Analysis of formation of pad stains in copper chemical mechanical planarization

A stain model was developed to simulate stain formation on the pad surface in copper chemical and mechanical planarization (CMP). The model consisted of the incompressible Navier-Stokes equations, the heat equation with advection, material removal rate model, a model for generation, transport and deposition of the polishing by-product that produces the stain. Slurry velocity simulations showed shear flow on the land areas and wafer-driven circulation in the grooves. The simulated temperature on the pad and the wafer surface increased gradually in the radial direction; furthermore, temperature simulations showed a 12 °C rise in the reaction temperature on the copper wafer surface. The simulated pad stains deposited on the copper land areas were darker in the direction of wafer rotation, suggesting that the generated staining agents were advected downstream by the slurry flow and deposited on the pad surface in the direction of the wafer rotation. Simulated stain images were in qualitative agreement with experimental results.