RU2173297C2 - Method for production of monosilane from silicon tetrachloride - Google Patents

Abstract

FIELD: inorganic compounds technologies. SUBSTANCE: invention, in particular, relates to monosilane appropriate for manufacturing especially pure semiconductor silicon. Method is characterized by that silicon tetrachloride is interacted with lithium hydride whose surface is subjected to activation with vibrating conveyer. Silicon tetrachloride gas flow is fed in counter-current mode into moving conveyer charged by lithium hydride and process is carried out at 290-300 C. EFFECT: increased yield of monosilane at lower temperature and reduced reaction time, enabled wasteless technology. 2 ex

Description

 The invention relates to a technology for producing highly pure semiconductor silicon and products for microelectronics. Since monosilane is one of the main sources of semiconductor silicon, it is important to develop a new method for its preparation.

 A known method of producing monosilane according to US patent N 477868, 1988, MKI C 01 B 33/04 "Obtaining a silane and a metal aluminum halide", comprising the interaction of tetrahalide or silicon hydrogen halide with an alkali metal lithium aluminum hydride in the presence of a Quaternary ammonium salt promoter.

There is also known a method of producing monosilane (A. Taylor, Purification and analytical Methods of Gaseous and Metallic Impurities in High Purity Silane. J. Crystal Growth. 1988, v. 89, p. 28-38), comprising the interaction of calcium hydride with a silicon-containing compound in euthetic salt melt of lithium chloride and potassium chloride at 360 ^o C, purification of monosilane, gaseous silicon tetrafluoride at a concentration of 50-90 vol.% is used as a silicon-containing compound. % in nitrogen pre-purified from oxygen. Purification of monosilane is carried out by adsorption on a solid sorbent - granular sodium fluoride in two stages.

 The common drawbacks of both analogues are the involvement of more than two substances as starting reagents, which obviously introduces additional pollution into the target product, requiring utilization or recycling, high energy costs of processes, and complicated hardware design. The result is contaminated monosilane, requiring additional deep purification, which leads to a rise in price of the product.

 The closest in technical essence and the achieved result - the prototype is a method for producing monosilane according to patent N 0105778, EP (Fr), 1984, MKI C 01 B 33/04 "Method and device for producing pure silane by the reaction of chlorosilane with lithium hydride". The method is carried out in two reactors with mixers and a separator for separating the gas mixture leaving the second reactor. In the first reactor, chlorosilanes and lithium hydride are reacted in a mixture of molten salts to form monosilane and a mixture containing molten salts and unreacted lithium hydride. Chlorosilane and a mixture containing molten salts and lithium hydride selected from the first reactor are fed into the second reactor, and a gaseous mixture containing monosilane and chlorosilanes and a mixture of molten salts not containing lithium hydride are obtained. The gaseous mixture leaving the second reactor is separated into monosilane and chlorosilanes, which can be recycled.

 The disadvantages of the method are: high temperature of the process, contamination of the finished product with impurities from a molten salt, the need for disposal of the resulting aluminum and alkali metal chlorides, and complicated hardware design.

 The objective of the invention is to increase the yield of monosilane at a lower temperature and reduced reaction time by a waste-free technology by the interaction of silicon tetrachloride with lithium hydride.

The problem is solved due to the fact that in the inventive method for producing monosilane by reacting silicon tetrachloride with lithium hydride, according to the invention, the surface of lithium hydride is subjected to activation by a vibrating conveyor, while the gas stream of silicon tetrachloride is supplied countercurrent to the movement of the conveyor with lithium hydride and the process is carried out at 290 -300 ^o C.

 The indicated set of features is new and has an inventive step, since the use of mechanochemical activation of lithium hydride and the use of reagents without the addition of solvents and catalysts can reduce the temperature, reaction time, and makes it possible to increase the yield of monosilane using waste-free technology.

Lowering the temperature of the reactor to 280 ^o C increases the reaction time to 25-30 minutes, while the yield of monosilane does not exceed 90%. Along with silicon tetrachloride and monochlorosilane up to 1-2%, dichlorosilane up to 3-4% and trichlorosilane up to 6-7% are present in the residues. Thus, a decrease in the temperature of the process below 290 ^o C can lead to contamination of the finished product with partially substituted chlorosilanes and requires a longer reaction time to complete the process.

The implementation of the process at 310 ^o C after 10-15 minutes leads to the release of monosilane 89%, simultaneously containing up to 10 ppm HCl. In addition, black plaque of metallic silicon is detected on the walls of the reactor and on lithium chloride, which is formed by the reaction
SiH ₄ ---> Si + 2H ₂
Hydrogen evolved can react with silicon tetrachloride, which has not yet had time to react, to form hydrogen chloride
SiCl ₄ + H ₂ ---> SiHCl ₃ + HCl
SiHCl ₃ + H ₂ ---> Si + 3HCl
Thus, the reaction at a temperature of 310 ^o C and higher leads to a partial thermolysis of the resulting monosilane and the possible contamination of the target product with hydrogen chloride and other chlorine-containing compounds.

 The use of mechanochemical activation of lithium hydride and the use of reagents without the addition of solvents and catalysts can reduce the temperature, reaction time, and makes it possible to increase the yield of monosilane by non-waste technology.

 The method is as follows.

 Example 1

Lithium hydride is placed in a rotating drum-type reactor made of stainless steel and equipped with stainless steel balls, so that the pressure of the vapor generated during the monosilane reaction will not be much more atmospheric (according to stoichiometry) (to avoid explosive situations). A vacuum of up to 10 ^-2 mm Hg is created in the reactor. with simultaneous heating to 310 ^o C. After that, reduce the temperature to 300 ^o C and inject an equimolar amount of tetrachloride, silicon. After 15 minutes, the reactor was cooled and the resulting monosilane was taken to the collection by freezing. In this case, monosilane (yield 97%) containing less than 0.1% hydrogen, unreacted silicon tetrachloride and lithium chloride is obtained. Extraneous impurities in the product containing compounds of carbon, boron, phosphorus, sulfur, arsenic and other elements up to 1 ppm were not detected.

 The resulting monosilane is a highly pure product suitable for the production of “solar” silicon.

 The liberated lithium chloride is converted to lithium hydride, which is re-launched into the cycle.

 Example 2

 The continuous process for producing monosilane is carried out in a reactor equipped with a vibrating conveyor with a frequency of 50 - 100 Hz. Silicon tetrachloride is supplied countercurrent to the movement of the conveyor with lithium hydride. The interaction time is 15 minutes. The yield of monosilane is 97%. The method is carried out in closed loop mode.

Claims (1)

A method of producing monosilane by reacting silicon tetrachloride with lithium hydride, characterized in that the surface of lithium hydride is subjected to activation by a vibrating conveyor, while the gas stream of silicon tetrachloride is supplied countercurrent to the movement of the conveyor with lithium hydride and the process is carried out at 290-300 ^o C.