Selective wet etching of gold-tin based solder

• US 20090050903A1
• Filed: 08/21/2007
• Published: 02/26/2009
• Est. Priority Date: 08/21/2007
• Status: Active Grant

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Inventors: Chitnis, Ashay
• Granted Patent: US 8,617,997 B2
• Time in Patent Office: Days
• US Class Current: 257/79
• 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 having 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 Au and Sn;

depositing at least one second layer comprising etch mask material adjacent to the at least one first surface;

introducing at least one liquid etching composition to the at least one first layer comprising solder material; 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.

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 1, wherein the at least one first layer comprises an AuSn preform.

4. The method of claim 3, further comprising reflow soldering the preform.

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

6. 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.

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

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

9. The method of claim 8, 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.

10. The method of claim 9, 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.

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

12. A device comprising the layer of claim 11.

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

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

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

16. A method for selective wet etching at least one blanket layer comprising AuSn solder material, the method comprising introducing the at least one blanket layer comprising AuSn solder material to at least one etch composition comprising aqua-regia.

17. The method of claim 16, further comprising introducing the at least one layer comprising AuSn solder material to at least one composition comprising at least one of HF, HCl and HNO₃.

18. The method of claim 17, 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.

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

20. A device comprising the layer of claim 19.