Model Correlating Polishing to Abrasive Particle Friction for Chemical Mechanical Polishing

Abstract

Material removal (wear) mechanism models of the chemical mechanical planarization (CMP) on integrated circuits are incomplete. Models typically must assume that wear results from two-body abrasion from particles that are “pinned” between the pad asperity contacts and the substrate being polished. The contribution of the particles “swept” in front of the pad asperities possibly contributed by three-body abrasion is largely ignored. Modeling applied to the CMP friction measurements has recently separated the overall friction from the contributions of the pinned and swept particles while removing the confounding friction of the bare pad asperity to substrate contacts. This article extends these friction contributions to wear. This article proposes a novel model to identify the slurry particles affecting wear by interpreting experimental data of polishing friction and wear with novel variations of pad materials. This novel model extends a previous friction model by incorporating a modified Preston relation to isolate the wear done by the friction forces of pinned and swept slurry particles. Data were collected from pin-on-disk tribometer experiments performed on fused silica wafers with various polymer polishing pads and flooded with a silica nanoparticle slurry. The independent wear factors for the pinned and swept slurry particles were 5.1 × 10−11 m3/N·m and −6.3 × 10−12 m3/N·m respectively. It is concluded that wear occurs only from the pinned particle at pad asperity contact sites and that the swept particles do not meaningfully contribute to wear.