Conditions for Thermal Nitridation of Si in N 2 ‐ O 2 Mixtures

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Abstract
Conventional thermodynamic calculations for the Si‐O‐N system ignore the presence of and lead to the conclusion that extremely low oxygen partial pressures (−18 atm at 1250°C) are required to permit thermal nitridation of Si in the presence of 1 atm of nitrogen. However, several published reports indicate that thermal nitridation at 1250°C in 1 atm nitrogen is possible in the presence of much higher oxygen levels (about 10−6 atm). Thus, there is disagreement between such thermodynamic calculations and experimental results. It is proposed that is the dominant oxygen bearing gaseous species near the sample surface during thermal nitridation in mixtures, due to active oxidation. Wagner's model for the active oxidation of Si in oxygen‐inert gas mixtures, in the viscous gas flow regime, is extended to the Si‐O‐N system to calculate maximum oxygen partial pressures that will permit thermal nitridation of Si to occur. These calculations are in much better agreement with experimental results.

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