Membrane based system for ultrapure hydrofluoric acid etching solutions

Abstract

The use of membranes to reprocess thousands of tons of hydrofluoric acid (HF) etching solutions per year is different from all previous applications of reverse osmosis (RO) and opens new opportunities for membrane based technologies. This novel application is based on both water and hydrofluoric acid permeating the RO membrane while all other impurities are rejected by it. For the first time, a spiral wound module was used here to process feeds representative of the complex multicomponent hydrofluoric acid etching solutions found in a wafer fabrication laboratory. Our new results were obtained with spiral wound membrane modules to determine the rejection and permeation of the various components along with the fluxes obtainable in realistic systems. HF was found to permeate almost 100% through the membranes while over 90% of the fluosilicic acid (the major impurity) is rejected, in a single pass. The higher the concentration of fluosilicic acid in the range of interest the better the rejection of it. Detailed analysis of the trace elements present in such HF etching solutions, which are responsible for “killer” defects in semiconductor device manufacturing, show over 99% removal of these elements in a single pass by the membranes. The economic analysis of the process indicates that reverse osmosis is attractive for the treatment of spent HF etching solutions. The performance of such spiral wound membrane systems, which represent closely the behavior of actual industrial HF reprocessors, is shown here to have tremendous potential both for reprocessing the etching solutions waste and may be feasible for ultrapurifying VLSI and ULSI grade virgin hydrofluoric acid.