JP5761099B2 - Polycrystalline silicon reactor - Google Patents

Description

  The present invention relates to a polycrystalline silicon reactor for producing polycrystalline silicon rods by depositing polycrystalline silicon on the surface of a heated silicon core rod.

  In general, the Siemens method is known as a method for producing high-purity polycrystalline silicon used as a semiconductor material. The Siemens method is a manufacturing method in which a raw material gas composed of a mixed gas of chlorosilane and hydrogen is brought into contact with a heated seed, and polycrystalline silicon generated by thermal decomposition of the raw material gas and hydrogen reduction is deposited on the surface. As an apparatus for carrying out this manufacturing method, a polycrystalline silicon reactor in which a large number of silicon core rods (starter filaments) are erected on an electrode unit installed at the bottom of a closed reactor is used (Patent Document 1). reference).

  Moreover, as shown in Patent Document 2, conventionally, in a polycrystalline silicon reactor, two rod-shaped silicon core rods provided along the vertical direction, and a connecting member that connects upper ends of these silicon core rods, The seed assembly formed in a square shape is fixed by the above. The seed assembly is heated to a high temperature by supplying current through the electrode unit and generating Joule heat. The electrode unit includes a core rod holding electrode made of a conductive material such as carbon, and is fixed to the bottom of the reaction furnace to hold the lower end portion of the silicon core rod.

  In the polycrystalline silicon reactor described in Patent Document 2, an opening extending in the vertical direction is provided at the tip of a carbon core rod holding electrode. The silicon core rod is erected by being inserted into the opening, and is fixed to the core rod holding electrode by a set screw screwed into the core rod holding electrode. The polycrystalline silicon is deposited so as to cover the entire silicon core rod and the upper portion of the core rod holding electrode, and the whole silicon core rod is cut and recovered as a polycrystalline silicon rod.

JP-A-5-213697 JP 2009-256191 A

  In the polycrystalline silicon reactor described in Patent Document 2, the core rod holding electrode and the set screw are made of carbon in order to suppress contamination of the deposited polycrystalline silicon. However, carbon is difficult to precisely process, and if the accuracy is poor, the screwing of the set screw may be loosened, or the screw thread may be shaved when screwed in, which may result in incomplete fixing of the silicon core rod.

  If the silicon core is not fixed enough, the contact between the silicon core and the core holding electrode will be insufficient, causing a current to flow locally, and the silicon core will melt due to local temperature rise. In addition, there is a risk that the amount of deposited silicon may be reduced due to insufficient energization of the silicon core rod. Furthermore, when the silicon core rod is tilted, it may collapse due to its own weight, or when the silicon core rod is installed adjacent to each other, continuous collapse due to contact with each other or abnormal energization due to a ground fault occurs. Such a problem occurs. For this reason, a stable reaction cannot be maintained, and the production amount of silicon is reduced. Therefore, a structure in which a set screw is reliably screwed to the core rod holding electrode is required.

  This invention is made | formed in view of such a situation, and it aims at providing the polycrystalline silicon reactor which can support a silicon | silicone core rod reliably.

  The present invention supplies a raw material gas containing a silicon compound such as chlorosilanes into the reaction furnace, energizes the silicon core rod in the reaction furnace to generate heat, and deposits polycrystalline silicon on the surface of the silicon core rod. A polycrystalline silicon reactor that grows as a rod, an electrode provided in an electrically insulated state with respect to the bottom plate portion of the reactor, and a silicon core rod standing on the electrode A core rod holder for holding the core rod, and a carbon core rod holder in which a screw hole communicating from the outer surface to the side of the core rod holding hole is formed, and the screw hole of the core rod holder And a set screw made of carbon for fixing the silicon core rod to the core rod holder. The set screw has a larger thermal expansion coefficient than the core rod holder.

