A Material Removal Model for CMP Based on the Contact Mechanics of Pad, Abrasives, and Wafer

Abstract

Applied pressure in chemical mechanical polishing (CMP) is shared by the two-body pad–wafer and the three-body pad–abrasive–wafer contacts. The fraction of applied pressure transferred through the particle contacts is a significant factor as most of the material removal is due to abrasive particles trapped in the pad–wafer interface. In this work, the contact of a rough, deformable pad and a smooth, rigid wafer with rigid particles in the contact interface is investigated by using contact mechanics and finite element modeling. The interactions between the pad, wafer, and abrasive particles are modeled at different scales of contact, starting from the particle–pad level and gradually expanding to the multiasperity contact of the pad and the wafer. Wear rate due to each abrasive particle is calculated based on the wafer–abrasive particle contact force and by considering adhesive and abrasive wear mechanisms. A thin passivated layer on the wafer surface is modeled to consider the effect of chemical reactions between slurry and wafer. Good agreement between the model and the experimental literature is found for the relationships between material removal rate and applied pressure, pad elastic modulus and porosity, particle size and concentration, and pad roughness and wafer hardness.