阅读说明：本技术 多晶硅的防污方法 (Method for preventing contamination of polycrystalline silicon ) 是由 浅野卓也 吉村聪子 于 2019-10-29 设计创作，主要内容包括：本发明的目的在于,在利用树脂片进行的多晶硅的防污中,有效防止源自树脂片的多晶硅的污染。本发明的多晶硅的防污方法的特征在于,使用具有内表面和外表面的管状树脂片来对多晶硅进行防污时,将该管状树脂片或其经切割而得的树脂片以不露出其内表面的状态保持,在即将使用之前使上述内表面露出并与多晶硅接触。(The invention aims to effectively prevent the pollution of polysilicon from a resin sheet in the antifouling of the polysilicon by the resin sheet. The method for preventing contamination of polycrystalline silicon according to the present invention is characterized in that, when the polycrystalline silicon is to be contaminated with the use of a tubular resin sheet having an inner surface and an outer surface, the tubular resin sheet or the cut resin sheet is held in a state where the inner surface thereof is not exposed, and the inner surface is exposed and brought into contact with the polycrystalline silicon immediately before use.)

1. A method for preventing contamination of polycrystalline silicon,

when a tubular resin sheet having an inner surface and an outer surface is used for antifouling of polycrystalline silicon, the tubular resin sheet is held in a state where the inner surface thereof is not exposed, and is cut in such a manner that the inner surface can be spread out immediately before use, leaving the inner surface exposed and in contact with the polycrystalline silicon.

2. A method for preventing contamination of polycrystalline silicon,

when a tubular resin sheet having an inner surface and an outer surface is used for antifouling of polycrystalline silicon, the tubular resin sheet is cut in such a manner that the inner surface thereof can be spread out, and is held in a state where the inner surface is not exposed, and the inner surface is exposed and brought into contact with the polycrystalline silicon immediately before use.

3. The method for preventing fouling of polycrystalline silicon according to claim 1 or 2,

the amount of iron present in the inner surface of the resin sheet immediately before use was 1pg/cm in terms of element²The following.

4. The method for preventing contamination of polycrystalline silicon according to any one of claims 1 to 3,

the resin sheet is a polyethylene sheet to which no additive is added.

5. A method for producing polycrystalline silicon, which comprises the method for preventing contamination according to any one of claims 1 to 4.

6. A resin sheet for preventing contamination of polycrystalline silicon,

the tubular resin sheet is wound so that the inner surface thereof is not exposed.

7. A resin sheet for preventing contamination of polycrystalline silicon,

the tubular resin sheet is cut so that the inner surface thereof can be spread and the wound product of the resin sheet is not exposed from the inner surface.

8. The resin sheet for preventing contamination of polycrystalline silicon according to claim 6 or 7,

the amount of iron present in the inner surface of the tubular resin sheet was 0.5pg/cm in terms of element²The following.

9. The resin sheet for preventing contamination by polysilicon according to any one of claims 6 to 8,

the resin sheet is a polyethylene sheet without additives.

Technical Field

The invention provides a novel antifouling method for polycrystalline silicon. Specifically, the method for preventing contamination of polycrystalline silicon can prevent surface contamination until use as much as possible, and can significantly reduce contamination of polycrystalline silicon from a resin sheet used in the case of contamination prevention of polycrystalline silicon.

Background

In order to prevent contamination of polycrystalline silicon, polycrystalline silicon in the form of a rod, a rod (cut rod), a crushed material, a powder, or the like is conveyed or stored, and the polycrystalline silicon is covered with a resin sheet in order to prevent contamination from the surrounding environment of the polycrystalline silicon. Since polysilicon is required to have high purity, the anti-contamination treatment is performed not only in an open atmosphere but also in a clean room (clean room).

As the resin sheet used for the above-mentioned antifouling property, for example, a resin sheet which is free from bleeding of a metal component and an organic component and to which no additive is added is generally used in order to prevent contamination of polycrystalline silicon by the resin sheet. In the above-described antifouling treatment, the wound resin sheet is unwound and cut in an appropriate length to cover the top of the polysilicon placed thereon; or, in some cases, by covering the polycrystalline silicon by laying it under the polycrystalline silicon (see patent documents 1 and 2).

