Device for producing polycrystalline silicon

Abstract

Apparatus for producing polycrystalline silicon using the Siemens process, comprising: a carbon core wire holder that holds a silicon core wire; an electrode section that excites the core wire holder, wherein the electrode section has an upper end in contact with a lower end of the core wire holder; a first screw section that is only provided around a lower part of the core wire holder to be fixed to the electrode section, and a second screw section provided around an upper part of the electrode section, wherein the first screw section of the core wire holder and the second screw section of the electrode section are fastened by an insulating nut element, and The core wire holder has a contact surface with the upper end of the electrode section, the contact surface having a lower electrical resistance than an area of ​​the first screw section to be fastened.

Description

TECHNICAL AREA

[0001] The present invention relates to a device for producing polycrystalline silicon using the Siemens process and a carbon core wire holder made of carbon. RELATED STATE OF THE ART

[0002] The Siemens process is known as a method for producing polycrystalline silicon, which is a raw material for single-crystal silicon used in semiconductors or for manufacturing solar cells. The Siemens process involves bringing a source gas containing chlorosilane into contact with a heated silicon core wire, thereby gas-phase growing polycrystalline silicon on the surface of the silicon core wire using a chemical vapor deposition (CVD) process.

[0003] In a reaction furnace for the gas-phase growth of polycrystalline silicon using the Siemens process, two vertical silicon core wires and one horizontal silicon core wire are assembled in a torii-shaped space within a chamber composed of an upper structure called the glass bell and a lower structure called the base plate. Both ends of the two silicon core wires are fixed to a pair of metal electrodes arranged on the base plate via a pair of carbon core wire holders. This configuration is disclosed, for example, in patent literature 1 (JP 2009-256 191 A).

[0004] The electrode penetrates the base plate in a sandwich-like arrangement, allowing it to be connected to another electrode via wiring or to a power source located outside the reaction furnace. The electrode, base plate, and glass bell jar are cooled by a coolant such as water to prevent the deposition of polycrystalline silicon during gas-phase growth or to prevent heavy metal contamination of the polycrystalline silicon, which can occur due to a rise in metal temperature.

[0005] The electrode and the carbon core wire holder are fixed in place by a fitting or similar device. The carbon core wire holder can be directly connected to the electrode or via a structure called an adapter to minimize electrode wear. Carbon is frequently used as the material for the adapter, which is then fixed to the electrode by a fitting or similar device.

[0006] High-purity silicon is gas-phase grown on the silicon core wire by passing an electric current from the electrode through the core wire holder to the silicon core wire. A mixed gas of trichlorosilane and hydrogen is then fed into the reaction furnace from a gas nozzle as a source gas. During this process, a surface of the silicon core wire is heated by Joule heating to a temperature range of approximately 900 °C to 1200 °C under a hydrogen atmosphere. At the same time, a silicon rod is deposited on one side of the carbon core wire holder, its diameter increasing as it is gradually integrated into the carbon core wire holder.Since the electrical resistance decreases with increasing silicone rod size, a current corresponding to the diameter of the silicone rod must also be increased until a desired diameter is reached in order to keep the surface of a silicon rod at reaction temperature.

[0007] Currently, the electric current required to apply to a silicon rod is between 2000 A and 4000 A when the reaction is complete. Since heat dissipation from the surface of a silicon rod increases with increasing rod diameter, electrical energy must be supplied to the rod, equivalent to heat dissipation, to maintain the temperature required for the reaction, which ranges from 900 °C to 1200 °C. Therefore, a carbon-core wire holder connecting a metal electrode and a polycrystalline silicon rod must have a structure and joining method capable of withstanding the increasing electric current and weight.

[0008] If the current density of a carbon core wire holder and an electrode increases, a local excitation zone can form, depending on the contact condition between the electrode and the carbon core wire. This can cause heavy metal contamination in polycrystalline silicon due to excessively high temperatures. Furthermore, if an electrode and a carbon core wire are placed in an unstable connection state, or if the contact area between them becomes unstable due to the increasing weight of a silicon rod, an electrical discharge occurs between the carbon core wire holder and the electrode, damaging both and potentially causing heavy metal and / or carbon contamination in polycrystalline silicon.

