RU2142909C1 - Method of production of high-purity trichlorosilane and device for realization of this method - Google Patents

Abstract

FIELD: production of silicon-containing materials; production of chlorosilanes used in microelectronics and high-purity silicon. SUBSTANCE: high-frequency plasma discharge is excited in plasma chemical reactor and reagents - hydrogen and silicon tetrachloride - are fed to zone of discharge; then their interaction is ensured and trichlorosilane is separated from products of reaction as target product. Plasma discharge is excited between two silicon electrodes in form of localized plasmoid of spherical form and reagents are fed to central zone of plasmoid by directional flow from its periphery to center. Device for reralization of this method includes plasma chemical reactor fitted with two electrodes made from high-purity silicon and located at distance relative to each other taking into account forming of plasmoid between them and unit for forming flow of reagents made in form of at least one circular slotted nozzle located coaxially relative to electrode; outer wall of nozzle is formed by surface of truncated cone whose vertex is located in center of zone of formation of plasmoid; outer wall of electrode is used as inner wall of nozzle. Device includes also high-frequency oscillator connected to electrodes. EFFECT: enhanced efficiency. 8 cl, 3 dwg, 1 tbl, 1 ex

Description

 The present invention relates to the production of silicon-containing materials by the plasma-chemical method and, more specifically, relates to a method for producing high-purity trichlorosilane and a device for its implementation. The invention can be successfully used in the production of chlorosilanes used as volatile silicon compounds in microelectronics and high-purity silicon technology.

A known method for producing high-purity trichlorosilane by reacting silicon tetrachloride with technical silicon and hydrogen chloride at 380-450 ^o C and separation of the mixture of chlorosilanes on diffusion membranes (SU, A, 2038297). The method allows to obtain trichlorosilane with a content of volatile impurities of 6 • 10 ^-2 vol.% And impurities of metals less than 1 • 10 ^-6 wt.%.

However, this method is characterized by a low specific productivity of the order of 1 g / cm ³ • hour.

 In addition, a method for producing trichlorosilane (US, A, 4309259) is known, consisting in the fact that a high-frequency plasma discharge between metal electrodes (in particular, tungsten and copper) is excited in a plasma chemical reactor, and a plasma discharge is formed near the tungsten electrode, and a copper electrode is a reactor vessel; reagents — hydrogen and silicon tetrachloride — are fed into the discharge zone through a hole in a tungsten electrode, and ensure their interaction at atmospheric pressure and from the reaction products, as left product recovered trichlorosilane and dichlorosilane.

 From the same source, a device is known for implementing the above-described method for producing high-purity trichlorosilane by reacting silicon tetrachloride with hydrogen, containing a plasma-chemical reactor equipped with two electrodes, a supply pipe for reactants and a pipe for removing reaction products, as well as an RF oscillator electrically connected to the electrodes.

 The known method requires for its implementation relatively high energy costs associated with the need to cool metal electrodes, especially copper, is characterized by a low yield of trichlorosilane (about 42%), since the reagents are fed into the reactor with a diverging stream and do not completely enter the zone of the bundle-like plasma clot . In addition, when implementing the known method using a device equipped with copper and tungsten electrodes, the possibility of contamination of the resulting product with electrode material is very high.

 The basis of the invention is the task to create a method for producing high-purity trichlorosilane suitable for use as a silicon source in microelectronics technologies, which would eliminate the possibility of contamination of the resulting product with electrode material, would increase the yield of the product and at the same time be characterized by low energy consumption, and also create reliable in operation and convenient to use device for implementing this method.

 This problem is solved by the fact that in the method for producing high-purity trichlorosilane, consisting in the fact that a high-frequency plasma discharge is excited in a plasma chemical reactor, reagents - hydrogen and silicon tetrachloride are fed into the discharge zone, ensure their interaction and trichlorosilane is isolated from the reaction products, according to the invention, a plasma discharge is excited in the gap between two electrodes of high-purity silicon in the form of a localized bunch, essentially spherical in shape, and the reagents are fed into the central zone of the bunch with a directed flow from its periphery to the center.

It is advisable to apply the reagents in two streams at an angle to each other, preferably at an angle of 90 ^o .

 It is possible, in addition, to apply the reagents in two flows directed in the opposite direction.

 It is desirable to maintain a pressure in the range of 0.5-5 atm in the plasma chemical reactor, however, it is preferable from the point of view of ensuring the highest (~ 60%) yield of trichlorosilane to maintain the pressure substantially equal to 0.7 atm.

 The problem is also solved by the fact that in the device for producing high-purity trichlorosilane by the interaction of silicon tetrachloride with hydrogen containing a plasma-chemical reactor equipped with two electrodes, a supply pipe for reactants and a pipe for removal of reaction products, as well as a generator of RF oscillations electrically connected to the electrodes, according to the invention, the electrodes are made of silicon and are located at a distance from each other selected taking into account the formation of a plasma bunch between them, essentially a spherical while the reactor is equipped with a reagent flow forming means made in the form of at least one slotted nozzle of a ring-shaped shape, located coaxially to the electrode, the outer wall of the nozzle being formed by the surface of a truncated cone with an apex essentially in the center of the clot forming zone, and the function of the inner wall the nozzle performs the outer surface of the electrode.

