STORAGE BAG FOR POLYCRYSTALLINE SILICON INGOT, METHOD FOR PACKING POLYCRYSTALLINE SILICON INGOT, AND METHOD FOR PRODUCING CZ SILICON SINGLE CRYSTAL

Abstract

In the present invention, as a bag to store polycrystalline silicon ingots, there is used a bag in which the concentration of paraffinic hydrocarbons in a concentrate of solvent-soluble components obtained by Soxhlet extraction using acetone as a solvent is lower than 300 ppmw as a value measured by GC-MS method; the concentration of antioxidants, lower than 10 ppmw; the concentration of ultraviolet absorbents, lower than 5 ppmw; and the concentration of antistatic agents and surfactants, lower than 50 ppmw. Then, when the polycrystalline silicon ingots are packed, preferably, the polycrystalline silicon ingots are put in the storage bag; thereafter, the storage bag is sealed; further, the storage bag is put and sealed in a linear low-density polyethylene bag containing an antistatic agent or a surfactant added in the bag material.

Claims

1. A storage bag for a polycrystalline silicon ingot, wherein the bag is a linear low-density polyethylene bag for storing the polycrystalline silicon ingot, and has a concentration of paraffinic hydrocarbons in a concentrate obtained by Soxhlet extraction using acetone as a solvent of lower than 300 ppmw as a value measured by a GC-MS method.

2. The storage bag for a polycrystalline silicon ingot according to claim 1, wherein the bag has a concentration of antioxidants in a concentrate obtained by Soxhlet extraction using acetone as a solvent of lower than 10 ppmw as a value measured by a GC-MS method.

3. The storage bag for a polycrystalline silicon ingot according to claim 2, wherein the bag has a concentration of ultraviolet absorbents in a concentrate obtained by Soxhlet extraction using acetone as a solvent of lower than 5 ppmw as a value measured by a GC-MS method.

4. The storage bag for a polycrystalline silicon ingot according to claim 3, wherein the bag has a total concentration of antistatic agents and surfactants in a solvent concentrate obtained by Soxhlet extraction using acetone as a solvent of lower than 50 ppmw as a value measured by a GC-MS method.

5. A method for packing a polycrystalline silicon ingot, comprising: putting the polycrystalline silicon ingot in a storage bag according to claim 1; thereafter sealing the storage bag; further putting the storage bag in a linear low-density polyethylene bag containing an antistatic agent or a surfactant added in the bag material; and sealing the latter bag.

6. A method for producing CZ silicon single crystal, comprising: using a polycrystalline silicon ingot put and stored in a storage bag according to claim 1 and having a total concentration of surface organic substances of lower than 4 ppbw as a value measured by a GC-MS method, as a raw material of the single crystal for CZ.

7. A method for producing CZ silicon single crystal, comprising using a polycrystalline silicon ingot packed by a method according to claim 5 as a raw material of the single crystal for CZ.

Description

DESCRIPTION OF EMBODIMENTS

[0020] It is demanded that a storage bag for polycrystalline silicon ingots provided as a raw material of single crystal for CZ be one not contaminating the surface of the polycrystalline silicon ingots put and stored therein. Therefore, it becomes necessary that basically, the bag material contain no additives and have no observed elution of low-molecular components of LLDPE itself; however, it has not been clarified what degree of the content of the additives is acceptable and what degree of the elution of the low-molecular components of LLDPE is acceptable.

[0021] Then, the present inventors have clarified by the following studies what sort of a polyethylene bag is suitable to store polycrystalline silicon ingots provided as a raw material of single crystal for CZ while maintaining cleanliness of the surface of the polycrystalline silicon ingots.

[0022] [Condition for evaluating amounts of organic components eluted from a LLDPE bag]

[0023] Various types of bags (A to G) were prepared from commercially available LLDPE bags; a LLDPE sheet of 1 g was cut out as a specimen from these bags each; and the specimen of 1 g was subjected to Soxhlet extraction using acetone as a solvent for 8 hours. An obtained extract (a concentrate of solvent-soluble components) was subjected to a GC-MS analysis (quadruple mass analysis) to thereby measure elution amounts of additives and low-molecular components eluted.

[0024] The apparatus used for the measurement was 8400 GC/320 MS, manufactured by Varian, Inc., and the separation column was HP-5 MS (0.25 mm in diameter×30 m×0.25 μm in membrane thickness). The column was held at 60° C. for 1 min, thereafter heated at 10° C./min, and held at 300° C. for 25 min. The carrier gas in the measurement was He; and the condition was set so that the amount of the extract injected was 1 μ1 and the split ratio was 10:1. The mass analysis was carried out by an electron impact ionization method, and the scanning range was m/z=40 to 700.

