erosion

Erosion in CMP refers to the undesirable thinning of dielectric material in areas with dense metal pattern features, caused by the polishing pad conforming to and removing oxide between and over closely spaced metal lines. In dense pattern areas where metal lines are tightly packed, the effective polishing rate of the dielectric increases because the pad bridges across narrow oxide spaces, applying higher localized pressure. Erosion magnitude depends on pattern density (higher density = more erosion), line spacing, overpolish time, slurry selectivity between metal and oxide, and pad stiffness. Typical erosion values range from 200-800 Angstroms for copper dual-damascene processes at advanced nodes. Erosion directly impacts device performance by reducing the effective dielectric thickness (increasing capacitance between interconnect layers), thinning copper lines (increasing resistance), and creating thickness non-uniformity that affects subsequent lithography focus. Mitigation strategies include high-selectivity slurries (stop on barrier with minimal oxide removal), harder polishing pads (less pad conformality into pattern features), optimized overpolish times, dummy fill insertion (adding non-functional metal features to equalize pattern density across the die), and multi-step CMP processes that separate bulk removal from final planarization. Erosion is measured using profilometry or cross-section SEM on dedicated test structures with varying pattern densities.