Patent ID: 6876454

Claim:
An apparatus for chemical polishing (CMP) of a wafer, comprising: (a) a rotatable polishing platen to support a polishing pad, the platen having a hole formed therethrough and rotatably mounted to a chassis; (b) a polishing head for holding the wafer against the polishing pad and, (c) an endpoint detector, comprising, (c1) a stationary light source capable of generating a light beam directed towards the wafer from a side of the wafer contacting the polishing pad, (c2) a window disposed adjacent to the hole formed through the platen, the window rotating with the platen and intermittently providing a pathway for the light beam to impinge on the wafer during at least a part of a period of time when the wafer overlies the window, and (c3) a stationary detector to receive light from the light beam reflected by the wafer through the window.