JP2012229144A - Device for producing polycrystalline silicon and method for producing polycrystalline silicon - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for effectively raising the temperature of a silicon core wire at the time for starting depositing reaction and at the time for starting energization by suppressing the grade in which the heat of the silicon wire heated by a carbon heater is radiated to an electrode side.SOLUTION: A metal made electrode 10 has a structure in which an adapter 14 can be mounted on the upper part thereof. A core wire holder 13 is fixed to the upper part of the adapter 14, further the silicon core wire 11 is fixed to the core wire holder 13. The device for producing a polycrystalline silicon is equipped with at least the carbon made core wire holder 13 for holding the silicon core wire 11 and the electrode 10 for energizing the silicon core wire 11, an insulation sheet 17 is arranged at least one point of an electroconductive passage from the electrode 10 to the silicon core wire 11. The thermal conductivity of the insulation sheet 17 in the thickness direction is lower than that of the core wire holder 13.

Description

  The present invention relates to a technique for producing polycrystalline silicon.

  A Siemens method is known as a method for producing polycrystalline silicon as a raw material for single crystal silicon for semiconductors or silicon for solar cells. The Siemens method is a method in which a source gas containing chlorosilane is brought into contact with a heated silicon core wire, and polycrystalline silicon is vapor-phase grown on the surface of the silicon core wire using a CVD (Chemical Vapor Deposition) method.

  The reactor for vapor-phase growth of polycrystalline silicon by the Siemens method has two vertical silicon core wires in a space composed of an upper structure called a bell jar and a lower structure called a base plate (bottom plate). One torii type is assembled, and both ends of the torii type silicon core wire are fixed to a pair of metal electrodes disposed on the base plate via a pair of carbon core wire holders. This configuration is disclosed in, for example, Japanese Patent Publication No. 37-18861 (Patent Document 1).

  The electrode passes through the base plate with an insulator interposed therebetween, and is connected to another electrode through wiring, or connected to a power source arranged outside the reactor. In order to prevent polycrystalline silicon from precipitating during vapor phase growth, the electrode, base plate and bell jar are cooled using a coolant such as water. The electrode and the core wire holder may be joined directly, but a carbon adapter is provided between the electrode and the core wire holder for the purpose of preventing damage to the electrode.

  When a silicon core wire is heated to a temperature range of 900 ° C. or higher and 1200 ° C. or lower in a hydrogen atmosphere by passing a current from the electrode, a mixed gas of, for example, trichlorosilane and hydrogen is supplied from a gas nozzle into the reactor as a source gas. Silicon is vapor-grown on the core wire, and a polycrystalline silicon rod having a desired diameter is formed in an inverted U shape.

  By the way, although the silicon core wire is made of polycrystalline or single crystal silicon, the silicon core wire used for manufacturing high-purity polycrystalline silicon needs to be high-purity with a low impurity concentration, specifically, The specific resistance is required to be high resistance of about 500 Ωcm or more. Since energization of such a high-resistance silicon core wire generally cannot be started at room temperature, it is necessary to energize the silicon core wire in advance by initially heating the silicon core wire to about 200 to 400 ° C. to lower the specific resistance (increasing conductivity). is there.

  For such initial heating, a carbon heater for initial heating is provided at the center or inner peripheral surface of the reaction furnace, and at the start of the reaction, this carbon heater is first heated by energization, and by the radiant heat generated at that time. A silicon core wire disposed around the carbon heater is heated to a desired temperature. When the temperature of the silicon core wire reaches 200 ° C. to 400 ° C. by such heating, the surface temperature of the silicon core wire is adjusted by applying a voltage of 2.0 V / cm to 8.0 V / cm per length to the silicon core wire. It is possible to start energization in the range of 900 ° C. or higher and 1300 ° C. or lower.

  Once energization of the silicon core wire is started, the precipitation reaction proceeds continuously since the surface temperature is maintained by the heat generated by the silicon core wire itself without using heating using a carbon heater. Therefore, after the energization of the silicon core wire is started, the power source of the carbon heater is turned off.

