Method and device for directionally solidifying and purifying polysilicon by vacuum extraction of tailing

Abstract

The method comprises: in an inert gas, melting the silicon material to form silicon melt and insulating; directionally solidifying; stopping ingot pulling when 85-90% of melt is solidified, then diving a quartz tube into the residual silicon melt, vacuum-pumping the other end of the quartz tube by a vacuum-pumping device, pushing the residual silicon melt into the quartz tube under the action of pressure difference, continuously and downwards pulling the ingot, and diving a tailing collecting box below the quartz tube when a crucible departs from a heating zone; cutting off power supply, and stopping heating. After spalling, the quartz tube following the tailing falls down to the collecting box, and the ingot casting obtained in the crucible is high purity silicon ingot casting. The method and the device prevent the diffusion of impurity, reduce technology, and raise yield of the ingot casting. Direct separation of impurity enrichment region is implemented in an end stage of solidification. The device has advantages of convenient reconstruction and installation, and simple operation, can effectively removes the impurity enriched in the tail part of the ingot casting, and saves a production period and cost.

Description

technical field [0001] The invention belongs to the technical field of metallurgical purification, in particular to a method and equipment for extracting tailings and performing directional solidification to purify polysilicon. Background technique [0002] The development of the solar photovoltaic industry relies on the purification of silicon raw materials. In the process of purifying silicon raw materials, the directional solidification method is very important for removing metal impurities with very small segregation coefficients in silicon raw materials. One of the most effective methods, moreover, the directional solidification technique is widely used in metallurgical purification. Directional solidification is the use of forced means to form a temperature gradient in a specific direction in the melt, so that the melt at the low temperature part crystallizes and nucleates, and becomes the starting point for the solidification of the melt. Solidify in the opposite dir...

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Problems solved by technology

[0003] However, at the end of the solidification of the ingot, impurities are enriched in the melt at the top of the crucible. During the final slow solidification process, the impurities with high content will diffuse to the parts with low impurity content, 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 removed tailings are as high as 25%~35%, that is, the yield is only 65-75%, and the hardness of silicon ingots is relatively large, which requires high-power cutting equipment to To separate the purified silicon ingot and the ingot tailings with high tail impurity content, wire cutting and diamond saw band cutting are generally used for cutting at present, but the cost of cutting equipment is high, and the consumption of saw band is large, which is not conducive to the cost of industrial production. reduce, but there are few effective methods in China to facilitate the removal of tailings

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