Manufacturing method for polycrystalline silicon

Abstract

To provide a method for producing a polycrystalline silicon by which the total amount of moisture brought into a reactor for producing the polycrystalline silicon is suppressed by a simple procedure, thereby enabling the production of the polycrystalline silicon having few impurities.SOLUTION: A method for producing a polycrystalline silicon by reducing chlorosilane in a reactor and depositing the polycrystalline silicon on a seed rod is provided. In the method, the moisture brought into the reactor by a carbon member used in the reactor is reduced.SELECTED DRAWING: Figure 2

Description

[[TECHNICAL FIELD]]

[0001] The present invention relates to a method for producing polycrystalline silicon. [[BACKGROUND ART]]

[0002] Single-crystal silicon used as a material for semiconductor wafers is generally produced by the Czochralski method, in which high-purity polycrystalline silicon is melted in a quartz crucible, a seed crystal is brought into contact with the silicon melt, and the single crystal is grown while being pulled up.

[0003] Polycrystalline silicon, which is a raw material for producing such single-crystal silicon, is produced as follows: a silicon core rod (hereinafter sometimes referred to as a seed rod) installed in a reaction furnace is energized to make it red-hot, and a mixed gas of trichlorosilane, which is a raw material gas, and hydrogen is supplied into the furnace. It is generally produced by the Siemens method, in which silicon is precipitated on the surface of the seed rod by reduction or thermal decomposition and grown into a rod shape. In the Siemens method, a carbon material is generally often used as a holding material for holding the seed rod in the reaction furnace, in order to energize the seed rod without contaminating the polycrystalline silicon to be grown.

[0004] With the advancement of semiconductor technology in recent years, quality requirements for polycrystalline silicon, which is a raw material for producing single-crystal silicon, have also become more advanced, and the concentration of metal impurities is ppt (10 -12 ) level, and thorough elimination of contamination sources is required. For example, in JEITA EM-3601A (Standard Specification for Electronic Information Technology Industry · High Purity Polycrystalline Silicon Standard Products) revised and issued in 2004, impurity concentration qualities are specified such that bulk phosphorus concentration is 0.30 ppba or less and surface Fe concentration is 3.0 ppbw or less. However, for high-quality polycrystalline silicon products in recent years, regardless of whether it is bulk or surface, impurity concentration levels such as 0.030 ppba or less for phosphorus concentration and 0.015 ppbw or less for Fe concentration have come to be required.

[0005] In the Siemens method for the synthesis of polycrystalline silicon, quartz glass is sometimes experimentally used as the synthesis vessel. However, industrially, to avoid the risk of vessel breakage that can occur when introducing highly reactive chlorosilanes or hydrogen gases into brittle quartz glass vessels, the reaction vessels are generally constructed from stainless steel materials.

[0006] However, a challenge with using stainless steel materials for the reaction vessel is the increased likelihood of metal contamination. The presence of moisture is known to be a major factor in metal contamination caused by the use of stainless steel materials. For example, moisture in the reactor reacts with chlorosilane gas to produce hydrogen chloride. In situations where hydrogen chloride and moisture coexist, a reactor made of stainless steel materials undergoes significant corrosion. If such corrosion occurs in the initial stages of the polycrystalline silicon deposition reaction, the quality of the deposited polycrystalline silicon may be significantly reduced.

[0007] One possible route for moisture to enter the reactor is through adsorbed water on the inner wall of the reactor. To address this, a method has been proposed in which chlorosilane gas is introduced into the reactor before the reaction starts, and the adsorbed water is removed by reacting with the chlorosilane gas (see, for example, Patent Document 1). Furthermore, a method is known in which seed rods are assembled to seal the inside of the reactor, the pressure is reduced, and an inert gas is introduced to remove moisture from inside the reactor (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2020-164348 [Patent Document 2] International Publication No. 2011 / 158404 [Overview of the project] [Problems that the invention aims to solve]

[0009] However, even after removing the water adsorbed on the inner wall of the reactor, as disclosed in Patent Documents 1 and 2, it was still difficult to suppress the generation of hydrogen chloride gas due to the reaction of water with chlorosilane gas, and the generation of metal particles due to the reaction of water with stainless steel material. In other words, it is thought that there are other factors besides adsorbed water on the inner wall of the reactor that introduce water into the reactor.

