JP2018087126A - Reaction furnace for producing polycrystalline silicon rod and production method thereof and production method of polycrystalline silicon rod using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a high-purity polycrystalline silicon rod by preventing discharge of outgas containing impurities such as metal compounds generated from a reaction furnace inner wall when depositing polycrystalline silicon, without largely increasing initial investment to the reaction furnace and the production cost of the polycrystalline silicon.SOLUTION: A reaction furnace for producing a polycrystalline silicon rod is constituted of metallic materials having heat resistance and has a silica coating layer on an inner wall surface. The silica coating layer is formed by coating and curing a silica coating liquid such as a polysilazane solution on the inner wall surface of the reaction furnace, or by controlling an atmosphere in the reaction furnace to a dew point of -30 to -50°C and introducing trichlorosilane, silicon tetrachloride or chlorosilane gas that is a mixture thereof as they are into the reaction furnace, or by introducing chlorosilane gas obtained by diluting the chlorosilane gas with hydrogen or inert gas.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a reactor for producing a high purity polycrystalline silicon rod by the Siemens method, a method for producing the same, and a method for producing a polycrystalline silicon rod using the same.

  High-purity polycrystalline silicon, which is a raw material for single-crystal silicon used in semiconductor devices, is obtained by distilling and purifying trichlorosilane and using a mixed gas of purified trichlorosilane and hydrogen as a raw material for a long time in a high-temperature atmosphere. And produced by reduction precipitation. In this precipitation reaction, high purity polycrystalline silicon placed on a base is used as a seed rod, and this seed rod is heated by energization, and a mixed gas of trichlorosilane and hydrogen is continuously introduced into the reaction furnace, The Siemens method, in which polycrystalline silicon is deposited on the surface of the seed rod, is the mainstream.

  The configuration of this reactor is disclosed in Patent Document 1. The reaction furnace shown in Patent Document 1 is provided with a holding base for holding a precipitation carrier, a reaction gas introduction pipe and a discharge pipe on a reaction substrate, and the holding base is covered with a quartz bell shape. In Patent Document 1, an auxiliary plate made of quartz is further disposed on the reaction substrate in this reaction furnace to keep the reaction space warm and to clean the surface of the reaction substrate. It has been shown to remove the cause of contamination and produce high purity polycrystalline silicon.

  On the other hand, when high-purity polycrystalline silicon is produced commercially, it is necessary to enlarge the reactor. In this case, in a quartz bell-shaped structure as in Patent Document 1, quartz glass, which is a brittle material, has a high risk of breakage in its handling, and therefore a steel reactor is generally used. However, it is known that when a steel reaction furnace is used at a high temperature, impurity gas is released from the inner wall surface of the reaction furnace and the polycrystalline silicon during reaction precipitation is contaminated.

  As another technique for producing high-purity polycrystalline silicon, the inner wall of the outer cylinder is 28 wt% of nickel in order to prevent contamination of the polycrystalline silicon by an impurity gas (hereinafter referred to as outgas) released from the furnace wall. An apparatus for decomposing / reducing silanes composed of a heat-resistant alloy containing at least% is disclosed (see Patent Document 2). In Patent Document 2, when this apparatus is used, a heat-resistant alloy containing 28% by weight or more of nickel has an outgas containing methane gas, phosphorus-hydrogen compound, boron-hydrogen compound, etc. as a component at a temperature of 600 ° C. or less. It has been shown that impurities caused by phosphorus (P), boron (B) and the like can be suppressed with little release.

  As another technique for producing high-purity polycrystalline silicon, the content of chromium (Cr), nickel (Ni), and silicon (Si) on the inner surface side of the inner wall of the reactor is set to [Cr], [ A corrosion-resistant layer having a composition in which the R value defined by R = [Cr] + [Ni] −1.5 [Si] is 40% or more when Ni] and [Si] is used is provided in the reactor. For production of polycrystalline silicon in which a cooling water flow path that can circulate pressurized cooling water with a normal boiling point or higher is arranged, and a heat conduction layer having a higher thermal conductivity than the corrosion resistance layer is provided between the corrosion resistance layer and the cooling water flow path A reactor is disclosed (see Patent Document 3). In Patent Document 3, when this reaction furnace is used, when the polycrystalline silicon is deposited in the reaction furnace, the temperature of the inner surface of the furnace is controlled to be equal to or lower than a certain temperature, so that dopant impurities from the inner wall of the reaction furnace can be obtained. It has been shown that high-purity polycrystalline silicon can be produced with reduced contamination.

  Patent Document 4 also discloses that the phosphorus-containing steel surface of the polycrystalline silicon reactor inlet pipe is passivated with the vapor of alpha-amino-functional alkoxysilane to reduce the phosphorus content in the deposited polycrystalline silicon. It has been shown.

