Thin amorphous SiN films grown on Si are studied with Near Edge X-Ray Absorption Fine Structure (NEXAFS). The NEXAFS spectra of N-rich films are characterized by a strong resonance line (RL) at the onset of the N K- edge. The intensity of the RL in N-rich films increases with the N/Si ratio, while the same RL is detected in the NEXAFS spectra of stoichiometric SiN films subjected to damage with Ar+ ion bombardment. The RL is attributed to a N-related defect which is strongly localized in a pure 2p orbital. The RL, which is identified as a bulk nitride property, can be annealed out at temperatures higher than the growth temperature. It is proposed that the annealing process of the RL, which is characterized by an activation energy of 0.87eV, is due to Si-N bond formation, where the Si atoms are provided by the stressed SiN/Si interface.