As described above, the present inventors have found that the resin sheet used for the stain-proofing has a very high purity in the interior thereof, but the surface thereof is contaminated with outside air from immediately after the production until before the use thereof, and that high contamination due to contaminants such as metal components, organic components, and dopant components contained in the outside air is observed during the use thereof. That is, in the method for producing a resin sheet, the resin extruded from the T-die of the extruder is stretched, formed into a sheet shape, and then wound into a roll shape as needed, but during this time, contaminants are attached to the surface due to contact with the outside air or contact with other contaminants, and the surface of the wound resin sheet is in a state in which contaminants have entered. As such a contamination source, a roller or the like used in winding may be considered.

In some cases, a resin sheet is produced by an inflation method using a ring die. In this case, a tubular resin sheet having an inner surface and an outer surface can be obtained, the inner surface having high cleanability. However, in the case of using as the resin sheet, both sides of the tubular resin sheet are generally cut and wound into individual rolls; or one side is cut off and then opened and wound, and the same contamination as described above may occur during winding.

Further, when the polycrystalline silicon is covered with a contaminated resin sheet, there is a problem that the polycrystalline silicon is contaminated by a contaminant attached to the resin sheet.

Documents of the prior art

Patent document

Patent document 1: japanese Kohyo publication 2017-524632

Patent document 2: japanese patent laid-open publication No. 2017-56959

Disclosure of Invention

Problems to be solved by the invention

Accordingly, an object of the present invention is to provide an antifouling method capable of effectively preventing contamination of polycrystalline silicon derived from a resin sheet in antifouling of polycrystalline silicon by the resin sheet.

Means for solving the problems

As a result of repeated studies to solve the above object, the present inventors have found that the stain-proofing is performed as follows: the above object can be achieved by treating the inner surface of the tube with a tubular resin sheet in such a manner that the inner surface is not in contact with the outside air immediately before the tube is used for stain resistance, and by exposing the inner surface immediately before the tube is used and bringing the inner surface into contact with the polycrystalline silicon.

That is, one embodiment of the present invention is a method for preventing contamination of polycrystalline silicon, which is characterized in that, when a tubular resin sheet having an inner surface and an outer surface is used to prevent contamination of polycrystalline silicon, the tubular resin sheet is held in a state where the inner surface thereof is not exposed, and is cut so that the inner surface can be spread out immediately before use, and the inner surface is exposed and brought into contact with the polycrystalline silicon.

Another embodiment of the present invention is a method for preventing contamination of polycrystalline silicon, comprising, when a tubular resin sheet having an inner surface and an outer surface is used to prevent contamination of polycrystalline silicon, cutting the tubular resin sheet so that the inner surface thereof can be spread and held in a state where the inner surface is not exposed, and exposing the inner surface to be brought into contact with polycrystalline silicon immediately before use.

In the above-mentioned antifouling method, the amount of iron present in the inner surface of the resin sheet immediately before use is preferably 1pg/cm in terms of elements²The following. Preferably, the resin sheet has a puncture strength of 10N or more.

Further, in order to prevent contamination caused by impurities inside the sheet, it is preferable that the resin sheet is a polyethylene sheet to which no additive is added.

Further, the present invention provides a method for producing polycrystalline silicon, which can effectively prevent contamination from a stain-proof sheet.

Further, the present invention provides a resin sheet for preventing contamination by polycrystalline silicon, wherein the resin sheet is configured as a wound product obtained by winding a tubular resin sheet in a state in which an inner surface thereof is not exposed. Further, the present invention provides a resin sheet for preventing contamination by polycrystalline silicon, wherein the resin sheet is cut into a tubular shape so that an inner surface thereof can be spread and the resin sheet is wound without exposing the inner surface.

Effects of the invention

According to the antifouling method of the present invention, the tubular resin sheet is used, and immediately before the resin sheet in which the inner surface of the tubular resin sheet is kept in a non-exposed state is used, the inner surface is exposed, and the clean sheet surface without contamination is brought into contact with the polycrystalline silicon, whereby the surface of the resin sheet free from contamination by the outside air or the like can be brought into contact with the polycrystalline silicon to prevent fouling, and therefore, the contamination of the polycrystalline silicon can be effectively prevented.

