Selective etching of TiW for C4 fabrication

Details Selective etching of TiW for C4 fabrication Selective etching of TiW for C4 fabrication

1994-06-15

1995-10-31

Powell, William

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

15665911, 752 794, 437192, 437228, 437245, H01L 2100, B44C 122, C23F 102

Patent

active

054626382

ABSTRACT:
A chemical etchant (and a method for forming the etchant) is disclosed for removing thin films of titanium-tungsten alloy in microelectronic chip fabrication. The alloy removed is preferably 10% Ti and 90% W, which is layered onto a substrate under chromium and copper seed layers for electrodeposition of C4 solder bumps. In this application the Ti--W etchant should not attack aluminum, chromium, copper, or lead-tin solders, and should dissolve Ti--W rapidly. The invention achieves this with a mixture of 30% by weight hydrogen peroxide and water, to which is added EDTA and potassium sulfate. The hydrogen peroxide etches Ti--W rapidly at temperatures between 40.degree. C. and 60.degree. C. EDTA forms a complex with tungsten to prevent plating of the Pb--Sn solder with W, and potassium sulfate forms a protective coating on the Pb--Sn solder to protect it from chemical attack.

REFERENCES:
patent: 4554050 (1985-11-01), Minford et al.
patent: 4671852 (1987-06-01), Pyke
patent: 4814293 (1989-03-01), Van Oekel
patent: 5041191 (1991-08-01), Watson
patent: 5130275 (1992-07-01), Dion

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