Polycrystalline silicon is purified from industrial silicon and can be divided into metallurgical grade, solar grade and electronic grade according to its purity. Industrial silicon, also known as metal silicon, is made of quartz and coke in the electric furnace smelting products, silicon content is generally more than 99% (2N), the remaining impurities are iron, aluminum, calcium, etc., is the upstream raw materials of polysilicon. At present, the preparation technology of polysilicon mainly includes chemical method and physical method. Chemical method is the current mainstream process, accounting for about 80% of the global output
Industrial silicon, also known as metal silicon or crystalline silicon, its main use is as an additive for non-iron based alloys, and the international commercial silicon is usually divided into metal silicon and semiconductor silicon. Silicon metal is made of quartz and coke in the electric furnace smelting products, the main component of silicon content of about 98% (silicon content of 99.99% is also included in silicon metal), the remaining impurities are iron, aluminum, calcium and so on. Metal silicon is the industrial purification of elemental silicon, mainly used in the production of organic silicon, high purity semiconductor materials and the preparation of special purpose alloys.
Polysilicon is a form of elemental silicon. When molten elemental silicon is solidified under supercooling conditions, the silicon atoms are arranged into multiple crystal nuclei in the form of a diamond lattice. If the nucleus grows into grains with different crystal orientations, the grains combine and crystallize into polysilicon.
Polysilicon can be used as raw material for drawing monocrystalline silicon, and the difference between polysilicon and monocrystalline silicon is mainly manifested in physical properties. For example, the anisotropy of mechanical properties, optical properties and thermal properties is far less obvious than that of monocrystalline silicon. In terms of electrical properties, the electrical conductivity of polysilicon crystals is also far less significant than that of monocrystalline silicon, or even almost no electrical conductivity. Polysilicon and monocrystalline silicon can be distinguished from the appearance, but the real identification must be determined by analyzing the crystal direction, conduction type and resistivity. Polysilicon is the direct raw material for producing monocrystalline silicon.
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