The deposition of amorphous hydrogenated silicon oxynitride thin films, varying the nitrogen and oxygen content in the solid phase, is reported. The films were deposited by plasma enhanced chemical vapor deposition at different nitrous oxide/silane flow ratios, keeping constant the silane flow and the deposition temperature at 320°C. The composition of the thin films was determined by Rutherford backscattering spectroscopy (RBS) and the morphological properties were investigated by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The composition data showed that the oxygen content increases and the nitrogen content decreases, inside the films, as the ratio between the nitrous oxide flow and silane flow goes toward larger values. The oxygen (x) plus nitrogen (y) content in the chemical formula (a-SiOxNy) is always close to two, suggesting that these atoms share the same atomic positions around the silicon atoms in a local structure similar to SiO2. The SAXS results revealed the presence of scatterers with an average radius 〈R〉 that varies from small values, like 10 Å, up to 100 Å. The TEM results showed the formation of particles with a circular cross-section, composed of Si, N and O spread in a matrix with the same elemental composition. These particles have a radius larger than 50 Å. © 2001 Elsevier Science B.V. All rights reserved.