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

February 8, 1994

Lawrence D. David, IBM Microelectronic

Fadi J. Bahouth
Cheryl Field
Gerarda Kilpatrick
James M. Nenni
Diane S. Scherpereel
Walter C. Seebold

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.