In this work metal/oxide/silicon (MOS) capacitors using SiO xNy and SiO2 films with different nitrogen concentrations as gate dielectrics were deposited by the plasma-enhanced chemical vapor deposition (PECVD) technique, fabricated and characterized. These films were obtained through the variation of the N2O/SiH 4 flow ratio (R) at low temperatures ( ∼ 320 °C). The refractive index results show that by varying the N2O/SiH 4 flow ratio it is possible to obtain a precise control of this parameter in the 1.46-1.57 range. From the low- and high-frequency C-V curves, the interface state density (Dit), the effective charge density (Nss), dielectric constant (k), among others were extracted. Optimized properties were found for the capacitor with a low nitrogen concentration (∼ 8%) SiOxNy gate dielectric. © 2003 Elsevier Inc. All rights reserved.