JPH10286434A - Decomposing method of fluorine-containing gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable continuous decomposition of a perfluoro compd. even among fluorine-contg. compds. by bringing a gaseous fluorine-contg. compd. into contact with molecular oxygen in the presence of alumina. SOLUTION: When a gaseous fluorine-contg. compd. (such as perfluoro compds. and fluorinated hydrocarbons) used as a chamber cleaning gas for plasma CVD in a semiconductor factory is to be decomposed, the fluorine-contg. gas is brought into contact with molecular oxygen in the presence of alumina as a catalyst. As for the alumina, for example, γ-alumina and δ-alumina can be used, and the specific surface area of the alumina is preferably about 120 to 200 m<2> /g. The shape of the alumina is not limited but properly selected such as granules and a honeycomb according to the reactor and the reaction method. As for the molecular oxygen, a gas prepared by diluting oxygen gas with inert gas such as nitrogen can be used, however, air is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a fluorine-containing compound, particularly a gaseous fluorine-containing compound (perfluoro compound, fluorinated hydrocarbon, etc.) used as a plasma CVD chamber cleaning gas in a semiconductor factory, and the like. ,
The present invention relates to a method for decomposing a gaseous fluorine-containing compound (such as chlorofluorocarbon) used in a refrigerant or the like.

[0002]

2. Description of the Related Art Fluorine-containing compounds (gaseous fluorine-containing compounds) affect the global environment, for example, by being involved in the destruction of the ozone layer.
Of these, perfluoro compounds (hereinafter abbreviated as PFCs) are those in which all of the hydrogen atoms of the hydrocarbon are replaced with fluorine atoms, and unlike fluorocarbon, do not contain chlorine and are very stable. Although not involved in the depletion of the ozone layer, it has a large global warming potential, and emissions after use may be regulated in the future.

In order to suppress the emission of such gaseous fluorine-containing compounds, it is necessary to recover or decompose the used exhaust gas by some method. However, considering the simplicity of the method, the latter exhaust gas is required. Is preferred. However, among the fluorine-containing compounds, PFC is very stable, so that it is difficult to treat the PFC by a method used in the usual chlorofluorocarbon decomposition. For example, in the method of decomposing by burning together with fuel, a high temperature of 1000 ° C. or more is required. In addition, a method of decomposing using silica, zeolite, or the like as a decomposing agent (Japanese Patent Application Laid-Open No. 7-116466,
No. 132211) requires a high temperature of about 1000 to 1500 ° C. in order to decompose PFC at a sufficient rate. It is complicated and complicated, and further improvement is required.

[0004]

SUMMARY OF THE INVENTION In view of the above technical background, the present invention relates to a method capable of continuously decomposing a fluorine-containing compound (a gaseous fluorine-containing compound), in particular, a PFC, particularly a catalytic continuous decomposition. It is an object to provide a method that can be used.

[0005]

The object of the present invention is achieved by a method for decomposing a fluorine-containing compound, which comprises contacting a gaseous fluorine-containing compound with molecular oxygen in the presence of alumina.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Examples of the fluorine-containing compound include gaseous fluorine-containing compounds (perfluoro compounds (PFC), fluorinated hydrocarbons, etc.) used in plasma CVD chamber cleaning gases at semiconductor factories. A gaseous fluorine-containing compound (such as chlorofluorocarbon) used for a refrigerant or the like is used. These fluorine-containing compounds (gaseous fluorine-containing compounds) may be diluted with an inert gas such as helium, argon, or nitrogen, or may be used alone or as a mixture of two or more. .

As PFC, CF_Four, C_TwoF₆, C_Three
F₈All hydrogen atoms of hydrocarbons such as
Perfluorocarbons (including saturated and unsaturated),
NF _ThreeSuch as nitrogen fluoride and SF₆Such as sulfur fluoride
No. As the fluorinated hydrocarbon, CH_ThreeF, CH
_TwoF_Two, (CH_TwoF)_TwoPart of hydrogen atoms of hydrocarbons such as
Is substituted with a fluorine atom. Flow
As C_TwoCl_ThreeF_Three(CFC-113), C_Two
Cl_TwoF_Four(CFC-114), C_TwoClF_Five(CFC
-115).

In the present invention, the fluorine-containing gas is decomposed by bringing the fluorine-containing gas into contact with molecular oxygen in the presence of alumina as a catalyst. As the alumina, for example, γ-alumina, δ-alumina, θ
-Commercially available alumina such as alumina can be used. The specific surface area of alumina is 120 to ²⁰⁰ m ² /
It is preferably about g. The shape of the alumina is not particularly limited, and a shape suitable for each, such as a granular shape, a powder shape, and a honeycomb shape, can be selected according to the reactor and the reaction method.

The above alumina is used at 100 to 1000 ° C., particularly 400 to 8 ° C. in an inert gas stream such as nitrogen or air.
After baking at 00 ° C. for several hours, it is preferably used to decompose the fluorine-containing gas. At this time, firing at an excessively high temperature is not preferable because the surface area decreases.
This baking may be performed using a muffle furnace or the like, or may be performed in advance before filling the reactor (reaction tube) for decomposing the fluorine-containing gas to start the decomposition reaction.