 It is advisable to make the electrodes in the form of rods and arrange them at an angle to one another, preferably at an angle of 90 degrees.

 It is also possible to make the electrodes in the form of rods and arrange them coaxially.

 The use of electrodes made of high-purity silicon, eliminates their contaminating effect, ensures the purity of the resulting trichlorosilane at the level of purity of the original silicon tetrachloride. Because the discharge region is located between two silicon electrodes and at the same time they are located at a fairly close distance from each other, an easily controlled local region of the plasma discharge is created. Each electrode is washed by the initial gas flow of the initial reaction mixture, while the flow is formed by the type of nozzle burner (concentration of the jet in the region of the center of the plasma discharge).

The invention is further explained in the description of specific options for its implementation and the accompanying drawings, in which:
FIG. 1 schematically shows a device for producing high-purity trichlorosilane according to the invention, the electrodes are angled;
FIG. 2 is the same as in FIG. 1, the electrodes are aligned;
FIG. 3 is a block diagram of a production plant for producing trichlorosilane comprising a device according to the invention.

A device for producing high-purity trichlorosilane by reacting silicon tetrachloride with hydrogen, schematically represented in FIG. 1, according to the invention, includes a plasma-chemical reactor 1, equipped with two high-purity silicon electrodes 2, located at an angle to each other, preferably at an angle of 90 ^o and at a sufficiently small distance from one another, selected taking into account the formation in the zone between them localized plasma clot 3, essentially spherical in shape. In the reactor 1, in addition, there is provided a means 4 for forming a reagent flow, made in the form of at least one, in the described example, two slotted nozzles 5, the wall 6 of which is farthest from the surface of the electrode 2, each of which is inclined to the surface of the electrode 2. In the described As an example, the electrodes 2 have the shape of rods, and the slotted nozzle 5 has an annular shape and its inclined wall 6 is concentric with the electrode 2, the outer surface of which forms the second wall of the annular nozzle 5. The inclined itself Tenkai 6 has the shape of a frustoconical surface whose apex is located substantially in the center zone forming plasma clot 3. In the upper part of the reactor 1 there are nozzles 7 and reactant feed pipe 8 outlet of the reaction products. Energy for the implementation of the chemical reaction is supplied from the generator 9 RF oscillations, electrically connected to the electrodes 2.

 Depicted in FIG. 2, the device for producing high-purity trichlorosilane differs from the variant of the device shown in FIG. 1 by the fact that in it the electrodes 2 'are aligned. This version of the device is more compact and easier to manufacture.

In FIG. 3 shows a block diagram of a production plant for the production of high-purity trichlorosilane. The installation includes a hydrogen source 10, a palladium filter 11, a bubbler 12 with liquid silicon tetrachloride, a plasma-chemical reactor 13, a trap 14, which maintains a temperature of -78 ^o C to isolate chlorosilanes from the reaction products, and an adsorber 15 sec activated carbon for trapping hydrogen chloride. To the electrodes of the reactor 13 through the matching device 16 is connected to the generator 17 of the RF oscillations.

 The method for producing high purity trichlorosilane according to the invention will become apparent from the description of the operation of the device shown in FIG. 1-3.

 The device operates as follows.

The initial vapor-gas mixture of reagents - hydrogen and silicon tetrachloride is fed through the nozzles 7 and nozzles 5 into the plasma chemical reactor 1. Moreover, due to the fact that the outer wall 6 of the slot nozzle 5 is made in the form of a surface of a truncated cone with an apex in the central part of the zone of formation of the plasma clot 3, the reagents are fed essentially to the center of the bunch 3 in a directed flow from its periphery. Moreover, in the embodiment of the device shown in FIG. 1, due to the arrangement of the electrodes 2 at an angle of 90 ^{o, it is} possible to organize the flow of reagents with a minimum of exposure to the electrodes 2 of chemically active particles.

 The creation of a plasma bunch 3 is carried out by organizing a high-frequency electric discharge between the electrodes 2. The discharge power is chosen to be minimal, provided that the discharge is stable. It is preferable to use an electrical frequency of 40 MHz. The starting reagents, passing through the region of the plasma clot 3, react with the formation of trichlorosilane and hydrogen chloride. The reaction products are discharged from the reactor through pipe 8. The exhaust gas-vapor mixture consists of unreacted hydrogen and silicon tetrachloride, as well as trichlorosilane and hydrogen chloride. The resulting mixture is separated, for example, by condensation to isolate trichlorosilane and hydrogen chloride as a useful product. Hydrogen and silicon tetrachloride are trapped by trap 14 and adsorber 15 and returned to the cycle.

 The use of silicon electrodes 2 allowed to reduce energy consumption by 4 times and to reduce the pollution of the target product. The reagent flow forming device allowed to increase the yield of trichlorosilane from 42% to 60%.

