Carbon holder regeneration method and silicon manufacturing method

Abstract

To obtain silicon of sufficiently guaranteed quality by reusing a carbon holder.SOLUTION: A method of regenerating a carbon holder (30) that consists of carbon and is bonded between a core wire holding section (20) and an electrode (40), wherein a side surface (33) of the carbon holder (30) that extends between a first end surface (31) formed with a first part (34) to be bonded to the core wire holding section (20) and a second end surface (32) formed with a second part (35) to be bonded to the electrode (40), is ground up to a surface roughness (Ra) of 50 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for regenerating a carbon holder, a method for producing silicon, and a carbon holder. [Background technology]

[0002] Patent Document 1 discloses a method for regenerating carbon parts, which involves scraping off the deposits attached to the surface of the carbon parts together with the carbon matrix, for carbon parts used in the production of polycrystalline silicon in a reduction furnace. In this method for regenerating carbon parts, after the process of scraping off the deposits attached to the surface of the carbon parts, the carbon parts are treated with chlorine gas in a flow-type reactor and reused in the production of polycrystalline silicon in the reduction furnace. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-26481 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the carbon part regeneration method disclosed in Patent Document 1, unless the carbon part is treated with chlorine gas after the treatment to scrape off the deposits adhering to the surface of the carbon part, it is difficult to obtain polycrystalline silicon with a sufficiently guaranteed quality. One aspect of the present invention aims to obtain silicon with a sufficiently guaranteed quality by reusing a carbon holder. [Means for solving the problem]

[0005] In order to solve the above problems, a method for regenerating a carbon holder according to one embodiment of the present invention is a method for regenerating a carbon holder that is made of carbon and is joined between a core wire holding part that holds a silicon core wire for precipitating silicon and an electrode for passing current through the silicon core wire, and after the carbon holder has been used for a silicon deposition process on the silicon core wire, in order to reuse the carbon holder, a side extending between a first end face of the carbon holder in which a first portion to be joined with the core wire holding part is formed, and a second end face of the carbon holder in which a second portion to be joined with the electrode is formed is ground so that the surface roughness (Ra) is 50 μm or less.

[0006] After the silicon deposition process, foreign matter adheres to the surface of the carbon holder. Therefore, it is preferable to grind the side of the carbon holder so that the surface roughness of the carbon holder is 50 μm or less. This sufficiently removes the foreign matter adhered to the surface of the carbon holder, and the carbon holder can be reused to obtain silicon with sufficiently guaranteed quality without performing chlorine gas treatment on the ground carbon holder.

[0007] In addition to the side surface of the carbon holder, the first end surface of the carbon holder may also be ground so that the surface roughness (Ra) is 50 μm or less. By grinding the first end surface of the carbon holder, foreign matter adhering to the first end surface of the carbon holder is also sufficiently removed compared to a case where the first end surface is not ground. This makes it possible to improve the quality of silicon obtained by the silicon deposition process when the ground carbon holder is reused.

[0008] The first end face of the carbon holder may be provided with an annular member that covers at least a portion of the first end face and surrounds the periphery of the core wire holding portion. By providing the annular member on the first end face of the carbon holder, it is possible to reduce adhesion of foreign matter to the first end face. As a result, when the carbon holder is reused after grinding, the quality of silicon obtained by the silicon precipitation process can be improved compared to when no annular member is provided on the first end face.

[0009] The annular member may be provided on the first end surface of the carbon holder so that a gap is formed between the annular member and the core wire holding portion. When a silicon deposition process is performed, it is possible to prevent silicon deposited on the silicon core wire from being integrated with the annular member. This makes it possible to reuse the annular member.

[0010] A silicon manufacturing method according to one embodiment of the present invention may include joining a carbon holder regenerated by the carbon holder regeneration method between the core wire holding portion and the electrode, and precipitating silicon from the silicon core wire.

[0011] A carbon holder according to one embodiment of the present invention is a carbon holder made of carbon and joined between a core wire holding part that holds a silicon core wire for precipitating silicon and an electrode for passing current through the silicon core wire, and after being used in a silicon deposition process on the silicon core wire, a side extending between a first end face of the carbon holder on which a first portion to be joined with the core wire holding part is formed, and a second end face of the carbon holder on which a second portion to be joined with the electrode is formed, is ground so that the surface roughness (Ra) is 50 μm or less.

[0012] An annular member may be provided on the first end surface of the carbon holder, the annular member covering at least a portion of the first end surface and surrounding a periphery of the core wire holding portion.

