JP3268193B2 - Method for producing shielded argon for welding from furnace exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silicon single crystal or the like used as a semiconductor substrate material, in which an argon gas supplied as a furnace atmosphere gas is used and then discharged as an exhaust gas. The present invention relates to a method for producing a shielded argon gas for welding from furnace atmosphere exhaust gas which is recovered, purified and recovered as a shielded argon gas for welding.

[0002]

2. Description of the Related Art Argon is contained in air at about 0.93%, and its boiling point is between oxygen and nitrogen, so that it is concentrated to 95-98% during cryogenic air separation. This crude argon is hydrogenated to remove water and oxygen with a catalyst, and then nitrogen is removed by rectification to produce high-purity argon of 99.999% or more. Utilizing its inert nature, argon gas is widely used in various industrial fields such as a shielding gas for welding, an atmosphere gas for metal refining and heat treatment, and a protective gas for the electronics industry.

[0003] The remarkable development of the semiconductor industry in recent years is
Due to the remarkable increase in the number of semiconductor single crystal plates serving as the substrate, an increase in the number of silicon single crystal production furnaces for the production of semiconductor single crystal plates and the demand for higher quality single crystals have led to the depletion of silicon gas from argon gas, which is an inert gas. The use as atmospheric gas in crystallization furnaces is increasing rapidly.

A high-purity argon gas used as an atmosphere gas in a single crystal manufacturing furnace for semiconductors is usually stored in a storage tank as a liquid, and when used, exchanges heat with the atmosphere in a vaporizer to release cold heat. It was used as a room temperature gas and was released into the atmosphere after use. This released gas is a gas containing argon as a main component, and after being used as an atmosphere gas in a single crystal manufacturing furnace and then discharged by an exhaust pump, not only heavy metal powder, oil mist and the like are mixed and entrained, but also ,
It contains a small amount of impurities such as hydrogen, oxygen, carbon monoxide, and carbon dioxide, as well as nitrogen, hydrocarbons, and moisture. Therefore, it is extremely uneconomical if the gas containing argon as a main component used as an atmosphere gas in a single crystal manufacturing furnace for semiconductors is released into the atmosphere as it is without effective use.

As a method for recovering high-purity argon gas from a gas containing argon as a main component used as an atmosphere gas in a silicon single crystal manufacturing furnace, argon used as an atmosphere gas in a silicon single crystal manufacturing furnace contains argon as a main component. The gas is pressurized and reacted with oxygen or air in a reactor to convert the combustible components contained in the gas into carbon dioxide and water, and then further reacted with hydrogen to produce a gas containing argon as a main component. The remaining oxygen is converted to water, cooled and introduced into the adsorption tower to remove water, and heat exchanged with low-temperature, high-purity argon gas in a heat exchanger. A method in which the gas is cooled by exchanging heat with high-purity liquefied argon gas in a heat exchanger and then cryogenically liquefied and separated in a distillation column (Japanese Patent Application Laid-Open No. 59-46473). A gas containing gon as a main component and containing dust, hydrocarbons, carbon monoxide, oxygen, hydrogen, nitrogen, etc. is first removed from solids such as dust, and then oxygen is converted into water by a catalytic reaction by hydrogenation, and then Carbon monoxide and hydrogen are reacted in the presence of copper oxide to convert them into carbon dioxide and water, cooled with a Freon refrigerator and the converted water and carbon dioxide are removed through the adsorption column, and cooled again with a Freon refrigerator. (About -50 ° C.) and introduced into an adsorption tower, and a high-purity argon is recovered by removing impurity nitrogen by a temperature fluctuation type adsorption / desorption method (hereinafter referred to as TSA method) (Japanese Patent Laid-Open No. 62-119104).
Publication).

[0006]

SUMMARY OF THE INVENTION The above-mentioned JP-A-59-46 is disclosed.
The method disclosed in Japanese Patent No. 473 uses a method of cryogenic liquefaction and separation in a distillation column, so that the apparatus becomes large and complicated, and operation management is not easy. Also, Japanese Patent Application Laid-Open
In the method disclosed in JP-A-119104, since nitrogen is removed by the TSA method, cooling (about −50 ° C.) and heating (about 70 ° C.) are performed.
° C) operation, and since flammable components are removed in the presence of copper oxide, it is necessary to add oxygen every certain time to perform oxidation. Further, JP-A-62-11
The method disclosed in Japanese Patent Application No. 9104 is disclosed in Japanese Patent Application Laid-Open No. 59-4647.
Although the apparatus can be reduced in size as compared with the method disclosed in Japanese Patent Publication No. 3 (1993), it has the drawback that the apparatus becomes more complicated, operation management is not easy, and the argon recovery is as low as about 70%. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned disadvantages of the prior art and to use a process mainly based on a pressure fluctuation type adsorption / desorption method (hereinafter referred to as PSA), and mainly contain argon discharged from a single crystal manufacturing furnace. From the gas to be produced, as a welding shield argon gas, inexpensively and relatively easily .
It is to provide a method of manufacturing .

