JP2002085939A - Decomposition treatment process of fluorine-based waste gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a decomposition treatment process of a fluorine-based waste gas, by which such a waste gas can safely be subjected to electric discharge treatment under a pressure in the vicinity of ordinary pressure, in a stable state. SOLUTION: This treatment process comprises: diluting a waste gas containing a fluorine-based gas with an inert gas to form a gaseous mixture of a 13.3-133 kPa pressure; thereafter, introducing the gaseous mixture into an electric discharge reactor 1 formed from a solid dielectric material containing silicon; applying a high frequency voltage to between electrodes 10 and 11 each placed outside the discharge reactor 1 so as to be opposite to the other, to cause a plasma discharge within the reactor 1, thereby to subject the fluorine- based gas to discharge decomposition and to form active fluorine; concurrently, allowing the active fluorine to react with silicon contained in a reaction vessel of the reactor 1 to form a gaseous silicon fluoride compound(s); and withdrawing the treated gas out of the reactor 1 to subject the silicon fluoride compound(s) to adsorption treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a treatment method for detoxifying an exhaust gas containing a hardly decomposable fluorine-based gas.

[0002]

2. Description of the Related Art Recently, nitrogen trifluoride (NF ₃ ) and carbon tetrafluoride (CF) have been used for dry etching in forming a semiconductor thin film and dry cleaning of a plasma CVD apparatus.
_Although fluorine-based gases such as ₄ ) are widely used, these fluorine-based gases are not necessarily consumed in their entirety during the formation of the thin film, and some of them are discharged out of the system as unreacted gases. Further, a part of the fluorine-based gas used for cleaning the inside of the reaction tank after forming the thin film is also discharged as an unreacted gas to the outside of the system.

[0003] However, if the fluorine-based gas is released into the atmosphere as it is, it may cause disasters and pollution,
The allowable concentration in the atmosphere is set, and it is necessary to reduce the concentration of fluorine-based gas to make it harmless in accordance with the allowable concentration. As a method for treating such a fluorine-based gas,
Conventionally, a combustion-type treatment method using a burner flame such as hydrogen or natural gas, and an adsorption-type treatment method in which a gas is adsorbed at normal pressure using various adsorbents according to the type of gas have been mainly performed. .

[0004]

SUMMARY OF THE INVENTION
Is carried out at a high temperature, so that a high concentration of NO
_xGenerates and F_TwoSince acidic gas such as is generated, piping
Etc. are susceptible to corrosion. Also, the above adsorption
In the case of high-concentration, large-flow gas,
The frequency of changing the adhesive increases, increasing costs or
There is a problem that the maintenance frequency increases. In addition,
Among nitrogen-based gases, NF_ThreeAnd CF_FourFor
No special adsorbent is required due to lack of effective adsorbent
There is also a problem.

[0005] For example, NF ₃ is plasma and CVD.
It is a useful gas that is attracting attention as a cleaning gas for equipment and is expected to grow in demand in the future.
It is a toxic gas of pm (TWA-TLV), and its mutagenicity has been recognized in the Ames test. However, at room temperature
There is no suitable adsorbent because it is a very stable substance at normal pressure. In order to detoxify the NF ₃ , a method of reacting it with a metal at a high temperature to form a metal fluoride and then performing an adsorption treatment is performed. However, the treatment process is complicated. Have various problems.

That is, when iron (Fe), copper (Cu), or the like is used as the metal for reacting NF ₃ , the problem is that highly toxic dinitrogen tetrafluoride (N ₂ F ₄ ) is simultaneously produced. There is. In the method of reacting metallic silicon (Japanese Patent Application Laid-Open No. 63-12322), the metallic silicon surface is oxidized depending on the gas composition and the like, and the reaction temperature for decomposing NF ₃ rises extremely, and NO _x is reduced. There are problems such as occurrence.

