JPH10216479A - Detoxifying method of gaseous nitrogen trifluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To safely and efficiently treat NF3 by allowing a gas containing the NF3 and ammonia to contact with a catalyst and subjecting at least a part of a product to an adsorptive removal or an absorptive removal by solvent. SOLUTION: After mixing a gas containing the NF3 such as waste gas from a super LSI etching device, waste gas of a CVD clanging gas and leakage gas from a NF3 vessel with the ammonia, the mixture is introduced to a reactor provided with a catalyst such as metal, oxide, carbonate, sulfate and fluoride of Na, K, Cs, Mg, Ca, Sr, Ba, Al and Ga and decomposed. The NF3 is previously diluted with the gas such as nitrogen preferably since a large exothermic reaction is caused when the NF3 is brought into contact with the catalyst. Since hydrogen fluoride is formed as a result of a catalytic reaction with the catalyst, the hydrogen fluoride is adsorbed and removed with a basic oxide such as alkaline earth oxide and soda lime or washed and removed with alkali aq. soln. In such a way, the NF3 is completely and economically removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the nitrogen trifluoride gas about abatement method (hereinafter, referred to as NF _3).

[0002]

2. Description of the Related Art At present, it is well known that restrictions are imposed on chlorofluorocarbons and CO ₂ which have a bad influence on the global environment, and NF ₃ is also a substance which is not easily decomposed in nature. In recent years, a large amount of NF ₃ gas has been used as a cleaning gas in semiconductor manufacturing. However, since it is toxic, it is necessary to remove NF ₃ remaining in the exhaust gas.

As a method for solving the above problem, there is known a method in which an exhaust gas containing NF _{3 is} passed through a column filled with activated carbon at a high temperature (Japanese Patent Application Laid-Open No. 62-237929). However, in this method, resulting in the release of CF _4, also referred to as one of the causes of global warming.

[0004] A method for removing harm by reacting with a metal oxide is also known (Japanese Patent Application Laid-Open No. 3-181316). There is a problem of generating.

Further, a method is known in which NF _{3 is} passed through a column filled with a metal which generates gaseous fluoride at a high temperature (JP-A-61-204025). It requires a facility for treating gaseous fluorides, which is disadvantageous in that the apparatus becomes large.

As a method for removing NF ₃ by reacting with NF ₃ with another gas, a method of decomposing by reacting with hydrogen (JP-A-2-303524) or hydrocarbon (JP-A-8-131774) is known. It is. However, the former has a problem in using hydrogen with a wide explosion range, and the latter has C
F ₄ not to the preferred method to release.

[0007]

[0008] The present invention is intended to provide a method of processing a NF ₃ safe, and efficient.

[0008]

The present inventors have SUMMARY OF THE INVENTION may, prior disadvantages of the prior improved result of intensive studies on possible ways of industrial implementation, NF ₃ by contacting the catalyst with NF ₃ and ammonia The present invention has been completed by finding a method for eliminating harmful substances.

That is, the present invention provides a method for contacting a gas containing nitrogen trifluoride gas and ammonia with a catalyst to decompose and decompose, adsorbing and removing at least a part of the product, further decomposing the product, A method for removing nitrogen trifluoride gas, wherein at least a part of the gas is absorbed by a solvent and removed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in more detail. The abatement method of the present invention is applied to abatement of a gas containing NF ₃ such as an exhaust gas from a super LSI etching apparatus, an exhaust gas of a CVD cleaning gas, and a leak gas from an NF ₃ container. After the gas containing NF ₃ is mixed with ammonia, it is led to a reactor containing a catalyst and decomposed.

The catalyst used in the present invention is Na, K, Cs,
Mg, Ca, Sr, Ba, Al, Ga, In, Sn, P
b, Sb, Bi, Cu, Zn, Cd, Sc, Y, La,
Hf, V, Cr, Mn, Tc, Fe, Co, Ni, Z
Metals such as r, Pd, and Os, oxides, carbonates, sulfates, fluorides and the like are used. In the case of oxides and the like, the catalyst is fluorinated by a fluorine compound generated by a decomposition reaction.
It is preferable to use metal fluoride.

The catalyst may have any shape such as a sphere, a tablet, a ring, and a crushed product (irregular type). Supporting the active ingredient on a carrier such as alumina or titania is also included in the scope of the present invention.

The temperature at which the catalyst comes into contact with the catalyst is from room temperature to 600 ° C.
Is suitably selected in the range of 200 to 600 ° C., preferably 300 to 550 ° C. If the contacting temperature is too low, the reaction cannot proceed at an industrially acceptable rate, and if the contacting temperature is too high, the heat resistance and corrosion resistance of the device will be problematic, and equipment costs will increase, which is not preferable.

[0014] Ammonia is added in a molar ratio to NF ₃ 1 to 10, preferably 1 to 4 preferred. When the molar ratio is less than 1, the decomposition rate of NF ₃ becomes low, which is not preferable.
On the other hand, when the molar ratio exceeds 10, the decomposition rate of NF ₃ does not increase, and it is necessary to take measures for treating residual ammonia, which is not preferable.

Since a large exothermic reaction occurs upon contact with the catalyst, NF ₃ is preferably diluted in advance with a gas such as nitrogen. The NF3 concentration after dilution is 0.1 to 10% by volume, preferably 0.3 to ₃ % by volume. Space velocity at the time of contact with the catalyst is 100 to 100,000 hr
⁻¹ , preferably 1,000 to 50,000 hr ⁻¹ .