  According to this polycrystalline silicon reactor, since the thermal expansion coefficient of the set screw is larger than the thermal expansion coefficient of the core rod holder, the heated core rod holder and the set screw become hot and the screw hole of the core rod holder The clearance between the set screw and the screw becomes small, the screwing becomes strong, the set screw is difficult to loosen, and the silicon core rod can be reliably supported.

  In this polycrystalline silicon reactor, it is preferable that the mechanical strength of the set screw is larger than that of the holder. In this case, even when the set screw is loosened or retightened several times for the purpose of attaching / detaching the silicon core rod or adjusting the holding state, it is possible to reduce wear and breakage of the set screw thread. Therefore, it is possible to maintain a state in which the set screw is difficult to loosen, and to reliably support the silicon core rod.

In the polycrystalline silicon reactor, the core rod holder has a bending strength of 20 MPa to 30 MPa, a thermal expansion coefficient of 2.0 × 10 ⁻⁶ / ° C. to 4.0 × 10 ⁻⁶ / ° C., It is preferable that the bending strength of the set screw is 40 MPa or more and 60 MPa or less, and the thermal expansion coefficient is 3.5 × 10 ⁻⁶ / ° C. or more and 5.0 × 10 ⁻⁶ / ° C. or less.

  If the bending strength of the core rod holder is lower than the above range, if the silicon core rod is tilted by shaking the raw material gas flow during the silicon deposition process on the silicon core rod, There is a fear that the core rod holder may be damaged without being able to support the increasing weight of the silicon rod, or the silicon rod may be collapsed. On the other hand, when the bending strength of the core rod holder is higher than the above range, it becomes difficult to cut during collection after the polycrystalline silicon is deposited, which takes time for the collection work.

  Further, when the thermal expansion coefficient of the core rod holder is not within the above range, the difference in thermal expansion coefficient from silicon is large during cooling after silicon deposition, and silicon cracks and cracks are likely to occur. When the thermal expansion coefficient of the core rod holder is higher than the above range and the bending strength of the set screw is lower than the above range, the set screw may be missing when the set screw is inserted into the core rod holder. There is a risk that it cannot be fixed. Moreover, when the bending strength of a set screw is higher than the said range, it is difficult to process and mass production becomes difficult.

  On the other hand, if the thermal expansion coefficient of the set screw is lower than the above range, the effect of strengthening the screwing becomes insufficient. On the other hand, if the thermal expansion coefficient of the set screw is higher than the above range, the threaded portion of the core rod holder or the main body may be damaged during energization.

The thermal expansion coefficient of the core rod holder and the set screw is preferably in the above range so that the thermal expansion coefficient of the core rod holder <the thermal expansion coefficient of the set screw. Further, the difference between the thermal expansion coefficient of the core rod holder and the thermal expansion coefficient of the set screw is 1.5 × 10 ⁻⁶ in order to prevent damage to the core rod holder during energization and enable stable silicon deposition. / ° C or less is desirable.

  In this polycrystalline silicon reactor, the core rod holder is preferably formed by cutting an extrusion molding material, and the set screw is formed by cutting a cold isostatic press molding material. In general, a carbon extrusion molding material has a low coefficient of thermal expansion, which is suitable for obtaining the material for the core rod holder. On the other hand, the carbon cold isostatic press-molded material is suitable for the set screw material in the polycrystalline silicon reactor of the present invention because it has higher mechanical strength and higher linear expansion coefficient than the extruded material. is there.

  According to the present invention, it is possible to provide a polycrystalline silicon reactor that can reliably support a silicon core rod.

It is the perspective view which notched the bell jar of the reaction furnace partially in the polycrystalline silicon manufacturing apparatus. It is a schematic sectional drawing of the reaction furnace shown in FIG. It is a figure which shows the electrode unit and seed assembly in the reaction furnace shown in FIG. It is sectional drawing which follows the IV-IV line of FIG.

  Hereinafter, an embodiment of a polycrystalline silicon reactor of the present invention will be described with reference to the drawings. In FIG. 1, a raw material gas containing a silicon compound such as chlorosilanes is supplied into a reaction furnace 10 and the silicon core rod 20 in the reaction furnace 10 is energized to generate heat. 1 is an overall view of a polycrystalline silicon manufacturing apparatus in which crystalline silicon is deposited and grown as a rod.

