Temperature Dependence of the Solubility of Nitrogen in Liquid Silicon Equilibrated with Silicon Nitride

Abstract

The solubility of nitrogen in liquid silicon equilibrated with silicon nitride and its dependence on the composition of the atmosphere has been studied in the temperature region 1428–1542°C. High purity silicon was melted in silicon nitride crucibles under Ar and N₂ atmospheres. The equilibrium was observed to be established within minutes, after which no evolution of the nitrogen content with time could be observed. The nitrogen transfer between the Si₃N₄-crucible and the melt was faster than the transfer via the gas-phase to such an extent that the composition of the atmosphere did not influence the solubility limit. The solubility limit as a function of temperature was found to follow: C_N(T,C_B) = 7957.9*exp(-24376/T) At the melting point of silicon, this equation gives the solubility of nitrogen as 42 ppm mass. From this equation, a thermodynamic derivation led to the following expression for the dissolution energy of nitrogen: ΔG^0 = -1.63 * 10^4 + 26T