Comparative evaluation of organic contamination sources from roller and pencil type PVA brushes during the Post-CMP cleaning process

Abstract

In post-CMP (chemical mechanical polishing) processing, the use of poly vinyl acetal (PVA) brushes to clean the wafer surface is one of the most effective and prominent techniques applied for the removal of CMP contaminants. Recently, organic contaminants induced in different types of PVA brushes during brush manufacturing have been drawing substantial research interest in CMP communities. In this study, investigated the root cause of these residual organic impurities in two different types of PVA brushes was investigated: roller and pencil type brushes. PVA roller brushes have a skin layer due to the brush molding process, but pencil-type PVA brushes do not have the skin layer. Extraction of organic impurities from both types of brushes was accomplished using an ultrasound-assisted technique at a sonication frequency of 40 kHz, and input power of 600 W. Further evaluation of these organic impurities using Field Emission Scanning Electron Microscopy (FE-SEM) revealed a large number of organic impurities in roller brushes and negligible impurities in pencil brushes. Time of flight secondary ion mass spectrometry (TOF-SIMS) analysis confirmed polydimethylsiloxane (PDMS) as the organic impurities extracted from PVA roller brushes, which were generated during the brush manufacturing process. The PDMS content in PVA roller brushes was further analyzed using FE-SEM micrographs via dissolving the organic impurities in tetramethylammonium hydroxide solution (TMAH). During brush fabrication, the high content of PDMS organic impurities in roller PVA brushes is essentially attributed to the presence of the additional skin layer formed by the mold releasing agent at the mold-cavity interface.