Japanese Examined Patent Publication No. 37-18861 (Detailed Description of the Invention, Drawing) JP-A-8-259211 (Claim 1, paragraphs [0006], [0008], [0044], FIG. 1) JP 2011-57526 A (Claim 1, paragraph [0001], FIG. 2) Special table 2015-505340 gazette

  According to the apparatus and the reactor shown in Patent Documents 2 to 4, the material constituting the reactor is made of a heat-resistant alloy or a corrosion-resistant alloy, or the surface of the raw material gas pipe at the inlet of the reactor is passivated. Thus, the dopant impurity accompanying the emission of outgas generated from the metal surface during the precipitation reaction in the high temperature region can be reduced, and the reduction effect is considered to be large. However, impurities other than the dopant, such as metal impurities, are not considered as impurities contained in the outgas. In addition, when the reactor becomes larger, selecting a material with a specific composition or material and using this material for the inner wall or corrosion-resistant layer of the reactor increases the initial investment cost for the reactor and increases the This leads to an increase in the manufacturing cost of crystalline silicon.

  In general, a stainless steel sheet has a surface (passive film) with a stable chromium oxide having a thickness of 1 to 3 nm formed on the surface, and metal compounds and the like contained in outgas, which is a non-contact contamination source, are problematic. It was thought not to be. However, in recent years, the inventors have investigated that the quality requirements for polycrystalline silicon have become more severe as the performance of semiconductor devices has improved, and the contamination of metal impurities below 0.1 ppbw has become a problem. As a result, when the stainless steel material is used as the inner wall material of the reactor and the inner wall of the reactor is cooled to a temperature range of approximately 100 ° C. or higher and 300 ° C. or lower to perform the precipitation reaction of polycrystalline silicon, It became clear that outgas containing a metal compound or the like was generated from the dynamic film itself and adhered to the polycrystalline silicon rod, and it was not sufficient to deposit high-purity polycrystalline silicon with further reduced contamination.

  Therefore, the present inventor has applied a coating on the inner wall of the reactor for the purpose of reducing outgas including impurities such as metal compounds from the surface of the passive film of stainless steel constituting the reactor for depositing polycrystalline silicon. As a result, the coating layer formed using a silica coating solution such as a polysilazane solution is easy to apply, dense and durable, and has a great effect of suppressing contamination from the inner wall of the reactor. In order to coat the inner wall of the furnace, if the material constituting the reaction furnace is heat resistant, a metal material other than stainless steel can be used, and further, chlorosilane gas is added immediately before or at the initial stage of precipitation of polycrystalline silicon. A coating method that introduces a silica coating layer on the inner wall of the reactor and begins to deposit polycrystalline silicon. Below referred to as "in situ coating" or "in situ coating method".) Also proved to be practical and effective, have completed the present invention.

  An object of the present invention is to provide an outgas containing impurities such as a metal compound generated from the inner wall of a reaction furnace when depositing polycrystalline silicon without significantly increasing the initial investment cost to the reaction furnace and the manufacturing cost of polycrystalline silicon. It is intended to provide a reaction furnace for producing a high purity polycrystalline silicon rod while preventing the release of carbon, a method for producing the same, and a method for producing a polycrystalline silicon rod using the same.

  A first aspect of the present invention is a reaction furnace for producing a polycrystalline silicon rod in which the reaction furnace is made of a heat-resistant metal material, and has a silica coating layer on the inner wall surface of the reaction furnace. This is a reactor for producing polycrystalline silicon rods.

  According to a second aspect of the present invention, polycrystalline silicon is formed by forming a silica coating layer on the inner wall surface of the reactor of the polycrystalline silicon rod manufacturing reactor in which the reactor is made of a heat-resistant metal material. This is a method of manufacturing a reactor for manufacturing a rod.

  A third aspect of the present invention is the polycrystalline silicon rod according to the second aspect, wherein the formation of the silica coating layer is performed by applying and curing a silica coating liquid on the inner wall surface of the reaction furnace. It is a manufacturing method of the reactor for manufacture.

  A fourth aspect of the present invention is an invention based on the third aspect, and is a method for manufacturing a reactor for manufacturing a polycrystalline silicon rod, wherein the silica coating solution is a polysilazane solution.

  A fifth aspect of the present invention is the invention based on the second aspect, wherein the formation of the silica coating layer sets the atmosphere in the reactor for producing the polycrystalline silicon rod to a dew point of −30 to −50 ° C. Control the chlorosilane gas, which is trichlorosilane, silicon tetrachloride or a mixed gas thereof, as it is, or dilute the trichlorosilane, silicon tetrachloride or the mixed gas with hydrogen or an inert gas. This is a method for producing a reactor for producing a polycrystalline silicon rod, which is carried out by introducing chlorosilane gas.