[0010] This invention has been made in view of the above background, and aims to provide a method for producing polycrystalline silicon that suppresses the total amount of water introduced into a reaction furnace for the production of polycrystalline silicon using a simple procedure, thereby enabling the production of polycrystalline silicon with fewer impurities. [Means for solving the problem]

[0011] Through various verifications of the manufacturing process of polycrystalline silicon, the inventors have obtained a new finding that carbon components used in the reaction furnace bring a large amount of moisture into the furnace. Carbon components are usually sintered at high temperatures of 2000°C or higher, and for processed products requiring high purity, high-temperature treatment in a halogen gas atmosphere is performed to remove contamination during processing. After the treatment is completed, they are sealed and stored in storage bags made of resin such as polyethylene. Immediately after the high-temperature treatment, there is almost no residual moisture, but because the resin storage bags allow a certain amount of water vapor from the air to pass through, the inventors found that the carbon components absorb moisture over time during storage.

[0012] The present invention is based on the above-mentioned findings, and in order to solve the problem, the following means are proposed for a method of producing polycrystalline silicon according to one embodiment of the present invention. (1) A method for producing polycrystalline silicon according to embodiment 1 of the present invention is a method for producing polycrystalline silicon by reducing chlorosilane in a reaction furnace and depositing polycrystalline silicon on a seed rod, The carbon component used in the reactor has a resin layer and a metal layer or silica vapor-deposited layer until use, and has a water vapor transmission rate of 0.5 g / m³. 2 By storing in a storage container that is less than or equal to one day, The carbon component prevents moisture from being introduced into the reactor. Less than 0.80 mg per kg of polycrystalline silicon It is characterized by reducing.

[0013] According to the method for producing polycrystalline silicon of embodiment 1 of the present invention, by reducing the amount of water introduced into the reactor via a carbon member, it is possible to produce polycrystalline silicon with fewer impurities, such as phosphorus and iron. Using such polycrystalline silicon with fewer impurities as a raw material contributes to the production of high-quality single-crystal silicon.

[0014] (2) Embodiment 2 of the present invention is a method for producing polycrystalline silicon according to Embodiment 1, characterized in that the amount of water released from the carbon member per 24 hours at room temperature is 0.020 mg / g or less.

[0015] (3) Embodiment 3 of the present invention is a method for producing polycrystalline silicon according to Embodiment 1 or 2, characterized in that the phosphorus concentration in the polycrystalline silicon deposited on the seed rod is 0.030 ppb (atoms) or less, and the iron concentration is 0.015 ppb (mass) or less.

[0016] (4) Aspect 4 of the present invention is a method for producing polycrystalline silicon according to any one of aspects 1 to 3, characterized in that the carbon member is stored in a storage container having a resin layer and a metal layer or a silica vapor deposition layer until use, thereby reducing the amount of moisture brought into the reaction furnace by the carbon member. It is also preferable to reduce the pressure inside the storage container after storing the carbon member in the storage container. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a method for producing polycrystalline silicon that suppresses the total amount of water introduced into a reaction furnace for the production of polycrystalline silicon using a simple procedure, thereby enabling the production of polycrystalline silicon with fewer impurities. [Brief explanation of the drawing]

[0018] [Figure 1] This is a schematic diagram showing an example of a polycrystalline silicon manufacturing apparatus used in the method for manufacturing polycrystalline silicon according to this embodiment. [Figure 2] It is a schematic diagram showing an example of a reactor.

Mode for Carrying Out the Invention

[0019] Hereinafter, a method for producing polycrystalline silicon according to an embodiment of the present invention will be described. Each embodiment shown below is specifically described to facilitate a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified. In addition, in the drawings used in the following description, for the sake of convenience, main portions may be shown in an enlarged manner to make the features of the present invention easier to understand, and the dimensional ratios of respective constituent elements are not necessarily the same as those in actual practice.

[0020] First, an example of a polycrystalline silicon production apparatus used in the method for producing polycrystalline silicon of the present embodiment will be described. FIG. 1 is a schematic configuration diagram showing an example of a polycrystalline silicon production apparatus used in the method for producing polycrystalline silicon of the present embodiment. FIG. 2 is a schematic diagram showing an example of a reactor. The polycrystalline silicon production apparatus 10 includes a chlorination furnace 11, a distillation facility 12, a reactor 13, and a hydrogen purification facility 14.