[0013] A carbon holder according to one embodiment of the present invention is a carbon holder made of carbon and joined between a core wire holding portion that holds a silicon core wire for precipitating silicon and an electrode for passing current through the silicon core wire, wherein the surface roughness (Ra) of a side extending between a first end face of the carbon holder on which a first portion to be joined with the core wire holding portion is formed and a second end face of the carbon holder on which a second portion to be joined with the electrode is formed is 50 μm or less, and a ring-shaped member is provided on the first end face of the carbon holder to cover at least a portion of the first end face and surround the core wire holding portion.

[0014] By providing an annular member on the first end face of the carbon holder, it is possible to reduce the amount of silicon precipitation adhering to the first end face and side face when the carbon holder is used (including when it is reused). Even when a ring-shaped member is provided on a brand new, unused carbon holder with a surface roughness (Ra) of 50 μm or less, it is possible to naturally reduce the amount of silicon precipitation adhering to the first end face and side face. As a result, it is possible to reduce the load of the grinding work required to remove silicon adhering to the first end face and side face when the carbon holder is reused (including repeated use). Effect of the Invention

[0015] According to one aspect of the present invention, it is possible to obtain silicon with a sufficiently guaranteed quality by reusing a carbon holder. [Brief description of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing a cross-sectional configuration of a carbon holder and its surroundings according to a first embodiment of the present invention. [Diagram 2] 2 is a view for explaining a process for grinding the side surface of the carbon holder shown in FIG. 1. FIG. [Diagram 3] FIG. 5 is a cross-sectional view showing a cross-sectional configuration of a carbon holder and its surroundings according to a second embodiment of the present invention. [Figure 4]4 is a cross-sectional view showing a cross-sectional configuration of the carbon holder shown in FIG. 3 and its vicinity, and a cross-sectional configuration of a carbon holder different from the configuration shown in FIG. 3 and its vicinity. [Diagram 5] FIG. 11 is a cross-sectional view showing a cross-sectional configuration of a carbon holder and its surroundings according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] [Embodiment 1] <Carbon holder 30 and its surrounding structure> Fig. 1 is a cross-sectional view showing a cross-sectional configuration of a carbon holder 30 according to a first embodiment of the present invention and its vicinity. In Fig. 1, a direction from an electrode 40 toward a silicon core 10 is referred to as an upward direction, and a direction from the silicon core 10 toward the electrode 40 is referred to as a downward direction. The silicon core 10, a core holder 20, and the carbon holder 30 are housed in a reactor for producing silicon. The reactor is composed of a bottom 60 and a lid that is detachable from the bottom 60. The lid is not shown in the figure.

[0018] 1, the core wire holding part 20 holds a silicon core wire 10 and is made of carbon. The silicon core wire 10 is for depositing silicon. The silicon core wire 10 has a U-shape and is electrically connected to an electrode 40 via the core wire holding part 20 and a carbon holder 30.

[0019] As silicon precipitates on the silicon core wire 10, an upper part of the core wire holding part 20 is embedded in a silicon rod formed by the precipitation of silicon on the silicon core wire 10. The core wire holding part 20 holds the silicon core wire 10, thereby holding the silicon rod formed in the silicon core wire 10.

[0020] The core wire holding part 20 has an inclined surface 21 that tapers upward when joined to the silicon core wire 10 and the carbon holder 30. The core wire holding part 20 also has a protruding part 22 that protrudes downward. The core wire holding part 20 is joined to a first part 34 of the carbon holder 30 at the protruding part 22. The core wire holding part 20 is disposable.

[0021] The carbon holder 30 is joined between the core wire holding part 20 and the electrode 40, and is made of carbon. When the inside of the electrode 40 is cooled by a cooling medium 50, the carbon holder 30 reduces heating of the electrode 40 by heat from the core wire holding part 20 due to thermal conduction. The carbon holder 30 has a first end face 31, a second end face 32, and a side face 33.

[0022] The first end face 31 is the upper surface of the carbon holder 30 on the side of the core wire holding portion 20. The first end face 31 has a first portion 34 formed thereon to be joined to the protruding portion 22 of the core wire holding portion 20. The first portion 34 has a concave shape that fits with the protruding portion 22 of the core wire holding portion 20. The second end face 32 is the lower surface of the carbon holder 30 on the side of the electrode 40. The second end face 32 has a second portion 35 formed thereon to be joined to the protruding portion 41 of the electrode 40. The second portion 35 has a concave shape that fits with the protruding portion 41 of the electrode 40. The side surface 33 of the carbon holder 30 extends between the first end face 31 and the second end face 32.