  According to a sixth aspect of the present invention, after assembling a silicon seed rod and sealing a reaction furnace composed of a metal material having heat resistance, the atmosphere in the reaction furnace is controlled to a dew point of −30 to −50 ° C. A chlorosilane gas in which trichlorosilane, silicon tetrachloride or a mixed gas thereof is introduced into the reactor as it is, or trichlorosilane, silicon tetrachloride or a mixed gas thereof is diluted with hydrogen or an inert gas. In this method, a silica coating layer is formed on the inner wall surface of the reaction furnace, and polycrystalline silicon is deposited on the surface of the silicon seed rod without opening the reaction furnace. is there.

  A seventh aspect of the present invention is the invention based on the sixth aspect, wherein when the chlorosilane gas is introduced after energizing the silicon seed rod, the deposition rate of the polycrystalline silicon is 0.5 mm / h or less. This is a method for manufacturing a polycrystalline silicon rod under control.

  According to an eighth aspect of the present invention, there is provided a reactor for manufacturing a polycrystalline silicon rod manufactured by the method for manufacturing a polycrystalline silicon rod according to the first aspect or the method according to any one of the second to fourth aspects. This is a method for producing a polycrystalline silicon rod.

  In the reaction furnace for producing a polycrystalline silicon rod according to the first aspect of the present invention, the silica coating layer formed on the inner wall surface of the reaction furnace made of a metal material having heat resistance causes reaction when the polycrystalline silicon is precipitated. It has a gas barrier property of outgas containing impurities such as metal compounds from the inner wall of the furnace, and suppresses contamination of the polycrystalline silicon rod by the metal contained in the metal material.

  In the method of the second aspect of the present invention, a silica coating layer is formed on the inner wall surface of a reaction furnace made of a metal material having heat resistance without selecting a special material as the reaction furnace material. Thus, it is possible to realize a reaction furnace that does not contaminate the polycrystalline silicon with impurities such as a metal compound due to outgas from the inner wall of the reaction furnace when the polycrystalline silicon is deposited.

  In the method according to the third aspect of the present invention, the silica coating layer can be formed by a simple operation of applying the silica coating liquid to the inner wall surface of the reactor and then curing the coating liquid.

  In the method according to the fourth aspect of the present invention, by applying a silica coating solution as a polysilazane solution, application by spraying and curing by a hydrolysis reaction using water vapor can be easily performed.

  In the method of the fifth aspect of the present invention, an appropriate amount of moisture is retained on the inner wall surface of the reaction furnace by controlling the atmosphere in the reaction furnace to a dew point of −30 to −50 ° C. In this state, When chlorosilane, silicon tetrachloride or a mixed gas thereof is introduced as it is, or when chlorosilane gas obtained by diluting trichlorosilane, silicon tetrachloride or a mixed gas thereof with hydrogen or an inert gas is introduced, the chlorosilane is easily dissolved with the above moisture. And a silica coating layer is formed on the inner wall surface of the reactor.

  In the method of the sixth aspect of the present invention, in a state where the reaction furnace is sealed, chlorosilane gas is introduced into the reaction furnace, and a small amount of water held in the reaction furnace is reacted with chlorosilane, A silica coating layer is formed on the inner wall surface of the reaction furnace, and in situ coating is performed in which the precipitation reaction is started without opening the reaction furnace as it is. Since the reactor is not opened, contaminants in the outside air are not adsorbed on the silica coating layer and the polycrystalline silicon rod. As a result, while the polycrystalline silicon rod is being manufactured, it is possible to suppress contamination due to outgas from the inner wall surface of the reactor to the polycrystalline silicon.

  In the method according to the seventh aspect of the present invention, the silica coating layer formed by introducing chlorosilane gas exhibits the above-mentioned effects, but the outgas components generated until the effects are exhibited are discharged outside the furnace. By controlling the deposition rate of polycrystalline silicon to 0.5 mm / h or less, it is possible to suppress the deposition of silicon while taking in metal impurities contained in the outgas from the inner wall of the reactor. It leads to reduction of pollution.

  If polycrystalline silicon is produced using the reactor described above by the method of the eighth aspect of the present invention, outgas including impurities such as metal compounds from the inner wall of the reactor is suppressed, and high purity polycrystalline silicon is produced. A rod can be manufactured. Moreover, it can suppress that the hydrogen chloride etc. which generate | occur | produce during reaction turn into hydrochloric acid at the time of reaction furnace opening, etc., and corrode the reaction furnace inner wall. Moreover, it can suppress that a chlorosilane polymer adheres to the inner wall face of a reaction furnace during reaction, and corrodes.

