Study for removing of silica nanoparticle in pure isopropyl alcohol with a cation exchange membrane

Abstract

Semiconductors are becoming increasingly miniaturized and structurally complex. During their manufacture, isopropyl alcohol (IPA), which has a low surface tension, is often used to prevent structural corruption during cleaning. A previous study examined the removal of impurities (silica nanoparticles (SNPs)) in IPA/water solutions using an anion exchange membrane and reported the removal mechanism. That study found that SNP removal in high ratio IPA was difficult. In the present study, SNP removal in IPA was tested using three different cation exchange membranes, and the differences in their removal performance were evaluated. Zeta potential measurements and molecular dynamics (MD) simulations were performed to elucidate the removal mechanism, and membrane surface-SNP interactions were evaluated by atomic force microscopy (AFM). The zeta potential of the cation exchange membrane in IPA was positive. The reason for this phenomenon is discussed based on the results of MD simulations. The results suggested that Na+, which is the counter ion in the ion exchange group, remains near the membrane surface. The difference in the removal ratio between the cation exchange membranes was examined by AFM, suggesting that the tentacle effect of the graft chains on the surface suppressed the re-desorption of SNPs once adsorbed, contributing to the high removal ratio. These results are expected to contribute significantly to developing membranes with a high removal ratio of SNPs in IPA.