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WO2013035498A1 - Method for manufacturing polycrystalline silicon ingot - Google Patents

Method for manufacturing polycrystalline silicon ingot Download PDF

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Publication number
WO2013035498A1
WO2013035498A1 PCT/JP2012/070605 JP2012070605W WO2013035498A1 WO 2013035498 A1 WO2013035498 A1 WO 2013035498A1 JP 2012070605 W JP2012070605 W JP 2012070605W WO 2013035498 A1 WO2013035498 A1 WO 2013035498A1
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WIPO (PCT)
Prior art keywords
crucible
polycrystalline silicon
silicon ingot
silicon
resistance heater
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PCT/JP2012/070605
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French (fr)
Japanese (ja)
Inventor
直行 塩塚
大石　隆一
和也 上野
梶本　公彦
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シャープ株式会社
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Publication of WO2013035498A1 publication Critical patent/WO2013035498A1/en

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C30B11/003—Heating or cooling of the melt or the crystallised material
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C30B11/007—Mechanisms for moving either the charge or the heater
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon

Definitions

  • the present invention relates to a method for producing a polycrystalline silicon ingot.
  • the casting method is a method for producing a silicon ingot by solidifying molten silicon in a crucible serving as a mold.
  • a method for solidifying molten silicon in a crucible a solid silicon raw material is charged into a crucible and melted into molten silicon, and then a molten silicon is solidified in the same crucible.
  • a silicon raw material is charged into a crucible and melted to form molten silicon, then the molten silicon is transferred into another crucible, and the molten silicon is solidified in the crucible.
  • the molten silicon is solidified while applying a temperature gradient in one direction from the bottom of the crucible, so that metal impurities (Fe, Al, Ti, etc.) with a small segregation coefficient are siliconized.
  • metal impurities Fe, Al, Ti, etc.
  • One-way solidification is widely performed by agglomerating at the upper end of the ingot and reducing the metal impurity concentration in a portion other than the upper end to about several ppm.
  • a wafer having a low impurity concentration can be obtained by manufacturing a wafer from a silicon ingot from which the upper end portion having a high metal impurity concentration is removed.
  • foreign matter including impurities such as nitrides and carbides precipitated in the silicon ingot may be generated. Large ones of these foreign substances can be identified visually or with a camera, but it is difficult to remove the foreign substances contained in the silicon ingot.
  • the small foreign material is about 10 ⁇ m in size, as described in, for example, 22nd European Photovoltaic Solar Energy Conference, 3-7 September 2007, Milan, Italy, p.994-997 (Non-patent Document 1). It is very small. Therefore, it is very difficult to identify foreign substances contained in the silicon ingot before putting the silicon ingot into the solar cell production line.
  • the wire saw wire When a silicon ingot containing foreign material is put into a solar cell production line, the wire saw wire may be cut when the wafer is cut out.
  • a device such as a solar cell is manufactured using a wafer including a foreign substance, a leakage current is generated by the foreign substance and the solar cell becomes defective, which causes a decrease in yield.
  • compositional supercooling occurs at the solid-liquid interface when solidifying molten silicon, resulting in instability of the solid-liquid interface and dendrite growth and cell growth.
  • the quality of the polycrystalline silicon is deteriorated due to the occurrence of a large disturbance in the crystalline state.
  • Patent Document 1 Japanese Patent Laid-Open Nos. 5-254817 (Patent Document 1) and 10-182135 (Patent Documents). 2) and JP-A-10-25190 (Patent Document 3).
  • JP-A-5-254817 Japanese Patent Laid-Open No. 10-182135 Japanese Patent Laid-Open No. 10-25190
  • the molten silicon is agitated by an induction heating method in which a magnetic field is applied using a coil to discharge impurities, but the apparatus is very expensive, There is a need to use a conductive material such as a graphite member as a material, and there is no freedom in selecting a material for the crucible.
  • the molten silicon is stirred by blowing an inert gas into the molten silicon above the solidification interface, but the gas pipe for blowing the inert gas is provided in the molten silicon. Therefore, the molten silicon is contaminated, and the degree of freedom in selecting the material of the gas pipe is low in terms of heat resistance.
  • Patent Document 3 when preparing a melt to be fed into a crystal growth crucible of a single crystal pulling furnace, a solid material is supplied to a melting vessel held in an Ar atmosphere, Three-phase alternating current is supplied to 3n (n is a natural number) resistance heaters arranged at equal intervals around the solid material, and the solid material is heated and dissolved while a rotating magnetic field generated by the three-phase alternating current is applied.
  • 3n is a natural number
  • the present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a polycrystalline silicon ingot capable of producing a high-quality polycrystalline silicon ingot.
  • the method for producing a polycrystalline silicon ingot according to the present invention supplies a three-phase alternating current to 3n (n is a natural number) resistance heaters arranged around a crucible, and acts on a rotating magnetic field generated by the three-phase alternating current.
  • the frequency of the three-phase alternating current is 50 Hz or more and 1000 Hz or less.
  • a high-quality polycrystalline silicon ingot can be produced.
  • FIG. 5 It is a partial cross section figure which shows the structure of the manufacturing apparatus for enforcing the manufacturing method of the polycrystalline silicon ingot which concerns on one Embodiment of this invention. It is the figure seen from the II-II line arrow direction of FIG. 5 is a graph showing changes in wire disconnection rate, foreign matter contamination rate, and leakage current failure rate with three-phase AC frequency in the method for producing a polycrystalline silicon ingot according to the embodiment.
  • FIG. 1 is a partial cross-sectional view showing a configuration of a manufacturing apparatus for carrying out a method for manufacturing a polycrystalline silicon ingot according to an embodiment of the present invention.
  • FIG. 2 is a view as seen from the direction of arrows II-II in FIG.
  • a manufacturing apparatus 1 for carrying out a method for manufacturing a polycrystalline silicon ingot according to an embodiment of the present invention includes a substantially rectangular parallelepiped casing 10 made of stainless steel.
  • An opening 11 for introducing one end of a gas supply pipe 13 to be described later into the interior of the housing 10 is provided in the upper portion of the housing 10.
  • An exhaust port 12 for exhausting the inside of the housing 10 is provided in the lower portion of the housing 10.
  • a crucible 20 is arranged inside the housing 10.
  • the crucible 20 is mounted on the mounting table 40.
  • the crucible 20 is made of silica.
  • the material of the crucible 20 is not limited to silica but may be graphite.
  • Silicon nitride powder is applied to the inner surface of the crucible 20 in order to prevent reaction with molten silicon. The silicon nitride powder is dried and then sintered.
  • the mounting table 40 is mounted on the support table 50.
  • the mounting table 40 and the support table 50 are formed of a material having high thermal conductivity and heat resistance.
  • the support base 50 is connected to the support part 71 at the lower part.
  • the support portion 71 is connected to a drive portion 70 disposed outside the housing 10 so as to be movable up and down as indicated by an arrow 72.
  • the drive unit 70 has a motor.
  • the driving unit 70 is connected to a cooling unit 90 disposed outside the housing 10.
