JP2009249013A - Silicone packaging method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and surely prevent the generation of the catastrophic oxidation phenomenon called spots on the surface of polycrystalline silicone crushed lump during the storage of the lump in a bag. <P>SOLUTION: A silicone product 10 packed with a predetermined amount of crushed silicone lump in a bag is sealed in a large polyethylene sheet bag 20, and the bag 20 is airtightly enclosed in a moisture barrier packing material 40 made of a SiO deposition film. A plurality of desiccating agents 50 made of silica gel, etc. are placed between the bag 20 and the material 40. The inside of the material 40 is kept at a low-moisture atmosphere. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for packing polycrystalline silicon crushed lump used for semiconductor raw materials or solar cell raw materials.

  Polycrystalline silicon used as a silicon single crystal raw material, a solar cell raw material, or the like is manufactured as a rod by a vapor phase method called a Siemens method. Polycrystalline silicon rods manufactured by the Siemens method are often packaged in the form of crushed lumps and shipped to users such as silicon single crystal manufacturers. The crushed pieces of polycrystalline silicon are called chunks, clamps, nuggets, etc. After the rods are crushed, first, hydrofluoric acid, which is a mixture of hydrofluoric acid and nitric acid, is used to remove metal impurities attached to the surface. Etching with aqueous solution. Subsequently, it is subjected to a water washing treatment and a drying treatment, and then, in order to prevent re-contamination of the surface, a plurality of bags are packed and shipped. A polyethylene bag is generally used as the packaging material.

  One problem with such bagged bulk polycrystalline silicon products is that spots may form on the surface of the silicon mass during storage. This stain is a coloring phenomenon in which a part of the surface of a part of the silicon lump is changed to brown, and the prevention from the user who needs a high-purity raw material is strongly demanded. And as one of the countermeasures against the spot, Patent Document 1 proposes to convert Si—H bonds existing on the surface of the silicon lump after the etching process into Si—O bonds.

Japanese Patent No. 2834600

This measure is based on the knowledge that the cause of the stain is an abnormal oxide film on the surface of the silicon lump after the etching process, more specifically, the Si-H bond. By irradiating the surface of the substrate with microwaves or high-temperature air in an oxygen-containing atmosphere, the Si-H bonds existing on the surface are converted into Si-O bonds, and the entire surface of the silicon lump is healthy. It is covered with an oxide film (SiO ₂ ).

  However, in the case of this measure, it is necessary to irradiate the whole surface of each irregular crushed lump with microwaves or high-temperature air without any unevenness. Not technically easy. Furthermore, as will be described later, it is common for the crushed pieces of polycrystalline silicon to be put into a basket by a predetermined amount and subjected to etching treatment, washing treatment, and drying treatment. It is difficult to uniformly irradiate waves or high-temperature air, and in order to irradiate the entire surface of each crushed lump with microwaves or high-temperature air without any unevenness, individual crushed lump from batch processing with scissors Conversion to treatment is required.

  For this reason, there is a problem that this measure is inefficient and uneconomical, and it cannot be said that there is no problem in effectiveness. Under such circumstances, there is a demand for a measure that can reliably prevent spots generated on the surface of the bag-filled polycrystalline silicon lump by a simple method.

  An object of the present invention is to easily and surely prevent the occurrence of an abnormal oxidation phenomenon called a stain on the surface of a packed bulk silicon product.

  In order to achieve the above object, the present inventors investigated the cause of the occurrence of stains from various angles. As a result, the following facts were found.

  Etching, washing with water, and drying of the crushed polycrystalline silicon are performed as follows. A predetermined amount of silicon lump is placed in an acid-resistant tub and immersed in a hydrofluoric acid mixed solution in an etching tank. In the next washing step, the soot pulled up from the etching bath is immersed in pure water in the washing bath. It sends to several washing tanks in order and raises the cleanliness step by step. Alternatively, it is treated with running water in a single washing tank. Finally, drying is performed. In the final drying step, the silicon lump in the basket pulled up from the washing tank is treated with warm air or the like.