[0010] As the molecular oxygen, oxygen gas diluted with an inert gas such as nitrogen can be used, but air is preferably used. The supply amount of molecular oxygen is not particularly limited as long as it is an amount sufficient to convert the carbon content (carbon atom) in the fluorine-containing compound into carbon dioxide and carbon monoxide. That is, the supply amount of molecular oxygen is at least equimolar to the carbon atom in the fluorine-containing compound, preferably about equimolar to about 10 times. The method for supplying molecular oxygen is not particularly limited, and examples thereof include a method of mixing with a fluorine-containing compound and supplying the mixture to a reactor (reaction tube).

In the present invention, water can be added in the contact. By adding water, the throughput of the fluorine-containing compound per unit alumina weight or volume can be increased. When water is not added, fluoride and the like accumulate on the alumina surface as the decomposition reaction proceeds, and the decomposition rate of the fluorine-containing compound gradually decreases. Become. The amount of water added may be at least equimolar to the halogen content (fluorine atom and chlorine atom) in the fluorine-containing compound, and preferably about equimolar to about 10-fold molar. For example, CF
If ₄ 4 moles or more, preferably a 4 to 40-fold moles, C ₂ F ₆ in the case when 6 moles or more, preferably 6
It may be about 60-fold molar. The method of adding water is not particularly limited, and examples thereof include a method of supplying a liquid to a reactor (reaction tube) using a microfeeder, and a method of using a saturator to accompany the fluorine-containing compound.

In the decomposition of the fluorine-containing compound of the present invention, for example, a mixed gas of the above-mentioned fluorine-containing compound and molecular oxygen (containing water if necessary) is mixed with 300 to 1000.
C., preferably at 400 to 800.degree. C., by feeding to a reactor (reaction tube) filled with alumina.
At this time, the feed rate of the mixed gas is 50000Hr ^-1 or less, preferably 100~10000hr about ^-1.
Further, the reaction pressure can be in a wide range from a reduced pressure of 1 torr to a pressurized pressure of 100 atm, but is preferably from normal pressure to about 10 atm. The decomposition reaction can be carried out by a flow system or a batch system, but the former flow system is preferred because of its simplicity. In the case of a flow type, the reaction can be carried out in any of a fixed bed and a fluidized bed.

[0013]

Next, the present invention will be described specifically with reference to examples and comparative examples. The following operations were performed under normal pressure unless otherwise specified. In addition, fluorine-containing compounds (C
Conversion of ₂ F ₆₎ was determined by the following equation.

[0014]

(Equation 1)

Example 1 A granular γ-alumina (1.0 m) was placed in a reaction tube having an inner diameter of 10 mm.
l) and fired at 600 ° C. for 1 hour in a nitrogen stream. Thereafter, a C ₂ F ₆ / air mixed gas (C ₂ F ₆ : 1% by volume) was supplied at a rate of 100 ml / min, and water was supplied at a rate of 0.96 g / hr.
And supplied to the reaction tubes to perform a decomposition reaction at the same temperature. When the concentration of C ₂ F ₆ in the outlet gas (remaining amount of C ₂ F ₆ ) was analyzed by gas chromatography, it was found that C ₂ F ₆
The conversion was 4.5% one hour after the start of the reaction. In addition,
As reaction products, carbon dioxide was confirmed by gas chromatography, and carbon monoxide was confirmed by FT-IR.

Example 2 A reaction was carried out in the same manner as in Example 1 except that the reaction temperature was changed to 700 ° C. As a result, C ₂ F
_{6 The} conversion was 10.0% one hour after the start of the reaction.

Comparative Examples 1-4 In Example 1, silica instead of γ-alumina was used.
The reaction was carried out in the same manner as in Example 1 except that 1.0 ml of each of silica-titania, titania and zirconia was used. As a result, the C ₂ F ₆ conversion was 0.0%, 0.0%, 0.0%, and 0.2%, respectively, one hour after the start of the reaction.

Example 3 In Example 1, 5.0 ml of granular γ-alumina was charged, and a mixed gas of C ₂ F ₆ / air (C ₂ F ₆ : 1% by volume) was used.
The reaction was carried out in the same manner as in Example 1 except that water was supplied at 20 ml / min and water was supplied at 0.36 g / hr. As a result, the C ₂ F ₆ conversion was 59% one hour after the start of the reaction,
Two hours after the start of the reaction, it was 21%.

Example 4 A reaction was carried out in the same manner as in Example 3 except that the reaction temperature was changed to 700 ° C. and water was not supplied.
As a result, the C ₂ F ₆ conversion was 100 hours after the start of the reaction.
% After 3 hours.

[0020]

According to the present invention, it is possible to use a readily available and relatively inexpensive alumina as a catalyst in a simple reactor and to perform plasma CVD in a semiconductor plant such as PFC which is very stable and difficult to process. It is possible to continuously decompose a fluorine-containing compound used for a chamber cleaning gas or the like. This method is a method for treating a gaseous fluorine-containing compound, which is very friendly to the global environment because the generated gas is carbon dioxide or the like.

Continued on the front page (72) Inventor Tokuo Matsuzaki 5 Ube Kogushi 1978 Kobe, Ube City, Yamaguchi Prefecture

Claims (2)

[Claims] 1. A method for decomposing a fluorine-containing compound, comprising contacting a gaseous fluorine-containing compound with molecular oxygen in the presence of alumina. 2. The method for decomposing a fluorine-containing compound according to claim 1, wherein the gaseous fluorine-containing compound is a perfluoro compound, a fluorinated hydrocarbon or chlorofluorocarbon.