[0023] The shape of the side surface 33 is preferably a straight line a predetermined distance away from the central axis in a cross section obtained by cutting the carbon holder 30 along a plane including the central axis along the up-down direction of the carbon holder 30. The shape of the side surface 33 is preferably a shape formed by rotating the straight line once around the central axis of the carbon holder 30 as a rotation axis.

[0024] As an example of such a shape, the side surface 33 may have a cylindrical shape, or may have the same shape as the side surface of a figure obtained by cutting off the apex of a cone. By having the side surface 33 have such a shape, when grinding the side surface 33 for reusing the carbon holder 30, the side surface 33 can be easily ground using a lathe.

[0025] The electrode 40 is for passing current through the silicon core wire 10. The electrode 40 is placed on the bottom 60 of the reactor. An insulating member 70 is provided between the electrode 40 and the bottom 60 to prevent current from flowing from the electrode 40 to the bottom 60. The material of the electrode 40 may be a carbon material, or may be a metal material such as SUS to provide a structure that can be cooled by the cooling medium 50.

[0026] The inside of the electrode 40 is water-cooled to prevent the electrode 40 from becoming hot due to resistance heating caused by passing a high current when silicon is deposited on the silicon core wire 10. The electrode 40 is preferably cooled by a cooling medium 50 to prevent the electrode 40 from overheating due to a high current passing through the electrode 40 and thermal radiation from the reactor.

[0027] <Silicon manufacturing method> Next, a method for producing silicon will be described. The silicon produced by this method is, for example, polycrystalline silicon. First, a raw material gas for silicon deposition is supplied into the reactor with the reactor lid attached to the bottom 60 of the reactor. In this case, a current is passed from the electrode 40 to the silicon core wire 10 to perform a silicon deposition process on the silicon core wire 10. As the raw material gas for silicon deposition supplied into the reactor, for example, a gas of a silane compound such as trichlorosilane or monosilane is used.

[0028] <How to regenerate Carbon Holder 30> Fig. 2 is a diagram for explaining a process for grinding the side surface 33 of the carbon holder 30 shown in Fig. 1. A method for regenerating the carbon holder 30 will be explained with reference to Fig. 2. After the carbon holder 30 has been used in a process for depositing silicon on the silicon core 10, the lid of the reactor is opened from the bottom 60 of the reactor. The silicon rod including the silicon core 10 that has been subjected to the deposition process is removed from the reactor together with the core holder 20. The carbon holder 30 from which the core holder 20 has been removed is detached from the electrode 40. Then, the carbon holder 30 is removed from the reactor.

[0029] In order to reuse the carbon holder 30, the side surface 33 of the carbon holder 30 removed from the electrode 40 is ground so that the surface roughness (Ra) is 50 μm or less. The surface roughness (Ra) according to this embodiment indicates the arithmetic mean roughness Ra. Hereinafter, the arithmetic mean roughness Ra will be simply referred to as the surface roughness. The surface roughness of the side surface 33 of an unused carbon holder 30 is 50 μm or less.

[0030] 2, in order to reuse the carbon holder 30, a process is performed to grind the side surface 33 in a range where the depth from the surface of the carbon holder 30 is 0.20 mm or more, more preferably 0.25 mm or more. Note that the upper limit of the grinding depth when reusing the carbon holder 30 once is preferably about 0.50 mm, because if the depth is too high, the number of times the carbon holder 30 can be reused will naturally decrease.

[0031] In this way, it is preferable to grind the range of the side surface 33 where the depth is 0.20 mm or more. If the diameter of a cut surface obtained by cutting the carbon holder 30 along a plane perpendicular to the up-down direction before use is 100 mm, grinding the side surface 33 will result in the following:

[0032] After the silicon deposition process is performed using this carbon holder 30, the carbon holder 30 is taken out and the side surface 33 is ground in an area having a depth of 0.25 mm from the surface. After the side surface 33 is ground, the carbon holder 30 with the ground side surface 33 is reused and the silicon deposition process is performed again. Furthermore, the reused carbon holder 30 is taken out and the side surface 33 is ground again in an area having a depth of 0.25 mm from the surface, and the carbon holder 30 is reused. At this time, the carbon holder 30 is reused for the second time, and the diameter of the carbon holder 30 when reused for the second time is 99 mm.