  Since the plurality of silicon chunks housed in the basket are crushed chunks with a complicated shape, a sufficient gap is formed between adjacent silicon chunks, and there is an etching solution, pure water for washing, and temperature for drying. Because the wind etc. can pass sufficiently, in any process, the individual silicon chunks in the cage are treated without any problem, and as a result, the etching solution components and moisture remain on the surface of the dried silicon chunk. It was thought not. However, when a component of an abnormal oxide film portion called a stain generated during the storage period was analyzed, a very small amount of fluorine component was confirmed from that portion. The fluorine component is considered to be a fluorine component in the etching solution, and it is known that if the fluorine component is present on the surface of the silicon lump, the progress of oxidation may be accelerated in the atmosphere. .

  Based on such facts, the present inventors investigated the possibility that an etchant component remains on the surface of the crushed polycrystalline silicon lump. As a result, the following became clear. The surface shape of the polycrystalline silicon crushed lump is a complex indefinite shape in which large and small irregularities are combined in a complex manner. Further, in the normal water washing step, as described above, a plurality of crushed lumps are placed in a basket as one lot for washing. For these reasons, even if careful rinsing treatment is performed, there is an unavoidable risk that the washing liquid will stay in the concave portions of the complex shape of the crushed lump and the contact portion between the crushed lump.

  That is, in the case of a crushed piece of polycrystalline silicon, it is virtually impossible to completely avoid the situation where the drainage is locally insufficient due to the shape of the lump and the water washing method. In this case, it is impossible to completely eliminate the concern that the fluorine component remains due to insufficient draining. And in the portion where draining is insufficient, even if the drying proceeds as it is, it is unavoidable that more components in the liquid remain than the other portions, so that the portion may develop into an abnormal oxide called a stain.

  Apart from this, the present inventors have found that abnormal oxides called stains are generated in bagged silicon lumps when they are stored in a hot and humid environment in the summer, based on many years of research. When storing silicon lumps in a low-temperature, low-humidity environment in winter, etching, washing, and drying are performed under the same conditions, although abnormal oxidation should not occur. Experiences that things tend to be less likely to occur.

  The present inventors paid attention to the difference in the state of occurrence of abnormal oxide due to the difference in storage environment, and thought that the change in the atmosphere in the bag due to the difference in storage environment was also involved in the generation of abnormal oxide. In other words, the crushed mass of polycrystalline silicon is sealed in a bag made of polyethylene film, but the polyethylene bag is highly permeable to moisture, and the moisture penetrates into the bag when exposed to high temperatures and humidity. To do. The moisture permeated into the bag is also involved in the generation of abnormal oxides in the silicon mass packed in the bag. More specifically, the moisture permeated into the bag remains in a part of the silicon mass in the bag. The present inventors thought that an abnormal oxide called a stain was generated by combining with components. This also coincides with the idea that when the fluorine component is present on the surface of the silicon block, the progress of oxidation is promoted in the atmosphere.

  From these facts, the present inventors believe that maintaining the inside of the bag in a low-humidity environment by selecting the material of the bag for packing the silicon mass of polycrystalline silicon is effective in suppressing the generation of abnormal oxides. Various experiments were repeated. As a result, it is effective to take measures such as changing the packaging material from polyethylene film to a material with water vapor barrier property, or double packaging with a bag of water vapor barrier material material from above the polyethylene bag. Has proved effective to put a desiccant in the bag. By the way, in the case of polyethylene bags, even if the silicon lump is packed in a clean room where the temperature and humidity are controlled, moisture will permeate if the storage environment becomes hot and humid, and if left in a room temperature environment, Condensation may occur and the surface of the silicon mass inside may get wet, and as long as the fluorine component remains on the surface of the silicon mass, it can be confirmed that it is difficult to prevent abnormal oxides without using packaging materials. It was.

The present invention has been completed on the basis of such knowledge. One or a plurality of bulk silicon obtained by crushing polycrystalline silicon has a water vapor transmission rate of 1.0 g / m ² day (temperature: 40 ° C., The gist of the present invention is a silicon packaging method characterized by packaging with a packaging material having a water vapor barrier property having a humidity of 90% RH or less.

