Combined Effects of PVA Brush Scrubbing Parameters and Processes on Post-CMP Cross-Contamination

Abstract

In post-chemical mechanical polishing cleaning, polyvinyl acetal (PVA) brush scrubbing is considered the most effective way to remove the abrasive particles remaining on the wafer surface after the CMP process. During cleaning, the brush can become contaminated by abrasives, and the brush loading can cross-contaminate the wafer. This study investigated the effects of brush cleaning parameters and processes on the cross-contamination magnitude of particles on wafers, focusing on the break-in process, brush gap distance, brush rotation speed, wafer rotation speed, de-ionized water (DIW) rinsing, DIW supply through the brush core, and nozzle position. The results showed that a break-in process and brush gap distance demonstrated that closer contact (up to -1.5 mm) drastically reduced contamination. Similarly, increased brush rotation speeds improved particle removal, reducing contamination to approximately 100 particles at 400 RPM as the wafer rotation speed initially decreased contamination at 100 RPM. The DIW rinsing after scrubbing and DIW through the brush core significantly reduced the particle count, emphasizing the importance of hydrodynamic forces in particle removal. Additionally, side DIW nozzles significantly mitigated contamination, with centrally positioned nozzles. This study provides new directions regarding brush cross-contamination in advanced nodes post-CMP scrubbing.