JP2012055836A - Method of treating gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of treating a gas, capable of making the life of a decomposer longer and of efficiently treating a gas comprising a fluorine-containing compound.SOLUTION: The method of treating a gas comprises causing a carrier gas containing oxygen, and a gas containing a fluorine-containing compound as an object to be treated to flow through a reaction tube 3 filled with a decomposer comprising γ-ALOas an oxide catalyst and CaO as a solid alkali while heating the gas mixture, whereby the life of the decomposer can be made longer and the gas containing a fluorine-containing compound can efficiently be treated.

Description

  The present invention relates to a gas processing method for detoxifying a fluorine-containing compound gas.

  In the semiconductor field, a gas containing a fluorine-containing compound such as PFC (perfluorocarbon) is often used as an etching agent or a cleaning agent. Since it has been found that many of these fluorine-containing compound gases generally have a global warming effect, it has become an important issue to detoxify the exhaust gas after use by an appropriate method.

  In recent years, a technique has been proposed in which a halogen-containing compound can be decomposed by a dry treatment that does not use water at a temperature significantly lower than that of a conventional decomposition agent obtained by adding a catalyst to a solid alkaline agent (see Patent Document 1).

JP 2009-202091 A

  However, in the technique as described above, since the lifetime of the solid alkaline agent that is a decomposing agent is not so long, the decomposing agent has to be frequently replaced, and the processing efficiency has been a problem.

  The present invention has been completed based on the above circumstances, and has an object to provide a gas treatment method capable of realizing a long life of a decomposition agent and efficiently treating a gas of a fluorine-containing compound. To do.

  As means for solving the above-mentioned problems, the present invention is a gas treatment method for detoxifying a gas containing a fluorine-containing compound, comprising an oxide catalyst or mineral catalyst exhibiting solid acidity, and a solid It includes a decomposition step of decomposing the fluorine-containing compound by aerating a carrier gas containing oxygen and the gas containing the fluorine-containing compound in a reaction vessel filled with a decomposition agent containing an alkali agent while heating. .

Here, examples of the “fluorine-containing compound” to be treated include compounds containing fluorine and at least one of silicon, carbon, nitrogen, sulfur, aluminum, and phosphorus. More specifically, PFC ( Fluorocarbons such as perfluorocarbon), HCFC (hydrochlorofluorocarbon), HFC (hydrofluorocarbon), CF ₄ (carbon tetrafluoride), SF ₆ (sulfur hexafluoride), and the like can be given.

  The “carrier gas containing oxygen” may be, for example, the atmosphere, or a mixture of oxygen and a gas that does not react with the gas to be processed (for example, an inert gas such as nitrogen) in a desired ratio. It may be.

Examples of the oxide-based catalyst among the “oxide-based catalyst or mineral-based catalyst showing solid acidity” include, for example, SiO ₂ , TiO ₂ , Al ₂ O ₃ , ZrO ₂ , La ₂ O ₃ , Y ₂ O ₃ , Examples thereof include metal oxides such as Cr ₂ O ₃ , ZnO, Sn ₂ O ₃ , V ₂ O ₅ , and WO ₃ . Examples of mineral catalysts include zeolite minerals and clay minerals. These oxide catalysts and mineral catalysts may be used alone or in combination of two or more.
The “solid alkali agent” is preferably, for example, an oxide, hydroxide, or carbonate of an alkali metal or alkaline earth metal, and more specifically, one containing calcium oxide, magnesium oxide, sodium oxide, or lithium oxide. Can be mentioned. These may be used individually by 1 type, and may mix and use 2 or more types.

  ADVANTAGE OF THE INVENTION According to this invention, the lifetime of a decomposition agent can be implement | achieved and the gas processing method which can process the gas of a fluorine-containing compound efficiently can be provided.

Overall schematic diagram of gas processing equipment Overall schematic diagram of test equipment The graph which shows the relationship between the oxygen concentration in carrier gas, and PFC decomposition | disassembly ability in the case of an alumina compounding rate of 40%, 50%, and 60% The graph which shows the relationship between an alumina compounding rate and PFC decomposition | disassembly ability at the time of using nitrogen as carrier gas and the case of using the mixed gas of nitrogen and oxygen

  An embodiment of the present invention will be described with reference to FIG. In the present embodiment, a case where a gas containing PFC 14 (perfluoromethane) discharged in a semiconductor manufacturing process is treated will be described as an example.