  The reaction furnace 10 of the polycrystalline silicon manufacturing apparatus includes a bottom plate portion 12 that constitutes a furnace bottom, and a bell-shaped bell jar 14 that is detachably attached to the bottom plate portion 12. The upper surface of the bottom plate part 12 is formed in a substantially flat horizontal plane. The bell jar 14 has a bell shape as a whole, the ceiling is a dome shape, and the inner space is formed so that the central portion is the highest and the outer peripheral portion is the lowest. The walls of the bottom plate portion 12 and the bell jar 14 have a jacket structure (not shown) and are cooled by cooling water.

  The bottom plate portion 12 has an electrode unit 30 to which a silicon core rod 20 serving as a seed rod (seed) of polycrystalline silicon is attached, and an ejection nozzle for ejecting a raw material gas containing chlorosilane gas and hydrogen gas into the furnace ( (Gas supply port) 16 and a plurality of gas discharge ports 18 for discharging the reacted gas to the outside of the furnace are provided.

  A plurality of source gas ejection nozzles 16 are installed while being distributed at an appropriate interval and distributed over almost the entire upper surface of the bottom plate portion 12 of the reactor 10 so that the source gas is uniformly supplied to each silicon core rod 20. Has been. These ejection nozzles 16 are connected to a source gas supply source 50 outside the reaction furnace 10. Further, a plurality of gas discharge ports 18 are installed in the vicinity of the outer peripheral portion on the bottom plate portion 12 with appropriate intervals in the circumferential direction, and are connected to an external exhaust gas treatment system 52. A power circuit 54 is connected to the electrode unit 30.

  The silicon core rod 20 is fixed in a state in which a lower end portion is inserted into the electrode unit 30, and extends upward. A connecting member 22 that connects the two silicon core rods 20 as a pair is attached to the upper end portion of each silicon core rod 20. The connecting member 22 has cylindrical through holes 22a formed at both ends thereof engaged with columnar boss portions 20a formed at the upper ends of the silicon core rods 20 (see FIG. 3). This connecting member 22 is also formed of the same silicon as the silicon core rod 20. The two silicon core rods 20 and the connecting member 22 that connects them constitute a seed assembly 24 having a generally square shape. The seed assembly 24 is arranged substantially concentrically as a whole by arranging the electrode unit 30 substantially concentrically from the center of the reaction furnace 10.

  More specifically, as shown in FIG. 2, the electrode unit 30 holds an electrode unit 30 (30A) for holding one silicon core rod 20 and two silicon core rods 20 in a reaction furnace 10. An electrode unit 30 (30B) is disposed. A plurality of seed assemblies 24 are provided so as to straddle the plurality of electrode units 30A, 30B. These electrode units 30A and 30B are arranged in the order of one electrode unit 30A, a plurality of electrode units 30B, and one electrode unit 30A, and a plurality of seed assemblies 24 are connected in series. That is, both the silicon core rods 20 of one seed assembly 24 are held by the adjacent different electrode units 30A and 30B.

  That is, one of the two silicon core rods 20 of the seed assembly 24 is held in the electrode unit 30A, and one silicon core rod 20 of the two sets of seed assemblies 24 is held in the electrode unit 30B. Is retained. And it is comprised so that an electric current may flow through the power cable connected to electrode unit 30A of the both ends of a row | line | column.

  In the polycrystalline silicon manufacturing apparatus configured in this way, after heating with a heater or the like (not shown), the silicon core rod 20 is energized from each electrode unit 30 to cause the silicon core rod 20 to be in a heat generation state due to electrical resistance. To do. Further, each silicon core rod 20 is heated by receiving radiant heat from the adjacent silicon core rod 20. Then, the raw material gas reacts on the surface of the silicon core rod 20 where the Joule heat and the radiant heat are synergistically brought into a high temperature state, and polycrystalline silicon is deposited.

