JP2010150131A - Method and device for producing polycrystalline silicon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stabilize the treatment for converting an exhaust gas into a raw material, to rise the productivity of a polycrystalline silicon and to improve and stabilize a quality by appropriately separating gas and liquid by cooling the exhaust gas without generating a liquid state mist and. <P>SOLUTION: In the method for producing the polycrystalline silicon wherein the polycrystalline silicon is deposited by reacting the raw material gas containing chlorosilane at high temperature, the exhaust gas is subjected to gas-liquid separation by cooling with a heat exchanger, the gas part and the liquid part are purified and distilled and used as a part of the raw material gas, the raw material gas is passed at a flow rate of 4-7 m/sec in a heat exchanger when the exhaust gas is cooled. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and a production method for producing polycrystalline silicon that is reused as a part of a raw material gas by cooling, gas-liquid separation, purifying or distilling the exhaust gas generated by the reaction in the polycrystalline silicon production process Relates to the device.

  As a manufacturing method of polycrystalline silicon, a manufacturing method by a Siemens method is known. In this method for producing polycrystalline silicon, a number of silicon core rods serving as seed rods are arranged and heated in the reaction furnace, and a raw material gas containing chlorosilane gas and hydrogen gas is supplied to the reaction furnace, This is a method in which a heated silicon core rod is brought into contact, and polycrystalline silicon generated by thermal decomposition of the raw material gas and hydrogen reduction is deposited on the surface thereof.

Moreover, since the exhaust gas from the reactor contains unreacted gas, by-product silicon tetrachloride, hydrogen, and the like, chlorosilanes and chlorides are cooled by cooling to -30 ° C or lower through a heat exchanger. (Polymer) is separated, and the separated chlorosilane component and polymer component are again converted into semiconductor-purity chlorosilane through a distillation step, and are introduced into the polycrystalline silicon production step as part of the raw material gas. The remaining hydrogen gas is purified, and is again input to the polycrystalline silicon manufacturing process as part of the source gas.
In such a series of methods for producing polycrystalline silicon, the gas component from which the condensate has been separated by cooling the exhaust gas from the reactor is pressurized by a compressor, as shown in Patent Document 1, and then cooled by a cooler. By passing through, chloride is removed, and then purified to high purity hydrogen gas.

JP 2003-95635 A

  By the way, the temperature of exhaust gas discharged from the reactor decreases as it passes through the system. For example, when it is cooled from a high temperature of about 200 ° C. to −30 ° C. or less by a heat exchanger, the temperature rapidly decreases. When cooling and condensation is performed, liquid mist is generated and may float and flow in the exhaust gas. If the exhaust gas is sent to the compressor while containing liquid mist, the compressor will break down due to liquid compression, the frequency of open maintenance will increase, and the raw material treatment of the exhaust gas will become unstable. It tends to hinder the productivity of silicon. In addition, since liquid mist may be a polymer contained in exhaust gas during condensation, ignition of the polymer in the air is necessary when performing maintenance or removing it due to adhesion to the interior of the compressor or surrounding equipment. In some cases, the process is time-consuming and expensive. Furthermore, when the compressor is opened, the system or equipment is corroded due to hydrolysis or the like, and impurities such as phosphorus, boron, and arsenic contaminate the quality of semiconductor grade silicon production.

  The present invention has been made in view of such circumstances, and by cooling the exhaust gas without generating liquid mist and appropriately separating the gas and liquid, the raw material treatment is stabilized, and polycrystalline silicon is obtained. The purpose is to improve the productivity and to improve quality and stability.

  The method for producing polycrystalline silicon according to the present invention reacts a raw material gas containing chlorosilane at a high temperature to precipitate polycrystalline silicon, and cools the exhaust gas by a heat exchanger to perform gas-liquid separation. In the polycrystalline silicon manufacturing method in which a part of the raw material gas is refined and distilled to cool the exhaust gas, the heat exchanger is passed through the heat exchanger at a flow rate of 4 m / sec to 7 m / sec. It is characterized by.

