Investigation of Particle Kinetic Energy for EKF-CMP Process

Abstract

The particle kinetic energy (PKE) in a slurry film between the pad and wafer during chemical-mechanical polishing (CMP) under the assistance of electro-kinetic force (EKF) was investigated. Novel simulation results of a three-dimensional electro-osmosis flow (3D-EOF) model have been well-verified by velocity fields of particle image velocimetry analysis. The velocity magnitudes of EOF under various simulation conditions have been compared with both experimental and theoretical results. Analysis results for PKE indicate that the PKE value at the top layer is smaller compared to that at the bottom layer due to dissipating PKE in the interactions between the abrasive nanoparticles and the wafer surface. Effective nanoparticle kinetic energy contacting the wafer surface increased with increased electrode voltage and achieved an optimal value at an electrode gap of 2000 μm. Compared with our previous study at a down pressure of 1.5 psi, the optimized polishing performance for a Cu blanket wafer at a loading pressure of 2.5 psi improved 0.32 % for material removal rate, 10.8 % for non-uniformity, and 2.14 %, 3.87 %, 8.1 %, and 8.32 % of surface roughness for Sa, Sq, Ra, and Rq, respectively. The results explain the significant role of kinetic energy affecting abrasive nanoparticles's motion speed contacting the wafer to achieve an ultra-smooth surface for IC fabrication.