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An analytical model for dishing and step height reduction in chemical mechanical planarization (CMP) is presented. The model is based on the assumption that at the feature scale, high areas on the wafer experience higher pressure than low areas. A Prestonian material removal model is assumed. The model delineates how dishing and step height reduction depend on slurry properties (selectivity and Preston's constants), pad characteristics (stiffness and bending ability), polishing conditions (pressure, relative velocity and overpolishing) and wafer surface geometry (linewidth, pitch and pattern density). Model predictions are in good agreement with existing experimental observations. The present model facilitates understanding of the CMP process at the feature scale. Based on the proposed model, design avenues for decreasing dishing and increasing the speed of step height reduction may be explored through modification of appropriate parameters for slurry, pad and polishing conditions. The proposed model may also be used as a design tool for pattern layout to optimize the performance of the CMP process.
Date of Publication: Aug. 2003