DEVICE FOR THE PRODUCTION OF POLYCRYSTALLINE SILICON

Abstract

Apparatus for the production of polycrystalline silicon, which produces polycrystalline silicon by a Siemens process, comprising: an electrode adapter which electrically connects a core wire holder and a metal electrode, wherein the electrode adapter is non-conductive with respect to a screw part formed in the metal electrode.

Description

BACKGROUND ARTTECHNICAL FIELDAn embodiment of the present invention relates to an apparatus for manufacturing polycrystalline silicon by a Siemens method, more particularly, to the structure of an electrode adapter electrically connecting a core wire holder and a metal electrode.This application claims priority to Japanese Patent Application Serial No. 2019-137105 filed on July 25, 2019, the entire contents of which are incorporated herein by reference.PRIOR ARTPolycrystalline silicon is a raw material of single-crystal silicon for manufacturing a semiconductor or silicon for manufacturing a solar cell. As a method for producing a polycrystalline silicon, a Siemens method is known. In this method, generally, a silane-based starting gas is contacted with a heated silicon core wire to deposit a polycrystalline silicon on a surface of the silicon core wire by a chemical vapor deposition (CVD) method.In the Siemens method, two silicon core wires in the vertical direction and one silicon core wire in the horizontal direction are assembled to form an inverted U. Both ends of the set of silicon core wires in inverted U-shape are connected to a core wire holder and fixed to a respective metal electrode disposed on a base plate. Generally, a reaction furnace includes a plurality of sets of inverted U-shaped silicon core wires. Such a configuration is disclosed, for example, in JP 2010-235 438 A.When an inverted U-shaped silicon core wire is heated to a deposition temperature by conduction and a mixed gas of, for example, trichlorosilane and hydrogen as a starting gas is brought into contact with the silicon core wire, a polycrystalline silicon vapor phase grows on the silicon core wire, and a polycrystalline silicon rod is formed in an inverted U-shape having a desired diameter.An electrode penetrates a base plate with an insulator interposed between the electrode and the base plate, and is connected to another electrode or connected to a power source disposed outside a reaction furnace.In order to prevent deposition of a polycrystalline silicon on this electrode during a polycrystalline silicon deposition step and prevent metal contamination of the polycrystalline silicon from being deposited by a temperature rise of the electrode, and the like, the electrode, the base plate, and a bell jar are cooled by a coolant such as water.FIG. 1 is a conceptual diagram illustrating an aspect according to a conventional technique in which an electrode holder is attached to an electrode to hold a core wire holder. In the example illustrated in this drawing, for example, a metal electrode 20 and a carbon core wire holder 24 are connected to each other via an electrode adapter 23 to reduce the wear of the electrode 20, and the electrode adapter 23 is threadedly attached to the electrode 20.A current is supplied from the electrode 20 via the core wire holder 24 to a silicon core wire (not shown) held on top of a core wire holder 24, and a surface of the silicon core wire is heated to about 900° C. to 1200° C. by Joule heat in a hydrogen environment. In this state, a mixed gas of, for example, trichlorosilane and hydrogen as a starting gas is introduced into a reaction furnace. This causes high purity silicon in vapor phase to be grown on the silicon core wire to form a polycrystalline silicon rod.In this step, as the diameter of the polycrystalline silicon rod increases, deposition of a polycrystalline silicon also proceeds on one side of the carbon core wire holder 24, and the polycrystalline silicon is gradually integrated into the core wire holder 24. Note that the electric resistance decreases with the growth of the polycrystalline silicon rod. Therefore, a current to be supplied is gradually increased to maintain the surface temperature of the polycrystalline silicon rod at a temperature suitable for the deposition reaction.Generally, a high current of 2000 to 4000 amperes is supplied to the polycrystalline silicon rod at the end of the deposition reaction. As the diameter of the polycrystalline silicon rod increases, the amount of heat emitted from a surface of the rod increases. It is therefore necessary to increase the electric energy to be supplied to the polycrystalline silicon rod in order to equalize the amount of heat lost by the heat dissipation in order to maintain a temperature (900 to 1200° C.) required for the deposition reaction.Under these circumstances, a structure that resists the above-described supply of a large current and the increased weight of the polycrystalline silicon rod due to diameter enlargement is required to connect the metal electrode, the electrode adapter, and the core wire holder to each other.BRIEF DESCRIPTION OF THE SUBJECT MATTERTherefore, it is necessary to securely fix the electrode adapter because the electrode adapter is formed of carbon having a high self-lubricating property. Particularly, when the metal electrode and the adapter are threadedly connected to each other and loosening of a screw occurs, discharge may occur from a gap generated by the loosening to damage both the metal electrode and the adapter, and a metal and carbon diffused by the discharge into the reaction furnace may cause contamination into polycrystalline silicon.As for the connection between the metal electrode, the electrode adapter and the core wire holder, a novel structure has been proposed heretofore.For example, JP 2010-235 438 A discloses an aspect in which a core rod holding portion having a holding hole into the upper end of which a silicon core wire is inserted and having a screw strip on its circumferential surface is fixed by a holder having an internal thread screwed to the core rod holding portion. In this regard, both the core rod holding portion and the holder are made of a conductive material, and a current also flows through a screw member. However, the present inventors have found that a discharge occurs in a slight gap of a screw part generated by, for example, a difference in thermal expansion coefficient between a metal electrode and a carbon electrode adapter when a large current flows in the screw part by newly increasing the diameter of the screw part because the screw part has an uneven surface even when the core rod holding portion sufficiently engages with a holder.Note that JP 2010-235 438 A also discloses an aspect in which a lower part of a core rod holding portion is inserted into a holding hole of a holder main body, and the core rod holding portion is supported by a base plate part using a nut member screwed to the holder main body having an external thread on an outer circumferential surface. However, since these members are also conductive as in the