Elasto-partial hydrodynamic contact model for chemical mechanical polishing

Chemical mechanical polishing (CMP) has become a primary technique for the planarization of semiconductor wafers in submicrometer device fabrication. Increasing demands for high uniformity and dimensional precision make previously discountable levels of asperity, powder slurry, and wafer-pad contact significant. In this study, an improved model considering both the elastic microcontact mechanism and the grain flow with roughness effects is proposed. The model applies the average lubrication equation with the partial hydrodynamic lubrication theory and elastic microcontact theory proposed by Greenwood and Williamson. The external force acting on the wafer is supported by the partial hydrodynamic slurry pressure in the noncontact area and the surface asperity contact force in the contact area. This model predicts slurry flow film thickness under a variety of the CMP parameters, including applied load, rotation speed, particle size, and pad roughness. The results compare well with experimental data in the literature. Furthermore, the contact ratio of area and removal rate are studied and discussed. (c) 2006 The Electrochemical Society.