Characterization of Pad–Wafer Contact Area and Distance in Chemical-Mechanical Polishing

Abstract

Chemical-mechanical polishing (CMP) has been an important process step in microelectronic device manufacturing for more than three decades. Physical CMP modeling utilizes the interactions between the polishing pad and the wafer. This requires data on important physical properties such as the real contact area and the effective pad-to-wafer distance under near-process conditions, as these are directly related to the removal rate, defects, etc. In the present study, a FTIR spectrometer and a custom ATR equipment with micro-structured single reflection elements (mSRE) were used to quantify the volume fraction and contact area of a IC1000 polishing pad in dry and wet state under different static loads. No stable contact over time was observed even at very high pressures of up to 350 kPa. Viscoelastic behavior of an air-dried and water-soaked pad was proven on a microscale by using load response, creep-recovery and stress relaxation tests. This leads to a memory effect of the pad that should be taken into account during dynamic loading as the wafer-pad contact has a direct impact on the material removal. The presented method can therefore provide valuable information about dynamic effects of the pad behavior in near-process environment and thus help to improve the CMP modelling.