  • the cooling unit 90 cools the drive unit 70 and the support unit 71 by circulating a cooling medium inside the drive unit 70 and the support unit 71.
  • the cooling unit 90 includes a pump and a heat exchanger. By cooling the support part 71 by the cooling part 90, the bottom part of the crucible 20 can be cooled via the support table 50 and the mounting table 40.
  • a resistance heater 30 is disposed around the crucible 20.
  • the resistance heater 30 includes a first resistance heater 31, a second resistance heater 32, and a third resistance heater 33 arranged so as to surround the crucible 20 with a space therebetween.
  • each of the first resistance heater 31 and the second resistance heater 32 has a bent shape and the third resistance heater 33 has a linear shape in plan view.
  • the shapes of the first resistance heater 31, the second resistance heater 32, and the third resistance heater 33 are not limited to the above, and may be curved in plan view.
  • Each of the first resistance heater 31, the second resistance heater 32, and the third resistance heater 33 is connected to a three-phase AC power supply 34 disposed outside the housing 10.
  • the three-phase AC power supply 34 has three systems u, v, and w. Three systems of the three-phase AC power supply 34 and the resistance heater 30 are connected to each other.
  • the u system of the three-phase AC power supply 34 and the first resistance heater 31 are connected.
  • the v system of the three-phase AC power supply 34 and the second resistance heater 32 are connected.
  • the w system of the three-phase AC power supply 34 and the third resistance heater 33 are connected.
  • An inner lid 60 made of a heat insulating material is disposed above the support base 50.
  • the inner lid 60 has a side wall that surrounds the resistance heater 30 and a ceiling that faces the support base 50.
  • the ceiling is provided with a hole for introducing one end of the gas supply pipe 13 into the inner lid 60.
  • the inner side of the inner lid 60 surrounded by the side wall portion and the ceiling portion is a heating region 61.
  • thermocouple (not shown) is arranged in the heating area 61.
  • the thermocouple is connected to a three-phase AC power source 34.
  • the voltage applied to the resistance heater 30 is controlled by feeding back the temperature measured by the thermocouple to the three-phase AC power supply 34.
  • the gas supply pipe 13 One end of the gas supply pipe 13 is positioned above the crucible 20 in the heating region 61, and the other end is connected to a gas supply unit (not shown) disposed outside the housing 10.
  • An inert gas such as Ar sent from the gas supply unit passes through the inside of the gas supply pipe 13 and is supplied into the heating region 61.
  • the gas supply unit includes a plurality of gas cylinders storing various gases and a mass flow controller.
  • the exhaust port 12 is connected to an exhaust unit (not shown) disposed outside the housing 10.
  • the exhaust part includes various vacuum pumps.
  • the inert gas supplied into the heating region 61 passes through the exhaust port 12 and is discharged to the outside of the housing 10.
  • the three-phase AC power supply 34 is turned on and a voltage is applied to the resistance heater 30.
  • a voltage is applied to the resistance heater 30
  • the temperature in the heating region 61 rises.
  • the temperature in the heating region 61 is raised to 1550 ° C. and held for 2 hours. Silicon having a melting point of 1410 ° C. is completely melted in the crucible 20.
  • molten silicon previously melted may be put into the crucible 20, and similarly, decompression, Ar gas supply, and exhaust amount adjustment may be performed.
  • the three-phase AC power supply 34 is turned on and a voltage is applied to the resistance heater 30 so that the molten silicon placed in the crucible 20 does not solidify. Good.
  • a rotating magnetic field in the direction indicated by an arrow 81 acts on the molten silicon 80 by three-phase alternating current supplied to the resistance heater 30. Specifically, the voltages of the three systems u, v, and w whose phases are shifted by 120 degrees are applied to the first resistance heater 31, the second resistance heater 32, and the third resistance heater 33, respectively. The rotational force in the same direction as the rotational direction of the rotating magnetic field acts on the molten silicon 80. As a result, the molten silicon 80 is stirred in the circumferential direction. In the vertical direction, the molten silicon 80 is stirred by thermal convection.
  • the voltage applied to the resistance heater 30 is lowered so that the temperature of the molten silicon 80 is close to the melting point.
  • the voltage applied to the resistance heater 30 is further lowered while operating the drive unit 70 to move the support unit 71 downward.
  • the bottom of the crucible 20 is positioned outside the heating region 61. Therefore, the bottom of the crucible 20 is cooled by operating the cooling unit 90. As a result, the crucible 20 is cooled from the bottom toward the top. In this way, the molten silicon 80 is gradually cooled at a cooling rate of about 1 ° C./hour while a rotating magnetic field is applied to the molten silicon 80 located in the heating region 61.
  • the molten silicon 80 is solidified in order from the bottom, and stirring of the unsolidified molten silicon 80 by the rotating magnetic field is maintained.
  • the generation of foreign substances including impurities such as carbides and nitrides precipitated in the polycrystalline silicon ingot is effectively suppressed. it can. It is also possible to suppress destabilization of the solid-liquid interface due to the occurrence of compositional supercooling.
  • the concentration of impurities contained in solid-phase silicon follows the following Scheil equation using a distribution (segregation) coefficient at the solid-liquid interface.
  • C s k ⁇ C 0 (1-f s ) k-1
  • C s Concentration of impurities contained in silicon in solid phase
  • C 0 Initial concentration of impurities contained in molten silicon before solidification
  • k Distribution (segregation) coefficient
  • fs Ratio of solid phase Distribution coefficient k is type of impurity element It varies depending on factors such as the solidification speed of molten silicon and the stirring speed of molten silicon.
  • the distribution coefficient k is reduced by stirring the molten silicon with a rotating magnetic field. Therefore, the concentration of impurities contained in the solid phase silicon is reduced, and precipitation of impurities such as silicon nitride and silicon carbide can be suppressed.
  • the gas sent from the gas supply unit is changed from Ar to He. Thereafter, the polycrystalline silicon ingot is cooled to room temperature.
  • ⁇ Remove the ends containing many impurities and crystal defects from the polycrystalline silicon ingot, cut into a predetermined size, and form blocks. Further, a plurality of wafers can be obtained by cutting the block-shaped polycrystalline silicon ingot to a predetermined thickness with a wire saw. Since this wafer is made of high-quality polycrystalline silicon in which the precipitation of impurities such as carbides and nitrides is suppressed, it contributes to improving the characteristics of the solar cell when used as a substrate.
  • a solar cell was manufactured using a wafer manufactured by the method for manufacturing a polycrystalline silicon ingot according to this embodiment.
  • the inventor focused on the frequency of the three-phase alternating current supplied to the resistance heater 30 and experimented with the relationship between the frequency and various characteristics of the polycrystalline silicon ingot. Details of the experiment will be described below.
  • the wire disconnection rate of the wire saw that was disconnected when the block-shaped polycrystalline silicon ingot was cut to a predetermined thickness was calculated.
  • the wire breakage rate is the ratio of the number of wire saw breaks to the number of wire saw cuts. The reason why the wire saw is disconnected is that the cutting resistance is rapidly changed by the foreign matter contained in the polycrystalline silicon ingot.
  • the contamination rate of foreign matter contained in the wafer was calculated by visual inspection or image analysis.
