Selective wet etching of gold-tin based solder

• US 8,617,997 B2
• Filed: 08/21/2007
• Issued: 12/31/2013
• Est. Priority Date: 08/21/2007
• Status: Active Grant

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Chitnis, Ashay
• Primary Examiner(s): Le, Thao
• Assistant Examiner(s): JONES, ERIC W
• Application Number:
  US11/894,917
• Publication Number:
  US 20090050903A1
• Time in Patent Office: 2,324 Days
• Field of Search: 438/689, 438/614, 438/694, 438/714, 257/E21.17, 257/E21.508
• US Class Current: 438/714
• CPC Class Codes: C23F 1/02 Local etching
• CPC Class Codes: C23F 1/30 for etching other metallic material
• CPC Class Codes: C23F 1/44 Compositions for etching metallic material from a metallic material substrate of different composition
• CPC Class Codes: H01L 33/005 Processes
• CPC Class Codes: H01L 33/36 characterised by the electrodes

Abstract

The present invention is directed to post-deposition, wet etch processes for patterning AuSn solder material and devices fabricated using such processes. The processes can be applied to uniform AuSn layers to generate submicron patterning of thin AuSn layers having a wide variety of features. The use of multiple etching steps that alternate between different mixes of chemicals enables the etch to proceed effectively, and the same or similar processes can be used to etch under bump metallization. The processes are simple, cost-effective, do not contaminate equipment or tools, and are compatible with standard cleanroom fabrication processes.

Claims

1. A method for fabricating an electronic device using selective wet etching, the method comprising:

providing at least one wafer comprising at least one first surface;

depositing at least one first layer comprising solder material adjacent to the at least one first surface, wherein the solder material comprises composite AuSn;

depositing at least one second layer comprising etch mask material on said at least one first layer comprising solder material;

introducing a plurality of liquid etching compositions to the at least one first layer comprising solder material, each of said plurality of liquid etching compositions comprising a different chemical composition, said plurality of liquid etching compositions introduced in a repeating, alternating fashion; and

etching the at least one layer comprising solder material for a period of time sufficient to selectively etch at least one portion of the at least one solder layer with the plurality of liquid etching compositions;

wherein selective wet etching is achieved using a wet etch process comprising;

introducing the at least one first layer to at least one composition comprising at least one of HF, HCl and HNO₃; and

introducing the at least one first layer to at least one composition comprising aqua-regia.

2. The method of claim 1, further comprising:

depositing at least one additional layer of material adjacent to the least one first surface; and

etching the at least one additional layer for a period of time sufficient to selectively etch at least one portion of the at least one additional layer.

3. The method of claim 2, wherein the at least one additional layer comprises at least one of Ti, Pt, Au, Si, Ti, Ni, and Pt.

4. The method of claim 2, wherein the at least one additional layer comprises SiO₂.

5. The method of claim 1, wherein the at least one first layer comprises an AuSn preform.

6. The method of claim 5, further comprising reflow soldering the preform.

7. The method of claim 1, wherein the at least one second layer comprises at least one of photo resist and GaN.

8. The method of claim 1, wherein the plurality of liquid etching compositions comprises at least two of HF, HCl, HNO₃ and aqua-regia.

9. The method of claim 1, wherein introduction of the at least one composition comprising at least one of HF, HC, and HNO₃ alternates with the introduction of the at least one composition comprising aqua-regia.

10. A patterned layer fabricated according to the method of claim 1.

11. A device comprising the layer of claim 10.

12. A device fabricated by the method of claim 1.

13. The device of claim 12, wherein the device is at least one of a flip chip device and a light emitting device.

14. The device of claim 13, wherein the device is a light emitting diode.

15. A method for selective wet etching at least one blanket layer comprising AuSn solder material, the method comprising:

repeatedly introducing the at least one blanket layer comprising AuSn solder material to a first etch composition comprising aqua-regia, wherein an etch mask layer is on said at least one blanket layer; and

repeatedly introducing the at least one layer comprising AuSn solder material to a second composition comprising at least one of HF, HCl and HNO₃ when said at least one layer is not being introduced to said first etch composition;

wherein introduction of the second composition comprising at least one of HF, HC, and HNO₃ alternates with the introduction of the first composition comprising aqua-regia.

16. A patterned layer fabricated according to the method of claim 15.

17. A device comprising the layer of claim 16.

18. A method for selectively wet etching a AuSn composite layer of solder material using repeated, alternating etchants, the method comprising:

forming a mask layer on the solder layer, said mask layer comprising openings to said solder layer;

a first etching of said solder layer through said mask layer openings using a first etch comprising a first chemical composition;

a second etching of said solder layer through said mask opening using a second etch comprising a second chemical composition, said first and second etchings occurring at different times;

wherein said first chemical composition comprises at least one of HF, HCl, and HNO₃ or aqua-regia; and

wherein said second chemical composition comprises at least one of HF, HCl, and HNO₃ or aqua-regia.

19. The method of claim 18, etching said solder layer faster than an etching method using only one of said first and second compositions.

20. The method of claim 18, wherein said first chemical composition comprises aqua regia.

21. The method of claim 18, wherein said second chemical composition comprises HF, HCl or HNO₃.