Method for producing polysilicon chunks

Abstract

The present disclosure aims to provide a method for obtaining polysilicon chunks by a simple method, in which the generation of fine powder is highly suppressed, from a group of crushed fragments obtained by crushing a polysilicon rod manufactured by the Siemens process. In one embodiment of the present disclosure, the method for producing polysilicon chunks includes, for polysilicon chunks collected from a group of crushed fragments obtained by crushing a polysilicon rod manufactured by the Siemens process, chipping off any of the crushed fragments that have depressions on their surfaces with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, and more preferably, chipping off the depressions at a rate of 0.1 / cm2 relative to the total surface area of ​​the crushed fragments. 2 When the recesses are contained in the above proportion, the chipping is continued until the proportion of the recesses becomes less than the lower limit.

Description

[Technical Field]

[0001] The present invention relates to a method for producing polysilicon chunks, and more particularly to a method for producing polysilicon chunks obtained by crushing polysilicon rods produced by the Siemens process. [Background technology]

[0002] The Siemens process is a well-known method for producing polysilicon. In the Siemens process, a silicon core wire placed inside a bell-jar-shaped reactor is heated to the silicon deposition temperature by passing an electric current through it, and then silane compound gases such as trichlorosilane (SiHCl3) or monosilane (SiH4) and hydrogen are supplied to the reactor, depositing polysilicon on the silicon core wire by chemical vapor deposition to produce a polysilicon rod.

[0003] The polysilicon rod obtained by the Siemens process is then mechanically crushed using a hammer made of a hard metal such as tungsten carbide, and the resulting crushed pieces are classified into desired particle sizes as needed and subjected to etching or other processes to produce polysilicon chunks, which are useful as raw materials for producing single crystal silicon.

[0004] The polysilicon chunks may generate fine powder due to vibration during classification or transportation, for example. The fine powder not only makes the polysilicon chunks difficult to handle, but may also cause contamination of the polysilicon. Therefore, it is desirable to remove such polysilicon chunks in a state where fine powder is likely to be generated from the group of broken pieces of the polysilicon rod before classification or transportation.

[0005] Polysilicon chunks include those having various irregularities on their surfaces, such as undulations, holes, grooves, and other irregularities, and discolored areas, and methods have been proposed for classifying those having such irregularities according to their state. Some of these methods are intended to distinguish chunks that include a rod surface with a dense concentration of coarse undulations, a so-called popcorn surface, formed due to unstable supply of raw material gas during the production of polysilicon rods (e.g., Patent Documents 1 and 2).

[0006] On the other hand, when a polysilicon rod includes such a popcorn-like surface, it is also known that, rather than crushing the rod as described above and then removing the lumps including the defective surface, the defective surface layer portion is first struck and removed while the polysilicon rod is still in the state of being, so that the lumps including the popcorn-like surface are not included in the group of crushed pieces (Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japan Special Publication No. 2022-537014 [Patent Document 2] Japan Special Publication No. 2016-516666 [Patent Document 3] Japan Special Publication No. 2022-547425 Summary of the Invention [Problem to be solved by the invention]

[0008] Among the above-mentioned prior arts, the techniques disclosed in Patent Documents 1 and 2 do not focus on the fine powder generated from polysilicon. They merely distinguish between agglomerates containing popcorn-like surfaces, and make no mention of the likelihood of fine powder generation in the agglomerates remaining after removing these. However, simply removing the agglomerates containing popcorn-like surfaces in this way means that the remaining polysilicon agglomerates still contain a certain amount of material that is likely to generate fine powder, and the problem of fine powder generation cannot be fully resolved.

[0009] Furthermore, Patent Document 3 discloses that the popcorn-like surface of a polysilicon rod is removed using a hammer. However, it is highly difficult to precisely remove this defective surface layer from the arc-shaped surface of a large-diameter polysilicon rod by hammering, and the work requires a long time without skill. Furthermore, Patent Document 3 discloses that the popcorn-like surface layer is removed to a depth of 1 to 10 mm from the rod surface (see paragraph 0034 of Patent Document 3). However, according to the inventors' investigations, even if the surface layer is removed to this depth, the polysilicon mass obtained by crushing the treated rod still does not sufficiently suppress the generation of fine powder.