above-described aspect, the inventors have found that even in this aspect, discharges easily occur when a large current flows in a screw part as described above.JP 2002-338 226 A discloses an aspect in which a stand supporting a lower end of a seed core is supported by a first support of a male screw member, and the first support is supported by a fixed second support of a female screw member so as to be able to move up and down. However, since the first and second pillars are both conduction paths, the inventors have found that the discharge occurs by the flow of a large current in a screw part as in the aspect of JP 2010-235 438 A.As described above, the structure connecting an electrode adapter to a metal electrode in the conventional technique does not have sufficient countermeasures against the discharge. Therefore, after-treatment is extremely cumbersome when a component inside a furnace is damaged by discharge. Specifically, an electrode needs to be replaced with a new one, and also a polycrystalline silicon rod is contaminated. In addition, a hydrocarbon compound is also contained as impurity in a reaction off gas trapped and circulated as a result of contamination of a bell jar and a base plate, which deteriorates production of a polycrystalline silicon in subsequent batches.The present invention has been realized in view of such problems, and an object of the present invention is to provide a novel structure of an electrode adapter which is simple but can be stably conductive with respect to a metal electrode and a core wire holder.[Concept 1]A polycrystalline silicon manufacturing apparatus according to the present invention may be a polycrystalline silicon manufacturing apparatus that manufactures a polycrystalline silicon by a Siemens method, including an electrode adapter that electrically connects a core wire holder and a metal electrode, wherein the electrode adapter may be non-conductive with respect to a screw part formed in the metal electrode.[Concept 2]A polycrystalline silicon manufacturing apparatus according to the present invention may be a polycrystalline silicon manufacturing apparatus that manufactures a polycrystalline silicon by a Siemens method, including an electrode adapter that electrically connects a core wire holder and a metal electrode, the electrode adapter may be fixed to the metal electrode by a fixing mechanism part, and the electrode adapter may be non-conductive with respect to the fixing mechanism part.[Concept 3]In the polycrystalline silicon manufacturing apparatus according to Concept 1 or 2, wherein the electrode adapter and the core wire holder may be formed of an identical material.[Concept 4]In the polycrystalline silicon manufacturing apparatus according to any one of Concepts 1 to 3, at least one of the electrode adapters and the core wire holder may be formed of a carbon material.[Concept 5]In the polycrystalline silicon manufacturing apparatus according to any one of Concepts 1 to 4, a conductive member may be interposed between conductive parts of the electrode adapter and the metal electrode.[Concept 6]In the polycrystalline silicon manufacturing apparatus according to any one of Concepts 1 to 5, the electrode adapter may be fixed to the metal electrode via an insulating frame (Jig).[Concept 7]In the polycrystalline silicon manufacturing apparatus according to any one of Concepts 2 to 6, an insulating treatment may be applied to at least one surface of the fixing mechanism part.An embodiment of the present invention provides an electrode adapter which can be stably conductive to a metal electrode and a core wire holder. In addition, since the structure is extremely simple, the core wire holder can be easily removed.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a conceptual diagram for exemplarily illustrating an aspect according to a conventional technique in which an electrode holder is fixed to an electrode to hold a core wire holder; FIG. 2 is a schematic diagram for explaining a configuration example of a polycrystalline silicon manufacturing apparatus according to an embodiment of the present invention; FIG. 3 is a conceptual diagram illustrating an aspect in which an electrode holder is fixed to an electrode to hold a core wire holder; FIG. 4 is a conceptual diagram illustrating another aspect in which an electrode holder is attached to an electrode to hold a core wire holder; FIG. 5 is a conceptual diagram illustrating another aspect in which an electrode holder is attached to an electrode to hold a core wire holder; FIG. 6 is a conceptual diagram illustrating another aspect in which an electrode holder is fixed to an electrode to hold a core wire holder; and FIG. 7 is a conceptual diagram illustrating a conductive part inserted between conductive parts of an electrode adapter and a metal electrode.DETAILED DESCRIPTIONFIG. 2 is a diagram showing the outline of a configuration example of a reaction furnace of a polycrystalline silicon manufacturing apparatus according to an embodiment of the present invention. A reaction furnace 100 has an electrode 10 insulated from a base plate 5 disposed under a bell jar 1 on the base plate 5. The electrode 10 is connected to an electrode holder 13 via a fixing mechanism part 17 (see FIGS. 3, 4, 5 to 6 ) formed of an insulating material, and a carbon core wire holder 14 holding a silicon core wire 15 is fixed to the electrode holder 13. The connection is made such that a current supplied from the electrode 10 flows through the electrode holder 13 and the core wire holder 14, and a polycrystalline silicon 16 is deposited on the silicon core wire 15 by a reaction of a source gas.Note that reference numeral 2 in FIG. 2 denotes a viewing window. A refrigerant for cooling the bell jar 1 is supplied through a refrigerant inlet 3 and discharged from the furnace through a refrigerant outlet 4. A refrigerant for cooling the base plate 5 is supplied through a refrigerant inlet 6 and discharged from the furnace through a refrigerant outlet 7. A refrigerant for cooling the electrode 10 is supplied through a refrigerant inlet 11 and discharged from the furnace through a refrigerant outlet 12. A deposition source gas of polycrystalline silicon is supplied through a source gas supply nozzle 9 and discharged from the furnace through a reaction off-gas outlet 8.FIGS. 3, 4, 5 to 6 are conceptual diagrams illustrating each aspect, wherein, in the polycrystalline silicon manufacturing apparatus according to an embodiment of the present invention, an electrode holder is fixed to an electrode to hold a core wire holder.In the aspect illustrated in FIG. 3, a screw part is formed on the upper surface of the electrode 10. The electrode adapter 13 is fixed via the fixing mechanism part 17 screwed to this screw part. A recess at a lower end of the core wire holder 14 is fitted into a protrusion on an upper surface of this electrode adapter 13. Since the fixing mechanism part 17 is formed of an insulating material, the screw part is non-conductive, and the power supply from the electrode 10 to the core wire