Method for producing trichlorosilane and method for producing polysilicon rod

Abstract

Provided is a method for effectively utilizing discharged hydrogen-containing off-gas in the production of trichlorosilane. The present invention provides a method for producing trichlorosilane, characterized in that trichlorosilane is produced by reacting metallic silicon, tetrachlorosilane, and a hydrogen-containing mixed gas containing 1 to 500 mol ppm of hydrogen chloride and 100 to 10,000 mol ppm of hydrogen silane, after heating the mixed gas at 100 to 450°C.

Description

Technical Field

[0001] This invention relates to a method for manufacturing trichlorosilane. More specifically, it relates to a method for manufacturing trichlorosilane in which exhaust gases are efficiently utilized during the manufacturing process. Background Technology

[0002] Trichlorosilane (SiHCl3) is a useful compound for manufacturing polycrystalline silicon. By reacting it with hydrogen at a high temperature above 1000°C, the following reactions (1) and (2) mainly occur, precipitating high-purity polycrystalline silicon.

[0003] 4SiHCl3→Si+3SiCl4+2H2(1)

[0004] SiHCl3 + H2 → Si + 3HCl (2)

[0005] Such trichlorosilanes are typically produced by reacting metallic silicon with hydrogen chloride. For example, Patent Document 1 discloses a method for producing trichlorosilanes by reacting metallic silicon and hydrogen chloride in the presence of an iron- and aluminum-containing catalyst using a fluidized bed reactor.

[0006] In the above manufacturing method, trichlorosilane is generated from metallic silicon and hydrogen chloride through the reaction of the following formula (3).

[0007] Si + 3HCl → SiHCl3 + H2 (3)

[0008] On the other hand, tetrachlorosilane (SiCl4), a byproduct of polycrystalline silicon manufacturing, is converted into trichlorosilane and reused in polycrystalline silicon production. For example, Patent Document 2 discloses a method for manufacturing trichlorosilane by reacting metallic silicon with tetrachlorosilane and hydrogen in a flow layer in the presence of a copper silicide catalyst. In this manufacturing method, trichlorosilane is generated from metallic silicon with tetrachlorosilane and hydrogen via the following reaction formula (4).

[0009] 3SiCl4 + 2H2 + Si → 4SiHCl3 (4)

[0010] Compared with the aforementioned method for manufacturing trichlorosilane, this manufacturing method has the following disadvantages: it requires a high reaction temperature, has a slow reaction rate, and has high production costs. Therefore, the manufacturing of trichlorosilane is mainly carried out through the previous reaction of metallic silicon with hydrogen chloride, and the manufacturing method of formula (4) is carried out as an auxiliary method to reuse the tetrachlorosilane byproduct of polycrystalline silicon manufacturing.

[0011] Furthermore, in the method of producing trichlorosilane by reacting hydrogen chloride with metallic silicon via the reaction of formula (3), the side reaction of formula (5) occurs, producing not only tetrachlorosilane but also a trace amount of dichlorosilane.

[0012] Si + 4HCl → SiCl4 + 2H2 (5)

[0013] Therefore, the gas generated by the reaction of metallic silicon with hydrogen chloride is cooled to below a specified temperature to condense and separate the chlorosilane mixture containing trichlorosilane. Trichlorosilane is then recovered from the resulting condensate by distillation, and the recovered trichlorosilane is used as a raw material for polycrystalline silicon manufacturing. In addition, the tetrachlorosilane separated by distillation is mainly reused in the trichlorosilane manufacturing process based on the reaction of formula (4), which is implemented as an auxiliary process.

[0014] Furthermore, the waste gas obtained by condensing and separating chlorosilanes from the reaction product gas is mainly composed of hydrogen, but in addition to unreacted hydrogen chloride and a small amount of chlorosilanes remaining after condensation and separation, it also contains trace amounts of boron, which is an unavoidable impurity in metallic silicon. Such impurities degrade the quality of polycrystalline silicon, therefore, it is necessary to strictly control the contamination of impurities in trichlorosilane, which is used as a raw material for polycrystalline silicon manufacturing. Therefore, regarding the aforementioned waste gas containing impurities, a portion is recycled as a carrier gas in the reaction system that generates the waste gas, while the majority is discarded after appropriate treatment. However, with the increase in the production of trichlorosilane, the amount of waste gas discarded after separating chlorosilanes also increases, and it is desirable to establish an effective method for the reuse of such waste gas.

[0015] On the other hand, Patent Document 3 proposes a method for manufacturing trichlorosilane, which involves supplying metallic silicon particles, hydrogen chloride, tetrachlorosilane, and hydrogen into a flow layer reactor filled with metallic silicon particles, and simultaneously carrying out a trichlorosilane generation reaction based on metallic silicon and hydrogen chloride, as well as a trichlorosilane generation reaction based on the reaction of metallic silicon, tetrachlorosilane, and hydrogen in the reaction vessel.