Drawings

Fig. 1 shows a tubular resin sheet.

Fig. 2a is a schematic view showing one embodiment of a resin sheet used in the stain-proofing method of the present invention.

Fig. 2b is a schematic view showing one embodiment of a resin sheet used in the stain-proofing method of the present invention.

Fig. 2c is a schematic view showing one embodiment of a resin sheet used in the stain-proofing method of the present invention.

Fig. 3 is a schematic view showing a typical process for producing a tubular resin sheet.

Detailed Description

As described above, the method for preventing contamination of polycrystalline silicon according to one embodiment of the present invention is characterized in that a tubular resin sheet having an inner surface and an outer surface is used, the tubular resin sheet is cut so that the inner surface thereof can be spread and held in a state where the inner surface is not exposed, and the inner surface is exposed immediately before use and brought into contact with the polycrystalline silicon to be protected against contamination. Fig. 1 shows a tubular resin sheet 1 having an inner surface 2 and an outer surface 3. As shown in fig. 1, the contact of the inner surface 2 with the outside air or other devices is restricted, and the inner surface is in a clean state. In the present invention, a resin sheet 10 is prepared which has been cut so that the inner surface 2 of the tubular resin sheet 1 can be spread. The cutting scheme is not particularly limited, and includes all schemes that can be unfolded to expose the inner surface 2. In the resin sheet 10 obtained by cutting the tubular resin sheet 1, the inner surfaces 2 are in close contact with each other, and the inner surfaces 2 are not exposed.

Fig. 2a to 2c show a representative embodiment of the resin sheet in which the inner surface of the tubular resin sheet 1 can be spread and is not exposed. Fig. 2a shows the resin sheet 10 cut on one side in the long dimension direction of the tubular resin sheet. In the resin sheet of this embodiment, the wound material 11 wound in a roll shape is formed without opening the cut portion, and thus the inner surface 2 can be held without being exposed. Then, in use, the resin sheet 10 is unwound from the winding 11, and is opened from the cut single side so that the inner surface 2 thereof is brought into contact with the polysilicon.

Fig. 2b shows the resin sheet 10 in which both sides in the long dimension direction of the tubular resin sheet are cut. The resin sheet of this embodiment is a two-layer sheet in which the inner surfaces 2 are in close contact with each other, and can be held without exposing the inner surfaces 2 by forming the wound material 11 wound into a roll shape without peeling the layers. Then, in use, the resin sheet 10 is unwound from the winding 11, and is peeled between the two layers, so that the surface on the inner surface side is brought into contact with the polysilicon.

Fig. 2c is a modification of fig. 2a, showing the resin sheet 10 in which the central portion in the longitudinal direction of the tubular resin sheet is cut. The resin sheet of this embodiment is juxtaposed to the resin sheet shown in fig. 2 a. In use, the resin sheet 10 is unwound from the roll 11, and is opened from the cut single side so that the inner surface 2 thereof is in contact with the polysilicon.

In the embodiment of the present invention, the tubular resin sheet may be wound up, held so that the inner surface thereof is not exposed, and then unwound and cut as shown in fig. 2a to 2c immediately before use.

In the present invention, "contamination prevention" is a method for protecting polycrystalline silicon from contamination of the surrounding environment by a sheet, and specifically includes: a method of covering the mounted polycrystalline silicon with a sheet for the purpose of storage or the like, a method of laying a sheet below the polycrystalline silicon, a method of wrapping the polycrystalline silicon, or the like. Further, the method includes a method of laying a sheet on the bottom of a container for transportation and storing polycrystalline silicon above the container; a method of covering the polycrystalline silicon contained in the container with a sheet is also included. Further, since high purity is required for polycrystalline silicon, the above method is performed not only in an open atmosphere but also in a clean room. Although the cleanliness in the clean room is extremely high, the contamination is increased if the polycrystalline silicon is left for a long time. Therefore, by using the method of preventing contamination of the present invention in a clean room, polycrystalline silicon can be kept in a clean state for a long time.

