JP2002029884A - Inert gas recovering device for single crystal pulling-up device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inert gas recovering device with which a used inert gas passed through a CZ furnace can be purified and efficiently recovered. SOLUTION: The inert gas discharged from a dry vacuum pump 25 and containing dust is trapped in the flow of water while being cooled by the flow of water. Thereby, the inert gas can be recovered at a low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for recovering an inert gas used in a CZ pulling apparatus for producing a single crystal such as silicon.

[0002]

2. Description of the Related Art In a CZ method (Czochralski method) single crystal pulling apparatus used for producing a single crystal such as silicon, a seed crystal held in a seed chuck is converted into a silicon melt in a CZ furnace. A single crystal is grown by bringing the liquid into contact and pulling it up while rotating.

Here, the CZ method single crystal pulling apparatus comprises a crucible for filling flake-like polycrystalline silicon, a heater for melting the silicon in the crucible, a heat insulating material, and the like. The lifting operation is performed with an inert gas (Ar or the like) flowing in the CZ furnace.

In the CZ furnace, by raising the temperature of the crucible by a heater, the nugget-like (or lump) silicon filled in the crucible is melted, while SiO generated from the silicon melt surface is melted. Dust and impurity gas released from a graphite heater, a heat insulating material, and the like are generated. Therefore, in order to quickly discharge these gases, an inert gas is introduced into the furnace from the upper part of the apparatus, and the inside of the furnace is sucked by a vacuum pump from an exhaust port provided at the lower part of the apparatus. Is increased to discharge impurities together with the inert gas. However, from the viewpoint of economy, it is preferable to recover the discharged inert gas.

However, since the discharged inert gas (used inert gas) is mixed with impurities and dust by passing through the chamber, if the recovered gas is returned to the chamber as it is, The silicon cannot be directly reused because it would contaminate the silicon.

Therefore, in the invention described in Japanese Patent Application Laid-Open No. H11-199388, one of the used argon gas discharged from the single crystal pulling apparatus 11 by the dry vacuum pump 13 by the system shown in FIG. The part is cooled through the heat exchanger 15 and sent to the dry vacuum pump 13 again to cool the dry vacuum pump to collect and reuse the argon gas. Here, it is necessary to draw cooling air into the dry vacuum pump 13 into the pump, but since air is not allowed to be mixed in when collecting used argon gas, the dry vacuum pump 13 passes through a heat exchanger. The pump is cooled by sending the pumped argon gas to the pump.

[0007]

However, in such a system, only a part of the used argon gas flowing out of the dry vacuum pump 13 is passed through the heat exchanger 15, and the remaining gas is directly recovered and purified. It will be sent to.

Here, when used argon gas containing SiO dust passes through a dry vacuum pump and flows into a heat exchanger and a recovery / purification device, first, dust accumulates in the heat exchanger to reduce its heat exchange efficiency. In order to maintain efficient heat exchange performance, frequent cleaning is required.

Further, the recovery and purification apparatus has a precise structure, and a precise filter is used at the inlet in order to prevent the ingress of dust. Loss due to the non-operation time of the device, and the result of impairing the merit of low cost by recovering the inert gas is brought about.

[0010] The present invention has been made in view of the above problems, and an object of the present invention is to purify spent inert gas that has passed through a CZ furnace as much as possible and to efficiently recover it. An object of the present invention is to provide an inert gas recovery device.

[0011]

In order to achieve the above object, in the present invention, an inert gas accompanied by dust discharged from a dry vacuum pump is cooled by flowing water into the flowing water. Purify by trapping,
The inert gas can be recovered at low cost.

More specifically, the present invention provides the following.

(1) An inert gas recovery unit connected downstream of a dry vacuum pump for evacuating the single crystal pulling apparatus, wherein the upstream pipe is connected to the downstream pipe of the dry vacuum pump. An inert gas recovery unit, comprising: a water ring pump to be connected; and a connecting pipe for connecting an upstream pipe and a downstream pipe of the water ring pump.