  By the way, if the silicon core wire does not reach a sufficient temperature due to the initial heating at the start of the precipitation reaction (at the start of energization), the specific resistance of the silicon core wire is not sufficiently lowered. For this reason, the applied voltage at the start of energization needs to be set higher. However, if the applied voltage is increased, spark discharge is likely to occur between the core wire holder and the silicon core wire, and the silicon core wire is damaged. . Such damage also causes the silicon core wire to collapse during the precipitation reaction.

  That is, from the viewpoint of stable production of polycrystalline silicon, it is required to raise the silicon core wire to a sufficient temperature at the start of the precipitation reaction (at the start of energization) under conditions that do not cause discharge or the like. One of the methods for this purpose is to increase the capacity of the heater or to heat the silicon core wire by infrared irradiation (for example, see Japanese Patent Application Laid-Open No. 2001-278611 (see Patent Document 2, etc.). However, the cost of the heating equipment and the operating cost must be increased.

  In order to efficiently raise the temperature of the silicon core wire during the initial heating, it is important to suppress heat dissipation from the silicon core wire. The silicon core wire is heated by radiant heat from the carbon heater, but is radiated from the silicon core wire by convection heat transfer to the surrounding gas and conduction heat transfer to the cooled electrode.

  In order to reduce heat dissipation due to conduction heat transfer, the material of the core wire holder and the adapter may be low in thermal conductivity. However, carbon is often used for these members from the viewpoints of heat resistance, the amount of impurities contained, or cost, and the thermal conductivity of carbon is relatively high at 80 to 180 W / mK. In addition, there is a choice of making the core wire holder or adapter longer to increase the distance from the electrode, but in this case, there are problems that the cost of the carbon member is increased and the space in the reactor must be increased.

Japanese Patent Publication No. 37-18861 JP 2001-278611 A JP 58-128807 A JP 2006-62922 A

  The present invention has been made to solve such a problem, and suppresses the degree to which the heat of the silicon core wire heated by the carbon heater is dissipated to the electrode side. To provide a technique for efficiently increasing the temperature of the silicon core wire.

  In order to solve the above-described problems, the polycrystalline silicon manufacturing apparatus according to the first aspect of the present invention supplies a raw material gas to a silicon core wire heated in a reaction furnace, so A polycrystalline silicon manufacturing apparatus for depositing crystalline silicon, comprising: a carbon core wire holder for holding the silicon core wire; and an electrode for energizing the silicon core wire, from the electrode to the silicon core wire The heat insulation sheet is arrange | positioned at at least one place of the electrically conductive path | route, and the heat conductivity of the thickness direction of the said heat insulation sheet is lower than the heat conductivity of the said core wire holder, It is characterized by the above-mentioned.

  The polycrystalline silicon manufacturing apparatus according to the second aspect of the present invention is for depositing polycrystalline silicon on the surface of the silicon core wire by supplying a raw material gas to the silicon core wire heated in the reactor. A polycrystalline silicon manufacturing apparatus comprising: a carbon core wire holder for holding the silicon core wire; and an electrode for energizing the silicon core wire, and a heat insulating sheet is provided at a contact portion between the silicon core wire and the core wire holder. It is arrange | positioned and the heat conductivity of the thickness direction of the said heat insulation sheet is lower than the heat conductivity of the said core wire holder, It is characterized by the above-mentioned.

  Furthermore, the polycrystalline silicon manufacturing apparatus according to the third aspect of the present invention is for depositing polycrystalline silicon on the surface of the silicon core wire by supplying a raw material gas to the silicon core wire heated in the reaction furnace. A polycrystalline silicon manufacturing apparatus, comprising: a carbon core wire holder for holding the silicon core wire; an electrode for energizing the silicon core wire; and a carbon adapter for mounting the core wire holder on the electrode; A heat insulating sheet is disposed in at least one of a contact portion between the silicon core wire and the core wire holder, a contact portion between the core wire holder and the adapter, and a contact portion between the adapter and the electrode, and The thermal conductivity in the thickness direction of the sheet is lower than the thermal conductivity of the core wire holder and the adapter.