[0008]

SUMMARY OF THE INVENTION According to the present invention, a gas mainly containing argon discharged from a single crystal manufacturing furnace is pressurized, and hydrogen, hydrocarbon, and carbon monoxide in the gas are catalyzed in a reactor. After being converted into carbon dioxide and water by reaction with oxygen by operation, it is cooled and introduced into PSA using synthetic zeolite to adsorb and remove nitrogen, carbon dioxide and water, and then oxygen
Oxygen concentration in gas through a concentration controller for welding shield
After adjustment, it is liquefied high purity liquid argon and allowed to heat exchange be used as a single crystal production furnace atmosphere gas in the heat exchanger. As described above, hydrogen, hydrocarbons, and carbon monoxide in a gas mainly containing argon discharged from a single crystal manufacturing furnace are converted into carbon dioxide and water, and then introduced into PSA to supply nitrogen, carbon dioxide, and water. To remove oxygen , and then adjust the oxygen concentration.
Adjust the oxygen concentration in the gas for the welding shield via the integrator
After that, by exchanging heat with high- purity liquefied argon for liquefaction, the gas can be recovered relatively inexpensively and relatively easily as shielded argon gas for welding.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is to vaporize high-purity liquefied argon stored in a storage tank (most of the cold during vaporization is used in this process) and use it as an atmospheric gas in a silicon single crystal manufacturing furnace. The gas containing argon gas as a main component is recovered, and heavy metal powder and oil mist entrained in the gas are separated and removed using a dust remover. The gas mainly composed of argon gas from which heavy metal powder and oil mist have been removed is pressurized and reacted with oxygen by a catalytic operation in the reactor to convert hydrogen, hydrocarbons and carbon monoxide in the gas into carbon dioxide,
After being converted to water, it is cooled and introduced into a pressure fluctuation type adsorption / desorption column using synthetic zeolite to adsorb and remove nitrogen, carbon dioxide and water. After that, the gas in the gas passes through the oxygen concentration controller.
After adjusting the oxygen concentration for the welding shield, it is liquefied by heat exchange with high-purity liquefied argon used as an atmosphere gas in a silicon single crystal manufacturing furnace.

The welding shield argon gas in the present invention is MAG welding (MetalActive Ga).
s Welding) means shield argon gas, which used to be a mixture of high-purity argon gas and carbon dioxide, but in recent years it has been better to use a mixture of carbon dioxide and argon gas containing less than 5% oxygen. Its use has been expanding for reasons such as excellent weldability of steel sheets and the like and low cost. Therefore, the shield argon gas for welding in the present invention means an argon gas of 5% or less of oxygen and 0.1% or less of nitrogen. In addition, 0.1% or less of nitrogen in the welding shield argon gas is a limit nitrogen concentration at which the impact characteristics of the molten metal do not deteriorate.

According to the present invention, a welding shield argon gas is recovered from a gas containing argon gas as a main component after being used as an atmosphere gas in a silicon single crystal manufacturing furnace,
Since the silicon single crystal is not reused in the silicon single crystal manufacturing furnace, it is possible to prevent the quality of the silicon single crystal from being deteriorated due to the deterioration of the purity of the heavy metal and the recovery gas contained in a small amount during recycling.

In the present invention, the concentration adjustment for the welding shield is usually unnecessary for the special user because the oxygen concentration is 5% or less. If the gas containing argon gas as a main component after use as an atmosphere gas in the silicon single crystal production furnace has a small amount of oxygen, and oxygen for removing combustible components is insufficient in the reaction apparatus, the reaction apparatus may be used. It is necessary to supply oxygen gas and adjust the oxygen concentration before introducing the oxygen gas.

[0013]

Embodiment 1 The details of the method of the present invention will be described below with reference to FIG. 1 showing an embodiment. FIG. 1 shows a welding shield argon gas from a gas containing argon gas as a main component after use as an atmosphere gas in a silicon single crystal manufacturing furnace according to the present invention.
It is a system diagram of a manufacturing process.