In the present invention, the water ring pump cools the inert gas with flowing water by bringing the used inert gas flowing into the pump into contact with the liquid in the pump and vigorously agitating the liquid. SiO dust etc. will be taken in. In general, in a dry vacuum pump, it is necessary to avoid negative pressure on the discharge side. However, in the present invention as shown in FIG. By adopting a structure in which the downstream pipe (exhaust port) is connected, the pressure difference between the upstream side and the downstream side is eliminated, and the function of the water ring pump as a pump is lost. It works as a kind of filter. In this way, the "water-sealed pump-connection pipe" structure according to the present invention enables the used inert gas from which SiO dust and the like have been removed to be sent to the recovery device.

Here, the "dry vacuum pump" includes:
A dry mechanical vacuum pump can be used.

(2) The inert gas recovery unit according to the above (1), wherein another water ring pump driven in a direction opposite to the water ring pump is attached to the connecting pipe.

In the present invention as shown in FIG.
A water ring pump is also attached to the connecting pipe. Further, by mounting this water ring pump so as to be driven in a direction opposite to that of another water ring pump, the inert gas can be circulated. By doing so, purification is performed even in the reflux process, so that further cooling and cooling
Purification action can be achieved.

(3) An inert gas recovery unit connected downstream of a dry vacuum pump for evacuating the single crystal pulling apparatus, wherein the pipe on the upstream side of the water ring pump of the inert gas recovery apparatus is The inert gas recovery unit according to the above (1) or (2), wherein the inert gas recovery unit is connected to downstream pipes of the plurality of dry vacuum pumps.

In the present invention as shown in FIG. 4, inert gas exhausted from a plurality of dry vacuum pumps is taken into one water ring pump, and the inert gas is vigorously stirred by the water ring pump. Then, dust in the gas from a plurality of dry vacuum pumps is trapped by one water ring pump, and simultaneously cooled by flowing water. As described above, since the exhaust gas of a large number of dry vacuum pumps is processed by one water ring pump, the cost increase due to the addition of the water ring pump in the present invention is reduced as a result. .

Further, when the exhaust of a plurality of dry vacuum pumps is processed by one water ring pump as described above, there are cases where an inoperable machine is included in the plurality of dry vacuum pumps, a single crystal pump, or the like. If there is an inoperable machine in the pulling process, or if the inert gas flow rate is changed in the single crystal pulling process, the total failure will occur. The flow rate of the active gas fluctuates, and as a result, the pressure in the pipe (suction port) on the upstream side of the water ring pump may fluctuate significantly. When this pressure fluctuation occurs, the lubricating oil of the gear used in the dry vacuum pump passes through the bearing seal and enters the inside of the pump, which hinders the operation of the pump. Pipe downstream of the sealed pump (exhaust port)
And the upstream pipe (suction port), thereby eliminating the pressure difference between them and stably operating the dry vacuum pump connected to the water ring pump.

(4) A branch pipe branched from the pipe on the downstream side of the water ring pump and connected to the pipe on the upstream side of the dry vacuum pump, and a part of the inert gas passing through the water ring pump. The inert gas recovery unit according to any one of the above (1) to (3), wherein cooling of the dry vacuum pump is performed by:

In the present invention, the cooling of the dry vacuum pump is enabled by returning a part of the inert gas cooled and purified by the water ring pump to the dry vacuum pump. Since the water ring pump contains almost no dust and a cooled inert gas is obtained, it can be cooled by sending it to the dry vacuum pump, and the dry vacuum pump can operate stably. Will be able to do that.

(5) The inert gas recovery unit according to any one of (1) to (4), wherein a cooler is attached to a pipe on the downstream side of the water ring pump.

That is, in the present invention, a cooler is attached to the pipe on the downstream side of the water ring pump, whereby the inert gas is cooled by the cooler, and the water condensed there is immediately sent to the water ring pump. Can be refluxed. Therefore, if the sealing water of the water ring pump cannot be cooled sufficiently, the temperature of the sealing water rises and the amount that is dissipated as water vapor increases, but this water vapor is condensed by the cooler, thereby The generated water can be immediately returned to the water ring pump. In other words, the cooler condenses the water vapor emitted by the water ring pump and returns it to the water ring pump, thereby reducing the replenishment amount of the water seal and reducing the running cost. As an embodiment of the cooler,
For example, a heat exchanger provided with a normal cooling mechanism can be mentioned.

(6) The inert gas recovery unit according to any one of the above (1) to (5), wherein a jet scrubber type dust removing device is attached instead of the water ring pump.