[0010] In light of the above, an object of the present invention is to provide a simple method for obtaining polysilicon chunks from a group of fragments obtained by crushing polysilicon rods produced by the Siemens process, with the generation of fine powder being significantly suppressed. [Means for solving the problem]

[0011] In view of the above-mentioned problems, the present inventors have conducted extensive research and have found that the above-mentioned problems can be satisfactorily solved by observing the fracture surface of each of the polysilicon bulk fragments, which are fragments collected from a group of fragments obtained by crushing the polysilicon rod, and if a depression of a specific size is present in the fragment, lightly striking the vicinity of the depression with a striking tool such as a hammer to break it into smaller pieces (i.e., chipping), and scraping away the depression (hereinafter referred to as "chipping removal"). This finding led to the completion of the present invention.

[0012] That is, the present invention relates to a polysilicon bulk material, which is a crushed piece collected from a group of crushed pieces obtained by crushing a polysilicon rod produced by the Siemens process, and This method for producing polysilicon chunks is characterized in that if any of the crushed pieces has a depression on the crushed surface with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, the depression is removed by chipping. [Effects of the Invention]

[0013] According to the present invention, a polysilicon mass can be obtained by a simple method from a group of crushed pieces obtained by crushing a polysilicon rod produced by the Siemens process, in which the generation of fine powder is highly suppressed even when vibration is applied. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram showing an outline of an example of a flow for sorting crushed fragments of a polysilicon rod, suitable for incorporating the method of the present invention. [Figure 2] FIG. 2 is a photograph of a representative embodiment of a fragment containing the popcorned rod surface, which was collected from a group of fragments obtained by crushing a polysilicon rod. [Figure 3] FIG. 3 is a photograph of a representative example of a group of fragments obtained by crushing a polysilicon rod, the fragments having the above-mentioned recesses on the crushed surface. [Figure 4]FIG. 4 is a graph showing vibration data measured by a vibrometer installed on the truck bed during a transportation test in measuring the likelihood of generating fine powder from polysilicon agglomerates, which was tested in the examples and comparative examples. [Figure 5] FIG. 5 is a graph showing the particle size distribution of the polysilicon rod fragments packed in a polyethylene bag when measuring the likelihood of the polysilicon rod fragments generating fine powder in the examples and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0015] In order to solve the above-mentioned problems, in a method for producing polysilicon chunks according to one embodiment of the present invention, a group of crushed pieces obtained by crushing a polysilicon rod produced by the Siemens process is used as a bulk polysilicon chunk. Here, the polysilicon rods produced by the Siemens process can be produced without limitation by the known method of depositing polysilicon on a silicon core wire by chemical vapor deposition, as described above. The diameter of the polysilicon rods is generally 6 to 20 cm.

[0016] In the production of polysilicon rods by the Siemens process, the surface of the rod becomes rough at locations where the source gas is supplied unstably, and undulations, holes, grooves, etc. tend to occur. This unstable supply of source gas tends to be particularly severe at the upper part of the rod, where the distance from the source gas supply port increases. Therefore, near the upper end of the obtained polysilicon rod, such roughening becomes more pronounced, and the popcorn-like surface tends to form.

[0017] A photograph of a representative embodiment of the fragments containing the popcorned rod surface, which were collected from a group of fragments obtained by crushing a polysilicon rod described below, is shown in Figure 2. In Figure 2, the area surrounded by a dotted line is the popcorned rod surface, and this popcorned rod surface is observed as a surface with an accumulation of coarse undulations and grooves.

[0018] On the surface of the popcorned rod, the diameter of the undulations is usually about 5 to 30 mm, and the number of such undulations is 0.1 / cm 2 or more, in some cases 0.1 to 1.0 pieces / cm 2 The popcorned surface is densely packed at a ratio of 1 to 30 mm. The length from the top of the undulations to the bottom of the grooves is usually about 1 to 30 mm, with locally scattered depressions exceeding 10 mm in depth. The deepest depressions can be as deep as 50 mm.

[0019] The crushing of the polysilicon rod may be performed on the entire length of the rod produced by the Siemens process, or may be performed on cut rods partially cut in the axial direction. Among polysilicon chunks, those obtained by crushing a portion including the popcorn surface are particularly likely to produce fine powder, as will be described later. Therefore, it is efficient to divide the polysilicon rod in the axial direction into a rod region (usually the upper portion of the rod) that is likely to include the popcorn surface and another rod region (usually the lower portion of the rod), crush the cut rods of each region separately, and subject only the group of crushed pieces obtained from the former cut rod to the present embodiment.