  Specifically, the bulk silicon is packed into a plurality of layers with a plurality of packing materials, such as a polycrystal silicon crushed lump is put into a polyethylene bag, and it is packaged with a packaging material having a water vapor barrier property. It is effective to use a packaging material having a water vapor barrier property for at least one other than the above. This is because, if a packaging material having a water vapor barrier property is disposed in the innermost layer, there is a risk that the water vapor barrier property may be deteriorated due to damage by the horny silicon lump.

  According to the silicon packing method of the present invention, moisture penetration from the outside to the inside of the packing material is suppressed, so that the storage environment of the packing material, that is, the silicon lump can be maintained in a low-humidity atmosphere. Generation of abnormal oxides can be prevented. Preferably, a desiccant is arrange | positioned inside by the packaging material with water vapor | steam barrier property. In this way, moisture that has penetrated inside is also absorbed by the desiccant, and the generation of abnormal oxides called stains can be more effectively prevented. The preferable atmosphere inside the packaging material is 70% or less in humidity regardless of summer or winter. When the humidity inside the packaging material is 70% or less, it is possible to stably prevent a risk that an abnormal oxide called a stain is generated in a part of the silicon lump inside the packaging material during storage for a long period of time. .

  As a packaging material having a water vapor barrier property, a SiO deposited film obtained by depositing SiO on a base film is effective in terms of performance and economy. Even if the packaging material has a water vapor barrier property, it does not transmit water vapor at all, and a slight water permeation is inevitable, so it is more effective to keep the humidity inside the packaging material constant by adding a desiccant. It is.

The performance of a packaging material having a water vapor barrier property is represented by a water vapor transmission rate. The smaller this value is, the better the water vapor barrier property is, and it is suitable for packing silicon lump, while the one with low water vapor permeability is expensive. Considering these, the water vapor permeability of the packaging material having a water vapor barrier property is preferably 1.0 g / m ² day (temperature 40 ° C., humidity 90% RH) or less. If the water vapor transmission rate is larger than this, moisture penetration into the packing material increases, and it becomes difficult to suppress the occurrence of stains, and the burden on the desiccant increases, resulting in a deterioration in economic efficiency. As for satisfying such water vapor transmission rate, aluminum vapor deposition film (water vapor transmission rate of 0.7 to 1.0 g / m ² day (temperature 40 ° C., humidity 90% RH)), SiO vapor deposition film [water vapor transmission rate] The rate is about 0.1 to 0.7 g / m ² day (temperature 40 ° C., humidity 90% RH).

On the other hand, an alumina vapor-deposited film, which is a vapor-deposited film, has a water vapor transmission rate as large as about 1.5 g / m ² day (temperature 40 ° C., humidity 90% RH) and cannot be used. On the other hand, the water vapor permeability of the polyethylene film is 10 to 20 g / m ² day (temperature 40 ° C., humidity 90% RH). Considering the possibility of mixing P-type impurities in the characteristics of the semiconductor, it is necessary to give more consideration to the aluminum-based vapor deposition film so that it does not come into direct contact with the silicon block. Non-aluminum-based SiO deposited films are easy to use and have a low water vapor transmission rate.

  There are calcium chloride, quicklime, silica gel, aluminosilicate, etc. as the desiccant to be put inside the packing material, but silica gel or aluminosilicate that does not cause deliquescence (liquefaction due to moisture absorption) is preferable from the viewpoint of guaranteeing the quality of the product silicon lump. . Among the silica gels, A-type silica gel is particularly preferable from the viewpoint of keeping the humidity inside the packing material constant. The amount of the desiccant used is determined according to the ability of the desiccant so as to absorb the amount of moisture permeation predicted from the hydrogen barrier property and the storage days of the packaging material to be combined.

