Amorphous hydrogenated Si-N (a-SiNx:H) alloys were deposited by plasma immersion ion processing using a working pressure of 1.3 Pa of mixtures of SiH4 and N-2. Films with N/Si ratios from 0.6 to 1.2 were obtained, as determined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERD). A fixed total H content of 9 at.% was observed in all films. Chemical bonding was investigated by infrared, Raman and X-ray photoelectron (XPS) spectroscopies. These techniques revealed a complex Si chemical environment that evolves towards that Of Si3N4 for higher N/Si ratios. This evolution was correlated with the increase of film hardness. (c) 2005 Elsevier B.V. All rights reserved.