Method of forming a polishing pad having reduced striations

A method of forming a chemical mechanical polishing pad, comprising:

• providing a tank with polymeric materials;
• providing a storage hopper with hollow polymeric microspheres having an initial bulk density, wherein the storage hopper further comprises a helical agitator and a porous membrane provided over a plenum;
• providing a recirculation loop for recirculating the hollow polymeric microspheres and controlling the bulk density of the hollow polymeric microspheres, wherein the recirculation loop has a mass flow sensor for measuring a continuous bulk density of the hollow polymeric microspheres passing therethrough,
• connecting a fluidizing gas source to the plenum through a gas inlet line;
• fluidizing the hollow polymeric microspheres by feeding a fluidizing gas from the fluidizing gas source into the plenum through the porous membrane into the storage hopper and thereby reducing the bulk density of the hollow polymeric microspheres below the initial bulk density;
• providing a delivery system for delivering the polymeric materials and the hollow polymeric microspheres having a bulk density below the initial bulk density to a mixer;
• forming a mixture of the polymeric materials and the hollow polymeric microspheres;
• pouring the mixture into a mold to a form a molded product;
• and
• cutting the molded product into the polishing pad.