Production of semiconductor grade silicon by recycling

研究了用含少量杂质的废硅为原料生产太阳能电池或半导体用高纯硅的新工艺，在10 ~ 4Pa的高真空下，用电子束（EB）熔融法除去硅中的磷、锑等杂质<-3>。然而，由于硼的蒸气压小，不能通过简单的EB熔化技术从硅中除去硼。因此，在EB熔化期间，将反应性气体吹到硅表面上，目的是通过与气体反应来去除硼。在硅熔体中加入水蒸气可降低熔融初期硅中硼的浓度，在高真空下精炼已被证明是有效的，但维持10^ Pa的高真空度需要较高的成本<-3>。因此，研究了在低真空下精炼的可能性。尝试通过使用冷阴极辉光放电电子束枪在1-10 Pa的压力下在低真空下熔化硅来去除硅的杂质。该枪可以在高真空下与用普通灯丝型EB枪熔化的情况一样稳定地熔化硅。在10 Pa的低真空下，用辉光放电电子束熔化硅，可以成功地去除硅中的磷和锑。去除率与高真空下的去除率几乎相同。

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.