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6 July 1999 Measurement of convective temperature fluctuations in free silicon melt zones
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Abstract
Growing silicon crystals form free melt zones, the flow regime is usually dominated by time-dependent convection, resulting in temperature fluctuations in the melt and subsequently in irregular dopant distributions in the crystal. The contribution of buoyancy and thermocapillary convection can be separated and their specific characteristics determined by taking advantage of microgravity conditions. For quantification of convective temperature fluctuations, temperature measurements have been performed in liquid silicon zones. Both half zone and full zone and full zone arrangements have been investigated. In case of the latter one, temperature measurements have been performed during the growth process to analyze the relation between the temperature fluctuations and the dopant distribution. All experiments have been carried out in monoellipsoid mirror furnaces. For temperature measurements, sheathed thermocouples or graphite-coated blackbody sensors have been used. The maximum temperature fluctuations were up to 7K in the half-zone case and 0.7K in the full-zone one. In both cases the main frequencies are in the range of 0.05 to 0.5Hz but they are slightly shifted to higher values with increasing Marangoni number. For the half-zone configuration, four thermocouples and up to two black-body sensor were inserted into the melt. Between certain pairs of thermocouples and sensors, a well developed phase correlation or 180 degrees anti-phase correlation has been detected indicating a pulsating flow regime. In the case of the floating zone experiments, a very good agreement is found between the frequency characteristics of the temperature signal and the frequency distribution of dopant irregularities.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Peter W. Dold, A. Croll, M. Schweizer, Shinya Nakamura, Taketoshi Hibiya, and Klaus-Werner Benz "Measurement of convective temperature fluctuations in free silicon melt zones", Proc. SPIE 3792, Materials Research in Low Gravity II, (6 July 1999); https://doi.org/10.1117/12.351291
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