Mechanical interactions and their effects on chemical mechanical polishing

Mechanical interactions, such as contact stress and fluid pressure are of e xtreme importance in silicon wafer polishing, especially for the wafer-scal e planarity of the finished surfaces. In this paper, the measurements of in terfacial fluid pressure and friction, as well as their dependence on some major process variables, are presented. A nonuniform subambient fluid press ure was measured, and the resulting wafer/pad contact stress, obtained by c ombining the effects of both applied normal load and interfacial fluid pres sure, is determined. An analytical model was developed to predict the magni tude and distribution of the interfacial fluid pressure. The results of pol ishing experiments show good evidence of the effects of this subambient flu id pressure on with in-wafer nonuniformity (WIWNU). By properly designing t he polishing process variables, the fluid pressure may be tailored, and a r elatively uniform material removal can be achieved.