Study on PVA Brush Loading and Conditioning during Shallow Trench Isolation Post-CMP Cleaning Process

Abstract

Polyvinyl acetal (PVA) brush cleaning is a widely accepted and efficient cleaning process for removing contaminants of the CMP process during semiconductor processing. However, these contaminants can adhere to the PVA brush, due to its highly hydrophilic and porous nature, and can deteriorate brush performance. This contamination has become a serious problem especially for processing devices smaller than 10 nm. In this work, the effect of cleaning solution pH (2, 7, and 12) was investigated for ceria removal from oxide wafers and subsequent transfer to the PVA brush during scrubbing. A cleaning solution of pH 7 resulted in lower ceria removal efficiency compared to pH 2 and 12. The pH 2 and pH 7 cleaning conditions resulted in high brush loading (pH 2 > pH 7) compared to the pH 12 condition. High brush contamination at pH 7 further resulted in higher cross-contamination, whereas very low cross-contamination was observed at pH 2 and pH 12. For improvement of brush performance and lifetime, the effect of conditioning processes (ultrasonication and scrubbing) was evaluated. Scrubbing in the presence of NH4OH efficiently removed all ceria particles from contaminated brushes. Since the bonding between brush and ceria particles is strong, only a robust physical force combined with a high chemical action can remove ceria particles loaded onto a PVA brush.