JP3188830B2 - Method and apparatus for removing NF3 exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for removing NF ₃ exhaust gas generated during the production of semiconductors and the like.

[0002]

2. Description of the Related Art In recent years, NF ₃ has been used as a cleaning gas for a CVD apparatus, but about 1/3 to 1/2 of it is discharged from the apparatus without being reacted. Since NF ₃ is a gas having a toxicity similar to that of CO, it is necessary to remove exhaust gas containing NF ₃ in advance when releasing it into the environment.

[0003] As a method of removing NF ₃ , (a) NF ₃
A gas containing water and NF ₃ reacted with water to decompose (JP-A-3-65218), (b) NF ₃
And a method of reacting the oxidative decomposition product with NH ₃ while heating and oxidatively decomposing an exhaust gas containing the same (JP-A-4-290524).

However, in the above method (a), since the NO _X is produced as a by-product in a large amount with harmful hydrogen fluoride, it is necessary these secondary abatement, also large corrosive by acidic gases Therefore, there is a problem that an expensive material device is required. In addition, in the method (b), corrosion due to acidic gas is reduced, but the reaction requires a high temperature (about 1000 ° C.) by external heating, and furthermore, the decomposition reaction section is in an oxidizing atmosphere, which is caused by it. Since the corrosion occurs, there is a problem that an expensive device is required as in the method (a).

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to treat NF ₃ exhaust gas safely, efficiently and at low cost so that there is no problem of environmental pollution. It is an object of the present invention to provide a method and apparatus for removing NF ₃ exhaust gas which is rendered harmless.

[0006]

Means for Solving the Problems The inventors of the present invention mixed NF ₃ -containing exhaust gas with ammonia gas, and heated and reacted in a reducing atmosphere in the presence of steam, whereby NF ₃ was converted to nitrogen and fluorine. By neutralizing and removing the hydrogen fluoride generated as a result of being decomposed into hydrogen fluoride as an ammonium salt, NF ₃ is produced at a lower temperature than before and with no by-product of NO _x.
Was found to be harmless, and the present invention was completed. That is, the gist of the present invention is to add water and ammonia gas to a gas containing NF ₃ and heat and react the mixture under a reducing atmosphere to decompose NF ₃ into nitrogen and hydrogen fluoride. A method for removing NF ₃ exhaust gas, which neutralizes and removes generated hydrogen fluoride as an ammonium salt, and an apparatus therefor.

[0007] In the present invention, NF ₃ reacts with water, hydrogen fluoride is believed to be degraded in the NO _X, etc. _{(2NF 3 + 3H 2 0 →} N0 + N0 2 + 6HF). The hydrogen fluoride generated here reacts with ammonia to form ammonium fluoride, and NO _X also reacts with ammonia to be finally decomposed into nitrogen and water. Further, NF ₃ is considered both direct reaction with ammonia is decomposed into hydrogen fluoride and nitrogen _{(NF 3 + NH 3 → N} 2 + 3HF).

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the method and apparatus of the present invention will be described in detail. FIG. 1 is a diagram showing an outline of an NF ₃ exhaust gas abatement apparatus according to the present invention.

In the present invention, water and ammonia gas are added to the NF ₃ -containing exhaust gas, and the reaction is carried out in a reducing atmosphere free of oxygen, air and the like. In the method of heating and reacting in a reducing atmosphere, particularly, ammonia gas is flammable, so that when both gases are mixed, explosive gas is formed in a certain concentration range. Therefore, for the purpose of avoiding detonation, NF
₍₃₎ A method of diluting the solution so that the concentration becomes 1 vol% or less, preferably 0.5 vol% or less is suitable. For example, the NF ₃ -containing exhaust gas may be diluted to the above concentration with N ₂ supplied from the N ₂ inflow pipe (11).

The NF ₃ -containing exhaust gas introduced from the exhaust gas inflow pipe (1) is diluted with nitrogen gas from the N ₂ inflow pipe (11). By introducing the diluted exhaust gas into the inlet scrubber (8), spraying water from above and bringing it into contact with the gas,
Add water. In this case, the amount of water added is determined by the amount of N in the exhaust gas.
Although it is proportional to the amount of F ₃ , it is usually preferably at least twice as much as NF ₃ .

The exhaust gas to which a predetermined amount of water has been added is
NH ₃ from the inflow pipe (6) is added NH ₃ gas, the reaction portion (2)
Is led to and heated by the heater element (5), NF ₃ is reduced and decomposed into hydrogen fluoride and NO _X react with water. The amount of ammonia used is proportional to the amount of reaction products of NF ₃ and NF ₃ and water, or 4 fold molar usually NF ₃ are preferred.

