JPH0699033A - Hazardous gas purification method - Google Patents

Abstract

PURPOSE:To very efficiently remove nitrogen fluorides as harmful components in gas and to prevent the formation of harmful by-products by bringing the gas into contact with calcium and/or magnesium. CONSTITUTION:Calcium such as metallic calcium or magnesium such as metallic magnesium is used as a purifying agent. This purifying agent is packed into a purifying tube and used in a fixed, moving or fluidized bed. When gas contg. nitrogen fluorides such as nitrogen trifluoride and dinitrogen tetrafluoride is treated, it is allowed to flow in the purifying tube and brought into contact with the purifying agent. The nitrogen fluorides as harmful components contained in the gas are removed, the gas is purified and by-products having a harmful effect on environment are not formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying harmful gases, and more particularly to a method for purifying nitrogen fluoride such as nitrogen trifluoride used in a semiconductor manufacturing process. In recent years, nitrogen trifluoride has been used in dry etching of silicon, silicon oxide and the like, and is also used as a chamber cleaning gas for a CVD apparatus, and the amount thereof is increasing with the development of the semiconductor industry. This gas has a low solubility in water and is fairly stable at room temperature, such as hardly reacting with acids and alkalis, but its permissible concentration is 10 ppm.
Since it is reported that it is highly toxic and adversely affects the human body and the environment, it is necessary to remove harmful components from the gas containing nitrogen trifluoride before it is released into the atmosphere after being used in a semiconductor manufacturing process. Further, although nitrogen trifluoride is stable at room temperature, it produces nitrogen fluorides such as dinitrogen tetrafluoride, dinitrogen difluoride, and dinitrogen hexafluoride due to heat and discharge during the etching and cleaning processes. However, since they are more toxic than nitrogen trifluoride, they must be removed similarly to nitrogen trifluoride.

[0002]

2. Description of the Related Art As a method for removing nitrogen fluoride contained in a gas, (1) 1 has been proposed so far.
Method of contacting with metallic silicon at a temperature of 00 ° C or higher (JP-A-63-12322), (2) Method of contacting with metallic titanium at a temperature of 200 ° C or higher (Japanese Patent Publication No. 63-4857).
1), (3) Si, B, W, Mo, V, Se, Te, G
e and these non-oxide compounds and 200 to 800 ° C.
Contact method (Japanese Patent Publication No. 63-48570), (4)
A method of contacting nitrogen trifluoride with a metal halide capable of halogen exchange (Japanese Patent Publication No. 63-48569), (5) a method of contacting with an oxide of a transition metal at a temperature of 250 ° C. or higher (JP-A-3-181316), (6) Activated carbon and 300-
Method of contacting at 600 ° C. (JP-A-62-23792)
9) etc. have been proposed.

[0003]

However, in the above methods (1), (2), and (3), volatile fluorides, in the method (4), halogens such as chlorine, and (5) are used. In the method, there is a problem that nitrogen oxides are generated respectively, and it is costly to treat them. In the method (6), the reaction is vigorous, and since it is performed at high temperature, there is a risk of explosion, There is a problem that carbon tetrafluoride, which is stable and difficult to remove, is by-produced.

[0004]

The inventors of the present invention have conducted extensive studies to solve these problems, and as a result, by using a purifying agent containing calcium or magnesium, nitrogen fluoride can be extremely efficiently produced. The present invention has been completed by finding that it can be removed and does not produce a substance that adversely affects the environment. That is, the present invention is a method for purifying harmful gas, which comprises contacting a gas containing nitrogen fluoride, which is a harmful component, with calcium and / or magnesium to remove the harmful component. The present invention relates to nitrogen trifluoride contained in air, nitrogen and hydrogen,
Nitrogen fluoride such as dinitrogen tetrafluoride can be efficiently removed.

The purifying agent used in the present invention is metal calcium, metal magnesium or the like, which is usually a commercial product and can be easily obtained. These metals are usually in the form of particles or small particles of about 10 mesh,
Alternatively, it is used as a purifying agent in the form of pellets formed of fine particles of about 100 mesh.

