Purification of Waste Silicon Powder Derived from Kerf Loss Slurry by Radial Directional Solidification and Comparison with Other Directional Solidification Practices

Abstract: Radial directional solidification, in which a liquid is solidified toward the radial center, was explored as a technique for recycling kerf loss silicon powder into SOG-Si. The purification behavior of the metallic impurities Fe, Al, Ca, Mg, Ti, Mn, and Ni was examined experimentally and numerically. Specific resistivity after solidification achieved a range of 0.00029 to 0.00075 Ωm and an average value of 0.0005 Ωm. From the calculation of the concentration and specific resistivity profiles of each element in the silicon sludge, specific resistivity was estimated to be determined by Fe and Ca. The Fe and Al concentration profiles in three different directional solidification practices were computed under the same solidification time and distance conditions. In radial directional solidification, Fe purification was promoted most strongly close to the solid fraction of 0.8 and then rapidly diminished. This purification behavior depended on the lower instantaneous solidification rate in the radial direction at the position before the solid fraction of 0.8 and was followed rapidly by a higher solidification rate. Al purification in the radial directional solidification practice was slightly different from that in longitudinal solidification due to the small difference in the effective distribution coefficient in this calculation situation. Graphical Abstract: [Figure not available: see fulltext.]