Hydrogenation during thermal nitridation of silicon dioxide

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Abstract
The incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000 °C and for ammonia pressures of 1, 5, and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford-backscattering spectrometry and elastic-recoil detection. Nitrogen in-depth profiles were obtained applying Auger analysis combined with ion sputtering. Hydrogen profiles in the films were measured using nuclear-reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions, up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in-depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen: measured H/N ratios varied between 0.25 and 0.85, the smaller values being obtained for the thinner oxides and higher nitridation temperatures. The model previously postulated to explain the nitrogen incorporation during atmospheric nitridation of SiO2 proves to be valid at higher pressures as well. By considering the role of OH as a reaction product of the nitridation process, the hydrogen results can be accommodated within the same concept. The model predicts a low H/N-incorporation ratio for a thin surface and interface layer and a substantially larger ratio for the bulk of the film. If this prediction is correct, which seems to be indicated by the etch-rate behavior of the nitrided oxides, then this would have considerable importance for the electrical properties of this material.