A Model for the Gas-Phase Chemistry Occurring in a Furnace N2O Oxynitride Process

The nitridation of thin film oxides has been found to lead to enhanced device performance. Previous work by one of the authors has shown a falloff of nitrogen levels at the Si/SiO 2 interface across the wafer stack in the direction of the gas flow, which was attributed to gas-phase chemistry. The present work is a continuation of this investigation using a numerical solution of an enhanced reaction scheme. This work assumes that the primary gas-phase species responsible for nitrogen incorporation into the oxide thin film is NO. The enhanced set shows that gas-phase NO levels come into equilibrium over the time scales considered in a diffusion furnace using a purely chemical model. The presence of water is shown to affect the level of NO found at equilibrium, but does not show a monotonic falloff over time. The thermal kinetics are finally input into the chemistry model, taking into account gas temperature changes over time induced by endothermic and exothermic reactions. A simple model for heat transfer outside the system is used to investigate the rate of heating and cooling of the gas by the wall. The modified chemistry, together with the change in gas temperature due to this chemistry, is shown to be the likely source for the NO falloff observed previously.