holder 14 is performed via a part of the electrode adapter 13 other than the screw part. Thereby, it is possible to fully suppress the conductivity in the screw part in which discharges easily occur (a part having an extremely uneven surface), and to prevent damage due to discharges.In the aspect illustrated in FIG. 4, a hole having a screw part (female thread) is formed on the upper surface of the electrode 10, and the fixing mechanism part 17 having a screw part (male thread) is screwed to this hole portion. The electrode adapter 13 is fixed by this fixing mechanism part 17, and a protrusion formed at a lower end of the core wire holder 14 is fitted into a recess formed on an upper surface of this electrode adapter 13. Since this attachment mechanism part 17 is also formed of an insulating material, the screw part is non-conductive, and the power supply from the electrode 10 to the core wire holder 14 is performed via a part of the electrode adapter 13 other than the screw part. Thereby, it is possible to fully suppress the conductivity in the screw part in which discharges easily occur (a part having an extremely uneven surface), and to prevent damage due to discharges.In the aspect illustrated in FIG. 5, a screw part (external thread) is formed on an upper surface of the electrode 10, and the electrode adapter 13 is disposed on an upper surface of this screw part (external thread). The electrode adapter 13 is fixed by the fixing mechanism part 17 having a screw part on its inner surface, and a recess formed at a lower end of the core wire holder 14 is fitted into a protrusion formed on an upper surface of this electrode adapter 13. Since this fastening mechanism rope 17 is also formed of an insulating material, the screw part is non-conductive, and the power supply from the electrode 10 to the core wire holder 14 is made via a part of the electrode adapter 13 other than the screw part. Thereby, it is possible to fully suppress the conductivity in the screw part in which discharges easily occur (a part having an extremely uneven surface), and to prevent damage due to discharges.In the aspect illustrated in FIG. 6, a screw part (external thread) is formed on an upper surface of the electrode 10. A screw part formed on an inner surface of the electrode adapter 13 is screwed to this screw part via the insulating fixing mechanism part 17. In this case, it is to be noted that insulation treatment may be applied to the screw part formed on the inner surface of the electrode adapter 13 so that the inner surface portion of the electrode adapter 13 functions as the attachment mechanism part 17. A protrusion is formed on an upper surface of the electrode adapter 13, and a recess formed at a lower end of the core wire holder 14 is fitted in this protrusion. In this case as well, since the fixing mechanism part 17 is formed of an insulating material, the screw part is non-conductive, and the power supply from the electrode 10 to the core wire holder 14 is performed via a part of the electrode adapter 13 other than the screw part. Thereby, it is possible to completely suppress the conductivity in the screw part in which discharges easily occur (a part having an extremely uneven surface) and to prevent damage due to discharges.As described above, an embodiment of the present invention provides a polycrystalline silicon manufacturing apparatus that manufactures a polycrystalline silicon according to a Siemens method, including an electrode adapter that electrically connects a core wire holder and a metal electrode, the electrode adapter being non-conductive with respect to a screw part formed in the metal electrode.Moreover, an embodiment of the present invention provides a polycrystalline silicon manufacturing apparatus that manufactures polycrystalline silicon by a Siemens method, including an electrode adapter that electrically connects a core wire holder and a metal electrode, the electrode adapter being fixed to the metal electrode by a fixing mechanism part, and the electrode adapter being non-conductive with respect to the fixing mechanism part.In this case, the electrode adapter and the core wire holder may be formed of the same material.Moreover, at least one of the electrode adapters and the core wire holder may be made of a carbon material. When connecting parts of the core wire holder and the electrode adapter are formed of carbon, contact surfaces become accustomed to each other by sliding the core wire holder and the electrode adapter when the core wire holder and the electrode adapter are configured. Therefore, even if the connecting parts of the core wire holder and the electrode adapter each have a simple conical shape, sufficient fixation can be achieved and discharge can be suppressed effectively.Note that, in order to efficiently power the core wire holder, a conductive part 30 such as a carbon plate may be inserted between conductive parts of the electrode adapter and the metal electrode.As with the aspect shown in FIG. 5, the electrode adapter may be attached to the metal electrode via an insulating device.Note that the entire fastening mechanism part may be formed of an insulating material, but an insulating treatment may be applied to at least one surface of the fastening mechanism part.Note that the above insulating material only needs to have an electric resistivity sufficiently higher than that of carbon (about 10 μΩm). Examples of such a material are silicon nitride (about 1·10 15 μΩm) and quartz glass (about 1·10 18 μΩm). A material having an electrical resistivity almost equal to that of germanium (about 5·10 5 μΩm) can also be used as the above insulating material.[Examples]A reaction for growing a polycrystalline silicon until the weight of a pair of polycrystalline silicon rods reached 80 to 200 kg was carried out according to a Siemens method for 20 batches, and it was confirmed whether a metal electrode has a defect to be considered as produced by discharge. As a result, when the configuration shown in FIG. 3 (in which the fixing mechanism part is formed of silicon nitride) was used, no defect was observed in the metal electrode. On the other hand, when the configuration shown in FIG. 1 was used, broken parts were observed in two batches corresponding to 10%, and in these batches in which the breakage occurred, defects to be considered to be generated by discharge were confirmed in the screw threads of the metal electrodes.An embodiment of the present invention is an electrode adapter that can be stably conductive with respect to a metal electrode and a core wire holder.LIST OF REFERENCE CHARACTERS1 Bell 2 Observation window 3 Refrigerant inlet (bell) 4 Refrigerant outlet (bell) 5 Base plate 6 Refrigerant inlet (base plate) 7 Refrigerant outlet (base plate) 8 Reaction exhaust gas outlet 9 Source gas supply nozzle 10, 20 Metal electrode 11 Refrigerant inlet (electrode) 12 Refrigerant outlet (electrode) 13, 23 Electrode adapter 14, 24 Core wire holder 15 Silicon core wire 16 Polycrystalline silicon 17 Fixing mechanism part 30 Conductive part 100 Reaction furnace