  • the foreign matter mixing rate is the ratio of the number of wafers in which foreign matter has been confirmed to the number of manufactured wafers.
  • the leakage current defect rate under the reverse voltage of the fabricated solar cell was calculated.
  • the leakage current defect rate is the ratio of the number of solar cells in which a current of 2.5 A or more flows when a voltage of ⁇ 12 V is applied to the number of manufactured solar cells.
  • the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate in the polycrystalline silicon ingot manufacturing method according to this embodiment were calculated.
  • the frequency of the three-phase alternating current was varied in the range of 1 Hz to 2000 Hz, and the wire breakage rate, foreign matter contamination rate, and leakage current failure rate calculated in the comparative example were normalized to 1 respectively.
  • FIG. 3 is a graph showing changes in the wire disconnection rate, foreign matter contamination rate, and leakage current failure rate due to the three-phase AC frequency in the method of manufacturing a polycrystalline silicon ingot according to the present embodiment.
  • the vertical axis shows the wire disconnection rate, foreign matter contamination rate and leakage current failure rate of the example normalized with the calculation result of the comparative example as 1, and the horizontal axis shows the frequency of the three-phase alternating current.
  • the frequency of the three-phase alternating current is 50 Hz or more
  • the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate were significantly reduced.
  • the frequency of the three-phase alternating current is in the range of 50 Hz to 1000 Hz
  • the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate gradually decreased as the frequency of the three-phase alternating current increased.
  • a high-quality polycrystalline silicon ingot can be manufactured by setting the frequency of the three-phase alternating current to 50 Hz or more and 1000 Hz or less.
  • three resistance heaters are arranged around the crucible 20, but the number of resistance heaters is not limited to this, and may be a natural number multiple of 3 (3n). For example, six resistance heaters may be provided, and two resistance heaters may be connected to each of u, v, and w systems.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Silicon Compounds (AREA)

Abstract

This method for manufacturing a polycrystalline silicon ingot is provided with: a heating step wherein a three-phase alternating current is supplied to 3n resistive heaters (n is a natural number) disposed on the circumference of a crucible (20), and a molten silicon inside of the crucible (20) is heated, while having a rotating magnetic field operate, said rotating magnetic field having been generated due to the three-phase alternating current; and a cooling step wherein the silicon is solidified by cooling the silicon from a bottom portion of the crucible (20) toward an upper portion, while having the rotating magnetic field operate.

Description

多結晶シリコンインゴットの製造方法Method for producing polycrystalline silicon ingot
　本発明は、多結晶シリコンインゴットの製造方法に関する。 The present invention relates to a method for producing a polycrystalline silicon ingot.
　太陽電池などに用いられる多結晶シリコンインゴットの製造方法として、キャスト法により製造されたインゴットからウエハを切り出す方法が広く用いられている。 As a method for manufacturing a polycrystalline silicon ingot used for a solar cell or the like, a method of cutting a wafer from an ingot manufactured by a casting method is widely used.
　キャスト法とは、鋳型となる坩堝内で溶融シリコンを凝固させてシリコンインゴットを製造する方法である。溶融シリコンを坩堝内で凝固させる方法としては、固体状のシリコン原料を坩堝内に投入し、溶解させて溶融シリコンにした後、同一の坩堝内でシリコン溶湯を凝固させる方法、または、固体状のシリコン原料を坩堝内に投入し、溶解させて溶融シリコンにした後、別の坩堝内に溶融シリコンを移し、その坩堝内で溶融シリコンを凝固させる方法などがある。 The casting method is a method for producing a silicon ingot by solidifying molten silicon in a crucible serving as a mold. As a method for solidifying molten silicon in a crucible, a solid silicon raw material is charged into a crucible and melted into molten silicon, and then a molten silicon is solidified in the same crucible, There is a method in which a silicon raw material is charged into a crucible and melted to form molten silicon, then the molten silicon is transferred into another crucible, and the molten silicon is solidified in the crucible.
　キャスト法においては、シリコンインゴットを製造する際に、坩堝の底部から一方向に温度勾配をつけながら溶融シリコンを凝固させることで、偏析係数が小さな金属不純物類(Ｆｅ，Ａｌ，Ｔｉなど)をシリコンインゴットの上端に凝集させて、上端以外の部分の金属不純物濃度を数ｐｐｍ程度にまで低減可能な一方向凝固が広く行なわれている。金属不純物濃度の高い上端部分を取り除いたシリコンインゴットからウエハを製造することにより、不純物濃度の少ないウエハが得られる。 In the casting method, when manufacturing a silicon ingot, the molten silicon is solidified while applying a temperature gradient in one direction from the bottom of the crucible, so that metal impurities (Fe, Al, Ti, etc.) with a small segregation coefficient are siliconized. One-way solidification is widely performed by agglomerating at the upper end of the ingot and reducing the metal impurity concentration in a portion other than the upper end to about several ppm. A wafer having a low impurity concentration can be obtained by manufacturing a wafer from a silicon ingot from which the upper end portion having a high metal impurity concentration is removed.
　上記の製造方法を用いてウエハを製造する過程で、シリコンインゴットの内部に析出する窒化物および炭化物などの不純物を含む異物が発生する場合がある。この異物のうち大きいものは目視またはカメラにて識別可能であるが、シリコンインゴットの内部に含まれる異物を除去することは難しい。 In the process of manufacturing a wafer using the above manufacturing method, foreign matter including impurities such as nitrides and carbides precipitated in the silicon ingot may be generated. Large ones of these foreign substances can be identified visually or with a camera, but it is difficult to remove the foreign substances contained in the silicon ingot.
　異物のうち小さいものは、たとえば、22nd　European　Photovoltaic　Solar　Energy　Conference,3-7　September　2007,Milan,Italy、p.994-997(非特許文献１)に記載されているように、１０μｍ程度の大きさであり非常に小さい。そのため、シリコンインゴットを太陽電池の製造ラインに投入する前に、シリコンインゴットに含まれる異物を識別することは非常に困難である。 The small foreign material is about 10 μm in size, as described in, for example, 22nd European Photovoltaic Solar Energy Conference, 3-7 September 2007, Milan, Italy, p.994-997 (Non-patent Document 1). It is very small. Therefore, it is very difficult to identify foreign substances contained in the silicon ingot before putting the silicon ingot into the solar cell production line.
　異物を含むシリコンインゴットが太陽電池の製造ラインに投入されると、ウエハを切り出す際にワイヤーソーのワイヤーを切断させることがある。また、異物を含むウエハを用いて太陽電池などのデバイスを作製した場合、異物によりリーク電流が発生して太陽電池が不良となり、歩留まり低下の原因となる。 When a silicon ingot containing foreign material is put into a solar cell production line, the wire saw wire may be cut when the wafer is cut out. In addition, when a device such as a solar cell is manufactured using a wafer including a foreign substance, a leakage current is generated by the foreign substance and the solar cell becomes defective, which causes a decrease in yield.
