Polishing Pad Surface Morphology and Chemical Mechanical Planarization

Polishing pad surface morphology has been demonstrated to be an important parameter in the optimization of chemical mechanical planarization (CMP) processes. In this work, the mechanical behavior of the asperity layer of a polishing pad and its effect on CMP is modeled. A Greenwood-Williamson microcontact model describes the asperity contact with the wafer. The local strain fields on individual asperities are calculated and then averaged, and an average elastic modulus is extracted to describe the asperity layer. The asperities are assumed to behave as an effective layer subject to this average strain field. The model is implemented on a previously developed locally relevant removal rate model for CMP. Comparison of the modeling results with polishing results obtained using a commercial CMP system shows important improvements in removal rate and uniformity prediction on the wafer-scale.