Process for removing impurities from a silicon melt by directed solidification

摘要

In a process for removing impurities from a silicon melt by directed solidification (4), the silicon melt is brought to solidification only to such an extent that the impurities collect in a residual melt (3). Calcium or calcium oxide is then added to this residual melt (3) and the solidification (4) is continued. After complete solidification, there results a silicon block (1) having a "block head" (3) which contains the impurities. The block head (3) is removed mechanically and/or by acid treatment. This separation process is preferable to the otherwise customary sawing process, since the material (3), as a result of the calcium silicide phase separating out at the grain boundaries, is mechanically less stable and therefore cannot be removed without losses and great effort. Silicon crystals present in the block head (3) are again fed to the process. The process is used for the production of silicon for solar cells, in particular subsequent to the carbothermic reduction of SiO2. IMAGE