It is a longitudinal cross-section block diagram of the apparatus which manufactures the polycrystalline silicon rod of this embodiment. It is the A section expanded sectional view of Drawing 1 showing the structure of the inner wall of another embodiment, and an outer wall.

<First Embodiment>
First, a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the polycrystalline silicon rod manufacturing apparatus 10 includes a reaction furnace 11. The reaction furnace 11 includes a base 12 that forms the furnace bottom, and a bell-shaped bell jar 13 that is detachably attached to the base 12. A gas introduction pipe 14 and a gas discharge pipe 15 are provided through the base 12. The base 12 is provided with electrode bodies 17, 17 that hold the lower end of the inverted U-shaped silicon seed rod 16. The seed bar 16 is fixed to the inside of the reaction furnace 11 by being held by these electrode bodies 17 and 17. An output terminal of a power feeding device 18 is electrically connected to the electrode bodies 17 and 17, and the seed bar 16 is configured to be heated by electric power from the power feeding device 18. From the gas introduction pipe 14, for example, a mixed gas of trichlorosilane (SiHCl ₃ ) and hydrogen is introduced into the reaction furnace 11 as a raw material gas, and a polycrystalline silicon precipitate 19 is deposited on the surface of the seed rod 16 to form polycrystalline silicon. It is configured to manufacture the rod rod 20. In addition, the code | symbol 21 in FIG. 1 is an insulator which electrically insulates the electrode bodies 17 and 17 from the base 12. FIG.

  The bell jar 13 of the first embodiment preferably has a structure having an inner wall 23 and an outer wall 24 that covers the outside of the inner wall 23 as shown in the enlarged view of part A of FIG. The present invention also includes a bell jar in which the bell jar is not composed of a plurality of furnace wall structures of an inner wall and an outer wall. The bell jar 13 is made of a metal material. The inner wall 23 of the bell jar 13 of this embodiment is a single layer, and all the inner walls are made of a metal material. A refrigerant flow path 26 through which the refrigerant 25 flows is formed between the inner wall 23 and the outer wall 24. A refrigerant supply system and a refrigerant recovery system are connected to the refrigerant flow path 26. In the refrigerant supply system, the refrigerant 25 is supplied from below the reaction furnace 11 via the supply pump 27, and the supplied refrigerant 25 passes through the refrigerant flow path 26 and is discharged from the top of the reaction furnace 11 to the refrigerant recovery system. It has become so. All of the base 12 is made of the same metal material as the bell jar 13.

  The metal material constituting the reaction furnace 11 has heat resistance. As the metal material, austenitic stainless steel is preferable, and examples thereof include SUS304, SUS316, SUS317, SUS309S, and SUS347. As other metal materials, iron-containing metals such as nickel-clad steel, nickel-chrome steel, carbon steel, Inconel, and Hastelloy may be used.

A characteristic configuration of the present invention is to have a silica coating layer 28 on the inner wall surface of the reactor 11 made of a metal material. In the first embodiment, the silica coating layer 28 is formed by applying a silica coating solution to the inner wall surface of the reaction furnace 11 and curing it. As the silica coating solution, a polysilazane solution in which polysilazane is dissolved in a solvent is preferable. The simplest polysilazane is a perhydropolysilazane which is an inorganic polymer compound soluble in an organic solvent having “— (SiH ₂ —NH) —” as a basic unit and all side chains are hydrogen. Perhydropolysilazane, for example, as represented by the following reaction formula, reacts with water (H ₂ O) to generate ammonia (NH ₃ ), and produces a dense silica glass film.
_{(-SiH 2 NH -) + 2H} 2 O → (-SiO 2 -) + NH 3 + 2H 2

  Examples of the solvent include dibutyl ether and xylene.

  The amount of polysilazane in the silica coating solution needs to be selected according to the surface properties of the metal material, and the solid content concentration with respect to the total silica coating solution is preferably 1 to 20% by mass.

  Examples of the method for applying the inner wall surface of the reaction furnace 11 include spray coating. Curing of the silica coating liquid after application is performed at, for example, 80 ° C. or higher, more preferably 100 ° C. or higher. When this curing treatment is performed in a water vapor atmosphere, the conversion from the liquid layer containing polysilazane to the silica coating layer is accelerated, and preferable results are obtained. This is because the hydrolysis reaction of polysilazane in the silica coating solution accelerates with water vapor, and a substantial silica coating layer is formed completely. On the other hand, this hardening process can also obtain a silica coating layer by leaving to stand in air | atmosphere of 150 to 450 degreeC for 1 to 3 hours.

