Thermodynamic evaluation of new metallurgical refining processes for SOG-silicon production

With the aim of developing a new silicon refining process for production of solar grade silicon, a low-temperature refining technique referred to as “solidification refining of silicon with a Si-Al solvent at low temperature” was studied. The refinability of silicon by the partial solidification from a Si-Al solvent was discussed with thermodynamic evaluation for the impurity segregation between solid silicon and a Si-Al solvent. Impurity segregation ratios were measured by using temperature gradient zone melting method for phosphorus and boron and were estimated by the thermodynamic calculation for metallic impurities. The excellent refinability was clarified from the extremely small segregation ratios of impurities at lower temperature and was also confirmed by the test refining with the partial solidification under the induction heating. Furthermore, silicon crystal growth was studied by directional solidification experiments of a Si-Al alloy, and was estimated to be diffusion controlled.