METHOD OF PRODUCING POLYCRYSTALLINE SILICON Russian patent published in 2013 - IPC C01B33/03 C01B33/35 C30B28/14 C30B29/06 

FIELD: chemistry.

SUBSTANCE: invention relates to the technology of semiconductor materials and can be used in production of polycrystalline silicon. The method involves preparation of a vapour-gas mixture from chlorosilanes and hydrogen in an evaporator under pressure by bubbling hydrogen through a layer of chlorosilanes, hydrogen reduction of silicon on heated silicon rods in a reactor, low-temperature condensation of chlorosilanes with the vapour-gas mixture coming out of the reactor, rectification of chlorosilanes, absorptive separation of hydrogen and hydrogen chloride, desorption of hydrogen chloride from the absorbent and compression of the purified hydrogen, wherein at the first step in the evaporator, a first vapour-gas mixture is prepared at pressure of 0.8-1.0 MPa, for which a mixture is fed into the evaporator, said mixture consisting of silicon-containing products with a predominant volume ratio of trichlorosilane and hydrogen at temperature of 250-300°C, which is heated by recuperating heat of the vapour-gas mixture coming out of the reactor, wherein the molar ratio of hydrogen to chlorosilanes pH₂/pCS is equal to (3-4): 1; the obtained vapour-gas mixture is fed into the reactor, the temperature field inside of which is evened out on the diameter and height by a heat mirror which is obtained by coating the reactor walls with material with low transverse thermal conductivity of 3-5 W/m K, and the diameter of the starting silicon rods heated to temperature of 1050-1100°C is increased fourfold; at the second step a second vapour-gas mixture is prepared in the evaporator at pressure of 0.8-1.0 MPa, said mixture consisting of silicon-containing products with a predominant volume ratio of silicon tetrachloride and hydrogen at temperature of 250-300°C, heated by recuperating heat from the vapour-gas mixture coming out of the reactor, wherein molar ratio of hydrogen to chlorosilanes pH₂/pCS is equal to (6-8): 1; the obtained vapour-gas mixture is fed into the reactor on silicon rods heated to temperature of 1150-1200°C in order to simultaneously carry out hydrogenation of silicon tetrachloride to trichlorosilane and dichlorosilane and hydrogen reduction of silicon from the formed silicon-containing products; the vapour-gas mixture coming out of the reactor is fed for low-temperature condensation in order to separate gaseous hydrogen with hydrogen chloride and liquid chlorosilanes; gaseous hydrogen and hydrogen chloride at pressure of 0.6-0.8 MPa are fed into an absorber for separation; separation of hydrogen chloride from the absorbent is carried out in a desorber, wherein pressure is at least 10 times lower than pressure in the absorber, while simultaneously heating the absorbent; before feeding hydrogen from the absorber into the adsorber in order to remove traces of chlorosilanes and hydrogen chloride, said hydrogen at temperature of minus 62°C to minus 65°C is fed into a chlorosilane condensation unit to recuperate "cold" through counter-flow of a vapour-gas mixture from the reactor for hydrogen reduction of silicon.

EFFECT: invention provides additional formation of trichlorosilane and dichlorosilane from silicon tetrachloride (more than 30 mol %), keeping the formed trichlorosilane and dichlorosilane near the surface of heated silicon rods by maintaining a stable even heat field inside the reaction zone due to presence of a heat mirror on the inner surface of the reactor, which reduces power consumption and production cost of polycrystalline silicon.

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