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 process for removing contaminants of the chemical mechanical planarization process during semiconductor processing. However, contaminants can adhere to the PVA brush, due to its highly hydrophilic and porous nature, and deteriorates its performance. This contamination is a serious problem, especially for processing devices smaller than 10 nm. Here, the effect of cleaning solution pH 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 7 cleaning conditions resulted in high brush loading compared to the pH 12 condition. High brush contamination at pH 7 resulted in higher cross contamination, whereas very low cross-contamination was observed at pH 2 and 12. The effect of ultrasonication and scrubbing on improvement of brush performance and lifetime was evaluated. Scrubbing in the presence of NH4OH efficiently removed all ceria particles from contaminated brushes. Because 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.

Effect of Skin Layer on Brush Loading, Cross-Contamination, and Cleaning Performance during Post-CMP Cleaning

“…Ceria slurry (0.1 wt%) prepared at pH 4 was used for brush contamination experiments to facilitate electrostatic interaction between brush and ceria particles. 14 The brush nodules, with and without skin layers, were attached to the brush holder (Fig. 1) to investigate the effect of the skin layer on brush contamination.…”

“…The pH-dependent electrostatic interaction forces between ceria particles (removed from oxide wafer) and brush surface and its subsequent effect on these abrasives loading over the PVA brush was reported. 14 Despite these yield-reducing issues, less attention has been put on the systematic study to consider the effect of the brush skin layer on brush-abrasives interaction resulting in entrapment of abrasives in brush porous structure during scrubbing (transfer of abrasives from contaminated wafers to brush). Some reports confirm that the skin layer of the brushes provides higher friction forces due to the larger contact areas and leads to higher brush deformations.…”