Spring 1994

Process Control and Etchant Life Extension in a Copper-Ammonium Persulfate Thin Films Etching System

Lawrence D. David, Fadi J. Bahouth, Cheryl Field, Cerarda Kilpatrick, James M. Nenni, Diane Scherpereel, and Walter Seebold, IBM Micro-Electronics

Ammonium persulfate (APS) is employed at IBM-East Fishkill to panem 2 -1J.ffi-thick sputtered or evaporated copper thin nIms 0':1 multichip packaging modules. A line width of 27 +5 ±, with a 3.5 -m maximum undercut, must be achieved. APS is used instead of cupric chloride or ferric chloride because a chloride·free etchant is mandatory in this application. Control of the etching parameters is crucial to achieving 100% yield at this step. Since the copper etch is near the end of a sequence of hundreds of steps, yield losses here are costly.