[0016] Existing technical documents

[0017] Patent documents

[0018] Patent Document 1: Japanese Patent No. 3324922

[0019] Patent Document 2: Japanese Patent No. 3708648

[0020] Patent Document 3: Japanese Patent Application Publication No. 56-73617

[0021] Patent Document 4: Japanese Patent Application Publication No. 2011-168443 Summary of the Invention

[0022] The problem that the invention aims to solve

[0023] In the trichlorosilane manufacturing method proposed in Patent Document 3 above, two trichlorosilane generation reactions are carried out simultaneously in the same reaction vessel. This has the following advantages: the tetrachlorosilane and hydrogen produced as byproducts in one generation reaction (based on the generation reaction of metallic silicon and hydrogen chloride) are consumed in the trichlorosilane generation reaction in the other reaction, effectively suppressing the generation of tetrachlorosilane itself in the waste gas. Furthermore, the generated waste gas can be recycled back to the reactor, effectively solving the problem of large quantities of waste gas generated.

[0024] However, the above method has the following fatal problem: since two reactions with different reaction conditions must be carried out simultaneously, there is an unavoidable problem of reduced conversion rate to trichlorosilane.

[0025] For example, in the reaction of metallic silicon with hydrogen chloride to produce trichlorosilane according to formula (3), there is a tendency for the conversion rate to trichlorosilane to decrease as the reaction temperature increases, and the reaction temperature is set in the range of 250 to 400°C. On the other hand, in the reaction of tetrachlorosilane, metallic silicon, and hydrogen to produce trichlorosilane, in order to ensure a suitable reaction rate and selectivity, the reaction temperature is set in the range of 400 to 700°C, preferably in the range of 450 to 600°C. It can be understood that when two reactions are carried out simultaneously in the same reaction vessel, if the reaction temperature is set to match the reaction of one reaction, it will lead to a decrease in the conversion rate of the other reaction, and if the reaction temperature is set to match the reaction of the other reaction, it will lead to a decrease in the conversion rate of the first reaction. As a result, the reaction temperature is set near the boundary region of the two reactions (around 400°C), but it is not the optimal range for either reaction, so it is impossible to carry out the two reactions under optimal conditions.

[0026] As a method to solve the technical problem in the aforementioned Patent Document 3, Patent Document 4 proposes a method for manufacturing trichlorosilane, characterized by comprising a first manufacturing process that reacts hydrogen chloride with metallic silicon to generate trichlorosilane and a second manufacturing process that reacts tetrachlorosilane and hydrogen with metallic silicon to generate trichlorosilane, wherein the trichlorosilane is condensed and separated from the reaction product gas containing the trichlorosilane obtained by the first manufacturing process, and the waste gas after the trichlorosilane is condensed and separated is supplied as a hydrogen source to the second manufacturing process.

[0027] The method for manufacturing trichlorosilane proposed in Patent Document 4 has the following advantages: the waste gas, which is mainly composed of hydrogen, generated in the first manufacturing process can be supplied as a hydrogen source to the second manufacturing process without special purification treatment. Moreover, the second manufacturing process does not require the addition of special purification equipment and can be carried out as before.

[0028] However, through research conducted by the inventors, it was determined that when the waste gas, which is mainly composed of hydrogen and recovered by the method described in Patent Document 4, is used as a hydrogen source in the second manufacturing process—that is, when tetrachlorosilane and hydrogen react with metallic silicon to generate trichlorosilane—corrosion and corrosion cracking sometimes occur inside the manufacturing apparatus used for the reaction. In particular, it was determined that corrosion and corrosion cracking occur significantly when the second manufacturing process is carried out continuously for a long period of time, and it was determined that there is room for improvement from the viewpoint of using the aforementioned waste gas as a hydrogen source continuously for a long period of time.

[0029] Therefore, the object of the present invention is to provide a method for effectively utilizing the hydrogen-containing waste gas discharged during the manufacture of trichlorosilane in an industrial manner.

[0030] Solution for solving the problem

[0031] The inventors have conducted in-depth research on the aforementioned technical problems. Initially, the main causes of corrosion and corrosion cracking inside the manufacturing apparatus were investigated. It was determined that although the trichlorosilane was condensed and separated from the reaction product gas containing trichlorosilane, the waste gas after condensation and separation of trichlorosilane was mainly composed of hydrogen, but contained trace amounts of hydrogen chloride. Furthermore, it was determined that corrosion and corrosion cracking occurred inside the manufacturing apparatus when the gas containing hydrogen chloride was heated to the aforementioned reaction temperature. On the other hand, it was also observed that corrosion and corrosion cracking are less likely to occur when hydrogen silane is present in addition to hydrogen and hydrogen chloride.

