Amorphous silicon-nitrogen, (a-Si,N-1-x(x),:H) alloys with x in the range 0.01-0.57 have been deposited in a dedicated chamber by ultra high vacuum plasma enhanced chemical vapour deposition (PECVD) in SiH4,+NH3, gas mixtures with different molecule dwell time and by hydrogen diluting the plasma. By optical spectroscopy, Rutherford backscattering spectrometry (RES), elastic recoil detection analysis (ERDA) and infrared spectroscopy (IR) a complete picture of bonding distribution and structural properties of device-quality a-Si,(1-x),N-x:H films as a function of deposition conditions has been drawn.;Annealing experiments under vacuum up to 500 degrees C have shown that in all the compositional range the films are thermally stable up to 400 degrees C, for higher temperature bonded hydrogen effuses from both silicon and nitrogen atoms with behaviours dependent on nitrogen content in the film.