Nitrogen Solubility in Liquid Silicon

The nitrogen solubility in liquid silicon equilibrated with β-Si₃N₄was determined in the temperature range between 1723 and 1873 K. A silicon nitride crucible and an N2-H2 atmosphere (N₂:H₂=4:1, total pressure=0.1 MPa) were employed for the melting of silicon to secure the Si(l)/Si₃N₄(s) equilibrium. Nitrogen in silicon was analyzed by the Kjeldahl method. The temperature dependence of nitrogen solubility (CN) in liquid silicon was represented by the following equation: log (C_N/mass%)=2.410 -9759/T (α0.24)(T:1723-1873 K). Since oxygen contents in the silicon melt were much smaller than the oxygen solubility, the effect of oxygen in liquid silicon on the nitrogen solubility could be ignored. The nitrogen solubility at the melting point of silicon (1685 K) by extrapolation was around 4 ppm (4x 10¹⁷atoms cm^-3), which was one order of magnitude smaller than the literature values reported previously. The standard free energy change for nitrogen dissolution could be represented as: l/2N₂=N(mass%, in liquid silicon), AG°= -4.45 x 10⁴+ 66.4T(J). The correlation between the standard enthalpy change for nitrogen dissolution in liquid silicon and the standard enthalpy of formation of silicon nitride at 298 K per mol of nitrogen agreed with those for other liquid metals. Therefore, the values of nitrogen solubility obtained in the present work were considered to be reasonable.