Siliconoxynitride layers with thicknesses between 5 and 10 nm were grown on (100) oriented silicon by rapid thermal processing (RTP) using either N2O or NH3 as nitridant. In order to study the trapping behaviour at the interface and in the insulator bulk, capacitance-voltage (CV) and current-voltage (IV) measurements have been performed combined with different magnitudes of Fowler-Nordheim stress. In addition, Deep Level Transient Spectroscopy (DLTS) has been applied for interface state detection. Auger Electron Spectroscopy (AES) has been used to obtain depth profiles for Si, N, O and C. The deconvolution of the AES signal displays significant peak contributions related to intermedium oxidation states. Nuclear Reaction Analysis (NRA) was successfully applied for hydrogen detection in buried SiOxNy thin films.