We report the growth of an ultrathin 1.0 nm (equivalent oxide thickness = 0.86 nm) oxynitride gate dielectric by rapid thermal processing (RTP) in high-N-2 but low-O-2 gas flow ambient. The effect of the changing N-2/O-2 gas flow ratio on the characteristics of oxynitride films was investigated. High-quality oxynitride film could be formed by RTP in an optimum N-2/O-2 gas flow ratio of 5/1. Detailed characterization (transmission electron microscopy, J-E capacitance-voltage, stress-induced leakage current, charge-trapping properties! demonstrated the high quality of the oxynitride dielectric and showed that low leakage current density J(g) = 0.1 A/cm(2) at 1 V, was 1.85 orders of magnitude lower than that of SiO2. These improvements are attributed to the presence of nitrogen at the interface and in the bulk of the oxynitride. (C) 2004 The Electrochemical Society.