Claims

A polycrystalline silicon manufacturing apparatus manufacturing a polycrystalline silicon by a Siemens method, comprising: an electrode adapter electrically connecting a core wire holder and a metal electrode, wherein the electrode adapter is non-conductive with respect to a screw part formed in the metal electrode.A polycrystalline silicon manufacturing apparatus manufacturing a polycrystalline silicon by a Siemens method, comprising: an electrode adapter electrically connecting a core wire holder and a metal electrode, wherein the electrode adapter is fixed to the metal electrode by a fixing mechanism part, and the fixing mechanism part is fixed to a screw part of the electrode and is non-conductive with respect to the screw part of the electrode.The polycrystalline silicon manufacturing apparatus according to claim 1 or 2, wherein the electrode adapter and the core wire holder are formed of an identical material.The polycrystalline silicon manufacturing apparatus according to any preceding claim, wherein at least one of the electrode adapters and the core wire holder is formed of a carbon material.The polycrystalline silicon manufacturing apparatus according to any preceding claim, wherein a conductive member is interposed between conductive members of the electrode adapter and the metal electrode.The polycrystalline silicon manufacturing apparatus according to any preceding claim, wherein the electrode adapter is fixed to the metal electrode via an insulating frame.The polycrystalline silicon manufacturing apparatus according to claim 2, wherein an insulating treatment is applied to at least one surface of the fixing mechanism part.

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