Production of semiconductor grade silicon by recycling

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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.