Effects of mechanical parameters on CMP characteristics analyzed by two-dimensional frictional-force measurement

The effects of mechanical parameters on the characteristics of chemical mechanical polishing (CMP) were evaluated by directly measuring frictional force acting on a wafer in terms of two components, i.e., the tangential and axial components of the platen's rotation. It was found that, when the platen and the wafer were rotated at the same speed, the tangential component of the frictional force was dominant. Also, frictional force was in linear proportion with removal rate. Though frictional force increased in linear proportion to down force when mechanical-effect-dominant CMP for silicon (Si) or silicon dioxide (SiO2) was carried out, it decreased gradually as platen rotational speed was increased. Copper (Cu) polishing using abrasive-free polishing solutions, a typical example of chemical-effect-dominant CMP, showed much more complex behavior. Namely, dependence of frictional force on down force and on platen rotational speed showed nonlinear characteristics. Even when a nonlinear characteristic slurry was used, it was found that removal rate and frictional force were almost linearly correlated. It can thus be considered that frictional force is a basic parameter to determine CMP characteristics. From these results, an experimental equation was proposed to describe CMP characteristics by modifying Preston's empirical equation. (C) 2003 The Electrochemical Society.