Mixed Strategy Combination of Pressure and Velocity Control for Chemical Mechanical Planarization of Patterned Wafers

Abstract

The Preston equation suggests interoperability of material removal rate (MRR) by either pressure or velocity. Traditionally, planarization is pursued by pressure control. A novel velocity control strategy for a single step on a blanket wafer is recently proposed. The effectiveness of both strategies on patterned wafers is numerically investigated here, using the MIT Mask layout. Superiority is observed to be pattern dependent, scaling with MRR and material choice. However, improved quality at feature scale induces deterioration at the die scale. Scratch generation propensity, which is a micro- or even nano-scale phenomenon, is typically invariant to macro-level control strategies. A mixed control strategy produces better results in terms of finish quality and productivity, by attaining the targeted local and global planarization in less polishing time, compared to individual strategies.