JP2010042955A - Inert gas recovery device in single crystal pulling device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inert gas recovery device having a function of removing SiO in an inert gas at a low cost in a simple configuration in a silicon single crystal pulling device. <P>SOLUTION: The inert gas recovery device introduces an inert gas discharged from a single crystal pulling device 2 via a dry vacuum pump 5 into a purifying device 8 to highly purify and recycles the gas again into the single crystal pulling device 2, wherein a device 3 having a function of vaporizing and removing SiO included in the discharged gas is disposed as a preceding stage of the dry vacuum pump 5. The device having a function of removing SiO includes a carbon heater in a sealed tank having a gas flow inlet and a gas flow outlet; and the device heats the inert gas containing SiO to a predetermined temperature to vaporize SiO, allows the vapor to react with carbon such as carbon fibers or solid graphite to obtain SiC, deposits the SiC on carbon such as carbon fibers or solid graphite to remove it. The recovery device may be equipped with an electric dust collector and a filter in a subsequent stage of the dry vacuum pump. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inert gas recovery apparatus in a silicon single crystal pulling apparatus, and more particularly, an apparatus capable of efficiently removing SiO fine powder with a simple configuration at a stage preceding a dry vacuum pump. It relates to an active gas recovery device.

  The Czochralski method is generally used as a method for producing a silicon single crystal. In this method, an inert gas such as argon gas is introduced into a metal chamber of a pulling apparatus, and a quartz crucible filled with polycrystalline silicon is heated with a graphite heater in a reduced pressure atmosphere by a vacuum pump connected to the outlet side. The silicon single crystal is grown while melting and then rotating the quartz crucible and the pulling shaft.

At this time, the silicon melt and the quartz crucible react to generate SiO, and the SiO and graphite heater further react to generate CO and CO ₂ . In addition, since there is degassing from other graphite parts, generally, argon gas discharged from a single crystal pulling apparatus contains fine powder of SiO, CO, CO ₂ , O ₂ , N ₂ , H _2. And impurities such as H ₂ O are contained.

  Further, the argon gas most frequently used as an inert gas contains only about 0.9% in the air. The production is performed by an air separation device, and extraction is performed by utilizing the difference in boiling points of oxygen, nitrogen, etc., which are components of air, and argon is extracted to the oxygen side having a near boiling point. Therefore, a large amount of argon is produced in ironworks and chemical factories that consume a large amount of oxygen.

  In recent years, the demand for argon has been increasing year by year for silicon single crystal production, stainless steel production and automobile welding, so the domestic supply of argon has already exceeded 90% of the production capacity. That is, although it is predicted that the argon-tightening process will be prolonged, there may be a situation where supply cannot be made if there is a decrease in production at an ironworks or the like.

  By the way, in the manufacture of silicon single crystals in an industry with a large amount of argon consumption, since air does not enter argon discharged from the pulling apparatus, the purity of argon in the exhaust gas is 90% or more. ing. And if it is not mixed with air, it can be purified and recovered at a low cost. Therefore, it can be purified on-site and purified to high purity argon for recycling.

  On the other hand, the argon gas discharged from the pulling device through the vacuum pump is mixed with other impurities such as fine SiO powder as described above. In particular, SiO is an unstable compound that reacts violently with oxygen (combustion), so air is mixed in during maintenance of fans, scrubbers, and piping during release to the atmosphere, including equipment such as pulling equipment and vacuum pumps. It is regarded as a safety issue because of the danger of a dust explosion.

As a countermeasure, a water-sealed vacuum pump is adopted as a vacuum pump after the pulling device, and a method is proposed in which the exhaust gas is stirred in a water tank to react SiO with water and remove it as SiO ₂ and hydrogen. (Patent Document 1). However, in the case of such a method, there are problems such as a high equipment cost, a high power cost and a high maintenance cost when the mechanical booster is installed in two stages due to insufficient capacity.