[0033] When grinding the side surface 33, it is preferable to use a lathe equipped with a diamond blade. In this case, foreign matter that may cause contamination of the side surface 33 is not generated from the diamond blade. Therefore, contamination of the side surface 33 can be reduced. When grinding the side surface 33, a polishing machine such as a grinder, sandpaper, or waterproof paper may be used.

[0034] More preferably, the side surface 33 is ground so that the surface roughness is 30 μm or less. Still more preferably, the side surface 33 is ground so that the surface roughness is 1 μm or more and 30 μm or less. If the surface roughness is more than 50 μm, foreign matter adhering to the recesses of the side surface 33 cannot be sufficiently removed, and chlorine gas treatment is required for the carbon holder 30 after grinding.

[0035] When the surface roughness is 30 μm or less, the quality of the silicon obtained when the carbon holder 30 is reused can be further improved, compared with when the surface roughness is greater than 30 μm and less than 50 μm. Also, when the surface roughness is 1 μm or more, the side surface 33 can be finished by processing with a cutting machine, which makes the grinding operation easier and improves economy.

[0036] In addition to the side surface 33 of the carbon holder 30, it is preferable to grind the first end surface 31 of the carbon holder 30 so that the surface roughness is 50 μm or less. The above description regarding the grinding of the side surface 33 also applies to the grinding of the first end surface 31.

[0037] By grinding the first end face 31 as well, foreign matter adhering to the first end face 31 is also sufficiently removed compared to a case in which the first end face 31 is not ground. As a result, when the ground carbon holder 30 is reused, the quality of the silicon obtained by the silicon deposition process can be improved.

[0038] Furthermore, the surface roughness of the second end face 32 may be the same as or different from the surface roughness of the side face 33. However, the surface roughness of the second end face 32 is preferably smaller than the surface roughness of the side face 33. For example, it is preferable that the surface roughness of the second end face 32 is 1 μm or more and 5 μm or less, and the surface roughness of the side face 33 is 10 μm or more and 30 μm or less.

[0039] After the grinding process for the carbon holder 30, air is blown onto the surface of the carbon holder 30 to remove any foreign matter remaining on the surface of the carbon holder 30. By carrying out the processes up to this point, the carbon holder 30 is regenerated.

[0040] The carbon holder 30 regenerated by the method for regenerating the carbon holder 30 is joined between the core wire holding part 20 and the electrode 40. Then, with the reactor lid attached to the reactor bottom part 60, a raw material gas for silicon deposition is supplied into the reactor. In this case, a current is passed from the electrode 40 to the silicon core wire 10, thereby causing silicon to deposit from the silicon core wire 10.

[0041] After the silicon deposition process, foreign matter adheres to the surface of the carbon holder 30. Therefore, it is preferable to grind the side surface 33 of the carbon holder 30 so that the surface roughness of the carbon holder 30 is 50 μm or less. This sufficiently removes the foreign matter adhered to the surface of the carbon holder 30, and the carbon holder 30 can be reused to obtain silicon with sufficiently guaranteed quality, even if the ground carbon holder 30 is not treated with chlorine gas.

[0042] More specifically, the surface roughness of the carbon holder 30 is 50 μm or less, and the surface of the carbon holder 30 is highly smoothed, which makes it possible to suppress contamination of silicon obtained by reusing the carbon holder 30. Therefore, the carbon holder 30 can be reused even if chlorine gas treatment is not performed.

[0043] In addition, since it is not necessary to subject the ground carbon holder 30 to chlorine gas treatment, there is no need to install equipment for chlorine gas treatment, and the cost of installing the equipment can be reduced. In addition, the cost of consuming chlorine gas can also be reduced. In this embodiment, the ground carbon holder 30 may be subjected to chlorine gas treatment. In this case, the quality of silicon obtained by reusing the carbon holder 30 can be further improved.

[0044] [Embodiment 2] A second embodiment of the present invention will be described below. For ease of explanation, the same reference numerals are given to members having the same functions as those described in the first embodiment, and the explanations thereof will not be repeated. Fig. 3 is a cross-sectional view showing a cross-sectional configuration of a carbon holder 30 according to the second embodiment of the present invention and its vicinity.

