METHOD AND APPARATUS FOR SMELTING AND PURIFYING POLYCRSTALLINE SILICON BY MEANS OF ELECTRON BEAM AND SHALLOW MELT POOL

摘要

Disclosed is a method for smelting and purifying polycrystalline silicon by means of electron beam and shallow melt pool wherein a bulky polycrystalline silicon ingot with high contents of phosphorus and metal elements to be purified is put onto a water cooled lifting tray, and thereafter the top of the ingot is melted by an electron beam so that a shallow melt pool can be formed by the molten silicon liquid inside a space formed by the top of the ingot, water cooled copper sleeve and graphite ferrule; after smelting for a certain time, the impurity of phosphorus is removed; subsequently the water cooled lifting tray is raised and silicon liquid with low phosphorus content flows into a quartz crucible through a flow-guide hole after the raise of the liquid level; an ingot is pulled down by the action of heat preservation and directional solidification is performed so that the impurity of metals could get together toward the top of silicon ingot; the top of the silicon ingot is cut off after solidification so as to remove the impurity of metals. The impurities of phosphorus and metals are removed by combination of smelting by means of the electron beam and shallow melt pool with solidifying directionally. The purity of polycrystalline silicon meets the requirements of application for solar-grade silicon, and the method is energy saving, simply, high in productivity and suitable for batch production.