Effects of trace O-2 levels on the nitriding kinetics of high-purity silicon powders

The effects of trace O-2 levels on the nitridation of compacts made from si lane-derived Si powders were studied in N-2 atmospheres, with oxygen levels of either 5 ppm or 10 ppb (approximately). The nitriding kinetics were stu died by thermogravimetric analysis as a function of temperature (1100-1200 degrees C) and heating rate (5 degrees C/min and 100 degrees C/min), Reduci ng the O-2 level in the nitriding gas enhanced conversion to Si3N4 at lower temperatures, reduced the composition variations within the samples, and d ecreased the alpha/beta ratios. The results suggest that nucleation and rap id growth of Si3N4 at relatively low temperatures are possible only when th e oxygen partial pressure in the system is below the threshold value for pa ssive oxidation.