[0045] 3, the first end face 31 of the carbon holder 30 is provided with an annular member 80 that covers at least a portion of the first end face 31 and surrounds the periphery of the core wire holding portion 20. This configuration can reduce adhesion of foreign matter to the first end face 31. As a result, when the ground carbon holder 30 is reused, the quality of silicon obtained by the silicon precipitation process can be improved compared to when the annular member 80 is not provided on the first end face 31.

[0046] The annular member 80 is made of carbon and protrudes, for example, 1 cm from the side surface 33 in a direction away from the central axis of the carbon holder 30 along the up-down direction. In other words, when viewed from above, the annular member 80 protrudes, for example, 1 cm from the outer periphery of the carbon holder 30. By providing the annular member 80 on the first end face 31, it is possible to reduce adhesion of foreign matter to the first end face 31, and therefore it is possible to omit a process of grinding the first end face 31. This allows the manufacturing cost to be reduced.

[0047] When viewed from above, the annular member 80 has an annular shape, and has an inner wall surface 81 and an outer wall surface 82. The inner wall surface 81 surrounds a portion of the inclined surface 21 of the core wire holding portion 20, and when viewed from above, the outer wall surface 82 is located outward from the side surface 33 of the carbon holder 30.

[0048] 3, consider a cross section of the core wire holding part 20, the carbon holder 30, and the annular member 80 cut by a plane including a central axis along the up-down direction of the carbon holder 30. In this cross section, the shortest distance between the inclined surface 21 of the core wire holding part 20 and the inner wall surface 81 of the annular member 80 is defined as UM, and the thickness of the annular member 80 along the up-down direction is defined as D1. In addition, the shortest distance between the side surface 33 of the carbon holder 30 and the outer wall surface 82 of the annular member 80 is defined as WM. The distance WM is the distance along the left-right direction perpendicular to the up-down direction.

[0049] Furthermore, when viewed from above, the outer diameter of the annular member 80 is LO, the inner diameter of the annular member 80 is LI, the outer diameter of the core wire holding part 20 on the same plane as the first end face 31 is MO, and the outer diameter of the carbon holder 30 is NO. Hereinafter, the above-mentioned MO will be referred to as the outer diameter MO of the core wire holding part 20. The outer diameter LO of the annular member 80 is, for example, 100 mm or more and 120 mm or less, the inner diameter LI of the annular member 80 is, for example, 50 mm or more and 60 mm or less, and the outer diameter MO of the core wire holding part 20 is, for example, 35 mm or more and 40 mm or less. The above sizes may be appropriately adjusted depending on the desired size of the silicon rod (the size of the silicon rod to be precipitated), the size of the carbon holder 30 used, the size of the core wire holding part 20, and the like.

[0050] It is preferable that the thickness D1 is 5 mm or more and 15 mm or less, and the distance WM is 5 mm or more and 15 mm or less. It is preferable that the inner diameter LI of the annular member 80 is larger than the outer diameter MO of the core wire holding part 20, and the outer diameter LO of the annular member 80 is larger than the outer diameter NO of the carbon holder 30. When tan θ=D1 / UM is defined, it is preferable that the angle θ is 40° or more and 60° or less. This makes the difference between the inner diameter LI of the annular member 80 and the outer diameter MO of the core wire holding part 20 appropriate, and a gap SP is formed between the annular member 80 and the core wire holding part 20.

[0051] That is, it is preferable that the annular member 80 is provided on the first end surface 31 of the carbon holder 30 so that a gap SP is formed between the annular member 80 and the core wire holding portion 20. When a silicon deposition process is performed, it is possible to prevent the silicon deposited on the silicon core wire 10 from becoming integrated with the annular member 80. This allows the annular member 80 to be reused.

[0052] Fig. 4 is a cross-sectional view showing the cross-sectional configuration of the carbon holder 30 shown in Fig. 3 and its vicinity, and a cross-sectional configuration of a carbon holder and its vicinity that is different from the configuration shown in Fig. 3. Reference numeral 101 in Fig. 4 indicates a case where the inner diameter of the annular member 80A is substantially the same as the outer diameter of the core wire holding part 20A on the same plane as the first end face 31. In this case, silicon S1 deposited on the upper surface of the annular member 80A and silicon S2 deposited on the core wire holding part 20A are integrated together.

[0053] The size of the silicon rod to be precipitated is not limited, since the shape of the device can be changed to the desired size. However, if the silicon rod is too large, silicon S1 is likely to precipitate on the upper surface of the annular member 80A. Therefore, particularly when the outer diameter of silicon S2 when viewed from above is greater than 150 mm, the upper surface of the annular member 80A is heated by thermal radiation from silicon S2, and silicon S1 is more likely to precipitate on the upper surface of the annular member 80A.

