JPH0720537B2 - Chemical vapor deposition exhaust gas treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to chemical vapor deposition (CVD).
The present invention relates to a method for treating exhaust gas generated during treatment, and more particularly to a method for removing volatile fluoride contained in the exhaust gas.

[Conventional technology and problems]

CVD is used in many industrial fields such as cutting tools, cemented carbide for press molds, high temperature oxidation resistant coatings, special composite materials for space development, and semiconductors.

The principle of this CVD method is to bring a mixed gas consisting of a metal compound, hydrogen and, in some cases, a third component into contact with the surface of a heated base material in a system in which the base material is heated to cause a gas-phase chemical reaction. In this method, a metal is deposited on the surface to form a coating. By using this method, it becomes possible to plate metals and metal compounds such as W, Mo, Re, Ti, and Zr, which are difficult to obtain by ordinary plating, and the various applications described above have been developed.

Although various metal compounds are used for CVD, they have been widely used recently because the use of volatile fluorides enables CVD at relatively low temperatures. A so-called wet alkaline cleaning method is used to treat the exhaust gas in this CVD, but it is difficult to use when performing CVD under reduced pressure, and back diffusion of water becomes a problem when high accuracy is required. Become.

It is an object of the present invention to provide a dry exhaust gas treatment method applicable to CVD under reduced pressure, which is difficult to apply by a conventional wet alkaline cleaning method, and CVD that requires high accuracy.

[Means for solving problems]

The present invention is to cool the exhaust gas deeply, and then to remove the fluoride by performing an adsorption treatment.First, the exhaust gas from the CVD apparatus is cooled to -100 to -170 ° C using liquid nitrogen or the like. In this method, most of the volatile fluorides in the exhaust gas are condensed or solidified and removed, and the uncondensed fluorides are removed by an adsorbent. Liquid nitrogen is most preferable as the cooling medium for deep cooling because of its ease of handling and cooling temperature, but it is not limited to liquid nitrogen.

The adsorbent used is a combination of sodium fluoride and soda lime, and optionally activated alumina. Sodium fluoride primarily removes hydrogen fluoride and soda lime removes other volatile fluorides by chemisorption. Alumina adsorbs and removes soda-lime powder and water, and also adsorbs water mixed in by back diffusion.

〔Example〕

 The present invention will be specifically described below with reference to examples.

Reference Example 1 H ₂ gas 5 / min containing 50 vol% HF was introduced into a cold trap device that had been cooled to about −150 ° C. with liquid nitrogen in advance. Most of the HF is removed and the gas exhausted here is
The HF concentration was 0.07vol%. HF is removed by passing this gas through an adsorption tower filled with sodium fluoride particles. The HF gas concentration discharged from the adsorption tower became 0.5 ppm or less.

Reference example 2 The pressure inside the system was set to about 100 torr using an ejector. H ₂ gas containing 50 vol% HF therein was passed through the cold trap of Reference Example 1 and an adsorption tower of sodium fluoride particles at a rate of 700 ml / min. At this time, the HF concentration discharged from the adsorption tower is about 5 p
It was pm. When this gas is passed through a soda lime packed tower, HF
The concentration fell below 0.1 ppm.

Reference Example 3 As a result of conducting an experiment by mixing 10 ml / min of WF _{6 under} the same conditions as in Reference Example 2, most of WF ₆ was removed by a cold trap. However, about 100 ppm of WF ₆ was contained in the exhaust gas, which could not be removed by sodium fluoride particles.
However, it was completely removed with soda lime, and W was not detected after passing through this adsorption tower.

Example 1 Exhaust gas 4 consisting of HF 48 vol%, WF _{6 2} vol% and H ₂ 50 vol% 4
00 / min (50 torr) was introduced into the cold trap device which had been previously cooled to about -150 ° C with liquid N ₂ . Although most of HF and WF ₆ were removed with this cold trap device,
HF 3% and WF ₆ 60ppm were desired in the exhaust gas.

As a result of passing this exhaust gas through a sodium fluoride particle packed tower and then a soda lime packed tower (both inner diameter 250 mm, packed height 500 mm), HF in the gas discharged from the soda lime packed tower was
It became 0.1 ppm or less, and WF ₆ was not detected.

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Claims (2)

[Claims] 1. A method for treating a chemical vapor deposition exhaust gas, which comprises chilling a chemical vapor deposition exhaust gas under reduced pressure, followed by adsorption treatment with sodium fluoride and soda lime to remove fluoride. 2. The processing method according to claim 1, wherein deep cooling is performed using liquid nitrogen.