  The thickness of the silica coating layer is preferably in the range of 0.05 to 5 μm. If it exists in this range, a coating layer will closely_contact | adhere to the inner wall face of the reaction furnace 11 comprised with metal materials, and a coating layer will not peel, a crack, a crack, etc. generate | occur | produce. If it exceeds 5 μm, the coating layer becomes rigid and easily cracked. If it is less than 0.05 μm, the substantial effect of the present invention may not be obtained.

  In the above embodiment, the form in which all of the inner wall 23 is composed of a single layer of metal material has been described. However, in the present invention, the inner wall 23 has a two-layer structure as shown in FIG. When the inner layer 23a on the inner side of the furnace and the outer layer 23b on the outer wall side are configured, the outer layer 23b has an inner layer for efficiently conducting heat in the reaction furnace 11 from the inner wall to the refrigerant flow path 26. Examples thereof include a heat conductive layer made of a metal material having a higher heat conductivity than 23a.

  A method of manufacturing the polycrystalline silicon rod 20 using the polycrystalline silicon rod manufacturing apparatus 10 configured as described above will be described. A seed rod 16 made of polycrystalline silicon is prepared in advance. The seed bar 16 is preferably washed with an acid chemical before use. Thereby, impurities and the like attached to the surface of the seed rod 16 can be removed, so that a high-purity polycrystalline silicon rod 20 with little contamination can be obtained.

First, the seed rod 16 is placed in the reaction furnace 11. The arrangement of the seed bar 16 is performed by holding the lower ends of the seed bar 16 on the electrode bodies 17, 17 provided on the base 12. Then, after preheating the seed rod 16 with an in-furnace heater or the like, the seed rod 16 is heated by energization through the electrode bodies 17 and 17 by the power feeding device 18. The heating temperature is a predetermined temperature within a range of about 1000 to 1300 ° C. (for example, about 1100 ° C.). As the seed rod 16 is heated, a mixed gas of trichlorosilane and hydrogen is introduced from the gas introduction pipe 14 into the reaction furnace 11 as a raw material gas. The introduced gas rises inside the reaction furnace 11 heated by the heated high temperature seed rod 16 and is expressed by the following equations (1) and (2) while the gas is convection. As described above, trichlorosilane (TCS: SiHCl ₃ ) is thermally decomposed or reduced by hydrogen, and a polycrystalline silicon precipitate 19 is formed on the surface of the seed rod 16. The gas in the reaction furnace 11 used for the deposition of polycrystalline silicon is discharged from the gas discharge pipe 15.
4SiHCl ₃ → Si + 3SiCl ₄ + 2H ₂ (1)
SiHCl ₃ + H ₂ → Si + 3HCl (2)

  While the polycrystalline silicon precipitate 19 is formed on the surface of the seed rod 16, the coolant 25 is supplied from the supply pump 27 of the coolant supply system to the coolant channel 26. Since the inner wall surface of the reaction furnace 11 is covered with the silica coating layer 28 while the polycrystalline silicon precipitate 19 is formed while heating at a temperature exceeding 1000 ° C., the metal on the inner wall surface of the reaction furnace 11 Outgas including impurities such as metal compounds is suppressed from the manufacturing material. By the reaction furnace 11 in which the silica coating layer 28 is formed, a high-purity polycrystalline silicon rod 20 in which each impurity amount is less than 0.1 ppbw can be manufactured. The impurity concentration can be determined by inductively coupled plasma mass spectrometry (ICP-MS). As a method, a polycrystalline silicon piece as an analysis sample is dissolved in a mixed acid solution of hydrofluoric acid and nitric acid, evaporated to dryness, and the residue is dissolved in a mixed acid solution of hydrofluoric acid and nitric acid. The concentration of iron, chromium, and nickel in the aqueous solution is analyzed using ICP-MS.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. In the second embodiment, the silica coating layer 28 formed on the inner wall surface of the reaction furnace 11 shown in FIG. 1 controls the atmosphere in the reaction furnace 11 to a dew point of −30 to −50 ° C. This is done by introducing chlorosilane gas. As a method for introducing chlorosilane gas into the reaction furnace, firstly, a method of introducing chlorosilane gas, which is trichlorosilane, silicon tetrachloride or a mixed gas thereof, into the reaction furnace as it is, and secondly, trichlorosilane, silicon tetrachloride or There is a method of introducing a chlorosilane gas obtained by diluting the mixed gas with hydrogen or an inert gas into a reaction furnace.

  Although the silica coating formed in the second embodiment is slightly less effective than the silica coating formed using the polysilazane solution in the first embodiment, chlorosilane gas is used to achieve the object of the present invention. The aforementioned “in-situ coating method” used is also a practical and effective coating method.