[0009] According to related prior art, as disclosed, for example, in patent literature 2 (JP H05-213 697 A) and patent literature 3 (JP 2011-195 439 A), an electrode and a carbon core wire holder are frequently connected by a fitting. While such a connection has the advantage of easy installation, the contact surface between the electrode and the carbon core wire holder is unstable. Since a type of control corresponding to the "tightening torque control" used in screw connections is not applicable, it is difficult to verify whether sufficient surface pressure is applied to a contact surface.Furthermore, the contact area itself and / or the distribution of pressure applied to a contact area can be varied by slight differences in the shape of matching mating surfaces or by a change in the force applied to a carbon core wire holder due to a setting process or an imbalance in the growth of a polycrystalline silicon rod. This has the disadvantage that the contact area and non-contact area are ambiguous and unstable, and consequently, a local excitation zone and a high-temperature zone can easily be formed.

[0010] In the method disclosed in patent literature 4 (JP 2010-235 438 A), a carbon core wire holder is fixed to an electrode by means of a screw. This fixing of the carbon core wire holder is mechanically strong; however, since a screw is designed as the excitation section, an electrical discharge can easily occur when the screw is excited, and the electrical connection is unstable because the position of a contact surface cannot be controlled.

[0011] As described above, the connection methods known in the prior art for a carbon core wire holder and an electrode are insufficient with regard to the stability of the excitation surface and can cause a local high-temperature section and an electrical discharge. If elements in the furnace are damaged by an electrical discharge, repairing the damage is extremely difficult. An electrode must be replaced, and a silicon rod becomes contaminated. Furthermore, since a glass bell jar and a base plate are contaminated, and a hydrocarbon compound is present as an impurity in the reaction gas, which must be collected and circulated, the production of a subsequent batch is negatively affected. For this reason, it is necessary to clean everything more thoroughly than usual. List of reference works Patent literature [Patent literature 1] JP 2009- 256 191 A [Patent Literature 2] JP H05- 213 697 A [Patent literature 3] JP 2011- 195 439 A [Patent literature 4] JP 2010- 235 438 A BRIEF DESCRIPTION OF THE INVENTION Technical Problem

[0012] The present invention is made in consideration of the problems mentioned above, and one objective of this invention is to provide a device for producing polycrystalline silicon, wherein the device is used with a technique that provides stable excitation between a core wire holder and an electrode section, so that not only damage to an electrode section is avoided, but also contamination of a silicon rod. Solution to the problem

[0013] To achieve the above objective, a first aspect of the present invention is an apparatus for producing polycrystalline silicon using the Siemens process, comprising: a carbon core wire holder holding a silicon core wire; an electrode section co-excitates the core wire holder, the electrode section having an upper end in contact with a lower end of the core wire holder; and a first screw section provided only around a lower part of the core wire holder for fixing to the electrode section, the core wire holder having a contact surface with the upper end of the electrode section, the contact surface having a lower electrical resistance than a region of the first screw section to be fastened.

[0014] The first screw section can be positioned below the contact surface of the core wire holder with the upper end of the electrode section.

[0015] The device for producing polycrystalline silicon can further comprise a second screw section provided around an upper part of the electrode section, wherein the first screw section of the core wire holder and the second screw section of the electrode section can be fastened by an insulating nut element.

[0016] The upper end of the electrode section and the contact surface of the core wire holder with the upper end of the electrode section can each be horizontally oriented.

[0017] The device for producing polycrystalline silicon may further comprise a conductive element inserted between the lower end of the core wire holder and the upper end of the electrode section. Advantageous effects of the invention

[0018] According to the present invention, a device for producing polycrystalline silicon is used, wherein the device is applied with a technique that provides stable excitation between a core wire holder and an electrode section, so that not only damage to the electrode section is avoided, but also contamination of a silicon rod. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a schematic explanatory view showing an example of a reaction furnace comprising a core wire holder according to the present invention; Fig. Figure 2 is a conceptual diagram showing a comparative configuration with a core wire holder attached to an electrode section; Fig. Figure 3 is a conceptual diagram showing an embodiment in which a core wire holder according to the present invention is attached to an electrode section; and Fig. Figure 4 is a conceptual diagram showing a mode in which a core wire holder is attached to an electrode section according to the related prior art. DESCRIPTION OF EXECUTION FORMS

