Effect of alkaline-earth fluorides on the nitridation of silicon

Abstract

Effects of one per cent of alkaline earth fluorides (BaF2, CaF2, SrF2) on the first stage nitridation of silicon have been studied. The fluorides enhances the reaction rate and changes the parabolic kinetics for silicon-nitrogen reaction to a linear kinetics. The accelerating effect being in the order BaF2>CaF2>SrF2 with activation energies of 96.23, 146.44 and 251.04 kJ/mole respectively as compared to 385.43 kJ/mole for silicon-nitrogen reaction without additive. Thermodynamic consideration reveal that the fluorides accelerates the reaction by removing the SiO2 layer formed on the silicon grain by the reaction SiO2 (s) + 2MF2 (g) � SiF4 (g) + 2MO (s). Evidences have been cited to show that the reaction Si (g) + MF2 (g) � SiF2 (g) + M (g) also occurs. © 1984