[0032] Based on these insights, the conditions for using the waste gas after trichlorosilane is condensed and separated as a hydrogen source when tetrachlorosilane and hydrogen react with metallic silicon to generate trichlorosilane were studied. It was found that by setting the concentration of hydrogen chloride and silane in the gas used as the hydrogen source to a specific range, and by heating the gas at a specified temperature before supplying it to the reaction, corrosion and corrosion cracking inside the manufacturing apparatus can be suppressed, and the gas can be used continuously for a long period of time, thus completing the present invention.

[0033] The present invention is a method for manufacturing trichlorosilane, characterized in that metallic silicon, tetrachlorosilane and a mixed gas containing hydrogen are reacted to generate trichlorosilane, wherein the mixed gas containing hydrogen contains 1 to 500 mol ppm of hydrogen chloride and 100 to 10000 mol ppm of hydrogenated silane, and the mixed gas is heated at 100 to 450°C to allow it to react.

[0034] The first embodiment of the present invention can preferably be implemented using the following scheme.

[0035] (1) The hydrogen-containing mixed gas is kept at 100-450°C for at least 3 seconds to allow it to react.

[0036] (2) The hydrogen-containing mixed gas is mixed with tetrachlorosilane, and then the mixed gas containing the tetrachlorosilane is heated at 100-450°C.

[0037] (3) The hydrogen-containing mixed gas includes the waste gas after the trichlorosilane is condensed and separated from the reaction product gas containing trichlorosilane, which is generated by reacting hydrogen chloride with metallic silicon to produce trichlorosilane.

[0038] (4) The hydrogen-containing mixed gas includes the trichlorosilane produced by reacting metallic silicon, tetrachlorosilane and hydrogen to produce trichlorosilane, and the waste gas after the trichlorosilane is condensed and separated.

[0039] (5) The hydrogen-containing mixed gas includes the waste gas from which trichlorosilane is condensed and separated after reacting trichlorosilane with hydrogen to generate polycrystalline silicon.

[0040] (6) A reaction-generated gas containing trichlorosilane is obtained by any manufacturing method of the present invention, and then the trichlorosilane is condensed and separated from the reaction-generated gas.

[0041] The second invention is a method for manufacturing polycrystalline silicon rods, wherein a reactor with the following structure is used: the interior is sealed by a bell jar and a base plate; the base plate is provided with electrode pairs for holding multiple silicon core wires and energizing the silicon core wires; and a plurality of gas supply nozzles are further provided for supplying silicon precipitation raw material gas to the interior space of the bell jar. In the method for manufacturing polycrystalline silicon rods, while energizing the silicon core wires, silicon precipitation raw material gas is ejected from the gas supply nozzles, thereby causing polycrystalline silicon to precipitate on the silicon core wires. The silicon precipitation raw material gas contains trichlorosilane obtained by the method described in (6).

[0042] Invention Effects

[0043] According to the method for manufacturing trichlorosilane of the present invention, a waste gas mainly composed of hydrogen, obtained by separating trichlorosilane from the reaction product gas containing trichlorosilane during the manufacturing of trichlorosilane, can be used as a hydrogen source when tetrachlorosilane and hydrogen react with metallic silicon to generate trichlorosilane. In particular, it can suppress corrosion and corrosion cracking inside the manufacturing apparatus during the reaction, and therefore the waste gas can be used stably for a long period of time.

[0044] In this way, the waste gas produced during the manufacturing of trichlorosilane can be effectively utilized, thereby significantly reducing the amount of hydrogen used (newly supplied hydrogen) other than the hydrogen contained in the waste gas, and greatly reducing the manufacturing cost of trichlorosilane. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of an example of an apparatus used to illustrate the composition of the mixed gas used in the preparation examples.

[0046] Figure 2 This is a schematic diagram illustrating an example of the configuration of the manufacturing apparatus in the embodiments and comparative examples. Detailed Implementation

