Analysis on Wafer Tilt Effects in CMP Process

Abstract

A preliminary one-dimensional model taking the wafer tilt into consideration is put forward in an attempt to facilitate the analysis of contact stress and flow features of chemical mechanical polishing (CMP) process, which is mainly based on the contact theories and tribology principles. The model provides an explanation for counter intuitive experimental results, i.e., the existence of negative fluid pressure (subambient pressure), and predictions of the pad substrate deformation, contact stress, and fluid pressure, etc. In CMP process, contact pressure will result in a divergence area in the leading part and a converging area in the trailing part, by which the larger subambient area than the positive one is formed, due to the minor tilt of the wafer resulted from an moments due to the fluid pressure. The prediction accords with experiment results very well, which validates the model.