid-forming cellulose, a chemically modified hydrocolloid forming cellulose, a physically modified starch, a chemically modified starch, a strongly hydrolyzed polyacrylamide gel, combinations thereof, and derivatives thereof.

28. The method according to claim 17, wherein the etching paste comprises an etchant comprising potassium hydroxide, a thickener comprising sodium carboxymethylcellulose, and a solvent comprising water.

29. The method according to claim 17, wherein the etching paste is applied by a selective deposition method.

30. The method according to claim 29, wherein the selective deposition method comprises screen-printing.

31. The method according to claim 17, wherein the etching paste further comprises a solvent.

32. The method according to claim 31, wherein the solvent comprises water.