[0047] The manufacturing method of the present invention is characterized in that, when the waste gas after trichlorosilane is condensed and separated is used as a hydrogen source for the reaction of tetrachlorosilane and hydrogen with metallic silicon to generate trichlorosilane, the concentrations of hydrogen chloride and silane contained in the gas used as the hydrogen source are set within a specific range, and the gas is heated at a temperature of 100 to 450°C before being supplied to the reaction. By employing such a manufacturing method of the present invention, corrosion and corrosion cracking inside the manufacturing apparatus can be suppressed when the aforementioned waste gas is used as a hydrogen source, thus enabling the long-term stable production of trichlorosilane. The detailed reasons why the manufacturing method of the present invention can suppress corrosion and corrosion cracking inside the manufacturing apparatus are not yet clear, but the inventors speculate as follows: The main component of the waste gas after trichlorosilane is condensed and separated is hydrogen, but it contains trace amounts of hydrogen chloride. Therefore, it is speculated that in the manufacture of trichlorosilane, which involves reacting tetrachlorosilane and hydrogen with metallic silicon, if this waste gas is supplied as a hydrogen source, the reaction temperature during the manufacture is high (450–600°C). Consequently, the trace amounts of hydrogen chloride in the waste gas cause corrosion and corrosion cracking inside the manufacturing apparatus. On the other hand, in the manufacturing method of the present invention, waste gas containing a predetermined amount of hydrogen chloride and silane is heated to a predetermined temperature and then supplied to the trichlorosilane manufacturing process. In this case, it is speculated that the waste gas contains trace amounts of silanes such as dichlorosilane and trichlorosilane. Heating causes these silanes to react with hydrogen chloride, reducing the hydrogen chloride content in the waste gas. Therefore, it is speculated that the hydrogen chloride content in the heated waste gas is reduced, and even if this waste gas is supplied to the trichlorosilane manufacturing process, corrosion and corrosion cracking inside the manufacturing apparatus can be suppressed, enabling the long-term stable manufacture of trichlorosilane.

[0048] In this specification, unless otherwise specified, the expression "A~B" refers to "above A and below B" when referring to numerical values ​​A and B. When only numerical value B is assigned a unit in this expression, the unit also applies to numerical value A. The method for manufacturing the trichlorosilane of the present invention will now be described in detail.

[0049] <Method for manufacturing trichlorosilane>

[0050] In the manufacturing method of the present invention, trichlorosilane is produced by reacting metallic silicon, tetrachlorosilane, and a mixed gas containing hydrogen. The trichlorosilane formation reaction is as previously described and is represented by the following formula (4).

[0051] 3SiCl4 + 2H2 + Si → 4SiHCl3 (4)

[0052] <Mixed Gases>

[0053] The manufacturing method of the present invention is characterized in that, as the hydrogen source used in the manufacture of the above-mentioned trichlorosilane, a mixed gas mainly composed of hydrogen and containing 1 to 500 mol ppm of hydrogen chloride and 100 to 10,000 mol ppm of hydrosilane is used. By heating the mixed gas containing hydrogen chloride and hydrosilane within the above range to a predetermined temperature before use, corrosion and corrosion cracking inside the manufacturing apparatus can be suppressed, thus enabling the long-term stable manufacture of trichlorosilane.

[0054] From the viewpoint of corrosion and corrosion cracking inside the manufacturing apparatus, it is preferable that the hydrogen chloride content in the above-mentioned mixed gas is low, preferably in the range of 1 to 400 mol ppm, and particularly preferably in the range of 1 to 200 mol ppm.

[0055] The hydrogenated silane contained in the aforementioned mixed gas refers to a silane having at least one Si-H bond in its molecule. Specifically, examples of such hydrogenated silanes include: SiH4, SiH3Cl, SiH2Cl2, SiHCl3, SiH3(CH3), SiH2(CH3)2, SiH(CH3)3, SiH2Cl(CH3), SiHCl2(CH3), SiHCl(CH3)2, Si2H6, and Si3H8. These hydrogenated silanes may be contained individually or in mixtures. From the viewpoint of effectively utilizing the waste gas from polycrystalline silicon manufacturing and trichlorosilane manufacturing (described later), it is preferable that the aforementioned hydrogenated silane contains at least one selected from monochlorosilane (SiH3Cl), dichlorosilane (SiH2Cl2), and trichlorosilane (SiHCl3). Furthermore, from the viewpoint that hydrogen chloride can be efficiently consumed by heating, the content of hydrogen silane is preferably in the range of 100 to 2000 mol ppm, and particularly preferably in the range of 100 to 1000 mol ppm.

[0056] Furthermore, from the same viewpoint, the molar ratio of hydrogen chloride to silane in the mixed gas used in the manufacturing method of the present invention is preferably set to a range of 1.0 to 100 for silane / hydrogen chloride, more preferably a range of 1.1 to 30, and particularly preferably a range of 1.5 to 10.

[0057] Examples of such mixed gases, primarily composed of hydrogen and containing hydrogen chloride and silanes, include: 1. Waste gas from which tetrachlorosilane, a byproduct of polysilicon manufacturing, is condensed and separated; 2. Waste gas from which trichlorosilane is condensed and separated after reacting metallic silicon with hydrogen chloride to produce trichlorosilane; 3. Waste gas from which trichlorosilane is condensed and separated after reacting metallic silicon, tetrachlorosilane, and hydrogen to produce trichlorosilane; etc.