The reaction section (2) used in the present invention is not particularly limited. For example, a reaction section having an electrically controllable heater element inside the reaction section is preferable. Reaction temperature is usually 300 ° C to 700 ° C, more preferably 450 ° C.
In the range of ~ 650 ° C. In the present invention, since the thermal decomposition of the NF ₃ -containing exhaust gas is performed in a reducing atmosphere to which oxygen, air, and the like are not added, the reaction can be performed at a low temperature of 100 ° C. or more as compared with the conventional thermal oxidative decomposition. is there.

Furthermore, NO _X and fluorinated Mizugyo reacts with ammonia N _2, H ₂ 0, decomposed into ammonium fluoride,
Neutralized. The heated and decomposed exhaust gas continues to
It is introduced into the outlet scrubber (9) and washed with water. The method of this water washing treatment is not particularly limited, but it can be carried out by spraying water from above and contacting with a treatment gas. This makes it possible to absorb and remove water-soluble components such as ammonium fluoride generated from hydrogen fluoride and ammonia. After being washed and cooled with cooling water to absorb and remove ammonium fluoride and the like to render them harmless, they are discharged from the exhaust pipe (4).

Cooling water is supplied from a water supply pipe (7) to a washing water tank (3), is pressurized by a pump (10), and is supplied to an inlet scrubber (8).
And the water is supplied to the outlet scrubber (9). The inlet scrubber (8) performs the functions of dissolving and separating acidic components in the exhaust gas and supplying water. The outlet scrubber (9) has a main function of absorbing and removing ammonium fluoride and excess ammonia, and gas cooling. The acidic washing water in the inlet scrubber (8) is neutralized by the water in the washing water tank (3) and discharged from the drain pipe (13).

[0015]

【Example】

[Example 1] Nitrogen containing 10 vol% of NF ₃ was introduced into the inlet scrubber (8) from the exhaust gas inlet pipe (1) at 5 liter / minute and nitrogen from the N ₂ inlet pipe (11) at 250 liter / minute. Then, water was added at a rate of 5 liters / minute in terms of steam. Then, NH ₃ gas from the NH ₃ inlet tube (6), was added at 10 l / min was introduced into the reaction unit (2), reaction temperature 550 ° C., and reacted at the contact time of 5 seconds. The gas after the reaction is the outlet scrubber (9)
And washed with water. NF ₃ gas concentration in outlet gas is 5ppm, NO
_{The X} concentration was 3 ppm or less, and the hydrogen fluoride concentration was 0.5 ppm or less.

Example 2 CV containing about 1.5 vol% of NF ₃
D cleaning exhaust gas at 50 l / min
Except for introducing from (1), treatment was performed under the same conditions as in Example 1. NF ₃ gas concentration in the outlet gas is 8 ppm, NO _X concentration 5ppm or less, the hydrogen fluoride concentration was less than 0.5 ppm.

[0017]

According to the present invention, NF ₃ can be decomposed at a relatively low temperature and in a short time, and there is no by-product of NO _X or corrosion of the device, and NF ₃ is safe and has a low running cost.
An exhaust gas removing method and a removing device can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of an NF ₃ exhaust gas abatement apparatus according to the present invention.

[Explanation of symbols]

(1) Exhaust gas inlet pipe (2) Reactor (3) Rinse water tank (4) Exhaust pipe (5) Heater element (6) NH ₃ inlet pipe (7) Feed pipe (8) Inlet scrubber (9) Outlet scrubber ( 10) Pump (11) N ₂ inlet pipe (12) Baffle plate (13) Drain pipe

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-65218 (JP, A) JP-A-4-290524 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53/68 B01D 53/54

Claims (2)

(57) [Claims] 1. Water and ammonia gas are added to a gas containing NF ₃ , and the mixture is heated and reacted under a reducing atmosphere to decompose NF ₃ into nitrogen and hydrogen fluoride, and to generate HF. Neutralizes hydrogen hydride as ammonium salt,
A method for removing NF ₃ exhaust gas, which comprises removing the harmful substances. 2. A heating unit having a reaction unit for adding water and ammonia gas to a gas containing NF ₃ and heating and reacting the mixture in a reducing atmosphere to decompose NF ₃ into nitrogen and hydrogen fluoride. An abatement device for NF ₃ exhaust gas, comprising: a decomposition device; and an abatement device that neutralizes and removes generated hydrogen fluoride as an ammonium salt.