In the present invention, the "inner surface" refers to the inner surface of the tubular resin sheet 1. In the present invention, the tubular resin sheet 1 is cut and unfolded to be used as the resin sheet 10. The "inner surface" of the resin sheet refers to the surface on the inner side of the tubular resin sheet 1 before being spread.

The form of the polycrystalline silicon is not limited, and examples thereof include a state of a rod taken out from a reaction apparatus of the Siemens (Siemens) method, a state of a short rod obtained by cutting the rod, and a state of a crushed polycrystalline silicon product obtained by crushing the rod. Generally, polycrystalline silicon is broken and then cleaned by etching or the like to have a clean surface. The anti-fouling method of the present invention can be applied to polysilicon before etching, and can also be applied to polysilicon after etching.

In the present invention, the tubular resin sheet 1 is a resin sheet obtained by a known method such as an inflation method, and is not particularly limited. Specifically, as shown in fig. 3, the resin can be extruded into a tubular shape by an extruder 4 provided with an annular die 5, and the resin sheet 1 can be formed into a tubular resin sheet by stretching the resin sheet through a mandrel as necessary and then wound into a roll to obtain a wound product 12. The roll 12 may be unwound at the time of use, and cut as described above to obtain the resin sheet 10. Before winding the tubular resin sheet 1, the resin sheet 10 of the present invention may be obtained by cutting as described above, and then wound into a roll to obtain a wound product 11. Further, the air for the blower 6 to be supplied for molding into the tubular resin sheet 1 is preferably clean air so as not to contaminate the inner surface of the resulting tubular resin sheet. Specifically, air having 0.3 μm particles of 10 particles/L or less is preferably used. Therefore, the filter 7 may be interposed between the blower 6 and the die 5. As the filter 7, for example, a HEPA filter or the like can be used.

The resin used is not particularly limited as long as it is a thermoplastic resin, but as a resin having appropriate flexibility and being inexpensive, a polyethylene resin such as Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), or Linear Low Density Polyethylene (LLDPE) is preferably used.

The thickness of the resin sheet may be appropriately selected depending on the shape, size and mass of the polycrystalline silicon, and is usually 50 to 2mm, particularly 150 to 300 μm. The resin sheet preferably has a puncture strength of 10N or more.

In order to suppress contamination due to bleeding of metal elements and organic substances derived from the additives, the resin constituting the resin sheet is preferably free from additives such as antistatic agents, plasticizers, and antioxidants.

The inner surface of the tubular resin sheet is always in a clean state without contacting with the outside air from the time of production to the time of winding into a roll shape. For example, in the stain-proofing method, it was confirmed that the amount of iron present in the inner surface of the resin sheet immediately before use was 1pg/cm in terms of element²The following cleanliness. On the other hand, the amount of iron present on the surface of a normal resin sheet contaminated by contact with the outside air was 10pg/cm²Left and right. Further, as long as the amount of iron present is in the above range, the amount of other metals present is also reduced to the same extent or more. For example, sodium may be set to 2pg/cm²Hereinafter, calcium may be set to 5pg/cm²Hereinafter, the zinc content may be set to 1pg/cm²The following.

The present invention utilizes the characteristics of the tubular resin sheet to effectively prevent the contamination of polycrystalline silicon caused by the resin sheet during the antifouling. That is, the stain-proofing method of the present invention includes all the steps of treating the inner surface of the tubular resin sheet without exposing the inner surface, and exposing the inner surface of the tubular resin sheet immediately before the treatment for stain-proofing, and specifically, the method is preferably performed by the following steps.

1. A method for antifouling in the following manner: the tubular resin sheet is held as a roll wound into a roll, and is unwound at the time of use, the tubular resin sheet is cut as described above, and one surface of the tubular resin sheet which becomes an inner surface is opened and brought into contact with the polycrystalline silicon to be prevented from fouling.

2. A method for antifouling in the following manner: in the resin sheet manufacturing process, a tubular resin sheet is cut as described above, and two sheets of the tubular resin sheet, the inner surfaces of which are not exposed, are wound in a state of being overlapped and held as a wound body, the resin sheet is unwound from the wound body, and one surface of the tubular resin sheet, which is the inner surface, is opened, and the resin sheet is brought into contact with the polycrystalline silicon to be prevented from being stained.