[0058] The cooling temperature of the gas from which tetrachlorosilane and trichlorosilane are condensed and separated from the aforementioned waste gas only needs to be below the condensation temperature of tetrachlorosilane and trichlorosilane. This temperature is appropriately determined considering the cooling capacity of the cooling device, and is typically set to below -10°C, and particularly below -30°C. Similarly, the pressure during condensation and separation is typically set to 300 kPaG or higher, and particularly above 500 kPaG. The waste gas after the condensation and separation of tetrachlorosilane and trichlorosilane typically contains 95-99 mol% hydrogen, 100-6000 mol ppm hydrogen chloride, and 5000-50000 mol ppm hydrosilane. This waste gas can be used alone as the hydrogen of the present invention, or it can be mixed and used as the hydrogen of the present invention. Furthermore, if the content of hydrogen chloride and hydrosilane in this hydrogen is not within the above range, it can be appropriately prepared and used, for example, by mixing high-purity hydrogen that does not contain hydrogen chloride with this waste gas in a manner that brings the content of hydrogen chloride and hydrosilane within the above range.

[0059] <Tetrachlorosilane>

[0060] There are no particular limitations on the tetrachlorosilane used in the manufacturing method of the present invention. In particular, tetrachlorosilane produced as a byproduct in the manufacturing process of polycrystalline silicon from trichlorosilane is used. In addition, tetrachlorosilane recovered from trichlorosilane by distillation from a condensate containing chlorosilane produced as a byproduct in the production of trichlorosilane from metallic silicon and hydrogen chloride by the reaction of the following formula (3) above can be used. Alternatively, tetrachlorosilane recovered from trichlorosilane by distillation from a condensate containing chlorosilane produced as a byproduct in the production of trichlorosilane from metallic silicon and hydrogen chloride by distillation can be used.

[0061] Si + 3HCl → SiHCl3 + H2 (3)

[0062] Si + 4HCl → SiCl4 + 2H2 (5)

[0063] <Silicon Metal>

[0064] As the metallic silicon used in the manufacturing method of the present invention, known substances such as metallurgical metallic silicon, ferrosilicon, or polycrystalline silicon, which are solid substances containing silicon in a metallic state, can be used without any limitations. Furthermore, there are no particular limitations on the composition or content of impurities such as iron compounds contained in these metallic silicon materials. Moreover, the metallic silicon can also be used in the form of a fine powder with an average particle size of approximately 100 μm to 300 μm.

[0065] <Catalyst>

[0066] Furthermore, from the viewpoint of accelerating the reaction rate and producing trichlorosilane with high efficiency and selectivity, a catalyst is preferred when carrying out the manufacturing method of the present invention. As this catalyst, a conventionally used catalyst in the reaction system is used, such as a copper-based catalyst like copper powder, copper chloride, or copper silicide. Additionally, iron, or iron and aluminum, can also be used in combination with these catalysts. The catalyst is used in an amount of 0.1 to 40% by weight, particularly 0.2 to 20% by weight, relative to metallic silicon (calculated as copper).

[0067] <Manufacturing Equipment>

[0068] As the manufacturing apparatus for implementing the manufacturing method of the present invention, known manufacturing apparatuses can be used. For example, a fixed-bed reactor or a fluidized-bed reactor can be used as the reactor apparatus. In particular, considering the ability to continuously supply metallic silicon, tetrachlorosilane, and hydrogen as reactants to continuously produce trichlorosilane, a fluidized-bed reactor is preferred. In the manufacturing method of the present invention, hydrogen is heated to a predetermined temperature and then supplied to the aforementioned reactor apparatus. As the method for heating hydrogen, known methods can be used without limitation. For example, the following methods can be listed: a method of heating the hydrogen supply pipe connected to the aforementioned reactor by means of an external heating unit; or a method of supplying hydrogen to the aforementioned reactor after heating the hydrogen in the supply pipe by means of a hydrogen storage tank by means of a unit that heats the storage tank; or a method of supplying hydrogen to the aforementioned reactor after heating the hydrogen by means of heat exchange with the exhaust gas from the aforementioned reactor in a heat exchanger.

