Maximum Scratch Width in Chemical-Mechanical Polishing

摘要

This paper presents lower- and upper-limits to the width and depth of scratches in CMP. First, single-particle models that use elastic and plastic analyses for the lower- and upper-bound loads are summarized [1]. Then, multi-particle models are presented for the elastic and plastic deformation of the pad asperities. These models use contact mechanics at the pad/particle and particle/coating interfaces to relate the global CMP parameters (pressure, particle radius, slurry volume fraction, and the mechanical and geometrical properties of the pad and the coating) to the width and depth of scratches. Using these models, lower- and upper-limits for the scratch width and depth are established. The upper-limit for the semi-width of a scratch is the product of the particle radius and the square-root of the ratio of pad hardness to coating hardness. For typical CMP pads and coatings, this upper-limit is one-fifth of the particle radius. Additionally, polishing experiments have been conducted to preliminarily validate the limits. Finally, based on the models and the experiments, practical solutions for mitigating scratching in CMP, especially low-k CMP, are suggested.