JP2010162475A - Treatment method for waste gas containing sf6 - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide waste gas treatment method excellent in durability for efficiently decomposing SF<SB>6</SB>. <P>SOLUTION: The treatment method is for decomposing SF<SB>6</SB>by bringing a fluorine-containing compound treatment agent, which is obtained by molding a mixture of Al(OH)<SB>3</SB>and Ca(OH)<SB>2</SB>with an average particle diameter (median diameter) of at least 55 μm and at most 160 μm in a mole ratio of (3:7) to (5:5), drying the molded mixture, and firing the dried mixture in a temperature range higher than 430°C and 890°C or lower in a nitrogen current or air current, and a waste gas containing SF<SB>6</SB>into contact with each other in a temperature range of 550 to 650°C, and when the SF<SB>6</SB>removal efficiency is lowered to 95% or lower during the operation, the fluorine-containing compound treatment agent is replaced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to treatment of exhaust gas containing a fluorine-containing compound, and more particularly to a method of treating exhaust gas containing SF ₆ discharged from a W (tungsten) or polysilicon etching process.

In semiconductor factories, many kinds of harmful gases are used during the semiconductor manufacturing process, and there is concern about environmental pollution due to exhaust into the environment. In particular, in a cleaning process of an inner surface of a semiconductor manufacturing apparatus in the semiconductor industry, an etching process, a CVD process, or the like, a fluorinated hydrocarbon such as CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , C ₄ F _6. , C ₄ F ₈ , C ₅ F ₈ , SF ₆ , and fluorine-containing compounds such as perfluoro compounds (PFC) such as NF ₃ are used. The fluorine-containing compounds contained in the exhaust gas from these processes are: As a global warming gas, it is urgently required to establish a removal system.

  As a method for treating exhaust gas containing a fluorine-containing compound, for example, a method of decomposing fluorocarbon in exhaust gas using a treatment agent containing aluminum oxide and an oxide of an alkaline earth metal (Patent Document 1); aluminum oxide and alkali A method of decomposing sulfur fluoride in exhaust gas using a treating agent containing an earth metal oxide (Patent Document 2); alumina and alkaline earth metal compounds, and in some cases metals such as copper, tin, vanadium, etc. Method for Decomposing Fluorine Compound in Exhaust Gas Using Treatment Agent Containing Oxide (Patent Document 3); Method for Decomposing PFC in Exhaust Gas Using Treatment Agent Containing Aluminum Hydroxide and Calcium Hydroxide (Patent Document 4); and the like have been proposed.

  However, the conventional processing method as described above has a problem that the processing temperature is as high as 800 to 1000 ° C., so that the processing apparatus is rapidly deteriorated by heat and the energy consumption of the apparatus is large. Moreover, the conventional processing agent included the problem that service life is short and replacement frequency is high. For example, in the methods disclosed in Patent Documents 1 to 3, PFC gas is decomposed by reacting PFC with aluminum oxide (alumina) to produce aluminum fluoride. However, since the reaction activity of aluminum oxide is low, high-temperature reaction conditions are necessary to allow this reaction to proceed efficiently. Further, the generated aluminum fluoride forms a layer on the surface of the aluminum oxide, which may poison the aluminum oxide and lose the catalytic activity in a short time. There is a problem of becoming high.

  PFC gas is reacted with aluminum hydroxide, fluorine is converted to hydrogen fluoride with hydrogen of the hydroxyl group of aluminum hydroxide, and then the generated hydrogen fluoride is reacted with calcium hydroxide to generate calcium fluoride. A method that can efficiently decompose PFC such as PFC gas at a temperature lower than that of the conventional method has been proposed (Patent Document 4). However, although this method is effective in a small apparatus, it has been confirmed that when it is scaled up to an actual scale, the activity of aluminum is inhibited and a sufficient removal effect may not be exhibited.