　また、上記の製造方法を用いてウエハを製造する過程で、溶融シリコンを凝固させる際に固液界面において組成的過冷却が発生することで、固液界面が不安定になりデンドライト成長およびセル成長などが発生、または、結晶状態に大きな乱れが発生することにより多結晶シリコンの質が低下する。 In addition, during the process of manufacturing a wafer using the above manufacturing method, compositional supercooling occurs at the solid-liquid interface when solidifying molten silicon, resulting in instability of the solid-liquid interface and dendrite growth and cell growth. The quality of the polycrystalline silicon is deteriorated due to the occurrence of a large disturbance in the crystalline state.
　異物の発生を抑制するために溶融シリコンを攪拌してシリコンインゴットを製造する方法を開示した先行文献として、特開平５－２５４８１７号公報(特許文献１)、特開平１０－１８２１３５号公報(特許文献２)および特開平１０－２５１９０号公報(特許文献３)がある。 As prior literatures that disclose a method for producing a silicon ingot by stirring molten silicon in order to suppress the generation of foreign substances, Japanese Patent Laid-Open Nos. 5-254817 (Patent Document 1) and 10-182135 (Patent Documents). 2) and JP-A-10-25190 (Patent Document 3).
特開平５－２５４８１７号公報JP-A-5-254817 特開平１０－１８２１３５号公報Japanese Patent Laid-Open No. 10-182135 特開平１０－２５１９０号公報Japanese Patent Laid-Open No. 10-25190
　特許文献１にて開示されている方法によれば、コイルを用いて磁界を加える誘導加熱方式により溶融シリコンを撹拌して不純物を排出させているが、装置が非常に高価となり、また、坩堝の材料として黒鉛部材などの導電性材料を使用する必要性があり、坩堝の材料選択の自由度がない。 According to the method disclosed in Patent Document 1, the molten silicon is agitated by an induction heating method in which a magnetic field is applied using a coil to discharge impurities, but the apparatus is very expensive, There is a need to use a conductive material such as a graphite member as a material, and there is no freedom in selecting a material for the crucible.
　特許文献２にて開示されている方法によれば、凝固界面より上方の溶融シリコン内に不活性ガスを吹き込むことにより溶融シリコンを撹拌しているが、不活性ガスを吹き込むガス管を溶融シリコン内に直接浸漬させる必要があり、溶融シリコンが汚染され、また、耐熱温度の面からガス管の材料選択の自由度が少ない。 According to the method disclosed in Patent Document 2, the molten silicon is stirred by blowing an inert gas into the molten silicon above the solidification interface, but the gas pipe for blowing the inert gas is provided in the molten silicon. Therefore, the molten silicon is contaminated, and the degree of freedom in selecting the material of the gas pipe is low in terms of heat resistance.
　特許文献３にて開示されている方法によれば、単結晶引上げ炉の結晶成長用坩堝に送り込まれる融液を調製する際、Ａｒ雰囲気に保持された溶解容器に固体原料を供給し、溶解容器の周囲に等間隔で配置された３ｎ個(ｎは自然数)の抵抗加熱ヒータに三相交流を供給し、三相交流によって生じる回転磁場を作用させながら固体原料を加熱溶解している。しかしながら、この方法にて多結晶シリコンを成長させると上記の組成的過冷却が発生し、多結晶シリコンの品質が低下する。 According to the method disclosed in Patent Document 3, when preparing a melt to be fed into a crystal growth crucible of a single crystal pulling furnace, a solid material is supplied to a melting vessel held in an Ar atmosphere, Three-phase alternating current is supplied to 3n (n is a natural number) resistance heaters arranged at equal intervals around the solid material, and the solid material is heated and dissolved while a rotating magnetic field generated by the three-phase alternating current is applied. However, when polycrystalline silicon is grown by this method, the above compositional supercooling occurs and the quality of the polycrystalline silicon is lowered.
　本発明は上記の問題点に鑑みてなされたものであって、高品質な多結晶シリコンインゴットを作製できる多結晶シリコンインゴットの製造方法を提供することを目的とする。 The present invention has been made in view of the above problems, and an object of the present invention is to provide a method for producing a polycrystalline silicon ingot capable of producing a high-quality polycrystalline silicon ingot.
　本発明に基づく多結晶シリコンインゴットの製造方法は、坩堝の周囲に配置された３ｎ個(ｎは自然数)の抵抗加熱ヒータに３相交流を供給し、３相交流によって生じる回転磁場を作用させつつ、坩堝内の溶融シリコンを加熱する加熱工程と、上記回転磁場を作用させつつ、坩堝の底部から上部に向けて冷却してシリコンを凝固させる冷却工程と備える。 The method for producing a polycrystalline silicon ingot according to the present invention supplies a three-phase alternating current to 3n (n is a natural number) resistance heaters arranged around a crucible, and acts on a rotating magnetic field generated by the three-phase alternating current. A heating step of heating the molten silicon in the crucible, and a cooling step of solidifying the silicon by cooling from the bottom to the top of the crucible while applying the rotating magnetic field.
　好ましくは、３相交流の周波数が５０Ｈｚ以上１０００Ｈｚ以下である。 Preferably, the frequency of the three-phase alternating current is 50 Hz or more and 1000 Hz or less.
　本発明によれば、高品質な多結晶シリコンインゴットを作製できる。 According to the present invention, a high-quality polycrystalline silicon ingot can be produced.
本発明の一実施形態に係る多結晶シリコンインゴットの製造方法を実施するための製造装置の構成を示す一部断面図である。It is a partial cross section figure which shows the structure of the manufacturing apparatus for enforcing the manufacturing method of the polycrystalline silicon ingot which concerns on one Embodiment of this invention. 図１のＩＩ－ＩＩ線矢印方向から見た図である。It is the figure seen from the II-II line arrow direction of FIG. 同実施形態に係る多結晶シリコンインゴットの製造方法において、３相交流の周波数によるワイヤ断線率、異物混入率およびリーク電流不良率の変化を示すグラフである。5 is a graph showing changes in wire disconnection rate, foreign matter contamination rate, and leakage current failure rate with three-phase AC frequency in the method for producing a polycrystalline silicon ingot according to the embodiment.
　以下、本発明の一実施形態に係る多結晶シリコンインゴットの製造方法について説明する。以下の実施形態の説明においては、図中の同一または相当部分には同一符号を付して、その説明は繰り返さない。 Hereinafter, a method for manufacturing a polycrystalline silicon ingot according to an embodiment of the present invention will be described. In the following description of the embodiments, the same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.
　図１は、本発明の一実施形態に係る多結晶シリコンインゴットの製造方法を実施するための製造装置の構成を示す一部断面図である。図２は、図１のＩＩ－ＩＩ線矢印方向から見た図である。 FIG. 1 is a partial cross-sectional view showing a configuration of a manufacturing apparatus for carrying out a method for manufacturing a polycrystalline silicon ingot according to an embodiment of the present invention. FIG. 2 is a view as seen from the direction of arrows II-II in FIG.
