Patent ID: 7414080

Claim:
A method of forming a polishing pad suitable for planarizing semiconductor substrates comprising the steps of: casting polyurethane polymeric material, a curative agent and expandable polymeric microspheres in a mold of a cake, the polyurethane polymeric material being from a prepolymer reaction of a prepolymer polyol and a polyfunctional aromatic isocyanate to form an isocyanate-terminated reaction product, the polyfunctional aromatic isocyanate having less than 1 weight percent aliphatic isocyanate and less than 0.5 weight percent free isocyanate monomer, the isocyanate-terminated reaction product having 4.5 to 8.7 weight percent unreacted NCO and an OH or NH 2 to unreacted NCO stoichiometric ratio of 80 to 110 percent, and the expandable polymeric microspheres containing pre-expanded or expanded in situ microspheres; gelling the isocyanate-terminated reaction product with a gel time sufficient to control porosity distribution from the expandable polymeric microspheres in the mold; limiting exotherm of the cast isocyanate-terminated reaction product to a temperature below 120° C. to control density uniformity of the expandable polymeric microspheres within polishing pads from the cake and maintain average volume of the expandable polymeric microspheres in the polishing pads within 7 percent of average volume of the expandable polymeric microspheres before casting; curing the gelled isocyanate-terminated reaction product with the curative agent and the expandable polymeric microspheres within the isocyanate-terminated reaction product to form the cake, the curative agent being selected from the group comprising curative polyamines, curative polyols, curative alcoholamines and mixtures thereof; and skiving the cake to form the polishing pads; and the polishing pads containing a porosity of 0.1 to 70 volume percent from the expandable polymeric microspheres, the expandable polymeric microspheres having a weight average diameter of 10 to 100 μm and the polishing pads having a density of 0.6 to 1.15 g/cm 3 .