The inventors of the present invention have previously developed the treatment agent shown in Japanese Patent Application No. 2008-71336, but these optimum treatment temperatures are mainly 650 to 750 ° C. because they are mainly perfluorocarbons. When SF ₆ was processed at a high temperature, there was a problem that harmful SO ₂ was discharged to a TLV value or more before the breakthrough time as SF ₆ .
JP 2002-224565 A JP 2002-370013 A JP 2001-190959 A JP-A-2005-262128

Accordingly, the present invention is to solve such prior art problems, and breakthrough of SF _6, or narrowing the time SO ₂ discharges above the allowable value, or, prior to the time of breakthrough of the SF _6, It is an object of the present invention to provide an exhaust gas treatment method having excellent durability for efficiently decomposing SF ₆ without causing harmful SO ₂ to be discharged beyond an allowable value.

In order to solve the above problems, according to the present invention, in an exhaust gas treatment method containing SF ₆ , the exhaust gas is treated with Al (OH) ₃ and Ca (OH) having an average particle diameter (median diameter) of 55 μm to 160 μm. _A fluorine-containing mixture obtained by molding and drying a mixture having a molar ratio of ₂ : 7 to 5: 5 and calcining in a nitrogen flow or an air flow in a temperature range higher than 430 ° C. and not higher than 890 ° C. This is an exhaust gas treatment method containing SF ₆ , which is brought into contact with a compound treatment agent at a temperature of 550 to 650 ° C.
In the exhaust gas treatment method, the contact temperature is preferably 600 to 650 ° C., and the fluorine-containing compound treatment agent is preferably exchanged when the SF ₆ removal rate is reduced to 95% or less.

According to the present invention, the harmful SO generated by the decomposition of SF ₆ by contacting the fluorine-containing compound treating agent and the exhaust gas containing SF ₆ at a temperature of 550 to 650 ° C., more preferably 600 to 650 ° C. without generating ₂ TLV value (2 ppm) or more, long-term stability and efficiently, it was possible to decompose the SF _6.

The present invention is described in detail below.
The fluorine-containing compound treating agent used in the present invention will be described. Al (OH) _{3 as} a raw material of the treating agent has an average particle size of 55 μm or more, preferably 60 μm or more and 160 μm or less, more preferably 90 μm or more and 120 μm. It is as follows. Here, the average particle diameter means the median diameter, and is the particle diameter at which the frequency (content) is integrated for each particle diameter, and the accumulation of the content reaches 50% from the minimum particle diameter.
The average particle diameter of Ca (OH) ₂ which is another raw material of the treatment agent varies depending on the average particle diameter of A1 (OH) ₃ , but the average particle diameter of Ca (OH) ₂ is higher than that of A1 (OH) _3. A smaller (median diameter) is preferable. The average particle diameter (median diameter) of Ca (OH) ₂ is preferably 1 μm to 10 μm, more preferably 3 μm to 8 μm, and most preferably 4 μm to 6 μm.

The activity of A1 (OH) ₃ and Ca (OH) ₂ is maintained by efficiently arranging Ca (OH) _{2 on the} surface layer of A1 (OH) ₃ having a large average particle diameter as a nucleus. it is conceivable that. Thus, Ca _(OH) particle size of ₂ covers without gaps an entire surface of the too small A1 _{(OH) 3} than the average particle size of A1 _{(OH) 3,} by preventing the contact between the fluorine-containing compound results In contrast, if the particle size of Ca (OH) ₂ is too large compared to the average particle size of A1 (OH) ₃ , the contact efficiency with F during decomposition of the fluorine-containing compound decreases. As a result, the decomposition becomes insufficient, and in any case, it is considered that the decomposition efficiency of the fluorine-containing compound is lowered.

The molar ratio of A1 (OH) ₃ and Ca (OH) ₂ in the above mixture is 3: 7 to 5: 5, preferably 3: 7 to 4: 6. If the molar ratio of A1 (OH) ₃ and Ca (OH) ₂ is outside the above range, desired treatment performance as a fluorine-containing compound treating agent cannot be obtained, and the CF ₄ removal rate is 95% or less in a short time. It will deteriorate and will not be practical.
The fluorine-containing compound treating agent used in the present invention is obtained by drying a molded product obtained by extruding the above mixture, and a temperature range of 430 ° C. to 890 ° C., preferably 580 ° C. to 850 ° C., more preferably. It is obtained by calcining in a nitrogen flow or air flow in a temperature range of 650 ° C. to 780 ° C.

