sputter deposited over the entire substrate 10 copper 26 adhesively contacts the exposed surfaces of titanium tungsten 24 without contacting silicon oxide layer 16 or semiconductors 12 copper 26 is thick enough to completely fill channels 20 and vias 22 above titanium tungsten 24 titanium tungsten 24 provides a diffusion barrier which prevents copper 26 from diffusing or migrating into silicon oxide 16 the use of titanium tungsten as a barrier in silicon semiconductor processing of npn devices is described in u s pat no 4 486 946 to jopke jr et al copper diffusion barriers are disclosed in u s pat no 5 164 332 to kumar and in japanese patent nos 1 99239 to tsuya 1 204449 to fukada 1 231351 to hoshino 1 232746 to inoue and 1 239954 to shimizu referring now to fig4 a chemical mechanical polish comprising a rotating soft pad 30 and a wet chemical such as an oxidizer reducer or etchant is applied to attack and remove copper 26 without removing titanium tungsten 24 polishing techniques are disclosed for instance in u s pat nos 5 142 828 to curry ii and 5 137 597 to curry ii et al and in bennett et al 34 selective planarization process and.