PREPARATION OF FINE AMORPHOUS-SILICON NITRIDE POWDER IN THE SYSTEM SIH4-AR-NH3

Amorphous silicon nitride powders have been prepared in a tube reactor in the system silane-argon-ammonia in the temperature range 500-1100 degrees C. The powders prepared at 500 degrees C show the presence of elementary silicon. The powders prepared above 650 degrees C are near stoichiometric in composition, isometric in morphology and the particl e size distribution is in the range of 0.05-0.2 mu m. The powders prep ared at 1100 degrees C are nearly monodispersive, having the particle size 0.1 mu m. The influence of molar ratio of ammonia to silane shows that silicon nitride powder of near stoichiometric composition can be prepared above 11.62 and below this ratio the powders contain element ary silicon. The change in total gas flow rate shows that below 300 cm (3) min(-1) the powders again contain elementary silicon and with furt her increase in flow rate the powders are near stoichiometric at 400 c m(3) min(-1) and little hyperstoichiometric in nitrogen content at and above the flow rate of 500 cm(3) min(-1). Surface characterization by X-ray photoelectron spectroscopy indicates that most of the oxygen is confined on the surface and is present in the form of SiO2.