Patent ID: 7662025

Claim:
A polishing apparatus comprising: a polishing pad configured to polish a wafer; a polishing head configured to hold the wafer, said polishing head comprising: a retainer ring for retaining the wafer in an in-plane direction of the wafer, said retainer ring comprising: a first member depressed toward said polishing pad by a head body, said first member having a substantially ring shape and an inner diameter and thickness respectively greater than an outer diameter and thickness of the wafer; and a second member interposed between an inner edge of said first member and a periphery of said wafer to retain said periphery of said wafer in the in-plane direction of the wafer, said second member having a thickness substantially equal to the thickness of the wafer; a membrane sheet for depressing the wafer and said second member toward said polishing pad; and said head body supporting thereon said retainer ring and said membrane sheet; and an edge-depressing ring member having a diameter less than a diameter of the second member disposed within the head body and directly above the periphery of the wafer, wherein the edge-depressing member depresses only a portion of the membrane sheet and only the periphery of the wafer.