US Patent 7137867 Thickness control method and double side polisher

The object of the present invention is to provide a thickness control method for a double side polisher, accuracy of which is not affected by wearing of polishing pad and applicable to polishing of nonconductive work pieces. An eddy current sensor in a cavity of an upper polishing plate measures distance from the senor to the upper surface of carrier with holes for the work pieces being inserted respectively. The measured distance is successively monitored and polishing is stopped when the distance has become a predetermined value corresponding to target amount of material removal from the work piece.