EVAPORATION OF OXYGEN-BEARING SPECIES FROM SI MELT AND INFLUENCE OF SB ADDITION

Evaporation loss from undoped and Sb-doped Si melt in both SiC-coated carbon and a silica crucible was measured in the temperature range of 1440-1560-degrees-C. For undoped Si melt in a silica crucible, the eva poration rate changed with temperature in an exponential manner and de pended on the area ratio, A(c)/A(s), where A(c) is the contact area of the Si melt and silica crucible, and A(s) the free surface area of th e Si melt. There were three trends of the dependence, and the evaporat ion rate tended to reach a certain saturation value when the area rati o approached infinity, which can be regarded as the intrinsic evaporat ion rate due to oxygen saturation in Si melt. It was concluded that th e oxygen concentration in the Si melt was not saturated under the pres ent experimental conditions. Evaporation from Sb-doped Si melt seemed complex. Under the assumption that the evaporating species from an Sb- containing Si melt in a SiC-coated carbon crucible was antimony vapor only and that the gb evaporation rate did not change in different cruc ibles, the total evaporation from the silica crucible was analyzed. Fr om the linear time dependence and nonexponential temperature dependenc e, the evaporation rate excluding Sb evaporation was concluded to be t hat of some oxide species but not pure SiO. Such evaporation was great er than the evaporation of SiO from undoped Si melt; more than three t imes as large at the melting point of Si. Therefore oxygen reduction i n highly Sb-doped Cz-Si crystals can be attributed mainly to the enhan cement of oxygen evaporation.