[0021] The chlorination furnace 11 causes metallic silicon as a raw material to react with hydrogen chloride gas at approximately 300° C. to generate trichlorosilane (SiHCl3) (see formula (1)). At this time, silicon tetrachloride is also produced by a side reaction (see formula (2)). Si+3HCl→SiHCl3+H2···(1) Si+4HCl→SiCl4+2H2···(2)

[0022] The distillation facility 12 purifies trichlorosilane by the difference in boiling point between trichlorosilane and silicon tetrachloride to obtain high-purity trichlorosilane.

[0023] The reactor 13 reacts high-purity trichlorosilane obtained in the distillation equipment 12 with high-purity hydrogen obtained in the hydrogen purification equipment 14 at approximately 1000°C to precipitate polycrystalline silicon by chemical vapor deposition (CVD) (see equations (3) and (4)). 4SiHCl3→Si+3SiCl4+2H2...(3) SiHCl3 + H2 → Si + 3HCl···(4)

[0024] The hydrogen purification equipment 14 purifies the process gas (hydrogen, hydrogen chloride, silicon chloride, etc.) generated in the reactor 13 and supplies high-purity hydrogen to the reactor 13, while refluxing the silicon chloride to the distillation equipment 12 to use as a raw material for trichlorosilane.

[0025] As shown in Figure 2, the reactor 13 includes, for example, a heat-resistant chamber 21 made of a stainless steel alloy, a plurality of electrodes 22, a carbon member 23 that supports the seed rod S, and a support plate 24 that hermetically closes the open surface of the heat-resistant chamber 21. The electrodes 22 and the support plate 24 are insulated to avoid ground faults.

[0026] The electrode 22 is made of a metal such as stainless steel and is connected to a power supply at the bottom as shown in Figure 2, forming a pair of electrodes. Between this pair of electrodes, a seed rod S made of, for example, U-shaped silicon is erected using a carbon member 23. Since contact between the seed rod S and the electrode 22 could lead to metal contamination, it is necessary to use the carbon member 23 as a relay.

[0027] The carbon member 23 is a support member that supports the seed rod S. The carbon member is porous, and moisture that penetrates and adsorbs into the interior of the carbon member is difficult to remove. The support plate 24 is connected to an air supply pipe 25 for introducing trichlorosilane and hydrogen gas, and an exhaust pipe 26 for discharging the gas of by-products generated by the reaction.

[0028] By heating the inside of such a reactor 13 to, for example, about 1000°C and introducing trichlorosilane and hydrogen gas into the reactor 13, the reactions of equations (3) and (4) described above proceed, and polycrystalline silicon precipitates around the seed rod S. By separating the polycrystalline silicon together with the seed rod S from the carbon member 23, a polycrystalline silicon rod R with a diameter of, for example, about 11 to 14 cm can be obtained.

[0029] The method for manufacturing polycrystalline silicon according to this embodiment, using the polycrystalline silicon manufacturing apparatus 10 configured as described above, will now be explained. The method for producing polycrystalline silicon in this embodiment reduces the amount of moisture introduced into the reactor 13 via carbon members used in the reactor 13, such as the carbon member 23 that supports the seed rod S. Specifically, a carbon member 23 is used that releases 0.020 mg / g or less of moisture per 24 hours at room temperature (25°C).

[0030] By using carbon components 23 with low water release, the amount of water brought into the reactor 13 can be reduced. This makes it possible to reduce the phosphorus concentration in the polycrystalline silicon deposited on the seed rod S within the reactor 13 to 0.030 ppb (atomic) or less, and the iron concentration to 0.015 ppb (mass) or less.

[0031] One specific example of reducing the amount of moisture released from the carbon member 23, as described above, is to reduce the moisture permeability of the storage bag that stores the carbon member 23 for supporting the seed rod S.