On the other hand, an exhaust gas treatment method using discharge (discharge treatment method) has been studied, and is expected as an effective technique in that the fluorine-based gas can be decomposed at a relatively low temperature. However, in general, in the discharge treatment, the decomposition treatment of the fluorine-based gas is performed by exciting the plasma in the exhaust gas which is usually in a pressure range of 13.3 to 1330 Pa before reaching the vacuum pump of the reduced pressure exhaust system. There is a problem that it is extremely difficult to maintain a stable plasma state with respect to flow rate fluctuations, especially pressure fluctuations.
Further, even if the fluorine-based gas is once converted into plasma and decomposed, the fluorine-based gas is easily recombined with the original gas or another harmful fluorine-based gas, resulting in a problem that the final decomposition efficiency is low. Furthermore, since it is necessary to maintain a certain degree of vacuum, a special device structure, pressure control device, pressure measuring device, etc. are required, which increases the cost of the device and causes accidents such as the breakage of the vacuum. If so, there is a problem that the damage is large.

Also, a method of decomposing exhaust gas containing a high concentration of fluorine-based gas by corona discharge, silent discharge, or the like in a state similar to the above at a pressure downstream of a vacuum pump of a plasma processing apparatus at approximately normal pressure (particularly). Kaihei 10-2351
No. 38) has also been proposed, but in this case, decomposition products generated during the discharge treatment of a high-concentration fluorine-based gas at around normal pressure simultaneously absorb the energy injected during the discharge. In order to increase the efficiency of decomposition, there is a problem that a large amount of electric energy must be supplied or decomposition products must be removed during the treatment in order to increase the decomposition efficiency.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a fluorine-based exhaust gas decomposition treatment method capable of safely performing discharge treatment in a stable state at about normal pressure.

[0010]

In order to achieve the above object, the present invention provides a method for treating an exhaust gas containing a fluorine-based gas, wherein the exhaust gas containing the fluorine-based gas is diluted with an inert gas. Pressure 13.3 ~ 133kPa
After that, the mixed gas is introduced into an electrically insulating container formed of a solid dielectric material containing silicon, and a high-frequency voltage is applied between a plurality of electrodes opposed to the outside of the container. Then, a plasma discharge is generated in the container to discharge-decompose the fluorine-based gas, and the generated active fluorine is reacted with silicon contained in the container to form a gaseous silicon fluoride compound. The first gist is a fluorine-based exhaust gas decomposition treatment method in which a gas is taken out of a container and the silicon fluoride compound is adsorbed.

[0011] Among the above methods, a method for decomposing a fluorine-based exhaust gas in which the electrically insulating container formed of the solid dielectric material also serves as a discharge decomposition accelerator that reacts with the fluorine-based gas. In a second aspect, the fluorine-based gas is NF ₃ , CF ₄ , C ₂ F ₆ , SF ₆ , CCl
_{A third aspect} is a method for decomposing a fluorine-based exhaust gas, which is at least one gas selected from the group consisting of ₂ F ₂ , C ₃ F ₈ and CHF _3, wherein the inert gas is argon,
A fourth gist of the present invention is a method of decomposing a fluorine-based exhaust gas, which is at least one gas selected from the group consisting of helium, neon, nitrogen, and air.

Further, among the above-mentioned methods, particularly, the fluorine-based exhaust gas decomposition treatment method in which the volume concentration of the fluorine-based gas in the mixed gas of the fluorine-based gas and the inert gas is set to 40% or less is described in the fifth method. In summary, a sixth aspect of the present invention relates to a fluorine-based exhaust gas decomposition treatment method in which a plurality of containers are connected and arranged in at least one of a series and a parallel, and a plasma discharge is simultaneously generated in each container. The summary of the

[0013]

Next, embodiments of the present invention will be described in detail.

FIG. 1 schematically shows an example of an apparatus used in an embodiment of the present invention. In the figure, reference numeral 1 denotes a discharge reactor formed in a square cylindrical shape using a solid dielectric material containing silicon in order to provide electrical insulation. 3 is detachably fitted. Reference numeral 4 denotes an exhaust gas introduction line provided with a flow meter 5 and a pressure gauge 6, and an exhaust gas containing a high-concentration fluorine-based gas at normal pressure is introduced into a gas mixer 7. I have. An inert gas for dilution is also introduced into the gas mixer 7 from an inert gas introduction line 8. In this portion, the inert gas is mixed with the exhaust gas so that the fluorine-based gas concentration becomes a predetermined ratio. The gas and the gas are mixed at a predetermined ratio. Then, the mixed gas mixed in the gas mixer 7 passes through a mixed gas introduction line 9 and
It is connected to a gas passage jig 3 fitted to the lower part of the discharge reactor 1 so that a mixed gas is introduced into the discharge reactor 1.