　図１，２に示すように、本発明の一実施形態に係る多結晶シリコンインゴットの製造方法を実施するための製造装置１は、ステンレスからなる略直方体状の筐体１０を含む。筐体１０の上部には、後述するガス供給管１３の一端を筐体１０の内部に導入するための開口１１が設けられている。筐体１０の下部に、筐体１０内を排気するための排気口１２が設けられている。 As shown in FIGS. 1 and 2, a manufacturing apparatus 1 for carrying out a method for manufacturing a polycrystalline silicon ingot according to an embodiment of the present invention includes a substantially rectangular parallelepiped casing 10 made of stainless steel. An opening 11 for introducing one end of a gas supply pipe 13 to be described later into the interior of the housing 10 is provided in the upper portion of the housing 10. An exhaust port 12 for exhausting the inside of the housing 10 is provided in the lower portion of the housing 10.
　筐体１０の内部に、坩堝２０が配置されている。坩堝２０は、載置台４０上に載置されている。坩堝２０は、シリカで構成されている。ただし、坩堝２０の材質はシリカに限られずグラファイトなどでもよい。坩堝２０の内面には、溶融シリコンとの反応を防止するために、窒化珪素粉が塗布されている。窒化珪素粉は、乾燥された後、焼結されている。 A crucible 20 is arranged inside the housing 10. The crucible 20 is mounted on the mounting table 40. The crucible 20 is made of silica. However, the material of the crucible 20 is not limited to silica but may be graphite. Silicon nitride powder is applied to the inner surface of the crucible 20 in order to prevent reaction with molten silicon. The silicon nitride powder is dried and then sintered.
　載置台４０は、支持台５０上に載置されている。載置台４０および支持台５０は、高い熱伝導性および耐熱性を有する材料で形成されている。支持台５０は、下部で支持部７１に接続されている。支持部７１は、矢印７２で示すように上下に移動可能となるように、筐体１０の外に配置された駆動部７０に接続されている。駆動部７０は、モータを有している。 The mounting table 40 is mounted on the support table 50. The mounting table 40 and the support table 50 are formed of a material having high thermal conductivity and heat resistance. The support base 50 is connected to the support part 71 at the lower part. The support portion 71 is connected to a drive portion 70 disposed outside the housing 10 so as to be movable up and down as indicated by an arrow 72. The drive unit 70 has a motor.
　駆動部７０は、筐体１０の外に配置された冷却部９０と接続されている。冷却部９０は、冷却媒体を駆動部７０および支持部７１の内部で循環させることにより、駆動部７０および支持部７１を冷却している。冷却部９０は、ポンプおよび熱交換器を有している。冷却部９０により支持部７１を冷却することにより、支持台５０および載置台４０を介して、坩堝２０の底部を冷却することができる。 The driving unit 70 is connected to a cooling unit 90 disposed outside the housing 10. The cooling unit 90 cools the drive unit 70 and the support unit 71 by circulating a cooling medium inside the drive unit 70 and the support unit 71. The cooling unit 90 includes a pump and a heat exchanger. By cooling the support part 71 by the cooling part 90, the bottom part of the crucible 20 can be cooled via the support table 50 and the mounting table 40.
　坩堝２０の周囲に抵抗加熱ヒータ３０が配置されている。抵抗加熱ヒータ３０は、互いに間隔を置いて坩堝２０を取り囲むように配置された第１抵抗加熱ヒータ３１、第２抵抗加熱ヒータ３２および第３抵抗加熱ヒータ３３から構成されている。 A resistance heater 30 is disposed around the crucible 20. The resistance heater 30 includes a first resistance heater 31, a second resistance heater 32, and a third resistance heater 33 arranged so as to surround the crucible 20 with a space therebetween.
　本実施形態においては、平面視において、第１抵抗加熱ヒータ３１および第２抵抗加熱ヒータ３２の各々は屈曲形状を有し、第３抵抗加熱ヒータ３３は直線形状を有している。ただし、第１抵抗加熱ヒータ３１、第２抵抗加熱ヒータ３２および第３抵抗加熱ヒータ３３の形状は上記に限られず、平面視において湾曲形状でもよい。 In the present embodiment, each of the first resistance heater 31 and the second resistance heater 32 has a bent shape and the third resistance heater 33 has a linear shape in plan view. However, the shapes of the first resistance heater 31, the second resistance heater 32, and the third resistance heater 33 are not limited to the above, and may be curved in plan view.
　第１抵抗加熱ヒータ３１、第２抵抗加熱ヒータ３２および第３抵抗加熱ヒータ３３の各々は、筐体１０の外に配置された３相交流電源３４に接続されている。３相交流電源３４は、ｕ，ｖ，ｗの３系統を有している。３相交流電源３４の３系統と抵抗加熱ヒータ３０とがそれぞれ接続されている。 Each of the first resistance heater 31, the second resistance heater 32, and the third resistance heater 33 is connected to a three-phase AC power supply 34 disposed outside the housing 10. The three-phase AC power supply 34 has three systems u, v, and w. Three systems of the three-phase AC power supply 34 and the resistance heater 30 are connected to each other.
　具体的には、３相交流電源３４のｕ系統と第１抵抗加熱ヒータ３１とが接続されている。３相交流電源３４のｖ系統と第２抵抗加熱ヒータ３２とが接続されている。３相交流電源３４のｗ系統と第３抵抗加熱ヒータ３３とが接続されている。 Specifically, the u system of the three-phase AC power supply 34 and the first resistance heater 31 are connected. The v system of the three-phase AC power supply 34 and the second resistance heater 32 are connected. The w system of the three-phase AC power supply 34 and the third resistance heater 33 are connected.
　支持台５０の上方に断熱材からなる中蓋６０が配置されている。中蓋６０は、抵抗加熱ヒータ３０の周囲を囲む側壁部と、支持台５０に対向する天井部とを有している。天井部には、ガス供給管１３の一端を中蓋６０の内側に導入するための孔が設けられている。側壁部と天井部とに囲まれた中蓋６０の内側が加熱領域６１となる。 An inner lid 60 made of a heat insulating material is disposed above the support base 50. The inner lid 60 has a side wall that surrounds the resistance heater 30 and a ceiling that faces the support base 50. The ceiling is provided with a hole for introducing one end of the gas supply pipe 13 into the inner lid 60. The inner side of the inner lid 60 surrounded by the side wall portion and the ceiling portion is a heating region 61.
　加熱領域６１には、図示しない熱電対が配置されている。熱電対は３相交流電源３４に接続されている。熱電対による測定温度が３相交流電源３４にフィードバックされることにより、抵抗加熱ヒータ３０への印加電圧が制御される。 In the heating area 61, a thermocouple (not shown) is arranged. The thermocouple is connected to a three-phase AC power source 34. The voltage applied to the resistance heater 30 is controlled by feeding back the temperature measured by the thermocouple to the three-phase AC power supply 34.
　ガス供給管１３の一端は加熱領域６１内において坩堝２０の上方に位置し、他端は筐体１０の外に配置された図示しないガス供給部に接続されている。ガス供給部から送られるＡｒなどの不活性ガスは、ガス供給管１３の内部を通過して加熱領域６１内に供給される。ガス供給部は、各種のガスを貯蔵した複数のガスボンベおよびマスフローコントローラを含む。 One end of the gas supply pipe 13 is positioned above the crucible 20 in the heating region 61, and the other end is connected to a gas supply unit (not shown) disposed outside the housing 10. An inert gas such as Ar sent from the gas supply unit passes through the inside of the gas supply pipe 13 and is supplied into the heating region 61. The gas supply unit includes a plurality of gas cylinders storing various gases and a mass flow controller.