In FIG. 1, reference numeral 1 denotes a gas mainly composed of argon gas recovered after use as an atmosphere gas in a silicon single crystal manufacturing furnace, and 2 denotes a heavy metal entrained in the gas 1 mainly composed of argon gas. A dust remover for separating and removing powder and oil mist 3 is a dust remover 2 for 8 kg of gas mainly composed of argon gas from which heavy metal powder and oil mist are separated and removed.
Compressor for increasing pressure to f / cm ² · G, 4 for compressor 3
This is a heater for raising the temperature of the gas pressurized to gf / cm ² · G to about 250 ° C. or higher. Reference numeral 5 denotes a combustible component removal tower filled with a palladium catalyst.
Oxygen contained in the gas supplied at a temperature of not less than ° C. reacts with hydrogen, hydrocarbon, and carbon monoxide as combustible components by a catalytic action, and is converted into carbon dioxide and water. Since the temperature of the outlet gas of the combustible component removal tower 5 rises to about 350 ° C. due to reaction heat, it is introduced into the water cooler 6 and cooled.
At this time, since the water vapor in the gas partially precipitates as water, the water drain valve 7 is opened to release only water.

Reference numeral 8 denotes a nitrogen removal tower filled with activated alumina and synthetic zeolite, which selectively adsorbs and removes nitrogen, carbon dioxide, and water from a gas whose flammable components have been converted to carbon dioxide and water. The nitrogen removal tower 8 is operated in the adsorption, recovery / regeneration, and pressure increasing steps by a three-tower switching system. For example, the nitrogen removal tower 8a is an adsorption step, the switching valves 9a and 10a are opened, the switching valves 11a and 12a are closed, and the pressure in the gas is 8 kgf / cm ² . Nitrogen is adsorbed to 0.1% or less together with carbon dioxide and water to obtain a shielded argon gas for welding. The nitrogen removal tower 8b is a recovery / regeneration step, and the switching valves 9b, 10b,
12b is closed, the switching valves 11b, 13 and 14 are opened, and the pressure is from 8 kgf / cm ² · G to 2 kgf / cm ² · G.
The argon-rich gas generated at the time of pressure reduction to the extent is returned to the suction line of the compressor 3 via the buffer tank 15 to improve the argon recovery rate. When the pressure in the nitrogen removal tower 8b has dropped to about ² kgf / cm ² · G, the switching valves 13 and 14 are closed, the switching valve 16 is opened, and the vacuum pump 17 is started to reduce the pressure to about 10 Torr or less. As a result, nitrogen, carbon dioxide and water adsorbed on the activated alumina and the synthetic zeolite are desorbed and released outside the system. In addition, the switching valve 18 controls the inside of the nitrogen removal tower 8 by 2 k.
Open when pressure is reduced from about gf / cm ² · G to atmospheric pressure. The nitrogen removal tower 8c is a pressure step, and the switching valve 9
c, 10c, and 11c are closed, and the outlet gas of the nitrogen removal tower 8a, which is the adsorption step, is supplied to the nitrogen removal tower 8c via the switching valve 19 and the switching valve 12c, and the adsorption pressure of 8 kg
The pressure in the tower is increased to f / cm ² · G. By repeating the above operation, a welding shield argon gas having a nitrogen concentration of 0.1% or less can be continuously obtained.

Reference numeral 20 denotes an oxygen concentration controller. Since the gas from which nitrogen, carbon dioxide and water are adsorbed and removed in the nitrogen removal tower 8 contains only about 1.6% of oxygen, a predetermined oxygen concentration is provided. Oxygen is supplied via the flow control valve 21 such that However, if the welding shield argon gas can be used at an oxygen concentration of 1.6% or less, the oxygen concentration adjuster 20 can be omitted.

Reference numeral 22 denotes an argon heat exchanger, and the gas whose oxygen concentration has been adjusted is liquefied by indirect heat exchange with the high-purity liquefied argon from the high-purity liquefied argon tank 23 in the argon heat exchanger 22 to obtain a liquefied argon gas. Collected in the tank 24. On the other hand, the high-purity argon gas that has been vaporized by heat exchange with the gas whose oxygen concentration has been adjusted in the argon heat exchanger 22 is supplied as an atmosphere gas to a silicon single crystal manufacturing furnace (not shown). The flash gas generated when liquefied argon is supplied to the liquefied argon tank 24 is returned to the suction line of the compressor 3 via the valve 25 to prevent the argon recovery rate from deteriorating. Reference numeral 26 denotes an evaporator for vaporizing high-purity liquefied argon, and the high-purity argon gas vaporized by the evaporator 26 is supplied as an atmosphere gas to a silicon single crystal manufacturing furnace (not shown). The liquefied argon collected in the liquefied argon tank 24 is loaded on the tank truck 28 by the liquid argon pump 27 and supplied to the user.

