The reliability of 1.5-nm-thick silicon oxide gate films grown at 150 degrees C by modified reactive ion beam deposition (RIBD) with in situ pyrolytic-gas passivation (PGP) using N2O and NF3 was investigated. RIBD uses low-energy-controlled reactive, ionized species and potentializes low-temperature film growth. Although the oxide films were grown at a low temperature of 150 degrees C, their fundamental indices of reliability, such as the time-dependent dielectric breakdown lifetime and interface state density, were almost equivalent to those of oxide films grown at 850 degrees C using a furnace. This is probably due to localized interfacial N and F atoms. The number density of interfacial N atoms was about seven times larger than that for the furnace-grown oxide films, and this is a key factor for improving the reliability through the compensation of residual inconsistent-state bonding sites. (C) 2008 American Vacuum Society.