　排気口１２は、筐体１０の外に配置された図示しない排気部に接続されている。排気部は、各種の真空ポンプを含む。加熱領域６１内に供給された不活性ガスは、排気口１２を通過して筐体１０の外部に排出される。 The exhaust port 12 is connected to an exhaust unit (not shown) disposed outside the housing 10. The exhaust part includes various vacuum pumps. The inert gas supplied into the heating region 61 passes through the exhaust port 12 and is discharged to the outside of the housing 10.
　以下、本実施形態に係る多結晶シリコンインゴットの製造方法について説明する。
　まず、約４００ｋｇの粒状または塊状のシリコンを坩堝２０内に入れる。その後、排気部の真空ポンプを稼動させて筐体１０内を減圧する。ガス供給管１３から加熱領域６１内にＡｒガスを１０リットル／分程度供給する。この状態で、筐体１０内の圧力が０．６Ｐａ以上０．９Ｐａ以下程度となるように排気部による排気量を調節する。 Hereinafter, a method for manufacturing a polycrystalline silicon ingot according to the present embodiment will be described.
First, about 400 kg of granular or lump silicon is put into the crucible 20. Thereafter, the inside of the housing 10 is depressurized by operating the vacuum pump of the exhaust part. Ar gas is supplied from the gas supply pipe 13 into the heating region 61 at about 10 liters / minute. In this state, the exhaust amount by the exhaust unit is adjusted so that the pressure in the housing 10 is about 0.6 Pa to 0.9 Pa.
　次に、３相交流電源３４をＯＮにして抵抗加熱ヒータ３０に電圧を印加する。抵抗加熱ヒータ３０に電圧が印加されることにより、加熱領域６１内の温度が上昇する。本実施形態においては、加熱領域６１内の温度を１５５０℃まで上昇させて２時間保持する。融点が１４１０℃であるシリコンは、坩堝２０内で完全に融解する。 Next, the three-phase AC power supply 34 is turned on and a voltage is applied to the resistance heater 30. When a voltage is applied to the resistance heater 30, the temperature in the heating region 61 rises. In the present embodiment, the temperature in the heating region 61 is raised to 1550 ° C. and held for 2 hours. Silicon having a melting point of 1410 ° C. is completely melted in the crucible 20.
　なお、粒状または塊状のシリコンに代えて予め溶融状態とした溶融シリコンを坩堝２０に入れ、同様に、減圧、Ａｒガス供給および排気量調節を行なってもよい。この場合、溶融シリコンを坩堝２０に入れる前に、３相交流電源３４をＯＮにして抵抗加熱ヒータ３０に電圧を印加しておいて、坩堝２０に入れた溶融シリコンが凝固しないようにしておけばよい。 In addition, instead of granular or lump silicon, molten silicon previously melted may be put into the crucible 20, and similarly, decompression, Ar gas supply, and exhaust amount adjustment may be performed. In this case, before putting the molten silicon into the crucible 20, the three-phase AC power supply 34 is turned on and a voltage is applied to the resistance heater 30 so that the molten silicon placed in the crucible 20 does not solidify. Good.
　溶融シリコン８０には、抵抗加熱ヒータ３０に供給される３相交流によって矢印８１で示す向きの回転磁場が作用する。具体的には、１２０度ずつ位相がずれた３系統ｕ，ｖ，ｗの電圧のそれぞれが第１抵抗加熱ヒータ３１、第２抵抗加熱ヒータ３２および第３抵抗加熱ヒータ３３に印加されることにより、溶融シリコン８０に回転磁場の回転方向と同じ方向の回転力が働く。その結果、溶融シリコン８０が円周方向に攪拌される。鉛直方向においては、熱対流により溶融シリコン８０が攪拌される。 A rotating magnetic field in the direction indicated by an arrow 81 acts on the molten silicon 80 by three-phase alternating current supplied to the resistance heater 30. Specifically, the voltages of the three systems u, v, and w whose phases are shifted by 120 degrees are applied to the first resistance heater 31, the second resistance heater 32, and the third resistance heater 33, respectively. The rotational force in the same direction as the rotational direction of the rotating magnetic field acts on the molten silicon 80. As a result, the molten silicon 80 is stirred in the circumferential direction. In the vertical direction, the molten silicon 80 is stirred by thermal convection.
　溶融シリコン８０を攪拌することにより、溶融シリコン８０の温度ムラ、および、溶融シリコン８０に含まれる炭化物および窒化物などの不純物の濃度ムラを低減できる。 By stirring the molten silicon 80, temperature unevenness of the molten silicon 80 and uneven concentration of impurities such as carbides and nitrides contained in the molten silicon 80 can be reduced.
　その後、溶融シリコン８０の温度が融点付近になるように抵抗加熱ヒータ３０に印加する電圧を下げる。融点より少し高い温度まで溶融シリコン８０が冷却されると、駆動部７０を稼動させて支持部７１を下方に移動させつつ、抵抗加熱ヒータ３０に印加する電圧をさらに下げる。 Thereafter, the voltage applied to the resistance heater 30 is lowered so that the temperature of the molten silicon 80 is close to the melting point. When the molten silicon 80 is cooled to a temperature slightly higher than the melting point, the voltage applied to the resistance heater 30 is further lowered while operating the drive unit 70 to move the support unit 71 downward.
　支持部７１が下降することにより、坩堝２０の底部が加熱領域６１の外側に位置するようになる。そこで、冷却部９０を稼動することにより坩堝２０の底部を冷却する。その結果、坩堝２０は、底部から上部に向けて冷却される。このようにして、加熱領域６１内に位置する溶融シリコン８０に回転磁場を作用させつつ、溶融シリコン８０を１℃／時間程度の冷却速度で徐冷する。 When the support portion 71 is lowered, the bottom of the crucible 20 is positioned outside the heating region 61. Therefore, the bottom of the crucible 20 is cooled by operating the cooling unit 90. As a result, the crucible 20 is cooled from the bottom toward the top. In this way, the molten silicon 80 is gradually cooled at a cooling rate of about 1 ° C./hour while a rotating magnetic field is applied to the molten silicon 80 located in the heating region 61.
　その結果、坩堝２０内において、底部から順に溶融シリコン８０が凝固し、凝固していない溶融シリコン８０の回転磁場による攪拌は維持される。このように加熱中および冷却中に回転磁場を作用させて多結晶シリコンインゴットを作製することにより、多結晶シリコンインゴット内に析出する炭化物および窒化物などの不純物を含む異物の発生を効果的に抑制できる。また、組成的過冷却の発生による固液界面の不安定化を抑制することも可能である。 As a result, in the crucible 20, the molten silicon 80 is solidified in order from the bottom, and stirring of the unsolidified molten silicon 80 by the rotating magnetic field is maintained. By producing a polycrystalline silicon ingot by applying a rotating magnetic field during heating and cooling in this way, the generation of foreign substances including impurities such as carbides and nitrides precipitated in the polycrystalline silicon ingot is effectively suppressed. it can. It is also possible to suppress destabilization of the solid-liquid interface due to the occurrence of compositional supercooling.
