Improvement of Material Removal Rate and Within Wafer Non-Uniformity in Chemical Mechanical Polishing Using Computational Fluid Dynamic Modeling

Chemical mechanical polishing (CMP) is a widely used technique in semiconductor manufacturing to achieve a flat and smooth surface on silicon wafers. A key challenge in CMP is enhancing the material removal rate (MRR) while reducing within-wafer non-uniformity (WIWNU). A computational fluid dynamics (CFD) model is employed to analyze the slurry flow between the wafer and the polishing pad. Several factors influence the CMP process, including the type of abrasives, slurry flow rate, pad patterns, and contact pressure distribution. In this study, two polishing pad patterns with concentric and radial grooves are proposed to address how morphology variations influence wafer removal rate and consistency. Under the same operating conditions, the CFD simulations show that (i) the radial grooves have higher wall shear stress, a more significant negative pressure region, and a more evenly distributed mass on the wafer surface than the concentric grooves, and (ii) the radial grooves exhibit superior slurry mass distribution. It is noted that reducing the negative pressure differential field area results in a less pronounced back-mixing effect. A comparison of radial and concentric polishing pad grooves reveals that radial grooves improve slurry distribution, reduce the slurry saturation time (SST), and increase wall shear stress, leading to higher MRR and improved non-uniformity (NU). Precisely, the errors between the experimental SST values of 21.52 s and 16.06 s for concentric circular and radial groove pads, respectively, and the simulated SST values of 22.23 s and 15.73 s are minimal, at 3.33% and 3.35%.