Method for purifying polycrystalline silicon by using electron beam smelting furnace

Abstract

The invention relates to a method for purifying polycrystalline silicon by using an electron beam smelting furnace. The method comprises: adding unit amount of a silicon material to each smelting crucible every time, smelting the unit amount of the silicon material for a first predetermined time period according to a first predetermined power by controlling an electron beam gun, repeatedly performing the previous steps until the amount of the silicon material added to the smelting crucible is corresponding to a predetermined amount, smelting for a second predetermined time period, making the molten raw materials of the two smelting crucibles sequentially and alternately flow into a water cooling copper crucible, and scanning the inflowing raw material by using the electron beam gun positioned above the water cooling copper crucible in an area-changing surface scanning manner, wherein it is ensured that the molten pool exists in the water cooling copper crucible, such that impurities are continuously collected in the molten pool and volatilize; after the water cooling copper crucible is completely filled with the raw material, reducing the power by controlling the electron beam gun positioned above the water cooling copper crucible in a constant-area surface scanning manner, and collecting the impurities in the silicon ingot to the center of the top portion of the silicon ingot; and cooling, discharging the ingot, and sawing the impurity enriching zone so as to obtain the polycrystalline silicon.

Description

technical field [0001] The invention relates to the technical field of polysilicon production, in particular to a method for purifying polysilicon by using an electron beam melting furnace. Background technique [0002] With the rapid development of the photovoltaic industry in recent years, reducing the cost of photovoltaic systems and shortening the energy payback period has become a hot spot in the industry. Reducing the production cost of polysilicon is a prerequisite for the development of photovoltaics, and metallurgical methods stand out with their advantages of low cost and low energy consumption. At present, the main industrial process of physical metallurgy in my country is: industrial silicon → refining and removing B → crushing and pickling → directional solidification → electron beam removing P. [0003] Among them, the electron beam phosphorus removal process is mainly to drop the added silicon block into the bottom of the silicon liquid. With the bombardment o...

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Problems solved by technology

[0004] However, the above-mentioned electron beam dephosphorization process has the following problems: 1. It has high requirements on the quality and particle size of the feed material. For example, it is required that the particle size of the raw material must reach the range of 5-20mm. The purity of the material reaches more than 99.999%;

[0005] 2. The structure of the electron beam furnace is divided into three guns: left, middle and right, and the total power reaches more than 1800kw when running at the same time. Since the existing electron beam dephosphorization process takes a long time, the melting time is more than 30 hours. The weight of the finished ingot produced by each furnace is about 750kg. According to the market demand for polysilicon, its energy consumption is high, the cost is high, and the efficiency is low;

[0006] 3. In the solidification process of the existing electron beam dephosphorization process, the coupling effect of the segregation of impurities at the solid-liquid interface and the evaporation at the gas-liquid interface can deeply remove impurities such as phosphorus and aluminum that have both segregation and evaporation properties elements, but its removal effect on non-metallic impurities that are difficult to volatilize and metal impurities with poor segregation effect is not good;

[0007] 4. The feeding speed of the two horizontal crucibles on the left and right is too fast, and the weight of each feeding is 2.4kg, resulting in a high material accumulation thickness in the water-cooled copper crucible. Always translate according to the diagonal and symmetry axis of the rectangular frame. Due to the long smelting time, the raw materials volatilize greatly during the smelting process, and the volatilization rate is about 15%, resulting in low yield and high cost.