Abstract
A soft EHL analysis model of Chemical Mechanical Polishing (CMP) is developed in the present study. Since a surface of a polishing pad is filled with micro asperities due to conditioning, the polishing pad deforms in a nonlinear manner by contacting to a wafer. A viscosity of the polishing pad also affects stress concentration beneath the edge of the wafer. In order to take into account both effects, damping behavior of the polishing pad and macroscopic characteristics of the polishing pad asperity deformation are considered at the same time in the proposed analysis. Based on the traditional contact model, i.e., Greenwood-Williamson model, nonlinear elasticity of the surface asperity layer of the polishing pad is formulated, and Arbitrary Lagrangian-Eulerian (ALE) method is applied to deal with dynamic structure analysis. A series of three-dimensional EHL analysis was conducted using the proposed model. Effects of viscosity of the polishing pad and the nonlinear elasticity caused by the polishing pad asperities on distributions of contact stress and fluid pressure were examined. Analytical results indicated that both distributions greatly depend on the viscosity and the nonlinear elasticity of the polishing pad, and thus the consideration of nonlinear viscoelastic behavior in the pad-wafer contact is important to predict the polishing pressure distribution, especially beneath wafer leading edge.
