Dewar flask, photoluminescence measuring device, concentration measurement method, and silicon manufacturing method

Abstract

The present invention aims to significantly reduce the burden on vacuum workers and the cost of vacuuming when measuring the concentration of impurities contained in silicon by photoluminescence in liquid helium. The inner cylinder Dewar flask (2) is formed of a material, i.e., glass, having a SiO2 content of 65% by weight or more and 75% by weight or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 ‑7 / ℃ and above 55×10 ‑7 / ℃ below.

Description

Technical Field

[0001] The invention relates to a Dewar flask, a photoluminescence measuring device, a concentration measuring method and a silicon manufacturing method. Background Art

[0002] Various methods for measuring the concentration of impurities such as phosphorus and boron in polycrystalline silicon have been studied. As an example, Non-Patent Document 1 discloses the following method. First, a polycrystalline silicon rod is crystallized (single crystal rod) using the FZ method (Float-Zone method). Next, a sample is cut from any straight portion of the single crystal rod, and the impurity concentration in the sample is measured using photoluminescence. The measured value is then converted to the impurity content in the polycrystalline silicon rod through theoretical calculation.

[0003] A common method for measuring the concentration of impurities in a sample using photoluminescence is to place liquid helium in a glass Dewar flask housed in a cryostat within a photoluminescence measurement device, immersing the entire sample in the liquid helium. The glass Dewar flask used in this concentration measurement method is typically made of hardness grade 1 glass. Hereinafter, this hardness grade 1 glass Dewar flask will be referred to as a "conventional measurement Dewar flask."

[0004] Here, because helium has the property of penetrating glass, when liquid helium is placed in a conventional measurement Dewar flask for concentration measurement, the helium gas generated by the liquid helium rapidly penetrates the glass wall of the Dewar flask, causing the vacuum degree of the vacuum layer inside the glass wall to drop sharply. Furthermore, the thermal insulation effect of the heat insulating layer formed by the vacuum layer is reduced, and the liquid helium evaporates actively, making it impossible to maintain the sample at the measurement temperature (about 4K). As a result, it is impossible to measure the concentration of impurities in the sample by photoluminescence. Here, "vacuum degree" refers to the degree of vacuum under extremely low pressure conditions, expressed by the pressure of residual gas. Specifically, it refers to the pressure of the gas remaining in the vacuum layer. When the vacuum degree of the vacuum layer inside the glass wall decreases, it is necessary to evacuate the vacuum layer to restore it to the level before the concentration measurement. Therefore, if the vacuum degree drops sharply, the number of evacuations will increase accordingly.

[0005] In order to avoid such an undesirable decrease in vacuum, a related idea is disclosed in, for example, Non-Patent Document 2. Non-Patent Document 2 suggests that there is a correlation between the SiO 2 content in glass and the penetration speed of helium gas when penetrating the glass.

[0006] Prior art literature

[0007] Non-patent literature

[0008] Non-Patent Document 1: "JEITAEM-3601A High-Purity Polysilicon Standard Specification," Electronics and Information Technology Industries Association, September 2004.

[0009] Non-patent document 2: FJ Norton, "Helium Diffusion Through Glass" (Journal of the American Ceramic Society, 36, 1953, 90-96). Summary of the Invention

[0010] Problems to be solved by the invention

[0011] However, in non-patent document 2, the correlation between the content of SiO2 in the glass and the penetration speed is only provided as an empirical rule, and there is no record that cooling from room temperature (about 23°C = about 296.15K) to ultra-low temperature (about 4K) will cause deformation. In addition, non-patent document 2 also does not involve the ease of processing the glass mother material into a Dewar flask. In a glass Dewar flask, this ease of processing is a factor in selecting the glass mother material for the Dewar flask. Against this background, the correlation between the content of SiO2 in the glass and the penetration speed has not been applied to the previous measuring Dewar flask. Therefore, when using the previous measuring Dewar flask and measuring the concentration of impurities in the sample by photoluminescence, it is necessary to vacuumize multiple times, which increases the burden on the vacuuming operator and increases the vacuuming cost.

[0012] One aspect of the present invention has been made in view of the above-mentioned problems, and its object is to significantly reduce the burden on vacuum workers and the vacuuming costs when measuring the concentration of impurities contained in silicon by photoluminescence in liquid helium.

[0013] Means used to solve problems

[0014] In order to solve the above-mentioned problems, one aspect of the present invention relates to a Dewar flask made of glass for use in measuring the concentration of impurities contained in silicon by photoluminescence in liquid helium, wherein the SiO2 content in the glass is 65% by weight or more and 75% by weight or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 The term "average thermal expansion coefficient" is used because, when the thermal expansion coefficient of the glass is measured at a temperature of 20°C to 300°C, the average value of the thermal expansion coefficient is actually measured.

[0015] To solve the above-mentioned problem, one aspect of the present invention relates to a concentration measurement method for measuring the concentration of impurities contained in silicon, wherein liquid helium and the silicon are contained in a Dewar flask formed of glass, and the concentration of the impurities is measured by photoluminescence, wherein the SiO2 content in the glass is greater than or equal to 65% by weight and less than or equal to 75% by weight, and when the temperature of the glass is greater than or equal to 20°C and less than or equal to 300°C, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 / ℃ below.

[0016] To solve the above-mentioned problem, a method for producing silicon according to one aspect of the present invention includes a concentration measurement step, in which liquid helium and silicon are placed in a Dewar flask formed of glass, and the concentration of impurities contained in the silicon is measured, wherein the content of SiO2 in the glass is 65% by weight or more and 75% by weight or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 / ℃ below.

[0017] Effects of the Invention

[0018] According to one aspect of the present invention, when the concentration of impurities contained in silicon is measured by photoluminescence in liquid helium, the burden on vacuum workers can be greatly reduced, and vacuum costs can be significantly cut. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a diagram showing a schematic configuration of a photoluminescence measurement device according to one embodiment of the present invention.

[0020] Figure 2 In the figure, reference numeral 201 is a schematic diagram showing a state where a sample is immersed in liquid helium in a measurement Dewar flask according to an embodiment of the present invention, and reference numeral 202 is a cross-sectional view showing the structure of a glass wall of the measurement Dewar flask.