[0054] This makes it impossible to reuse the annular member 80A, and increases the cost of the annular member 80A. Although the size of the silicon rod to be precipitated is not limited as described above, in one embodiment of the present invention, the outer diameter of the silicon rod is preferably 100 mm or more and 150 mm or less.

[0055] Reference numeral 102 in Fig. 4 indicates a case where the difference between the inner diameter of the annular member 80B and the outer diameter MO of the core wire holding portion 20 is smaller than that indicated by reference numeral 103 in Fig. 4. In this case, silicon S3 deposited on the upper surface of the annular member 80B and silicon S4 deposited on the core wire holding portion 20 become one body. This makes it impossible to reuse the annular member 80B.

[0056] Reference numeral 103 in Fig. 4 indicates a case similar to the configuration shown in Fig. 3. In this case, since the difference between the inner diameter LI of the annular member 80 and the outer diameter MO of the core wire holding part 20 is appropriate, silicon S5 deposited on the upper surface of the annular member 80 and silicon S6 deposited on the core wire holding part 20 do not become one with each other. For this reason, the annular member 80 can be reused.

[0057] Reference numeral 104 in Fig. 4 indicates a case where the difference between the inner diameter of the annular member 80C and the outer diameter MO of the core wire holding part 20 is larger than that indicated by reference numeral 103 in Fig. 4. In this case, a large portion of the first end face 31 of the carbon holder 30 is exposed from the annular member 80C, and foreign matter adheres to the first end face 31 of the carbon holder 30. This reduces the quality of silicon obtained when the carbon holder 30 is reused.

[0058] As shown in the configuration indicated by reference numeral 103 in Fig. 4, that is, as shown in Fig. 3, it is preferable that the difference between the inner diameter LI of the annular member 80 and the outer diameter MO of the core wire holding portion 20 is appropriate. In this case, the difference between the inner diameter LI of the annular member 80 and the outer diameter MO of the core wire holding portion 20 becomes appropriate, silicon S5 deposited on the upper surface of the annular member 80 and silicon S6 deposited in the core wire holding portion 20 do not become one with each other, and the annular member 80 can be reused.

[0059] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. EXAMPLES

[0060] The present invention will be further described below with reference to examples, but the present invention is not limited to these examples. For ease of explanation, the symbols used in the second embodiment are used for each member. In the following examples 1 to 3 and comparative examples 1 to 3, experiments were performed using 100 carbon holders 30 and annular members 80 whose surfaces were ground as specified after silicon deposition was completed. A plurality of carbon holders 30 and annular members 80 were placed in the reactor.

[0061] <Prerequisites> In the following examples and comparative examples, the manufacturing conditions for the silicon rods (including the length of the silicon core wire used) were the same except for changing the form of the carbon holder 30 and the annular member 80 (flange). The silicon core wire 10 used was a rectangular column with a cross-sectional area of ​​10 mm × 10 mm.

[0062] <Quality evaluation of silicon rods; non-standard product ratio αi / αo> The off-standard product ratio αi / αo evaluated in the examples and comparative examples is a value used in the following silicon quality evaluation method. Usually, as shown in Fig. 5, a silicon rod including a silicon core 10 after the precipitation treatment is taken out from a reactor together with the core holding part 20 because the silicon rod includes a part of the core holding part 20.

[0063] The extracted silicon rod incorporates impurities (phosphorus, boron, arsenic, aluminum, carbon, metal components) from the core wire holding part 20 and the carbon holder 30 during silicon precipitation. For this reason, in Fig. 5, silicon located up to a certain height from the upper end surface of the core wire holding part 20 may be classified as non-standard product and separated and sorted by mechanical crushing (crushing with a hammer, etc.). Note that silicon near the core wire holding part 20 may contain a large amount of impurities, so this portion may be removed before commercialization.

[0064] In this experiment, the weight of the silicon rod portion (non-standard product) in which the total amount of impurities was equal to or more than a specific amount (all of the examples and comparative examples, including the reference example, had the same amount of impurities or more) was evaluated. When the same manufacturing conditions were used, a manufacturing device (bell jar) was used in which the variation in the average weight of the non-standard products (removed silicon rod portions) in each manufactured silicon rod was 5% or less.

