Tribological approaches to material removal rate during chemical mechanical polishing

In this study, the effect of the friction and wear of a polishing pad on the material removal rate of a silicon oxide wafer was investigated during chemical mechanical polishing (CMP) with ceria slurry. Further, the effect of surface properties of the polishing pad, such as surface roughness and hardness, on the variation in the material removal rate was examined. From a tribological viewpoint, the in-situ friction force was monitored during the CMP process, and wear of the polishing pad was controlled by different types of conditioners. After CMP, the pad surface roughness was measured by optical profiling and scanning electron microscopy. Experimental results showed that the material removal rate was almost linearly proportional to the friction force between the pad and the wafer surface, irrespective of the properties of the pad. Experiments on the dependency of the pad wear rate on the material removal rate showed that the material removal rate increased with a decrease in the pad wear rate. Experiments and pad characterization confirmed that such a correlation was attributed to the pad surface roughness and the friction force.