We studied the influence of process parameters on the composition and the electrical properties of thin SiO2films nitrided in a plasma reactor of a novel design. The process parameters investigated include pressure, temperature, reactant gas species and flow rate, plasma frequency and power, and process duration. The structure and morphology of these films were examined by cross‐sectional transmission electron microscopy. Their composition was analyzed using Auger electron spectroscopy, secondary ion mass spectroscopy, and etch rate measurements. Metal–oxide–semiconductors capacitors were fabricated and electrically characterized byC–V, time‐dependent breakdown, and charge trapping measurements. Our results show that more nitrogen is incorporated in films treated in a NH3plasma than in a N2plasma. Yet, the latter films present better electrical properties. Compositional variations between different films are not sufficient by themselves to explain their electrical properties. It appears that the effect of ion bombardment in the plasma plays an important role. By properly optimizing process parameters, the charge to breakdown of nitrided films can be enhanced over that of SiO2. This improvement is ascribed to a lower electron trapping rate.