JP2002068716A - Method of refining high purity nf3 gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method to continuously and consistently refine a high purity NF3 gas. SOLUTION: This is a method to clean a crude NF3 gas containing impurities such as HF, CO2, N2O and the like by water and/or aqueous alkaline solution and/or aqueous reducing solution and thereafter to remove water content from the NF3 gas containing moisture by liquefaction or solidification with a heat exchange refining device using liquid NF3 as cooling medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying NF ₃ gas, and more particularly to a method for removing water from NF ₃ gas.

[0002]

2. Description of the Related Art NF ₃ gas is used for electronic materials, especially for CV.
In recent years, it has attracted attention as a cleaning gas for D devices and as a cleaning agent for semiconductor dry etching and for cleaning single-wafer devices in the field of TFT liquid crystals. And NF ₃ used for these applications
Gases are increasingly required to be of high purity.

[0003] NF_ThreeThe gas production method is NH_FourF ・ χHF
(Χ = 1 to 2) is used as an electrolytic solution.
F obtained by electrolysis and electrolysis using HF as an electrolyte
_TwoNH in gas_ThreeThere is an indirect electrolysis method of contacting with. these
In either method, the obtained NF_ThreeSome are HF, O
F_Two, N_TwoF_Two, N _TwoF_Four, CO_Two, N_TwoContains impurities such as O
It is rare. Of these impurities, HF, OF_Two, C
O_TwoRemoval using an aqueous alkaline solution,_TwoO
Removal method using aqueous sodium thiosulfate solution
("Fluorine Chemistry and Industry, Progress and Applications", edited by Shinjun Watanabe: Chemistry
Published by Kogyosha (1973), p. 208).

[0004] However, the N 2 which has been cleaned by these methods is used.
Each of the F ₃ gases results in containing moisture. Therefore,
Usually, in the post-washing step, a refrigerant such as liquid nitrogen or liquid carbon dioxide is used to liquefy or solidify the water to separate it, or an adsorbent is used to adsorb and remove these impurities (US Patent No. No. 4,156,598). In a purification method using a cold trap, NF
_When these separation and purification operations are performed using liquid nitrogen (bp: -196 ° C), which is a refrigerant having a boiling point lower than ₃ , NF ₃ (b.
(p: -129 ° C) Because it liquefies itself, the pressure balance in the system is modulated, making it difficult to continue operation.

In order to prevent NF ₃ from being liquefied, if a refrigerant having a high boiling point such as liquid carbon dioxide (bp: -79 ° C.) is used or the cooling temperature is controlled, the gas dew point can be sufficiently lowered. However, the separation of water is insufficient and the purity of the product is reduced, and there are problems such as insufficient capacity of the purification device.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the drawbacks of the above-mentioned refining apparatus and to stably produce high-purity NF ₃ gas.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for stably purifying NF ₃ gas to a high purity, and as a result, it has been found that crude NF ₃ gas containing water after being subjected to cleaning treatment is used. In the method of liquefying or solidifying, separating and refining, by using liquefied NF ₃ as a refrigerant, it is possible to prevent liquefaction of a conventionally difficult product NF _{3 in} a purification device, It has been found that it enables stable continuous operation and can meet the needs of high purity.
The present invention has been completed.

That is, in the present invention, after removing crude NF ₃ gas containing impurities such as HF, CO ₂ and N ₂ O by washing with water and / or an alkaline aqueous solution and / or a reducing aqueous solution, water is removed. and the water of the crude NF ₃ gas is liquefied or solidified, including the separation of these impurities, a method of performing purification by using a liquefied NF ₃ as the refrigerant, which has heretofore been difficult, liquefaction of NF ₃ as a product This is a method for purifying high-purity NF ₃ gas that prevents the occurrence of NF ₃ gas and enables stable continuous operation.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. As a method for removing the crude NF ₃ gas containing impurities such as HF, CO ₂ and N ₂ O using an alkaline aqueous solution and / or a reducing aqueous solution, a gas scrubber is used to circulate the above aqueous solution. A method of passing a crude NF ₃ gas is preferably used.

The alkaline aqueous solution used in the present invention includes:
An aqueous solution of a hydroxide of an alkali metal or alkaline earth metal group is used. KI, H
At least one aqueous solution selected from the group consisting of I, Na ₂ S, Na ₂ S ₂ O ₃ and Na ₂ SO ₃ is used. The NF ₃ gas cleaned by the gas scrubber using the alkaline aqueous solution and / or the reducing aqueous solution varies depending on the temperature of the aqueous solution, the structure of the gas scrubber, and the like, but the crude NF ₃ gas containing tens to thousands of ppm of water. As discharged from the scrubber. Therefore, the crude NF ₃ gas containing water is purified using a heat exchange type purification device using liquefied NF ₃ as a refrigerant.

The structure of the heat exchange type refining apparatus used in the present invention is not particularly limited, and a general double tube type, multi-tube type, coil type, or the like is used. Although it is not particularly limited as long as it is a material in consideration of the above, a material made of SUS is usually used.

