ADVANCED ULTRAPURE WATER-SYSTEMS WITH LOW DISSOLVED-OXYGEN FOR NATIVE OXIDE FREE WAFER PROCESSING

In the manufacture of submicron or deep submicron ULSIs, it is important to completely suppress native oxide growth on the silicon wafer surfaces. Especially, in order to suppress the native oxide growth in a wet process, dissolved oxygen must be removed from the ultrapure water used for the final rinsing of the wafer. Two independent systems for the supply of ultrapure water, augmented with new techniques to remove dissolved oxygen, have been installed in the mini-super-clean room at Tohoku University. Both systems use two-stage dissolved oxygen removing methods. System 1 uses vacuum degassing through membrane and catalytic resin-based reduction, while System 2 uses vacuum degassing through membrane and nitrogen gas bubbling. Both systems can supply ultrapure water of 10 ppb or less in dissolved oxygen concentration. The concentrations of other impurities such as TOC, silica and total residue are also 1 ppb or less.