A pair of metal parallel plane electrodes 10 and 11 are attached to the outside of the discharge reactor 1 along two opposing side walls of the discharge reactor 1.
The electrodes 10 and 11 are detachable from the discharge reactor 1 and each has a jacket structure provided with a flow path for a cooling medium such as water. One electrode 10 is connected to a power supply device 13 for discharging via an automatic impedance matching device 12, and the other electrode 11 is grounded.

The gas passage jig 3 fitted to the upper part of the discharge reactor 1 is connected to a gas lead-out line 14 for taking out the gas after the discharge treatment from the inside of the discharge reactor 1. The treated gas taken out through the gas outlet line 14 is supplied to a conventionally known wet scrubber or the like (not shown), where the silicon fluoride compound contained in the gas is adsorbed and removed. ing.

Using the above apparatus, for example, the treatment of exhaust gas can be performed as follows. That is, first, C
Exhaust gas discharged from a semiconductor manufacturing apparatus such as a VD apparatus or an etching apparatus is passed through an exhaust gas introduction line 4 to a gas mixer 7.
And an inert gas is introduced into the gas mixer 7 from the inert gas introduction line 8. Then, in the gas mixer 7, the mixed gas of the exhaust gas and the inert gas is mixed, and at this time, the volume concentration of the fluorine-based gas in the mixed gas is adjusted to be 40% or less. This is set based on the following concept.

That is, in the mixed gas adjusted before the discharge treatment, it is preferable to set the concentration of the fluorine-based gas to be high from the viewpoint of the treatment efficiency and the use of the inert gas without waste. It has been found that as the concentration of fluorine-based gas increases, the decomposition rate by plasma tends to decrease. Therefore, the optimum concentration at which the fluorine in the active fluoride in the plasma can be almost completely fixed as SiF ₄ is the fluorine-based gas discharge reactor 1.
The internal residence time, ie, the amount of exhaust gas to be treated, the uniformity of the plasma, or the plasma generation conditions such as the applied voltage, and also the gas physical properties such as the type of fluorine-based gas and the type of decomposition product. For this reason, it is necessary to adjust the concentration according to the type of gas to be processed and the processing amount.
It has been found that it is preferable to set the volume concentration of the fluorine-based gas to 40% or less. More specifically, when the fluorine-based gas is NF ₃ , the volume concentration is preferably set to 15 to 40%, and when the fluorine-based gas is CF ₄ , the volume concentration is set to 10 to 20%. It is preferred to do so.

The mixed gas thus adjusted is introduced into the discharge reactor 1 through the gas passing jig 2, and a high-frequency voltage is applied to the electrodes 10 and 11 from the discharge power supply 13 to , 11 to generate a high-frequency induction electromagnetic field. Thereby, the mixed gas is excited by plasma and decomposed. Fluorine in the activated fluoride generated by this decomposition reacts with solid silicon which is a component of the discharge reactor 1 to be fixed as a silicon fluoride compound.
Therefore, the discharge reactor 1 functions not only as a reaction vessel but also as a discharge decomposition accelerator for fluorine-based gas.

For example, when the fluorinated gas contained in the mixed gas is NF ₃ , NF ₃ reacts with solid silicon (Si) as shown in the following formula (1) to form a silicon fluoride compound. It is immobilized as silicon tetrafluoride (SiF ₄ ).

[0021]

Embedded image

The above SiF_FourHas a sublimation temperature of -96 ° C.
Discharges during the reaction because it evaporates immediately in the plasma.
Without adhering to the inner wall of reactor 1 for discharge
Solid silicon on the inner wall of reactor 1 is used for the reaction
Is not disturbed. Moreover, SiF_FourCombined energy
Lugie (565.177 × 10^ThreeJ / mol) is NF
_ThreeBinding energy (239.023 × 10^Three~ 29
7.210 × 10^ThreeJ / mol).
SiF generated once in plasma_FourCan be dissociated again
As a by-product as a stable gaseous compound without
Nitrogen gas (N_Two), Oxygen gas (O_Two) And for discharge
It is discharged from the reactor 1. Therefore, the decomposition products
To avoid the problem of reduction in decomposition rate due to recombination of
it can.