  The operation of packing the silicon lump into the packing material is preferably performed in a low-temperature and low-humidity atmosphere, and the initial atmosphere in the packing material is preferably set to low-temperature and low-humidity. A preferable atmosphere is specifically a temperature of 18 to 22 ° C. and a humidity of 30 to 50%. This is especially important when no desiccant is used.

  The silicon packing method of the present invention prevents the generation of stains by preventing the trace amount of fluorine components present on the surface of the crushed polycrystalline silicon from reacting with moisture. It is effective for packing the received silicon mass. As a cleaning liquid containing fluorine, a hydrofluoric acid solution, which is a mixed liquid of hydrofluoric acid and nitric acid, has a high etching ability and is generally used as a cleaning liquid for a silicon lump. Even in a silicon lump that is used to remove an oxide film covering the surface and has been treated with these cleaning liquids, stains due to residual fluorine components become a problem. For this reason, this invention is effective also to the silicon lump which received the process by the washing | cleaning liquid containing fluorine other than a hydrofluoric acid solution.

  Since the silicon packing method of the present invention can keep the inside of the packing material in a low-humidity atmosphere by using a packing material having a water vapor barrier property for packing bulk silicon obtained by crushing polycrystalline silicon, Occurrence of the abnormal oxide called can be prevented regardless of the season, and high-quality products can be stably supplied to users. This effect can be further enhanced by placing a desiccant in the packing material.

  Embodiments of the present invention will be described below with reference to the drawings. 1 (a), (b) and (c) are schematic views showing an embodiment of the silicon packing method of the present invention in comparison with a conventional silicon packing method, where (a) is a conventional method and (b) is a conventional method. 1st Embodiment of this invention, (c) shows 2nd Embodiment of this invention, respectively.

  In the conventional silicon packing method, as shown in (a), a plurality of silicon lumps obtained by crushing rod-shaped polycrystalline silicon produced by the Siemens method are sealed in a double polyethylene bag for products. Has been. Each silicon lump has been subjected to an etching cleaning process, a water cleaning process, and a drying process using a hydrofluoric acid solution using acid-resistant soot. The bag-packed silicon product 10 is sealed in a large bag 20 made of a polyethylene sheet, with a predetermined number as one unit, and stored in a pallet 30 of a returnable container. As described above, in such a silicon packing method, it is inevitable that an abnormal oxide called a stain is generated in a part of a part of a silicon lump during storage, particularly in a high temperature and high humidity period.

  On the other hand, in the silicon packing method of the first embodiment shown in FIG. 1B, the large bag 20 made of a polyethylene sheet containing a predetermined number of bag-packed silicon products 10 is replaced with a water vapor barrier packing material 40 made of a SiO vapor-deposited film. It is hermetically sealed inside and is stored in the pallet 30 in this state. A plurality of desiccants 50 made of silica gel are arranged in the water vapor barrier packing material 40 so as to surround the large bag 20.

  In the silicon packing method of this embodiment, since the bag-packed silicon product 10 is packed with the water vapor barrier packing material 40 having a low water vapor transmission rate, the penetration of moisture from the outside into the packing material is suppressed. The slight moisture that has penetrated into the packaging material is also absorbed by the desiccant 50. Thereby, the humidity in the water vapor barrier packing material 40 can be maintained at 70% or less regardless of the season, and as a result, generation of abnormal oxides in the bag-packed silicon product 10 can be prevented even under high temperature and high humidity. .

  Further, in the silicon packaging method of the second embodiment shown in FIG. 1C, a predetermined number of polyethylene bag-packed silicon products 10 are directly enclosed in a water vapor barrier packaging material 40 made of a SiO vapor deposition film. That is, the large bag 20 made of a polyethylene sheet is omitted here. It is the same as the silicon packaging method of the first embodiment that a plurality of desiccants 50 made of silica gel are disposed in the water vapor barrier packaging material 40 so as to surround the product group.

  In the silicon packing method of the second embodiment, the humidity in the packing material is maintained at 70% or less regardless of the season by using the water vapor barrier packing material 40 and the desiccant 50, similarly to the silicon packing method of the first embodiment. The generation of abnormal oxides in the bagged silicon product 10 can be prevented even under high temperature and high humidity.

