Effect of slurry particles on PVA brush contamination during post-CMP cleaning

Abstract

PVA (polyvinyl acetal) brush scrubbing is a widely used post-CMP cleaning process due to its low cost and high cleaning efficiency. However, during these processes, the PVA brush gets contaminated with abrasive particles that result in wafer cross-contamination and reduced cleaning efficiency. This study investigated the effects of abrasive types such as silica and ceria, the slurry pH, and the scrubbing process parameters on brush contamination. Ceria slurries showed significantly more contamination of brushes compared to silica slurries. The brush contamination increased with a decrease in pH from 7 to 4 due to increased electrostatic attractive forces between the ceria particles and the brush surfaces, although very low brush contamination was observed by the ceria slurries at pH 10 due to a strong electrostatic repulsion. Conversely, very low brush contamination was observed for the silica slurries at all pH values due to the reduced interaction between the particles and the brush surface (electrostatic repulsion). Furthermore, there was no significant effect of gap distance and brush rotation speed on brush contamination. The abrasive concentration and the contamination process time showed a linear relationship as the contamination was significantly increased by increasing the abrasive concentration in slurry and process time. These results indicate that brush contamination is more sensitive to the abrasive nature and concentration, the slurry pH, and the process time than to other parameters.