[0065] The same manufacturing conditions refer to all the same manufacturing conditions, including the equipment used, the amount of gas supplied, the use of unused (brand new; satisfying the same standards) carbon holder 30 and core wire holding part 20, and the use of the same length of silicon core wire 10. Depending on the conditions of the quality standards, the weight ratio of non-standard products to the total weight of the silicon rod including the silicon core wire 10 after silicon deposition is about 1% by mass or more and 2% by mass or less.

[0066] In the examples and comparative examples, first, a silicon rod is manufactured using an unused carbon holder 30. Then, the weight ratio αo of non-standard products to the total weight of the silicon rod is calculated (αo when the original carbon holder 30 is used is calculated). Next, as examples and comparative examples, a used carbon holder 30 is treated under the conditions shown in Table 1 (including providing an annular member 80) to manufacture a silicon rod under the same manufacturing conditions. The non-standard products are removed from the obtained silicon rod so that the quality standard is the same as when the original carbon holder 30 is used, and the weight ratio αi of the non-standard products in the examples and comparative examples (when the carbon holder is reused) is calculated.

[0067] Then, the ratio of nonstandard products αi / αo for the examples and comparative examples was calculated by dividing the corresponding αi value by each αo value. If the ratio of nonstandard products αi / αo is high, it means that the carbon holder 30 contains a lot of impurities when reused, making it difficult to reuse.

[0068] <Other evaluations> In the examples and comparative examples, when the carbon holder 30 was reused to produce a silicon rod, the silicon adhering to the reused carbon holder 30 was visually confirmed and evaluated. In the examples in which the annular members 80 were used during reuse, the reuse ratio of the annular members 80 was the ratio of the annular members 80 that could be reused to the number of the annular members 80 that were used.

[0069] <Reference Examples, Examples 1 to 7, and Comparative Examples 1 to 2> The conditions (reuse conditions of the carbon holder 30) of the Reference Example, Examples 1 to 7, and Comparative Examples 1 to 2, as well as the evaluation results thereof, are shown in Table 1. The Reference Example is a representative result when an unused carbon holder 30 was used. Before carrying out each of Examples 1 to 7 and Comparative Examples 1 to 2, naturally, a silicon rod was produced using each unused carbon holder 30, and the weight proportion αo of non-standard products of the origin was determined.

[0070] As shown in Table 1, Comparative Example 1 is an example in which a silicon rod was manufactured using an unused carbon holder 30 (reference example), and the carbon holder 30 (the surface roughness of the first end face 31 and the side face 33 was 400 μm) that had been used was reused as is to manufacture a silicon rod.

[0071] Comparative Example 2 is an example in which a silicon rod was manufactured using an unused carbon holder 30 (Reference Example), the first end face 31 and the side face 33 of the used carbon holder 30 were ground to a surface roughness of 100 μm (depth of 0.05 mm), and a silicon rod was manufactured using the ground carbon holder 30. In these Comparative Examples 1 and 2, the nonstandard product ratio αi / αo was 3 or more, which was a high nonstandard product ratio, and it was found that the carbon holder 30 was unsuitable for reuse.

[0072] Example 7 is an example in which a silicon rod was manufactured using an unused carbon holder 30 (reference example), the first end face 31 and the side face 33 of the used carbon holder 30 were ground so that the surface roughness was 25 μm (depth: 0.25 mm), and a silicon rod was manufactured using the ground carbon holder 30. In Example 7, the nonstandard product ratio αi / αo was 1.6, and it was found that the carbon holder 30 could be reused by sufficiently grinding the surface of the carbon holder 30 after use.

[0073] Examples 1 to 6 are examples in which a silicon rod was manufactured using an unused carbon holder 30 (reference example), the first end face 31 and side face 33 of the carbon holder 30 that was used were ground so that the surface roughness was 25 μm (depth 0.25 mm), and further, a carbon annular member 80 having the shape shown in Table 1 was provided on the first end face 31, and a silicon rod was manufactured again.

[0074] In Examples 1 to 6, it was confirmed that the non-standard product ratio αi / αo was smaller than that in Example 7, and the quality of silicon was improved. In particular, in Examples 1 and 2, there was no silicon deposition on the first end surface 31, and the reuse rate of the annular member 80 was high, and it was found to be a preferable condition. Furthermore, from the results of Examples 1 to 6 above, it is clear that the quality of the obtained silicon rod is maintained even when the annular member 80 is provided on an unused carbon holder 30.

