JP7585148B2 - Cut rod packaging - Google Patents

Description

The present invention relates to a package of multiple cut rods cut from a polycrystalline silicon rod produced by the Siemens process.

When polycrystalline silicon is melted in a crucible to produce silicon single crystals by the Czochralski (CZ) method, it has been required to load as much raw material as possible into the crucible at one time in order to produce a large single crystal. To meet this requirement, in actual operation, chips or granular raw material are often loaded to fill the gaps between the raw materials after loading L-size and S-size lump raw materials. This loading method is also advantageous in terms of reducing raw material costs because chips can be used effectively. However, even with this loading method, the surface area of each raw material is large and many gaps remain between the raw materials, so the raw material loading rate in the crucible does not increase sufficiently, and the amount of polycrystalline silicon that can be loaded into the crucible at one time is still limited, making it difficult to produce a large single crystal.

In order to solve this problem, a method for melting silicon single crystal raw material has been disclosed that can increase the amount of raw material loaded in a crucible beyond the current level without increasing the size of the crucible or the raw material loading level in the crucible, and further reduce the power costs required for melting (for example, see Patent Document 1 (Claim 1, paragraphs [0005], [0008], and [0009]). In this melting method, when polycrystalline silicon, which is a manufacturing raw material when manufacturing silicon single crystals by the CZ method, is melted in a crucible, a rod-shaped polycrystalline silicon (hereinafter referred to as a cut rod) cut from a crystalline silicon rod is loaded into the crucible and the polycrystalline silicon is melted.

Such cut rods have been widely used in recent years to increase the amount of raw material loaded into the crucible without increasing the size of the crucible or the raw material loading level in the crucible, and also to reduce the power costs required for melting. These cut rods are made by cutting them to an appropriate length (see, for example, Patent Document 2 (Claim 2)).

Japanese Patent Application Publication No. 11-100298 Patent No. 3496021

The total mass of polycrystalline silicon filled in the crucible when producing silicon single crystals by the CZ method is an important parameter for obtaining silicon single crystals of the desired size. When the polycrystalline silicon is made into the form of cut rods, as shown in Patent Document 1, there are many advantages, but as shown in Patent Document 2, when the cut rods are cut into multiple pieces of appropriate length from the polycrystalline silicon rod, the diameters of each piece vary. In addition, the high-purity polycrystalline silicon rod produced by the Siemens method has a roughly cylindrical shape with a distorted circle in cross section, and does not become a perfect circle (hereinafter referred to as a perfect circle) in cross section, and as mentioned above, the diameter also varies slightly depending on the point where it is measured. Therefore, even if multiple cut rods are cut to the same length, the mass of the cut rods varies. As a result, it was necessary to consider the excess or deficiency of the cut rods and the amount of lump-shaped polycrystalline silicon to be replenished, etc., relative to the target total filling mass in the crucible, while weighing each cut rod.

The object of the present invention is to provide a package for cut rods that can simplify the process of filling a crucible with polycrystalline silicon.

A first aspect of the present invention is a cut rod package in which a plurality of cylindrical cut rods cut from a cylindrical polycrystalline silicon rod are packaged in a single airtight packaging bag, characterized in that the total mass of the plurality of cut rods is a specific adjustment value , cushioning material is interposed between the plurality of cut rods, the plurality of cut rods are vacuum packaged in a state in which the plurality of cut rods are arranged to form a single cylindrical shape, and the plurality of cut rods are tightly attached and fixed to each other .
In this specification, the term "cylindrical" refers not only to a cylindrical shape that is a perfect circle with no distortion in cross section, but also to an approximately cylindrical shape that is not a perfect circle with a distortion in cross section.

A second aspect of the present invention is the invention based on the first aspect, characterized in that the number of the plurality of cut rods is any one of 2 to 6.

The fourth aspect of the present invention is an invention based on any one of the first to third aspects, characterized in that the specific adjustment value is a specific value within the range of 2500g to 15000g.