[0019] Fig. Figure 1 is a diagram illustrating an outline of a reaction furnace configuration for a device for producing polycrystalline silicon, using a carbon core wire holder according to the present invention. A reaction furnace 100 comprises an electrode section 10 penetrating a base plate 5 provided on a lower section of a glass bell jar 1 such that the electrode section 10 is insulated from the base plate 5, and a carbon core wire holder 14, which holds a silicon core wire 13, is fixed to the electrode section 10. The core wire holder 14 is either directly connected to the electrode section 10 or fixed by a clamping device (not shown) to be connected to the electrode section 10.The majority of the electric current supplied by the electrode section 10 is transported to the core wire holder 14 via a contact surface between the core wire holder 14 and the electrode section 10. Polycrystalline silicon 15 is deposited on the silicon core wire 13 by reaction with a source gas.

[0020] In Fig. Figure 1 shows, in addition to the above-mentioned, an observation window 2, an inlet 3 and an outlet 4 of a coolant for cooling the glass bell 1, an inlet 6 and an outlet 7 of a coolant for cooling the base plate 5, an inlet 11 and an outlet 12 of a coolant for cooling the electrode section 10, a feed nozzle 9 of a source gas and an outlet 8 of a reaction exhaust gas.

[0021] There are no particular restrictions on how the core wire holder 14 is fixed to the electrode section 10. However, due to the ease of manufacturing required by standards such as JIS (Japanese Industrial Standards), fixing by screwing is preferred. Alternatively, a tool can be used for fixing. For example, a desired pressure (a contact surface pressure) can be applied to a contact surface between a lower end of the core wire holder 14 and an upper end of the electrode section 10 using a torque wrench. In this case, it is easy to suppress batch variations in contact surface pressures by controlling the torque value. Furthermore, a conductive element with a low impurity level, such as a carbon plate, can be placed between the core wire holder 14 and the electrode section 10 (i.e.,A contact surface is inserted between the lower end of the core wire holder 14 and the upper end of the electrode section 10) to support an electrical connection.

[0022] After the core wire holder 14 is fixed to the electrode section 10, the reaction furnace 100 is sealed in a bell shape by the glass bell jar 1, and the air in the reaction furnace 100 is replaced by nitrogen and then by hydrogen. Subsequently, when an electric current is supplied from the electrode section 10 through the core wire holder 14 to the silicon core wire 13, a surface of the silicon core wire 13 is heated to approximately 900 °C to 1200 °C by Joule heating. Under this condition, a source gas containing trichlorosilane and hydrogen is sprayed, causing a high-purity polycrystalline silicon 15 to be deposited on the surface of the silicon core wire 13.

[0023] To maintain the surface temperature of the polycrystalline silicon 15 at a temperature required for a reaction, the electric current must be increased as the polycrystalline silicon 15 expands. This increases the mechanical load on the core wire holder 14 and the contact area between the core wire holder 14 and the electrode section 10 due to the increased weight of the silicon rod, and also increases the electrical load due to the increased current density. In this case, if the contact surface serving as the excitation surface is horizontal, the contact surface pressure increases, while the weight of the polycrystalline silicon 15, and thus the contact resistance, decreases, making the contact surface electrically stable. Therefore, it is preferred that the upper end of the electrode section 10 and a contact surface of the core wire holder 14 with the upper end of the electrode section 10 are both horizontally oriented.

[0024] Fig. Figure 2 is a conceptual diagram illustrating a comparative configuration of the core wire holder 14 provided in the apparatus for producing polycrystalline silicon using the Siemens process. As shown in Fig. As shown in Figure 2, a lower end of the core wire holder 14 is in contact with the upper end 18 of the electrode section 10, which excites the core wire holder 14. The core wire holder 14 is also provided with a fixing part 17 that extends downwards below the lower end of the core wire holder 14, and the fixing part 17 has a screw section 17a around its lower portion. The screw section 17a is positioned below the contact surface between the lower end of the core wire holder 14 and the upper end of the electrode section 10. It is noted that the screw section 17a is provided only on the lower portion of the core wire holder 14.

[0025] The contact surface between the lower end of the core wire holder 14 and the upper end 18 of the electrode section 10 is designed to have a lower electrical resistance than the area where the screw section 17a is attached. Thus, the majority of the electric current flowing through the silicon core wire 13 passes through the contact surface between the lower end of the core wire holder 14 and the upper end 18 of the electrode section 10. This makes it possible to obtain a stable connection, both structurally and electrically, without relying on an insulating clamping device.

