The mechanical effect of soft pad on copper chemical mechanical polishing

Abstract

Smaller transistor size challenges traditional chemical mechanical polishing (CMP) in semiconductor fabrication. Novel consumables and in-depth mechanism research can support defect mitigation and improve yield. This study focused on soft pad polishing of copper film from the perspective of mechanical effects. To reduce the defects, a soft pad is replacing the hard pad in the barrier layer polishing and over-polishing steps of copper CMP. When the contact behavior of pad asperity and wafer was in the elastic-plastic regime, the exponential influence factors of pressure, abrasive concentration, and sliding velocity on the material removal rate (MRR) were around 0.64, 0.22, and 0.64, respectively. Stick-slip friction with squeal noise scratched the copper film at the beginning and end of the CMP process. The pad conditioning removed polishing residues but deflected the pad asperity. Proper conditioning frequency is necessary to optimize the polishing process.