Ozone Decomposition in Ultrapure Water and Continuous Ozone Sterilization for a Semiconductor Ultrapure Water System

Ultrapure water production technology is basic to ultralarge scale integrated (ULSI) manufacturing. To improve cleanliness on the Si surface, impurities in ultrapure water must be reduced. In a study of ozone behavior in ultrapure water the reaction order of ozone decomposition was 1.5 in ultrapure water inside oxidation‐passivated stainless steel tubing. However, inside plastic tubing the reaction order of ozone decomposition was not 1.5 even when impurities including organic materials in ultrapure water were suppressed to an extremely low level. Oxidation‐passivated SUS316L stainless steel resisted elution and ozone attack excellently. To perform continuous ozone sterilization, a new ultrapure water production system employing oxidation‐passivated stainless steel was developed. Ozone was injected into ultrapure water immediately after point of use and was removed at the outlet of the ultrapure water tank. In this system, bacteria were not detected in ultrapure water even when ozone concentration at the inlet of the ultrapure water tank was as low as 50 ppb. Other impurities also were suppressed below the detection limit. Continuous ozone sterilization brings about nonstop ultrapure water production.