Thermal nitridation of silicon dioxide films

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Abstract
Thermal SiO2 films, ranging in thickness from 200 to 1200 Å, were thermally nitrided using NH3 at temperatures between 800 and 1160 °C and for times varying between 3 min and 5 h. The resulting films were analyzed with Auger electron spectroscopy in combination with argon ion sputtering, Rutherford backscattering spectrometry, spectroscopic ellipsometry, and infrared spectroscopy. The nitridation results in the formation of oxynitride layers in the oxide, the largest nitrogen concentration being found in the surface region and at the SiO2/Si interface. The reaction proceeds via a replacement of oxygen by nitrogen atoms under the action of hydrogen. Although the amount of nitrogen incorporated in the surface region is independent of the original oxide thickness, the interface nitrogen concentration is lower the larger the oxide thickness. This can be explained by assuming that the diffusion of NHx (0<x≤3) through the oxide limits the reaction rate. In the temperature range 1000–1160 °C the rate of the reaction in the surface region is independent of the temperature. During the nitridation reaction the films grow slightly in thickness, due to a further oxidation of the underlying silicon. Only very little nitridation of the substrate is found. The resulting oxide‐oxynitride layer structures may be used as oxidation resistance.