First, the gas processing apparatus 1 used for the gas processing of this embodiment is demonstrated. A schematic view of the gas processing apparatus 1 is shown in FIG. The gas processing apparatus 1 includes a reaction tower 2. The reaction tower 2 is a vertically arranged reaction tube 3 (corresponding to the reaction vessel of the present invention) formed in a cylindrical shape, and the inside thereof is filled with a granular decomposition agent. As the decomposition agent, a mixture of γ-Al ₂ O ₃ as an oxide catalyst and CaO as a solid alkali agent can be used. The mixing ratio of γ-Al ₂ O ₃ and CaO is preferably γ-Al ₂ O ₃ : CaO = 20: 80 to 80:20, more preferably 40:60 to 70:30. Is more preferable.

  Around the reaction tube 3, a pair of upper and lower external heaters 4 </ b> A and 4 </ b> B are disposed, and an internal heater 5 is disposed inside the reaction tube 3. These heaters 4A, 4B and 5 can heat the gas passing through the reaction tube 3. The reaction tube 3 and the heaters 4A, 4B, and 5 are accommodated in a casing 7 in which a heat insulating material 6 is stretched.

  A supply hopper 8 for supplying the decomposition agent to the inside of the reaction tube 3 is connected to the opening at the top of the reaction tube 3. Below the supply hopper 8, a gas inlet 9 for supplying a gas to be processed into the reaction tube 3 and a carrier inlet 10 for supplying a carrier gas into the reaction tube 3 are provided. The gas inlet 9 is connected to a pipe for exhaust gas discharge in a semiconductor manufacturing facility. The carrier inlet 10 is connected to a nitrogen and oxygen gas cylinder (not shown) through a pipe.

  A discharge hopper 11 for temporarily storing the decomposing agent discharged from the reaction tube 3 is connected to the lower opening of the reaction tube 3. A water cooling jacket 12 is provided around the discharge hopper 11, and cooling water is circulated inside the water cooling jacket 12 by a cooling water circulation device 13. Thereby, the inside of the discharge hopper 11 can be cooled.

  The lower end portion of the discharge hopper 11 is connected to one end portion of the conveyor device 14 so that the decomposition agent stored in the discharge hopper 11 is guided to the inside of the conveyor device 14. For example, a screw conveyor can be used as the conveyor device 14.

  The other end portion of the conveyor device 14 is provided with a decomposition agent discharge port 15 downward and a gas discharge port 16 upward. The decomposition agent discharge port 15 is connected to the storage tank 17, and the gas discharge port 16 is connected to the exhaust pipe 19 via the dust collector 18.

  Next, a gas processing method using the gas processing apparatus 1 configured as described above will be described.

  First, the decomposing agent is introduced from the supply hopper 8 with the conveyor device 14 stopped. The decomposition agent is added until the reaction tube 3 and the supply hopper 8 are almost full. Next, the external heaters 4A and 4B and the internal heater 5 are switched on to raise the temperature inside the reaction tube 3 to a necessary decomposition temperature. Although the decomposition temperature depends on the type of gas to be treated, it is usually preferable to set the decomposition temperature at about 600 ° C to 900 ° C.

  Next, the conveyor device 14 and the cooling water circulation device 13 are operated, and the gas containing the PFC 14 (perfluoromethane) discharged in the semiconductor manufacturing process and the mixed gas of nitrogen and oxygen as the carrier gas are respectively supplied to the gas inlets. 9. Introduce into the reaction tube 3 from the carrier inlet 10.

Inside the reaction tube 3, as shown in the following formula (1), PFC14 and CaO react, and PFC14 is decomposed and detoxified. At this time, γ-Al ₂ O ₃ plays a role as a catalyst.

CF ₄ + 2CaO → 2CaF ₂ + CO ₂ (1)

  Here, the inventors have clarified that the life of the decomposing agent can be improved more than twice by using a mixture of oxygen as a carrier gas. The reason for this is not necessarily clear, but is considered as follows.

