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

Abstract

The use of polyvinyl acetal (PVA) brushes is one of the most effective and prominent techniques applied for the removal of chemical mechanical planarization (CMP) contaminants. However, the brush can be a source of defects by entrapping the abrasives inside its porous structure during brush scrubbing. In this study, the effect of brush top skin layer was extensively studied on contamination, cross-contamination, and cleaning performance by comparing brushes with and without skin layer. The presence of a dense top skin layer resulted in larger contact areas and high ceria particle adsorption on the skin layer. This leads to higher cross-contamination of the wafers during scrubbing along with high cleaning performances. Conversely, the brushes without skin layer showed lower contamination and negligible cross-contamination with a reduced cleaning performance (removal of ceria particles from oxide surface). Therefore, the role of the brush skin layer is significant and needs to be considered while designing a post-CMP cleaning process.

Review—Post-Chemical Mechanical Planarization Cleaning Technology

“…However, the presence of the skin layer is necessary as it gives higher cleaning efficiencies. 64 Conventional brush break-in process (cleaning through pressurized water), 59 ultrasonic assisted physical break-in process (highly efficient) 65 or dipping in chemicals, 66 or scrubbing on dummy wafers 67 could be employed for the pretreatment of the incoming brush (brush conditioning) to avoid any contamination. Lee et al 56 compared different techniques and concluded that the ultrasonic-assisted physical break-in process is highly competent for rapid contaminant removal from the PVA brush.…”