[0069] <Heating of mixed gases>

[0070] The manufacturing method of the present invention is characterized in that, when producing trichlorosilane by reacting metallic silicon, tetrachlorosilane, and hydrogen, the aforementioned mixed gas is used as a hydrogen source, and the mixed gas is then heated at 100–450°C to allow it to react. As described above, it is presumed that when the mixed gas containing silane and hydrogen chloride is preheated to 100–450°C, the silane reacts with the hydrogen chloride, thereby reducing the hydrogen chloride content. Therefore, from the viewpoint of reliably ensuring the reaction between silane and hydrogen chloride, it is preferable to maintain the mixed gas at 100–450°C for at least 3 seconds, particularly preferably 5 seconds or more, and preferably 7 seconds or more. Furthermore, regarding the upper limit of the time for maintaining the mixed gas at 100–450°C, any time sufficient to sufficiently reduce the hydrogen chloride content is acceptable, and can be appropriately determined considering manufacturing conditions, apparatus capabilities, etc. From the viewpoint of reliably reacting hydrosilane with hydrogen chloride during the heating of the aforementioned gas mixture, the heating time for the gas mixture in the range of 100–450°C is, specifically, at least one hour when the heating temperature is 100–200°C, at least 30 seconds when the heating temperature is 200–300°C, at least 10 seconds when the heating temperature is 300–400°C, and at least 3 seconds when the heating temperature is 400–450°C. It should be noted that the time for holding the gas mixture within the range of 100–450°C refers to the time the hydrogen remains within that temperature range. Therefore, when heating the gas mixture within the range of 100–450°C, the heating time is also included in the holding time. Therefore, when heating from 100°C to 450°C, the heating rate can be appropriately determined so that the time to reach the temperature range is 3 seconds or more, and it is particularly preferable to make the time to reach the temperature range of 400 to 450°C 3 seconds or more.

[0071] In the manufacturing method of this invention, the mixed gas can be heated at 100–450°C before reacting with the metallic silicon, tetrachlorosilane, and the mixed gas; the order in which the metallic silicon, tetrachlorosilane, and the mixed gas are added is not particularly limited. Therefore, the mixed gas can be heated at 100–450°C and then brought into contact with the metallic silicon and tetrachlorosilane, or the mixed gas and tetrachlorosilane can be mixed to obtain a mixed gas, and then the mixed gas containing tetrachlorosilane can be heated at 100–450°C and brought into contact with the metallic silicon. The reaction of the metallic silicon, tetrachlorosilane, and the mixed gas can also be carried out at temperatures exceeding 450°C.

[0072] <Manufacturing conditions for trichlorosilane>

[0073] In the manufacturing method of the present invention, a mixed gas, mainly composed of hydrogen and containing a predetermined amount of hydrosilane and hydrogen chloride, is heated at the aforementioned temperature as described above, and then reacted with metallic silicon and tetrachlorosilane. The supply amount of each reactant can be appropriately determined by considering the type and capacity of the reaction apparatus. Regarding the ratio of tetrachlorosilane to hydrogen, 1 to 5 moles of hydrogen are generally relative to 1 mole of tetrachlorosilane, but a ratio of 1 to 3 moles of hydrogen relative to 1 mole of tetrachlorosilane is more preferred. Furthermore, the supply rate can be set to an appropriate range according to the type and size of the reaction apparatus used; for example, in the case of using a fluidized bed reactor, the supply rate is such that it forms a flow layer. Furthermore, tetrachlorosilane and hydrogen can also be supplied by dilution with an inert gas that does not participate in the reaction, such as nitrogen or argon.

[0074] The reaction temperature of the manufacturing method of the present invention is appropriately determined taking into account the material and capacity of the manufacturing apparatus, the catalyst used, etc., and the reaction temperature is usually set in the range of 400 to 700°C, and is particularly set in the range of 450 to 600°C.

[0075] The gas generated in the manufacturing method of the present invention contains generated trichlorosilane, unreacted tetrachlorosilane, hydrogen, and silane and hydrogen chloride from waste gas. After the gas generated by the reaction is filtered to remove solid substances such as metallic silicon particles, the chlorosilane is separated by cooling condensation. Then, the condensate is distilled, thereby recovering the generated trichlorosilane with high purity.

[0076] That is, the cooling temperature of the reaction product gas during the condensation separation of chlorosilanes only needs to be below the condensation temperature of the chlorosilanes. This temperature is appropriately determined considering the cooling capacity of the cooling device, and is typically set below -10°C, and particularly below -30°C. Similarly, the pressure during condensation separation is typically set above 300 kPaG, and particularly above 500 kPaG, utilizing cooling for the condensation separation of chlorosilanes.

[0077] In addition to the generated trichlorosilane, the chlorosilane recovered by condensation also contains tetrachlorosilane and dichlorosilane, which are separated from the trichlorosilane by distillation.

[0078] <Utilization of Trichlorosilane>

[0079] The trichlorosilane produced in the present invention is used as a precipitation raw material in the process of manufacturing polycrystalline silicon. That is, it can be used as a raw material gas in the so-called Siemens process for manufacturing polycrystalline silicon, wherein a silicon core wire is installed inside a reactor, the silicon core wire is heated to the silicon precipitation temperature by energizing it, and a silicon precipitation raw material gas composed of trichlorosilane and reducing gas is supplied to the reaction chamber under this state, and silicon is precipitated on the silicon core wire by chemical vapor deposition.

