JPH02265620A - Treatment of waste gas containing nitrogen fluoride - Google Patents

Abstract

PURPOSE:To remove a nitrogen fluoride highly efficiently, completely, and economically by bringing a waste gas containing a nitrogen fluoride into contact with an organic solvent after the waste gas is brought into contact with a boron nitride in a specific temperature range. CONSTITUTION:A waste gas containing a nitrogen fluoride such as NF3 is brought into contact with a boron nitride in a temperature range of 100-600 deg.C to produce BF3 and N2 by reaction. Then, the resulting waste gas is brought into contact with an organic solvent such as benzene, methanol, etc., to remove the products such as BF3 and the waste gas is discharged to air. By this method, the nitrogen fluoride in the waste gas is completely removed and therefore even if the resulting waste gas is discharged to air, it is safe and no bad effect on environments is caused. This method results in extension of NF3 application and high contribution in semiconductor fabrication industries.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for treating nitrogen fluoride-containing exhaust gas. More specifically, the present invention relates to a method of bringing nitrogen fluoride-containing exhaust gas into contact with boron nitride (ON) and then contacting it with an organic solvent to render the nitrogen fluoride contained harmless.

Nitrogen trifluoride (NFi) gas is a useful gas that has recently attracted particular attention as a dry etching gas in the production of VLSIs, a cleaning gas in CvD equipment, a fluorine source for chemical lasers, and the like.

[Conventional technology]

NF, gas, is a physically and chemically stable gas at room temperature, but decomposes under conditions such as heat, ultraviolet light, and electrical discharge, resulting in dinitrogen tetrafluoride (Nzp4) and dinitrogen difluoride as decomposition products. Nitrogen fluorides such as nitrogen (lhF2) and dinitrogen hexafluoride (NtFa) are generated.

However, when NFs gas is used for the above purpose,
In addition to these nitrogen fluorides, undecomposed NF is also present in the exhaust gas.
It also contains s.

NF gas is a toxic gas with an allowable concentration of 101), and the above nitrogen fluoride, which is a decomposition product, contains NFf gas.
NzFa and s, which are more toxic than f and highly explosive.
Contains gases such as gpx.

Therefore, in order to effectively use NFs gas as a gas for VLSI manufacturing, it is essential to remove these harmful nitrogen fluorides contained in the exhaust gas to below an economically permissible concentration and render it harmless. be.

Conventionally, as a method to detoxify nitrogen fluoride in exhaust gas, (1) Exhaust gas enters the burner flame that burns hydrocarbons.

How to send.

(2) A method of bringing exhaust gas into contact with high-temperature elemental carbon.

(J, Massonna et al, Angew, c
hem, 78, 336 (1966)) (3) A method of reacting NFs in exhaust gas with metal halogens such as aluminum chloride, iron chloride, chromium chloride, aluminum bromide, iron bromide, chromium bromide, etc. -35830 publication).

(4) A method of reacting Nh in exhaust gas with metals such as copper, bismuth, arsenic, antimony, and steel.

etc. are known.

[Problem to be solved by the invention]

However, in method (1), hydrogen fluoride (HP) and nitrogen oxides are produced by the decomposition of nitrogen fluoride, and these products must be subsequently processed, but this process is complicated. There is.

In method (2), nitrogen oxides and elemental carbon are reacted and completely decomposed into nitrogen gas and carbon tetrafluoride (CF) gas. Since this requires a high temperature of 500° C. or higher, there is a problem that the above reaction may go out of control in some cases, leading to the risk of explosion.

In method (3), the metal fluoride produced by the halogen exchange reaction forms a film on the surface of the metal halide, resulting in poor reaction efficiency and an increase in the residual rate of nitrogen fluoride in the exhaust gas after treatment. There is a problem with doing so. Further, the film formed on the surface of the metal halide may partially peel off and accumulate in the reactor, clogging the attached piping etc. and causing trouble. In addition, the above reaction results in chlorine (
Since C1g) gas and bromine (Brg) gas are generated,
There is also the problem that this requires treatment for removal.