Here, the "jet scrubber type removing device" means a jet scrubber (JP-A-9-3230).
No. 20, JP-A-11-207137, JP-A-11-253749, JP-A-2000-10754
No. 0, etc.), and refers to a dust removal device that sucks an inert gas by a jet water stream of the jet scrubber and quenches the inert gas into the jet water stream to quench it.

The connecting pipe according to the present invention has a thickness of 10 mmHg.
By providing a check valve that operates with a slight pressure difference, it is possible to prevent dust-containing gas from passing through the water ring pump to prevent gas purification. Also,
By adding a flow control valve, the amount of recirculation and the pressure at the inlet of the water ring pump can be adjusted.

[Water Ring Pump] FIG. 7 shows a configuration of the water ring pump.

As shown in FIG. 7, the water ring pump 27
Includes a liquid (water) between a rotor 71 and a casing 72, and carries gas from an inlet to an outlet by rotation of the rotor.

The impeller 7 attached to the rotor
Although the spacing of 3 is uniform, the pumping room is divided into several chambers of different sizes formed by the impeller and the seal. A suction port 77 is provided in a region where the size of the room is expanded with the rotation of the impeller, and a discharge port 75 is provided in a region where the size of the room is reduced.

The impeller 7 is eccentrically placed in the casing 72.
When the rotor 71 provided with 3 is rotated and water is sealed therein, the water forms an annular seal 70 along the casing by centrifugal force, and a void is created in the center. Then, the inert gas is sucked from the inlet 77 by the rotation of the rotor, and the gas is compressed as the rotor rotates, and the gas compressed to the atmospheric pressure is discharged from the outlet 75 to the outside. By performing this operation continuously, suction → compression → discharge is performed, and the whole functions as a pump.

In a series of processes from suction to compression to discharge, the used inert gas flowing into the pump is brought into contact with the liquid in the pump to be vigorously agitated. While being cooled by running water, washing is also performed.

[Jet Scrubber] FIG. 8 is a front view of a jet scrubber device.

As shown in FIG. 8, a jet scrubber 80 has a draft chamber 89 for temporarily storing used exhaust gas, and is mounted above the draft chamber to blow high-pressure water containing air bubbles downward. And a plurality of jet pumps 81 for jetting.

Here, each jet pump 81 has the same configuration as a configuration known as a Mochizuki-type air-fuel mixture jet pump. Specifically, cooling water is guided to the injection nozzle 85 through a high-pressure pipe. In other words, the jet nozzle 85 is configured to be jetted as a high-pressure water flow.

Below the draft chamber 89, gas-liquid mixing pipes 83 are provided corresponding to the jet pumps 81, respectively.
Are attached with the upper end opened to the draft chamber 89. That is, the high-pressure water flow mixed with air bubbles injected from the injection nozzle 85 of each jet pump 81 is configured to be introduced into the corresponding gas-liquid mixing pipe 83. As a result, the used exhaust gas temporarily staying in the draft chamber 89 is subjected to the high-pressure water flow through the gas-liquid mixing pipe 8.
Due to the strong absorbing force generated by the large negative pressure generated when the gas is ejected into the inside 3, the gas-liquid mixing pipe 83 together with the high-pressure water flow is provided.
While being drawn in and passing through the gas-liquid mixing pipe 83, dust in the inert gas is separated by gas-liquid mixing, collision between water droplets and dust, diffusion, and the like.

The dust thus separated is reliably collected in the sewage in the sewage tank 87 below the gas-liquid mixing pipe 83, so that only the washed inert gas is discharged into the discharge pipe 86.
Will be discharged more.

In the present invention, dust is removed by using a jet scrubber. However, a jet pump (injector pump) or the like which jets water and separates dust in an inert gas by its jetting force is also available. It is included in the concept of the present invention.

[0039]

FIG. 5 is a schematic diagram of a first configuration example of an inert gas recovery unit according to the present invention, and FIG. 6 is a schematic diagram of a second configuration example.

The inert gas recovery apparatus unit according to the present invention is constituted as a part of an apparatus for recovering a used inert gas generated during the production of a silicon single crystal, for example. This applies to systems that have been

First, in the configuration example shown in FIG. 5, an inert gas recovery unit according to the present invention was employed and an argon gas recovery mechanism was constructed using a dry vacuum pump which does not require introduction of a cooling gas. This is an example.

