Production of semiconductor grade silicon by recycling

研究了用含少量杂质的废硅精炼太阳能电池或半导体用高纯硅的新工艺。在约10^lt；-3&gt；pa的高真空下，用电子束(EB)熔融硅中的磷、锑等杂质。然而，由于硼的蒸汽压很小，简单的电子束熔炼技术不能从硅中去除硼。因此，在EB熔化过程中，反应性气体被吹到硅表面，目的是通过与气体的反应来去除硼。在硅熔体中加入水蒸气降低了熔化初期硅中的硼浓度。高真空下的精炼已被证明是有效的，但要保持10^&lt；-3&gt；pa的高真空度，需要很高的成本。因此，研究了在低真空下精炼的可能性。用冷阴极辉光放电电子束枪在1~10Pa低真空下熔化硅，以去除硅中的杂质。该电子枪可以像普通灯丝式电子枪在高真空下熔化硅一样稳定地熔化硅。用辉光放电电子束在低真空、压力为10Pa的条件下熔融，可以成功地脱除硅中的磷和锑。脱色率与高真空条件下的几乎相同。

New techniques to product high purity silicon for solar cells or semiconductors by refining scrap silicon containing small amounts of impurities were investigated.Impurities such as phosphorus and antimony could be removed from silicon by melting with electron beam(EB) under a high vacuum with a pressure of about 10^<-3> Pa. However, boron cannot be removed from silicon by the simple EB melting technique because the vapor pressure of boron is small. Thus, reactive gases were blown on the silicon surface during the EB melting with the intention of removing boron by a reaction with the gases. Addition of water vapor to silicon melt decreased the concentration of boron in silicon at the early stage of the melting.Refining under a high vacuum has been demonstrated to be effective but needs high cost for maintaining the high vacuum degree of 10^<-3> Pa. The possibility of refining under a low vacuum was therefore examined. The impurities of silicon was tried to be removed by melting silicon under a low vacuum with a pressure of 1-10 Pa using a cold cathode glow discharge electron beam gun. This gun could melt silicon stably as in the case of melting with a normal filament type EB gun under a high vacuum. Phosphorus and antimony could be successfully removed from silicon by melting with the glow discharge electron beam under a low vacuum with a pressure of 10 Pa. The removal rates were almost the same as those under the high vacuum.