WO2011099883A1 - Method for producing silicon - Google Patents

Abstract

The present invention pertains to the field of silicon production and, more specifically, to the use of the plasma chemical reaction of initial compounds to produce silicon, and can be used, for example, in semi-conductor technology and in the photo-electric industry for manufacturing solar panels. The technical result is that of reducing power consumption and simplifying implementation. The method for producing silicon comprises grinding an initial silicon-containing compound to a highly dispersed state in which the individual particles have a size of less than 1 micron, and injecting the resultant powder together with a carrier gas into the high-temperature stream of plasma-forming gases of a plasmatron connected with a reactor and provided in a chamber in which a vacuum is generated. The method comprises creating the conditions for the evaporation and pulverization of the silicon-containing compound so as to obtain pure silicon atoms and volatile reaction products by adjusting the powder feed rate and the plasmatron power, and the pure silicon is then condensed on the walls and the bed of the reactor while the volatile products are removed by means of the vacuum. The process is carried out at a temperature in the reactor higher than 3000°C, a powder feed rate of 1 to 10 cm³/sec., and a plasmatron power of 700 - 25000 W.

Description

 The method of producing silicon

 The present invention relates to a technology for producing silicon, namely, to use the plasma-chemical interaction of the starting compounds to obtain it, and may find application, for example, in semiconductor technology, in the photoelectronic industry in the manufacture of solar cells.

 A method is known for producing silicon and its dioxide from silicon tetrachloride by plasma-chemical interaction using a low-temperature plasma, in particular a high-frequency induction plasma (A.N. Krasnov et al. Low-temperature plasma in metallurgy. Publishing House Metallurgy, 1976). The method is energy-intensive and complicated in hardware design, receive not enough pure silicon.

 A known method of producing silicon (ΙΌ.Β. Tsvetkov, S. A. Panfilov. Low-temperature plasma in the recovery processes. Publishing House of Science, 1980, S. 16, 17, 228-235), including plasma-chemical interaction of the source gaseous compounds. For the plasma-chemical process, the energy of a low-temperature nonequilibrium microwave discharge plasma is used. As the plasma-forming gas, both the gases involved in the chemical conversion and inert gases can be used. The disadvantage of this method is the lack of pure silicon and high energy intensity.

A known method for the production of silicon (RF patent N "1602391, IPC СВВ 33/02, 1990) comprising generating gas plasma in a reactor, injecting silica-containing raw materials and a solid carbon-containing reducing agent. The plasma gas used is hydrogen and hydrocarbons, or an inert gas such as argon or nitrogen, or a mixture of a reducing and inert gas. Silicon dioxide, which is fed into the plasma, is taken in the form of powders, granules, pieces, pebbles, balls or briquettes. The disadvantage of this method is the lack of purity of the obtained silicon.

 A known method of producing silicon and its compounds (RF patent .153016, С01В 33/00, 2000) consists in the reduction or decomposition of silicon compounds in the presence of reagents in the zone of low-temperature thermoequilibrium plasma, with the addition of a combustible mixture, for example, hydrogen and oxygen, into the reaction zone and activating gaseous reagents with ultraviolet radiation using a low-temperature plasma element with a sliding surface discharge, which is located inside the reaction, as a source of low-temperature plasma and UV radiation hydrochloric chamber. In this method, the reaction of the plasma-chemical transformation of the starting gaseous compounds is carried out using the heat of the combustion reaction of the combustible substances introduced into the reactor, with the initiation of the combustion reaction by an energy impulse from a sliding surface discharge, combining the energy of a nonequilibrium discharge plasma between the electrodes and hard ultraviolet radiation from the surface of the dielectric. It is impossible to evaluate the purity of the silicon obtained by this method, since the example is given only of obtaining silicon dioxide from its tetrachloride.