[0021] Figure 3 This is a flowchart showing an example of a method for producing polycrystalline silicon according to one embodiment of the present invention.

[0022] Figure 4 401 is a diagram showing an example of a concentration measurement method according to an embodiment of the present invention. Reference numeral 402 is a diagram showing a liquid nitrogen storage step. Reference numeral 403 is a diagram showing a liquid helium storage step. DETAILED DESCRIPTION

[0023] Next, we will use Figures 1 to 4One embodiment of the present invention will be described in detail. In addition, unless otherwise specified in this specification, "A to B" indicating a numerical range means "A or more and B or less."

[0024] [Photoluminescence measurement device 100]

[0025] First, use Figure 1 A photoluminescence measurement device 100 according to one embodiment of the present invention will be described. Photoluminescence measurement device 100 is used to measure the concentration of impurities (not shown) contained in polycrystalline silicon (not shown) using a photoluminescence method. Polycrystalline silicon is an example of silicon according to the present invention.

[0026] The photoluminescence method involves irradiating a sample 4 (described below) obtained by crystallizing polycrystalline silicon into a single crystal by laser light, causing photoluminescence to be emitted from the sample 4. The emitted photoluminescence is then analyzed to measure the concentration of impurities in the sample 4. Photoluminescence is light emitted from the sample 4 during the process of recombination between excess electrons and holes generated in the sample 4 by irradiating the sample 4 with laser light.

[0027] In this embodiment, four atoms, namely P, B, Al, and As, are impurities whose concentrations are measured by the photoluminescence measurement apparatus 100. It is not necessary to measure the concentrations of all four atoms; it is sufficient to measure the concentrations of at least one of these four atoms. Alternatively, atoms other than these four atoms may be measured. Examples of atoms other than these four atoms that are impurity concentrations measured by the photoluminescence measurement apparatus 100 include C.

[0028] like Figure 1 As shown, the photoluminescence measurement apparatus 100 includes a cryostat 101 , a laser light source 102 , a first filter 103 , a plane mirror 104 , a condenser lens 106 , a second filter 107 , a spectrometer 108 , a photodetector 109 , an information processing device 110 , and a sample holder 111 .

[0029] The cryostat 101 is a device for keeping the sample 4 at a low temperature of about 4K. The cryostat 101 is provided with a measuring dewar 1 and an inner cylinder dewar 2 (see Figure 2 A sample 4 and liquid helium 5 are contained within the cryostat 101 (denoted by reference numeral 201, described below). The liquid helium 5 is used to cool the sample 4 to approximately 4K. Furthermore, the cryostat 101 is provided with a window 105. When the sample 4 is contained within the cryostat 101 (specifically, within the inner cylinder Dewar flask 2), the entire sample 4 can be observed from outside the window 105.

[0030] The laser light source 102 irradiates a laser beam toward the sample 4 housed within the cryostat 101. A first optical filter 103 and a plane mirror 104 are disposed between the cryostat 101 and the laser light source 102. The first optical filter 103, disposed between the laser light source 102 and the plane mirror 104, filters out infrared light contained in the laser beam emitted from the laser light source 102.

[0031] The plane mirror 104 is disposed between the first optical filter 103 and the cryostat 101 and is used to adjust the optical path of the laser light after passing through the first optical filter 103. Specifically, the plane mirror 104 is used to adjust the optical path of the laser light after passing through the first optical filter 103 so that the laser light irradiates the sample 4 in the cryostat 101. The sample 4 in the cryostat 101, irradiated by the laser light, emits photoluminescence.

[0032] The condenser lens 106 condenses the photoluminescence emitted from the sample 4 in the cryostat 101 and guides the condensed photoluminescence to the spectrometer 108. The second filter 107 is disposed between the condenser lens 106 and the spectrometer 108 to filter out laser light and high-order diffracted light.

[0033] Spectrometer 108 separates the photoluminescence guided by condenser lens 106. Photodetector 109 detects the light separated by spectrometer 108 and outputs the detection result as a detection signal to information processing device 110. Information processing device 110 processes the detection signal output from photodetector 109 and obtains a photoluminescence spectrum. Furthermore, information processing device 110 measures the concentration of impurities contained in sample 4 by analyzing the obtained photoluminescence spectrum. Examples of information processing device 110 include stationary PCs, tablet computers, and smartphones.

[0034] The sample holder 111 is a device for holding the sample 4 while immersing it entirely in liquid helium 5. The sample holder 111 also has a helium gas supply / exhaust port (not shown) and a liquid helium supply port (not shown). The helium gas supply / exhaust port is a vent for supplying helium gas into the inner cylinder Dewar 2 and for discharging any remaining helium gas therefrom. The liquid helium supply port is a port for supplying liquid helium 5 into the inner cylinder Dewar 2, thereby storing the liquid helium 5 within the dewar.

[0035] The structure of the photoluminescence measurement device 100 described above is merely an example. The photoluminescence measurement device 100 may have various structures, as long as the device 100 can contain the sample 4 and liquid helium 5 within the measurement Dewar flask 1 and measure the concentration of impurities in the sample 4 using photoluminescence.

[0036] 〔Measurement Dewar flask 1〕

[0037] Next, use Figure 2 The measurement Dewar flask 1 according to one embodiment of the present invention is described. The measurement Dewar flask 1 is used when measuring the concentration of impurities contained in a sample 4 by a photoluminescence method. Figure 2 As shown in the symbol 201, it is a double-layer structure Dewar flask obtained by accommodating the inner cylinder Dewar flask 2 in the outer cylinder Dewar flask 3.

[0038] Here, the Dewar flask according to one aspect of the present invention refers to a Dewar flask containing liquid helium. Regarding the measuring Dewar flask 1, since the inner cylinder Dewar flask 2 contains liquid helium 5, the inner cylinder Dewar flask 2 corresponds to the Dewar flask according to one aspect of the present invention. Furthermore, the measuring Dewar flask 1 can be said to utilize the inner cylinder Dewar flask 2 according to one embodiment of the present invention.

[0039] The following description assumes that the outer Dewar 3 is positioned outside the inner Dewar 2, with liquid nitrogen 6 positioned between them. This configuration allows for efficient cooling of the measurement Dewar 1. However, since the outer Dewar 3 contains liquid nitrogen 6 rather than liquid helium 5, it does not constitute a Dewar flask according to one aspect of the present invention. However, if a configuration is employed that contains liquid helium 5 rather than liquid nitrogen 6, the outer Dewar 3 also constitutes a Dewar flask according to one aspect of the present invention.

