Silicon oxynitride films have been grown with thermally excited N2O gas, which has a low toxicity in comparison with other oxynitridation agents. Dependences of reaction rates on excitation temperature and substrate temperature have been investigated by Auger electron and photoelectron spectroscopies. These results show that the thermal excitation of N2O obviously promotes the oxynitridation of the silicon surface, especially the oxidation reaction. At higher substrate temperatures, the nitridation of the silicon surface increases and the oxidation is reduced. By mass analysis of the residual gas in the reaction chamber, it was also found that the thermal excitation of N2O causes N2O to be decomposed into N-2 and O, This is consistent with the obtained effect that the thermal excitation of N2O promotes especially the oxidation reaction, because atomic oxygen (O) acts as a strong oxidant. (c) 2005 Elsevier B.V. All rights reserved.