When method (4) is employed, the metal used is exposed to air and forms a thin oxide film on its surface, so it is necessary to reduce this in advance. If the reduction treatment is omitted, there are problems such as increasing the contact temperature between the exhaust gas and the metal, and generating extremely harmful and highly reactive oxygen difluoride (OFg) gas. be.

[Means to solve the problem]

As a result of extensive studies to solve the above problems, the present inventors have discovered that if nitrogen fluoride-containing exhaust gas is brought into contact with BN at a specific temperature and then brought into contact with an organic solvent, it will produce highly toxic substances such as OF. The present invention has been completed based on the discovery that the above wandering gas can be rendered harmless safely and easily over a long period of time without producing any gas as a by-product.

That is, the method for treating nitrogen compound-containing exhaust gas of the present invention is characterized in that the exhaust gas is brought into contact with BN at a temperature in the range of 100 to 600°C, and then brought into contact with an organic solvent.

[Detailed disclosure of the invention]

The present invention will be explained in detail below.

As mentioned above, the present invention reduces nitrogen compound-containing exhaust gas to 100%
This is a method of carrying out a contact reaction with BN at a temperature in the range of ~600°C, followed by contacting with an organic solvent to remove the nitrogen fluoride contained therein.

In the present invention, the contact between the nitrogen compound-containing exhaust gas and BN is usually carried out by filling a reaction vessel, such as a column, with BN and passing the exhaust gas through the reaction vessel.

Therefore, the 8N used in the present invention is preferably in the form of particles or granules in order to prevent scattering due to ventilation of exhaust gas, and tableted BN can also be suitably used.

The crystal shape of BN used in the present invention is not particularly limited, and any shape can be used.
Among them, hexagonal BN (h-BN) is preferred for the following reasons.

That is, h-8N has a higher decomposition rate of nitrogen fluoride even at a lower contact temperature with exhaust gas than other crystal shapes, and is less expensive.

In the present invention, due to the contact between the exhaust gas and BN, the nitrogen thermal compound in the exhaust gas and BN easily react at the above temperature to generate boron trifluoride (Oh) and nitrogen (Nt). This reaction is illustrated by the following formula (1) using Nh as an example.

8N + NFs” BFs + Nt −・
(1) The boiling point of Bh thus produced is -100°C, and the boiling point of Nz is -196°C, both of which are gases.

Therefore, unlike in conventionally known methods, the reaction product does not form a film on the surface of the BH, so the reaction can be maintained continuously and satisfactorily.

In the present invention, the contact temperature between the nitrogen fluoride-containing exhaust gas and BN must be in the range of 100 to 600°C, preferably 200 to 400°C. Contact temperature is 10
At temperatures below 0°C, the progress of the reaction shown in equation (1) is significantly reduced, requiring a long contact time or requiring a larger reaction vessel, both of which are disadvantageous.

On the other hand, if the contact temperature exceeds 600° C., it is necessary to take into account the material of the reaction vessel, and this is disadvantageous as it also causes a loss of thermal energy.

In the method of the present invention, the reaction of formula (L) proceeds rapidly at the above temperature, so the contact time between the nitrogen fluoride-containing exhaust gas and BN may be short, and about 10 to 20 seconds is sufficient; As a precaution, this is usually done for about 30 to 60 seconds.

The thus treated exhaust gas is then guided outside the reaction vessel and brought into contact with an organic solvent by the method described below to remove BFff produced by the contact with the BN, and then released into the atmosphere.

In the present invention, any organic solvent can be used as long as it can dissolve BP produced by contact with BN or can form an addition compound or a composite compound with BF. Moreover, it is also possible to use materials that do not react with BF2 and generate noxious gases.

