Removal of Boron in Silicon by H2-H2O Gas Mixtures |
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Authors: | Kai Tang Stefan Andersson Erlend Nordstrand Merete Tangstad |
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Affiliation: | 1. SINTEF Materials and Chemistry, 7465, Trondheim, Norway 2. Department of Materials Science & Engineering, Norwegian University of Science and Technology, 7491, Trondheim, Norway
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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. |
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