[0020] In this embodiment, the polysilicon rod may be crushed using a hammer or a crusher made of a hard metal such as tungsten carbide. Generally, at least 90% by mass of the crushed fragments have a particle size with a major axis length in the range of 2 to 160 mm. Among these fragments, taking into consideration applications such as raw materials for producing single-crystal silicon, as well as the ease of chipping and removing recesses present on the crushed surface (described later), the polysilicon chunks are required to have a maximum side length of 50 mm or more, more preferably 70 to 160 mm, which is easy to grip. Therefore, the crushed fragments may be classified into fragments of the desired particle size before being used in this embodiment as polysilicon chunk bulk materials. Classification may be performed using a known classifier, such as a vibrating sieve or a roller classifier.

[0021] The greatest feature of this embodiment is that, for the polysilicon bulk fragments thus obtained, if any fragments have depressions on their fracture surfaces that are 0.5 to 5 mm in minimum diameter and 1 mm or more in depth, the depressions are removed by chipping. Figure 3 shows a photograph of a representative example of a group of fragments obtained by crushing a polysilicon rod, in which the depressions are present on the fracture surfaces. In the fragments in Figure 3, the multiple black shadows indicated by arrows represent the depressions with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more. In this embodiment, by chipping away the depressions formed on the fracture surfaces, the resulting polysilicon chunks are improved so that the amount of fine powder generated is significantly reduced, even when subjected to vibration during classification, transportation, etc.

[0022] In particular, the minimum diameter of the fractured surface to be chipped is preferably 1 to 4.5 mm, and most preferably 1.5 to 4 mm.

[0023] The depth of the recesses on the fractured surface where chipping is performed is preferably 3 mm or more, and most preferably 5 mm or more.

[0024] The diameter of the recess present on the fractured surface is the length of any line segment that passes through the center of the recess and has both ends on the periphery of the recess, and the minimum diameter is the shortest length of that line segment. The surface condition of the fractured surface often has a complex shape where cleavage planes intersect and large depressions, protrusions, etc. intersect, as described below. Therefore, the periphery of the recess opening there may not necessarily be at the same height all around, but the most curved corner (usually an intersection angle of 50 to 130 degrees) where the recess wall surface and the surface of the fractured fragment intersect in each case may be the periphery of the recess.

[0025] If the height of the periphery is not on the same plane and is not determined to a constant value depending on the periphery location, the depth of the recess may be determined by taking the highest periphery location as the reference and determining the depth from that height.

[0026] Here, the minimum diameter of the recess refers to the value determined by inserting a taper gauge into the recess. Furthermore, the depth of the recess refers to the value determined using a depth gauge with a rod tip diameter of 0.3 mm. It is not necessary to measure the minimum diameter and depth of the recess for each target piece to determine whether it should be chipped or removed. If it can be visually determined that the piece falls within this range, it may be visually determined and used for the chipping operation. Furthermore, similarly, as long as the results are essentially consistent with the actual measurements, it is also possible to take a surface photograph of the broken pieces of the polysilicon rod and calculate the minimum diameter of the recess or estimate the depth of the hole based on the image data.

[0027] In the fragments of the polysilicon rod, when the fracture surface on which the recesses of the above size are formed is a surface where the popcorned surface of the polysilicon rod is cracked and exposed, they are often formed by the bottoms of the grooves left behind by the popcorning. That is, in the case of the fragments shown in the photographic image of Figure 3, the recesses indicated by the arrows are concentrated on the fracture surface on the near side of the page in Figure 3. From this, it is presumed that the surface in question is a surface where the popcorned surface of the polysilicon rod is cracked and exposed, and that these recesses are formed by the locally deep bottoms of the grooves remaining.

[0028] Therefore, the popcorned portion of the polysilicon rod is weak in strength, and fine powder generated during the crushing of the polysilicon rod often penetrates and settles near the bottom of the groove. Therefore, when recesses resulting from the popcorned surface are formed on the crushed surface, the resulting polysilicon mass will generate a significant amount of fine powder when subjected to the vibration load.

[0029] In particular, as mentioned above, there are scattered grooves on the popcorned surface that are more than 10 mm deep in some places. Therefore, the method of striking and removing the popcorned surface layer in the polysilicon rod state before crushing, as in Patent Document 3, does not allow the defective surface layer to be precisely removed, and the problem of fine powder generation cannot be sufficiently prevented.

[0030] In contrast, in this embodiment, after the polysilicon rod is crushed, if any of the dents are present on the crushed surfaces of the resulting crushed pieces, they are chipped away. Each crushed piece has an appropriate grain size that makes it easy to grip, and the crushed surfaces are dotted with ridges and fissures that can act as starting points for cleavage when struck, so the removal of the dents can be carried out reliably and with ease.