When such organic solvents are listed, methyl alcohol (
CH! OH), ethyl alcohol (CJsOH), propyl alcohol (C3H?OR), butyl alcohol (C4H!OH), octyl alcohol (Csl(+
JH), ethylene glycol ((canon)z)
, allyl alcohol (C-H,OH), propargyl alcohol (CJsOH), benzyl alcohol (CJi
Alcohols such as CHtOH), methyl ether [(C
)1. )! 0], ethyl ether ((CJs)gO)
, methyl ethyl ether (CH!0Ctlls), n-
Ethers such as butyl ether ((C4HJ□0), methylamine (CH3NHz), ethylamine (C*1
Amines such as IsNHf), propylamine (CJ)NHz), ethanolamine (N)IzCfbCFIOH), formic acid (l(COOH), acetic acid (CHzCOOH)
), organic rllB such as phenol (CJsOH), benzene (C6) 16), dichlorobenzene (C!)! ,
Examples include compounds such as CI, chloroform (CHCIs), carbon tetrachloride (CCI4), carbon disulfide (C5t), tetrahydrofuran (C4HIO), pyridine (CsHsN), and piperidine (CsH++N).

Among these organic solvents, CJh, C1H4Cl□, C
uCl2, CCIg, CS, etc. merely dissolve BF3, whereas compounds such as ethers, amines, organic acids, tetrahydrofuran, pyridine, piperidine, etc. react with sps to form complex compounds. Alcohols simply dissolve BPx or form complex compounds with BFff.

The contact temperature between the exhaust gas and the organic solvent is usually around room temperature. Moreover, the pressure of the exhaust gas at the time of contact is not particularly limited (although it is preferable to use around normal pressure because the operation is simple.

The method of contact between the exhaust gas and the organic solvent is to use a gas flapper and spray the organic solvent from the top of the gas flapper while the exhaust gas is brought into contact with the organic solvent in a countercurrent flow. A method such as blowing exhaust gas into a filled tank and causing bubbling is preferred because it is simple.

The exhaust gas thus treated can be released into the atmosphere as it is because the concentration of nitrogen fluoride has been removed to a permissible concentration of 10 ppm or less and has been rendered harmless. Also,
BF3 generated by contact with BN is also substantially completely removed by contact with the above-mentioned organic solvent.

Note that the concentration of nitrogen fluoride in the nitrogen fluoride-containing exhaust gas that is the object of the present invention is not particularly limited, and even 100% Nh gas can be easily rendered harmless below the permissible concentration by the method of the present invention. It is.

Furthermore, as a cleaning gas or dry etching gas for CvD equipment, fluorocarbon gas R-13 (monochlorotrifluoromethane), fluorocarbon gas R-14 (
Various fluorocarbon gases such as fluorocarbon gas R-23 (trifluoromethane), fluorocarbon gas R-115 (monochloropentafluoroethane), fluorocarbon gas R-116 (hexafluoroethane), and fluorocarbon gas R-218 (octafluoropropane), Alternatively, a gas such as silicon tetrafluoride (S!F) may also be used.

Therefore, the nitrogen fluoride and nitrogen-containing exhaust gas treated in the present invention may also contain these various fluorocarbon gases and 5iFa gas, but in the present invention, even if these gases are contained, there will be no effect. There is no problem since the nitrogen fluoride is removed without any problem.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 A stainless steel column with an inner diameter of 25 mm and a height of 200 mm was filled with granular h-BN (filling height: 1701111)
After that, the column was heated externally using a heater to maintain the column internal temperature at 250 to 260°C. After that, NF, l gas (purity 99.99% by volume or more) is added to ION ffi/
The column was aerated at a flow rate of 1 h, and the treatment was carried out continuously for 24 hours at the above temperature.