  That is, when exhaust gas is passed through a heat exchanger, it is cooled to condense chlorosilanes and polymers, and is separated from the gas by falling as a droplet in the heat exchanger and falling from the gas stream. If the flow rate of the gas at that time is high, the fine liquid mist will be carried on the gas flow to the subsequent process before it is condensed and dropped into droplets. In the present invention, by restricting the gas flow rate when passing through the heat exchanger and passing the heat exchanger at a relatively slow flow rate, it is possible to ensure a sufficient time for growing as droplets, and for the heat exchanger The droplets are easily attached to the cooled side walls so as to be reliably recovered as a condensate. When the flow rate exceeds 7 m / sec, most of the liquid mist is caused to flow into the gas flow, and when the flow rate is less than 4 m / sec, the productivity decreases.

In the polycrystalline silicon manufacturing method of the present invention, the exhaust gas may be cooled stepwise by a plurality of heat exchangers, and the condensate of the exhaust gas may be recovered from each heat exchanger.
By passing through multiple heat exchangers in order, the exhaust gas is cooled in stages, so that the gas flow is relaxed when entering and exiting each heat exchanger, preventing the occurrence of supercooling phenomenon It is possible to reliably prevent mist from being brought into the exhaust gas.

In the method for producing polycrystalline silicon according to the present invention, dust in the exhaust gas may be separated and removed before the exhaust gas is cooled by the heat exchanger.
By separating and removing the dust from the exhaust gas, the generation of mist during subsequent cooling is suppressed, and gas-liquid separation can be performed efficiently, while maintaining the efficiency of the heat exchanger and preventing clogging. it can.

The polycrystalline silicon production apparatus of the present invention includes a reaction furnace in which a raw material gas containing chlorosilane is reacted at a high temperature to precipitate polycrystalline silicon, and an exhaust gas from the reaction furnace is cooled by a heat exchanger to be gas-liquid In the polycrystalline silicon manufacturing apparatus, comprising: a cooling device to be separated; and a purification / distillation device that refines and distills the gas and liquid components thereof to make a part of the raw material gas. A flow rate control means for controlling the flow rate of the exhaust gas in the vessel to 4 m / second to 7 m / second is provided.
As the flow rate control means, it is possible to adopt a configuration such as providing a valve on the downstream side of the heat exchanger.

  In the polycrystalline silicon production apparatus of the present invention, a dust separation device for separating and removing dust in the exhaust gas may be provided between the reaction furnace and the cooling device.

In the polycrystalline silicon manufacturing apparatus of the present invention, the heat exchanger is inclined downwardly from the exhaust gas inlet side to the outlet side, and a condensate transfer pipe for transferring the exhaust gas condensate to the outlet side is provided. It should be connected.
Since the outlet side of the heat exchanger is lowered, the condensate can be discharged efficiently. The inclination angle is preferably 1 to 5 °.

  According to the polycrystalline silicon manufacturing method of the present invention, by limiting the flow rate of the exhaust gas when passing through the heat exchanger, the exhaust gas is reliably condensed in the heat exchanger to form droplets. It is possible to improve the productivity by minimizing the amount of liquid mist brought into the exchanger and afterward, stabilizing the operation of equipment during continuous production.

It is a flowchart which shows the whole structure of one Embodiment of the polycrystalline-silicon manufacturing apparatus which concerns on this invention. It is a flowchart which shows the detailed structure of the cooling device in FIG.

Hereinafter, an embodiment of a method for producing polycrystalline silicon according to the present invention will be described with reference to the drawings.
FIG. 1 shows an overall flow of a polycrystalline silicon manufacturing apparatus for carrying out the manufacturing method of the present embodiment.
This polycrystalline silicon production apparatus 1 includes a reaction furnace 2 in which a raw material gas containing chlorosilane and hydrogen gas is reacted at a high temperature to deposit polycrystalline silicon, and silicon powder and a polymer compound in the exhaust gas from the reaction furnace 2. A dust separation device 3 for collecting the dust content contained in the filter, a cooling device 4 for cooling the exhaust gas that has passed through the dust separation device 3 for gas-liquid separation, and purifying and distilling the gas and liquid components, And a refining / distilling device 5 as a part of the raw material gas.