　一般に、固相のシリコンに含まれる不純物の濃度は、固液界面を境に分配（偏析）係数を用いた下記のＳｃｈｅｉｌの式に従う。
Ｃs＝ｋ・Ｃ0(１－ｆs)k-1
Ｃs：固相のシリコンに含まれる不純物の濃度
Ｃ0：凝固前の溶融シリコンに含まれる不純物の初期濃度
ｋ：分配（偏析）係数
ｆs：固相の割合
　分配係数ｋは、不純物元素の種類、溶融シリコンの凝固速度および溶融シリコンの攪拌速度などの要因により変化する。本実施形態においては、溶融シリコンの回転磁場による攪拌により分配係数ｋが小さくなる。そのため、固相のシリコンに含まれる不純物の濃度が低くなり、窒化珪素および炭化珪素などの不純物の析出を抑制することができる。 In general, the concentration of impurities contained in solid-phase silicon follows the following Scheil equation using a distribution (segregation) coefficient at the solid-liquid interface.
C s = k · C 0 (1-f s ) k-1
C s : Concentration of impurities contained in silicon in solid phase C 0 : Initial concentration of impurities contained in molten silicon before solidification k: Distribution (segregation) coefficient fs: Ratio of solid phase Distribution coefficient k is type of impurity element It varies depending on factors such as the solidification speed of molten silicon and the stirring speed of molten silicon. In the present embodiment, the distribution coefficient k is reduced by stirring the molten silicon with a rotating magnetic field. Therefore, the concentration of impurities contained in the solid phase silicon is reduced, and precipitation of impurities such as silicon nitride and silicon carbide can be suppressed.
　多結晶シリコンインゴットの温度が９００℃付近まで下がると、ガス供給部から送られるガスをＡｒからＨｅに変える。その後、多結晶シリコンインゴットを室温まで冷却する。 When the temperature of the polycrystalline silicon ingot drops to around 900 ° C., the gas sent from the gas supply unit is changed from Ar to He. Thereafter, the polycrystalline silicon ingot is cooled to room temperature.
　多結晶シリコンインゴットから不純物および結晶欠陥を多く含む端部を除去し、所定の大きさに切断してブロック状にする。さらに、ブロック状の多結晶シリコンインゴットをワイヤーソーにより所定の厚さに切断することにより複数枚のウエハが得られる。このウエハは、炭化物および窒化物などの不純物の析出が抑制された高品質の多結晶シリコンで構成されているため、基板として用いられることにより太陽電池の特性向上に寄与する。 ∙ Remove the ends containing many impurities and crystal defects from the polycrystalline silicon ingot, cut into a predetermined size, and form blocks. Further, a plurality of wafers can be obtained by cutting the block-shaped polycrystalline silicon ingot to a predetermined thickness with a wire saw. Since this wafer is made of high-quality polycrystalline silicon in which the precipitation of impurities such as carbides and nitrides is suppressed, it contributes to improving the characteristics of the solar cell when used as a substrate.
　本実施形態に係る多結晶シリコンインゴットの製造方法により作製したウエハを用いて太陽電池を製作した。本発明者は、抵抗加熱ヒータ３０に供給される３相交流の周波数に着目し、周波数と多結晶シリコンインゴットの諸特性との関係を実験した。以下、実験の詳細について説明する。 A solar cell was manufactured using a wafer manufactured by the method for manufacturing a polycrystalline silicon ingot according to this embodiment. The inventor focused on the frequency of the three-phase alternating current supplied to the resistance heater 30 and experimented with the relationship between the frequency and various characteristics of the polycrystalline silicon ingot. Details of the experiment will be described below.
　(実験例)
　まず、比較例として、抵抗加熱ヒータ３０に直流電源を接続し、その他は本実施形態の多結晶シリコンインゴットの製造方法と同様にしてウエハを作製した。すなわち、回転磁場を作用させないで加熱工程および冷却工程を行なった。作製されたウエハを用いて太陽電池を作製した。 (Experimental example)
First, as a comparative example, a DC power source was connected to the resistance heater 30, and the other processes were performed in the same manner as in the polycrystalline silicon ingot manufacturing method of this embodiment. That is, the heating step and the cooling step were performed without applying a rotating magnetic field. A solar cell was produced using the produced wafer.
　比較例において、ブロック状の多結晶シリコンインゴットを所定の厚さに切断する際に断線したワイヤーソーのワイヤ断線率を算定した。ワイヤ断線率は、ワイヤーソーによる切断回数に対するワイヤーソーの断線回数の割合である。ワイヤーソーが断線する理由は、多結晶シリコンインゴットに含まれる異物によって切断抵抗が急激に変化するためである。 In the comparative example, the wire disconnection rate of the wire saw that was disconnected when the block-shaped polycrystalline silicon ingot was cut to a predetermined thickness was calculated. The wire breakage rate is the ratio of the number of wire saw breaks to the number of wire saw cuts. The reason why the wire saw is disconnected is that the cutting resistance is rapidly changed by the foreign matter contained in the polycrystalline silicon ingot.
　また、目視または画像解析などによりウエハに異物が含まれている異物混入率を算定した。異物混入率は、作製されたウエハの枚数に対する異物が確認されたウエハの枚数の割合である。 Also, the contamination rate of foreign matter contained in the wafer was calculated by visual inspection or image analysis. The foreign matter mixing rate is the ratio of the number of wafers in which foreign matter has been confirmed to the number of manufactured wafers.
　さらに、作製された太陽電池の逆方向電圧下におけるリーク電流不良率を算定した。リーク電流不良率は、作製された太陽電池の個数に対して、－１２Ｖの電圧を印加した際に２．５Ａ以上の電流が流れた太陽電池の個数の割合である。 Furthermore, the leakage current defect rate under the reverse voltage of the fabricated solar cell was calculated. The leakage current defect rate is the ratio of the number of solar cells in which a current of 2.5 A or more flows when a voltage of −12 V is applied to the number of manufactured solar cells.
　次に、実施例として、本実施形態に係る多結晶シリコンインゴットの製造方法におけるワイヤ断線率、異物混入率およびリーク電流不良率を算定した。３相交流の周波数を１Ｈｚ～２０００Ｈｚの範囲で変化させ、比較例で算定されたワイヤ断線率、異物混入率およびリーク電流不良率をそれぞれ１として規格化した。 Next, as an example, the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate in the polycrystalline silicon ingot manufacturing method according to this embodiment were calculated. The frequency of the three-phase alternating current was varied in the range of 1 Hz to 2000 Hz, and the wire breakage rate, foreign matter contamination rate, and leakage current failure rate calculated in the comparative example were normalized to 1 respectively.