Further, N_TwoBinding energy (946.
047 × 10^ThreeJ / mol) is NO _xBinding energy
(167.442 × 10^Three~ 305.582 × 10^ThreeJ
/ Mol), and consequently N_TwoAnd O_Two
Is produced exclusively and harmful NO_xWhen the occurrence of
This has the advantage of: Then, the pump excited near normal pressure
In Zuma, the energy level of the generated free electrons is
High side, ions, atoms, or coexisting in the plasma
The energy levels of the molecules are relatively low, resulting in a discharge
Gas temperature in the reactor 1 is kept low.
Have signs. Therefore, if the gas temperature is at least
Than the combustion treatment method, metal contact method and adsorption treatment method
Because it is low enough,_TwoAnd O_TwoCompound by thermal reaction of
Accompany NO _xIs also suppressed.

Since the SiF ₄ contained in the gas discharged from the discharge reactor 1 can be easily adsorbed by an existing wet scrubber or the like using an alkaline aqueous solution or the like, the NF ₃ is rendered harmless. Processing can be easily achieved.

However, since NF ₃ has low water solubility and cannot be adsorbed by a wet scrubber, the discharge reactor 1
It is important to perform thorough immobilization on SiF ₄ so that undecomposed NF ₃ does not exceed the allowable concentration in the treated gas derived from the above.

In the case where a fluorine-based gas other than NF ₃ or a fluorine-based gas in which two or more fluorine-based gases are mixed is subjected to a discharge treatment, a reaction similar to the above formula (1) proceeds.
The fluorine in the activated fluoride generated in the plasma is Si
Immobilized as F _4, similarly, it can be detoxified.

In the above processing method, the plasma generation conditions in the discharge processing are set as follows. First, the gas pressure when applying plasma is 13.3.
It is set to 133 kPa, and plasma excitation at normal pressure is possible. However, in the case of plasma excitation at normal pressure, there is a tendency for the plasma current to easily transition to a non-uniform plasma state such as an arc discharge in which the degree of local concentration of the plasma current is large. There is a portion where the temperature rises sharply, and it is easily broken. To avoid this, it is important that the spatial uniformity of the plasma be maintained.

The discharge power supply has a voltage of 2 kHz which has a waveform such as a sine wave or a pulse wave.
Those having a frequency of z to 1 MHz, or those having a frequency of 13.56 MHz which is approved for use at frequencies other than the broadcast frequency can be used. However, in order to perform the discharge treatment at a temperature of 100 ° C. or lower, which is close to normal temperature, 200 to 500 kHz is preferable.
１５15 kHz is optimal. The voltage varies depending on the type of gas and the distance between the electrodes 10 and 11, but is usually set at 1000 to 8000V.

The distance between the electrodes 10 and 11 is usually 3 to
The thickness is set to 9 mm, and the thickness of the wall of the discharge reactor 1 disposed therebetween is set to 1 to 3 mm, but in some cases, it is set to other appropriate dimensions. However, as the distance between the electrodes 10 and 11 becomes shorter, it becomes easier to obtain uniform plasma, and the ratio of the internal surface area to the internal capacity of the discharge reactor 1 increases, so that the contact area between the plasma and the discharge reactor 1 increases. As a result, the discharge treatment effect is promoted. On the other hand, since the gas flow passage in the discharge reactor 1 becomes narrow, the flow pressure loss of the introduced gas increases, and the plasma pressure in the discharge reactor 1 increases,
It becomes difficult to obtain uniform plasma. Therefore, it is necessary to set the interval between the electrodes 10 and 11 to an optimum value while keeping the balance between them.

On the other hand, in the discharge reactor 1, the solid silicon as a component thereof is used and consumed in the reaction accompanying the plasma discharge, so that the thickness of the wall is gradually reduced, and electrical and dielectric properties, material strength and the like are reduced. Although the mechanical properties change, the progress of the immobilization reaction to SiF ₄ proceeds smoothly without hindrance until the material strength is significantly degraded. Also, a uniform plasma state is maintained. However, it is necessary to replace the discharge reactor 1 before a problem such as opening of a through hole due to deterioration of the material strength occurs. However, since the wall of the discharge reactor 1 is reduced at a micro level and the replacement frequency is small, the maintenance burden is not particularly large as compared with the conventional method.