The reaction furnace 2 is provided with a large number of silicon core rods 6 inside, and by bringing the silicon core rods 6 into a red-heated state and contacting the source gas supplied from the source gas supply system 7, Polycrystalline silicon S is deposited on the surface of the silicon core 6 by decomposition and hydrogen reduction. The gas subjected to the reaction is discharged from the exhaust gas pipe 8 and sent to the dust separation device 3.
The dust separator 3 is configured such that a large number of wire mesh filters (not shown) are provided in a laminated state in the middle of a pipe, and dust is collected by passing the filters.

As shown in detail in FIG. 2, the cooling device 4 has a configuration in which a plurality of heat exchangers 11 to 15 are connected in series, and the exhaust gas is passed through these heat exchangers 11 to 15 to, for example, about 200 ° C. To about −50 ° C. to condense trichlorosilane, silicon tetrachloride and the like in the exhaust gas into a liquid state, and separate hydrogen remaining in a gaseous state.
Specifically, five heat exchangers of the first to fifth heat exchangers are provided, and the first to fifth heat exchangers correspond to the heat exchangers 11 to 15 in order, and these heat exchangers 11 The exhaust gas is cooled in stages by sequentially passing through.

  The first heat exchanger 11 cools the exhaust gas sent from the dust separation device 3 via the exhaust gas transfer pipe 16 to about 40 ° C. because the exhaust gas is as high as about 200 ° C. In this case, two heat exchangers 11A and 11B are provided in parallel, one of them is operated, the other is kept on standby, and the polymer compound or the like that has not been completely removed by the dust separator 3 is attached. If the pressure loss increases due to the heat exchanger, the operation is switched to the standby heat exchanger and the heat exchanger that has been used up to now is maintained. Each heat exchanger 11A, 11B is a water-cooling type, and water is used as a refrigerant.

The second heat exchanger 12 cools the exhaust gas at about 40 ° C. sent from the first heat exchanger 11 via the exhaust gas transfer pipe 17 to about −10 ° C., and will be described later as a fifth heat exchanger. Heat exchange is performed with the exhaust gas at about −50 ° C. via 15.
In addition, the third to fifth heat exchangers 13 to 15 are configured to exchange heat with refrigerant (gas) supplied from the refrigerators 51 to 53, respectively. The exhaust gas of about −10 ° C. that has passed through the second heat exchanger 12 is cooled to about −17 ° C., the fourth heat exchanger 14 is further cooled to about −37 ° C., and the fifth heat exchanger 15 is −50 It is the structure cooled to about degreeC. Reference numerals 18 to 21 denote exhaust gas transfer pipes that transfer the exhaust gas between the heat exchangers 11 to 15, and the exhaust gas that has passed through the heat exchangers 11 to 15 in order by the exhaust gas transfer pipes 18 to 21 is second. It is sent from the heat exchanger 12 to the purification device in the subsequent process through the gas flow pipe 22.

  The flow rate of the exhaust gas when passing from the first heat exchanger 11 to the fifth heat exchanger 15 is 4 m / second to 7 m / second. In FIG. 1, reference numeral 55 denotes a flow meter that measures the flow rate of exhaust gas flowing through the gas flow pipe 22, and reference numeral 56 denotes a control valve that controls the flow rate from the measurement result of the flow meter 55. 56 constitutes a flow rate control means for adjusting the flow rate of the exhaust gas flowing through the heat exchangers 11 to 15 to 4 m / second to 7 m / second.