  The structure for holding the silicon core rod 20 in the electrode unit 30 (30A, 30B) will be described in more detail. As shown in FIG. 3, the electrode unit 30 </ b> A that holds one silicon core rod 20 is inserted into a through hole 12 a formed in the bottom plate portion 12 of the reaction furnace 10 and is electrically connected to the bottom plate portion 12. One core rod holder 34 is erected on the upper part of the electrode 32 provided in an insulated state. The electrode unit 30B that holds the two silicon core rods 20 is an electrode that is inserted into a through hole 12a formed in the bottom plate portion 12 of the reaction furnace 10 and is electrically insulated from the bottom plate portion 12. Two core rod holders 34 are erected on the top of 33.

  The core rod holder 34 provided in each electrode unit 30A, 30B is made of carbon, and a core rod holding hole 34a for inserting the silicon core rod 20 and holding it substantially vertically is formed from the upper end portion to the inside. Two screw holes 34b are formed in the upper portion of the core rod holder 34 so as to communicate with each other from the outer surface so as to be substantially orthogonal to the core rod holding hole 34a. A carbon set screw 36 for fixing the silicon core rod 20 is screwed into the screw hole 34b.

  As shown in FIG. 4, the holding hole 34 a of the core rod holder 34 has a rectangular shape in which a horizontal cross section intersecting the vertical direction has four corners. Screw holes 34b communicating from the outer surface are formed at two opposite corners in the holding hole 34a so as to be orthogonal to the holding hole 34a. A set screw 36 for fixing the silicon core rod 20 is screwed into one of the two screw holes 34b. The set screw 36 is made of carbon like the core rod holder 34, but has a higher mechanical strength and thermal expansion coefficient than the core rod holder 34, and a + -shaped or −-shaped driver tool groove is formed at one end thereof. ing.

The core rod holder 34 is formed by cutting an extruded material, and has a bending strength of 20 MPa to 30 MPa and a thermal expansion coefficient of 2.0 × 10 ⁻⁶ / ° C. to 4.0 × 10 ⁻⁶ / ° C. It is as follows. On the other hand, the set screw 36 is formed by cutting a cold isostatic press molding material (CIP molding material), the bending strength thereof is 40 MPa or more and 60 MPa or less, and the thermal expansion coefficient is 3.5 × 10. ^-6 / ° C or higher and 5.5 × 10 ^-6 / ° C or lower. Table 1 shows examples of suitable combinations of material characteristics used for the core rod holder 34 and the set screw 36.

  As shown in Table 1, the core rod holder 34 made of an extruded carbon material has a low coefficient of thermal expansion. On the other hand, the set screw 36 made of carbon cold isostatic press-molded material has higher mechanical strength and a larger thermal expansion coefficient than the extruded material.

  The silicon core rod 20 inserted into the holding hole 34a is a rod-like member having a substantially rectangular cross section smaller than the holding hole 34a. Accordingly, the silicon core rod 20 can move with respect to the core rod holder 34 within a range of a dimensional difference from the holding hole 34a, and the set screw 36 is tightened as shown in FIG. When the tip portion presses the corner (ridge line) of the silicon core rod 20, it is pressed against and fixed to the two surfaces indicated by the symbols F and G of the holding hole 34a facing the set screw 36, and the two surfaces F and G Due to this contact, the silicon core rod 20 and the core rod holder 34 are electrically connected.

  The set screw 36 may be screwed into any of the screw holes 34b. The relative position of the silicon core rod 20 with respect to the core rod holder 34 can be changed depending on which screw hole 34b is screwed. Thus, by changing the screw hole 34b to which the set screw 36 is attached, distortion of the seed assembly 24 can be reduced when the silicon core rod 20 is bent.