[0032] The carbon components 23 used in the polycrystalline silicon manufacturing apparatus 10 are typically manufactured by sintering at high temperatures of 2000°C or higher. For processed products requiring particularly high purity, high-temperature treatment in a halogen gas atmosphere is performed to remove contamination during processing. Afterward, the products are placed in storage containers, sealed, and stored until use. Examples of storage containers include flexible bag-shaped storage bags and rigid box-shaped storage boxes. However, the storage containers are not limited to any specific shape.

[0033] Immediately after high-temperature treatment, there is almost no moisture residue in the carbon component 23. Polyethylene, which is used for the storage container of the carbon component, has relatively low vapor permeability among resins, but LDPE has a vapor permeability of 2.7 g / m². 3 The transmittance data, such as "day," is shown, indicating that a significant amount of water vapor permeates when left in a high-humidity environment for several days. As a result, it is thought that moisture absorption occurred over time. Therefore, in this embodiment, when a storage bag is used as a storage container, a multi-layered storage bag is used in which, in addition to the conventional polyethylene layer (resin layer) that allows moisture to permeate, a metal layer or silica vapor-deposited layer with low water vapor permeability is formed as the constituent material of the storage bag.

[0034] When using a storage box as a storage container, for example, a combination of a polyethylene bag and a metal box body, or a rigid polyethylene box body with a metal or silica vapor-deposited layer formed on the inner or outer surface, can be used.

[0035] When a storage bag is used as a storage container, the metal layer of the storage bag can be, for example, a thin aluminum film layer. The storage bag of this embodiment can be formed by vapor-depositing aluminum or silica onto one side of a polyethylene layer (resin layer).

[0036] The storage bag for storing these carbon components 23 has a polyethylene layer (resin layer) to suppress contamination by metals on the surface, and a metal layer or silica vapor deposition layer to prevent water vapor permeation. The water vapor permeability of the storage bag is, for example, 0.5 g / m³. 2 (day) or less, preferably 0.3 (g / m²) 2 It is acceptable if it is less than or equal to one day.

[0037] By forming a metal layer or silica vapor-deposited layer in addition to the resin layer as a storage bag, and setting the water vapor transmission rate within the above-mentioned range, for example, even if the manufactured carbon component 23 is stored for about three months, the amount of moisture contained in the carbon component 23 can be maintained with almost no change.

[0038] By storing each carbon component in a storage bag with a polyethylene layer (resin layer) and a metal layer or silica vapor-deposited layer that suppresses moisture permeation, when these carbon components are used in the reactor 13, moisture release in the reactor 13 is almost eliminated, and the impurity concentration of the precipitated polycrystalline silicon, such as the phosphorus concentration, can be reduced to 0.030 ppb (atoms) or less, and the iron concentration to 0.015 ppb (mass) or less.

[0039] The inventors have found that when measuring the impurity concentrations of polycrystalline silicon produced using carbon components stored in polyethylene bags for more than three weeks under high temperature and humidity conditions in the summer, the concentrations of phosphorus and iron tend to be significantly higher compared to other materials, as shown in Table 1 below.

[0040] [Table 1]

[0041] Therefore, in order to quantitatively evaluate the amount of water absorbed by the carbon member 23 that supports the seed rod S, an evaluation method using a sealed container and a dew point meter was devised. As a measuring device used in this evaluation method, for example, a dew point meter is installed inside a desiccator (sealed container) connected to a vacuum pump, and during measurement, the carbon member 23 to be measured is placed inside the desiccator, and the inside of the desiccator is replaced with nitrogen gas.

[0042] According to JIS K1107, the dew point of nitrogen gas is defined as -65°C or lower for Grade 1 and -60°C or lower for Grade 2. Sufficiently dry nitrogen gas with a dew point of -65°C or lower is readily available. The measurement was performed by placing only a dew point meter in a desiccator, filling it with Grade 1 equivalent nitrogen gas by vacuum displacement, and measuring the dew point for 24 hours. After that, the dew point meter was removed from the desiccator, and the dew points immediately after nitrogen gas displacement and after 24 hours were compared to calculate the increase in moisture content. As an example of this result, the moisture content was 18 mg. Since this can be considered a constant of this measuring device, if a carbon sample is placed in the desiccator and the rise in dew point is measured in the same way, the difference from the empty state will represent the amount of water vapor released from the carbon sample.