Therefore, according to the above-mentioned processing method, the exhaust gas containing the fluorine-based gas is not treated as it is, but is diluted with an inert gas to obtain a pressure of 13.3 to 133 kP.
Since the discharge treatment is performed near the normal pressure of a, uniform and stable plasma decomposition can be generated, and there is an advantage that the decomposition rate of the fluorine-based gas is high. Then, the generated activated fluorine is reacted with solid silicon as a component of the discharge reactor 1 and taken out as a stable gaseous silicon fluoride compound, so that the detoxification treatment can be surely performed. In addition, since uniform plasma discharge is performed near normal pressure, the gas temperature is maintained at a low temperature, and NO _x is not generated, which is safe. And since the system is near normal pressure, the equipment cost is low and the maintenance is simple. Further, since the fluctuation of the exhaust gas flow rate is reduced by dilution with an inert gas and introduced into the discharge reactor 1 with the fluorine-based gas concentration kept constant, a stable plasma state can be maintained.

In the above method, the silicon-containing solid dielectric material constituting the discharge reactor 1 includes quartz, silica, silicon nitride, cordierite, mullite, and the like.
It is preferable to use a glass or ceramic material such as sialon. Further, as a material of the electrodes 10 and 11, a metal material such as copper having excellent heat conductivity and conductivity is suitable.

The fluorine-based gas contained in the exhaust gas includes NF ₃ , CF ₄ , C ₂ F ₆ , SF ₆ and CCl ₂
F ₂ , C ₃ F ₈ , CHF _{3 and the} like. They are,
It may be contained alone or in a state where two or more kinds of fluorine-based gases coexist. Examples of the inert gas used to dilute the fluorine-based gas into a mixed gas include argon, helium, neon, nitrogen, and air. These may be a single gas or a mixed gas of two or more types. Among them, argon or helium is preferable because uniform plasma is easily obtained.

It is to be noted that the discharge reactor 1 does not need to be in the shape of a square tube as in the above example, but may be in the form of a cylinder, disk, or the like.
Any suitable shape can be used. In particular, a device devised so as to increase the contact area between the mixed gas introduced therein and the inner surface of the discharge reactor 1 has a high reaction efficiency and is suitable.

Also, the electrodes 10 and 11 need not be in the form of a parallel plate as in the above-mentioned example, but may be in the form of a cylinder, a rod, etc., depending on the shape of the discharge reactor 1 described above. Any shape is acceptable. However, in order to avoid a temperature rise, it is preferable that a cooling mechanism is appropriately provided as in the above-described example. The surfaces of the electrodes 10 and 11 do not need to be smooth. If the surfaces are rough, such as a fine mesh or a fine sword, the uniformity of plasma is further improved.
It is effective.

Further, in the present invention, the mixed gas introduced into the discharge reactor 1 may contain chlorofluorocarbon (CF) in addition to the fluorine-based gas and the inert gas.
Even if a gas such as C), volatile organic compound (VOC), other fluorocarbons, or hydrofluoric acid (HF) is present, there is no problem in detoxification.

When the type of exhaust gas and the amount of treatment are large,
For example, as shown in FIG. 2, by arranging a plurality of discharge reactors 1 in parallel and performing processing by plasma discharge at the same time, the processing capacity can be increased. FIG.
As shown in (1), by arranging a plurality of discharge reactors 1 in series and performing the processing stepwise, the processing capacity can be increased. Of course, the parallel arrangement and the series arrangement may be further combined.

Furthermore, the exhaust gas treatment method of the present invention may be combined with another conventionally known exhaust gas treatment method to further enhance the treatment. The target exhaust gas is not limited to the one generated from the semiconductor manufacturing apparatus, and may be the one generated from, for example, a liquid crystal manufacturing process or other various industries.

Next, examples will be described together with comparative examples.

