Effect of Viscoelastic Characteristics on the Real Contact Area of Polishing Pad Surface

Abstract

Real contact area (RCA) between polishing pad and workpiece surface is one of the most important parameters indicating the mechanical action strength of chemical mechanical polishing (CMP), which has a dominated effect on the material removal. However, the effect of pad viscoelastic characteristics on RCA is not clear. In this study, a contact status measurement device that can apply cyclic load and record contact images is developed to study the viscoelastic behavior of the pad and its influence on RCA. The results show that when the pad undergoes cyclic compression load during CMP, the pad asperity layer gradually accumulates viscoelastic deformation and the RCA increases obviously, which can be mostly recovered after a long time. In particular, the accumulation and recovery of viscoelastic deformation lead to a significant change of the relationship between RCA and pressure, from linear to nonlinear and then to linear. Furthermore, an RCA model is established based on the viscoelastic constitutive model of pad and the mathematical relationship between RCA and pad deformation to explain the influence of pad viscoelastic behavior on RCA. This study is expected to provide new insights into RCA, and to give support for predictive control of the material removal during CMP.