[0040] The inner cylinder Dewar flask 2 is made of glass and is composed of a cylindrical glass wall 21 with a bottom. Moreover, as the inner cylinder Dewar flask 2, a space 22 is formed inside all parts of the glass wall 21, and a vacuum layer is formed in the space 22 by evacuating the space 22. When evacuating, an exhaust port (not shown) is formed at the bottom of the inner cylinder Dewar flask 2, and vacuum is drawn from the exhaust port. The exhaust port is an exhaust path for the air in the space 22 with an opening. After the evacuation is completed, the exhaust port is blocked. The vacuum degree of the vacuum layer formed in the space 22 is also adjusted by forming an exhaust port at the bottom of the inner cylinder Dewar flask 2. The inner cylinder Dewar flask 2 is an example of the Dewar flask involved in the present invention, and the sample 4 and liquid helium 5 are directly contained in the flask.

[0041] In this embodiment, the height of the inner cylinder Dewar flask 2 is about 800 mm, the outer diameter is about 90 mm, the thickness of the glass wall 21 is about 5 mm, and the glass plate 211 (see FIG. Figure 2 The thickness of the inner tube Dewar flask 2 is about 2 mm. In addition, in the present embodiment, as the forming material of the inner tube Dewar flask 2, that is, glass, a glass with a hardness of grade 2 among borosilicate glasses can be used.

[0042] The outer Dewar flask 3 is also made of glass and comprises a cylindrical, bottomed glass wall 31. Furthermore, as with the outer Dewar flask 3, a space 32 is formed within the entire glass wall 31. However, a vacuum layer is initially formed within the space 32, and the vacuum level of the vacuum layer formed within the space 32 is not adjusted. The reason for not adjusting the vacuum level of the vacuum layer formed within the space 32 is that liquid nitrogen 6 is housed within the outer Dewar flask 3 as described below. Of course, the outer Dewar flask 3 can also be configured so that the vacuum level can be adjusted.

[0043] Liquid nitrogen 6 is contained in the outer dewar 3 to prevent heat from being released from the glass wall 21 of the inner dewar 2. Furthermore, the inner dewar 2 is immersed in the liquid nitrogen 6 in the outer dewar 3, thereby forming the double-layered measurement dewar 1.

[0044] In this embodiment, the outer cylinder Dewar flask 3 has a height of about 700 mm and an outer diameter of about 140 mm. The thickness of the glass wall 31 is about 10 mm. The glass plate 311 (see FIG. 3 ) surrounding the space 32 in the glass wall 31 is about 10 mm. Figure 2 The thickness of the outer tube Dewar flask 3 (symbol 202) is about 5 mm. In this embodiment, Pyrex (manufactured by Corning Incorporated, a registered trademark) is used as the material for forming the outer tube Dewar flask 3. Pyrex is a glass with a hardness of Class 1 among borosilicate glasses.

[0045] By using the measurement dewar flask 1 having the above-described features, the rate at which the vacuum level of the vacuum layer decreases is significantly slower than with conventional measurement dewar flasks, and the following advantages can be achieved. Specifically, the concentration of impurities in polycrystalline silicon is typically measured at least daily throughout the year in the quality control process of polycrystalline silicon manufacturing using the photoluminescence method. Consequently, conventional measurement dewar flasks require daily evacuation to perform such concentration measurements.

[0046] On the other hand, using a measuring Dewar flask 1 equipped with the inner cylinder Dewar flask 2 according to this embodiment allows vacuuming to be performed at most once every three months. This significantly reduces the burden on vacuuming personnel and significantly reduces vacuuming costs. Furthermore, its durability under long-term use is comparable to that of conventional measuring Dewar flasks, keeping deformation and breakage of the glass wall that occurs with long-term use within an acceptable range.

[0047] The dimensions of the inner and outer Dewar flasks 2 and 3 are not limited to the above dimensions, and can be arbitrarily modified in accordance with the dimensions and shape of the sample 4, the internal structure of the cryostat 101, and the like. Furthermore, the material of the inner Dewar flask 2, i.e., glass, should have a SiO2 content of 65% to 75% by weight and an average thermal expansion coefficient of 25×10- -7 / ℃ to 55×10 -7 / °C, and does not need to be glass with a hardness of Class 2. Here, the lower limit of the glass temperature used to determine the average thermal expansion coefficient, 20°C, coincides with the lower limit of the room temperature that can be maintained in the room where the photoluminescence measurement device 100 is installed. The upper limit of the room temperature that can be maintained in the room is 25°C. Furthermore, the material forming the outer tube Dewar flask 3, that is, the glass, can be any glass with a hardness of Class 1 and does not necessarily have to be Pyrex.

[0048] Furthermore, although a double-layered measuring Dewar flask 1 is described as an example in this embodiment, the measuring Dewar flask 1 does not necessarily have to be a double-layered structure in which an inner cylinder Dewar flask 2 is housed within an outer cylinder Dewar flask 3. For example, a single-layered Dewar flask may be used, wherein the glass wall forming the flask is only one sheet. However, the material forming the single-layered Dewar flask, i.e., the glass, must at least have an SiO2 content of 65% to 75% by weight and an average thermal expansion coefficient of 25×10-10 at a temperature of 20°C to 300°C. -7 / ℃ to 55×10 -7 / ℃.

[0049] [Method for producing polycrystalline silicon]

[0050] Next, use Figure 3 A method for producing polycrystalline silicon according to an embodiment of the present invention will be described. The method includes a silicon precipitation step S1, a processing and inspection step S2, a separation step S3, and a distillation step S4.

[0051] <1. Silicon Precipitation Step S1>

[0052] First, a chlorosilane compound (not shown) is reacted with H2 to precipitate polycrystalline silicon (silicon precipitation step: S1). The structure of the reaction apparatus and the reaction conditions used in the silicon precipitation step S1 are not particularly limited, and known reaction apparatuses and reaction conditions can be used. Specifically, the silicon precipitation step S1 can be carried out by, for example, the Siemens method (bell jar method) or the melt precipitation method (VLD method, Vaporto Liquid Deposition method). Since the Siemens method and the melt precipitation method are known methods, the description of these methods is omitted. In addition, in order to effectively precipitate polycrystalline silicon, it is preferred to carry out the silicon precipitation step S1 by the Siemens method.

