Improvement of Material Removal Efficiency by Optimization of Anisotropic Contact of Pad Asperities

Abstract:
This paper presents a novel method to improve material removal efficiency by optimizing anisotropic contact of pad surface asperities. In chemical mechanical polishing process, asperities of the polishing pad surface affect material removal process indirectly. Past researchers have proposed several material removal models considering surface asperity. One of the models indicates interesting role of Feret’s diameter, where larger Feret’s diameter increases number of working abrasives, resulting in higher material removal rate. Based on Feret’s diameter model, an optimization method of the relative dress motion against the polishing pad is proposed by means of the dress simulation, where radial velocity component of the diamond dresser is maximized with respect to the tangential component. Three conditions, i.e., optimal (Cond. 1), worst (Cond. 2) and ordinary (Cond. 3), are compared in the present study. Analytical investigations clarified that the velocity ratio is improved significantly in Cond. 1, resulting in larger Feret’s diameter. Comparing with Cond. 2 and Cond. 3, not only the cumulative Feret’s diameter but also material removal rate are increased in Cond. 1. Hence, anisotropy control for pad asperities is effective to improve the material removal efficiency. Keywords: Material removal rate, Dress simulation, Pad asperity, Optimization, Feret’s diameter