Development of ozonated ultrapure water supplying system using direct-dissolving method

A new ozonated ultrapure water (O/sub 3/-UPW) supplying system has been established. In the new O/sub 3/-UPW supplying system, a direct dissolving method that can supply O/sub 3/-UPW to many separated points of use from a single unit has been employed. In this system, ozone-containing gas is directly introduced in ultrapure water (direct dissolving) and the water/gas mixture is transported to many points of use through a piping system. At each point of use, bubbles in water/gas mixture are separated and O/sub 3/-UPW without bubbles is supplied to the cleaning equipment. The concentration of dissolved ozone in water rapidly decreases because of self-decomposition. On the other hand ozone in the gas phase is more stable than in the water phase and ozone in the bubbles (gas phase) becomes dissolved in the water while transported through the piping system. As a result; O/sub 3/-UPW with the ozone concentration of higher than 5 ppm is supplied to the cleaning equipment that is installed at distant places as far as 100 m from ozone gas introducing point. We have provided the new system in one of the latest LCD fabrication plants, which is presently in operation.