Reliability of ultra-thin gate oxides grown in low-pressure N20 ambient or on nitrogen-implanted silicon

The influence of nitrogen incorporated at the gate oxide interface on the reliability and electrical behavior of MOS capacitors was investigated. Incorporation of nitrogen was accomplished either by either rapid thermal oxidation (RTO) in N2O or N2O/O2 atmosphere at pressures between 75 to 500 mbar or by implantation of nitrogen at 20 keV and doses between 1013 to 1015 cm-2 into the substrate prior to RTO. Characterization of MOS capacitors with oxide thicknesses between 2.9 to 3.9 nm was achieved by reliability measurements at constant current or constant voltage stress, respectively. These measurements were correlated to the nitrogen dose at the gate interface which was determined by SIMS analysis. Stress reliability showed a sensitive dependence on the processing conditions. An accurate adjustment of the nitrogen dose at the gate interface is mandatory to attain improved reliability of nitrided oxides.