EVAPORATION RATES OF OXIDES FROM UNDOPED AND SB-DOPED SI MELTS UNDER ATMOSPHERES OF PURE NE, AR, AND KR

The effect of gaseous Ne, Ar, and Kr on the evaporation rates of oxides from undoped and Sb-doped Si melts was investigated. By measuring the weight loss of a melt using a thermogravimetric method, we determined the evaporation rate of different species from the melts. The measurements were done at a melt temperature of 1442-degrees-C and a background gas pressure of 1.02 atm. Because Ar is predominantly used as the background gas in the semiconductor industry, we report evaporation rates relative to the rates under an atmosphere of pure Ar. For the evaporation of SiO from an undoped Si melt, Ne enhanced the evaporation rate by 37% and Kr suppressed the evaporation rate by 13%. For the evaporation of antimony from an Sb-doped Si melt, Ne enhanced the evaporation rate by 18% and Kr suppressed the evaporation rate by 24%. For the evaporation of antimony oxide from an Sb-doped melt, Ne enhanced the evaporation rate by 4% and Kr suppressed the evaporation rate by 63%. We therefore conclude that, compared with Ar, Ne enhances and Kr suppresses the evaporation of oxides from undoped and Sb-doped Si melts. We show that the background gas affects evaporation through gas-phase diffusion; the diffusion coefficient of the evaporating species is the highest in Ne and the lowest in Kr. In addition, we show that the transport of the evaporating species in the melt to the surface also influences the overall evaporation rates.