Method for producing polysilicon lump material

Abstract

The purpose of the present disclosure is to provide a method for obtaining a polysilicon lump material from a group of crushed pieces that are obtained by crushing a polysilicon rod produced by a Siemens method, by a simple methodi n which the generation of fine powder is highly suppressed. A method for producing a polysilicon lump material according to one embodiment of the present disclosure is characterized in that, with respect to polysilicon lump starting materials which are crushed pieces taken from a group of crushed pieces that are obtained by crushing a polysilicon rod produced by a Siemens method, in cases where the crushed pieces include a crushed piece in which a recessed part that has a minimum diameter of 0.5-5 mm and a depth of 1 mm or more is present on a crushed surface, the recessed part is removed by means of chipping, and more preferably, in cases where the recessed part is present at an abundance ratio of 0.1 or more per cm2 with respect to the total surface area of the crushed piece, the removal by means of chipping is performed until the abundance ratio of the recessed part falls to less than the lower limit value.

Description

Method for producing polysilicon chunks

[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.

[0002] The Siemens process is a known method for producing polysilicon. In the Siemens process, a silicon core wire placed inside a bell-jar-shaped reaction vessel is heated to a silicon deposition temperature by passing an electric current through it, and trichlorosilane (SiHCl) is introduced into the wire. ３ ) and monosilane (SiH ４ In this method, a silane compound gas such as silane fluoride (H2O) and hydrogen are supplied to deposit polysilicon on a silicon core wire by chemical vapor deposition, thereby obtaining 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, as well as discoloration, and methods have been proposed to classify those having such irregularities according to their state. Some of these methods are intended to distinguish chunks that have a rod surface with a dense concentration of coarse undulations, a so-called popcorn surface, formed due to an 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, rather than crushing the rod as described above and then removing the agglomerates including the defective surface, it is also known to first strike and remove the defective surface layer portion while the polysilicon rod is still in the state of a polysilicon rod, so that the agglomerates including the popcorn-like surface are not included in the group of crushed pieces (Patent Document 3).

[0007] Japan Special Table No. 2022-537014 Publication Japanese Special Table No. 2016-516666 Publication Japanese Special Table No. 2022-547425

[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 remaining agglomerates after removing the popcorn-like surfaces. However, simply removing the agglomerates containing popcorn-like surfaces in this manner still leaves the remaining polysilicon agglomerates with a certain amount of material that is likely to generate fine powder, and the problem of fine powder generation could not be fully resolved.

[0009] Furthermore, Patent Document 3 discloses that the popcorn-like surface of a polysilicon rod is removed using a hammer. However, precisely removing this defective surface layer from the arc-shaped surface of a large-diameter polysilicon rod by hammering is highly difficult, and 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.

[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 off the depression (hereinafter referred to as "chipping removal").This finding led to the completion of the present invention.

[0012] That is, the present invention provides a method for producing a polysilicon block, which comprises the steps of: obtaining polysilicon block bulk fragments, which are fragments collected from a group of fragments obtained by crushing a polysilicon rod produced by the Siemens process; and, if any of the fragments has a depression on its fracture surface that is 0.5 to 5 mm in minimum diameter and 1 mm or more in depth, chipping away the depression.

[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.

[0014] Figure 1 is a schematic diagram showing an example of a process for crushing polysilicon rods and separating fragments suitable for incorporating the method of the present invention. Figure 2 is a photograph of a representative example of fragments containing the popcorn-like rod surface collected from fragments obtained by crushing a polysilicon rod. Figure 3 is a photograph of a representative example of fragments obtained by crushing a polysilicon rod, the fragments having the recesses on the crushed surface. Figure 4 is a graph showing vibration data measured with a vibrometer installed on the truck bed during a transportation test in measuring the likelihood of fine powder generation from polysilicon chunks in the Examples and Comparative Examples. Figure 5 is a graph showing the particle size distribution of polysilicon rod fragments packed in polyethylene bags when measuring the likelihood of fine powder generation from polysilicon rod fragments in the Examples and Comparative Examples.

