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

February 8, 1994

Ammonium persulfate (APS) is employed at IBM-East Fishkill to pattern 2 -µm-thick sputtered or evaporated copper thin films on 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 1000/4 yield at this step. Since the copper etch is near the end of a sequence of hun­dreds of steps, yield losses here are costly.