Next, the process up to the formation of the silica coating layer of the second embodiment will be described in detail. Chlorosilanes such as silicon tetrachloride (SiCl ₄ ) and trichlorosilane (SiHCl ₃ ) are easily hydrolyzed when in contact with moisture. Ideally, this hydrolysis reaction is expected to be a reaction of the following formula (3). However, in reality, the dechlorination reaction and the dehydration condensation reaction of the following formulas (4) and (5) are performed.
SiCl ₄ + 2H ₂ O → SiO ₂ + 4HCl (3)
_{Si-Cl + H 2 O →} SiOH + HCl (4)
Si—OH + Si—OH → Si—O—Si + H ₂ O (5)

  As a result of the reactions of formulas (4) and (5), incomplete silica is formed, with some Si-OH bonds remaining. In addition, "Si-Cl" in Formula (4) and "Si-OH" in Formula (5) show the terminal structure of chlorosilane or silica. Therefore, when exposed to air, it is easy to adsorb contamination and lead to deterioration of quality, but if it has a certain thickness, it acts as a coating on the surface of metallic materials such as stainless steel, which suppresses the generation of outgas In addition, if the silica coating layer is formed by the “in-situ coating method” in which the precipitation reaction is started without opening the reaction furnace after the film is formed, the effect of reducing the contamination of the polycrystalline silicon rod can be obtained.

  In order to cause the hydrolysis reaction of chlorosilane represented by the formula (3), moisture is required, and the silica coating layer having a thickness of 0.05 to 5 μm is formed on the inner wall surface of the reaction furnace as in the first embodiment. In order to form the chlorosilane gas, it is necessary to introduce chlorosilane gas in a state where there is a sufficient amount of sufficient moisture. For this purpose, the atmosphere in the reactor is controlled to a dew point of −30 to −50 ° C. When chlorosilane gas is introduced in a state where the dew point exceeds −30 ° C., a reaction occurs in the gas phase to produce fine powder, and a silica coating layer is hardly formed on the entire inner wall surface of the reaction furnace. On the other hand, when chlorosilane gas is introduced in a state where the dew point is lower than −50 ° C., a portion where a silica coating layer having a sufficient thickness is not formed on the inner wall surface of the reaction furnace remains.

  A method for manufacturing a polycrystalline silicon rod in the second embodiment will be described. Similar to the first embodiment, a silicon seed rod is prepared, and the silicon seed rod is assembled to the electrode body disposed on the inner bottom of the reactor. The bell jar made of the same metal material as in the first embodiment is placed on the base of the reaction furnace made of the same metal material as in the first embodiment to seal the reaction furnace. Subsequently, the atmosphere in the reactor is controlled to a dew point of −30 to −50 ° C., and chlorosilane gas, which is trichlorosilane, silicon tetrachloride or a mixed gas thereof, is introduced into the reactor as it is, or trichlorosilane, A chlorosilane gas obtained by diluting silicon tetrachloride or a mixed gas thereof with hydrogen or an inert gas is introduced. Thereby, a silica coating layer is formed on the inner wall surface of the reactor. In this state, the deposition reaction is started without opening the reactor as it is, and in-situ coating is performed to deposit polycrystalline silicon on the surface of the silicon seed rod to produce a polycrystalline silicon rod.

  The introduction of the chlorosilane gas may be performed before or after energization to the silicon seed rod. Since the high temperature seed rod after energization absorbs metal impurities contained in the outgas, it is preferable in terms of quality before energization. When the chlorosilane gas is introduced after energization, the impurities taken into the seed rod can be minimized by controlling the deposition rate of polycrystalline silicon to 0.5 mm / h or less.

  By forming a silica coating layer on the inner wall of the reactor before energizing the silicon seed rod, or by forming it in the initial stage of manufacturing the polycrystalline silicon rod after energizing the silicon seed rod, the polycrystalline silicon rod Contamination due to outgas from the inner wall of the reaction furnace to the polycrystalline silicon during the production can be suppressed.

  Next, examples of the present invention will be described in detail together with comparative examples.

<Example 1>
A silica coating layer was formed based on the first embodiment. That is, a silica coating solution composed of a dibutyl ether solution having a polysilazane concentration of 10% by mass (manufactured by Sanwa Chemical Co., Ltd.) is applied at a coating amount of 20 cc / m ² over the entire inner wall surface of the reactor whose inner wall is made of austenitic stainless steel. After curing, spray coating was uniformly performed so that the thickness of the silica coating layer was 1 μm. After spray coating, it was kept at a temperature of 120 ° C. for 1 hour under atmospheric pressure, and further kept at a humidity of 80% and a temperature of 90 ° C. for 3 hours to cure the silica coating solution to form a silica coating layer.