[0043] As an example of measurement, the average temperature in Tokyo in August is around 28°C, and the average humidity is around 80%. Based on the water vapor transmission rate data for polyethylene, and assuming conditions equivalent to the average temperature and humidity in August, a carbon component (sample) was stored for 3 days in a constant temperature and humidity chamber at 40°C and 90% humidity. The moisture content was measured using the aforementioned measuring device and the aforementioned measurement method, and the moisture content per gram of carbon component was found to be 0.020 mg.

[0044] Since the amount of carbon material used depends on the design of the reactor 13, naturally, the more carbon is used, the more moisture is introduced into the reactor 13. From the actual weight of carbon used and the amount of polycrystalline silicon produced, it was found that if more than 0.80 mg of moisture is introduced per 1 kg of polycrystalline silicon product, it becomes difficult to obtain polycrystalline silicon that maintains the specified quality standards.

[0045] Therefore, it was confirmed that reducing the amount of water absorbed by the carbon component prevents an increase in the bulk phosphorus concentration and iron concentration of the polycrystalline silicon. Here, the evaluation was based on a phosphorus concentration of 0.030 ppb (atomic) or less and an iron concentration of 0.015 ppb (mass) or less in the polycrystalline silicon. However, it can be estimated that if the quality requirements become even stricter, the constraint on the amount of water will also become stricter. Therefore, by reducing the amount of water introduced into the reactor 13 from the carbon component, as in the present invention, it is possible to cope even when the constraint on the amount of water becomes stricter.

[0046] Although one embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0047] The method for producing polycrystalline silicon according to this embodiment was then verified. Each verification example was conducted under the following conditions. (Example 1) As a measure against moisture permeability, polyethylene is used as an inner layer for storing carbon components during maintenance, with a permeability of 0.1 g / m³. 2 A double-layered storage bag with aluminum as the outer layer was used.

[0048] Carbon components that had undergone purification treatment in a halogen gas atmosphere in a high-temperature processing furnace were placed in the double-packaged storage bags described above, sealed, and left for three weeks. After that, the carbon components were removed from the storage bags and the dew point was measured. Furthermore, polycrystalline silicon was produced using another carbon component that had been placed in the aforementioned double-packaged storage bag, sealed, and left for three weeks, and the impurity concentration was measured.

[0049] (Example 2) Similar to Example 1, the purified carbon material was packaged in a polyethylene bag, and the packaged carbon material was placed in an aluminum container (storage box), sealed, and left for 3 weeks. After that, the carbon material was removed from the container and the dew point was measured. Furthermore, polycrystalline silicon was produced using another carbon component that had been left for three weeks using the same storage method, and the impurity concentration was measured.

[0050] (Comparative Example 1) A carbon component that had undergone the same purification treatment as in Example 1 was placed in a storage bag consisting only of a polyethylene layer, sealed, and left for three weeks. After that, the carbon component was removed from the storage bag and the dew point was measured. Furthermore, polycrystalline silicon was produced using another carbon component that had been stored in a storage bag containing only the polyethylene layer described above, sealed, and left for three weeks, and the impurity concentration was measured.

[0051] (Dew point measurement method) The dew point measuring device described in the embodiment was used. (1) Place the carbon component to be measured and the dew point meter into the desiccator. (2) Activate the vacuum pump connected to the desiccator and reduce the pressure inside the desiccator until the gauge pressure on the vacuum gauge is -0.09 to -0.1 MPa. (3) After closing the line from the desiccator to the vacuum pump, open the nitrogen gas line and introduce nitrogen gas into the desiccator until the gauge pressure on the vacuum gauge is approximately -0.005 MPa. (Creating a slight negative pressure allows you to check for leaks.) (4) By performing the operations in (2) and (3) five times, the inside of the desiccator will be filled with dry nitrogen gas. (5) After 24 hours have elapsed since the desiccator has been replaced with nitrogen gas, the inside of the desiccator is returned to atmospheric pressure, and the carbon component to be measured and the dew point meter are removed.