Although the details of the reaction when NF ₃ and ammonia are brought into contact with the catalyst are not clear, hydrogen fluoride is generated as a result of the reaction. This hydrogen fluoride can be easily adsorbed and removed by a basic oxide such as an alkaline earth oxide or soda lime. These adsorbents are inexpensive and result in reduced running costs for the NF ₃ abatement process.

Alternatively, the hydrogen fluoride can be removed by washing with an alkaline aqueous solution. In many cases, a scrubber is installed in a treatment line for exhaust gas from a semiconductor manufacturing process, and in that case, it is advantageous to remove hydrogen fluoride using an existing scrubber.

[0018]

The present invention will be described below in more detail with reference to Examples and Comparative Examples. In addition,% of gas concentration represents volume%. Example 1 A tablet having a diameter of 5 mm and a height of 5 mm was formed by tableting calcium fluoride (CaF ₂ ) powder. Subsequently, the tablet was crushed, and a portion having a particle size of 1 to 2 mm was collected by sieving. 300m long with heater for heating
m, an inner diameter of 12 mmφ in a SUS column.
₂ was filled in 5 cc. The packed column is heated to 350 ° C., and NF ₃ gas 1% diluted with N ₂ gas 5
0 cc / min and 50 cc / min of a gas having an ammonia concentration of 4% diluted with N ₂ gas were mixed immediately before the column inlet, and the mixture was passed through the column. Five minutes after the start of the ventilation, the gas at the outlet was analyzed by gas chromatography. As a result, NF ₃ was not detected in the gas. In addition, 5 from the start of ventilation
During 35 minutes, the outlet gas was bubbled into a 5% aqueous sodium hydroxide solution, and the amount of fluorine ions in the aqueous solution was quantified. As a result, an amount of fluorine ions corresponding to the fluorine content in the fed NF ₃ was detected. Further, 24 hours after the start of ventilation, the gas at the outlet was again analyzed by gas chromatography, but NF ₃ was not detected.

[0019] Examples 2-5 chromium fluoride instead of CaF _{2 (CrF 2),} cobalt fluoride _(CoF 2), strontium fluoride (SrF
₂ ) and NF ₃ removal test was performed in the same manner as in Example 1 except that iron fluoride (FeF ₂ ) was used. The gas at the column outlet was analyzed by gas chromatography 5 minutes and 24 hours after the start of aeration.
₃ was not detected.

Example 6 A tablet having a diameter of 5 mm and a height of 5 mm was formed by tableting calcium fluoride (CaF ₂ ) powder. Subsequently, the tablet was crushed, and a portion having a particle size of 1 to 2 mm was collected by sieving. 300m long with heater for heating
m, an inner diameter of 12 mmφ in a SUS column.
₂ was filled in 5 cc. The particle size is 1-2m downstream of this column.
150m long filled with 10cc of calcium oxide
m and a second column made of SUS having an inner diameter of 12 mmφ were connected. The column packed with CaF ₂ was heated to 350 ° C.
NF ₃ diluted with ₂ gas ₃ % 1% gas 50cc / m
In and 50 cc / min of a gas having an ammonia concentration of 4% diluted with N ₂ gas were mixed immediately before the column inlet and passed through the column. Five minutes after the start of the ventilation, the gas at the outlet was analyzed by gas chromatography. As a result, NF ₃ was not detected in the gas. Further, between 5 and 35 minutes from the ventilation started bubbling outlet gas in 5% sodium hydroxide aqueous solution, was quantified fluorine ions in the aqueous solution, the fluorine ion was not detected at all, generated by the decomposition of NF ₃ It can be seen that all the fluorine-containing gases thus fixed were fixed on the calcium oxide. Further, 24 hours after the start of ventilation, the gas at the outlet was again analyzed by gas chromatography, but NF ₃ was not detected.

Comparative Examples 1 to 5 NF ₃ removal tests were performed in the same manner as in Examples 1 to 5 except that no ammonia gas was used. Five minutes after the start of aeration, the gas at the outlet was analyzed by gas chromatography.
F ₃ concentration is 0.8 to 1 percent, a decrease was observed.

[0022]

According to the present invention, by bringing NF ₃ and ammonia into contact with a catalyst, N 2 is not achieved by the prior art.
F ₃ can harm completely divided, it has become possible to provide an economical NF ₃ abatement techniques.

Claims (5)

[Claims] 1. A method for removing nitrogen trifluoride gas, comprising decomposing a gas containing nitrogen trifluoride gas and ammonia by contact with a catalyst. 2. A method for removing nitrogen trifluoride gas, comprising contacting a gas containing nitrogen trifluoride gas and ammonia with a catalyst to decompose and adsorbing and removing at least a part of a product. 3. A method for removing nitrogen trifluoride gas, comprising: bringing a gas containing nitrogen trifluoride gas and ammonia into contact with a catalyst, decomposing the catalyst, and absorbing and removing at least a part of a product in a solvent. Harm method. 4. The method for removing nitrogen trifluoride gas according to claim 1, wherein the molar ratio of ammonia to nitrogen trifluoride gas is 1 to 10. 5. The catalyst according to claim 1, wherein the catalyst is a metal fluoride.
3. The method for removing nitrogen trifluoride gas according to any one of 3.