Japanese Patent Publication No. 2-14315

  In addition, in order to make up for the drawbacks of adopting the above water-sealed vacuum pump, a dry vacuum pump is used as a vacuum pump, and a device having a humidifying function (a bubbling can) is disposed after the dry vacuum pump. A method has also been proposed in which a part of the fine powder is removed here to prevent accidents such as dust explosion in the pipe (Patent Document 2).

Japanese Patent No. 2853757

However, the reaction between SiO and water cannot completely become SiO ₂ unless there are certain reaction temperature and reaction time conditions. Therefore, not all of SiO is completely removed, and there is a possibility that a part of the SiO flows unreacted to the piping and the purification apparatus. For this reason, there is a risk of dust explosion at the time of maintenance, etc., and safety measures are taken such as injecting air again to completely burn it. Therefore, it takes extra time and effort. In addition, in the case of such a method, there is a problem of high cost because it is necessary to attach a scrubber and an electric dust collector in addition to a device having a humidifying function.

  The present invention has been made in view of the above points, and it is possible to efficiently remove SiO fine powder with a simple configuration at a low stage in the front stage of the dry vacuum pump, and at the same time, the problems of the above-described conventional apparatus. It is an object of the present invention to provide an inert gas recovery apparatus in a single crystal pulling apparatus that can solve the above problem.

  Therefore, the gist of the present invention is that the inert gas discharged from the single crystal pulling apparatus through the dry vacuum pump is led to a purification apparatus to be purified, and recycled to the single crystal pulling apparatus again. In the active gas recovery apparatus, an inert gas recovery apparatus in a single crystal pulling apparatus is provided with an apparatus having a function of evaporating and removing SiO contained in exhaust gas before the dry vacuum pump. .

As shown in the table of FIG. 8, SiO has a characteristic that the vapor pressure curve is higher than that of SiO ₂ or Si. Therefore, this characteristic is used to heat SiO to a predetermined temperature at which SiO evaporates. It is intended to remove SiO contained in the exhaust gas.

  In the above configuration, the device having a function of evaporating and removing SiO is specifically a device in which a heater is incorporated in a sealed tank provided with a gas inlet and a gas outlet, and includes SiO. The inert gas is heated to a predetermined temperature. Moreover, it is preferable to use a carbon heater as the heater. In this way, when a carbon heater is used as a heater, SiO can be evaporated by heat at a predetermined temperature, and SiO can be reacted with carbon to form SiC, which can be removed by attaching the SiC. It is.

  In the above configuration, the evaporated SiO is reacted with carbon such as carbon fibers or solid graphite to form SiC, and the SiC is attached to carbon such as carbon fibers or solid graphite to be removed. You may make it provide the apparatus which performs. As a result, almost no SiO is contained in the exhaust gas.

  The reaction between carbon and SiO is shown in Table 2. As described above, it is known that the reaction proceeds when the standard free energy of Gibbs is Δ10 G ° (kcal / mol) or lower and the temperature is 1,127 ° C. or higher. Therefore, it is necessary to heat above such a temperature. Therefore, an apparatus similar to the apparatus having the function of evaporating SiO contained in the exhaust gas may be manufactured separately. However, heat heated to a high temperature, which is a condition for evaporating SiO in the apparatus, is used. It is used as heat for the reaction between carbon and SiO, and carbon such as carbon fibers or solid graphite is arranged inside, and this is reacted with SiO to form SiC to form carbon fibers or solid graphite. It is also possible to use an integrated (combined) apparatus that is attached to carbon such as a carbon and removed.

  In the above configuration, an electric dust collector and a filter may be provided after the dry vacuum pump. Thereby, impurities in the exhaust gas that could not be removed by the above apparatus, that is, fine powders such as SiO and dopant that could not react with carbon can be removed almost completely. Further, as the filter, a non-woven filter medium is formed in a plate shape and alternately folded in the opposite direction into an accordion-like element, a cylindrical housing and a sealed housing provided with a gas inlet and a gas outlet at both ends; And a filter in which an element is fixed inside the hermetic housing so as to be orthogonal to the gas flow direction.