In the cut rod package of the first aspect of the present invention, a plurality of cut rods are packaged in a single airtight packaging bag, and the combined mass of the plurality of cut rods is a specific adjusted value. Therefore, when filling the crucible with polycrystalline silicon, if the cut rods are removed from the packaging material, the masses of the plurality of cut rods are known, so that the surplus or deficiency of cut rods and the amount of lump polycrystalline silicon to be replenished can be immediately calculated, simplifying the polycrystalline silicon filling operation.
Since a plurality of cut rods are vacuum-packaged and are fixed in close contact with one another, the cut rods can be packaged compactly while maintaining a clean state.
By placing a cushioning material between multiple cut rods, the cut rods are prevented from coming into direct contact with each other, and wear on the end faces of the cut rods due to contact or friction is prevented. This makes it possible to suppress the generation of silicon powder and chips due to collisions between the cut rods caused by vibrations during transportation of multiple cut rods.

In the cut rod packaging of the second aspect of the present invention, any number of 2 to 6 cut rods are arranged to form a single cylinder, and then vacuum-packed and any number of 2 to 6 cut rods are fixed in close contact with each other, so that the cut rods can be packaged compactly while maintaining their cleanliness.

In the cut rod package of the fourth aspect of the present invention, the specific adjustment value is a specific value within the range of 2500g to 15000g, so the package can be transported manually without using a special transport device. If it is less than 2500g, the number of packages tends to increase and the packaging work tends to become complicated. If it exceeds 15000g, it tends to become difficult to transport manually. A preferred specific adjustment value is 5000g to 11000g.

FIG. 2 is a diagram showing the process of packaging two cut rods into a package according to an embodiment of the present invention. This is a process diagram showing how 54 cut rods cut from six crystalline silicon rods are combined into two rods and then packaged.

Next, a description will be given of an embodiment of the present invention with reference to the drawings. The example of creating a package in which two cut rods are packaged as shown in the following Figures 1 and 2 is just one example, and the number of cut rods is not limited to two, but can be increased to three to six as necessary. Also, the method of combining two rods is just one example, and is not limited to this method.

As shown in FIG. 2, in this embodiment, six cylindrical polycrystalline silicon rods are prepared, and the long and short diameters of each polycrystalline silicon rod are measured. From these long and short diameters, the length of the rod is determined so that the volume is constant and the target mass of the polycrystalline silicon rod is 2504 g per rod, assuming that the weight is reduced by 4 g by washing with fluorinated and nitric acid in a subsequent process. The six polycrystalline silicon rods having an approximately cylindrical shape (hereinafter referred to as cylindrical) are cut into 54 cut rods.

The resulting 54 cut rods are placed in a plastic basket with many holes, and the basket is then immersed in an etching bath of oxidizing fluoronitric acid (a mixture of hydrofluoric acid and nitric acid) to etch and clean the 54 cut rods and remove impurities and natural oxide films from the surfaces of the cut rods. After cleaning, the cut rods are divided into groups of nine and placed in separate baskets with many holes. In this state, all the cut rods are immersed in pure water and rinsed. After rinsing, the 54 cut rods are placed in a dryer while still in the basket, and vacuum dried.

After drying, each of the 54 cut rods is visually inspected for any abnormalities in appearance, and those that pass the inspection are numbered in order and placed on a plastic sheet, such as polyethylene. In this embodiment, 4 do not pass the inspection, leaving 50 cut rods numbered (No. 1 to No. 50). The actual mass values of each are entered into a computer. This creates a database of actual mass values for the total of 50 rods that make up the population of 50 cut rods.