[0053] In this specification, the term "chlorosilane compound" refers to a compound containing Cl and Si. Examples of the chlorosilane compound contained in the raw material gas include trichlorosilane and dichlorosilane, regardless of whether the Siemens method or the melt precipitation method is used.

[0054] <2. Processing and Inspection Step S2>

[0055] Next, the polycrystalline silicon rods precipitated in the silicon precipitation step S1 are cut and crushed, and then processed into the shape and size required by the customer (processing step: S2). Furthermore, samples 4 are prepared from the polycrystalline silicon rods, and the impurity concentration in the sample 4 is measured using a photoluminescence measurement device 100 to inspect the quality of the polycrystalline silicon (inspection step: S2). If the inspection result is "acceptable," the surface of the processed product is cleaned, packaged, and shipped to the customer. The inspection step in the processing and inspection step S2 is an example of the concentration measurement step involved in the present invention.

[0056] <3. Separation Step S3>

[0057] Next, the exhaust gas discharged from the silicon precipitation step S1 is separated into chlorosilane condensate and gas components (separation step: S3). The exhaust gas contains chlorosilane compounds, H2, HCl, silicon powder, and may also contain silane oligomers.

[0058] The chlorosilane condensate may contain silicon powder. For example, the content of silicon powder in the chlorosilane condensate may be 0.01% to 0.3% by mass, particularly 0.05% to 0.2% by mass. The chlorosilane condensate may also be used for purposes other than the present production method. The gas component contains hydrogen and HCl as main components. The gas component also contains a few percent by volume of chlorosilane compounds, which are residual chlorosilane compounds that have not been condensed and separated into the chlorosilane condensate. Furthermore, it may contain very small amounts of boron and phosphorus derived from metallic silicon.

[0059] In the separation step S3, the cooling temperature of the gas component is not particularly limited as long as it is below the condensation temperature of the chlorosilane compound, and can be appropriately determined in consideration of the cooling capacity of the cooling device used, etc. The lower the cooling temperature, the better the condensation effect of the chlorosilane compound.

[0060] The separation method used in the separation step S3 is not particularly limited as long as it can separate the chlorosilane condensate into a gaseous component, but a condensation removal method is preferably used. The condensation removal method cools the exhaust gas to condense the chlorosilane compounds, thereby separating the chlorosilane condensate into a gaseous component.

[0061] The exhaust gas cooling method used in separation step S3 is not particularly limited, as long as it can be cooled to a temperature below the condensation temperature of the chlorosilane compound, and known cooling methods can be used. Specifically, methods include cooling the exhaust gas by passing it through a cooled heat exchanger, or cooling the exhaust gas using the condensate that has been condensed and cooled. These methods can be used alone or in combination.

[0062] <4. Distillation Step S4>

[0063] Next, the chlorosilane condensate obtained in the separation step S3 is distilled to obtain a chlorosilane compound, which is then circulated through the reaction apparatus used in the silicon precipitation step S1 (distillation step: S4). This process allows the chlorosilane compound obtained after distillation to be reused as a raw material for producing polycrystalline silicon in the silicon precipitation step S1.

[0064] Polycrystalline silicon is manufactured through the above-described steps S1 to S4. The above-described manufacturing method is merely an example, and various manufacturing methods may be employed as long as the concentration measurement using the photoluminescence measurement device 100 in the processing and inspection step S2 is performed. For example, a hydrogen chloride removal step may be included, in which the gas components obtained in the separation step S3 are brought into contact with a chlorosilane solution to remove HCl. Furthermore, a hydrogen purification step may be included, in which the gas components obtained in the hydrogen chloride removal step are brought into contact with activated carbon to remove chlorosilane compounds and obtain hydrogen. Furthermore, the "inspection step" in the processing and inspection step S2 may be used as a step in the method for manufacturing single crystal silicon.

[0065] [Method for measuring impurity concentration in polysilicon]

[0066] Next, use Figure 4 A method for measuring the concentration of impurities in polycrystalline silicon according to one embodiment of the present invention will be described. Specifically, the following steps, including pre-measurement preparation, actual measurement, and post-measurement operations, will be described for measuring the concentration of impurities in polycrystalline silicon using a photoluminescence method. The following description is merely an example and is not limited to the following steps. The following description assumes that an exhaust port is formed at the bottom of the inner tube Dewar flask 2 and that the inner tube Dewar flask 2 is placed within the outer tube Dewar flask 3.

[0067] First, a sample 4 is prepared from a polycrystalline silicon rod (production process). Specifically, a round rod is cut radially from the straight body portion of the polycrystalline silicon rod, and then the round rod is crystallized using the FZ method to obtain a single crystal rod. Next, a sample 4 is cut from any straight body portion of the single crystal rod to produce the sample 4. The above-described method for preparing the sample 4 is merely an example and can be modified depending on the diameter of the polycrystalline silicon rod, etc.

[0068] Next, a vacuum (insulation) layer is formed in the space 22 of the glass wall 21 of the inner cylinder Dewar flask 2. In the evacuation for forming the vacuum (insulation) layer, a rotary pump and a turbine pump (not shown) are used, for example, and the vacuum degree of the vacuum (insulation) layer reaches 1×10 -4 Vacuuming is performed with Pa as a target (vacuuming step).

[0069] Then, the vacuum (heat insulation) layer formed in the space 22 of the glass wall 21 is vacuumed to a degree of 1×10 -4 The vacuum degree is confirmed by a pressure gauge (not shown) connected to the vacuum (insulation) layer. -3 Pa, the vacuum process was performed again to make the vacuum degree reach 1×10 -4 Pa.

