Role of brush properties and pH on Cu ion-induced silica loading to polyvinyl acetal brushes during post-CMP cleaning

초록

Polyvinyl acetal (PVA) brush scrubbing is a critical post-chemical mechanical planarization (post-CMP) cleaning process in advanced semiconductor manufacturing. Despite their widespread application, PVA brushes are prone to contamination by colloidal silica, ceria particles, organic residues, and metal ions during their lifetime. This study elucidates the underlying mechanisms governing silica adsorption onto PVA brushes and the role of Cu ions in brush loading. The results indicate that silica loading is significantly increased under acidic conditions (pH = 3), primarily driven by electrostatic attraction between negatively charged silica species and the protonated brush surface. The presence of Cu ions promotes additional silica retention via chemisorptive interactions. The experimental data obtained from scrubbing tests on polished Cu wafers at pH 4 and 9 demonstrate increased silica contamination at lower pH conditions, which decreases with increasing pH. The influence of the brush hydroxyl functionality was further verified by employing brushes with different degrees of acetalization (DOA), where lower DOA brushes exhibited increased loading of both silica and Cu ions due to higher surface hydroxyl (–OH) availability. Additionally, brushes having a skin layer demonstrated greater silica particle retention than those without a skin layer. The dense skin layer acts as a barrier for the effective transport and release of contaminants. A comprehensive interaction mechanism involving physical and chemical interactions is proposed as the primary pathway for silica and Cu species retention within the PVA brush. © 2026

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