  On the other hand, a cleaned silicon seed rod is prepared, and this seed rod is erected on the electrode body disposed on the inner bottom portion of the reaction furnace, and the upper ends of these seed rods are connected by a connecting member to form a torii type. Assembled. A bell jar with a silica coating layer formed on the inner wall surface was placed on the base of a reactor having a silica coating layer formed on the inner wall surface.

  Subsequently, after the seed rod was preheated with a heater and energized to raise the temperature to about 1100 ° C., trichlorosilane (TCS) and hydrogen source gas were supplied into the reactor for about 100 hours. Silicon was deposited and grown on the surface of the seed rod to produce a polycrystalline silicon rod having a diameter of about 110 mm.

<Comparative Example 1>
A bellows in which no silica coating layer was formed on the inner wall surface was placed on the base of a reaction furnace in which no silica coating layer was formed on the inner wall surface, and a polycrystalline silicon rod was produced in the same manner as in Example 1.

<Example 2>
A silica coating layer was formed based on the second embodiment. That is, the same austenite stainless steel inner wall surface coated with a bellows as in Example 1 was assembled, and after assembling the seed rod, the same austenitic stainless steel inner wall surface as in Example 1 was coated with a reactor. The reactor was sealed on the stage. In this example, the reactor had an inner volume of about 15 m ³ and an inner wall surface area of about 30 m ² . The reactor was depressurized with a water ring pump and an oil rotary pump, and the air in the furnace was replaced with nitrogen. It was -32 degreeC when this was repeated 3 times and the dew point in a reaction furnace was measured. After reducing the pressure again (−0.1 MPaG) with an oil rotary pump, 0.5 L of silicon tetrachloride (liquid) was charged into the inlet pipe. The silicon tetrachloride solution was vaporized and the furnace pressure gradually increased. By this operation, silicon tetrachloride gas is uniformly supplied into the furnace, so that a silica coating layer is formed on the entire inner wall surface of the reaction furnace. After 10 minutes, when the pressure gauge needle showing the pressure in the furnace slightly swings, nitrogen gas is introduced to 0.02 MPaG, and the remaining silicon tetrachloride (gas) is discharged again by the water ring pump, and then the inside of the furnace is discharged. Replaced with argon gas. Subsequently, after preheating the seed rod with the in-furnace heater, the seed rod was energized, and then the inside of the reaction furnace was replaced with hydrogen, and the raw material gas of trichlorosilane (TCS) and hydrogen was supplied to start the precipitation reaction. . Silicon was deposited and grown on the surface of the seed rod to produce a polycrystalline silicon rod having a diameter of about 110 mm.

<Example 3>
A silica coating layer was formed based on the second embodiment. That is, after assembling the seed rod in the same manner as in Example 2, the same bell jar as in Example 2 was placed on the same reactor base as in Example 2 to seal the reaction furnace. The reactor was depressurized with a water ring pump, and the air in the furnace was replaced with nitrogen. It was -48 degreeC when this was repeated 3 times and the dew point in a reactor was measured. Subsequently, the inside of the reactor was replaced with argon, and the seed rod was energized. In this state, a mixed gas using about 8 times as much hydrogen as the carrier gas relative to silicon tetrachloride was supplied and continued for 30 minutes. Thereafter, the raw material gas of trichlorosilane (TCS) and hydrogen was supplied into the reaction furnace without opening the reaction furnace, and the precipitation reaction was started. The polycrystalline silicon rods before and after introducing the mixed gas of silicon tetrachloride and hydrogen for 30 minutes were photographed from the observation windows. From the difference in the outer diameter of the polycrystalline silicon before and after the introduction of the mixed gas, the growth amount of the polycrystalline silicon in 30 minutes after the introduction of the mixed gas was 0.1 mm or less. Subsequently, the raw material gas was supplied without opening the reaction furnace, the precipitation reaction was continued, and silicon was deposited and grown on the surface of the seed rod to produce a polycrystalline silicon rod having a diameter of about 110 mm.

<Comparative example 2>
Based on the second embodiment, a silica coating layer was formed by introducing silicon tetrachloride (liquid) into the reaction furnace in the same manner as in Example 2 using the same bell jar and base as in Example 2. When the silica coating layer was formed, the bell jar was once removed and the reaction furnace was opened, and it was confirmed whether the silica coating layer was formed on the inner wall surface of the reaction furnace. The test pieces previously attached to the reactor base and the inner wall of the bell jar were collected, and the surface of these test pieces was observed with an electron microscope. As a result, a silica coating layer of about 0.5 μm was formed. I was able to confirm. The bell jar was again placed on the base of the reactor, and the reactor was sealed. Thereafter, silicon was deposited and grown on the surface of the seed rod in the same manner as in Example 2 to obtain a polycrystalline silicon rod having a diameter of about 110 mm. Manufactured.