[0025] The amounts of organic substances (paraffinic hydrocarbons, antioxidants, ultraviolet absorbents, and antistatic agents and surfactants) eluted from the each bag and detected are collectively shown in Table 1. Here, in the calculation of the concentrations, for the organic substances excluding the paraffinic hydrocarbons, known-concentration reference specimens were used. For the paraffinic hydrocarbons, known-concentration reference specimens of decane were used and the concentration was calculated from the a real value of all peaks.

TABLE-US-00001 TABLE 1 Antistatic Storage Paraffinic Ultraviolet Agent Bag Hydrocarbon Antioxidant Absorbent Surfactant A 1100 300 10 <50 B 1200 <10 <5 <50 C <300 <10 <5 <50 D <300 <10 <5 <50 E 500 <10 <5 500 F 400 <10 <5 <50 G <300 <10 <5 <50 [Unit: ppmw]

[0026] The paraffinic hydrocarbons were detected, in chromatography of GC-MS, over the molecular weight region from low molecular to oligomeric, and as a result of an MS qualitative determination, were linear and branched paraffinic hydrocarbons.

[0027] The antioxidant was, as a result of an MS qualitative determination, di-t-butyl-4-ethylphenol.

[0028] As the ultraviolet absorbent, Irganox 1076, distributed as a commodity, was detected.

[0029] As the antistatic agent or the surfactant, hexadecanol was detected.

[0030] [Evaluation of organic substances adhered on the surface of the polycrystalline silicon ingots]

[0031] The polycrystalline silicon ingots are etched with a mixed acid of hydrofluoric acid and nitric acid; the polycrystalline silicon ingots of 5.0 kg were filled in the each bag (A to G), which were then sealed by heat sealing. Further, the bag was packed in a corrugated board, transported in Japan domestically, and unpacked after one year; and components adsorbed on the surface of the nuggets, that is, contaminating components, were qualitatively and quantitatively analyzed.

[0032] A specimen for analysis of 5 g (mostly, 20 to 30 mm in major diameter, 5 to 10 mm in minor diameter) was sampled, and heated at 250° C. for 10 min in an environment of He gas flowing (1 ml/min) to thereby make organic components adhered on the surface to be desorbed and make the organic components to be adsorbed on an adsorbent (Glass Wool f255). The adsorbent was instantaneously heated and the adsorbed components were again subjected to a GC-MS analysis (quadruple mass analysis). Here, the released components were made to be adsorbed on the adsorbent at −60° C. (liquid nitrogen); and the desorption of the adsorbed components from the adsorbent was carried out by heating the adsorbent from −60° C. to 250° C./25 sec.

[0033] The apparatus used for the measurement was 5975C-inert XL-MSD, manufactured by Agilent Technologies, Inc., and the separation column was Ultra2 (25 m×0.2 mm in diameter, 0.33 μm in membrane thickness), manufactured by Agilent Technologies, Inc. The column was held at 50° C. for 5 min, and thereafter heated at 10° C./min up to 300° C. The carrier gas in the measurement was He (flow volume: 1 ml/min), and the condition was set so that the column inlet port temperature was 300° C. and the split ratio was 20:1. The mass analysis mode was set to be an electron impact ionization mode.

[0034] The components thus detected were components detected as eluted components by the above-mentioned acetone extraction; and it was confirmed that components whose detected amounts were small in the acetone extraction had a tendency of being present in small amounts also as organic substances adhered on the surface of the polycrystalline silicon ingots.

[0035] The amounts of organic substances (paraffinic hydrocarbons, antioxidants, ultraviolet absorbents, and antistatic agents and surfactants) detected are collectively shown in Table 2. The quantitative determination was carried out by using n-tetradecane as a reference substance. Here, in the measurement result in the experiment using the bag E, CH.sub.3(CH.sub.2).sub.16CH.sub.2OH (stearyl alcohol) was clearly detected. CH.sub.3(CH.sub.2).sub.16CH.sub.2OH (stearyl alcohol) was a component which was not detected as an eluted organic substance from the bag E; and the reason was unknown, but was presumed to be due to the decomposition by the acetone extraction and heating.

TABLE-US-00002 TABLE 2 Antistatic Storage Paraffinic Ultraviolet Agent Bag Hydrocarbon Antioxidant Absorbent Surfactant A 24 5 <0.1 <0.1 B 17 <0.1 <0.1 <0.1 C 4 <0.1 <0.1 <0.1 D 3 <0.1 <0.1 <0.1 E 6 <0.1 <0.1 2 F 5 <0.1 <0.1 <0.1 G 3 <0.1 <0.1 <0.1 [Unit: ppmw]

[0036] From the results shown in Table 2, it can be read that a bag in which eluted amounts of low-molecular components or additives in the bag material is large has a tendency of bringing about larger adhered amounts thereof on the surface of the polycrystalline silicon ingots.