  Preferably, the heat conductivity in the thickness direction of the heat insulating sheet is 10 W / mK or less at 25 ° C., more preferably 5 W / mK or less.

  Further, preferably, the electrical resistivity in the thickness direction of the heat insulating sheet is 5000 μΩ · m or less at 25 ° C., and more preferably 2000 μΩ · m or less.

  Furthermore, preferably, the thickness of the heat insulating sheet is 0.1 mm or more and 4.0 mm or less, and more preferably 0.2 mm or more and 1.0 mm or less.

  The method for producing polycrystalline silicon according to the present invention uses the polycrystalline silicon production apparatus of the present invention to deposit polycrystalline silicon on the surface of the silicon core wire that is energized from the electrode to the silicon core wire and heated to a predetermined temperature. It is characterized by making it.

  In the present invention, the heat insulating sheet whose thermal conductivity in the thickness direction is lower than the thermal conductivity of the core wire holder is arranged in at least one part of the conductive path from the electrode to the silicon core wire. The degree to which the heat of the silicon core wire is dissipated to the electrode side is suppressed, thereby providing a technique for efficiently increasing the temperature of the silicon core wire at the start of the precipitation reaction (at the start of energization).

It is a schematic sectional drawing which shows an example of the structure of the reaction furnace for the polycrystalline silicon manufacture of this invention. It is a figure for demonstrating the combination of an electrode, an adapter, a core wire holder, and a silicon | silicone core wire when not arrange | positioning a heat insulation sheet. It is a figure for demonstrating an example of the arrangement | positioning relationship of an electrode, an adapter, a core wire holder, and a silicon | silicone core wire at the time of arrange | positioning a heat insulation sheet. It is a figure for demonstrating the other example of the arrangement | positioning relationship of an electrode, an adapter, a core wire holder, and a silicon | silicone core wire at the time of arrange | positioning a heat insulation sheet. It is a figure for demonstrating the other example of the arrangement | positioning relationship of an electrode, an adapter, a core wire holder, and a silicon | silicone core wire at the time of arrange | positioning a heat insulation sheet. It is a figure for demonstrating the other example of the arrangement | positioning relationship of an electrode, an adapter, a core wire holder, and a silicon | silicone core wire at the time of arrange | positioning a heat insulation sheet.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. In the following, the Siemens method using trichlorosilane as a source gas will be described as an example, but it goes without saying that it can also be used as another source gas such as monosilane or dichlorosilane.

  FIG. 1 is a schematic sectional view showing an example of a configuration of a reaction furnace 100 for producing polycrystalline silicon according to the present invention. The reactor 100 is an apparatus for obtaining a polycrystalline silicon rod 12 by vapor-depositing polycrystalline silicon on the surface of the silicon core wire 11 by the Siemens method, and is composed of a base plate 5 and a bell jar 1.

  The base plate 5 is provided with a metal electrode 10 for supplying a current to the silicon core wire 11, a gas nozzle 9 for supplying a process gas such as nitrogen gas, hydrogen gas, trichlorosilane gas, and an exhaust port 8 for exhausting the exhaust gas. . Further, the base plate 5 has a refrigerant inlet 6 and an outlet 7 for cooling itself.

  The bell jar 1 has a refrigerant inlet portion 3 and an outlet portion 4 for cooling itself, and further has a viewing window 2 for visually confirming the inside from the outside.

  FIG. 2 is a diagram for explaining an example of an arrangement relationship among the electrode 10, the adapter 14, the core wire holder 13, and the silicon core wire 11 when a heat insulating sheet to be described later is not arranged. The metal electrode 10 has a refrigerant inlet 15 and an outlet 16 for cooling itself, and has a structure on which an adapter 14 can be placed. The core wire holder 13 is fixed to the upper part of the adapter 14, and the silicon core wire 11 is fixed to the core wire holder 13. The adapter 14 and the core wire holder 13 do not need to be provided as separate members, and may be an integrated core wire holder in which the adapter 14 and the core wire holder 13 are a single member.