  The present invention is configured as described above, and can easily remove SiO fine powder before and after a dry vacuum pump with a simple structure at low cost. Problems such as equipment cost, power cost and maintenance cost due to insufficient capacity of vacuum pump due to two-stage installation of mechanical booster, and complete removal of SiO in equipment with humidification function when using dry vacuum pump It is possible to solve both of the lack of safety due to the inability to perform the operation and the high cost problem due to the need to install the scrubber and the electric dust collector in addition to the device having the humidifying function.

  Since SiO is removed before the dry vacuum pump, SiO does not adhere to the dry vacuum pump, so that the performance of the dry vacuum pump is not reduced, that is, energy saving and maintenance are performed. Costs are low. In addition, it is possible to extremely reduce the risk of causing a dust explosion as in the prior art during maintenance of piping.

  In addition, when an electrostatic precipitator and a filter are provided in the subsequent stage of the dry vacuum pump, impurities in the exhaust gas that could not be removed by the SiO removal device provided in the previous stage of the dry vacuum pump, that is, carbon fibers or solids The fine powders such as SiO and dopant that could not react with carbon such as graphite can be removed almost completely.

  Hereinafter, the best mode for carrying out an inert gas recovery apparatus in a single crystal pulling apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic explanatory view of an inert gas recovery apparatus in a single crystal pulling apparatus according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view of an apparatus having a function of evaporating and removing SiO contained in exhaust gas. 3 is a perspective view of an apparatus having both a function of evaporating and removing SiO and a function of adhering and removing evaporated SiO to carbon, and FIG. 4 is a cylindrical shape made of carbon fibers used in the apparatus of FIG. FIG. 5 is a perspective view of the operation of the apparatus of FIG. 3, FIG. 6 is a longitudinal sectional side view of the filter, FIG. 7 is a cross sectional plan view of the center of the filter of FIG. 6, and FIG. Table and FIG. 9 are tables showing the standard production energy of Gibbs.

  In the figure, 1 is an inert gas recovery device. In addition, the inert gas recovery device 1 includes a single crystal pulling device 2, a device 3 having a function of evaporating and removing SiO contained in exhaust gas, a cooling device 4, a dry vacuum pump 5, The electrostatic precipitator 6, the filter 7, and the refining device 8 are sequentially connected to form an inert gas circulation system that flows into the single crystal pulling device 2.

  The feature of the present invention is that the apparatus 3 having the function of evaporating and removing SiO contained in the exhaust gas is provided in the preceding stage of the dry vacuum pump 5 as described above. Further, specifically, the SiO evaporation apparatus 3 includes heaters 3B and 3B in a sealed tank 3A provided with a gas inlet 3a and a gas outlet 3b as shown in FIG.

  Thus, the SiO evaporation device 3 is exhausted from the single crystal pulling device 2 and the exhaust gas flowing from the gas inlet 3a is heated by the heaters 3B and 3B, and the temperature required to evaporate the SiO contained therein. To evaporate SiO. The exhaust gas after this treatment flows out from the gas outlet 3b, and is sent to the purification device 8 through the cooling device 4, the dry vacuum pump 5, and the like.

  In the present embodiment, the heaters 3B and 3B used in the SiO evaporation apparatus 3 are carbon heaters.

  In addition to the SiO evaporation device 3, the evaporated SiO is reacted with carbon such as carbon fibers or solid graphite to form SiC, and the SiC is converted into carbon fibers or solid graphite. You may make it provide the apparatus attached to carbon and removing.

  FIG. 3 shows an apparatus having both the function of the SiO evaporation apparatus 3 and the function of an apparatus for reacting SiO with carbon to form SiC and attaching and removing the SiC to carbon. The apparatus 3 'includes heaters 3B' and 3B 'in a closed reaction tank 3A' provided with a gas inlet 3a ', a gas outlet 3b' and a dust outlet 3c ', and further comprises carbon fiber in the center. The cylindrical carbon 3C 'is stored in a cartridge type.