That is, the reason why the lifetime of the decomposing agent has been shortened is that a part of γ-Al ₂ O ₃ reacts with PFC to generate AlF ₃ as shown in the following formula (2), and the catalytic action is lowered. It seems that there is.

3CF ₄ + 2Al ₂ O ₃ → 4AlF ₃ + 3CO ₂ (2)

By adding oxygen to carrier gas, or to re-generate Al ₂ O ₃ reacts with AlF ₃ that the oxygen was generated, or to proceed equilibrium of the reaction of the above formula (2) is to the right It is considered that the life of the decomposing agent can be extended.

  In this embodiment, the case where the gas to be processed is PFC 14 has been described as an example. For example, PFC 116 (perfluoroethane), PFC218 (perfluoropropane), PFC31-10 (perfluorobutane), PFC51-14 Even when other PFCs such as (perfluorohexane), PFCc318 (perfluorocyclobutane), and PFC41-12 (perfluorocyclopentane) are treated, the same effects can be obtained. The same applies to other halogen-containing compounds such as HFC (hydrofluorocarbon), CFC (chlorofluorocarbon), HCFC (hydrochlorofluorocarbon), or other halogen-containing compounds such as carbon tetrafluoride and sulfur hexafluoride. The effect is obtained.

  The treated gas decomposed by the decomposition agent inside the reaction tube 3 is cooled while passing through the inside of the discharge hopper 11, then passes through the inside of the conveyor device 14 and reaches the dust collector 18 from the gas discharge port 16. Then, after dust removal processing is performed by the dust collector 18, the dust is discharged from the exhaust pipe 19 to the outside.

  The decomposition agent filled in the reaction tube 3 is discharged from the lower opening of the reaction tube 3 by driving the conveyor device 14. And it cools while passing the inside of the discharge hopper 11, then passes the inside of the conveyor device 14, reaches the storage tank 17 from the decomposition agent discharge port 15, and is stored here. A new decomposing agent is replenished from the opening at the top of the reaction tube 3 by the supply hopper 8. In this way, the decomposition agent always flows inside the reaction tube 3, the used decomposition agent is discharged from below, and new decomposition agent is supplied from above.

As described above, according to this embodiment, the carrier containing oxygen is contained in the reaction tube 3 filled with the decomposition agent composed of the mixture of γ-Al ₂ O ₃ as the oxide catalyst and CaO as the solid alkali agent. The gas and the fluorine-containing compound gas to be treated are aerated while being heated. According to such a gas treatment method, it is possible to extend the life of the decomposition agent, and it is possible to efficiently treat the fluorine-containing compound gas.

1. Test Method <Test Example 1-1>
The test apparatus 20 shown in FIG. 2 was used. In this test apparatus 20, a core tube 22 formed of mullite is installed inside a tubular furnace 22, and the inside of the core tube 22 is filled with a decomposition agent. Oxygen, nitrogen, and cylinders B1, B2, and B3 of PFC 14 are connected to the inlet side of the core tube 22 through piping. An absorption bottle 23 is connected to the outlet side of the core tube 22 through a pipe, and water is stored inside the absorption bottle 23.
KT-1153R manufactured by Advantech Toyo Co., Ltd. was used as the tubular furnace, and HB-7 (diameter 24 mm, length 800 mm) manufactured by Nippon Chemical Ceramics Co., Ltd. was used as the furnace core tube.

As a solid alkali agent, calcium hydroxide (special calcium hydroxide manufactured by Ueda Lime Manufacturing Co., Ltd.) and water are kneaded and put into an electric furnace (Kyowa High Heat Industry Co., Ltd., high temperature heating small tankal super furnace C-1). The temperature was raised from room temperature to 900 ° C. in 1 hour, and then calcined by holding at 900 ° C. for 1 hour, cooled, ground, and activated CaO adjusted to a particle size of 1 to 2 mm was used. As an oxide-based catalyst, an alumina sol 200 manufactured by Nissan Chemical Industries, Ltd. was charged into an electric furnace (manufactured by Nishinomiya Electric Furnace) and heated from room temperature to 500 ° C. at a heating rate of 1 ° C./min. After maintaining at 5 ° C. for 5 hours, firing, cooling, γ-Al ₂ O ₃ crushed and adjusted to have a particle diameter of 1 to 2 mm was used. This active CaO and γ-Al ₂ O ₃ were mixed at 50:50 (wt%) to obtain a decomposing agent.