In the present invention, the purifying agent can be used not only as a fixed bed but also as a moving bed or a fluidized bed. Normally, the purifying agent is filled in the purifying cylinder, and the gas containing nitrogen fluoride is caused to flow in the purifying cylinder, and by contacting the purifying agent, the nitrogen fluoride which is a harmful component is removed,
The gas to be treated is purified.

There is no limitation on the flow rate of the gas to be treated to which the purification method of the present invention is applied, but it is generally desirable to reduce the flow rate as the concentration of nitrogen fluoride contained in the gas to be treated is higher. The purification column is designed according to the harmful gas concentration, the amount of gas to be treated, etc., but the harmful gas concentration is 1000 ppm
In the case of the following, it is desirable to design in the range of 20 cm / sec or less, and in the case of the concentration of more than that, it is desirable to design in the range of 5 cm / sec or less.

The contact temperature is usually lower than the melting points of calcium and magnesium (839 ° C. and 649 ° C.), but at least 50 ° C. lower than the respective melting points for the purpose of preventing metal sintering. It is preferable to carry out at temperature. These temperatures are appropriately selected according to the concentration of harmful components, for example, the concentration of nitrogen fluoride is 1
When the concentration is 000 ppm or less, the temperature is from room temperature to 300 ° C, preferably from 100 to 300 ° C, and when the concentration is higher, the temperature is from about 200 to 500 ° C. The pressure at the time of contact is usually normal pressure, but it is also possible to operate under reduced pressure or increased pressure such as 1 kg / cm ² . The filling length of the purifying agent in the purifying cylinder varies depending on the flow rate of gas and the concentration of harmful gas and cannot be specified unconditionally, but in practice, it is usually 50 to 50.
The inside diameter of the purifying cylinder is designed to be about 0 mm and the empty cylinder linear velocity (LV) of the gas flowing in the cylinder is about 5 to 20 cm / sec. Generally, these are determined by the pressure loss of the packed bed, the gas contact efficiency, the concentration of harmful gas, and the like.

[0009]

【Example】

Example 1 84.9 ml of a 6 to 12 mesh purifying agent obtained by sieving commercially available granular calcium (purity 99%) was used to obtain an inner diameter of 19 m.
m, 400 mm long quartz purifying cylinder filled with helium containing 1% nitrogen trifluoride at 400 ° C. under atmospheric pressure 424.5 ml / min (vacuum linear velocity LV = 2.5 cm)
/ Sec), and the outlet gas of the purification column was analyzed by gas chromatography (lower limit of detection: 10 ppm). As a result, nitrogen trifluoride was not detected, and it was allowed to flow for 10 hours, but no breakthrough was observed. In addition, generation of by-products was not observed.

[0010]

【Example】

Example 2 84.9 ml of the purifying cylinder used in Example 1 was filled with commercially available magnesium flakes (purity 97% or more), and nitrogen containing 5000 ppm of nitrogen trifluoride was added thereto at 250 ° C. under normal pressure of 424. 5 ml / min (Cylindrical linear velocity LV = 2.5
cm / sec), and the outlet gas of the purification column was analyzed by gas chromatography. As a result, nitrogen trifluoride was not detected, and it was allowed to flow for 15 hours, but no breakthrough was observed. In addition, generation of by-products was not observed.

[0011]

According to the method for purifying gas of the present invention, nitrogen fluoride contained in the gas can be efficiently removed and harmful by-products are not generated, and the gas can be discharged in the semiconductor manufacturing process or the like. An excellent effect for gas purification can be obtained.

Claims (2)

[Claims] 1. A method of purifying a harmful gas, which comprises contacting a gas containing nitrogen fluoride, which is a harmful component, with calcium and / or magnesium to remove the harmful component. 2. Nitrogen fluoride is nitrogen trifluoride, dinitrogen tetrafluoride,
One or two selected from dinitrogen difluoride and dinitrogen hexafluoride
The purification method according to claim 1, wherein the purification method is one or more kinds.