  The apparatus 3 'allows the exhaust gas discharged from the single crystal pulling apparatus 2 to flow into the hollow interior from the upper end opening of the cylindrical carbon 3C' made of carbon fiber, and is heated to a predetermined temperature by the heaters 3B 'and 3B'. By heating, the SiO contained therein is evaporated. When passing through the carbon 3C ′ in an atmosphere heated to a predetermined temperature, the evaporated SiO reacts with the carbon 3C ′ to become SiC, and the SiC adheres to the carbon 3C ′ and is removed. It will be. The carbon 3C ′ is periodically replaced so that its function does not deteriorate.

  Further, in the present invention, the electrostatic precipitator 6 and the filter 7 are provided in the subsequent stage of the dry vacuum pump 5, and in the present embodiment, as the filter, a non-woven filter medium is used as shown in FIGS. The element 7A has a plate shape and is alternately folded in the opposite direction into a bellows shape, and a sealed housing 7B having a cylindrical shape and provided with a gas inlet 7B ′ and a gas outlet 7B ″ at both ends. A filter in which the element 7A is fixed inside the housing 7B so as to be orthogonal to the gas flow direction is used.

  As a result, impurities in the exhaust gas that could not be removed by the SiO removal devices 3 and 3 'provided in the front stage of the dry vacuum pump, that is, fine powders such as SiO and dopant that could not react with carbon can be removed almost completely. It can be done.

It is a schematic explanatory drawing of the inert gas collection | recovery apparatus in the single crystal pulling apparatus which concerns on embodiment of this invention. It is sectional drawing of the apparatus with the function to evaporate and remove SiO contained in waste gas. FIG. 3 is a perspective view of an apparatus having both a function of evaporating and removing SiO and a function of attaching and removing evaporated SiO to carbon. It is a perspective view of the cylindrical carbon which consists of carbon fiber used in the apparatus of FIG. It is operation | movement explanatory drawing of the apparatus of FIG. It is a center longitudinal section side view of a filter. FIG. 7 is a central cross-sectional plan view of the filter of FIG. 6. It is a table | surface which shows Si type | system | group vapor pressure. It is a table | surface which shows the standard production free energy of Gibbs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inert gas collection | recovery apparatus 2 Single crystal pulling apparatus 3 The apparatus which evaporates and removes SiO 3 'The apparatus which combines the evaporation function of SiO and the function which makes SiO react with carbon, and makes it SiC 4 Cooling apparatus 5 Dry vacuum pump 6 Electric dust collector 7 Filter 8 Refiner

Claims (6)

  In the inert gas recovery device that introduces the inert gas discharged from the single crystal pulling device through the dry vacuum pump to the purification device to be highly purified and recycles it again to the single crystal pulling device, in the front stage of the dry vacuum pump, An inert gas recovery apparatus in a single crystal pulling apparatus, wherein an apparatus having a function of evaporating and removing SiO contained in exhaust gas is provided.   2. The inert gas recovery in a single crystal pulling apparatus according to claim 1, wherein the apparatus having a function of evaporating and removing SiO is an apparatus in which a heater is incorporated in a closed tank provided with a gas inlet and a gas outlet. apparatus.   The inert gas recovery device in a single crystal pulling apparatus according to claim 2, wherein the heater is a carbon heater.   Evaporated SiO is reacted with carbon such as carbon fibers or solid graphite to form SiC, and is equipped with a device for removing the SiC by attaching it to carbon such as carbon fibers or solid graphite. The inert gas recovery device in the single crystal pulling apparatus according to claim 1, 2 or 3.   The inert gas recovery apparatus in a single crystal pulling apparatus according to claim 1, further comprising an electrostatic precipitator and a filter after the dry vacuum pump. The filter is composed of a non-woven filter medium in the form of a plate and alternately folded in the opposite direction to form a bellows, and a cylindrical housing with a gas inlet and a gas outlet at both ends. 6. The inert gas recovery device in a single crystal pulling apparatus according to claim 5, wherein the filter is formed by fixing an element inside the housing so as to be orthogonal to the gas flow direction.

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