[0040]

Example 1 NF ₃ was decomposed using an experimental apparatus having the same structure as the apparatus shown in FIG. The discharge reactor was a rectangular duct made of hard glass (external dimensions: 10
0 mm × 100 mm × 3 mm) water-cooled parallel plate electrode made of copper (electrode area: 100 mm × 100 mm = 10000)
mm ² ). And the interval between the electrodes was 7 mm. And, in argon, NF ₃
At a volume concentration of 15% and a pressure of 101.08 kPa
Was introduced into the discharge reactor. The gas flow path in the discharge reactor has a cross-sectional area of 100
mm × 3 mm = 300 mm ² , and passed through this flow path at a flow rate of 0.02 liter / min. At this time, a sinusoidal voltage having a frequency of 15 Hz and a peak voltage of 7 kV was applied to the electrode, and a power of 350 W was applied. As a result, extremely uniform plasma close to a glow discharge state was visually observed. In addition, as a result of performing gas analysis after the discharge decomposition treatment using a differential exhaust quadrupole mass spectrometer, SiF ₄
And NF ₃ were detected, and it was found that the decomposition of NF ₃ was achieved at 99.99% or more by the reaction of the formula (1). NO _x was not detected. The above as "decomposition rate", by subtracting the NF ₃ amount after treatment from NF ₃ amount of the pretreatment, is a representation as a percentage by dividing the value NF ₃ amount of the pretreatment.

[0041]

Example 2 As a mixed gas to be introduced into a discharge reactor, helium was mixed with NF ₃ at a volume concentration of 15%.
A mixed gas having a pressure of 101.08 kPa was used. Other conditions were the same as in Example 1 above, and the treatment of NF ₃ was performed. Also during this treatment, extremely uniform plasma close to a glow discharge state was visually observed. Then, as a result of gas analysis after discharge decomposition treatment by differential pumping quadrupole mass spectrometer, SiF ₄ and NF ₃ only being detected, by the reaction of the formula (1) occurs, the decomposition of NF ₃ Rate 9
It was found that 8% or more was achieved. NO
_x was not detected.

[0042]

Example 3 As a mixed gas to be introduced into a discharge reactor
And CF in argon_FourAt a volume concentration of 10%,
A mixed gas having a pressure of 101.08 kPa was used. other
Is the same as in Example 1 above,_FourProcessing
went. In this process, too, it is very close to the glow discharge state.
A uniform plasma was visually observed. And differential exhaust
Gas analysis after electrolysis was performed using a quadrupole mass spectrometer.
As a result, SiF_FourAnd CF_FourAnd CO_TwoAnd only CO detected
And the reaction of the following formula (2) occurs,
F_FourIt was found that a decomposition rate of 90% or more was achieved.
Was. NO _xWas not detected.

[0043]

Embedded image

[0044]

Example 4 As a mixed gas introduced into a discharge reactor, helium was mixed with CF ₄ at a volume concentration of 10%.
A mixed gas having a pressure of 101.08 kPa was used. Other conditions were the same as in Example 3 above, and the treatment of CF ₄ was performed. Also during this treatment, extremely uniform plasma close to a glow discharge state was visually observed. As a result of performing gas analysis after the discharge decomposition treatment by the differential exhaust quadrupole mass spectrometer, only SiF ₄ , CF ₄ , CO _2, and CO were detected, and the reaction of the above formula (2) occurred. , CF
It was found that the decomposition rate of No. ₄ was 87% or more. NO _x was not detected.

[0045]

Comparative Example 1 As a gas to be introduced into a discharge reactor,
Only NF ₃ which was not diluted with an inert gas was used. Otherwise, the treatment of NF ₃ was performed in the same manner as in Example 1. In this case, a non-uniform red plasma was visually observed. Then, as a result of performing gas analysis after the discharge decomposition treatment using a differential exhaust quadrupole mass spectrometer, it was found that the decomposition rate of NF ₃ was as low as 30%. Further, NO _x were detected trace.

[0046]

COMPARATIVE EXAMPLE 2 In the same manner as in Comparative Example 1, the reduced pressure state (106
6Pa) to perform NF ₃ treatment. In the case of this treatment, red uniform plasma was visually observed, but it was found that the decomposition rate of NF ₃ was as low as 30%. NO _x was also detected.

[0047]

Examples 5 to 8 A mixed gas of helium and NF ₃ was used as a mixed gas to be introduced into a discharge reactor. The NF ₃ concentration in the mixed gas was set in four ways as shown in Table 1 below. did. Otherwise, as in Example 1, N
Performs processing F _3, by performing gas analysis in the same manner as described above, were calculated degradation rate. The results are shown in Table 1 below.