[0026] Thus, a material with low electrical resistance, such as copper or SUS (Steel Use Stainless), is generally used for the electrode section 10, and its electrical resistance is much lower than that of the carbon core wire holder 14. If the upper end 18 (a contact surface) of the electrode section 10 is positioned higher than the screw section 17a, the electrical resistance of a path across the contact surface becomes lower than that of a path across the screw section 17a. Consequently, most of the electric current flows through the contact surface (the upper end 18) to the silicon core wire 13, while the amount of current through the screw section 17a can be almost negligible.

[0027] The configuration of the core wire holder 14 according to the present invention is not in Fig. 2 shown.

[0028] Fig. Figure 3 is a conceptual diagram illustrating an embodiment of the core wire holder 14, which is provided in the apparatus for producing polycrystalline silicon using the Siemens process, according to the present invention. In the embodiment shown in Figure 3, the core wire holder is provided in the apparatus for producing polycrystalline silicon using the Siemens process. Fig. As shown in 3, the core wire holder 14 resembles the one in Fig. In the configuration shown in Figure 2, a lower end of the core wire holder 14 is in contact with the upper end 18 of the electrode section 10, which excites the core wire holder 14. The core wire holder 14 has a screw section 17a for use in fixing it to the electrode section 10, and a contact surface between the lower end of the core wire holder 14 and the upper end 18 of the electrode section 10 is designed to have a lower electrical resistance than the area where the screw section 17a is attached. The core wire holder 14 differs from the first embodiment in that a screw section 17a is also provided on an upper part of the electrode section 10, and the screw sections 17a of the core wire holder 14 and the electrode section 10 are fastened by a nut element 16 formed from an insulator as a fixing clamping device.

[0029] Even in such an embodiment, since no electric current flows through the nut element 16, which is formed from an insulator, most of the current flows through the contact surface (the upper end 18) to the silicon core wire 13.

[0030] Using the core wire holders 14 as described above according to the present invention, it is possible to maintain a stable excitation while simultaneously ensuring sufficient clamping force. This suppresses local high temperatures and the occurrence of electrical discharges, and prevents contamination of polycrystalline silicon by impurities such as heavy metals and carbon.

[0031] In patent literature 1, a section corresponding to the screw section 17a of the present invention is provided entirely over a side surface of a core wire holder, and thus an electrical discharge, etc., is likely to occur unintentionally in such an unevenly shaped section. In contrast, the screw section 17a according to the present invention is provided only on the lower part of the core wire holder 14, and thus it is possible to suppress the occurrence of such an electrical discharge, etc.

[0032] In patent literature 2, a core wire holder is designed in a so-called fitting type, and thus an electrical discharge, etc., likely occurs unintentionally due to unstable fixation to an electrode. In contrast, the core wire holder 14 according to the present invention is fixed by the screw section 17a, and it is therefore possible to suppress the occurrence of such an electrical discharge, etc.

[0033] In patent literature 3, a core wire holder is also designed in a so-called fitting type, and thus an electrical discharge, etc., likely occurs unintentionally due to unstable fixation to an electrode. In contrast, the core wire holder 14 according to the present invention is fixed by the screw section 17a, and it is therefore possible to suppress the occurrence of such an electrical discharge, etc.

[0034] In patent literature 4, a core wire holder resembles at first glance the core wire holder 14 according to the embodiment of the present invention. However, it is designed in a stepped column shape, with the outer diameter of a lower part being larger than the outer diameter of an upper part, and thus an electrical discharge, etc., is likely to occur unintentionally because the electric current flows unevenly through a screw section. In contrast, the core wire holder 14 according to the present invention is fixed by the screw section 17a, and it is therefore possible to suppress the occurrence of such an electrical discharge, etc. <Examples>

[0035] Examples are described below. Polycrystalline silicon was deposited on the silicon core wire 13 in the reaction furnace 100 of the apparatus for producing polycrystalline silicon using the Siemens process until a pair of polycrystalline silicon rods weighing 125 kg to 200 kg had been grown. After the reaction was complete, a pair of polycrystalline silicon rods was collected, and then it was checked whether an anomaly, such as a discharge sign or discoloration due to anomalous heat generation, had occurred on the electrode section 10 and the core wire holder 14. <Beispiel 1>