  About 60 g of the decomposition agent prepared as described above was filled into the core tube 22. Next, the center temperature of the tubular furnace 22 was raised to 800 ° C. and kept constant at the temperature. As a carrier gas, a mixture of nitrogen and oxygen at 90:10 (vol%) is used, and PFC 14 as a reaction gas is mixed with this carrier gas so that the concentration becomes 1.5 vol%, and the flow rate is 500 mL / min. Then, it was made to flow in the furnace core tube 22 and decomposed.

  After the treated gas discharged from the core tube 22 was passed through the water in the absorption bottle 23, the concentration of the remaining PFC 14 was measured by FT-IR (FG-110A manufactured by Horiba, Ltd.). Further, a part of the gas discharged from the core tube 22 is collected in the tedlar pack 24 upstream from the absorption bottle 23, and the concentration of HF contained in the treated gas as a by-product of PFC decomposition is detected by gas detection. Measurement was performed using a tube. As a gas detection tube, # 17 for hydrogen fluoride manufactured by Gastec was used.

<Test Example 1-2>
As the carrier gas, a mixture of nitrogen and oxygen at 80:20 (vol%) was used. The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 1-3>
As the carrier gas, a mixture of nitrogen and oxygen at 70:30 (vol%) was used. The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 2-1>
As a decomposing agent, a mixture of active CaO and γ-Al ₂ O ₃ at 40:60 (wt%) was used. A carrier gas in which nitrogen and oxygen were mixed at 80:20 (vol%) was used. The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 2-2>
As the carrier gas, a mixture of nitrogen and oxygen at 70:30 (vol%) was used. The other tests were performed in the same manner as in Test Example 2-1.

<Test Example 3-1>
As a decomposing agent, a mixture of active CaO and γ-Al ₂ O ₃ at 60:40 (wt%) was used. A carrier gas in which nitrogen and oxygen were mixed at 90:10 (vol%) was used. The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 3-2>
As the carrier gas, a mixture of nitrogen and oxygen at 80:20 (vol%) was used. The others were tested in the same manner as in Test Example 3-1.

<Test Example 4>
Air was used as the carrier gas. The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 5-1>
Nitrogen was used as a carrier gas. The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 5-2>
Nitrogen was used as a carrier gas. Active CaO and γ-Al ₂ O ₃ were mixed at 40:60 (wt%). The other tests were performed in the same manner as in Test Example 1-1.

<Test Example 5-3>
Nitrogen was used as a carrier gas. Active CaO and γ-Al ₂ O ₃ were mixed at 30:70 (wt%). Others were tested in the same manner as in Test Example 1-1.

<Test Example 5-4>
Nitrogen was used as a carrier gas. Active CaO and γ-Al ₂ O ₃ were mixed at 20:80 (wt%). Others were tested in the same manner as in Test Example 1-1.

2. Results When one of the following i) and ii) is detected, it is determined that the decomposition agent has reached the breakthrough point, and the time from the start of the PFC 14 flow until the decomposition agent reaches the breakthrough point is broken. It was overtime.
i) Concentration of residual PFC14 measured by FT-IR is 95 vol% or more
ii) The concentration of HF contained in the treated gas collected in the Tedlar pack 24 is 5 ppm or more.

Table 1 shows the alumina mixing ratio of the decomposition agent (ratio of γ-Al ₂ O ₃ weight to the total weight of the decomposition agent; wt%), decomposition temperature, type and flow rate of the carrier gas used, and carrier in each test example. Mixing concentration (ratio of oxygen flow rate to total flow rate of nitrogen and oxygen; vol%), PFC gas flow rate and concentration (relative to total flow rate of carrier gas and PFC 14) when a mixed gas of nitrogen and oxygen is used as the gas PFC 14 flow rate ratio; vol%), the residence time of PFC gas in the furnace core tube 22, and the weight of the decomposition agent filled in the furnace core tube 22 are shown.

