Patent ID: 7510933

Claim:
A method of fabrication of a semiconductor integrated circuit device, comprising the steps of: (a) introducing first water into a first water purifying system, and sending out first purified water from said first water purifying system; (b) introducing said first purified water into a second water purifying system having a pure water circulating loop including an ultrafiltration filter having a hollow fiber type ultrafiltration membrane; and sending out second purified water from a first supply point on said pure water circulating loop; (c) providing a first wet treatment apparatus with said second purified water, thereby carrying out a first wet treatment to a wafer in said first wet treatment apparatus, wherein step (c) including the sub-steps of: (c1) removing ions from said second purified water through use of an ion removing filter, at least capable of removing cations, disposed between said first supply point and a use point in said first wet treatment apparatus, and (c2) providing said use point with said second purified water which has passed through said ion removing filter, and wherein (i) said ion removing filter is a membrane type ion filter having a membrane sheet as a filter member; (ii) said semiconductor integrated circuit device has a flash memory cell; and (iii) said first wet treatment is a cleaning treatment prior to a thermal treatment for forming a gate insulating film of said flash memory cell.