After that, the gas treated above is continuously transferred to the inner diameter 2
00mm, height 1000- led to the bottom of Sono's gas flapper type cleaning tower, and 34 CJh from the top of the tower! Spraying was performed at a flow rate of /sin, and gas cleaning was performed by countercurrent flow. The gas discharged from the top of the column was analyzed over time by gas chromatography, and the main component of the discharged gas was NO, and the concentration of NFs was 1 ppm or less. Also, 8N
BF produced by contact with the gas was not detected, indicating that Nh in the gas was removed extremely well.

In addition, the gas treated by contact with BN was also analyzed by gas chromatography every 2 hours, and the results showed that NF
It can be seen that the concentration of s is less than 1 pp-, and Nh is decomposed extremely well.

Example 2 The column used in Example 1 was filled with granular h-BN (
The filling height is the same as in Example 1), and then a gas having a composition of Nh concentration of 40 volume%, NtPt concentration of 2 volume%, and N2 concentration of 58 volume% was charged at a flow rate of ION fi /h as in Example 1. It was vented and gas treatment was carried out for 24 hours. (however,
(The temperature inside the column was maintained at 200 to 210°C.) Thereafter, the gas treated above was successively introduced to the bottom of the washing tower used in Example 1, and CH30H was poured from the top of the tower by 3i off1i.
Gas cleaning was performed by spraying at a flow rate of n.

The gas discharged from the top of the tower was analyzed by gas chromatography in the same manner as in Example 1. The results showed that the main component of the discharged gas was N2, and the concentration of NF3 was II) 911 or less, Nzh
and BP were not detected, indicating that nitrogen fluoride in the gas was removed extremely well.

Example 3 The column used in Example 1 was filled with Wurzhi BN instead of h-BN, and the temperature inside the column was changed to 350°C, under exactly the same conditions as Example 1. The NFs gas was treated, and then the gas treated above was cleaned under exactly the same conditions as in Example 1. The gas after cleaning was analyzed by gas chromatography, and as in Example 1, the main component of the exhaust gas was N! and NFs
The concentration of NFs was 1 ppm or less, indicating that NFs were removed extremely well.

Example 4 In a tank with an inner diameter of 200+u+ and a height of 5001 (CJs
) t.

(liquid level height: 30 hm), and introduce the gas treated with BN in the same manner as in Example 1 into the bubbling tube (dispersion tube) provided at the bottom of the tank. The gas after cleaning was analyzed by gas chromatography, and the results showed that the main component of the exhaust gas was Nt, as in Example I, and the concentration of NPs was Il1l).
It can be seen that Nh is removed satisfactorily with a value of 11 or less.

Example 5 Exhaust gas was cleaned in the same manner as in Example 4, except that CgllsNHg was used in the tank used in Example 4 instead of (CJsO). The results of gas chromatography analysis of the gas after cleaning showed that the main component of the exhaust gas was N, as in Example 2, and the concentration of NFs was I99m.
It can be seen from the following that NFs is removed extremely well.

〔Effect of the invention〕

As explained in detail above, the present invention involves bringing nitrogen fluoride-containing exhaust gas into contact with BN at a specific temperature, or
This is a simple method in which the contacted exhaust gas is subsequently brought into contact with an organic solvent.

As shown in the examples, the harmful nitrogen fluoride contained in the exhaust gas treated by the method of the present invention has been substantially completely removed, so it is safe to release it into the atmosphere as it is.
It does not have any negative impact on the environment.

Further, since the method of the present invention is as described above, it is possible to detoxify nitrogen fluoride in exhaust gas extremely efficiently and economically. Therefore, the present invention not only contributes to expanding the uses of NF2, but also makes an extremely large contribution to industries such as semiconductor manufacturing.

Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (1)

[Claims] 1) A method for treating nitrogen fluoride-containing exhaust gas, which comprises bringing the nitrogen fluoride-containing exhaust gas into contact with boron nitride at a temperature in the range of 100 to 600°C, and then contacting the nitrogen fluoride-containing exhaust gas with an organic solvent.