Nonuniformity of material removal in a double-sided polishing process: Formation of convex curves

Abstract

In a double-sided polishing (DSP) process, a workpiece typically takes on a convex shape due to the nonuniformity of material removal in the radial direction. This convexity causes significant difficulties in satisfying the required surface flatness for workpieces, especially in the manufacture of silicon wafers. However, the reason for the nonuniformity of material removal is unknown, resulting in no theoretical approach for solving the convexity. This study aims to provide an understanding of the cause of the above typical DSP results regarding global workpiece shape and construct guiding principle for determining better DSP conditions in terms of solving the convexity. To that end, this study explores the radial distribution of relative speed between a workpiece and polishing pads because the relative speed is the primary factor that determines material removal. The relation between DSP conditions and the radial uniformity of the relative speed is investigated analytically. The findings are used to construct an indicator as guiding principle for determining DSP conditions to obtain additional uniform relative speed in the radial direction.