The firing temperature of the molded product of A1 (OH) ₃ and Ca (OH) ₂ needs to be a temperature that allows dehydration and does not deactivate. Since the dehydration temperature of A1 (OH) ₃ is about 270 ° C. and the dehydration temperature of Ca (OH) ₂ is about 430 ° C., it is preferable to exceed at least 430 ° C. When the temperature range exceeds 890 ° C., the SF ₆ removal rate decreases.
From this, it is considered that aluminum oxide is crystallized by the high-heat firing process, and the activity is deteriorated.

A molded product of A1 (OH) ₃ and Ca (OH) ₂ is fired in a nitrogen stream or an air stream. The flow of nitrogen or air preferably reverses the inflow direction for a certain time. This is because moisture generated as a result of the dehydration reaction that proceeds by firing is not allowed to stay around the mixture, but is quickly evaporated and removed. When a molded product of A1 (OH) ₃ and Ca (OH) ₂ is continuously fired in a high-heat and high-humidity atmosphere, aluminum oxide is crystallized due to the presence of moisture (meaning crystallization at the fine structure level at the active site). Therefore, the activity is considered to deteriorate. Therefore, it is necessary to quickly remove the generated water by flowing an inert gas around A1 (OH) ₃ or aluminum oxide obtained by baking. The countercurrent airflow of nitrogen flow or air flow is given by, for example, filling a column with a molded product of A1 (OH) ₃ and Ca (OH) ₂ and sending nitrogen flow or air flow from the top and bottom of the column. be able to.

The firing time is not particularly limited and varies depending on the amounts of A1 (OH) ₃ and Ca (OH) ₂ used, but generally 6 to 12 hours is the point of dehydration effect and energy consumption efficiency. Preferably, the time is 8 to 10 hours. Technically, it is considered sufficient that the temperature is raised to a temperature at which Ca (OH) ₂ dehydrates (about 430 ° C.) and then baked for an additional 1-2 hours. If the rate of temperature rise until reaching the firing temperature is too fast, dehydration may be insufficient, and if it is too slow, it is not preferred for economic reasons (consuming energy and time). Usually, a temperature increase rate of 100 ° C./hr is optimum. Further, if the firing time is too long, the treatment agent excessively adsorbs CO ₂ generated from the fuel during firing, which is not preferable because the fluorine adsorption performance deteriorates.

Examples of the fluorine-containing compound that can be treated with the fluorine-containing compound treating agent of the present invention include fluorinated hydrocarbons such as CHF ₃ , CF ₄ , C ₂ F ₆ , C ₃ F ₈ , SF ₆ , NF _{3 and the} like. fluoro compounds (PFC), and the like, but the present invention, particularly the SF _6, can be decomposed without drained harmful SO ₂ or more TLV value. Examples of the process in which SF ₆ is a main exhaust gas component include exhaust gas discharged in the process of etching W (tungsten) or poly (polysilicon).
The treatment temperature at which the fluorine-containing compound of the present invention is brought into contact with the exhaust gas containing SF ₆ is 550 to 650 ° C., preferably 600 to 650 ° C., based on the SF ₆ treatment amount and the SO ₂ leakage amount. If the temperature is increased within this range, the SF ₆ removal rate is 95% or more and the SF ₆ treatment amount is increased, but the SO ₂ leakage amount is also increased, and if the temperature is lowered, the SO ₂ leakage amount is decreased. SF ₆ throughput is also reduced. When the processing temperature is 750 ° C., the SF ₆ processing amount is small and the SO ₂ leakage amount is also increased.

In the reaction between the fluorine-containing compound treating agent of the present invention and SF ₆ , the reaction component in the treating agent is considered to be CaO. First, CaO and SF ₆ react as follows,
SF ₆ + CaO → CaF ₂ + SO ₂
CaF ₂ and SO ₂ are produced, and this SO ₂ and CaO react,
CaO + SO ₂ → CaSO ₄
Thus, it is considered that the compound is changed into a stable compound.
If the treatment agent deteriorates or the temperature is high, all CaO is used for the decomposition of SF ₆ , and SO ₂ does not change to CaSO ₄ , but SO ₂ is discharged as it is. It is done.

