Ultrasound-induced break-in method for an incoming polyvinyl acetal (PVA) brush used during post-CMP cleaning process

The presence of particle contamination on a wafer surface is one of the most critical issues performed by chemical mechanical planarization (CMP) and post-CMP cleaning processes. Among the various sources of contaminations, an incoming polyvinyl acetal (PVA) brush generates fine impurities in the form of particulate residue during post-CMP cleaning. This study deals with removal of this particulate residue from the incoming PVA brush via a new ultrasound-assisted physical break-in process. Strong microturbulence and shock waves generated during the ultrasound-assisted cleaning process removed the particulate residue present in the incoming PVA brush in a short cleaning time of 5 min. A detailed study involving the effects of ultrasound frequency and input power and change in dissolved gas ratio was investigated on particulate residue using a liquid particle count test. Among the variously used ultrasonic parameters, a frequency of 40 kHz and an input power of 600 W showed the highest particulate residue removal from the incoming PVA brush without damaging the brush morphology. This removal of impurities from the brush is essentially attributed to the physical effect of ultrasound and cavitation due to generation of strong microturbulence and shock waves during the PVA brush cleaning process.