  The electrode 10, the adapter 14, the core wire holder 13, and the silicon core wire 11 are required to have a contact area necessary for energization. Moreover, it is necessary to have sufficient strength to hold the polycrystalline silicon rod obtained by the polycrystalline silicon precipitation reaction.

  FIG. 3 is a diagram for explaining an example of an arrangement relationship among the electrode 10, the adapter 14, the core wire holder 13, and the silicon core wire 11 when the heat insulating sheet is arranged.

  The polycrystalline silicon manufacturing apparatus of the present invention includes at least a carbon core wire holder 13 that holds the silicon core wire 11 and an electrode 10 for energizing the silicon core wire 11, and reaches from the electrode 10 to the silicon core wire 11. A heat insulating sheet 17 is disposed in at least one part of the conductive path. The heat conductivity in the thickness direction of the heat insulating sheet 17 is lower than the heat conductivity of the core wire holder 13.

  In the example shown in FIG. 3, the heat insulating sheet 17 is provided at the contact portion between the adapter 14 and the electrode 10.

  In addition to such an embodiment, as shown in FIGS. 4 to 6, an embodiment (FIG. 4) in which a heat insulating sheet 17 is disposed at a contact portion between the core wire holder 13 and the adapter 14, the silicon core wire 11, the core wire holder 13, and the like. The aspect (FIG. 5) by which the heat insulation sheet 17 is arrange | positioned in the contact part of FIG. 5, the contact part of the silicon core wire 11 and the core wire holder 13, the contact part of the core wire holder 13 and the adapter 14, and the contact of the adapter 14 and the electrode 10 The aspect (FIG. 6) etc. with which the heat insulation sheet 17 is arrange | positioned at the part may be sufficient.

  In short, in the case of including a carbon core holder 13 for holding a silicon core wire, an electrode 10 for energizing the silicon core wire 13, and a carbon adapter 14 for mounting the core wire holder 13 on the electrode 10. The heat insulating sheet 17 may be disposed in at least one of a contact portion between the silicon core wire 11 and the core wire holder 13, a contact portion between the core wire holder 13 and the adapter 14, and a contact portion between the adapter 14 and the electrode 10.

  A material with low thermal conductivity generally has low conductivity. For this reason, it has not been envisaged so far to intervene a material having low thermal conductivity in the conductive path leading to the silicon core wire 11 and the electrode 10. However, according to the knowledge of the present inventors, the sheet is made of a material having a degree of conductivity necessary for heating the silicon core wire, and is more thermally conductive than the carbon material that is a constituent material of the core wire holder 13 and the adapter 14. If the property is low, it is effective to use this as a heat insulating sheet. That is, by using such a heat insulating sheet 17, heat radiation to the cooled electrode 10 when the silicon core wire 11 is heated is suppressed, while initial heating of the silicon core wire 11 is also efficiently performed. .

  The heat insulating property and the electrical conductivity of the heat insulating sheet 17 are basically a trade-off. However, the thermal conductivity in the thickness direction of the sheet is preferably 10 W / mK or less at 25 ° C., more preferably 5 W / mK or less. Further, from the viewpoint of ensuring the conductivity necessary for energization, the electrical resistivity in the thickness direction is preferably 5000 μΩ · m or less, more preferably 2000 μΩ · m or less at 25 ° C. Furthermore, the preferable thickness of a heat insulation sheet is 0.1 mm or more and 4.0 mm or less, More preferably, it is 0.2 mm or more and 1.0 mm or less. When the heat insulating sheet is too thick, it causes unnecessary energy loss, and when it is too thin, the heat blocking effect may not be sufficiently obtained.

  The heat insulating sheet 17 is not particularly limited as long as it has a heat conductivity and conductivity as described above and has a heat resistance, but a preferable material is a carbon sheet obtained by rolling graphite. Specifically, carbon sheets obtained by heating and rolling acid-treated graphite (for example, those described in JP-A-58-128807 (Patent Document 3) and JP-A-2006-62922 (Patent Document 4)). Etc.). Since such a material has high conductivity in the area direction, it is easy to ensure sufficient conductivity while obtaining a heat insulating effect. In addition, the carbon sheet of such a physical characteristic is marketed, and can be obtained easily.