[0031] Here, in the fractured pieces of the polysilicon rod, the fractured surface usually exhibits a complex structure where cleavage planes intersect and large depressions, protrusions, etc. are also intersected. In contrast, the surface of the polysilicon rod where the rod surface is disposed as is forms a gently sloping part of a circular arc. In such a surface derived from the rod surface, even in the popcorned portion, the surface of the undulating part excluding the holes and grooves is highly smooth, so that the surface derived from the rod surface and other surfaces, such as the fractured surface, can be clearly distinguished visually.

[0032] In the fracture surface, the recesses generally have an aspect ratio defined by the longest diameter / the smallest diameter of 10 or less, and particularly preferably 8 or less.

[0033] In addition, in the fragments from which the recesses are chipped off, the proportion of the recesses (having a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more) is 0.1 pieces / cm of the total surface area of ​​the fragments. 2 (Usually, the upper limit of the ratio of recesses is 1.0 / cm 2 ), the generation of fine powder when subjected to vibration becomes more severe. Therefore, when the proportion of such recesses is at the lower limit (0.1 pieces / cm 2 ) or more, it is effective to chip away the recesses until the ratio of the recesses becomes less than the lower limit. In particular, when the ratio of the recesses becomes 0.1 to 1.0 / cm of the total surface area of ​​the fragments, 2 In this case, it is more effective to remove the recesses by chipping until the proportion of the recesses falls below the lower limit.

[0034] Furthermore, by removing chips, the proportion of recesses was reduced to 0.05 / cm 2It is preferable to reduce the number of recesses to 0.01 / cm or less from the viewpoint of preventing the generation of fine powder. 2 From the viewpoint of preventing the generation of fine powder, it is most preferable to reduce the ratio of the recesses to the value below. By removing the chips in this way, it is preferable to randomly select 100 fragments and make the average ratio of the recesses to the value below.

[0035] The total surface area of ​​the fragments required to determine the proportion of recesses in the fragments is determined by measuring the mass of the fragments to be measured, calculating the volume from the specific gravity of the polysilicon based on the obtained mass, and then converting the obtained volume into a sphere to calculate the surface area of ​​the sphere.

[0036] In this embodiment, chipping and removal of the recesses in the broken pieces is generally performed manually using a striking tool such as a hammer, but in some cases, an electric chipping hammer or the like may also be used. The hammer used for manual work preferably has a striking part made of a hard metal such as tungsten carbide, and the striking surface is preferably flat, but may also be spherical or pointed. The diameter of the striking part is 5 to 50 mm, preferably 10 to 40 mm, the length of the handle is 100 to 400 mm, preferably 150 to 300 mm, and the total weight is 300 to 5000 g, preferably 500 to 4000 g.

[0037] Using such an impact tool, the vicinity of the recesses present on the fracture surface can be lightly struck to break them into smaller pieces, and the recesses can be scraped away. This scraping is preferably limited to the minimum extent necessary to ensure a high yield of polysilicon blocks. Since the maximum depth of the recesses is typically about 30 mm, it is preferable to scrape away the recesses to a depth of 30 mm or less, and more preferably to a depth of 40 mm or less.

[0038] In the present embodiment, when the crushed polysilicon rods contain the popcorn surface, the crushed pieces include not only those having the crushed surface on which the recesses are present, but also those having the popcorn surface as it is. As described above, the popcorn surface is prone to generating fine powder more violently due to the load of vibration, so that in the chipping removal, it is preferable to remove the popcorn surface in parallel with or before or after removing the recesses present on the crushed surface.

[0039] The polysilicon chunks thus obtained may be subjected to classification, etching, or other treatments as required, and then used as a raw material for producing single crystal silicon.

[0040] An example of a flow for crushing polysilicon rods and sorting fragments suitable for incorporating the above-described method for producing polysilicon chunks is outlined in the schematic diagram of Figure 1. The polysilicon rod P obtained by the Siemens process has a rod region P1 including a popcorn surface on part of its surface. In order to obtain polysilicon fragments that are less likely to produce fine powder, the polysilicon rod P is first subjected to a rough crushing step S1 in which it is divided into the rod region P1 including the popcorn surface and the other rod regions.

[0041] After the coarse crushing step S1, the rod region P1 containing the divided popcorn surface and the other rod regions are crushed into small pieces in the crushing step S2. As a result, the latter rod region produces a group of crushed pieces from the rod region that does not contain the popcorn surface ("no-popcorn" crushed pieces), which exhibit good properties and are less likely to produce fine powder even when subjected to vibration.

