Abstract
The removal of boron in pure silicon by gas mixtures has been examined in the laboratory. Water-vapor-saturated hydrogen was used to remove boron doped in electronic-grade silicon in a vacuum frequency furnace. Boron concentrations in silicon were reduced from 52 ppm initially to 0.7 ppm and 3.4 ppm at 1450°C and 1500°C, respectively, after blowing a H2-3.2%H2O gas mixture for 180 min. The experimental results indicate that the boron removal as a function of gas-blowing time follows the law of exponential decay. After 99% of the boron is removed, approximately 90% of the silicon can be recovered. In order to better understand the gaseous refining mechanism, the quantum chemical coupled cluster with single and double excitations and a perturbative treatment of triple excitations method was used to accurately predict the enthalpy and entropy of formation of the HBO molecule. A simple refining model was then used to describe the boron refining process. This model can be used to optimize the refining efficiency.
Highlights
The removal of boron in metallurgical grade silicon (MG-Si) is one of the most crucial tasks for upgrading to the photovoltaic silicon feedstock
Ikeda and Maeda[6] tested the Ar-H2O plasma gases with different water vapor pressures. They concluded that the highest water vapor pressure, 1.24 vol.% H2O, has the highest apparent rate constant for boron removal
Andersson, Nordstrand, and Tangstad temperatures, it implies that the kinetics of boron removal by the H2-H2O gas mixture is controlled by chemical reactions occurring in the gas–liquid interface
Summary
The removal of boron in metallurgical grade silicon (MG-Si) is one of the most crucial tasks for upgrading to the photovoltaic silicon feedstock. Molten flux treatment[1,2,3,4] and plasma[5,6,7,8,9,10,11] are two of the most common methods for the removal of boron in silicon. The molten flux treatment can effectively remove boron, it will inevitably contaminate the silicon feedstock. Ikeda and Maeda[6] tested the Ar-H2O plasma gases with different water vapor pressures They concluded that the highest water vapor pressure, 1.24 vol.% H2O, has the highest apparent rate constant for boron removal. After a 3-min treatment by the Ar-H2O-H2 plasma gas, more than 60% of the boron could be removed from silicon melts
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