Method for purifying industrial silicon for preparing solar grade silicon

Abstract

The invention discloses a method for preparing solar-grade silicon through purification of industrial silicon (2N). The method comprises that: the industrial silicon is subjected to primary pulverization pretreatment and is put into a high-temperature solid-phase reaction furnace; the industrial silicon and active gas are subjected to gas-solid reaction at high temperature to achieve the aim of removing metal impurities; then crystalline silicon is cleaned; the purity of the crystalline silicon reaches as high as 99.999 percent (5N), and is further subjected to vacuum melting of electron beams and oriented condensation treatment; finally, active atmosphere plasma is adopted to further purify the crystalline silicon, and volatile elements which have high activity and are easily oxidized to generate high saturated vapor pressure are removed; and polysilicon is cast in an integrated furnace for casting plasma polysilicon and is directly used for manufacturing a cell chip. The method combines high-temperature gas-solid reaction to remove the metal impurities, the electron beams to remove the volatile elements and a plasma purification and casting integrated furnace technology, improves the purity of the polysilicon to 99.99999 percent (7N) and, fully meets requirement of a solar cell industry on the solar-grade silicon.

Description

technical field [0001] The invention relates to the technical field of preparation and purification of polysilicon, in particular to a method for directly preparing solar grade silicon by purifying industrial silicon. Background technique [0002] In today's situation of increasingly tense energy and increasing environmental pressure, renewable energy has been paid more and more attention by governments of various countries. As an important renewable energy, solar energy has sufficient cleanliness, absolute safety, and relatively extensive resources. With the advantages that other conventional energy sources do not have, such as safety and sufficiency, long life and maintenance-free, photovoltaic energy is considered to be the most important new energy in the 21st century. Its development and utilization have become an important part of the sustainable development strategies of various countries. At present, my country's renewable energy scale is only 8%, and the future dev...

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Problems solved by technology

[0003] Polysilicon is the basic material of the electronics industry and solar photovoltaic industry. In recent years, driven by the development of the solar cell industry, the polysilicon market has grown rapidly. However, at present, the methods for producing solar-grade high-purity silicon in countries around the world mostly use Siemens method or improved Siemens method , this kind of method adopts thermal chemical vapor deposition process, which has long process flow, high energy consumption, high investment cost, various toxic gases involved in the production process, and difficult recovery and treatment of by-products, especially in China, where the polysilicon market is in short supply. It has become increasingly prominent and has attracted widespread attention from all over the world. Therefore, it is of great significance to directly purify and prepare solar-grade silicon by using industrial silicon as raw material and has a bright future.

[0004] For the oxidation refining method adopted in the physical purification technology patent CN101066762A, although the method is simple and feasible, it cannot satisfy the sufficient contact between the oxidizing gas and the liquid silicon material, and the purity of the produced silicon material cannot meet the requirements of silicon for solar cells

Patent CN101122047A uses the disproportionation reaction to prepare high-purity silicon, followed by plasma and electron gun purification. Although this method is theoretically possible, the disproportionation reaction is a reversible process. In the end, it is necessary to drop from high temperature to low temperature. How to avoid the reverse reaction, and It is still a big problem to realize the separation of various products and ensure that other elements can be separated in the disproportionation reaction. It is difficult to realize a large number of industrialization

Patent CN1803598 adopts vacuum oxidation refining after pickling, vacuum degassing, and directional solidification process; oxidation refining, and vacuum degassing have a better effect on the removal of non-metallic elements and volatile elements, but volatilization is carried out on the surface, oxidation Refining requires full contact between oxidizing substances and silicon materials. How to realize the volatilization of impurities inside liquid silicon materials is still a difficult problem; the pickling used in this patent is an effective method for purifying industrial silicon, but its The disadvantage is that industrial silicon cannot be purified to more than 4N, that is to say, metal elements that are difficult to volatilize need to be further removed. Although directional solidification is an important means of separating metal impurities with small segregation coefficients, metal elements with large segregation coefficients will not be able to Once directional solidification is removed, the head and tail of the silicon ingot after directional solidification must be cut off at the same time. Due to the limitation of the height of the silicon ingot (no one has achieved the height of the silicon ingot to 0.55 meters), the product yield of this method will be very low.

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