[0052] Table 2 shows the measurement results of the carbon components (samples) of Examples 1 and 2 and Comparative Example 1, measured using the dew point measurement method described above. ("Blank" in the table refers to the result when the carbon component was not placed in the desiccator and only the dew point meter was used. See also paragraph "0041".) [Table 2]

[0053] The results shown in Table 2 confirm that carbon components stored in storage containers containing an aluminum layer or aluminum material that suppresses water vapor permeability (Examples 1 and 2) can have significantly lower moisture content than carbon components stored in storage bags consisting only of a polyethylene layer that allows water vapor to permeate (Comparative Example 1).

[0054] Furthermore, Table 3 shows the measurement results of the impurity concentration of polycrystalline silicon produced using the carbon components of Examples 1 and 2 and Comparative Example 1. [Table 3]

[0055] As shown in Table 3, the results confirm that the polycrystalline silicon produced using the carbon components of Examples 1 and 2, in which moisture absorption was suppressed, had lower phosphorus and iron concentrations compared to the polycrystalline silicon produced using the carbon component of Comparative Example 1, in which moisture absorption was not suppressed.

[0056] Next, we calculated the amount of moisture introduced by the carbon components into each reactor and the amount of moisture mixed into the reactor per kilogram of manufactured polycrystalline silicon. Considering the total weight of the carbon components used per reactor and the amount of polycrystalline silicon manufactured per reactor, we determined the moisture content for storage in storage bags containing only the polyethylene layer, storage bags containing the aluminum layer, and storage bags containing the polyethylene layer and aluminum containers.

[0057] Assuming a total weight of 200 kg of carbon components used per reactor, and that the carbon components are stored in a polyethylene-only storage bag, the amount of water absorbed is 4000 mg, and that the amount of silicon produced per reactor using these carbon components as electrode support members is 5000 kg, then the amount of water entering the reactor is 0.80 mg per kg of polycrystalline silicon.

[0058] Therefore, the amount of moisture introduced by the carbon component was 4000 mg, and the amount of moisture per kg of polycrystalline silicon entering the furnace was 0.80 mg. Similarly, when calculated for storage in a storage bag containing an aluminum layer, the amount of moisture introduced by the carbon component was 1600 mg, and the amount of moisture per kg of polycrystalline silicon entering the furnace was 0.32 mg. Similarly, when calculated for storage in a storage bag containing a polyethylene layer and an aluminum container, the amount of moisture introduced by the carbon component was 800 mg, and the amount of moisture per kg of polycrystalline silicon entering the furnace was 0.16 mg.

[0059] From these results, we have demonstrated that, as in the present invention, by suppressing the amount of water introduced into the reaction furnace, the impurity concentration of the polycrystalline silicon produced can be reduced, thereby obtaining high-quality polycrystalline silicon. [Industrial applicability]

[0060] The present invention's method for producing polycrystalline silicon suppresses the total amount of water introduced into the reaction furnace for silicon polycrystal production, thereby enabling the production of high-quality polycrystalline silicon with fewer impurities, which is necessary for the production of single-crystal silicon. Therefore, it has industrial applicability. [Explanation of symbols]

[0061] 10…Polycrystalline silicon manufacturing equipment 11… Chloride reactor 12…Distillation equipment 13… Reactor 14…Hydrogen purification equipment 21… Heat-resistant chamber 22...Electrode 23…Carbon fiber components

Claims

1. A method for producing polycrystalline silicon, comprising reducing chlorosilane in a reactor to precipitate polycrystalline silicon on a seed rod, The carbon components used in the reactor are stored in a storage container having a resin layer and a metal layer or silica vapor-deposited layer, and having a water vapor transmission rate of 0.5 g / m²day or less, until use. A method for producing polycrystalline silicon, characterized in that the amount of water introduced into the reactor by the carbon member is reduced to less than 0.80 mg per kg of polycrystalline silicon.

2. The method for producing polycrystalline silicon according to claim 1, characterized in that the amount of moisture released from the carbon member per 24 hours at room temperature is 0.020 mg / g or less.

3. A method for producing polycrystalline silicon according to claim 1 or 2, characterized in that the phosphorus concentration in the polycrystalline silicon precipitated on the seed rod is 0.030 ppb (atoms) or less, and the iron concentration is 0.015 ppb (mass) or less.

4. The method for producing polycrystalline silicon according to claim 1 or 2, characterized in that the carbon member is stored in the storage container and then the inside of the storage container is depressurized.

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