NITROGEN SOLUBILITY IN LIQUID SILICON

The nitrogen solubility in,liquid silicon equilibrated with beta-Si3N4 was determined in the temperature range between 1723 and 1873 K. A silicon nitride crucible and an N-2-H-2 atmosphere (N-2:H-2=4:1, total pressure=0.1 MPa) were employed for the melting of silicon to secure the Si(1)/Si3N4(s) equilibrium. Nitrogen in silicon was analyzed by the Kjeldahl method. The temperature dependence of nitrogen solubility (C ($) under bar($) under bar N) in liquid silicon was represented by the following equation: log (C-$ under bar N/mass%)=2.410-9759s/T (+/-0.24) (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 (4 x 10(17) atoms 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: 1/2N(2)=($) under bar N(mass%, in liquid silicon), Delta G degrees= -4.45 x 10(4)+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