Optimization of Double-Sided Polishing Conditions to Achieve High Flatness: Consideration of Relative Motion Direction

Abstract

Silicon (Si) wafers are the most commonly used substrates of semiconductor devices. The device design rule is miniaturization, and the device chip size is being increased to improve device integration, requiring that Si wafers be manufactured with higher flatness and larger diameters. The polishing used as a finishing process of Si wafers, however, has a serious problem; it is very difficult to set the appropriate conditions for polishing the Si wafer while wearing the polishing pad stably to high flatness. In our previous work, a method of optimizing polishing conditions based on kinematical analysis was proposed to achieve high flatness of the wafer and pad. The method, however, did not consider the effect of the relative motion direction between the wafer and the pads as an important factor in polishing behaviors. Therefore, in this study, an optimization method considering the relative motion direction is newly developed, and a series of double-sided polishings of silicon wafers shows that the wafer flatness calculated by the method corresponds well with that in the polishing experiments. Furthermore, to make the distribution of pad wear more uniform, the optimization of polishing conditions, including the wafer carrier specifications, is conducted, and the feasibility is clarified.