Apparatus for forming a polishing pad having a reduced striations

摘要

The present invention provides an apparatus 20 for forming a striation-reduced chemical mechanical polishing pad 4 . The polishing pad 4 comprises a first delivery line 66 for delivering a polymeric material 52 into a mixer 68 and a second delivery line 44 for delivering microspheres 48 into the mixer 68 with the polymeric material 52 . The second delivery line 44 is connected to a bulk density control unit 21 . The bulk density control unit 21 comprises a storage hopper 22 for storing the microspheres 48 . The storage hopper 22 further comprises a porous membrane 24 provided over a plenum 26 . A fluidizing gas source 23 is connected to the plenum 26 through a gas inlet line 27 . Gas 28 fed into the plenum 26 from the fluidizing gas source 23 permeates through the porous membrane 24 and reduces the initial bulk density of the microspheres 48 in the storage hopper 22.