From this database, the computer combines two cut rods so that the total mass of the two cut rods is the target value (5000g). In other words, the computer performs the work of combining two cut rods so that the total mass of the two cut rods is a specific adjustment value. For example, the maximum actual mass value (1) to the minimum actual mass value (50) are arranged on the computer, and the following primary combination is performed. The actual mass value (1) and the actual mass value (50), the actual mass value (2) and the actual mass value (49), the actual mass value (3) and the actual mass value (48), ..., the actual mass value (25) and the actual mass value (26) are combined. If the total mass of the two cut rods is within the tolerance range (5000g ± 50g) close to the target value (5000g) in the primary combination, it is considered to be passed, and the work is completed with the primary combination. Based on the numbers of the two cut rods that have been combined, each of the two cut rods is picked up from the population by hand or an automatic sorting machine and combined. The specific adjustment value is a value within the range of 5000g ± 50g (same below).

If the result of the primary combination is that the total weight of the two cut rods is far from the target value (5000g) and outside the tolerance range (5000g ± 50g), the two cut rods that are furthest from the mass target value (2500g) are deleted from the database, and a secondary combination is performed on the remaining 48 rods in the same manner as the primary combination, based on the database of the 48 rods that remain. If the total weight of the two cut rods in the secondary combination is within the tolerance range (5000g ± 50g) and close to the target value (5000g), it is deemed to have passed, and the work ends with the secondary combination. Based on the numbers of the two combined cut rods, each of the two cut rods is picked up from the population either manually or by an automatic sorting machine and combined.

Then, n-th combination (n is an integer of 3 or more) is performed until the total mass falls within the allowable range (5000g ± 50g), and based on the numbers of the two combined cut rods, each of the two cut rods is picked up from the population manually or with an automatic sorting machine and combined. In this way, two cut rods are prepared whose total mass falls within the allowable range (5000g ± 50g).

Next, as shown in Figure 1(a), two combined cut rods 1 and 2 and a cushioning material 3 made of plastic, such as polyethylene, are prepared. As shown in Figure 1(b), clean cushioning material 3 is placed on the top surface of cut rod 1, and cut rod 2 is placed on top of that. In this way, the two cut rods 1 and 2 are arranged so that they form a single cylinder with the cushioning material 3 in between. If there are three cut rods, the total axial length of the cut rods that form a single cylinder will be greater than when there are two.

It is preferable to place the cushioning material 3 between the cut rods 1 and 2 to avoid direct contact between the cut rods and to prevent wear on the end faces of the cut rods due to unexpected contact friction. The two cut rods 1 and 2 arranged in this manner are housed in a clean plastic bag 4 that is open at the top and has an airtight bottom to prevent air from passing through. The plastic bag 4 has a volume sufficient to house the two cut rods 1 and 2.

Finally, as shown in FIG. 1(c), the air inside the plastic bag 4 is sucked out from the opening of the plastic bag 4 using an air suction machine (not shown), and the two cut rods 1, 2 are vacuum-packaged with the cushioning material 3 between them. This vacuum packaging causes the two cut rods 1, 2 to be tightly attached and fixed to each other. After that, the two cut rods 1, 2 are packaged in yet another plastic bag (not shown) if necessary, and then placed in a cardboard box for packaging.

When filling a crucible with cut rods to manufacture silicon single crystals by the CZ method, the two cut rods 1 and 2 in the vacuum-packaged plastic bag 4 shown in Figure 1 (c) are within the target allowable range of 5000 g (5000 g ± 50 g), so the excess or shortage of cut rods and the amount of lump polycrystalline silicon to be replenished can be calculated immediately, and the polycrystalline silicon can be easily filled by removing it from the vacuum-packaged plastic bag.

In the above embodiment, an example of combining two cut rods has been described, but when combining three to six cut rods, the total number of cut rods from the cut rod with the maximum actual mass value to the cut rod with the minimum actual mass value are arranged on a computer, and the population consisting of this total number is then divided into three to six. Cut rods are extracted from each of the divided child populations and combined in the same manner as above. The method of combining cut rods is not limited to the above method. The total target mass value of 5000g for two cut rods is just one example, and it is sufficient that the total mass of multiple cut rods is within a specific adjustment value, for example, within the range of 2500g to 15000g. The specific adjustment value of 5000g ± 50g can be determined as appropriate.

