Optimization of Dresser Shape in order to Improve Flatness and Life of Pad

Abstract

Surface of a polishing pad is shaved by using a rotating dresser in order to remove silicon scraps from the polishing pad. The dresser is held in a polishing apparatus touching with the rotating pad. In the first place, the motion of the dresser and the pad in the polishing apparatus was modeled mathematically in order to analyze the removal thickness of the pad. Distribution of removal thickness of the pad with an ordinary circular dresser was analyzed by using the mathematic model. The surface of the pad should be flat for flatness of silicon wafers. In the second place, a new oval-shaped dresser was proposed through the consideration of the circular dresser analysis. Finally a dresser shape optimization method was proposed in order to improve flatness of the pad. The Quasi-Newton method was used for the shape optimization. A penalty function was also used to take minimum removal thickness into consideration as constraints in the optimization. The optimized oval-shaped dresser gave better pad flatness and longer pad life.