Next-Generation Nanoporous PTFE Membrane

Sumitomo Electric Industries, Ltd. invented a technique to make polytetrafluoroethylene (PTFE) porous using PTFE stretching technology, which was patented in 1962.(1) Drawing on the technique, the company has subsequently released various porous PTFE products such as filters and hollow fiber products under the trade name of POREFLON. Porous PTFE filters, one of these porous PTFE products, use sheet-type porous PTFE membranes that have numerous micropores with a diameter of 10 μm or less. Taking advantage of their excellent chemical resistance, they have been used as microfiltration membranes in obtaining high-purity chemical solutions in the manufacturing processes of semiconductors, liquid crystal panels, and other electronic components. Porous PTFE membranes are also used to produce electrical wire insulating material due to their low dielectric properties and are used as gas permeable and waterproof films for automobiles and electronic components due to their excellent water repellency and gas permeability. Water treatment membrane modules, a porous PTFE hollow fiber product, are used for treatment of industrial wastewater and water treatment in food industries.(2) A porous PTFE membrane filter that has excellent chemical resistance, heat resistance, and non-elution properties is an essential component for the filtration of acidic or alkaline chemical solutions used in the manufacturing processes of semiconductor wafers, liquid crystal panels, and other electronic components. In the semiconductor industry, in particular, the development of higher density chips and wafers with a larger diameter increases the necessity of obtaining higher-purity chemical solutions to clean wafers. The need for porous PTFE membrane filters, which can remove minute foreign substances, has been increasing. We have developed a new technology that can replace the conventional stretching technology to create nanoporous PTFE membranes. This paper describes this unique technology for generating pores with a diameter of less than 50 nm, which cannot be generated by conventional technology. 2. Technology Trends and Development Goals for Liquid Filtration Membranes in Semiconductor Manufacturing