  Moreover, in any of the silicon packing methods of the embodiments, the plurality of silicon lumps in the polyethylene bag-packed silicon product 10 are packed with double or more packing materials including the polyethylene bag, and the water vapor barrier packing is used. Since the material 40 is excluded from the innermost layer, damage to the water vapor barrier packing material 40 due to silicon lump and excessive moisture intrusion due to this is prevented.

  In order to quantitatively verify the effectiveness of the silicon packaging method of the present invention, the following eight comparative tests were conducted.

As shown in FIG. 2, polycrystalline silicon was crushed and collected, and 100 silicon lumps 11 (each average weight 100 g, average surface area 237 cm ² ) that had been etched, washed and dried were doubled for products. It was enclosed in a polyethylene bag 12. The periphery of the polyethylene bag 12 that had been sealed with the silicon lump 11 was airtightly packed with a bag-shaped water vapor barrier packing material 40 made of a SiO vapor-deposited film. The SiO vapor deposition film used has a water vapor transmission rate of 0.15 g / m ² day (temperature 40 ° C., humidity 90% RH). A desiccant 50 made of silica gel was disposed between the polyethylene bag 12 and the bag-shaped water vapor barrier packing material 40. A humidity recorder 60 was also accommodated in the polyethylene bag 12. The amount of silica gel was the minimum necessary amount calculated based on the water vapor transmission rate of the SiO vapor-deposited film and the number of storage days. A series of packing operations was performed in an atmosphere at a temperature of 20 ° C. and a humidity of 40%.

  This packaged product was stored for 40 days in a high temperature and high humidity tank having a temperature of 40 ° C. and a humidity of 90% in order to promote oxidation. The humidity in the polyethylene bag 12 during storage was maintained at about 60% for 40 days. No stain was observed on any silicon mass 11 in the polyethylene bag 12. Even if it returned to normal temperature, the condensation was not recognized in the bag (Example 1-1).

In the packing form shown in FIG. 2, the desiccant 50 is omitted. This packaged product was stored in a high-temperature and high-humidity tank having a temperature of 40 ° C. and a humidity of 90% for 40 days. Although the humidity in the polyethylene bag 12 gradually increased with the passage of the storage period, it took 15 days to increase to 70%, and it became 90%, the same as the surrounding atmosphere, after 35 days. Until the humidity reached 90%, no stain was observed in any of the silicon masses 11 in the polyethylene bag 12. After that, stains started to appear, but they were very slight, and at the time when 40 days had passed, only a small spot having an average of 0.7 cm ² was generated in 5 out of 100 silicon blocks 11 (Example 1-2). ).

In the packing form shown in FIG. 2, the water vapor barrier packing material 40 and the desiccant 50 are omitted. This packaged product was stored in a high-temperature and high-humidity tank having a temperature of 40 ° C. and a humidity of 90% for 40 days. The humidity in the polyethylene bag 12 reached 90%, the same as the ambient atmosphere, after 2 days. At the time when 40 days passed, relatively large spots with an average of 0.9 cm ² were generated in 50 silicon masses 11. When the packaged product was returned to room temperature, condensation was observed in the bag (conventional example).

In the packing form shown in FIG. 2, the bag-shaped water vapor barrier packing material 40 made of a SiO vapor deposition film is changed to a bag made of an aluminum vapor deposition film. The packaging material has a water vapor transmission rate of 0.9 g / m ² day (temperature 40 ° C., humidity 90% RH). The amount of silica gel was the minimum required amount calculated based on the water vapor transmission rate of the aluminum vapor-deposited film and the number of storage days.

  This packaged product was stored in a high-temperature and high-humidity tank having a temperature of 40 ° C. and a humidity of 90% for 40 days. The humidity in the polyethylene bag 12 during storage was maintained at about 60%. No stain was observed on any silicon mass 11 in the polyethylene bag 12. Condensation was not observed in the bag even after returning to room temperature. However, the amount of silica gel used was 6 times that when the water vapor barrier packing material 40 made of a SiO vapor-deposited film was used (Example 2-1).