[0036] The core wire holder 14, which is in Fig. The electrode section 10, as shown in Figure 2, was fixed with a torque of 80 Nm. Two batches of deposition reactions were carried out until a pair of polycrystalline silicon rods had been grown to approximately 125 kg. No anomalies, such as discharge signs or discoloration, were observed in any batch. <Beispiel 2>

[0037] The core wire holder 14, which is in Fig. The core wire holder 14, as shown in Figure 2, was fixed to the electrode section 10 with a torque of 80 Nm. Three batches of deposition reaction were carried out until a pair of polycrystalline silicon rods had been grown to approximately 200 kg. No discharge sign was confirmed in any batch. However, the core wire holder 14 was partially bound to the electrode section 10 at a rate of 16.7%. <Beispiel 3>

[0038] The core wire holder 14, which is in Fig. As shown in Figure 2, the electrode section 10 was fixed with a torque of 80 Nm, with a plate-like element made of high-purity graphite (Na < 0.05, Cu < 0.08, Fe and Ni < 0.1, Zn < 0.1) inserted between the core wire holder 14 and the electrode section 10. Three batches of deposition reactions were carried out until a pair of polycrystalline silicon rods weighing approximately 200 kg had been grown. No anomalies, such as discharge signs or discoloration, were observed in any batch. <Vergleichsbeispiel 1 >

[0039] The core wire holder 14, which is in Fig. As shown in Figure 4, the electrode section 10 was fixed by twisting and fitting. Two batches of deposition reactions were carried out until a pair of polycrystalline silicon rods had been grown to approximately 125 kg. No discharge sign was confirmed in any batch. However, the electrode section 10 turned black at a rate of 4.2% at a contact surface with the carbon core wire holder 14, and the carbon core wire holder 14 was partially bonded to the electrode section 10 at a rate of 29.2%. <Vergleichsbeispiel 2>

[0040] The core wire holder 14, which is in Fig.The core wire holder 14, as shown in Figure 4, was fixed to the electrode section 10 by twisting and fitting. Three batches of deposition reactions were carried out until a pair of polycrystalline silicon rods had been grown to approximately 200 kg. A discharge sign was confirmed at a rate of 16.7% on a contact surface with the core wire holder 14 in the electrode section 10. The electrode section 10 also turned black at a rate of 25.0% on a contact surface with the core wire holder 14, and the core wire holder 14 was partially bonded to the electrode section 10 at a rate of 41.7%. Commercial applicability

[0041] According to the present invention, a device for producing polycrystalline silicon is provided, wherein the device is used with a technique that provides stable excitation between a core wire holder and an electrode section, so that not only damage to the electrode section is avoided, but also contamination of a silicon rod. List of reference symbols 1 glass bell jar; 2 observation windows; 3 Coolant inlet (in relation to the glass bell); 4 Coolant outlet (in relation to the glass bell); 5 Base plate; 6 Coolant inlet (relative to the base plate); 7 Coolant outlet (relative to the base plate); 8 Reaction exhaust outlet; 9 Supply nozzle for source gas; 10 Electrode section; 11 Coolant inlet (with respect to the electrode section); 12 Coolant outlet (with respect to the electrode section); 13 silicon core wire; 14 core wire holders; 15 Polycrystalline silicon; 16 nut element; 17 Fixing part; 17a Screw section; 18 Upper end of the electrode section; 19 Fitting part; and 100 reaction furnaces.

Claims

[1] Apparatus for producing polycrystalline silicon using the Siemens process, comprising: a carbon core wire holder that holds a silicon core wire; an electrode section that excites the core wire holder, wherein the electrode section has an upper end in contact with a lower end of the core wire holder; a first screw section that is only provided around a lower part of the core wire holder to be fixed to the electrode section, and a second screw section provided around an upper part of the electrode section, wherein the first screw section of the core wire holder and the second screw section of the electrode section are fastened by an insulating nut element, and The core wire holder has a contact surface with the upper end of the electrode section, the contact surface having a lower electrical resistance than an area of ​​the first screw section to be fastened. [2] Device for producing polycrystalline silicon according to claim 1, wherein the upper end of the electrode section and the contact surface of the core wire holder with the upper end of the electrode section are each horizontally formed. [3] Device for producing polycrystalline silicon according to claim 1 or 2, further comprising a conductive element inserted between the lower end of the core wire holder and the upper end of the electrode section.

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