  In the method for producing polycrystalline silicon according to the present invention, using the above-described polycrystalline silicon production apparatus, the silicon core wire 11 is energized from the electrode 10 to deposit polycrystalline silicon on the surface of the silicon core wire 11 heated to a predetermined temperature. .

  That is, the temperature of the silicon core wire 11 is increased to a temperature at which the silicon core wire 11 can be energized by heating the silicon core wire 11 using an external heater (not shown), and when the temperature of the silicon core wire 11 reaches 200 to 400 ° C. 11, a voltage is applied from the electrode 10 to the electrode 11, and the temperature of the silicon core wire 11 is set to 900 to 1300 ° C. A mixed gas of trichlorosilane and hydrogen, which is a raw material, is introduced from the raw material nozzle 9 to deposit polycrystalline silicon on the silicon core wire 11, and the reaction is stopped when the polycrystalline silicon has grown to a predetermined size.

  When the polycrystalline silicon manufacturing apparatus according to the present invention is used, the heating time of the silicon core wire 11 can be greatly shortened. In addition, since it is possible to start energization with a relatively low energization start voltage in a limited heating time, it is possible to suppress discharge between the silicon core wire 11 and the core wire holder 13 and the like. It is possible to prevent the core wire from falling down.

[Examples A and B]
Polycrystalline silicon was grown under the following conditions. First, four silicon core wires of 1500 mm length with a rectangle (8 mm □) with a side of 8 mm are installed in the reaction furnace, the furnace is in a hydrogen atmosphere, and initial heating is performed for 10 minutes by a carbon heater (110 kW, heater surface temperature 1250 ° C.). Went. Next, the voltage applied to the silicon core wire was gradually increased, the voltage when the current value began to increase was taken as the energization start voltage, and the voltage was adjusted so that a current of 10 A would flow after energization. After 15 minutes from the start of energization, the silicon core wire was taken out, and the depth of scratches generated on the silicon core wire was measured with a surface roughness measuring instrument.

Specific apparatus conditions are as follows.
Example A: A carbon sheet having a thickness of 1 mm and a thermal conductivity of 5 W / mK in the thickness direction was disposed between the electrode and the adapter.
Example B: A carbon heat insulating sheet having a thermal conductivity of 5 W / mK in the thickness direction of 1 mm is disposed between the electrode and the adapter, and further, a thermal conductivity of 5 mm having a thickness of 0.2 mm is provided between the core wire holder and the silicon core wire. A carbon sheet of / mK was placed.
Comparative example a: A heat insulating sheet is not installed between the electrode, the adapter, the core wire holder, and the silicon core wire.

  The results are summarized in Table 1. From this result, the depth of the flaw which is estimated to be the spark discharge trace which generate | occur | produces in a silicon | silicone core wire becomes small when it installs many heat insulation sheets.

[Examples C and D]
Two series of silicon core wires of 8 mm □ and 1500 mm length were installed in the reactor (8 in total), and under the same conditions as in Examples A and B, initial heating was performed with a carbon heater, and energization was started. Then, silicon precipitation reaction was performed by introducing trichlorosilane and hydrogen gas.

Specific apparatus conditions are as follows.
Example C: A carbon sheet having a thickness of 1 mm and a thermal conductivity of 5 W / mK in the thickness direction was disposed between the electrode and the adapter.
Example D: A carbon heat insulating sheet having a thermal conductivity of 5 W / mK in the thickness direction of 1 mm is disposed between the electrode and the adapter, and further, a thermal conductivity of 5 mm having a thickness of 0.4 mm is provided between the core wire holder and the silicon core wire. A carbon sheet of / mK was placed.
Comparative example b: A heat insulating sheet is not installed between the electrode, the adapter, the core wire holder, and the silicon core wire.

