一种新的精炼太阳能级多晶硅工艺的热力学分析

摘要

提出了一种新的硅精炼工艺生产太阳能级多晶硅,即Si-Al熔体低温凝固精炼硅技术.通过杂质在固相硅和Si-Al熔体中的分离热力学分析研究了采用Si-Al熔体分区凝固精炼硅的可行性.用温度梯度区域熔炼法来测定磷和硼的分离比,采用热力学计算金属杂质的分离比.新工艺具有很小的杂质低温分离比,表明其有很好的精炼能力.采用感应加热分区凝固实验进行验证;对Si-Al合金定向凝固中硅晶体生长进行了研究,结果表明,硅晶体的生长过程是受扩散控制的.%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.