Next, the apparatus used for the exhaust gas treatment method of the present invention will be described.
FIG. 1 is a sectional view showing an example of an apparatus used in the present invention.
In FIG. 1, 1a is a left reaction tank, 1b is a right reaction tank, 2a and 2b are heat exchange sections, 3a and 3b are heaters, 4a and 4b are fluorine-containing compound treatment agents, 5 is an exhaust gas inlet for treatment, and 6 is A treated exhaust gas outlet, 7 is an SF ₆ detector, and 8 is a suction fan. In the treatment of exhaust gas using this apparatus, two reaction tanks are connected in series. First, the exhaust gas containing SF ₆ is introduced from the exhaust gas inlet 5 by the intake air by the suction fan 8 and is heat-exchanged with the high temperature treated exhaust gas in the heat exchange part 2a of the left reaction tank 1a, and the fluorine-containing compound treatment agent 4a. Is introduced into the left reaction tank 1a and heated to 550 ° C. to 650 ° C. by the heater 3a to decompose SF ₆ in the exhaust gas. The exhaust gas treated in the left reaction tank 1a passes through the heating side of the heat exchange part 2a, enters the heated side of the heat exchange part 2b of the right reaction tank 1b, and is heat-exchanged with the high-temperature treated exhaust gas. The SF ₆ remaining in the exhaust gas is decomposed and removed by the fluorine-containing compound treating agent 4b introduced into 1b and heated to 550 ° C. to 650 ° C. by the heater 3b. The exhaust gas from which SF ₆ has been removed passes through the heating side of the heat exchange unit 2b and is discharged from the treated exhaust gas outlet 6.

Then, during the treated gas discharged from the right reaction vessel 1b, when detecting SF ₆ in SF ₆ detector 7, and stopping the introduction of the treated flue gas to the left the reaction vessel 1a, in the left reaction vessel 1a The fluorine-containing compound treating agent 4a is replaced with a new one, and the inflow of the exhaust gas to be treated is switched from the right reaction tank 1b to the left reaction tank 1a.
Thus, by changing the treatment path of the exhaust gas to be treated, the treatment agent in the reaction tank can be used up, and the treatment agent can be effectively used.

Hereinafter, the present invention will be described more specifically with reference to examples.
(1) Preparation of fluorine-containing compound treatment agent A1 (OH) ₃ and Ca (OH) ₂ were added to a small column (size: diameter 150 mm × height 850 mm) equipped with an external heater around the circumference so that it could be heated uniformly. A mixture of [average particle diameter of A1 (OH) ₃ of 90 μm, average particle diameter of Ca (OH) ₂ of 5 μm, blending ratio of A1 (OH) ₃ and Ca (OH) ₂ of 3: 7] is obtained by extrusion molding. The granulated product 14L was packed, and an N ₂ flow rate of 50 L / min was given by an upward flow and a downward flow so that a large amount of water vapor did not stay inside the column. The temperature of the reaction vessel is adjusted to 600 ° C., and the upper half of the packed bed of A1 (OH) ₃ and Ca (OH) ₂ is first fired by flowing N ₂ upward flow for 5 to 6 hours. Next, N ₂ downward flow was allowed to flow for 2 to 3 hours, and the lower half of the packing layer of A1 (OH) ₃ and Ca (OH) ₂ was fired.

(2) Treatment of exhaust gas containing SF _{6 A} treatment tube prepared in (1) is quantitatively filled into a quartz treatment cylinder, this is mounted in a ceramic tube furnace, heated to a predetermined temperature, and subjected to the following conditions: An exhaust gas containing SF ₆ was passed.
Gas flow rate: 65 ml / min
SF ₆ concentration: 10,000 ppm
Processing cylinder capacity: 49ml
Gas residence time: 45 sec
Processed temperature: 650 ° C, 600 ° C, 550 ° C

(3) Processing results Table 1 shows the processing results.
In Table 1 and Table 2 below, the SF ₆ throughput (L / L) was converted to the standard state per 1 L of the fluorine-containing compound treatment agent up to that point when the SF ₆ removal rate decreased to 95%. SF ₆ throughput (L / L).