[0037] [Checking of the influence on the carbon concentration in CZ silicon single crystal]

[0038] CZ silicon single crystal was grown by using as a raw material the polycrystalline silicon ingots prepared for the above-mentioned “Evaluation of organic substances adhered on the surface of the polycrystalline silicon ingots”, and the carbon concentration in the bulk was examined. Here, the carbon concentration was quantitatively determined by an FT-IR according to the procedure of ASTM F1391-93 (reapproved 2000). The measurement results are collectively shown in Table 3.

[0039] Here, when storage bags are unpacked to take out the polycrystalline silicon ingots, the work is carried out in a clean room, but at this time, static electricity by friction or the like is generated and not a few particles are generated. Hence, it is preferable that the unpacking work be carried out in the state where the polycrystalline silicon ingots are stored in bags containing an antistatic agent and a surfactant added in the bag materials. Then, in any Experimental Examples, the unpacking work was carried out in the state where the polycrystalline silicon ingots are stored in the bag E used in Comparative Example 3.

[0040] In order to more simplify such unpacking work, it is preferable that in packing, there be carried out double packing in which a bag containing the polycrystalline silicon ingots put therein and having been sealed is further put in a linear low-density polyethylene bag containing an antistatic agent or a surfactant added in the bag material, and the latter bag is sealed.

TABLE-US-00003 TABLE 3 Polycrystalline Si Chunk CZ-Si Surface Polycrystalline Carbon Organic Si Chunk Amount Substance Carbon in Single Experimental Amount Amount Crystal Example Bag [ppbw] in Bulk [ppba] [ppbw] [ppba] Comparative A 29 <21 33 80 Example 1 Comparative B 17 <21 25 60 Example 2 Example 1 C 4 <21 <21 <50 Example 2 D 3 <21 <21 <50 Comparative E 8 <21 25 60 Example 3 Comparative F 5 <21 21 50 Example 4 Example 3 G 3 <21 <21 <50

[0041] From the results, in order to reduce the carbon concentration in the CZ silicon single crystal, it is natural that the carbon concentration in bulks of the polycrystalline silicon ingots is needed to be reduced, but it is understandable that the concentration of the organic substances adhered on the raw material surface is simultaneously needed to be reduced. Then, it is preferable that polycrystalline silicon ingots having a total of the concentrations of surface organic substances of lower than 4 ppbw be used as a raw material for growing CZ silicon single crystal.

[0042] Specifically, it is preferable that the concentration of paraffinic hydrocarbons in a concentrate of solvent-soluble components obtained by Soxhlet extraction using acetone as a solvent be lower than 300 ppmw as a value measured by a GC-MS method.

[0043] Additionally, it is preferable that the concentration of antioxidants in the concentrate of the solvent-soluble components obtained by the Soxhlet extraction using acetone as a solvent be lower than 10 ppmw as a value measured by the GC-MS method.

[0044] Additionally, it is preferable that the concentration of ultraviolet adsorbents in the concentrate of the solvent-soluble components obtained by the Soxhlet extraction using acetone as a solvent be lower than 5 ppmw as a value measured by the GC-MS method.

[0045] Additionally, it is preferable that the total concentration of antistatic agents and surfactants in the concentrate of the solvent-soluble components obtained by the Soxhlet extraction using acetone as a solvent be lower than 50 ppmw as a value measured by the GC-MS method.

[0046] Then, when the polycrystalline silicon ingots are packed, it is preferable that the polycrystalline silicon ingots be put in the above-mentioned storage bag; thereafter, the storage bag be sealed; further, the storage bag be put in a linear low-density polyethylene bag containing an antistatic agent or a surfactant added in the bag material; and the bag be sealed.

[0047] In the method for producing CZ silicon single crystal according to the present invention, there is used, as a raw material of the single crystal for CZ, polycrystalline silicon ingots having been put and stored in the above-mentioned storage bag and having a total concentration of surface organic substances of lower than 4 ppbw as a value measured by the GC-MS method.

[0048] Further, in the method for producing CZ silicon single crystal according to the present invention, the polycrystalline silicon ingots packed by the above-mentioned method are used as a raw material of the single crystal for CZ.

INDUSTRIAL APPLICABILITY

[0049] According to the present invention, it has been clarified what sort of a polyethylene bag is suitable to store polycrystalline silicon ingots provided as a raw material of single crystal for CZ while maintaining cleanliness of the surface of the polycrystalline silicon ingots. By use of such a polyethylene bag, there can be suppressed the incorporation of carbon impurities from the raw material to the CZ silicon single crystal.