[0080] For the polycrystalline silicon manufacturing using the Siemens process described above, known manufacturing apparatus can be used. Specifically, a reactor with the following structure can be cited: the interior is sealed by a bell jar and a base plate, the base plate is provided with electrode pairs for holding and energizing multiple silicon core wires, and further provided with multiple gas supply nozzles for supplying raw material gas for silicon precipitation into the interior space of the bell jar.

[0081] Using the aforementioned reactor and while energizing the silicon core wire, a silicon precipitation feed gas containing trichlorosilane produced by the manufacturing method of the present invention is ejected from the gas supply nozzle, thereby causing polycrystalline silicon to precipitate on the silicon core wire, thus enabling the manufacture of polycrystalline silicon rods. The manufacturing conditions for the aforementioned polycrystalline silicon manufacturing can be any known conditions without particular limitation.

[0082] Example

[0083] The present invention will be further described below through embodiments, but the present invention is not limited to these embodiments in any way.

[0084] (Example 1)

[0085] <Preparation of Gas Mixtures>

[0086] The mixed gas used in the examples Figure 1 The components are prepared using the apparatus shown. Figure 1 The illustrated mixed gas preparation apparatus is connected to a gas bubbling container 140, a cooling device 150 for cooling the gas bubbling container 140, a hydrogen chloride supply pipe 120 for supplying hydrogen chloride to the gas bubbling container 140, and a hydrosilane supply pipe 130. Gas discharged from the gas bubbling container is discharged through a gas discharge pipe 160. A hydrogen supply pipe 110 is connected to the hydrogen chloride supply pipe 120 and the gas discharge pipe 160. Furthermore, a thermometer (not shown) for measuring the temperature in the gas bubbling container 140 is provided, and a pressure gauge (not shown) is provided in the gas discharge pipe 160.

[0087] About 3 kg of a hydrogenated silane liquid consisting of 5% by weight of dichlorosilane, 85% by weight of trichlorosilane, and 10% by weight of tetrachlorosilane was filled into the gas bubbling container 140, and the gas bubbling container 140 was cooled to -40°C.

[0088] In the aforementioned hydrogenated silane solution, a mixture of hydrogen containing 5 mol% hydrogen chloride at a flow rate of 0.1 NL (positive liter) / min and 9.99 mol% hydrogen at a flow rate of 2.0 NL / min was bubbled with a residence time of 30 seconds. The gas discharged from the gas bubbling vessel via bubbling at a flow rate of 2.1 NL / min was recovered and analyzed by gas chromatography. The results showed that the gas contained 0.24 mol% hydrogen chloride, 0.029 mol% dichlorosilane, 0.37 mol% trichlorosilane, and 0.013 mol% hydrogen tetrachlorosilane.

[0089] Hydrogen gas discharged from the gas bubbling container (flow rate 2.1 NL / min) and 99.99 mol% hydrogen (17 NL / min) are mixed, and the resulting mixed gas is stored in a hydrogen tank.

[0090] The hydrogen stored in the hydrogen tank was analyzed by gas chromatography, and the results were: hydrogen 99.71 mol%, hydrogen chloride 270 mol ppm, hydrogen silane 458 mol ppm, and tetrachlorosilane 15 mol ppm.

[0091] <Heating of mixed gases>

[0092] Figure 2 This is a schematic diagram illustrating an example of the configuration of the manufacturing apparatus in the embodiments and comparative examples. Figure 2 The manufacturing apparatus comprises a composition adjustment device 100 for preparing hydrogen composition, a hydrogen tank 200 for storing the prepared hydrogen, a mixer 300 for mixing hydrogen from the hydrogen tank 200 with tetrachlorosilane, a preheater 400 for heating the mixed gas to 100–450°C, and a reactor 500 for reacting the heated hydrogen and tetrachlorosilane with metallic silicon. Figure 2 In this configuration, preheater 400 consists of three preheaters (first preheater 410, second preheater 420, and third preheater 430). A piping (not shown) is provided in the hydrogen tank to extract gas. The extracted gas is connected to a gas sampler (not shown) of a gas chromatograph for online analysis of the gas in the tank.

[0093] Hydrogen from hydrogen tank 200 is supplied to mixer 300 at a rate of 19 NL / min, and 99.99 mol% tetrachlorosilane is supplied and mixed at a rate of 7 NL / min. This mixed gas is then sent to a first preheater 410 and heated to 100°C. The mixed gas from the first preheater 410 is then sent to a second preheater 420 and heated to 450°C. The heating time in the second preheater is calculated by dividing the volume of the heating zone (liters) by the gas flow rate (NL / min), resulting in 5.1 seconds.

[0094] The mixed gas from the second preheater 420 is sent to the third preheater 430 and heated to the reactor's reaction temperature (500°C). In the heating zone of the third preheater 430, where the expected gas temperature is 450–500°C, test pieces made of SUS304 and SUS316 are placed. The test pieces are plates approximately 10 mm long, 50 mm wide, and 2 mm thick, with 10 pieces of each material prepared. Small holes are provided in each plate to allow a metal wire to pass through and suspend it within the piping.