Similarly, the results of processing the SF ₆ concentration of 4320 ppm are shown in Table 2.


For comparison, when processing is performed at a processing agent temperature of 750 ° C., a gas flow rate of 100 ml / min, a gas residence time of 29 sec, and an SF ₆ concentration of 1830 ppm, the SF ₆ treatment is performed for 176 hours until the SF ₆ removal rate decreases to 95%. The amount was 39.4 (L / L) and the SO ₂ leak was 510 ppm. Moreover, the processing time until exhausted SO2 exceeded ₂ ppm was 56 hr.

(4) processing breakthrough 95% rate removal of analysis SF ₆ results SF ₆ treatment, and when the allowable value of SO ₂ to 2ppm a TLV value, at the time of 750 ° C. processing of the comparative example, the SF ₆ treatment The timing of breakthrough and discharge exceeding the allowable value of SO ₂ deviated greatly. However, when the treatment temperature to 550 to 650 ° C., SF ₆ concentration 10000 ppm, SO ₂ in the time difference within 5% with respect to 4320ppm time to reach the 95% SF ₆ removal rate in either case is above the 2ppm Alternatively, the SO ₂ emission concentration reaches 2 ppm later than the SF ₆ removal rate reaches 95%. Further, in order to increase the processing amount of SF ₆ and SO ₂ and to increase the time until SO ₂ breakthrough, it is more preferable to perform the processing at 600 to 650 ° C. In this example, the removal rate of SF ₆ was 95%, but the treatment agent breakthrough, but the same tendency is observed when the breakthrough value is 90%.

(5) Analysis result of SF _6- treated treatment agent (a) XRD analysis The crystalline compound was identified. The results are shown in FIG. 2 for 650 ° C., FIG. 3 for 600 ° C. and FIG. 4 for 550 ° C.
(B) XRF analysis The component content was analyzed. Table 2 shows the contents of F and S. Among SF ₆ , F and S were reaction-immobilized in the mixture.

From the above results, it was found that crystalline compounds such as CaF ₂ and CaSO ₄ were present in the mixture after the treatment, and SF ₆ was reactively immobilized on the mixture from the contents of F and S.

The cross-sectional block diagram which shows an example of the apparatus used for the waste gas processing method of this invention. XRD analysis data of the treated agent having a treated temperature of 650 ° C. XRD analysis data of the treated agent at a treated temperature of 600 ° C. XRD analysis data of the treated agent having a treated temperature of 550 ° C.

DESCRIPTION OF SYMBOLS 1a: Left reaction tank, 1b: Right reaction tank, 2a, 2b: Heat exchange part, 3a, 3b: Heater, 4a, 4b: Fluorine containing compound processing agent, 5: To-be-treated exhaust gas inlet, 6: Treated exhaust gas stream Outlet, 7: SF ₆ detector, 8: Suction fan

Claims (4)

In the method for treating exhaust gas containing SF ₆ , the exhaust gas has an average particle diameter (median diameter) of 55 μm to 160 μm in a molar ratio of Al (OH) ₃ and Ca (OH) ₂ of 3: 7 to 5: 5. Molding and drying a mixture, and contacting with a fluorine-containing compound treating agent obtained by firing in a nitrogen flow or an air flow in a temperature range higher than 430 ° C. and not higher than 890 ° C. at a temperature of 550 to 650 ° C. An exhaust gas treatment method containing SF ₆ characterized by the above. The contact temperature is, the exhaust gas processing method comprising the SF ₆ according to claim 1, characterized in that a 600 to 650 ° C.. The exhaust gas treatment method containing SF _{6 according} to claim 1 or 2, wherein the fluorine-containing compound treating agent is replaced when the SF ₆ removal rate is reduced to 95% or less. Exhaust gas treatment method comprising SF ₆ according to claim 1, wherein the exhaust gas treatment method comprising SF _6, which comprises treating the SF ₆ while kept below the allowable concentration emission concentration SO _2.