[0070] On the other hand, when the vacuum degree is confirmed to be 1×10 -4 At Pa, the sample 4 is placed on the sample holder 111 (sample placement step). Next, the inner cylinder Dewar flask 2 is placed inside the outer cylinder Dewar flask 3 so that it does not move inside the outer cylinder Dewar flask 3 (flask placement step). Specifically, for example, felt (not shown) or the like is bonded to the inner surface of the bottom of the outer cylinder Dewar flask 3, and the bottom surface of the bottom of the inner cylinder Dewar flask 2 is bonded to the felt, thereby securing the inner cylinder Dewar flask 2 so that it does not vibrate inside the outer cylinder Dewar flask 3. This fixation allows the bottom surface of the bottom of the inner cylinder Dewar flask 2 to be positioned at a predetermined height relative to the inner surface of the bottom of the outer cylinder Dewar flask 3.

[0071] Next, the measuring Dewar flask 1 formed into a double-layer structure of an inner cylinder Dewar flask 2 and an outer cylinder Dewar flask 3 by the flask setting step is installed in the cryostat 101 (installation step). Figure 4 As shown by reference numeral 401 , the sample holder 111 on which the sample 4 is placed is inserted into the inner cylinder Dewar flask 2 , and the sample holder 111 is fixed to the cryostat 101 (insertion step).

[0072] Next, the hose of the rotary pump is installed via a stopcock to a reduced pressure evacuation port (not shown) formed on the upper portion of the sample holder 111, thereby connecting the reduced pressure evacuation port to the rotary pump (connection step). The reduced pressure evacuation port is an opening formed to create a vacuum (reduced pressure) inside the inner cylinder Dewar flask 2 for accommodating liquid helium 5.

[0073] Next, a gas supply tube is attached to a gas supply port (not shown) also formed on the upper portion of the sample holder 111 via a gas bag (not shown) (installation step). The primary purpose of using the gas bag is to facilitate the placement of liquid helium 5 within the inner cylinder Dewar 2. Furthermore, the gas bag is also used to facilitate maintaining a reduced pressure within the inner cylinder Dewar 2. Furthermore, the gas bag is also used to facilitate the removal of water vapor and moisture within the inner cylinder Dewar 2 by supplying nitrogen gas, etc. The use of the gas bag is not essential.

[0074] Then, the rotary pump is operated and the stopcock on the rotary pump side is opened to depressurize the inner cylinder Dewar flask 2 (the first decompression step). Specifically, the rotary pump is used to depressurize the inner cylinder Dewar flask 2 until the pressure gauge shows 0.1×10 0 Pa. Next, the cock on the rotary pump side is closed, and the cock on the gas supply side is opened to supply nitrogen gas or the like into the inner cylinder Dewar flask 2 (gas supply step).

[0075] Next, after the process of supplying nitrogen gas or the like into the inner cylinder Dewar flask 2 is completed, the stopcock on the gas supply side is closed, and the stopcock on the rotary pump side is opened again to depressurize the inner cylinder Dewar flask 2 again (second depressurization step). As in the first depressurization step, the rotary pump is used to depressurize the inner cylinder Dewar flask 2 until the pressure gauge shows 0.1×10 0 Pa. In the examples and comparative examples described below, the decompression time in the first decompression step and the decompression time in the second decompression step were set to the same time.

[0076] In this embodiment, the gas supply process and the second depressurization process are repeated a necessary number of times. In the examples and comparative examples described below, the gas supply process and the second depressurization process are also repeated a necessary number of times.

[0077] The gas supply step and the second decompression step are repeated as many times as necessary to reduce the pressure in the inner cylinder Dewar flask 2 to a level sufficient to accommodate the liquid helium 5. The rotary pump is then stopped by closing the stopcock. After the rotary pump has stopped, the hose and supply tube attached to the upper portion of the sample holder 111 are removed (removal step).

[0078] Then, if Figure 4 As shown in reference numeral 402, liquid nitrogen 6 is placed in the gap formed between the outer surface of the glass wall 21 of the inner tube Dewar flask 2 and the inner surface of the glass wall 31 of the outer tube Dewar flask 3 (liquid nitrogen placement step). Specifically, liquid nitrogen 6 is supplied into the gap from a liquid nitrogen supply port (not shown) formed in the upper portion of the sample holder 111, thereby placing the liquid nitrogen 6 in the gap. After the liquid nitrogen 6 is placed, the liquid nitrogen supply port is closed to prevent volatilization of the liquid nitrogen.

[0079] Then, if Figure 4 As shown by reference numeral 403, liquid helium 5 is accommodated in the inner cylinder Dewar flask 2 under reduced pressure. In other words, liquid helium 5 is accommodated in the space where the sample 4 is located (liquid helium accommodation step). Specifically, liquid helium 5 is supplied to the space from a liquid helium supply port (not shown) formed in the upper portion of the sample holder 111, thereby accommodating the space.

[0080] The following is an example of a method for containing liquid helium 5 in the liquid helium containing process. First, a dedicated liquid helium conveyor (not shown) is used to connect the container containing liquid helium 5 to the liquid helium supply port of the sample holder 111. Since the inner cylinder Dewar flask 2 is under reduced pressure, the liquid helium 5 can be supplied from the container to the inner cylinder Dewar flask 2 through the liquid helium supply port through the connection. Here, as needed, the container containing liquid helium 5 can also be pressurized using nitrogen or the like, thereby supplying liquid helium 5 to the inner cylinder Dewar flask 2. Finally, as shown in FIG. Figure 4 As shown by reference numeral 403 , liquid helium 5 is placed in the inner cylinder Dewar flask 2 in an amount sufficient to immerse the entire sample 4 .

[0081] After the liquid helium 5 is placed in the inner cylinder Dewar flask 2, the liquid helium conveyor is removed from the container containing the liquid helium 5. Next, the outlet of the container and the liquid helium supply port of the sample holder 111 are closed (the final step of the measurement preparation).

[0082] Then, in Figure 4 In the state indicated by reference numeral 403, the concentration of impurities in sample 4 is measured using photoluminescence (concentration measurement step). First, the laser light source 102 of the photoluminescence measurement device 100 is activated to emit laser light. Prior to emitting the laser light, the shutter and slit width are checked. Next, the laser light is irradiated onto sample 4, which is placed on the sample holder 111 and immersed in liquid helium 5 within the inner cylinder Dewar flask 2. Measurement of the impurity concentration in sample 4 begins.