A known method for producing silicon (RF patent No. 2345949, MN C01 B 33/02, 2009), comprising introducing powdered silicon nitride into the reaction zone and carrying out the thermal decomposition reaction with the formation of the target product and technically pure nitrogen. In this method, in one embodiment, powdered silicon nitride is continuously fed into a plasmatron reactor into a high-temperature stream of plasma-forming gases, mainly argon and hydrogen, in an argon stream. The instant decomposition of silicon nitride with the formation of gaseous nitrogen and silicon. Silicon of semiconductor purity is obtained. j ->

 A known method of producing polycrystalline silicon of high purity (RF patent M> 2367599, MGZH C01B 33/021, 2009), which consists in feeding a mixture of silicon-containing compounds with a carrier gas through a coaxial pipe with a central electrode. A plasma discharge is ignited in a jet of cremated compounds between the central electrode and the pipe walls, and also between the central electrode and the target substrate. Pyrolytic decomposition (monosilane) or reduction (silicon dioxide) with the release of polycrystalline silicon occurs in the plasma discharge zone. The reaction mixture can be fed tangentially to the cylindrical surface of the pipe so that the silicon-containing compounds move in a spiral along the axis. A feature of the method is the use of highly pure substances (pure silicon) in the materials from which the device for implementing the method is made. The method is energy intensive and complicated in hardware design.

 The technical result is to reduce energy consumption and simplify its hardware design.

The technical result is achieved by the fact that the method for producing silicon includes grinding the initial silicon-containing compound to a finely dispersed state with individual particle sizes less than 1 μm, injecting the obtained powder with a carrier gas into a high-temperature jet of plasma-forming gases of a plasmatron connected to the reactor and placed in a chamber in which create a vacuum, providing conditions for the evaporation and atomization of a silicon-containing compound with the formation of pure silicon atoms and volatile reaction products and by controlling the powder flow rate and the power of the plasmatron, the pure silicon condenses on the walls of the reactor and the substrate, and the volatiles were removed by vacuum. Argon and hydrogen are used as carrier gases and plasma-forming gases, and silicon dioxide in the form of artificial quartz or natural quartzite is used as silicon-containing compounds.

The process is carried out at a temperature in the reactor above 3000 ° C, a powder feed rate in the range from 1 to 10 cm ³ / s and a plasmatron power of 700–25000 W.

 At least two jets of plasma-forming gases with a silicon-containing compound powder are simultaneously fed to the reactor at the same time as two parallel or oncoming or directed at an angle to each other.

 A vortex motion of a silicon-containing compound is created in the plasmatron and reactor.

 Silicon inert materials are used as the substrate, and silicon is deposited in the form of thin layers or films.

A vacuum is created in the chamber where the plasmatron and reactor are located. The flow of plasma-forming gases (argon and hydrogen) from the plasmatron, together with a jet of finely divided silicon dioxide powder, is fed into a reactor in which silicon dioxide particles, being a dielectric, acquire an effective negative charge on their surface in an RF discharge and are bombarded by positively charged argon ions from the plasma are sprayed onto silicon and oxygen atoms. Oxygen, interacting with hydrogen, forms water vapor, which is pumped out of the reactor and condensed beyond it, and pure silicon particles settle on the inner surface of the reactor, forming a powder or film, depending on the specific mode of the process. Pure silicon can be formed on the surface of substrates introduced into the reactor in the form of thin layers or films, for example, on substrates of silicon, silicon dioxide, silicon nitride. Or, to obtain films of its compounds with a substrate material — a substrate made of graphite, refractory materials, for example, titanium. Figure 1 shows a schematic diagram of a device for implementing the method. It includes:

 - camera 1

 - reactor 2

 - plasmatron 3

 - device 4 for producing silicon dioxide powder

 - a device 5 for feeding powder in an argon stream into a plasmatron 3

- control unit 6

 - device for removing gases and vapors 7

 - substrate 8

 - vacuum pump 9.

 This device provides various modes of plasma combustion and powder feed rates, the formation of plasma flows, the composition and structure of plasma-forming components and their interaction products.

