US Patent 7435161 Multi-layer polishing pad material for CMP

The invention is directed to a multi-layer polishing pad for chemical-mechanical polishing comprising a porous polishing layer and a porous bottom layer, wherein the bottom layer is substantially coextensive with the polishing layer, the polishing layer being joined to the bottom layer without the use of an adhesive; the polishing layer having an average surface roughness, Ra, that is greater than the Ra of the bottom layer.