The amount of silica gel used was reduced to the same amount as when the water vapor barrier packing material 40 made of a SiO deposited film was used. It took 7 days for the humidity in the polyethylene bag 12 to rise to 70%, and it became 90%, the same as the surrounding atmosphere, after 13 days. Until the humidity reached 90%, no stain was observed in any of the silicon masses 11 in the polyethylene bag 12. After that, stains started to appear, but they were very slight, and at the time when 40 days had passed, small spots of an average of 0.8 cm ² were generated on 15 out of 100 silicon blocks 11 (Example 2-2). )

When silica gel was omitted, the humidity in the polyethylene bag 12 gradually increased with the passage of the storage period, but it took 4 days to increase to 70%. became. Until the humidity reached 90%, no stain was observed in any of the silicon masses 11 in the polyethylene bag 12. After that, spots started to appear, but they were very slight, and at the time when 40 days passed, small spots with an average of 0.8 cm ² were generated in 15 out of 100 silicon blocks 11 (Example 2-3). ).

In the packing form shown in FIG. 2, the bag-shaped water vapor barrier packing material 40 made of a SiO vapor deposition film is changed to a bag made of an alumina vapor deposition film. Water vapor permeability of the packaging material is 1.0g / m ² day (temperature 40 ° C., humidity of 90% RH) of greater than 1.5g / m ² day (temperature 40 ° C., humidity of 90% RH). The amount of silica gel was the minimum required amount calculated based on the water vapor permeability of the alumina vapor-deposited film and the number of storage days.

  This packaged product was stored in a high-temperature and high-humidity tank having a temperature of 40 ° C. and a humidity of 90% for 40 days. The humidity in the polyethylene bag 12 during storage was maintained at about 60%. No stain was observed on any silicon mass 11 in the polyethylene bag 12. Condensation was not observed in the bag even after returning to room temperature. However, the amount of silica gel used reached 10 times that when the water vapor barrier packing material 40 made of a SiO vapor-deposited film was used (Comparative Example 1-1).

When silica gel was omitted, the humidity in the polyethylene bag 12 exceeded 70% when 3 days had elapsed from the start of storage, and became 90% the same as the surrounding atmosphere when 7 days had elapsed. Until the humidity reached 90%, no stain was observed in any of the silicon masses 11 in the polyethylene bag 12. After that, spots started to occur, and after 40 days, relatively large spots with an average of 1.0 cm ² were generated in 70 of the 100 silicon blocks 11. When the packaged product was returned to room temperature, dew condensation was observed in the bag (Comparative Example 1-2).

(A) (b) (c) is a schematic diagram which shows one Embodiment of the silicon packing method of this invention compared with the conventional silicon packing method, (a) is a conventional method, (b) is this invention. (C) shows 2nd Embodiment of this invention, respectively. It is a model explanatory drawing of the packing form in the experiment for verifying the effectiveness of the silicon packing method of this invention quantitatively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Silicone product in a bag 11 Silicon lump 12 Polyethylene bag 20 Large bag 30 Pallet 40 Water vapor barrier packing material 50 Desiccant 60 Humidity recorder

Claims (5)

One or a plurality of bulk silicon obtained by crushing polycrystalline silicon, a water vapor barrier packaging material having a water vapor transmission rate of 1.0 g / m ² day (temperature 40 ° C., humidity 90% RH) or less The silicon packing method characterized by packing with.   The silicon packing method according to claim 1, wherein lump silicon is packed in a plurality of layers with a plurality of packing materials, and a packing material having a water vapor barrier property is used for at least one other than the innermost layer.   The silicon packaging method according to claim 1 or 2, wherein a desiccant is placed inside a packaging material having a water vapor barrier property.   The silicon packing method according to claim 1, wherein the packing material is held in an atmosphere having a humidity of 70% or less.   The silicon packing method according to any one of claims 1 to 4, wherein the lump silicon is a crushed lump of polycrystalline silicon that has been treated with a cleaning liquid containing fluorine.

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