Thickness control method and double side polisher

A double side polisher comprising:

• a lower polishing plate rotatably supported on a machine base and comprising a polishing pad disposed on an upper surface thereof;
• a sun gear comprising external teeth and rotatably supported on the machine base;
• an internal gear comprising internal teeth and rotatably supported on the machine base;
• a carrier comprising external teeth for engaging with the external teeth of the sun gear and the internal teeth of the internal gear and having holes for work pieces to be inserted therein;
• an upper polishing plate, comprising a polishing pad disposed on a lower surface thereof and configured to apply a polishing pressure to the work pieces inserted in the holes, the upper polishing plate being rotatably supported on the machine base;
• a drive system for rotating the upper and lower polishing plates, the sun gear and the internal gear around the same axis;
• a slurry supplying unit for supplying a slurry to the work pieces;
• a timer for measuring a polishing duration time;
• a distance sensor mounted in a cavity of the upper polishing plate for measuring a distance from the distance sensor to an upper surface of the carrier;
• and
• a control unit configured to control the double side polisher so that a polishing operation for work pieces belonging to a first polishing group to start and finish starts and finishes based on the polishing duration time measured by the timer, a first calibration of the distance sensor is performed based on a difference between a thickness of the work pieces of the first polishing group calculated from the distance measured by the distance sensor and a thickness of the polished work pieces of the first polishing group measured by an external thickness measuring apparatus, a polishing operation for work pieces belonging to a second polishing group starts and finishes based on the distance measured by the calibrated distance sensor, and a second calibration of the distance sensor is performed based on a difference between a thickness of the work pieces of the second polishing group calculated from the distance measured by the distance sensor and a thickness of the polished work pieces of the second polishing group measured by the external thickness measuring apparatus.