  In the case of this embodiment, a multi-tube heat exchanger is used for any of the first to fifth heat exchangers. That is, as shown in FIG. 2, the multi-tubular heat exchanger has a cover 26, 27 at both ends and a fuselage inside the cylindrical shell 25, as represented by the symbols of the heat exchanger 11 </ b> B and the heat exchanger 14. A pair of tube plates 29 for partitioning the portion 28 are disposed, and a large number of heat transfer tubes 30 communicating with the internal spaces of the covers 26 and 27 are inserted into the body portion 28 between the tube plates 29. Is provided. The exhaust gas flowing into the one inlet side cover 26 is circulated in each heat transfer tube 30 and discharged from the inner space of the other outlet side cover 27, and the heat transfer tube in the body portion 28 of the cylindrical shell 25. A heat medium is circulated from the outside in the outer space 30, and heat exchange is performed between the fluid flowing in the heat transfer tubes 30 and the heat medium circulated to the outside.

  In the example shown in FIG. 2, an external heat medium other than the second heat exchanger 12 is circulated in the body portion 28, but in the second heat exchanger 12, as described above, the fifth heat exchanger 15. The exhaust gas sent out from the internal space of the outlet side cover 27 is guided to the body part 28 via the exhaust gas transfer pipe 21, and heat exchange is performed between the exhaust gas flowing in the heat transfer pipe 30 in the body part 28, and the gas It is configured to be sent to a purification device in a subsequent process through the distribution pipe 22.

Further, in the first heat exchanger 11, the cylindrical shell 25 is arranged along the vertical direction, exhaust gas is supplied from the upper entrance side cover 26, and is generated from the lower exit side cover 27 by exhaust gas and cooling. The condensate is discharged. Moreover, in the 2nd-5th heat exchangers 12-15, while the cylindrical shell 25 is arrange | positioned sideways, the exit side cover 27 becomes a lower position (it becomes lower) rather than the entrance side cover 26. In addition, it is provided with a slight downward slope from the inlet side cover 26 toward the outlet side cover 27, and the condensate produced in the heat transfer tube 30 is easily collected in the outlet side cover 27 by the downward slope. The inclination angle is 1 to 5 degrees with respect to the horizontal direction. The code | symbols 35-39 have shown the condensate transfer pipe connected to the bottom part of the outlet side cover 27 of each heat exchanger 11-15, and the condensation discharged | emitted from the inside of the outlet side cover 27 of these heat exchangers 11-15. The liquid is collected in the liquid collection pipe 40 through the respective condensate transfer pipes 35 to 39, and is temporarily collected and stored in the tank 41.
As the size of the heat exchangers 11-15, for example, a diameter of 0.8～1M, length is a 5～9M, heat transfer area is 150 to 300 m ^2.

  The refining / distillation device 5 includes a refining device 42 for purifying hydrogen gas in the exhaust gas sent from the cooling device 4 via the gas flow pipe 22 and a condensation sent from the tank 41 via the liquid flow pipe 43. A distillation apparatus 44 for distilling the liquid, and sends purified hydrogen and trichlorosilane obtained by distillation to the raw material gas supply system 7 via the hydrogen supply pipe 45 and the trichlorosilane supply pipe 46, Reuse as part. In this case, the purifier 42 compresses the exhaust gas obtained by condensing and separating the chlorosilanes with the compressor 47, cools it with the secondary cooling device 48, separates the hydrogen chloride gas contained in the exhaust gas, and then separates impurities in the adsorption tower 49. It is set as the structure which adsorb | sucks and refine | purifies.

  In the polycrystalline silicon production apparatus 1 configured as described above, in order to produce polycrystalline silicon, a large number of silicon core rods 6 are arranged in the reaction furnace 2 to make them red-heated, and the raw material is added thereto. A source gas containing trichlorosilane and hydrogen is supplied from the gas supply system 7 to deposit polycrystalline silicon S on the surface of the silicon core 6 by thermal decomposition and hydrogen reduction. On the other hand, the exhaust gas after being subjected to the reaction is discharged from the reaction furnace 2 to the exhaust gas pipe 8, and after the silicon powder and polymer compound are removed by the dust separation device 3, gas-liquid separation is performed by the cooling device 4, and gas components are separated. Is purified as hydrogen gas by the purifier 42, and the liquid is purified to trichlorosilane, silicon tetrachloride and the like via the distillation device 44. In particular, the hydrogen gas and trichlorosilane are used again as a raw material for producing polycrystalline silicon and supplied again from the raw material gas supply system 7 to the reaction furnace 2.