The used inert gas (eg, argon gas) passes from the chamber of the single crystal pulling apparatus 11 to the dust collector 21 through the collection pipe 41. This dust collector 21
It is composed of cyclones and filters that trap dust and graphite fibers larger than SiO dust contained in the used inert gas, and fragments of graphite and quartz glass,
Collects relatively large dust and the like contained in the inert gas.

Subsequently, the used inert gas passes through a mechanical booster 23 for increasing the evacuation speed of the dry vacuum pump 25 and is compressed by the dry vacuum pump 25 to a pressure slightly higher than the atmospheric pressure (+200 mmAq). Is sent out to the collection pipe 43.

Then, the water enters the recovery device through the recovery pipe 43. The upstream side and the downstream side of the water ring pump 27 are connected by a connecting pipe 47, and the upstream side (suction side) of the water ring pump 27. The pressure difference between the pump and the downstream side (discharge side) is kept very small, so that the downstream side of the dry vacuum pump is always maintained at a positive pressure, so that there is no oil leakage from the dry vacuum pump. There is no abnormality in its operation.

In this embodiment, nine dry vacuum pumps are collectively connected to one water-sealed pump, and the flow rate of argon gas flowing into the water-sealed pump 27 is the same as that of the connected single crystal pulling apparatus 11. It changes depending on each operating condition (in this embodiment, a maximum of 1.5 m ³ / min (1a
tm), varying between a minimum of 0.05 m ³ / min).
However, the pressure on the downstream side of the dry vacuum pump 25 does not change due to the operation of the connecting pipe 47. Therefore, even when only one of the nine connected single crystal pulling devices is operating, the dry vacuum pump 25 The downstream side is always maintained at a positive pressure, and there is no abnormality in its operation such as oil leakage of a dry vacuum pump.

If the above abnormal operation is to be avoided without using the connecting pipe 47 as in the present invention, an automatic pressure control valve is provided downstream of each dry vacuum pump to reduce the pressure on the downstream side. There is only automatic control or adding a water ring pump to each dry vacuum pump so that it operates while maintaining a constant argon gas flow rate, both of which significantly increase cost and complexity of the system,
Further, the reliability of the system is reduced.

Next, fine SiO dust in the argon gas that could not be trapped by the dust collector 21 is removed by the water ring pump 27. Since the pumping speed of the water ring pump is set to twice the total amount of the argon gas introduced into the nine single crystal pulling apparatuses, the pumping speed of the remaining portion circulates the argon gas to the water ring pump. It can be used for As a result, the used argon gas is washed twice with sealing water on average, and the dust collection efficiency is increased. When the number of operating single crystal pulling apparatuses is small, the number of circulations is further increased, and the dust collection efficiency is increased.

The used argon gas thus purified passes through the recovery pipe 45 while maintaining the pressure downstream of the dry vacuum pump 25 because no pressure difference occurs before and after the water seal pump due to the effect of the connecting pipe 47. , Together with the other recovery pipes 45, is introduced into the argon gas purification device 50. The used argon gas from which impurities have been removed by the purification device 50 is supplied to each single crystal pulling device 11 through the supply pipe 49.

The liquid Ar tank 53 supplies argon gas from the outside as a backup when the argon gas purifying apparatus is temporarily out of order or when the mass balance is out of order.

Next, FIG. 6 is a diagram showing a second configuration example using a dry vacuum pump requiring the introduction of a cooling gas.
Fig. 6 shows a changed part from Fig. 5.

In this example, a heat exchanger 51 is added downstream of the water ring pump 27, and the cooling water pipe 52 supplies cooling water lower than room temperature. By bringing the argon gas into contact with the cooling water, the concentration of water vapor in the argon gas is reduced, thereby suppressing condensation in the piping at room temperature. This cooled argon gas is
By using it as a cooling gas for a dry vacuum pump, the use of purified argon gas is reduced. Further, since the water condensed from the steam can be prevented from flowing into the dry vacuum pump through the pipe, the probability of failure of the dry vacuum pump can be reduced.