[0042] On the other hand, in the crushing step S2, a mixture of "no corn" crushed pieces and "with corn" crushed pieces ("corn mix" crushed pieces) is obtained from the rod region P1 including the popcorn forming surface.

[0043] Next, the "corn mix" crushed fragments are subjected to the corn mix sorting step S3. Here, the "no corn" crushed fragments are separated into "no corn, no recesses" crushed fragments that do not have the recesses on their crushed surfaces, and "no corn, with recesses" crushed fragments that do have the recesses. The "corn-containing" crushed fragments are also separated into "corn-containing, with recesses" crushed fragments that have the recesses on their crushed surfaces, and "corn-containing, without recesses" crushed fragments that do not have the recesses (in FIG. 1, the recesses on the crushed surfaces are indicated by small black dots). That is, in the corn mix sorting step S3, the "corn mix" crushed fragments are separated into four types of crushed fragments: "no corn, no recesses," "no corn, with recesses," "corn-containing, with recesses," and "corn-containing, without recesses."

[0044] In the subsequent chipping step S4, the recesses are removed from the "without cone, with recess" and "with cone, with recess" fragments in the four fragment fractions, which is the greatest feature of the method in Figure 1. This prevents the generation of fine powder due to the recesses in these fragments.

[0045] In addition, in the chipping step S4, in parallel with the chipping and removal of the recesses from the "without cone and recess" and "with cone and recess" crushed fragments, it is preferable to also chip and remove the popcorn surface portion from the "with cone and recess" crushed fragments and the "with cone and no recess" crushed fragments. That is, as mentioned above, the popcorn surface of the polysilicon rod exhibits a property that is particularly prone to the generation of fine powder, so it is advantageous to also remove this portion from crushed fragments having such a popcorn surface in order to reduce the total amount of fine powder generated in the resulting crushed fragments. Of course, it is more preferable to chip and remove the popcorn surface to a depth that does not leave any recesses corresponding to the bottom of the grooves on the removed surface.

[0046] Thus, by undergoing the chipping step S4, even if only a small portion of the "cone mix" crushed fragments are "no cone, no recess" crushed fragments in which the generation of fine powder is suppressed, by chipping away the "no cone, with recess", "cone with recess", and "cone with no recess" crushed fragments, the amount of these "no cone, no recess" crushed fragments can be greatly increased, and these crushed fragments can be handled as polysilicon lumps with good properties for transportation and further classification, even when subjected to vibration load, as they contain little fine powder.

[0047] 1, the crushed pieces obtained from the rod region not including the popcorn surface in the crushing step S2 are not subjected to the corn mix sorting step S3, but the present invention is not limited to this configuration. The crushed pieces may be subjected to the corn mix sorting step S3 to be separated into two types of crushed pieces: "no corn, no recess" and "no corn, with recess."

[0048] 〔summary〕 As can be understood from the above description, the present invention includes the following aspects.

[0049] Aspect 1: A method for producing polysilicon chunks, characterized in that, for polysilicon chunks, which are fragments collected from a group of fragments obtained by crushing a polysilicon rod produced by the Siemens process, if any of the fragments has a depression on the fracture surface with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, the depression is removed by chipping.

[0050] Aspect 2: The method for producing a polysilicon chunk according to Aspect 1, wherein the recess has an aspect ratio defined by the longest diameter / the smallest diameter of 10 or less.

[0051] Aspect 3: In the fragments from which the recesses are chipped off, the proportion of the recesses is 0.1 / cm with respect to the total surface area of ​​the fragments. 2 The method for producing a polysilicon chunk according to aspect 1 or 2, wherein the proportion of the recesses is reduced to below the lower limit by the chipping removal.

[0052] Aspect 4: The method for producing polysilicon chunks according to any one of Aspects 1 to 3, wherein the polysilicon rods to be crushed include a popcorn-like surface in which large undulations are densely concentrated on a part of the surface of the rods.

[0053] Aspect 5: A method for producing polysilicon chunks according to Aspect 4, characterized in that, in parallel with or before or after chipping away the recesses in the fragments where the recesses are present, chipping away the popcorned surface in the fragments that include the popcorned surface. [Example]

[0054] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these.

[0055] In the following examples and comparative examples, the characteristics of recesses present on the crushed surfaces of the crushed polysilicon rod fragments were measured by the following method. Furthermore, the tendency of the crushed polysilicon rod fragments to generate fine powder when subjected to vibration was measured by the following method.

