A Water Polishing Process to Improve Ceria Abrasive Removal

Abstract

This study details the improved ceria abrasive removal on SiO2 wafer during the post CMP water polishing (buff clean) process. Initially, the zeta potentials of the wafer and ceria abrasive were measured according to pH and compared with the zeta potential and pH change during water polishing. From these measurements, it was determined that the zeta potential difference between the ceria abrasive and the wafer decreased during water polishing. The electrical repulsion between them decreased as well. Additionally, ceria abrasive removal was measured using a surface defect inspection system. The abrasive removal increased when water polishing conditions such as pressure, rotation speed and processing time increased. Chemical enhancement and a pad cleaning process also increased the ceria abrasive removal. Consequently, the total defect counts were reduced by 91.8% with the optimized water polishing condition. These results provide useful data for determining optimal water polishing conditions for more effective post CMP cleaning.