[0015] In order to solve the above-mentioned problems, in one embodiment of the present invention, a method for producing polysilicon chunks uses a group of crushed pieces obtained by crushing a polysilicon rod produced by the Siemens process as a bulk polysilicon chunk. The polysilicon rods produced by the Siemens process can be produced by any known method, including the chemical vapor deposition (CVD) method, for depositing polysilicon on a silicon core. 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 example of a fragment containing the popcorned rod surface, 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 Furthermore, on the popcorned surface, the length from the top of the undulations to the bottom of the grooves is usually about 1 to 30 mm, and locally there are scattered depressions that are deeper than 10 mm. The deepest depressions can be as deep as about 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 in each region separately, and subject only the crushed fragments obtained from the former cut rod to the present embodiment.

[0020] In this embodiment, the polysilicon rods 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 account applications such as raw materials for the production of single-crystal silicon, as well as the ease of chipping and removing recesses present on the crushed surfaces (described below), 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 grasp. Therefore, the crushed fragments may be classified into the desired particle size and then used as polysilicon chunks in this embodiment. 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 shown in Figure 3, the multiple black hole 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 to have a significantly reduced amount of fine powder generated, 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 whose both ends are 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 is often a complex shape where cleavage planes intersect and large depressions, protrusions, etc. intersect, as described below. Therefore, the periphery of the recess that opens 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 every target piece each time to determine whether it is to be removed by chipping. If it can be visually determined that the piece falls within this range, it may be visually determined and used for chipping. 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 fractured 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, the recesses are often formed by the bottoms of the grooves formed 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 fractured surface on the front side of the paper 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 bottoms of the locally deep 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, on the popcorned surface, as mentioned above, there are scattered grooves with depths exceeding 10 mm 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 precisely remove the defective surface layer, 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 with respect to the total surface area of ​​the fragments. ２ or more (the upper limit of the proportion of recesses is usually 1.0 / cm ２ ), the generation of fine powder when vibration is applied becomes more severe. Therefore, when the proportion of such recesses is 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 manner, it is preferable that the average ratio of the recesses present among 100 randomly selected fragments is also reduced to the value above.

[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 away the recesses in the fragments is generally performed manually using a hammer or other impact tool, but in some cases, an electric chipping hammer or the like may also be used. The hammer used for manual chipping 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 5,000 g, preferably 500 to 4,000 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 sufficient 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, more preferably 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 process for crushing polysilicon rods and sorting the 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 the rod region P1 including the popcorn surface is divided from 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 ("corn-free" crushed pieces), which exhibit good properties such as being 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 further 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 and recess" and "with cone and recess" fragments in the four fragment fractions, which is the greatest feature of the method shown 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" fragments, it is preferable to also chip and remove the popcorn surface portions from the "with cone and recess" fragments and the "with cone and no recess" fragments. That is, as mentioned above, the popcorn surface of the polysilicon rod exhibits a property that is particularly prone to generating fine powder, so it is advantageous to also remove this portion from fragments having such a popcorn surface in order to reduce the total amount of fine powder generated in the resulting 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 bottoms of the grooves on the removed surface.

[0046] Thus, by undergoing the chipping step S4, even if only a very 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 separate them 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 a polysilicon block, comprising the steps of: obtaining polysilicon block bulk fragments from a group of fragments obtained by crushing a polysilicon rod produced by the Siemens process; and, if any of the fragments has a depression on its fracture surface with a minimum diameter of 0.5 to 5 mm and a depth of 1 mm or more, chipping away the depression.

[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 rod to be crushed includes a popcorned surface having a densely packed coarse undulations on a part of the surface of the rod.

[0053] Aspect 5: The 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 surfaces of the fragments including the popcorned surfaces is also carried out.

[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 each fragment to measure the minimum diameter of the recess. The average value of the minimum diameter of the recess was also calculated based on the results of the 100 fragments.