[0056] [Size of recess] 100 fragments were randomly selected from each group of target polysilicon fragments, and a taper gauge was inserted into the recesses in each fragment to measure the minimum diameter of the recesses. The average minimum diameter of the recesses was also calculated based on the results of the 100 fragments.

[0057] On the other hand, the depth of the recesses was measured using a depth gauge with a rod diameter of 0.3 mm at the tip. Recesses of less than 0.3 mm, which the tip of the depth gauge cannot insert, are outside the scope of this patent and were therefore not measured.

[0058] [Ratio of recesses] In determining the proportion of recesses present, 100 fragments having a maximum side length of 50 mm or more were randomly selected from the group of polysilicon fragments to be measured and used as the measurement targets.

[0059] The total surface area of ​​the crushed fragments, which is necessary to determine the proportion of recesses, was determined by measuring the mass of the crushed fragments to be measured, calculating the volume from the specific gravity of the polysilicon obtained from the mass, and converting the volume into a sphere to obtain the surface area of ​​the sphere. The specific gravity of polysilicon is 2.3 g / cm. 3 The calculation was carried out as

[0060] The number of recesses (minimum diameter 0.5 to 5 mm and depth 1 mm or more) to be chipped and removed was counted, and the value obtained by dividing the number of recesses by the total surface area of ​​the fragments calculated from the mass was used to calculate the ratio of recesses (number / cm 2 ) was decided.

[0061] [Size of polysilicon fragments] The size of the polysilicon fragments was obtained by measuring the major axis, which is the maximum side length, with a vernier caliper.

[0062] [Ease of generation of fine powder from polysilicon rod fragments] Five kilograms of the polysilicon rod fragments to be measured were packed into an 8.5-liter polyethylene bag and sealed. Six of these packages were packed into a 50-liter cardboard box, and a transport test was conducted over a round trip of approximately 400 km (approximately 200 km one way). These conditions correspond to the general transport conditions for polysilicon block products. The cardboard box was loaded into the rear of the loading space of a transport truck, and a vibrometer equipped with a triaxial acceleration sensor was installed on top of the cardboard box.

[0063] Figure 4 shows a graph of the vibration data measured by the installed vibrometer during the transportation test. The X-axis represents the direction of travel of the transport truck, the Y-axis represents the left-right direction relative to the direction of travel, and the Z-axis represents the up-down direction. The graph shows the results of measuring acceleration (G) in each direction over time on the vibrometer. For example, when a moving transport truck stops, acceleration occurs in the direction of travel, resulting in a positive value on the X-axis, and when it starts moving again, a negative value. The Y-axis is positive when the transport truck curves left relative to the direction of travel, resulting in acceleration to the right, resulting in a negative value when it curves right. The Z-axis is approximately -1G when stationary due to the influence of gravity. When the cardboard box bounces upward, the Z-axis becomes negative, more than -1G, and when the cardboard box is pushed from above, it becomes positive, more than -1G.

[0064] As shown in Figure 4, the cardboard box containing the group of broken polysilicon rod fragments moved significantly up and down and tilted more left and right than forward and backward. It was thought that the generation of fine powder from the group of broken polysilicon rod fragments was caused by the vibrations that occurred during transportation, causing the fragments to collide or rub against each other.

[0065] To evaluate the likelihood of fine powder generation during transportation, after the transportation test, five bags of the polysilicon rod fragment packages were randomly sampled from the cardboard box package, and the polysilicon rod fragments in each bag were sieved using a hand sieve with 5 mm meshes. The mass (g) of fine powder with a size of 5 mm or less that was obtained after sieving was measured, and the percentage of the polysilicon rod fragments packed in each bag (5 kg) was calculated and expressed as the average value for the five bags.

[0066] Furthermore, the same measurement was carried out on five randomly selected bags of packages of broken polysilicon rod fragments that were not subjected to the transportation test, and the percentage of fine powder (%) was determined and compared.

[0067] Example 1 A polysilicon rod P (4,000 kg) was prepared using the Siemens process, measuring 140 mm in diameter and 2,000 mm in length, and having a rod region P1 including a popcorn surface on part of its surface. In this polysilicon rod P, the popcorn surface was formed over approximately half of the circumference, from one end of the rod to near the middle of its length. Furthermore, the depth of the popcorn surface from the top of the undulations to the bottom of the grooves was approximately 1 to 30 mm, with locally scattered depressions exceeding 10 mm in depth.