Table 2 shows the breakthrough time, the PFC 14 throughput, the PFC decomposition ability of the decomposition agent, and the CaF ₂ conversion rate in each test example. The PFC 14 throughput is the total flow rate of PFC 14 from the start of PFC 14 flow until the decomposition agent reaches the breakthrough point, and is converted to a molar amount. The PFC decomposition capacity of the decomposition agent was calculated by dividing the PFC 14 throughput (unit: L) by the weight (unit: kg) of the decomposition agent charged in the core tube 22. Further, CaF ₂ conversion was calculated by the following equation (3).

CaF ₂ conversion rate = (((PFC throughput (ml) / 1000) /22.4) × 2) / ((decomposition agent weight (g) × ((100-alumina content) / 100)) / 56) × 100 ... (3)
In the formula, 22.4 is the volume of 1 mol of gas in the standard state, and 56 is the molecular weight of CaO.

FIG. 3 shows a graph showing the relationship between the oxygen concentration in the carrier gas and the PFC decomposition ability when the alumina blending ratio is 40%, 50% and 60%.
FIG. 4 shows a graph showing the relationship between the alumina mixture ratio and the PFC decomposition ability when nitrogen is used as the carrier gas and when a mixed gas of nitrogen and oxygen is used. In addition, in FIG. 4, the relationship between an alumina compounding rate and theoretical PFC14 processing amount was shown collectively. The theoretical PFC14 throughput is the treatment capacity (unit: L-PFC / kg-decomposition agent) of PFC14 per 1 kg of decomposition agent, assuming that all CaO contained in the decomposition agent has reacted with PFC14.

3. Consideration 1) Consideration on the difference in PFC decomposition ability depending on the mixing ratio of oxygen to the carrier gas As can be seen from Table 1, Table 2 and FIG. The results showed that the PFC decomposition ability was improved when oxygen was mixed at 10%, 20%, or 30%, compared with the case where nitrogen was used alone.
Moreover, in this test, the test which used the alumina compounding rate as 40% and used nitrogen alone as carrier gas was not performed. However, as shown in FIG. 4, when nitrogen is used alone as a carrier gas and the PFC decomposition ability is plotted on a graph when the alumina content is varied in the range of 50% to 80%, the data is almost linear. It is on a straight line, and it can be seen that the PFC decomposition capacity increases little by little as the alumina content increases. From this, the PFC decomposition capacity when the alumina blending rate is 40% and nitrogen is used alone as the carrier gas is higher than that when the alumina blending rate is 50% and nitrogen is used alone as the carrier gas. It can be expected to be slightly lower. Therefore, even when the alumina content is 40%, it may be considered that the PFC decomposition ability is improved when oxygen is mixed by 10% or 20%, compared with the case where nitrogen is used alone as a carrier gas. .
As described above, the result that the PFC decomposition ability is improved by mixing oxygen with the carrier gas is completely unexpected to those skilled in the art. Conventionally, in semiconductor processes, it is common knowledge to shut off oxygen to prevent oxidation of silicon, and it can be easily conceived that oxygen is mixed into a carrier gas when treating exhaust gas from the process. Because it is not.