[0083] The concentration measurement process itself can be performed in accordance with, for example, the method described in the JEITAEM-3601A standard disclosed in Non-Patent Document 1, or the JIS standard "JIS H0615-1996 Method for Measuring the Concentration of Impurities in Silicon Crystals by Photoluminescence," which is cited in this standard. In this embodiment, the concentration is measured using the method described in the JIS standard, and its description is omitted.

[0084] After the concentration measurement process is complete, the sample holder 111 is removed from the cryostat 101. Next, the inner dewar 2 is removed from the outer dewar 3, and the liquid helium 5 remaining in the inner dewar 2 is discarded. The outer dewar 3 is then removed from the cryostat 101, and the liquid nitrogen 6 remaining in the outer dewar 3 is discarded. Following this removal, the entire set of equipment, including the inner dewar 2, outer dewar 3, and sample holder 111, is thoroughly dried. To measure the concentration of another sample 4, the steps following the preparation process are repeated.

[0085] Vacuuming process

[0086] In this embodiment, the vacuuming step specifically involves the following operations. Furthermore, in the Examples and Comparative Examples described below, the same operations as those described below are also performed. First, a second pipe (not shown) is attached to a first pipe (not shown) via a vacuum hose to form a vacuum line. The first pipe is equipped with a valve connected to the space 22 within the glass wall 21 of the inner tube Dewar flask 2, and the second pipe is equipped with valves connected to the rotary pump and the turbine pump.

[0087] Next, the rotary pump is operated to open and close the valve included in the vacuum line, thereby evacuating the space 22 by the rotary pump. Then, when the pressure is roughly reduced (by 0.1×10 0 Pa as the target), the turbo pump is operated, the valve is opened and closed, and the vacuum is further drawn. During the vacuum drawing, the vacuum degree of the vacuum (insulation) layer formed in the space 22 is confirmed by visually observing the pressure gauge connected to the space 22. Next, when the vacuum degree of the vacuum (insulation) layer reaches 1×10 -4 Then, when it is confirmed that the vacuum degree of the vacuum (insulation) layer has reached 1×10 -4 After Pa, the valves included in the vacuum line are closed, and the rotary pump and the turbine pump are stopped. Next, the vacuum line and the like are removed from the inner cylinder Dewar flask 2 to maintain the vacuum degree of the vacuum (insulation) layer.

[0088] The contents and execution order of the above steps are merely examples and can be arbitrarily changed as long as the sample 4 and liquid helium 5 are placed in the measurement Dewar flask 1 and the concentration of impurities in the sample 4 is measured by photoluminescence.

[0089] [Variation]

[0090] The photoluminescence measurement device 100, measurement Dewar flask 1, and concentration measurement method according to this embodiment can be applied to single crystal silicon (not shown). Furthermore, by applying the concentration measurement method according to this embodiment to single crystal silicon, single crystal silicon can also be produced. In other words, single crystal silicon is also an example of silicon according to the present invention.

[0091] For example, the photoluminescence measurement device 100 and the measurement Dewar flask 1 can also be used in quality management of silicon wafers formed from single crystal silicon. Specifically, they can be used to measure the concentration of trace impurities contained in these silicon wafers using photoluminescence. In this case, in order to measure the concentration of trace impurities, it is necessary to eliminate the influence of thermal noise. Therefore, as in the present embodiment, liquid helium 5 is contained in the inner cylinder Dewar flask 2, and concentration measurement is performed at low temperatures.

[0092] 〔Overview〕

[0093] In order to solve the above-mentioned problems, one aspect of the present invention relates to a Dewar flask made of glass for use in measuring the concentration of impurities contained in silicon by photoluminescence in liquid helium, wherein the SiO2 content in the glass is 65% by weight or more and 75% by weight or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 The term "average thermal expansion coefficient" is used because, when the thermal expansion coefficient of the glass is measured at a temperature of 20°C to 300°C, the average value of the thermal expansion coefficient is actually measured.

[0094] According to the above configuration, the SiO2 content in the glass, the material forming the Dewar flask according to one aspect of the present invention, is 65% to 75% by weight. Therefore, compared to conventional measurement Dewar flasks, helium generated within the Dewar flask during photoluminescence measurements is less likely to penetrate the glass wall. Consequently, the vacuum level of the vacuum layer formed within the glass wall is less likely to decrease than in conventional measurement Dewar flasks, significantly reducing the number of vacuum pumping operations after measurement. This significantly reduces the burden on vacuum pumping operators and significantly reduces vacuum pumping costs.

[0095] Furthermore, for example, when the SiO2 content exceeds 75% by weight, the helium generated within the Dewar flask easily penetrates the glass wall of the Dewar flask, making it difficult to maintain a low temperature for a long time. On the other hand, when the SiO2 content is less than 65% by weight, components other than SiO2 actually increase, and the impact of these components becomes greater. For example, glass containing 20% ​​to 60% PbO by weight has a large average thermal expansion coefficient, so the deformation caused by cooling from room temperature to ultra-low temperatures increases. Therefore, it is not suitable as a material for forming a Dewar flask used at low temperatures. In addition, for example, glass containing 5% to 20% Al2O3 by weight has a high glass transition temperature, making it difficult to process it into a Dewar flask. Therefore, it is also not suitable as a material for forming a Dewar flask.

[0096] On the other hand, in the present invention, since the SiO2 content in the glass is 65% to 75% by weight, not only does it suppress the decrease in the vacuum level of the vacuum layer, but it also minimizes deformation caused by cooling from room temperature to ultra-low temperatures, making it easier to process into a Dewar flask. Furthermore, the number of vacuum pumping operations after measurement can be significantly reduced, and the dewar flask deteriorates due to repeated cooling and heating between room temperature and ultra-low temperatures, thereby reducing the production cost of the Dewar flask.

[0097] Furthermore, according to the above configuration, the average thermal expansion coefficient of the glass, which is the material of the Dewar flask, is 25×10 -7 / ℃ and above 55×10 -7 / °C or less. Therefore, even if the temperature of the Dewar's glass wall drops from room temperature to ultra-low temperatures during photoluminescence measurement, the glass wall is less susceptible to thermal contraction compared to conventional measurement Dewars. Furthermore, even if the temperature of the Dewar's glass wall rises from ultra-low temperatures to room temperature (20°C to 25°C) after the photoluminescence measurement process is completed, the thermal expansion of the glass wall remains within the allowable range based on continued measurement. Therefore, even with repeated photoluminescence measurements, deformation and breakage of the glass wall can be kept within allowable limits, resulting in a Dewar flask with guaranteed durability.