[0068] The polysilicon rods P were crushed and sorted according to the "Flowchart for crushing polysilicon rods and sorting of crushed fragments" shown in Figure 1, and from the "cone mix sorting step S3" following the "rough crushing step S1" and the "crushing step S2", 2,000 kg of crushed fragments "without cone and no recesses", 1,200 kg of crushed fragments "without cone and recesses", 400 kg of crushed fragments "with cone and recesses", and 400 kg of crushed fragments "with cone and no recesses" were obtained. In the sorting of each of the above crushed fragment groups, crushed fragments with a major axis length of 70 to 160 mm were collected.

[0069] After the above, 240 kg of the above "without cone, with recess" fragments were used as the polysilicon bulk material to measure the likelihood of generating fine powder from the polysilicon rod fragments. The measurement was carried out by packing 5 kg of the above "without cone, with recess" fragments into polyethylene bags so that the particle size distribution graph (weight distribution and cumulative weight distribution) shown in Figure 5 was obtained (the maximum side length of the fragments was in the range of 10 to 110 mm, with a median of approximately 70 mm).

[0070] Here, each piece constituting the group of crushed pieces "without cones and with recesses" has a recess on its crushed surface with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, and the proportion of such recesses is 0.1 pieces / cm of the total surface area of ​​the crushed pieces. 2 The average number of fragments per 100 is 0.54 / cm 2 The average minimum diameter of the recesses was 0.80 mm.

[0071] The measurement result of the tendency for fine powder to be generated was 2.0%, which means that fine powder was generated significantly.

[0072] Next, for the group of fragments with the same properties, "without cone and with recesses," each fragment was subjected to the "chipping process S4." The chipping operation was carried out manually using a hammer with a striking part of 20 mm in diameter, a resin handle of 230 mm in length, and a total weight of 1,200 g. The chipping was carried out so that the proportion of recesses present on the fracture surface of each fragment was 0.1 pieces / cm of the total surface area of ​​the fragment. 2 In the polysilicon block after chipping, the average number of fragments (100 fragments) in the recesses relative to the total surface area of ​​the fragments was 0.08 pieces / cm. 2 The average minimum diameter of the recesses also decreased to 0.69 mm.

[0073] The 240 kg of fragments from which the recesses had been removed by chipping were used as the polysilicon block bulk material, and the likelihood of generating fine powder from the fragmented polysilicon rod fragments was measured in the same manner as in the measurement of the 5 kg fragments from the "without cones but with recesses" fragments before chipping. The fragments were packed into polyethylene bags to obtain the particle size distribution shown in Figure 5.

[0074] The measurement result of the fine powder was 0.7%, which means that the generation of fine powder was greatly reduced.

[0075] Reference example 1 In Example 1, the polysilicon bulk material for which the tendency to generate fine powder was measured was changed from the group of fragments "without cones and with recesses" to a group of fragments "without cones and with recesses," and the tendency to generate fine powder was measured in the same manner as for the polysilicon bulk material without being subjected to the "chipping step S4." The measurement result was 0.5%, which was a result of the generation of fine powder being as low as that of the group of fragments "without cones and with recesses" in Example 1, which had been subjected to chipping to remove the recesses.

[0076] Example 2 The group of fragments "without cone and with recess" obtained in the same manner as in Example 1 was subjected to the "chipping step S4" for each fragment. The chipping operation was carried out manually using a hammer with a striking part having a diameter of 20 mm, a resin handle part having a length of 230 mm, and a total weight of 1,200 g. The chipping was carried out by measuring the number of recesses on the fracture surface of each fragment so that the ratio of the recesses present on the fracture surface was 0.05 / cm with respect to the total surface area of ​​the fragment. 2 The same procedure as in Example 1 was carried out except that the treatment was continued until the following was performed.

[0077] The 240 kg of fragments from which the recesses had been removed by chipping were used as polysilicon bulk materials, and the tendency of the fragments to generate fine powder was measured in the same manner. In these polysilicon bulk materials, the average number of recesses relative to the total surface area of ​​the fragments (100 fragments) was 0.03 pieces / cm. 2 The average minimum diameter of the recesses was 0.53 mm, both of which had decreased.

[0078] The measurement result was 0.6%, which was lower than in Example 1 in terms of the amount of fine powder generated.

[0079] Example 3 The same procedure as in Example 1 was carried out, except that a group of 240 kg of crushed pieces "without cones and with recesses" was used, and the recesses formed on the crushed surface of each piece constituting the group of crushed pieces were as follows: That is, the recesses formed on the crushed surface were those with a minimum diameter of 1.5 to 4 mm and a depth of 5 mm or more, and the proportion of the recesses was 0.1 / cm of the total surface area of ​​the crushed pieces. 2 or more, with an average (100 fragments) of 0.57 fragments / cm 2 The average minimum diameter of the recesses was 0.85 mm.

