planarization efficiency

Planarization efficiency quantifies how effectively CMP removes topography and creates a flat surface, expressed as the percentage reduction in step height between high and low features after polishing. It is calculated as: PE = (initial_step_height - final_step_height) / initial_step_height × 100%. A PE of 100% means perfect planarization (completely flat surface), while lower values indicate residual topography. Planarization efficiency depends on pad stiffness (stiffer pads bridge over features providing better global planarization but worse local conformality), slurry chemistry and selectivity, downforce pressure, pattern density and pitch, and the relative heights of features. For oxide ILD CMP, typical PE values exceed 95% for isolated features but may drop to 80-90% for dense arrays. High PE is critical for subsequent lithography steps—residual topography causes depth-of-focus issues at advanced nodes where DOF budgets are extremely tight (< 100nm at sub-7nm nodes). CMP recipes are optimized to maximize PE across all pattern types simultaneously, often requiring multi-step processes where different conditions address global vs. local planarity. PE is measured using profilometry or AFM scans across step-height test structures before and after CMP.