Experimental and Numerical Analysis of Slurry Flow in Chemical Mechanical Polishing

A slurry flow field in chemical mechanical polishing (CMP) was analyzed by using particle image velocimetry (PIV) and numerical simulations. PIV experiment for analyzing the CMP hydrodynamic regime is a novel approach and the first to combine both experimental measurements and numerical simulations. The quality of CMP in semiconductor production is characterized by its output properties, such as its removal rate (RR) and nonuniformity (NU). The nonuniformity of the wafer surface is due to the irregularity of the material removal rate across the wafer's surface and both NU and RR problems result from an uneven slurry flow distribution on the wafer surface. The slurry flow field was studied on the wafer scale under various pad and carrier rpm conditions. Direct measurement of the slurry flow field was first applied to the CMP process by adequately modifying a conventional PIV system. A numerical simulation was carried out for the validation of the current analysis and for future use under various CMP conditions. The analysis showed that the flow speed was strongly influenced by the pad velocity and that the overall flow field was characterized mainly by the ratio between the pad rpm and the carrier rpm.