[0075] In Example 4, since the angle θ is 73° which is larger than 60°, the distance UM is small, and the silicon precipitated on the upper surface of the annular member 80 and the silicon precipitated on the core wire holding portion 20 are integrated together, similar to the case shown by reference numeral 102 in Fig. 4. Therefore, the reuse rate of the annular member 80 is low.

[0076] In Example 3, when the angle θ was smaller than 40°, as in the case shown by reference numeral 104 in Fig. 4, the distance UM became large, causing foreign matter to adhere to the first end surface 31 of the carbon holder 30, and the nonstandard product ratio αi / αo became higher among Examples 1 to 6. In Example 5, the distance WM was 3 mm, which was smaller than 5 mm, causing silicon to precipitate on a part of the side surface 33 of the carbon holder 30, and the nonstandard product ratio αi / αo became higher among Examples 1 to 6. Note that when the distance WM is larger than 15 mm, the distance between adjacent annular members 80 becomes smaller, increasing the possibility of discharge occurring between the annular members 80, which is not practical.

[0077] In Example 6, the thickness D1 of the annular member 80 in the vertical direction was 3 mm, which was smaller than 5 mm, so that the annular member 80 was lightweight, and the position of the annular member 80 fluctuated due to the flow of the raw material gas in the reactor during the silicon deposition process. This resulted in a low reuse rate of the annular member 80.

[0078] If the thickness D1 is greater than 15 mm, the size of the annular member 80 will be large, and the cost of the annular member 80 will be high, making it impractical. Also, as is clear from a comparison between Examples 1 and 2 and Example 4, it is clear that when the annular member 80 is provided, the reuse rate of the annular member 80 can be increased by setting the angle θ to be 40° or more and 60° or less.

[0079] [Table 1] <Example 8> A silicon rod was manufactured using the core wire holding part 20 having the shape shown in Fig. 5. As in Examples 1 to 7, a silicon rod was first manufactured using an unused carbon holder 30 (reference example), and the first end face 31 and the side face 33 of the used carbon holder 30 were ground so that the surface roughness became 25 µm (depth: 0.25 mm), and further, a carbon annular member 80 having the shape shown in Fig. 5 was provided on the first end face 31, and a silicon rod was manufactured again. The thickness D1 in the vertical direction of the annular member 80 was 10 mm, and the distance WM was 10 mm.

[0080] In detail, a core wire holding portion 20 as shown in Fig. 5 was used. In Example 8, an annular member 80 with a distance UM of 8.5 mm was used as shown in Fig. 5. In Example 8, tan θ=D1 / UM≈1.18, and the angle θ was 45° or more and 60° or less. In Example 8, the non-standard product ratio αi / αo=1.0, no silicon was deposited on the first end face 31, and the reuse rate of the annular member 80 was 100%. [Explanation of symbols]

[0081] 10 Silicon core wire 20 Wire retaining part 30 Carbon Holder 31 First end surface 32 Second end face 33 Side 34 Part 1 35 Part 2 40 electrodes 80 Annular member SP Gap

Claims

1. A method for regenerating a carbon holder that is made of carbon and is joined between a core wire holding part that holds a silicon core wire for depositing silicon and an electrode that applies current to the silicon core wire, the method comprising the steps of: After the carbon holder has been used in a process for depositing silicon onto the silicon core, in order to reuse the carbon holder, a side extending between a first end face of the carbon holder on which a first portion to be joined to the core wire holding portion is formed and a second end face of the carbon holder on which a second portion to be joined to the electrode is formed is ground so that the surface roughness (Ra) is 30 μm or less; A method for regenerating a carbon holder, comprising the step of not treating the carbon holder with chlorine gas after grinding.

2. 2. The method for regenerating a carbon holder according to claim 1, further comprising grinding the first end face of the carbon holder in addition to the side face of the carbon holder so that the surface roughness (Ra) of the first end face of the carbon holder is 30 μm or less.

3. 2. The method for regenerating a carbon holder according to claim 1, further comprising providing an annular member on the first end face of the carbon holder, the annular member covering at least a portion of the first end face and surrounding the periphery of the core wire holding portion.

4. The carbon holder regenerating method according to claim 3, characterized in that the annular member is provided on the first end face of the carbon holder so that a gap is formed between the annular member and the core wire holding portion.

5. A method for producing silicon, comprising joining a carbon holder regenerated by the carbon holder regeneration method described in any one of claims 1 to 4 between the core wire holding portion and the electrode, and precipitating silicon from the silicon core wire.

Images