Next, the present invention will be described with reference to FIG.
Crude NF ₃ gas is washed with an alkaline washing tower or the like, the crude NF ₃
The water enters the purifier through a conduit, is cooled by liquefied refrigerant NF ₃ (bp: -129 ° C.) supplied from the NF ₃ storage tank, and water is condensed or solidified and separated in the purifier. The purified NF ₃ is passed through a purified NF ₃ conduit
It led to F ₃ storage tank, with a stored product is used as a refrigerant. Liquid nitrogen or the like is used to cool the NF _{3 in} the storage tank.

Since the condensed or condensed water accumulates in the refining apparatus which has been operated for a certain period of time, a plurality of refining apparatuses are usually installed and periodically switched. After switching the purifier, heated nitrogen is flowed in place of the refrigerant, and the frozen water is thawed and discharged outside the system to prepare for the next operation.

[0014]

The present invention will be described below with reference to examples and comparative examples. Hereinafter,% is represented by weight and ppm is represented by volume.

Embodiment 1 NF_FourElectrolysis using an electrolytic solution of F1.7 HF
NF_ThreeGas was evolved. This crude NF_ThreeMoth
Using a two-stage gas scrubber, the first stage has a 3%
Contact with aqueous sodium osulphate solution_TwoAs well as other oxidation
In the second stage, 10% sodium hydroxide is removed.
CO_TwoWas removed. This second stage gas
The gas at the outlet of the scrubber is analyzed by gas chromatography and / or
Is 6% when analyzed by FT-IR, moisture meter, etc.
Was included. Crude NF containing this water_ThreeThe gas in Figure 1
Liquefied NF for refrigerant_ThreeCirculating quantity and coarse
NF _ThreeWas purified. 24 hours after aeration, purified NF_Three
Dew point gauge at conduit outlet (Panametric Japan: SER
When the water content was analyzed by I-ES35), it was 1 ppm or less.
Was decreasing. In this state, operation was performed for 7 consecutive days.
But during the period NF_ThreeOperation due to pressure fluctuations in the system due to liquefaction
There was no trouble and stable operation was possible.

Comparative Example 1 The crude NF ₃ gas obtained in the same manner as in Example 1 was introduced into the purification apparatus shown in FIG. 1 by changing the refrigerant from liquid liquefied NF ₃ for cooling to liquid nitrogen, and the liquid nitrogen for refrigerant was obtained. The crude NF ₃ was purified by circulation. After 10 hours of aeration, the pressure was fluctuated in the system due to a phenomenon considered to be condensation of the crude NF ₃ gas in the purification device, and the operation was stopped.

[0017] The crude NF ₃ gas obtained in the same manner as in Comparative Example 2 Example 1, in place of the coolant from the cooling liquefied NF ₃ in the liquid carbon dioxide, leads to purification device shown in FIG. 1, liquid carbon refrigerant The gas was circulated to purify the crude NF ₃ . After 24 hours of aeration, purified NF ₃
Dew point gauge at conduit outlet (Panametric Japan: SER
When the water content was analyzed by I-ES35), the operation was stopped because it was 6 ppm, which greatly deviated from the standard (1 ppm).

[0018]

According to the present invention, HF and O in crude NF ₃ gas are used.
This is a method of removing moisture of NF ₃ gas including moisture after removing impurities such as F ₂ , N ₂ F ₂ , N ₂ F ₄ and CO ₂ by a washing tower or the like. By this method, it is possible to realize a NF ₃ production process that can prevent pressure fluctuation in the system due to condensation of crude NF ₃ generated in the conventional dehydration step and can operate stably for a long period of time. Big.

[Brief description of the drawings]

FIG. 1 is a diagram showing a flow of a purification device.

[Explanation of symbols]

1 purifier 2 NF ₃ storage tank 3 crude NF ₃ conduit 4 purified NF ₃ conduit 5 refrigerant liquefied NF ₃ 6 impurity exhaust valve 7 liquefied NF ₃ 8 liquid nitrogen 9 heated nitrogen inlet 10 heated nitrogen outlet 11 coolant liquid nitrogen or liquid Carbon dioxide inlet 12 Liquid nitrogen or refrigerant carbon dioxide outlet for refrigerant

Continued on the front page (72) Inventor Hiromi Hayashida 7-1-1, Hikoshimasako-cho, Shimonoseki-shi, Yamaguchi Prefecture F-term in Mitsui Chemicals Co., Ltd. HA12 JA02

Claims (1)

[Claims] 1. A method for cleaning and removing a crude nitrogen trifluoride (NF ₃ ) gas containing impurities using water and / or an alkaline aqueous solution and / or a reducing aqueous solution, and then removing the nitrogen trifluoride gas containing the water. via the use of an apparatus for purifying the heat exchange type, remove liquefied or solidified water, in the method for purifying a high-purity NF ₃ purification process of the gas, which comprises using a liquid NF ₃ into the refrigerant.