Hydrogen incorporation in ECR-CVD silicon oxynitride films deposited using tris dimemylaminosilane (TDAS) as the silicon precursor was investigated. The as-deposited silicon dioxide films were shown to contain little hydrogen (<2%) as determined by both FTTR and nuclear reaction analysis (15N profiling). Films were obtained with high breakdown fields (>10 MV/cm) and low interface state densities (2×l011cm−2) on silicon without special surface preparation. Silicon nitride films were found to contain large hydrogen concentrations, both bonded and unbonded, which evolved from the film due to beam irradiation during 15N profiling. We were able to demonstrate that dilution of the nitrogen plasma with both hydrogen and argon was effective in avoiding problems of trace oxygen contamination and poor film adhesion, and reducing the hydrogen concentration in the nitride films.