Comparison of microfiltration performances of ePTFE and PCTE membranes in IPA and deionized water

Abstract

Isopropyl alcohol (IPA) is widely used as a cleaning and drying agent in semiconductor manufacturing. The purity of chemicals is becoming increasingly stricter as the leading-edge node sizes become smaller. The microfiltration of nanoparticles (NPs) in water has been extensively studied by many research groups. However, studies on microfiltration in IPA are rare. In this study, we conducted experiments to determine the filtration of nanoparticles using expanded polytetrafluoroethylene (ePTFE) and polycarbonate track-etched (PCTE) membranes in both deionized water (DIW) and IPA. The zeta potentials (ZP) of the polymers and particles were measured. The Hamaker constant and its effect on particle capture were estimated using Derjaguin–Landau–Verwey–Overbeek theory. The results show that the retention efficiency of the two membranes (five different pore sizes) for Ag NPs (size: 20–100 nm) in IPA was much higher than that in DIW. However, the retention efficiencies of the two membranes in IPA and DIW increase monotonically upon increasing the particle size, which was completely different from the U-shaped curve for aerosol filtration predicted using the previous liquid model. In addition, the absolute ZP value of the NPs and membrane surface in IPA was found to be much smaller than that of DIW.