The kinetics of Ar/N2O remote plasma-assisted oxidation of Si(100) and the mechanism of nitrogen incorporation at the Si-SiO2 interface were investigated using mass spectrometry, optical emission spectroscopy, and on-line Auger electron spectroscopy. N-2, O-2, and NO are the stable products of N2O dissociation in the plasma. The maximum NO partial pressure occurs at 10 W applied rf power; N-2 and O-2 are the predominant products for applied powers greater than 50 W. Ar/N2O remote plasmas are prolific sources of atomic O; in contrast, atomic N is not produced in significant concentrations, Ar/N2O remote plasma-assisted oxidation was investigated at 300 degrees C for applied rf powers of 5, 20, and 50 W. The oxide growth kinetics are slower than expected for a purely diffusionally controlled process. A diffusion-reaction model that incorporates first-order loss of the oxidizing species as it diffuses through the growing oxide layer fits the data very well. The initial oxidation rate increases linearly with plasma density, suggesting that the near-surface concentration of oxidizing species scales with the surface flux of plasma electrons. Nitrogen is incorporated at the Si-SiO2 interface in direct proportion to the N-2 partial pressure in the Ar/N2O remote plasma. Molecular NO does not react at the Si-SiO2 interface at 300 degrees C, its role in Si thermal oxynitridation notwithstanding. Nitrogen incorporation at the Si-SiO2 interface was also achieved by exposure of ultrathin Ar/O-2 plasma oxides to a remote 20 W Ar/N-2 plasma.