[0098] Furthermore, for example, when the temperature of the glass is 20°C or higher and 300°C or lower, if the average thermal expansion coefficient of the glass is less than 25×10 -7 / ℃, even if the glass is exposed to a high temperature of more than 1000℃, it is difficult to soften and difficult to process, so it is not suitable as a material for forming a Dewar flask. On the other hand, if the average thermal expansion coefficient exceeds 55×10 -7 / ℃, the glass will easily deform when cooled from room temperature to ultra-low temperature, so it is also not suitable as a material for forming a Dewar flask.

[0099] Furthermore, in a Dewar flask according to one aspect of the present invention, the B2O3 content in the glass can be 10% to 30% by weight. This configuration tends to lower the average thermal conductivity of the glass compared to glass containing less than 10% or more than 30% by weight of B2O3. Consequently, the Dewar flask is less susceptible to temperature fluctuations inside and outside the Dewar flask during photoluminescence measurements. This improves the durability of the Dewar flask.

[0100] As mentioned above, when a specific amount of B2O3 is contained in glass, the average thermal conductivity, i.e., the average thermal expansion coefficient, tends to be lower. Furthermore, by containing a specific amount of B2O3, chemical durability can be maintained while simultaneously lowering the softening temperature of the glass. However, if the B2O3 content in the glass is less than 10% by weight, the effect of lowering the softening temperature is minimal, and the workability (ease of processing) of the glass may not be improved. On the other hand, when the B2O3 content exceeds 30% by weight, SiO2 and B2O3 tend to separate easily, making the use of the glass itself difficult.

[0101] In a Dewar flask according to one aspect of the present invention, the impurity may be at least one of P, B, Al, and As atoms. With this configuration, the presence of at least one of P, B, Al, and As atoms in silicon can be measured using the Dewar flask. Compared to conventional measurement Dewar flasks, this Dewar flask significantly reduces the burden on vacuum workers and significantly reduces vacuuming costs.

[0102] To address the above-mentioned issues, a photoluminescence measurement device according to one aspect of the present invention includes the Dewar flask according to any of the above-mentioned aspects. Due to the above-mentioned configuration, the photoluminescence measurement device according to one aspect of the present invention includes a Dewar flask. Compared to conventional measurement Dewar flasks, this Dewar flask significantly reduces the burden on vacuum evacuation personnel and significantly reduces vacuum evacuation costs, while also offering improved durability. Therefore, when the photoluminescence measurement device according to one aspect of the present invention is used to measure the concentration of impurities contained in silicon in liquid helium, the burden on measurement personnel is significantly reduced, and Dewar flask maintenance costs are significantly reduced.

[0103] To solve the above-mentioned problem, one aspect of the present invention relates to a concentration measurement method for measuring the concentration of impurities contained in silicon, wherein liquid helium and the silicon are contained in a Dewar flask formed of glass, and the concentration of the impurities is measured by photoluminescence, wherein the SiO2 content in the glass is greater than or equal to 65% by weight and less than or equal to 75% by weight, and when the temperature of the glass is greater than or equal to 20°C and less than or equal to 300°C, the average thermal expansion coefficient of the glass is 25×10-7 / ℃ and above 55×10 -7 / °C or less. With the above configuration, the same effects as those of the photoluminescence measurement device according to one aspect of the present invention can be achieved.

[0104] To solve the above-mentioned problems, one aspect of the present invention relates to a method for producing silicon, comprising a concentration measurement step, in which liquid helium and silicon are placed in a Dewar flask formed of glass, and the concentration of impurities contained in the silicon is measured, wherein the content of SiO2 in the glass is 65% by weight or more and 75% by weight or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 / ℃ below.

[0105] According to the above configuration, a silicon production method according to one aspect of the present invention includes a concentration measurement step. In this concentration measurement step, a dewar flask is used to measure the concentration of impurities contained in the silicon in liquid helium. Compared to conventional measurement dewar flasks, this dewar flask significantly reduces the burden on vacuuming workers and significantly cuts vacuuming costs. Consequently, the burden on production personnel is reduced while silicon production can be performed at a low cost.

[0106] [Notes]

[0107] The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the various technical means disclosed in the above-described embodiments are also included in the technical scope of the present invention.

[0108] [Example]

[0109] The following describes a process for measuring the concentration of impurities in a sample 4 using a photoluminescence method using a measurement Dewar flask 1 according to an embodiment of the present invention, compared with a measurement Dewar flask according to a comparative example of the present invention. The measurement Dewar flask according to the comparative example of the present invention also has a double-layer structure consisting of an inner and outer Dewar flask (neither shown). The inner and outer Dewar flasks according to the comparative example of the present invention have the same structure as the inner and outer Dewar flasks 2 and 3 according to the embodiment of the present invention, except for the glass composition and average thermal expansion coefficient.

[0110] <Glass Composition and Average Thermal Expansion Coefficient>

[0111] Table 1 below shows the composition and average thermal expansion coefficient of the glass materials used in the measurement Dewar flasks 1 according to Examples 1 to 3 of the present invention and the measurement Dewar flasks according to Comparative Examples 1 to 3 of the present invention. The glass components (e.g., SiO2) were determined using a calibration curve method using a wavelength dispersive X-ray fluorescence analyzer (WDX). The average thermal expansion coefficient of the glass was measured using a thermomechanical analyzer (TMA) at temperatures between 20°C and 300°C.

[0112] [Table 1]

[0113]

[0114] In all the measurement Dewar flasks 1 according to Examples 1 to 3 of the present invention, the inner Dewar flask 2 was made of glass B listed in Table 1. In all the measurement Dewar flasks according to Comparative Examples 1 to 3 of the present invention, the inner Dewar flask was made of glass A listed in Table 1. In all the following Examples 1 to 3, in the initial (first) concentration measurement, the vacuum degree of the vacuum (insulation) layer of the inner Dewar flask 2 and the vacuum degree of the vacuum (insulation) layer of the outer Dewar flask 3 were set to 1×10 -4 Dewar flask 1 for measuring Pa. This also applies to the Dewar flasks for measuring Comparative Examples 1 to 3 described below.