Example 2 2.4% of oxygen, 7% of nitrogen, 0.1% of hydrogen, 0.1% of carbon monoxide were recovered as impurities from a silicon single crystal manufacturing furnace.
1 and heavy metal powder, oil mist and the like are separated and removed by a dust remover 2 shown in FIG.
The pressure is increased to kg / cm ² · G and introduced into the heater 4, and the
Heated to 0 ° C. The gas mainly composed of argon gas heated to about 250 ° C. is supplied to a combustible component removal tower 5 filled with a palladium catalyst, and the combustible components of the gas, such as hydrogen, hydrocarbons, Carbon monoxide and oxygen react and convert to carbon dioxide and water. Impurities in the gas at the outlet of the combustible component removal tower 5 are oxygen 1.6
%, Nitrogen 7%, carbon dioxide 0.4%, water 3.5kg / H
r.

The outlet gas of the combustible component removing tower 5 is introduced into a water cooler 6 and exchanges heat with cooling water to cool to room temperature.
After the partially precipitated water is extracted by opening the drain valve 7, the water is supplied to a nitrogen removal tower 8 filled with activated alumina and synthetic zeolite, and is adsorbed under the conditions of a pressure of 8 kgf / cm ² · G and a temperature of normal temperature. Nitrogen was adsorbed to 0.1% or less together with carbon dioxide and water in the gas. Impurities in the gas at the outlet of the nitrogen removal tower 8 were 1.6% oxygen and 0.05% nitrogen. Since argon gas containing 1.6% of oxygen and 0.05% of nitrogen as this impurity could be used as it is as a shielding argon gas for welding, it was supplied to the argon heat exchanger 22 at a pressure of 8 kg / cm ² · G. Then, the liquid was liquefied by indirect heat exchange with the high-purity liquefied argon from the high-purity liquefied argon tank 23 and collected in the liquefied argon tank 24.
The argon recovery in this case was about 80%.

[0020]

According to the present invention, the gas containing argon gas as a main component from a silicon single crystal manufacturing furnace is converted into carbon dioxide and water by reacting oxygen and combustible components in the gas with a catalytic reactor. After that, by using a PSA apparatus to adsorb and remove nitrogen together with carbon dioxide and water to 0.1% or less, a shielded argon gas for welding can be produced at low cost and relatively easily.

In the present invention, a gas containing argon gas as a main component from a silicon single crystal manufacturing furnace is recovered as a shielding argon gas for welding and is not reused as an atmosphere gas of the silicon single crystal manufacturing furnace. It is also possible to prevent deterioration of the quality of the silicon single crystal due to the reduced purity of the heavy metal and the recovered argon gas.

[Brief description of the drawings]

FIG. 1 is a system diagram of a step of recovering a shielded argon gas for welding from a gas containing argon gas as a main component of the present invention.

[Explanation of symbols]

Reference Signs List 1 Gas mainly composed of argon gas 2 Dedusting device 3 Compressor 4 Heater 5 Flammable component removal tower 6 Water cooler 7 Drain valve 8, 8a, 8b, 8c Nitrogen removal tower 9a, 9b, 9c, 10a, 10b, 10c Switching valve 11a, 11b, 11c, 12a, 12b, 12c, 1
3, 14, 16, 18, 19 Switching valve 15 Buffer tank 17 Vacuum pump 20 Oxygen concentration controller 21 Flow rate control valve 22 Argon heat exchanger 23 High purity liquefied argon tank 24 Liquefied argon tank 25 Valve 26 Evaporator 27 Liquid argon pump 28 Tank Lorry

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-239309 (JP, A) JP-A-7-33581 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 20/18 B01D 53/02

Claims (1)

(57) [Claims] 1. A gas mainly containing argon discharged from a single crystal manufacturing furnace and containing impurities such as oxygen, nitrogen, hydrogen, hydrocarbons, carbon monoxide, etc., is first removed by removing heavy metal powder and oil mist and then pressurized. After converting hydrogen, hydrocarbons and carbon monoxide in the gas into carbon dioxide and water by reacting with oxygen by a catalytic operation in the reactor, it is cooled and introduced into a pressure fluctuation type adsorption / desorption column using synthetic zeolite. To remove nitrogen, carbon dioxide, and water, and then adjust the oxygen concentration in the gas for the welding shield via an oxygen concentration controller. welding shield argon production how from the furnace atmosphere gas, characterized in that the liquefied purity liquid argon and allowed to heat exchange.