Abrasive particle trajectories and material removal non-uniformity during chemical mechanical polishing

A mathematical model, a continuation of the work by Zhao et al. [1] that describes particle trajectories during chemical mechanical polishing, was extended to account for the effects of larger particles, particle location changes due to slurry dispensing and in-situ conditioning. Material removal rate (MRR) and within wafer non-uniformity (WIWNU) were determined based on the calculated particle trajectory densities in the absence of chemical activity from the slurry. The effect of pad-wafer rotary dynamics and reciprocating motion of the wafer carrier on MRR uniformity were included. It was also shown that in-situ conditioning improves the MRR uniformity of the polished wafers. Using the model, we also investigated the effect of particle size distribution and large particles (>200 nm in diameter) on WIWNU and scratch growth. It was shown that the presence of even 1 wt.% of larger particles can deteriorate the WIWNU.