No abstract

This study aims to develop a three-dimensional electro-osmosis flow (3D-EOF) cell model for effective particle analysis on the wafer at steady-state under electro-kinetic force (EKF) assistance during chemical mechanical polishing/planarization (CMP). A simulation software is used to simulate the abrasive particle motion with three functional modules including the electric current, the laminar flow, and the particle trajectories. Parameter designs of various simulation conditions such as electrode gap spacing, direct current voltages, and polishing pad thickness have been investigated to analyze the motion of silica abrasive nanoparticles due to EOF. Simulation results of the EOF velocity of slurry flow circulation in different conditions have compared with theoretical calculation results. Results have shown that the total number of effective particles intensifies significantly with increasing electrode voltage, but decreases in both cases as raising electrode gap and larger pad thickness. Experimental results of EKF-CMP process can improve 25.03%, 2.52 nm, 1.39% for material removal rate (MRR), surface roughness, non-uniformity, respectively. It can explain that the wafer surface polishing qualification is significantly by motion of effectual abrasive particles. Results of this study can be extended to contribute to improvement and optimization of EKF-CMP process for Copper CMP process used in IC fabrication.

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.