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 si licon nitride crucible and an N-2-H-2 atmosphere (N-2:H-2=4:1, total p ressure=0.1 MPa) were employed for the melting of silicon to secure th e 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 (+/-0.2 4) (T:1723-1873 K). Since oxygen contents in the silicon melt were muc h smaller than the oxygen solubility, the effect of oxygen in liquid s ilicon on the nitrogen solubility could be ignored. The nitrogen solub ility at the melting point of silicon (1685 K) by extrapolation was ar ound 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 cha nge for nitrogen dissolution in liquid silicon and the standard enthal py 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