Enhancement of direct nitridation of silicon by common metals in silicon nitride processing

Catalytic effects of metals, which are often involved in the fabrication of silicon nitride product, on the direct nitridation of silicon were investigated. Silicon granules impregnated with 0.125–2.0% by mass of ytterbium, yttrium, calcium, lutetium, magnesium or cerium were nitrided in a tubular flow reactor operated at temperature in the range of 1300–1390 °C. Enhanced selectivity of α-silicon nitride formation was observed when calcium, yttrium or ytterbium was used. It was also found that a stepwise increase in the nitridation temperature from 1300 to 1390 °C enhanced the conversion of silicon while keeping high content of α-silicon nitride. Yield of α-silicon nitride over 95% was achievable within 3 h of the reaction from an addition of calcium or ytterbium to silicon raw material. It is suggested that characteristic of the impregnated metal, rather than the presence of liquid phase formed during the reaction, has the dominant effects on the α-silicon nitride formation.