Patent ID: 7275856

Claim:
An apparatus for forming a striation-reduced chemical mechanical polishing pad, comprising: a first delivery line for delivering a polymeric material into a mixer; a second delivery line for delivering microspheres having an initial bulk density into the mixer with the polymeric material, the second delivery line being connected to a bulk density control unit, the bulk density control unit comprising: a storage hopper for storing the microspheres, wherein the storage hopper further comprises a porous membrane provided over a plenum and an agitator to facilitate fluidization of the microspheres in the storage hopper; a fluidizing gas source connected to the plenum through a gas inlet line; and a recirculation loop for recirculating the microspheres and controlling bulk density of the microspheres, wherein the recirculation loop has a mass flow sensor for measuring a continuous bulk density of the microspheres passing therethrough, and controlling the bulk density, wherein gas fed into the plenum from the fluidizing gas source permeates through the porous membrane and adjusts the initial bulk density of the microspheres in the storage hopper.