Reoxidation of silicon nitride studied using x-ray photoelectron spectroscopy and transmission electron microscopy

The chemical composition of oxynitride films obtained by furnace oxidation of silicon nitride (Si3N4) in a dry or wet oxygen ambient at a substrate temperature of 900–1000 °C is characterized using x-ray photoelectron spectroscopy and cross-sectional transmission electron microscopy. The dependence of the oxidation kinetics on the initial nitride thickness dnit is also investigated in the range of 18–500 Å. In the case of dnit=500 Å, only the surface of the nitride is oxidized after a 13 min 900 °C oxidation in a wet ambient. In contrast, for dnit=18 and 40 Å, under the same conditions condition, the underlying Si substrate is oxidized in addition to Si3N4. Furthermore, it is found that the oxidation rate of 500 Å Si3N4 increases by approximately 14%–21% when 2% hydrogen chloride (HCl) is added to the oxidizing ambient. Increases in HCl content beyond 2% do not result in any further enhancement of the oxidation of the nitride film.