[0080] When the likelihood of generating fine powder from the polysilicon rod fragments was measured for this bulk polysilicon mass, the measurement result for the likelihood of generating fine powder was 2.4%, indicating that fine powder was generated significantly.

[0081] Next, for the group of fragments with the same properties, "without cone and with recesses," each fragment was subjected to the "chipping process S4." The chipping operation was carried out manually using a hammer with a striking part of 20 mm in diameter, a resin handle of 230 mm in length, and a total weight of 1,200 g. The chipping was carried out by determining whether the proportion of recesses present on the fracture surface of each fragment was 0.01 pieces / cm of the total surface area of ​​the fragment. 2 In the polysilicon block after chipping, the average number of fragments (100 fragments) in the recesses relative to the total surface area of ​​the fragments was 0.008 fragments / cm. 2 The average minimum diameter of the recesses also decreased to 0.55 mm.

[0082] The 240 kg of fragments with the recesses removed by chipping were used as the polysilicon block raw material, and the likelihood of fine powder generation from the polysilicon rod fragments was measured in the same manner. The measurement result for fine powder was 0.55%, indicating a significant decrease in the generation of fine powder.

[0083] Example 4 In Example 1, the polysilicon block raw material for measuring the likelihood of fine powder generation was changed from the group of fragments with "no cone and with recess" to the group of fragments with "cone and with recess", and the state of fine powder generation was similarly tested.

[0084] In the above-mentioned group of crushed pieces "with cones and recesses," each piece has a recess on its crushed surface with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, and the proportion of such recesses is 0.1 pieces / cm of the total surface area of ​​the crushed pieces. 2 More than 0.32 particles / cm 2 The average minimum diameter of the recesses was 0.86 mm.

[0085] The measurement result of the tendency for fine powder to be generated was 2.3%, and the generation of fine powder was observed to be increased compared to Example 1.

[0086] In the subsequent "chipping step S4" for the group of crushed pieces "with cones and recesses," not only were the recesses present on the crushed surfaces removed, but essentially all of the popcorn-like surface was also removed.

[0087] The chipping removed both the cones and the recesses from the 240 kg of fragments, and the likelihood of generating fine powder from the polysilicon rod fragments was measured. The average number of recesses relative to the total surface area of ​​the fragments was 0.07 pieces / cm. 2 The average minimum diameter of the recesses was 0.61 mm, which was also a decrease.

[0088] The measurement result of the fine powder was 0.8%, which means that the generation of fine powder was greatly reduced.

[0089] [Table 1]

[0090] As shown in Table 1, the evaluation results for the Examples and Comparative Examples show that the higher the proportion of recesses on the polysilicon surface, the more easily fine powder is generated by vibration. 2 It has been experimentally shown that the rate of generation of fine powder increases more significantly when the density is above 0.1 / cm. In contrast, even when the rate of the presence of recesses on the polysilicon surface is high, the recesses are removed in a chipping process, and the rate of the presence of recesses is reduced to 0.1 / cm. 2 It was revealed that the generation of fine powder can be suppressed by setting the temperature to less than 100°C. [Explanation of symbols]

[0091] S1 Rough crushing process S2 crushing process S3 Corn mix sorting process S4 Chiseling process P Polysilicon rod P1 Rod region including popcorning surface

Claims

1. Regarding the polysilicon bulk material, which is a crushed piece collected from a group of crushed pieces obtained by crushing a polysilicon rod manufactured by the Siemens process, If any of the crushed pieces has a recess on the crushed surface with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, the recess is removed by chipping.

1. A method for producing polysilicon chunks, comprising:

2. 2. The method for producing polysilicon chunks according to claim 1, wherein the recess has an aspect ratio defined by the longest diameter / the smallest diameter of 10 or less.

3. In the fragments from which the recesses are chipped off, the ratio of the recesses to the total surface area of ​​the fragments is 0.1 pieces / cm ２ 3. The method for producing polysilicon chunks according to claim 1, wherein the proportion of the recesses is reduced to below the lower limit by chipping.

4. 3. The method for producing polysilicon chunks according to claim 1, wherein the polysilicon rods to be crushed include a popcorn-like surface having a high density of coarse undulations on a part of the surface of the rod.

5. In parallel with or before or after chipping and removing the recesses from the fragments in which the recesses exist, 5. The method for producing polysilicon chunks according to claim 4, wherein the popcorned surface of the broken pieces is also removed by chipping.

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