Analysis on Wafer Tilt Contributions to Contact Mechanics in Chemical Mechanical Polishing Process

A simple 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. The model provided is mainly based on the contact theories and tribology principles, as well as flow theories. The model provides an explanation for counter intuitive experimental results, i.e., the existence of negative fluid pressure (sub ambient 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 sub ambient area than the positive one is formed, due to the minor tilt of the wafer resulted from a moment resulting from the fluid pressure. The prediction accords with experiment results very well, which validates the model. The work will facilitate providing guidelines for the analysis of CMP mechanism and future applications.