In this series of manufacturing processes, in order to purify the hydrogen gas contained in the exhaust gas generated in the reactor 2, distill the chlorosilanes, and reuse them as raw material gases, respectively, trichlorosilane (SiHCl contained in the exhaust gas) ₃ ) It is important to reliably separate silicon tetrachloride (SiCl ₄ ), dichlorosilane (SiH ₂ Cl ₂ ) and the like from the exhaust gas containing hydrogen gas.

  In this embodiment, the exhaust gas generated in the reaction furnace 2 is first passed through the dust separation device 3 as it is. The dust in the exhaust gas is collected and removed by the filter, and then cooled by the cooling device 4 to be cooled with the chlorosilane component and the polymer. Are condensed and separated. And this cooling device 4 is made into the serial connection structure of the several heat exchangers 11-15, and while exhaust gas is cooled in steps, the flow velocity in each heat exchanger 11-15 is 4 m / sec-7 m / sec. Therefore, the exhaust gas is gradually cooled at a relatively slow speed. The pressure in the heat exchangers 11 to 15 is set to 0.03 to 0.3 MPa, for example.

  That is, as the exhaust gas is cooled, chlorosilanes and polymers reach saturation at the dew point temperature, and condensation occurs when the saturated vapor comes into contact with the solid surface at a temperature lower than that temperature. When the flow velocity is high, the fine mist-like liquid mist generated when condensing from the exhaust gas contacts the inner surface of the heat transfer tube 30 or the outlet side cover 27 and drops into droplets before riding on the exhaust gas flow downstream. Easy to flow. Therefore, by limiting the flow velocity, the saturated vapor is sufficiently brought into contact with the inner surfaces of the heat transfer tube 30 and the outlet side cover 27 to grow a large amount of liquid mist, and the droplets of the heat transfer tube 30 and the outlet side cover 27 are allowed to grow. It makes it easy to drop to the inner bottom. In particular, in the outlet side cover 27 of each of the heat exchangers 11 to 15, the channel area is rapidly expanded from the heat transfer tube 30, and the condensate is reliably condensed in the outlet side cover 27. It flows down along the bottom surface, can be discharged from the outlet side cover 27 and collected in the tank 41. In this case, since the heat exchangers 12 to 15 are inclined downwardly from the inlet side cover 26 to the outlet side cover 27, the condensate is easily collected and discharged in the outlet side cover 27, but the inclination angle is 5 Since the gas flow rate tends to increase when the value exceeds 40 °, the flow rate is limited to an inclination angle of 5 ° or less.

  Further, the exhaust gas that has passed through the dust separation device 3 is in a high temperature state of around 200 ° C., and is cooled to about −50 ° C., so that a supercooling phenomenon occurs, and a fine liquid mist is generated, resulting in the inside of the system. , And may be brought into the compressor 47 in the subsequent process, but by cooling while passing through the plurality of heat exchangers 11 to 15, the entrance-side cover in each of the heat exchangers 11 to 15 26, the heat transfer tube 30, and the outlet side cover 27, the flow is moderated moderately, and the occurrence of a supercooling phenomenon can be prevented. In this case, if the exhaust gas is cooled while dust is present, the dust becomes a nucleus and a large amount of mist is generated. However, since the dust is separated and removed by the dust separator 3 before the exhaust gas is cooled, The generation of mist at the time of cooling can be suppressed, and gas-liquid separation can be performed efficiently.

