Pyrolytic-gas passivation (PGP) with a small amount nitrogen gas enhances the breakdown reliability of silicon oxide gate films. To clarify the reliability retention of the PGP-grown films oxidized at low temperature, densities (rho(ox)'s) of the 3.5-6.5-nm-thick PGP-grown films on Si(100) oxidized at 700-900 degreesC were investigated. Since rho(ox)'s correlate well with the reliability and are useful as an index of the intrinsic structural characteristics of the films. Moreover, changes in pox and nitrogen content corresponding to oxidation temperature are similar to those in breakdown reliability and interface state density (D-it), respectively. In addition, rho(ox)'s of the 700 degreesC-grown PGP films do not deteriorate as much when compared with those of the films grown by normal ultradry oxidation at 800 degreesC and their D-it's are less than about 6 X 10(10)/eV cm(2). This suggests that PGP probably improves the reliability by generating the higher-rho(ox) microscopic structure with few Si dangling bonds and effective passivation. (C) 2004 American Vacuum Society.