Furthermore, the precision of the total mass of the cut rods after combining them is in a trade-off relationship with the loss rate of the cut rods that fall out of the combination and the number of cut rods in one set. Increasing the number of cut rods in one set increases the amount of work required, but the precision of the total mass of the cut rods after combining them can be improved. For the above reasons, the number of cut rods to be combined is preferably 2 to 6, and more preferably 2 to 3. If there are seven or more cut rods, the work required for combining increases too much, which is not preferable.

Next, we will explain in detail the examples of the present invention along with comparative examples.

Example 1
The target mass value was set to 5050 g and the allowable range was set to 5050 g ± 50 g for each of the two cut rods. For five cylindrical polycrystalline silicon rods (diameter 115 mm to 135 mm) manufactured by the Siemens process, the carbon electrode portion was cut off, and the diameter was measured in two perpendicular directions around the cut portion. From the cross-sectional area obtained assuming an ellipse, a cut length was determined to set the set mass to 2529 g, taking into account 2525 g, which is half of 5050 g, and an assumed weight loss of 4 g due to fluorine-nitric acid cleaning, and the five cylindrical polycrystalline silicon rods were cut to obtain 49 cylindrical cut rods.

After the 49 cut rods were washed with fluorinated nitric acid, dried, and visually inspected and weighed, they were combined in pairs of two cut rods using the method described above, with the target mass set at 5050 g and the tolerance set at 5050 g ± 50 g. The specific adjustment value was 5050 g ± 50 g. Finally, 24 combinations were made, with one cut rod being excluded from the combinations. Each combination of two cut rods was vacuum-packed in a plastic bag. Since 48 cut rods could be combined from the 49 cut rods, the yield was 98%. The two vacuum-packed cut rods were known in mass when they were filled into a crucible to manufacture silicon single crystals by the CZ method, making the filling process easier.

<Comparative Example 1>
The target mass value for one cut rod was set to 5050 g, and the allowable range was set to 5050 g ± 50 g. For five cylindrical polycrystalline silicon rods (diameter 115 mm to 135 mm) manufactured by the Siemens process, the carbon electrode portion was cut off, and the diameters were measured in two perpendicular directions around the cut portion, and from the cross-sectional area obtained assuming an ellipse, a cutting length was determined to set the set mass to 5058 g, taking into account the target mass value of 5050 g and an assumed weight loss of 8 g due to fluorinated nitric acid cleaning, and 25 cylindrical cut rods were obtained by cutting the five cylindrical polycrystalline silicon rods.

After the 25 cut rods were washed with fluoronitric acid, dried, visually inspected, and weighed, the mass of each cut rod was measured and those weighing 5000g to 5100g were individually packed in plastic bags. When the mass was measured, 14 cut rods were between 5000g and 5100g. Since 11 cut rods were outside the range of 5000g to 5100g, the yield was 56%. If the 25 cut rods were packed in plastic bags without being weighed after washing with fluoronitric acid, drying, and visually inspecting, it would be necessary to weigh the mass of each cut rod before filling the crucible to manufacture silicon single crystals by the CZ method, which could be cumbersome and could extend the filling time.

The cut rod packaging of the present invention can be used when melting polycrystalline silicon in a crucible to produce silicon single crystals by the CZ method.

1, 2 Cut rod 3 Cushioning material 4 Plastic bag

Claims (3)

A cut rod package in which a plurality of cylindrical cut rods cut from a cylindrical polycrystalline silicon rod are packaged in an airtight packaging bag,
the total mass of the plurality of cut rods is a specific adjustment value;
A cut rod package characterized in that the cut rods are arranged in a cylindrical shape with cushioning material interposed between them, and vacuum-packaged, and the cut rods are tightly attached and fixed to each other . 2. The cut rod package according to claim 1, wherein the number of said plurality of cut rods is any one of 2 to 6. 3. The cut rod packaging body according to claim 1 or 2 , wherein the specific adjustment value is a specific value within a range of 2500 g to 15000 g.

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