A mixed elastohydrodynamic lubrication model for simulation of chemical mechanical polishing with double-layer structure of polishing pad

Abstract

Mixed elastohydrodynamic lubrication (EHL) model has been used to study slurry flow and contact pressure distribution in the chemical mechanical polishing (CMP) process. However, in various mixed EHL simulation frameworks, only a single-layer polishing pad is considered. Consequently, the double-layer polishing pad, which is widely used in semiconductor industry, cannot be designed and optimized from the tribology perspective with the assistance of theoretical simulation. In this paper, multi-layered elastic theory (MLET), which is frequently used to calculate flexible pavement response to truck loading, is introduced into the mixed EHL model. Pad deformation calculated by the MLET has a similar accuracy to that by the 3D finite element method, but its computational cost is much lower. It is very important for accurate and efficient simulation of the tribological behavior and material removal rate (MRR) in CMP. Based on the new simulation method, advantages of a different double-layer structure of polishing pad are discussed. It is found that the upper-hard lower-soft pad has better performance for improving the uniformity of MRR when the wafer surface is uneven, but the boundary exclusion region is bigger than single-layer pad and upper-soft lower-hard pad. The upper-soft lower-hard pad has advantage to reducing the edge exclusion, but the effect is not remarkable when the thickness of the upper layer is not extremely thinner than the lower layer.