US Patent 6890249 Carrier head with edge load retaining ring

A carrier head for chemical mechanical polishing of a substrate having a front surface, a back surface and an edge. The carrier head has a base, an inner retaining ring positioned beneath the base, and an outer retaining ring surrounding the inner retaining ring to retain the inner retaining ring. The inner retaining ring has a main portion with a first surface to apply a load to a perimeter portion of the back surface of the substrate and an annular lower projection protruding downwardly from the main portion with a second surface to circumferentially surround the edge of the substrate to retain the substrate.