Effects of trace O2 levels on the nitriding kinetics of high-purity silicon powders

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