Method and equipment for controlled directional solidification and purification of polycrystalline silicon through taking tailing by graphite tube

Abstract

The invention belongs to the technical field of metallurgy purification, and particularly relates to a method and equipment for directional solidification and purification of polycrystalline silicon through taking tailing. According to the method, under the inert gas shielding environment, abluent silicon is melted so as to carry out directional solidification; ingot pulling is stopped when solidification is completed by 85-90%, a graphite tube is stretched into surplus melt silicon, then inert gas is led into a vacuum chamber, so that the surplus melt silicon enters the graphite pipe under the action of pressure difference and ingot pulling is continuously carried out, after the upper end of a crucible leaves a heating area, the water cooled crucible is stretched below the graphite tube, inert gas is stopped being led into the vacuum chamber, the vacuum chamber is vacuumed, the surplus melt silicon in the graphite tube falls into the water cooled crucible to be cooled and solidified; the power is cut off so as to stop heating, and cast ingot solidified in a crucible is silicon cast ingot of high purity. Due to the method, back-diffusion of impurity is prevented, technology processes are reduced, and the yield of cast ingot is improved. The equipment is convenient to improve and install, is easy to operate, can effectively remove impurities accumulated at the tail of the cast ingot, saves production period and cost, and is applicable to industrial production.

Description

technical field [0001] The invention belongs to the technical field of metallurgical purification, and in particular relates to a method and equipment for directional solidification and purification of polysilicon by tailing material extraction. Background technique [0002] The purification of silicon raw materials is an important link in the solar photovoltaic industry chain. The rapid development of the photovoltaic industry depends on high-efficiency and low-cost purification methods. Directional solidification technology has been widely used in many fields of metal purification, and has achieved remarkable results. In the process of purifying silicon raw materials, metal impurities whose segregation coefficient is far less than 1 will be enriched in the liquid phase during the directional solidification process and finally removed. This method is one of the key links in the current metallurgical preparation of solar-grade polysilicon, and is the most effective method f...

AI Technical Summary

Problems solved by technology

In the subsequent slow cooling process, the impurities in the high-concentration area will diffuse to the low-concentration area, so that the purity of silicon will gradually decrease with the prolongation of the holding time, which affects the purification effect, and in this case, the tail that needs to be removed The waste is as high as 25%~35%, and the finished product rate is only 65-75%

At the same time, due to the relatively high hardness of silicon, high-power cutting equipment is needed to separate the purified silicon ingot from the ingot tailings with high impurity content at the tail. At present, wire cutting and diamond saw band cutting are generally used for cutting, but cutting The high cost of equipment and the large consumption of saw bands are not conducive to the reduction of industrial production costs. At present, there are few effective methods in China to facilitate the removal of tailings

Images