During furnace N2O‐based silicon oxynitride growth, the total concentration of NOxspecies varies strongly with the flow rate of N2O. At low flow rates the N2O decomposes at least partially in the cooler region of the furnace near the gas inlet. This results in lower than expected NOx(x=1,2) concentrations in the oxidizing ambient. At high flow rates, the exothermic decomposition of N2O can heat the inlet region of the furnace, resulting in decomposition at a temperature above the nominal furnace temperature and higher than expected NOxconcentrations. These effects can lead to a substantial variation in the concentration of N in the oxynitride as a function of N2O flow. ©1996 American Institute of Physics.