  The results are summarized in Table 2. In Comparative Example b, collapse occurred at a silicon rod diameter of 20 mmφ, whereas in any of Examples C and D, the silicon rod did not collapse.

  The present invention suppresses the degree to which the heat of the silicon core wire heated by the carbon heater is dissipated to the electrode side, thereby efficiently increasing the temperature of the silicon core wire at the start of the precipitation reaction (at the start of energization). I will provide a.

DESCRIPTION OF SYMBOLS 1 Berja 2 Peep window 3 Refrigerant inlet part 4 Refrigerant outlet part 5 Base plate 6 Refrigerant inlet part 7 Refrigerant outlet part 8 Reacted exhaust gas outlet 9 Raw material gas supply nozzle 10 Electrode 11 Silicon core wire 12 Polycrystalline silicon rod 13 Core wire holder 14 Adapter 15 Refrigerant inlet Part 16 Refrigerant outlet part 100 Reactor

Claims (10)

A polycrystalline silicon production apparatus for depositing polycrystalline silicon on the surface of the silicon core wire by supplying a raw material gas to the silicon core wire heated in a reaction furnace,
A carbon core wire holder for holding the silicon core wire, and an electrode for energizing the silicon core wire,
A heat insulating sheet is disposed in at least one portion of the conductive path from the electrode to the silicon core wire,
The polycrystalline silicon manufacturing apparatus, wherein the thermal conductivity in the thickness direction of the heat insulating sheet is lower than the thermal conductivity of the core wire holder. A polycrystalline silicon production apparatus for depositing polycrystalline silicon on the surface of the silicon core wire by supplying a raw material gas to the silicon core wire heated in a reaction furnace,
A carbon core wire holder for holding the silicon core wire, and an electrode for energizing the silicon core wire,
A heat insulating sheet is arranged at a contact portion between the silicon core wire and the core wire holder,
The polycrystalline silicon manufacturing apparatus, wherein the thermal conductivity in the thickness direction of the heat insulating sheet is lower than the thermal conductivity of the core wire holder. A polycrystalline silicon production apparatus for depositing polycrystalline silicon on the surface of the silicon core wire by supplying a raw material gas to the silicon core wire heated in a reaction furnace,
A carbon core wire holder for holding the silicon core wire, an electrode for energizing the silicon core wire, and a carbon adapter for mounting the core wire holder on the electrode,
A heat insulating sheet is disposed in at least one of a contact portion between the silicon core wire and the core wire holder, a contact portion between the core wire holder and the adapter, and a contact portion between the adapter and the electrode;
The thermal conductivity of the heat insulation sheet in the thickness direction is lower than the thermal conductivity of the core wire holder and the adapter.   The polycrystalline silicon manufacturing apparatus according to any one of claims 1 to 3, wherein a thermal conductivity in a thickness direction of the heat insulating sheet is 10 W / mK or less at 25 ° C.   The polycrystalline silicon manufacturing apparatus according to claim 4, wherein the thermal conductivity in the thickness direction of the heat insulating sheet is 5 W / mK or less at 25 ° C.   The polycrystalline silicon manufacturing apparatus according to claim 1, wherein an electrical resistivity in a thickness direction of the heat insulating sheet is 5000 μΩ · m or less at 25 ° C. 6.   The polycrystalline silicon manufacturing apparatus according to claim 6, wherein an electrical resistivity in a thickness direction of the heat insulating sheet is 2000 μΩ · m or less at 25 ° C. 7.   The polycrystalline silicon manufacturing apparatus according to claim 1, wherein the heat insulating sheet has a thickness of 0.1 mm to 4.0 mm.   The polycrystalline silicon manufacturing apparatus according to claim 8, wherein the heat insulating sheet has a thickness of 0.2 mm to 1.0 mm.   The polycrystalline silicon manufacturing apparatus according to any one of claims 1 to 9, wherein the silicon core wire is energized from the electrode to deposit polycrystalline silicon on the surface of the silicon core wire heated to a predetermined temperature. A method for producing polycrystalline silicon.

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