Patent ID: 7534364

Claim:
A method of polishing, comprising: holding a substrate on a substrate mounting surface that is vertically movable relative to a rigid base of a carrier head in a chemical mechanical polishing apparatus; bringing the substrate into contact with a polishing surface; creating relative motion between the polishing surface and the substrate; and maintaining the substrate beneath the substrate mounting surface with a retaining ring that includes a generally annular lower portion having a bottom surface for contacting the polishing surface during polishing, and a generally annular upper portion having a bottom surface joined to the lower portion and a top surface fixed to and abutting the base such that the retaining ring is vertically fixed relative to the base, wherein the lower portion is made of a plastic and the upper lower portion is made of a metal which is more rigid than the plastic, and wherein the lower portion lacks any aperture from the top surface to the bottom surface of the lower portion.