[0048]

[Table 1]

[0049]

Embodiments 9 to 12 A mixed gas of helium and CF ₄ was used as a mixed gas introduced into a discharge reactor.
The CF ₄ concentration in the mixed gas was set to ₄ as shown in Table 2 below.
Set as follows. Otherwise, in the same manner as in Example 5-8, performs processing CF _4, by performing gas analysis in the same manner as described above, were calculated degradation rate. The results are shown in Table 2 below.

[0050]

[Table 2]

[0051]

As described above, according to the present invention, a fluorine-containing gas-containing exhaust gas diluted with an inert gas is discharged in a predetermined pressure range in an electrically insulating container formed of a silicon-containing solid dielectric material. , The fluorine-based gas is safely and efficiently decomposed and removed. According to this method, uniform and stable plasma decomposition can be generated, and there is an advantage that the decomposition rate of fluorine-based gas is high. Then, the generated activated fluorine is reacted with solid silicon, which is a constituent component of the electrically insulating container, and is taken out as a silicon fluoride compound, which is a stable gaseous substance, and is adsorbed and removed. it can. In addition, since uniform plasma discharge is performed near normal pressure, the gas temperature is maintained at a low temperature, and NO _x is not generated, which is safe. And because the system is near normal pressure,
The equipment cost is low and maintenance is easy. Further, fluctuations in the flow rate of the exhaust gas are reduced by dilution with an inert gas, and the processing is performed in a state in which the concentration of the fluorine-based gas is constant. Therefore, stable processing can be performed without changing the plasma conditions.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an example of an apparatus used in an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing a modified example of the above device.

FIG. 3 is a schematic configuration diagram showing another modified example of the device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Discharge reactor 4 Exhaust gas introduction line 9 Mixed gas introduction line 10, 11 Electrode 14 Gas lead-out line

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasushi Yamagishi 2-6-6 Chikushinmachi, Sakai City, Osaka Inside Air Water Co., Ltd. Sakai Plant (72) Inventor Ken Okubo 2-6 Chikushinmachi, Sakai City, Osaka Prefecture 40 Air Water Co., Ltd. Sakai Plant F-term (reference) 4D002 AA22 AC10 BA02 BA07 CA13 DA70 EA02 GA01 GA02 GB01 GB02 GB04 4G075 AA03 AA37 BA01 BA05 BB01 BB04 BD14 CA15 CA47 CA62 DA01 DA02 EA01 EA06 EB01 EB04 EB02 EC21 EB04

Claims (6)

[Claims] 1. A method for treating an exhaust gas containing a fluorine-based gas, wherein said exhaust gas containing a fluorine-based gas is diluted with an inert gas to a pressure of 13.3 to 133 kPa.
After that, the mixed gas is introduced into an electrically insulating container formed of a solid dielectric material containing silicon, and a high-frequency voltage is applied between a plurality of electrodes opposed to the outside of the container. Then, a plasma discharge is generated in the container to discharge-decompose the fluorine-based gas, and the generated active fluorine is reacted with silicon contained in the container to form a gaseous silicon fluoride compound. A method for decomposing fluorine-based exhaust gas, wherein a gas is taken out of the container and the silicon fluoride compound is adsorbed. 2. The method for decomposing fluorine-based exhaust gas according to claim 1, wherein the electrically insulating container formed of the solid dielectric material also serves as a discharge decomposition accelerator that reacts with the fluorine-based gas. 3. The method according to claim 2, wherein the fluorine-based gas is NF ₃ , CF ₄ ,
C ₂ F ₆ , SF ₆ , CCl ₂ F ₂ , C ₃ F ₈ and CH
_{3. The method according} to claim 1, wherein the gas is at least one gas selected from the group consisting of F3. 4. The decomposition of a fluorine-based exhaust gas according to claim 1, wherein the inert gas is at least one gas selected from the group consisting of argon, helium, neon, nitrogen and air. Processing method. 5. The fluorine-based exhaust gas decomposition treatment according to claim 1, wherein a volume concentration of the fluorine-based gas in the mixed gas of the fluorine-based gas and the inert gas is set to 40% or less. Method. 6. The electric insulating container according to claim 1, wherein a plurality of containers are arranged and connected in at least one of series and parallel, and a plasma discharge is simultaneously generated in each container. The method for decomposing a fluorine-based exhaust gas according to any one of the preceding claims.