 The method is implemented as follows.

Chamber 1, with the plasmatron 3 and reactor 2 located in it, is pumped out with a vacuum pump 9 to a residual pressure of 5-10 ^"3 Pa. A plasma-forming mixture of gases (argon and hydrogen) and silicon dioxide powder in the argon stream from device 5 are fed into reactor 2 at the same time. preliminarily crushed in the device 4 to particles no larger than 1 μm in size, setting the necessary process conditions using the device 6. Namely, the powder feed rate from the device 5 to the plasmatron 3 is from 1 cm / sec to 10 cm / sec and the power of the plasmatron 3 from 100 to 25000 W, The created conditions for vaporization and sputtering of silicon dioxide to form pure silicon atoms and silicon dioxide product recovery hydrogen (water vapor). Thus pure silicon condenses on the walls of the reactor 2 or the substrate 8, and the volatile reduction products are removed by device 7.

Example 1 The vacuum chamber 1 with the reactor 2 and the RF plasmatron 3 was pumped out

 3 -

to a residual pressure of 5 · 10 ^" Pa, a plasma-forming mixture of gases Ar and H ₂ and a powder of silicon dioxide in an argon stream with particle sizes of not more than 1 μm were simultaneously fed into the reactor.

The powder feed rate was 1 CM ^j per second. They ignited the rf discharge of the plasma torch at a frequency of 13.56 MHz, power 700 watts. The plasma jet of ionized gases and silicon dioxide powder are simultaneously blown into reactor 2, where they create a plasma vortex, while the particles of silicon dioxide are heated to temperatures above 3000 ° C due to the fact that they receive an effective negative charge in the RF discharge and are intensively bombarded by positively charged ions argon, and the energy of these ions is used both for heating and thermal evaporation of silicon dioxide particles, and for its atomization. As a result of the simultaneous action of these two factors, the particles of silicon dioxide are almost completely decomposed into silicon and oxygen atoms. Oxygen is bound by hydrogen atoms and ions from the plasma, forms water vapor that is pumped out by the device 7, and the flow of silicon atoms partially partially ionized in the plasma is directed to the surface of the substrate 8, for example, from silicon, silicon dioxide, graphite, a refractory metal, and forms on it a powder or film of pure silicon, or, depending on the state of the substrate, a layer of the products of interaction with its material — carbides, silicides, etc.

 Example 2

The vacuum chamber 1 to a reactor 2 and RF plasma torches 3, arranged on opposite sides of reactor 2 was evacuated to a residual pressure of 5 x 10 ^"Pa, was fed into the reactor while the plasma forming gas mixture of Ar and H ₂ and silica powder in an argon stream with particle sizes not more than 1 μm (-0, 1 μm). The powder feed rate was 5 cm ³ per second. They ignited the rf discharge of the plasma torches at a frequency of 13.56 MHz and a power of 12150 watts. The plasma jet of ionized gases and silicon dioxide powder are simultaneously blown into reactor 2, where they create a plasma vortex, while the particles of silicon dioxide are heated to temperatures above 3000 ° C due to the fact that they receive an effective negative charge in the RF discharge and are intensively bombarded by positively charged ions argon, and the energy of these ions is used both for heating and thermal evaporation of silicon dioxide particles, and for its atomization. As a result of the simultaneous action of these two factors, the particles of silicon dioxide are almost completely decomposed into silicon and oxygen atoms. Oxygen is bound by hydrogen atoms and ions from the plasma, forms water vapor that is pumped out by device 7, and the flow of silicon atoms partially partially ionized in the plasma is directed to the surface of the substrate 8, for example, from silicon, silicon dioxide, graphite, a refractory metal, and forms a powder or a film of pure silicon, or, depending on the state of the substrate, a layer of the products of interaction with its material — carbides, silicides, etc.