  Accordingly, the exhaust gas is reliably condensed in each heat exchanger from the first heat exchanger 11 to the fifth heat exchanger 15, and the liquid mist is brought into the compressor 47 in the subsequent process as much as possible. 47 can be prevented from occurring and stable continuous production can be performed. Further, if the dust remains and is sent to the heat exchangers 11 to 15, it may adhere to the inner surface of the heat transfer tube 30 and cause clogging, etc., but since it has been removed in advance, the heat transfer tube 30 is clogged. Is less likely to occur.

  The flow rate in the heat exchanger was changed, and the fluctuation of the gas outflow amount in the flow meter 55 of the gas circulation pipe 22 and the influence on the compressor 47 in the purification / distillation device 5 were investigated. It was. As is apparent from Table 1, it can be seen that the flow rate of 4 to 7 m / sec of the present invention does not change the outflow amount of gas and does not affect the subsequent compressor. Therefore, the soundness of the polycrystalline silicon manufacturing apparatus can be maintained for a long time.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the cooling device is configured by a plurality of multi-tube heat exchangers, but is not necessarily limited to the multi-tube type, and other types of heat exchangers may be used.
Further, the exhaust gas is cooled from about 200 ° C. to about −50 ° C. by passing the exhaust gas from the first heat exchanger to the fifth heat exchanger. Applicable to the case.

DESCRIPTION OF SYMBOLS 1 Polycrystalline silicon manufacturing apparatus 2 Reactor 3 Dust separation apparatus 4 Cooling apparatus 5 Purification / distillation apparatus 6 Silicon core rod 7 Raw material gas supply system 8 Exhaust gas pipe 11-15 Heat exchanger 16-21 Exhaust gas transfer pipe 22 Gas distribution pipe 25 Cylindrical shell 26 Entrance side cover 27 Exit side cover 28 Body part 29 Tube plate 30 Heat transfer pipe 35-39 Condensate transfer pipe 40 Liquid collection pipe 41 Tank 42 Purifier 43 Liquid flow pipe 44 Distillation apparatus 45 Hydrogen supply pipe 46 Trichlorosilane Supply pipe 47 Compressor 48 Secondary cooling device 49 Adsorption tower 51 to 53 Refrigerator 55 Flow meter 56 Control valve S Polycrystalline silicon

Claims (6)

The raw material gas containing chlorosilane is reacted at a high temperature to precipitate polycrystalline silicon, and the exhaust gas is cooled by a heat exchanger and separated into gas and liquid, and the gas and liquid are purified and distilled to produce the raw material. In the polycrystalline silicon manufacturing method as a part of gas,
A method for producing polycrystalline silicon, wherein when the exhaust gas is cooled, the heat exchanger is passed through the heat exchanger at a flow rate of 4 m / sec to 7 m / sec.   The method for producing polycrystalline silicon according to claim 1, wherein the exhaust gas is cooled stepwise by a plurality of heat exchangers, and the condensed liquid of the exhaust gas is recovered from each heat exchanger.   The method for producing polycrystalline silicon according to claim 1 or 2, wherein dust in the exhaust gas is separated and removed before the exhaust gas is cooled by the heat exchanger. A reaction furnace in which a raw material gas containing chlorosilane is reacted at a high temperature to deposit polycrystalline silicon; a cooling device that cools the exhaust gas from the reaction furnace by a heat exchanger; and a gas component and a liquid component thereof In a polycrystalline silicon production apparatus comprising a purification / distillation device that makes a part of the raw material gas by purifying / distilling
The polycrystalline silicon manufacturing apparatus, wherein the cooling device is provided with flow rate control means for controlling the flow rate of the exhaust gas in the heat exchanger to 4 m / second to 7 m / second.   The apparatus for producing polycrystalline silicon according to claim 4, wherein a dust separator for separating and removing dust in the exhaust gas is provided between the reaction furnace and the cooling device.   The heat exchanger is inclined downward from an inlet side to an outlet side of the exhaust gas, and a condensate transfer pipe for transferring the condensate of the exhaust gas is connected to the outlet side of the heat exchanger. Item 6. The polycrystalline silicon manufacturing apparatus according to Item 4 or 5.

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