Optimization of Material Removal Efficiency in Low Pressure CMP

Abstract

AbstractIn chemical-mechanical polishing (CMP) the material removal efficiency (MRE) can be defined as the fraction of the total pressure distributed on the abrasives, and it depends on the interplay between the direct contact of the pad-to-wafer, and the contact of the abrasives with the wafer. The MRE can be increased by minimizing pad-wafer direct contact, as this is not likely to help material removal, significantly. The objective of this work is to investigate parameters that control MRE. This may be especially important for low-pressure CMP used in the polishing of (ultra-low-k) ULK dielectric materials. The optimization of CMP parameters to maximize the MRE is described by modeling the contact interactions between pad, abrasives and wafer. A relationship for optimal abrasive concentration is presented for the external load values that mark the transition from pure pad-wafer-abrasive contact to mixed contact (combination of pad-wafer-abrasive and pad-wafer contacts) and for given pad porosity and pad surface parameters.