The microstructural properties of stoichiometric surface and buried Si3N4films, fabricated with15N ion implantation into Si wafers, are studied using the extended x‐ray absorption fine structure (EXAFS) and near‐edge x‐ray absorption fine structure (NEXAFS) spectroscopies. Complementary information about the film composition and structure is provided by nuclear reaction analysis (NRA) and cross‐section transmission electron microscopy (XTEM). The films have been characterized in the as‐implanted state and after annealing in the temperature range 1100–1200 °C. For all the examined films, the N/Si ratio at the peak of the nitrogen profile, as measured by NRA is 1.33, a value that corresponds to stoichiometric nitrides. However, small compositional deviations towards a N‐rich composition are detected by EXAFS in the surface nitrides. The excess nitrogen is also detectable in the NEXAFS spectra, where it introduces a characteristic resonance line superimposed to the absorption edge. Finally, XTEM observations confirm the formation of the nitride layers and reveal different degrees of damage at the Si3N4/Si interface for the low and high energy implantations, respectively. ©1996 American Institute of Physics.