In this work we study the structural properties of amorphous oxynitride films (a-SiOxNy), grown by plasma enhanced chemical vapour deposition (PECVD)at 320°C. The films were deposited at different flow ratio of N2O and SiH4. The atomic composition of the samples was determined by means of Rutherford backscattering spectrometry (RBS). The local order structure was studied by X-ray absorption spectroscopy (XAS) and the chemical bondings were investigated by Fourier transform infrared (FTIR) spectroscopy. The results evidence a tetrahedric arrangement of the oxynitride network. The tetrahedrons are similiar to SiO3N for x values between 1.43 and 1.64. For x values higher than 1.64 the tetrahedrons are similar to SiO4.