Process for preparing a polyurethane urea polishing pad

A process for preparing a polyurethane urea pad adapted to polish a microelectronic substrate, the pad comprising at least partially gas-filled cells substantially uniformly distributed throughout the pad, the process comprising:

• (1) providing a polyurethane prepolymer in a first feed of a mixing unit, said polyurethane prepolymer comprising the reaction product of a polyisocyanate and a hydroxyl-containing material;
• (2) providing an amine-containing material in a second feed of a mixing unit
• (3) forming a reaction mixture by adding the polyurethane prepolymer and the amine-containing material into the mixing unit;
• (4) mechanically mixing the reaction mixture at a pressure of less than 20 bar;
• (5) dispensing the reaction mixture into an open mold;
• and
• (6) curing the reaction mixture to form a polyurethane urea, wherein the at least partially gas-filled cells comprise carbon dioxide produced by the reaction of the mixture components.