In addition, as a whole, the smaller the alumina content, the more the PFC treatment amount was saturated at an early stage with respect to the increase in oxygen concentration, while the PFC treatment saturation amount tended to be small.
That is, when the alumina content is 40%, the PFC treatment amount is only slightly increased compared to the case where the oxygen concentration is 10% even if the oxygen concentration is 20%, and the same is true even if the oxygen concentration is increased to 30%. It is thought that. Therefore, it is presumed that the PFC processing amount has almost reached saturation at an oxygen concentration of 20%.
When the alumina blending ratio is 50%, when the oxygen concentration is 10%, the PFC throughput is greatly increased as compared with the case where oxygen is not added. When the oxygen concentration is 20%, the PFC treatment amount is increased as compared with the case where the oxygen concentration is 10%, but the growth is moderate as compared with the case where the oxygen concentration is increased from 0% to 10%. . Furthermore, when the oxygen concentration is set to 30%, the increase in the PFC processing amount is slight compared with the case where the oxygen concentration is 20%, and it is presumed that almost the saturation state has been reached.
When the alumina content is 60%, the amount of PFC treatment increases as the oxygen concentration is increased from 0% to 30%, and it is presumed that the saturated state is not reached even at an oxygen concentration of 30%.
FIG. 4 plots the saturation amount of the PFC treatment when a mixed gas of nitrogen and oxygen is used as the carrier gas and the alumina mixture ratio is 40%, 50%, and 60%. That is, when the alumina blending rate is 40%, the PFC processing amount when the oxygen concentration is 20% (Test Example 1-3), and when the alumina blending rate is 50%, the PFC processing amount when the oxygen concentration is 30% (test) Example 2-2) was plotted. When the alumina content is 60%, it is unclear whether the PFC treatment amount reaches the saturation amount even at an oxygen concentration of 30%. Therefore, the maximum PCF treatment amount within the tested range (when the oxygen concentration is 30%) : Test example 3-2) was plotted. The data is almost on the linear line rising to the right, and the saturation amount of the PFC treatment increases as the alumina content increases.

  Furthermore, the case where air | atmosphere was used as carrier gas was also examined. A comparison between Test Example 4 using air as the carrier gas and Test Example 2-1 in which nitrogen and oxygen were mixed at the same ratio as the air and the other conditions were the same, mixed gas of nitrogen and oxygen The results show that the PFC decomposition ability is higher when using. The reason for this is not necessarily clear, but is considered as follows. That is, since about 380 ppm of carbon dioxide is contained in the atmosphere, when the atmosphere is used as a carrier gas, it reacts with carbon dioxide containing CaO in the decomposition agent and is consumed. Thereby, it is thought that PFC decomposition | disassembly capability falls a little. Therefore, by mixing an inert gas such as nitrogen and oxygen as the carrier gas and using no other component that reacts with the components in the decomposing agent, this decrease in PFC decomposition capability is suppressed. It is considered possible.

2) Consideration of difference in PFC decomposition ability depending on mixing ratio of decomposition agent As can be seen from Table 1, Table 2 and FIG. 4, when nitrogen is used alone as a carrier gas, oxygen is mixed into nitrogen as the carrier gas. In any of the cases, the PFC decomposition ability of the decomposer improved as the alumina content increased. When nitrogen is used alone as the carrier gas, the alumina blending rate is 80%. When the mixed gas of nitrogen and oxygen is used as the carrier gas, the alumina blending rate is 70%. A PFC14 throughput close to the PFC14 throughput could be achieved.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.
(1) In the above embodiment, the decomposition agent always flows inside the reaction tube 3, the used decomposition agent is discharged from below, and new decomposition agent is supplied from above. The agent need not always flow inside the reaction tube 3, and the decomposition agent filled in the reaction tube 3 may be replaced every predetermined time. Alternatively, a cartridge filled with a decomposition agent may be used as the reaction tube, and the decomposition agent may be replaced with the cartridge every predetermined time.
(2) In the above embodiment, the pair of upper and lower external heaters 4A and 4B and the internal heater 5 are arranged as heaters for heating the inside of the reaction tube 3. However, the heater configuration is limited to that of the above embodiment. Instead, for example, only an external heater may be used.

3 ... Reaction tube (reaction vessel)

Claims (5)

A gas treatment method for detoxifying a gas containing a fluorine-containing compound,
A carrier gas containing oxygen and a gas containing the fluorine-containing compound are aerated while being heated in a reaction vessel filled with a decomposition agent containing an oxide catalyst or mineral catalyst showing solid acidity and a solid alkali agent. A gas treatment method comprising a decomposition step of decomposing the fluorine-containing compound.   The gas treatment method according to claim 1, wherein the fluorine-containing compound is chlorofluorocarbon.   The gas treatment method according to claim 2, wherein the fluorine-containing compound is perfluorocarbon.   The gas treatment method according to claim 1, wherein the solid alkaline agent is calcium oxide.   The gas treatment method according to claim 1, wherein aluminum oxide is used as the oxide catalyst.

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