<Evaluation 1>
Samples were cut from the two types of polycrystalline silicon rods obtained in Example 1 and Comparative Example 1, respectively. The concentration of impurities contained in the sample was measured using ICP-MS. Specifically, three samples were collected from each rod, and the concentrations of iron (Fe), chromium (Cr), and nickel (Ni) were measured for each sample, and the average value was obtained. The results are shown in Table 1.

  As is clear from Table 1, the Fe concentration was 0.15 ppbw in Comparative Example 1, but was reduced to 0.08 ppbw in Example 1. Further, regarding the Cr concentration and the Fe concentration, those in Comparative Example 1 were 0.08 ppbw, but in Example 1, each was reduced to 0.02 ppbw. From this, it was confirmed that suppression of outgas including a metal compound or the like by the silica coating layer was remarkably exhibited, and a high-purity polycrystalline silicon rod was obtained.

<Evaluation 2>
Samples were cut from the three types of polycrystalline silicon rods obtained in Examples 2 and 3 and Comparative Example 2, respectively. The concentration of impurities contained in the sample was measured using ICP-MS. Specifically, three samples are taken from each rod, and the concentrations of iron (Fe), chromium (Cr), nickel (Ni), boron (B), and phosphorus (P) are measured for each sample. The average value was obtained. The results are shown in Table 2.

  Comparing the results of Table 1 and Table 2, in Examples 2 and 3, the impurity concentrations of iron (Fe), chromium (Cr), and nickel (Ni) were slightly higher than those in Example 1. As is apparent from Table 2, it was found that in Examples 2 and 3, except for the Cr concentration, the impurity concentration was lower than that of Comparative Example 2 and the effect of suppressing impurity contamination was observed. In particular, in Comparative Example 2, in addition to iron (Fe) and chromium (Cr), the concentrations of boron (B) and phosphorus (P) were higher than those in Examples 2 and 3. This was presumed to be because the silica coating layer adsorbed impurity components from the air by removing the bell jar and opening the reactor once.

  The reactor for producing a polycrystalline silicon rod of the present invention can be used for producing a high-purity polycrystalline silicon rod as a raw material for producing single crystal silicon used in semiconductor equipment.

10 Polycrystalline silicon rod production apparatus 11 Reactor 13 Berja 20 Polycrystalline silicon rod 23 Inner wall 24 Outer wall 28 Silica coating layer

Claims (8)

  A reaction furnace for producing a polycrystalline silicon rod, wherein the reaction furnace is made of a metal material having heat resistance, and has a silica coating layer on an inner wall surface of the reaction furnace.   A method of manufacturing a reactor for manufacturing a polycrystalline silicon rod by forming a silica coating layer on an inner wall surface of a reactor for manufacturing a polycrystalline silicon rod, wherein the reactor is made of a heat-resistant metal material.   The method for producing a reactor for producing a polycrystalline silicon rod according to claim 2, wherein the formation of the silica coating layer is performed by applying a silica coating solution to an inner wall surface of the reaction furnace and curing it.   4. The method for producing a polycrystalline silicon rod reactor according to claim 3, wherein the silica coating solution is a polysilazane solution.   In the formation of the silica coating layer, the atmosphere in the reactor for producing the polycrystalline silicon rod is controlled to a dew point of −30 to −50 ° C., and the reactor is filled with trichlorosilane, silicon tetrachloride or a mixed gas thereof. 3. The polycrystalline silicon rod manufacturing method according to claim 2, wherein a certain chlorosilane gas is introduced as it is or a chlorosilane gas obtained by diluting trichlorosilane, silicon tetrachloride or a mixed gas thereof with hydrogen or an inert gas is introduced. A method for manufacturing a reactor.   After assembling a silicon seed rod and sealing a reaction furnace made of a metal material having heat resistance, the atmosphere in the reaction furnace is controlled to a dew point of −30 to −50 ° C., and trichlorosilane is contained in the reaction furnace. The chlorosilane gas which is silicon tetrachloride or a mixed gas thereof is introduced as it is, or a chlorosilane gas obtained by diluting trichlorosilane, silicon tetrachloride or a mixed gas thereof with hydrogen or an inert gas is introduced. A method for producing a polycrystalline silicon rod by forming a silica coating layer on an inner wall surface and depositing polycrystalline silicon on the surface of the silicon seed rod without opening the reactor as it is.   The method according to claim 6, wherein when introducing the chlorosilane gas after energizing the silicon seed rod, a polycrystalline silicon rod is manufactured by controlling the deposition rate of the polycrystalline silicon to be 0.5 mm / h or less. .   A method for producing a polycrystalline silicon rod using the reactor for producing a polycrystalline silicon rod according to claim 1 or the reactor for producing a polycrystalline silicon rod produced by the method according to any one of claims 2 to 4. .

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