 Example 3

A vacuum chamber 1 with reactor 2 and an RF plasmatron 3 was pumped out to a residual pressure of 5-10 ³ Pa, a plasma-forming mixture of gases Ar and H ₂ and silicon dioxide powder in an argon stream with particle sizes not exceeding 1 μm were fed to the reactor at the same time (~ 0, 1 μm).

The powder feed rate was 10 cm ^" per second. The RF discharge of the plasma torch 3 was ignited at a frequency of 13.56 MHz and a power of 25000 W. The plasma jet of ionized gases and silicon dioxide powder are blown into the reactor at the same time, where they create a plasma vortex, and the silicon dioxide particles are heated at volume to a temperature above 3000 ° C due to the fact that having received an effective negative charge in the RF discharge, they are intensively bombarded by positively charged argon ions, and the energy of these ions is used both for heating and thermal evaporation of silicon dioxide particles, and for its atomization. As a result of the simultaneous action of these two factors, the particles of silicon dioxide are almost completely decomposed into silicon and oxygen atoms. Oxygen is bound by hydrogen atoms and ions from the plasma, forms water vapor that is pumped out by the device 7, and the flow of silicon atoms partially partially ionized in the plasma is directed to the surface of the substrate 8, for example, from silicon, silicon dioxide, graphite, a refractory metal, and forms on it a powder or film of pure silicon, or, depending on the state of the substrate, a layer of the products of interaction with its material — carbides, silicides, etc.

 Example 4

A vacuum chamber 1 with a reactor 2 and an arc plasmatron 3 was pumped out to a residual pressure of 5 · 10 ° Pa, a jet of silicon dioxide powder with a particle size of less than 1 μm (-0.1 μm) and a feed rate of 1 cm per second in a stream was simultaneously fed into the reactor argon with hydrogen and a plasma jet formed in the arc plasmatron 3 from argon and hydrogen at a discharge power of 700 watts. As in Example 1, plasma flows from a plasma torch and silicon dioxide powder create a plasma vortex in reactor 2, in which silicon dioxide particles are heated to T> 3000 ° C, evaporate and atomize, forming silicon and oxygen atoms and ions. Moreover, oxygen is bound by hydrogen from the plasma to water vapor, which is pumped out by the device 7, and silicon is directed to the surface of the corresponding substrates 8. In the case of using an arc plasma torch, the bulk of the plasma discharge energy is spent on the thermal heating of the silicon dioxide powder and its evaporation. In this case, since the arc discharge is ignited outside the reaction zone, and the already formed jet of plasma and silicon dioxide is blown into the reactor, then such the mode allows one to sharply reduce the likelihood of contamination of the final products — silicon and its compounds with impurities from the material of the electrodes of the arc plasma torch, which is a significant advantage of the proposed method compared to the known methods, which also use the arc method of plasma excitation.

 Example 5

A vacuum chamber 1 with a reactor 2 and an arc plasmatron 3 was pumped out to a residual pressure of 5-10 ^'3 Pa, a jet of silicon dioxide powder with a particle size of less than 1 μm (~ 0.1 μm) and a feed rate of 5 cm ³ second in a stream of argon with hydrogen and a plasma jet formed in an arc plasmatron from argon and hydrogen at a discharge power of 12150 W. As in Example 1, plasma flows from a plasma torch and silicon dioxide powder create a plasma vortex in the reactor in which silicon dioxide particles are heated to T> 300 (HS, evaporate and atomize, forming silicon and oxygen atoms and ions. Moreover, oxygen is bound by hydrogen from plasma to water vapor, which are pumped out by device 7, and silicon is directed to the surface of the respective substrates 8. In the case of using an arc plasma torch, the bulk of the plasma discharge energy is spent on thermal heating of the silicon dioxide powder and e Moreover, since the arc discharge is ignited outside the reaction zone, and the already formed jet of plasma and silicon dioxide is blown into the reactor, this mode can drastically reduce the likelihood of contamination of the final products — silicon and its compounds by impurities from the material of the electrodes of the arc plasma torch, which It is an essential advantage of the proposed method in comparison with the known ones, where the arc method of plasma excitation is also used.

