By Michael Lurie, Ishay Wexler, Haim Peri, Milan Shtal, Tower Semiconductor Ltd., Migdal Haemek, Israel

Environmental regulations regarding fluorides in industrial waste in Israel are quite stringent. Hydrofluoric acid and ammonium fluoride are widely used in semiconductor processes, and large volumes of rinse water from manufacturing tools and acidic-exhaust scrubber waste contain fluorides in relatively low concentrations. Traditional methods of fluoride removal were found unacceptable for this application. A reverse osmosis system based on technology called HERO (high-efficiency reverse osmosis), from Aquatech International Corp., was selected for treatment of dilute fluoride waste. In operation for about one year, the system has provided high water recovery and low concentration of fluorides in permeate.

Water resources are limited in Israel, where Tower Semiconductor Ltd. operates two wafer fabs for silicon foundry services. The potential for waste dilution in natural water sources or due to rainfall is negligible in the arid country. Thus, environmental regulations for industrial waste in general – and for content of fluorides in particular – are stringent in Israel.

Hydrofluoric acid and ammonium fluoride are widely used throughout the semiconductor manufacturing process, and low volumes of concentrated fluoride waste typically are accumulated and treated on-site or off-site from the fab. But the treatment of large volumes of dilute fluoride waste (DFW) containing tens to hundreds of parts per million (ppm) of fluorides still presents a major problem.