Effect of Background Gas Pressure on Evaporation of Oxides from Sb-Doped Si Melt

Evaporation losses of oxide species from undoped and Sb-doped Si melt in a silica crucible were measured by the thermogravimetric method. The melts were maintained at 1450° C under an atmosphere of pure Ar at pressures ranging from 100 to 780 Torr. The evaporation rate of all species decreased with increasing Ar pressure, although the pressure dependence of the evaporation rate was species-dependent. Increasing the Ar pressure from 100 to 780 Torr resulted in a 50% decrease in the SiO evaporation rate, whereas, over the same pressure range, the evaporation rate of Sb2O decreased by only 17%. We therefore conclude that the pressure of the background gas over a melt can be used to control the evaporation of oxide species from Si melts.