  However, when the set screw 36 attached to one screw hole 34b is removed and reattached to the other screw hole 34b, if the set screw 36 is broken or the thread of the set screw 36 is damaged due to attachment / detachment, the silicon core 20 May be insufficiently fixed. On the other hand, in the present invention, since the mechanical strength of the set screw 36 is higher than the mechanical strength of the core rod holder 34, the screw thread of the set screw 36 is not easily damaged, and it is securely attached to the other screw hole 34b. And the silicon core rod 20 can be stably held.

  Further, in the polycrystalline silicon reactor 10, the core rod holder 34 and the set screw 36 are both made of carbon in order to produce high-purity silicon. There is a possibility that the screwing of the screw 36 and the screw hole 34b becomes loose. On the other hand, in the present invention, since the thermal expansion coefficient of the set screw 36 is larger than the thermal expansion coefficient of the core rod holder 34, the thermal expansion of the screw hole 34b is small relative to the thermal expansion of the set screw 36, and the silicon core rod As the temperature of the core rod holder 34 and the set screw 36 increases with heating, the play between the set screw 36 and the screw hole 34b decreases. As a result, the fastening force between the set screw 36 and the screw hole 34b increases, so that the silicon core rod 20 can be securely fixed.

  As described above, according to the present invention, since the mechanical strength of the set screw attached to the core rod holder and fixing the silicon core rod is higher than the mechanical strength of the core rod holder, the set screw is prevented from being damaged. Thus, even when the set screw is attached to and detached from the screw hole in order to correct the distortion of the seed assembly, reliable screwing is possible. In addition, since the thermal expansion coefficient of the set screw is larger than the thermal expansion coefficient of the core rod holder, the processing of the set screw and core rod holder is not precise, and even if the screwing is loose at room temperature, the temperature in the reactor increases. Play is reduced and tightened strongly. Therefore, the silicon core rod can be reliably supported in the polycrystalline silicon reactor.

  In addition, this invention is not limited to the thing of the structure of the said embodiment, In a detailed structure, it is possible to add a various change in the range which does not deviate from the meaning of this invention.

DESCRIPTION OF SYMBOLS 10 Reactor 12 Bottom plate part 12a Through-hole 14 Berja 16 Injection nozzle (gas supply port)
18 Gas discharge port 20 Silicon core rod 20a Boss portion 22 Connecting member 22a Through hole 24 Seed assembly 30 (30A, 30B) Electrode unit 32, 33 Electrode 34 Core rod holder 34a Holding hole 34b Screw hole 36 Set screw

Claims (4)

A raw material gas containing a silicon compound such as chlorosilanes is supplied into the reaction furnace, and the silicon core rod in the reaction furnace is energized to generate heat, and polycrystalline silicon is deposited on the surface of the silicon core rod as a rod. A polycrystalline silicon reactor to be grown,
An electrode provided on the bottom plate portion of the reactor in an electrically insulated state with respect to the bottom plate portion;
A carbon-made core rod which is erected on this electrode, has a core-rod holding hole for holding the silicon core rod, and has a screw hole communicating from the outer surface to the side of the core-rod holding hole A holder,
A carbon set screw that is screwed into the screw hole of the core rod holder to fix the silicon core rod;
The polycrystalline silicon reactor, wherein the set screw has a larger coefficient of thermal expansion than the core rod holder.   The polycrystalline silicon reactor according to claim 1, wherein the set screw has higher mechanical strength than the core rod holder. The bending strength of the core rod holder is 20 MPa or more and 30 MPa or less, the thermal expansion coefficient is 2.0 × 10 ⁻⁶ / ° C. or more and 4.0 × 10 ⁻⁶ / ° C. or less, and the bending strength of the set screw is 40 MPa. The polycrystalline silicon reactor according to claim 2, wherein the polycrystalline silicon reactor has a thermal expansion coefficient of 3.5 × 10 ⁻⁶ / ° C. or higher and 5.0 × 10 ⁻⁶ / ° C. or lower.   4. The core rod holder is formed by cutting an extrusion molding material, and the set screw is formed by cutting a cold isostatic press molding material. The polycrystalline silicon reactor.

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