3. A method for antifouling in the following manner: the tubular resin sheet is cut and held in a wound state as described above, the cut resin sheet is unwound from the wound body, and one surface of the tubular resin sheet that becomes an inner surface is opened and brought into contact with the polycrystalline silicon to be prevented from fouling.

As described above, according to the above-described method for preventing contamination of a resin sheet of the present invention, the clean surface of the resin sheet is brought into contact with the polycrystalline silicon, and therefore contamination from the resin sheet can be effectively prevented.

Even in the case of film formation by inflation, when both sides are cut immediately after film formation and the resin sheet is wound into individual rolls, both sides of the resin sheet come into contact with outside air or an unwinding roll and are contaminated. As a result, even when the resin sheet is used for antifouling of polysilicon, antifouling property is insufficient. Therefore, it is very important to wind the resin sheet so that the inner surface of the resin sheet is not exposed to achieve the effect of the present invention.

Examples

Embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

(example 1)

(production of tubular resin sheet)

Polyethylene (LDPE) containing no additives such as antistatic agent was blow molded using the apparatus shown in fig. 3 to obtain a tubular resin sheet. The thickness of the sheet was set to 250 μm (satisfying a puncture strength of 10N or more). The obtained tubular resin sheet was wound into a roll to obtain a wound product.

In the inflation molding, air adjusted to 10 particles/L or less with 0.3 μm particles was used.

(cutting of tubular resin sheet)

Simultaneously with unwinding the tubular resin sheet, one side of the sheet in the longitudinal direction is cut as shown in fig. 2 a. The sheet is opened from the cutting portion to expose the inner surface, and the polysilicon is covered with a resin sheet so that the inner surface side is in contact with the polysilicon. The above operations were all performed in a class 1000 clean room. The following evaluations were performed.

(amount of Metal present)

The amount of metal present on the inner and outer surfaces of the resin sheet was measured as follows.

The adhesion metal was extracted from the surface of the resin sheet to be measured using a nitric acid aqueous solution having a concentration of 1 mass% as an extraction solution, and the amount of iron, Na, Ca, and Zn as impurities was measured by quantitative analysis by ICP-MS (inductively coupled plasma mass spectrometry). The measurement was performed on 10 samples obtained by cutting a resin sheet into a size of 50 × 50cm, and the average value is shown in table 1.

(evaluation of antifouling Property)

After the polysilicon was covered with a resin sheet, it was left in a 1000-class clean room for 10 days. The surface contamination of polycrystalline silicon was evaluated as follows.

The amount of iron, Na, Ca, and Zn present as impurities was measured by extracting the adhering metal from the surface of the polycrystalline silicon using a nitric acid aqueous solution having a concentration of 1 mass% as an extracting solution and quantitatively analyzing the extracted metal by ICP-MS (inductively coupled plasma mass spectrometry). For the measurement, 10 pieces of polycrystalline silicon arbitrarily picked up were taken as 1 unit, and the average value of the 10 pieces was shown in table 2.

Comparative example 1

The same operation as in example 1 was performed except that the outer surface of the resin sheet (one surface of the tube which becomes the outer surface) was brought into contact with the polysilicon to prevent contamination. The results are shown in Table 2.

[ Table 1]

Analysis value (pg/cm) of the surface of the polyethylene resin sheet²)

	Na	Ca	Fe	Zn
					Inner surface	1.5	1.1	＜1	＜1
Outer surface	16.6	50.8	8.4	13.7

[ Table 2]

Contamination of polysilicon (pptw)

	Na	Ca	Fe	Zn
					Example 1	＜10	＜20	＜10	＜10
Comparative example 1	＞30	＞4v	＞40	＞30

Description of the reference numerals

1: a tubular resin sheet; 2: an inner surface; 3: an outer surface; 4: an extruder; 5: an annular die head; 6: a blower; 7: a filter; 10: resin sheet (cut); 11: a wound product of a resin sheet; 12: a roll of tubular resin sheet.