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

[0058] [Ratio of Presence of Depressions] In determining the ratio of presence of depressions, 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 required for determining 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 polysilicon from the obtained mass, and converting the obtained 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 crushed pieces calculated from the mass was used to calculate the ratio of recesses (number / cm ２ )

[0061] [Size of Polysilicon Fragment] The size of the polysilicon fragment 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 kg of the polysilicon rod fragments to be measured were packed into an 8.5 L polyethylene bag and sealed. Six of the bags were packed into a 50 L cardboard box and subjected to a transportation test of approximately 400 km round trip (approximately 200 km one way). These conditions correspond to the general transportation conditions for polysilicon block products. The cardboard box was loaded into the rear of the loading space of a transportation 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 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 the truck starts moving, 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 the truck 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, five bags of the polysilicon rod fragment packages were randomly sampled from the cardboard box after the transportation test, 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 as the undersieve was measured, and the percentage of the amount of 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. The rod had a diameter of 140 mm, a total length of 2,000 mm, and a rod region P1 including a popcorned surface on part of its surface. The popcorned surface of this polysilicon rod P covered approximately half of the circumference, from one end of the rod to the middle of its total length. The depth of the popcorned 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.

[0068] The polysilicon rod P was 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 cones and no recesses, 1,200 kg of crushed fragments without cones and recesses, 400 kg of crushed fragments with cones and recesses, and 400 kg of crushed fragments with cones and no recesses were obtained. In the sorting of each of the 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 "without cone, with recess" fragments were used as the bulk polysilicon rod fragments to measure the likelihood of generating fine powder. The measurement was carried out by packing 5 kg of the "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 the recesses is 0.1 pieces / cm of the total surface area of ​​the crushed pieces. ２ or more, with an average (100 fragments) of 0.54 fragments / 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%, indicating 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 step S4." The chipping operation was performed 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 performed by measuring the number of recesses on the surface of each fragment to determine whether the number of recesses was 0.1 / cm2 relative to the total surface area of ​​the fragment. ２In 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 fragments / cm. ２ The average minimum diameter of the recesses was also reduced 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 for the 5 kg fragments from the "without cones but with recesses" fragments before chipping. The fragments were packed into polyethylene bags so as to have 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 a cone and with recesses to a group of fragments without a cone and with recesses. This was used as a polysilicon bulk material without being subjected to the chipping step S4, and the tendency to generate fine powder was measured in the same manner. The measurement result was 0.5%, which was about the same as the result of removing the recesses by chipping the group of fragments without a cone and with recesses in Example 1.

[0076] Example 2: For the group of "coneless, recessed" fragments obtained in the same manner as in Example 1, each fragment was subjected to the "chipping step S4." The chipping operation was performed 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 performed such that the proportion of recesses present on the fracture surface of each fragment was 0.05 pieces / cm of 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 likelihood of generating fine powder from the polysilicon rod fragments 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, which was a decrease.

[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 below had the following characteristics: That is, the recesses formed on the crushed surface had 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] 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 step S4." The chipping operation was performed 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 performed by measuring the number of recesses on the surface of each fragment to determine whether the number of recesses was 0.01 / cm2 relative to the total surface area of ​​the fragment. ２ In the polysilicon block after chipping removal, 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 was also reduced to 0.55 mm.

[0082] 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 the fragments of the polysilicon rods generating fine powder 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 a group of fragments with "cone and with recess," and the state of fine powder generation was tested in the same manner.

[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 the 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 also substantially all of the popcorn-like surfaces were removed.

[0087] The 240 kg of fragments from which both the cones and the recesses had been removed by chipping were similarly measured for the likelihood of generating fine powder from the polysilicon rod fragments. 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]

[0090] As shown in Table 1, the evaluation results for the Examples and Comparative Examples, 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 rate 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.

[0091] S1 Rough crushing process S2 Crushing process S3 Corn mix sorting process S4 Chip chipping process P Polysilicon rod P1 Rod region including popcorn surface

Claims

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. 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. 　 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.

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. 　 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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