Modification of the Preston equation for the chemical–mechanical polishing of copper

Chemical-mechanical polishing (CMP) of copper was conducted in two acidic (pH 1.3 and 3.8) slurries and one alkaline pH (10∼12) slurry with alumina particles as the abrasives. In acidic media with 0.1 M Fe(NO3)3 as a copper etchant and [1]H-benzotriazole (BTA) as an inhibitor, copper polish rate increases linearly with solids concentration in the polishing slurry. The polish rate increased linearly with increasing downward pressure and rotational speed with all of the above slurries. However, the Preston equation does not represent the polish rate data. Inclusion of an additional velocity term, representing the greater dependence of removal rate on the velocity and a constant, representing the purely chemical reactivity of the slurry which is, in general, higher than the static dip rate in the Preston equation, provided a more satisfactory representation of the data. The effect of the concentration of various slurry chemicals on the added constant term was investigated using a bench-top Struers DAP-V polisher. As expected, addition of BTA significantly reduces the value of this constant. Also some data on polish selectivity and the effect of alumina morphology are presented.