Here, in both structural examples 1 and 2, argon gas containing dust exceeding the pumping speed of the water ring pump may flow in due to malfunction of the single crystal pulling apparatus. In such a case, There is a possibility that the argon gas flows backward through the connecting pipe 47 and flows into the argon gas purifying device 50, clogging the filter of the purifying device and lowering the purifying ability. In order to prepare for such a situation, a check valve that operates with a slight differential pressure may be inserted into the connecting pipe 47.

The mechanism of the collection device unit (the area indicated by the broken line in FIGS. 5 and 6) described in this embodiment is as follows.
Any of the mechanisms shown in FIG. 2 or FIG. 3 may be used.

In this embodiment, argon gas is used as the inert gas. However, the gas used in the present invention is an inert gas other than argon gas (for example, helium,
Neon, xenon, etc.).

[0055]

As described above, according to the present invention, by connecting the upstream side and the downstream side of the water ring pump with the connecting pipe, C
The used inert gas that has passed through the Z furnace is purified as much as possible and can be efficiently collected.

In particular, when one water ring pump is used to process inert gas discharged from a plurality of dry vacuum pumps, the flow rate of the inert gas greatly varies depending on the operating conditions of the dry vacuum pumps. Nevertheless, the pressure at the outlet of the dry vacuum pump can be kept constant and the operation can be stabilized. In addition, it is possible to improve the dust collection efficiency and reduce the running cost of the refining device.

Further, since the inert gas discharged from a plurality of dry vacuum pumps can be processed by one water ring pump, a single crystal pulling apparatus including a recovery apparatus can be configured at low cost. Becomes

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a conventional inert gas recovery device.

FIG. 2 is a block diagram illustrating a configuration example of an inert gas recovery device unit according to the present invention.

FIG. 3 is a block diagram showing one configuration example of an inert gas recovery device unit according to the present invention.

FIG. 4 is a block diagram showing a configuration example of an inert gas recovery device unit according to the present invention.

FIG. 5 is a schematic diagram for explaining a first configuration example of an inert gas recovery device unit according to the present invention.

FIG. 6 is a schematic diagram for explaining a second configuration example of the inert gas recovery device unit according to the present invention.

FIG. 7 is a diagram illustrating a functional configuration of a water ring pump of the inert gas recovery device unit according to the present invention.

FIG. 8 is a diagram for explaining a functional configuration of the jet scrubber removing device according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Single crystal pulling apparatus 13 Dry vacuum pump 15 Heat exchanger 17 Recovery / purification apparatus 21 Dust collector 23 Mechanical booster 25 Dry vacuum pump 27 Water ring pump 41, 43, 45 Recovery pipe 47 Connecting pipe 50 Argon gas purification apparatus 51 Cooler (Heat Exchanger) 52 cooling water pipe 53 LAr (liquid argon) tank 71 rotor 72 casing 73 impeller 75 discharge port 77 suction port 80 jet scrubber 81 jet pump 83 gas-liquid mixing pipe 84 suction pipe 85 injection nozzle 86 discharge pipe 87 waste water tank

Claims (6)

[Claims] An inert gas recovery unit connected downstream of a dry vacuum pump for evacuating a single crystal pulling apparatus, wherein an upstream pipe is connected to a downstream pipe of the dry vacuum pump. An inert gas recovery device unit, comprising: a water-sealed pump to be used; and a connecting pipe that connects an upstream pipe and a downstream pipe of the water-sealed pump. 2. The inert gas recovery unit according to claim 1, wherein another water ring pump driven in a direction opposite to the water ring pump is attached to the connection pipe. 3. An inert gas recovery unit connected downstream of a dry vacuum pump for evacuating a single crystal pulling apparatus, wherein the inert gas recovery apparatus has a plurality of pipes on the upstream side of a water ring pump. 3. The inert gas recovery unit according to claim 1, wherein the unit is connected to a downstream pipe of the dry vacuum pump. 4. A branch pipe branched from a pipe on the downstream side of the water ring pump and connected to a pipe on the upstream side of the dry vacuum pump, and a part of the inert gas passing through the water ring pump. The inert gas recovery unit according to any one of claims 1 to 3, wherein the dry vacuum pump is cooled. 5. The inert gas recovery unit according to claim 1, wherein a cooler is attached to a pipe downstream of the water ring pump. 6. An inert gas recovery unit for a single crystal pulling apparatus according to claim 1, wherein a jet scrubber type dust removing apparatus is attached in place of said water ring pump. .