[0095] <Reaction of metallic silicon, tetrachlorosilane, and the aforementioned hydrogen>

[0096] Reactor 500 uses a stainless steel fluidized bed reactor with an inner diameter of 25 mm. Initially, 240 g of metallic silicon powder (98% purity, containing iron, aluminum, carbon, etc. as impurities) and 15 g of copper chloride powder are packed into the gas dispersion plate inside the reactor. The reaction temperature is set to 500℃, and the pressure is set to 0.7 MPa (gauge pressure). The metallic silicon powder is replenished into the fluidized bed at a rate of 300 g / hr. The piping through which the gas passes is insulated to maintain the temperature of the exhaust gas from the reactor at 500℃. The reaction is carried out continuously for 500 hours. After the reaction, the test pieces are removed, and the corrosion rate is measured. The corrosion rate is calculated by dividing the weight change before and after the reaction by the reaction time. The results show that the corrosion rate for either SUS304 or SUS316 test pieces is less than 0.1 mm / year.

[0097] <Examples 2, 3 and Comparative Example 1>

[0098] The mixed gas shown in Table 1 was prepared, and after heating the mixed gas under the conditions shown in Table 1, it was reacted with metallic silicon and tetrachlorosilane in the same manner as in Example 1. It should be noted that Example 2 is an example where the gas bubbling container 140 was cooled at -20°C, and Example 3 is an example where the amount of 99.99 mol% hydrogen mixed with hydrogen gas discharged from the gas bubbling container was doubled. Furthermore, Comparative Example 1 is an example without hydrogenated silane. The residence time in the second preheater and the corrosion rate of the test piece placed in the third preheater are shown in Table 1.

[0099] [Table 1]

[0100]

[0101] Explanation of reference numerals in the attached figures

[0102] 100: Composition adjustment device; 110: Hydrogen supply pipe; 120: Hydrogen chloride supply pipe; 130: Hydrogen silane supply pipe; 140: Gas bubbling container; 150: Cooling device; 160: Gas discharge pipe; 200: Hydrogen tank; 300: Mixer; 400: Preheater; 410: First preheater; 420: Second preheater; 430: Third preheater; 500: Reactor.

Claims

1. A method for manufacturing trichlorosilane, characterized in that, Trichlorosilane is produced by reacting metallic silicon, tetrachlorosilane, and a mixture of gases containing hydrogen. The hydrogen-containing gas mixture comprises 1 to 500 mol ppm of hydrogen chloride and 100 to 10,000 mol ppm of hydrosilane. The mixed gas is heated at 100–450°C to allow it to react.

2. The method for manufacturing trichlorosilane according to claim 1, wherein, The mixed gas is held at 100–450°C for at least 3 seconds to allow it to react.

3. The method for manufacturing trichlorosilane according to claim 1, wherein, The mixed gas is mixed with tetrachlorosilane, and then the mixed gas containing tetrachlorosilane is heated at 100–450°C.

4. The method for manufacturing trichlorosilane according to claim 1, wherein, The mixed gas contains the trichlorosilane condensed and separated from the reaction product gas containing trichlorosilane, which is produced by reacting hydrogen chloride with metallic silicon to generate trichlorosilane, and the exhaust gas after the trichlorosilane is condensed and separated.

5. The method for manufacturing trichlorosilane according to claim 1, wherein, The mixed gas contains the trichlorosilane produced by reacting metallic silicon, tetrachlorosilane, and hydrogen to generate trichlorosilane, and the waste gas after the trichlorosilane is condensed and separated.

6. The method for manufacturing trichlorosilane according to claim 1, wherein, The mixed gas contains the trichlorosilane condensed and separated from the exhaust gas after the trichlorosilane has been reacted with hydrogen to produce polycrystalline silicon.

7. A method for producing trichlorosilane, comprising obtaining a reaction product gas containing trichlorosilane by the method according to any one of claims 1 to 6, and then condensing and separating the trichlorosilane from the reaction product gas.

8. A method for manufacturing a polycrystalline silicon rod, wherein, The reactor uses the following structure: the interior is sealed using a bell jar and a bottom plate; The base plate is provided with electrode pairs for holding multiple silicon core wires and energizing the silicon core wires; Furthermore, multiple gas supply nozzles are provided for supplying the raw material gas for silicon precipitation into the internal space of the bell jar. In the method for manufacturing the polycrystalline silicon rod, while energizing the silicon core wire, a raw material gas for silicon precipitation is ejected from the gas supply nozzle, thereby causing polycrystalline silicon to precipitate on the silicon core wire. The raw material gas for silicon precipitation contains trichlorosilane obtained by the manufacturing method as described in claim 7.

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