Example 6 A vacuum chamber 1 with a reactor 2 and an arc plasmatron 3 was pumped out to a residual pressure of 5-10 ^"3 Pa, a jet of silicon dioxide powder with a particle size of less than 1 μm (-0, 1 μm) and a feed rate of 10 CM ^J B was simultaneously fed into reactor 2 second in a stream of argon with hydrogen and a plasma jet formed in argon plasma torch 3 from argon and hydrogen at a discharge power of 25,000 W. As in “Example” 1, plasma flows from a plasma torch and silicon dioxide powder create a plasma vortex in the reactor in which particles silica are heated to T> 3000 ° C, using moreover, they atomize and atomize, forming atoms and ions of silicon and oxygen, with oxygen being bound by hydrogen from plasma to water vapor, which are pumped out by device 7, and silicon is directed to the surface of the corresponding substrates 8. In the case of using an arc plasma torch, the bulk of the plasma discharge energy is spent on thermal heating of silicon dioxide powder and its evaporation.At the same time, since the arc discharge is ignited outside the reaction zone, and an already formed plasma and silicon dioxide jet is blown into the reactor, this mode Will dramatically reduce the likelihood of contamination of final products- silicon compounds and impurities from the electrode material of the arc plasma torch, which is a significant advantage of the proposed method in comparison with the known, which also uses arc plasma excitation method.

The above examples show the range of parameters of those modes in which the proposed method is implemented: the feed rate of silicon dioxide powder into the reactor is from 1 CM ^j / s to 10 cm ³ / s, and the corresponding power, which the plasmatron — RF or arc, must develop — from 700 W at a minimum powder feed rate of 1 cm ³ / s, up to 25,000 W at a maximum powder feed rate of 10 cm ³ / s. The above examples show that silicon obtained by the proposed method can either form a powder or film of pure silicon on the surface with which it does not chemically interact under the conditions of its production, or form chemical compounds with the surface material of the substrate, for example, silicon carbide with the substrate graphite, metal silicides with substrates of these metals, refractory, for example, titanium silicide with a titanium substrate. The fact that silicon obtained by the proposed method forms silicon carbide or metal silicides is a confirmation of its purity, since it is known that impurities, especially oxygen, interfere with the formation of these chemical compounds.

Claims

Claim  1. A method of producing silicon, including grinding the original silicon-containing compound to a finely dispersed state with individual particle sizes less than 1 μm, injecting the obtained powder with a carrier gas into a high-temperature jet of plasma-forming gases of a plasmatron connected to a reactor and placed in a chamber in which a vacuum is created, providing conditions for evaporation and atomization of a silicon-containing compound with the formation of pure silicon atoms and volatile reaction products, by controlling the feed rate oroshka and power of the plasmatron, the pure silicon condenses on the walls of the reactor and the substrate, and the volatiles were removed by vacuum.  2. The method according to claim 1, characterized in that argon and hydrogen are used as carrier gases and plasma forming gases, and silicon dioxide in the form of artificial quartz or natural quartzite is used as silicon-containing compounds.  3. The method according to claim 1, characterized in that the process is carried out at a temperature in the reactor above 3000 ° C, a powder feed rate in the range from 1 to 10 cm / s and a plasmatron power of 700-25000 watts.  4. The method according to claim 1, characterized in that at least two jets of plasma-forming gases with a powder of a silicon-containing compound are supplied simultaneously to the reactor at least two parallel or oncoming or directed at an angle to each other.  5. The method according to claim 1, characterized in that in the plasmatron and the reactor create a vortex motion of a silicon-containing compound.  6. The method according to claim 1, characterized in that the substrate uses silicon inert material, and silicon is deposited in the form of thin layers or films.