[0115] <Examples 1 to 3>

[0116] The outer cylinder Dewar flask 3 involved in Example 1 of the present invention was made of glass A shown in Table 1. Using the measuring Dewar flask 1 equipped with the outer cylinder Dewar flask 3 made of glass A, 36 samples 4 were placed on the sample holder 111, and the initial (first) concentration measurement was performed. After the initial concentration measurement was completed, the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask 2 was measured. The measurement results showed that the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask 2 was maintained at 1×10 - 4 Therefore, the second concentration measurement can be performed without performing the vacuuming operation described in the [Vacuuming process] column above.

[0117] As the measuring Dewar flask 1 involved in Example 2 of the present invention, the same Dewar flask as the measuring Dewar flask 1 involved in Example 1 of the present invention is used. Next, 36 samples 4 are placed on the sample holder 111, and the initial (first) concentration measurement is performed. Then, each process described in the above-mentioned [Method for measuring the concentration of impurities in polycrystalline silicon] is performed once a day and repeated for 3 months (about 75 times). After the final concentration measurement is completed, the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask 2 is measured. The measurement results show that the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask 2 is maintained at 1×10 - 4 In addition, in each concentration measurement, the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask 2 was maintained at 1×10 -4 Pa. Therefore, no vacuuming is required from the time the first concentration measurement is completed until the time the last concentration measurement is completed.

[0118] The outer Dewar flask 3 according to Example 3 of the present invention was made of glass B listed in Table 1. The same procedures as in Example 2 were then performed. The results of measuring the vacuum level of the vacuum (insulation) layer of the inner Dewar flask 2 were also the same as those in Example 2. That is, in Example 3, no vacuuming was required from the completion of the initial concentration measurement until the completion of the final concentration measurement.

[0119] <Comparative Examples 1 to 3>

[0120] (Comparative Example 1)

[0121] The outer cylinder Dewar flask involved in Comparative Example 1 of the present invention was made of glass A shown in Table 1. Using a measuring Dewar flask equipped with an outer cylinder Dewar flask made of glass A, 36 samples 4 were placed on a sample holder 111, and the initial (first) concentration measurement was performed. After the initial concentration measurement was completed, the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask was measured. The measurement results showed that the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask dropped to 6×10 -2 Pa. Therefore, the vacuuming operation described in the above column [Vacuuming step] was performed.

[0122] Then, the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask was again increased to 1×10 -4 The second concentration measurement of Pa was performed using a Dewar flask. The first concentration measurement took approximately 5 hours and 30 minutes. Furthermore, the vacuuming process took approximately 2 hours and 50 minutes. Furthermore, the second concentration measurement took approximately 5 hours and 40 minutes.

[0123] (Comparative Example 2)

[0124] As the measuring Dewar flask involved in Comparative Example 2 of the present invention, the same Dewar flask as the measuring Dewar flask involved in Comparative Example 1 of the present invention was used. Next, 36 pieces of sample 4 were placed on the sample holder 111, and the initial (first) concentration measurement was performed. After the initial concentration measurement was completed, the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask was measured. The measurement results showed that the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask was reduced to 6×10 -2 Pa.

[0125] Here, if the second concentration measurement is performed without performing the vacuum operation, the liquid level of liquid helium 5 in the inner cylinder Dewar flask will shift below the sample 4 15 minutes after the measurement begins. Therefore, after this shift, the second concentration measurement cannot be continued. As a result, at the time when the second concentration measurement cannot be continued, only four samples 4 can be measured. It is believed that this is because the vacuum degree of the vacuum (insulation) layer of the inner cylinder Dewar flask is low at the beginning of the second concentration measurement, resulting in a decrease in the insulation effect and an accelerated evaporation rate of liquid helium 5, resulting in a rapid downward shift of the liquid helium 5 level.

[0126] (Comparative Example 3)

[0127] The outer Dewar flask of Comparative Example 3 of the present invention was made of Glass B listed in Table 1. The same procedures as in Comparative Example 2 were then performed. After the initial concentration measurement, the vacuum level of the vacuum (insulation) layer of the inner Dewar flask was measured. The measurement results showed that the vacuum level of the vacuum (insulation) layer of the inner Dewar flask had dropped to 7×10 -2 Pa.

[0128] Explanation of symbols

[0129] 2: Inner cylinder Dewar flask (Dewar flask)

[0130] 4: Sample (silicon)

[0131] 5: Liquid Helium

[0132] 100: Photoluminescence measurement device

[0133] S2: Processing and inspection process (concentration measurement process)

Claims

1. A Dewar flask made of glass used for measuring the concentration of impurities contained in silicon by photoluminescence in liquid helium, characterized in that: The content of SiO2 in the glass is 65 wt% or more and 75 wt% or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 / ℃ below.

2. The Dewar flask according to claim 1, characterized in that The content of B2O3 in the glass is greater than or equal to 10 wt% and less than or equal to 30 wt%.

3. The Dewar flask according to claim 1 or 2, characterized in that: The impurities are at least one atom of P, B, Al and As.

4. A photoluminescence measuring device, characterized in that: A Dewar flask according to any one of claims 1 to 3.

5. A concentration measurement method for measuring the concentration of impurities contained in silicon, characterized in that: Liquid helium and the silicon are placed in a Dewar flask made of glass, and the concentration of the impurity is measured by photoluminescence. The content of SiO2 in the glass is 65% by weight or more and 75% by weight or less, and when the temperature of the glass is 20°C or more and 300°C or less, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 / ℃ below.

6. A method for producing silicon, characterized in that: include: a silicon precipitation step of reacting a chlorosilane compound with H2 to precipitate polycrystalline silicon; a processing step of cutting and crushing the polycrystalline silicon rods deposited by the treatment in the silicon precipitation step; and A concentration measurement step, in which liquid helium and silicon are placed in a Dewar flask formed of glass, and the concentration of impurities contained in the silicon is measured, wherein the content of SiO2 in the glass is greater than or equal to 65% by weight and less than or equal to 75% by weight, and when the temperature of the glass is greater than or equal to 20°C and less than or equal to 300°C, the average thermal expansion coefficient of the glass is 25×10 -7 / ℃ and above 55×10 -7 / ℃ below.

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