We present a physicochemical and thermodynamic investigation of insulating thin films such as Si3N4, SiO2, etc. deposited on silicon by electric-discharge-assisted chemical vapor deposition (CVD) at moderate temperatures (T < 300degreesC) and low pressures(P = 1-2 Torr). Monocrystalline silicon is treated with a SiH4 + NH3 mixture in the presence of a low partial pressure of oxygen O-2 (from 0 to 2%). Infrared and Auger spectroscopies were used to analyze the deposited layers. The effect of temperature and that of the presence of O-2 in the mixture were examined. Thermodynamic calculations were performed to investigate the competition between simultaneous processes. The essential competition occurs between oxidation and nitridation. (C) 2002 Elsevier Science B.V. All rights reserved.