　図３は、本実施形態に係る多結晶シリコンインゴットの製造方法において、３相交流の周波数によるワイヤ断線率、異物混入率およびリーク電流不良率の変化を示すグラフである。図３においては、縦軸に比較例の算定結果を１として規格化した実施例のワイヤ断線率、異物混入率およびリーク電流不良率、横軸に３相交流の周波数を示している。 FIG. 3 is a graph showing changes in the wire disconnection rate, foreign matter contamination rate, and leakage current failure rate due to the three-phase AC frequency in the method of manufacturing a polycrystalline silicon ingot according to the present embodiment. In FIG. 3, the vertical axis shows the wire disconnection rate, foreign matter contamination rate and leakage current failure rate of the example normalized with the calculation result of the comparative example as 1, and the horizontal axis shows the frequency of the three-phase alternating current.
　図３に示すように、３相交流の周波数が５０Ｈｚ以上でワイヤ断線率、異物混入率およびリーク電流不良率が著しく低下していた。３相交流の周波数が５０Ｈｚ以上１０００Ｈｚ以下の範囲では、３相交流の周波数が大きくなるに従ってワイヤ断線率、異物混入率およびリーク電流不良率が徐々に低下していた。 As shown in FIG. 3, when the frequency of the three-phase alternating current is 50 Hz or more, the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate were significantly reduced. When the frequency of the three-phase alternating current is in the range of 50 Hz to 1000 Hz, the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate gradually decreased as the frequency of the three-phase alternating current increased.
　ただし、３相交流の周波数が１０００Ｈｚより大きくなると、ワイヤ断線率、異物混入率およびリーク電流不良率は略横ばいになった。これは、３相交流の周波数の増加に対する回転磁場の回転数の増加率が低下するすべり現象が原因と推測される。 However, when the frequency of the three-phase alternating current was higher than 1000 Hz, the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate were almost flat. This is presumed to be caused by a slip phenomenon in which the rate of increase in the number of rotations of the rotating magnetic field with respect to the increase in the frequency of the three-phase alternating current decreases.
　上記の結果から、３相交流の周波数を５０Ｈｚ以上１０００Ｈｚ以下にすることにより、ワイヤ断線率、異物混入率およびリーク電流不良率を著しく低減できる。すなわち、３相交流の周波数を５０Ｈｚ以上１０００Ｈｚ以下にすることにより、高品質の多結晶シリコンインゴットを製造することができる。 From the above results, by setting the frequency of the three-phase alternating current to 50 Hz or more and 1000 Hz or less, the wire disconnection rate, the foreign matter contamination rate, and the leakage current failure rate can be significantly reduced. That is, a high-quality polycrystalline silicon ingot can be manufactured by setting the frequency of the three-phase alternating current to 50 Hz or more and 1000 Hz or less.
　本実施形態においては、坩堝２０の周囲に３個の抵抗加熱ヒータを配置したが、抵抗加熱ヒータの数はこれに限られず、３の自然数倍(３ｎ)個であればよい。たとえば、６個の抵抗加熱ヒータを設け、ｕ，ｖ，ｗの各系統に対して２個の抵抗加熱ヒータを接続してもよい。 In the present embodiment, three resistance heaters are arranged around the crucible 20, but the number of resistance heaters is not limited to this, and may be a natural number multiple of 3 (3n). For example, six resistance heaters may be provided, and two resistance heaters may be connected to each of u, v, and w systems.
　このように抵抗加熱ヒータの数を多くすることにより強力な回転磁場を発生させて、溶融シリコン８０の攪拌をさらに強力に行なうことができる。その結果、多結晶シリコンインゴット内に析出する炭化物および窒化物などの不純物を含む異物の発生と組成的過冷却による固液界面の不安定化とをさらに抑制できる。 In this way, by increasing the number of resistance heaters, a strong rotating magnetic field can be generated, and the molten silicon 80 can be stirred more strongly. As a result, it is possible to further suppress the generation of foreign matters including impurities such as carbides and nitrides precipitated in the polycrystalline silicon ingot and the destabilization of the solid-liquid interface due to compositional supercooling.
　今回開示された実施形態はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて請求の範囲によって示され、請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。 The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
　１　製造装置、１０　筐体、１１　開口、１２　排気口、１３　ガス供給管、２０　坩堝、３０　抵抗加熱ヒータ、３１　第１抵抗加熱ヒータ、３２　第２抵抗加熱ヒータ、３３　第３抵抗加熱ヒータ、３４　交流電源、４０　載置台、５０　支持台、６０　中蓋、６１　加熱領域、７０　駆動部、７１　支持部、８０　溶融シリコン、９０　冷却部。 DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus, 10 housing | casing, 11 opening, 12 exhaust port, 13 gas supply pipe, 20 crucible, 30 resistance heater, 31 1st resistance heater, 32 2nd resistance heater, 33 3rd resistance heater, 34 AC power source, 40 mounting table, 50 support table, 60 inner lid, 61 heating area, 70 drive unit, 71 support unit, 80 molten silicon, 90 cooling unit.

Claims (2)

  1. 　坩堝(２０)の周囲に配置された３ｎ個(ｎは自然数)の抵抗加熱ヒータ(３０)に３相交流を供給し、前記３相交流によって生じる回転磁場を作用させつつ、前記坩堝(２０)内の溶融シリコンを加熱する加熱工程と、
    　前記回転磁場を作用させつつ、前記坩堝(２０)の底部から上部に向けて冷却して前記シリコンを凝固させる冷却工程と
    備える、多結晶シリコンインゴットの製造方法。     A three-phase alternating current is supplied to 3n (n is a natural number) resistance heaters (30) arranged around the crucible (20), and a rotating magnetic field generated by the three-phase alternating current is applied to the crucible (20). A heating step for heating the molten silicon inside,
    A method for producing a polycrystalline silicon ingot, comprising: a cooling step in which the silicon is solidified by cooling from the bottom to the top of the crucible (20) while applying the rotating magnetic field.
  2. 　前記３相交流の周波数が、５０Ｈｚ以上１０００Ｈｚ以下である、請求項１に記載の多結晶シリコンインゴットの製造方法。 The method for producing a polycrystalline silicon ingot according to claim 1, wherein the frequency of the three-phase alternating current is 50 Hz or more and 1000 Hz or less.
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JPH03177392A (en) * 1989-12-06 1991-08-01 Nippon Steel Corp Pulling up of single crystal and device therefor
JPH05254817A (en) * 1992-03-12 1993-10-05 Kawasaki Steel Corp Production of polycrystal silicon ingot
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JPH10182135A (en) * 1996-12-20 1998-07-07 Kawasaki Steel Corp Solidification refining of silicon
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JPS6236097A (en) * 1985-08-07 1987-02-17 Kawasaki Steel Corp Production of single crystal and device therefor
JPH03177392A (en) * 1989-12-06 1991-08-01 Nippon Steel Corp Pulling up of single crystal and device therefor
JPH05254817A (en) * 1992-03-12 1993-10-05 Kawasaki Steel Corp Production of polycrystal silicon ingot
JPH1025190A (en) * 1996-07-11 1998-01-27 Super Silicon Kenkyusho:Kk Melting by three-phase current heating of polycrystalline raw material for producing single crystal and apparatus therefor
JPH10182135A (en) * 1996-12-20 1998-07-07 Kawasaki Steel Corp Solidification refining of silicon
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