 It is preferable to carry out the method at a pressure of 0.5-5 atmospheres, and the electrodes are used in the form of sufficiently long rods to minimize the flow of energy in the form of heat to the electrode holders. The rods have a cylindrical configuration, which, in turn, provides a time-stable plasma discharge.

 Carrying out the process at a pressure of less than 0.5 atm leads to the release of trichlorosilane less than 20%. At a pressure of more than 5 atm, technical difficulties arise in the implementation of the process.

 The use of electrodes made of high-purity silicon, eliminates their contaminating effect, ensures the purity of the resulting trichlorosilane at the level of purity of the original silicon tetrachloride. Because The discharge region is located between two silicon electrodes, while they are located at a fairly close distance from each other, an easily controlled local region of a stable plasma discharge is created. Each electrode 2 is washed by the gas stream of the initial reaction mixture, while the flow is formed by the type of nozzle burner (concentration of the jet in the region of the center of the plasma discharge). Carrying out the process at a pressure of 0.5-5 atmospheres with the supply of the starting reagents in the form of a gas stream formed according to the invention increases the yield of trichlorosilane up to 45-60%, while it is preferable to use the above characteristics simultaneously. When carrying out the process without using a gas flow former, the yield of trichlorosilane is less than 40%. It is preferable to use silicon electrodes in the form of rods, because they create a cylindrical configuration, which allows for a stable plasma discharge in time.

 For a clearer understanding of the essence of the present method below is a specific example of its implementation.

Example
Silicon electrodes were installed in a reactor made of quartz glass. Filling the reactor with hydrogen to a pressure of 0.7 atm, a high-frequency discharge was ignited. The discharge power was set to ensure stable combustion. A vapor-gas mixture containing silicon tetrachloride with an impurity content (see table) and hydrogen purified by diffusion through a palladium filter were passed through the discharge plasma in a volume ratio of 1: 4.5. The flow rate of the gas-vapor mixture was maintained equal to 0.058 mol / min. The passed gas-vapor mixture was analyzed for the content of trichlorosilane, molecular impurities and impurities in the form of suspended particles. According to chromatographic analysis, the content of trichlorosilane in the mixture of chlorosilanes was 60%, the content of molecular impurities in the resulting product is shown in the table. Impurities in the form of suspended particles were analyzed by the chemical atomic emission method, the content of these impurities is shown in the table.

 Depending on the performance, the optimal discharge power, reagent consumption and their ratio, corresponding to the specific implementation of the method, were established. If necessary, we selected the conditions for the process in a continuous form, in which the etching of the electrodes does not occur.

 Such features as process control at a pressure of 0.5-5.0 atm do not depend on the design features of the installation (by varying the pressure within the indicated limits, the trichlorosilane yield is 45-60%); the use of silicon electrodes (if it is necessary to obtain high-purity trichlorosilane and in case of possible etching of the electrodes, they are prepared from high-purity silicon); and use of a gas flow former.

Claims (8)

 1. A method for producing high-purity trichlorosilane, consisting in the fact that a high-frequency plasma discharge is excited in a plasma-chemical reactor, reagents hydrogen and silicon tetrachloride are fed into the discharge zone, they interact, and trichlorosilane is isolated from the reaction products, characterized in that the plasma the discharge is excited in the gap between two electrodes of high-purity silicon in the form of a localized bunch, essentially spherical in shape, and the reagents are fed into the central zone of the plasma gustka directional flow from the periphery to the center. 2. The method according to claim 1, characterized in that the reactants are fed in two streams at an angle to each other, preferably at an angle of 90 ^o .  3. The method according to claim 1, characterized in that the reagents are fed in two streams directed in the opposite direction.  4. The method according to any one of claims 1 to 3, characterized in that the pressure in the range of 0.5 to 5 atm is maintained in the plasma chemical reactor.  5. The method according to claim 4, characterized in that the pressure is maintained equal to essentially 0.7 atm.  6. A device for producing high-purity trichlorosilane by the interaction of silicon tetrachloride with hydrogen, containing a plasma-chemical reactor equipped with two electrodes, a supply pipe for reactants and a pipe for removing reaction products, as well as an RF oscillator electrically connected to the electrodes, characterized in that the electrodes are made of silicon and are located at a distance from each other, selected taking into account the formation between them of a plasma clot, essentially spherical in shape, while the reactor is equipped with ormirovaniya reactant stream, formed in the form of at least one slot nozzle annular shape disposed coaxially with the electrode, wherein the outer wall of the nozzle formed surface of a truncated cone with the apex at substantially the center of the zone of formation of the clot, and the inner wall of the function of the nozzle performs outer surface of the electrode. 7. The device according to claim 6, characterized in that the electrodes are made in the form of rods and are located at an angle to one another, preferably at an angle of 90 ^o .  8. The device according to claim 6, characterized in that the electrodes are made in the form of rods and are located coaxially.

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