JPS61247609A - Purifying method for nitrogen trifluoride - Google Patents

Abstract

PURPOSE:To purify NF3 contg. N2F2 or N2F2 plus N2O as impurities by removing impurities by one step without requiring troublesome procedures with continuous operation being realized for a long period by allowing NF3 contg. the impurities to contact with active carbon. CONSTITUTION:NF3 contg. N2F2 or N2F2 puls N2O is allowed to contact with active carbon. Impurities are removed by one step at room temp. continuously for a long period without requiring troublesome procedures. Any kind of active carbon, such as coconut shell active carbon, or that derived from petroleum or coal, etc., is useful. Crude NF3 and relatively low purity NF3 prepd. by the conventional process are both purified by this method. When NF3 is used as cleaning gas of a CVD device, both waste gas can be treated by this process to purify the contaminated NF3 thus permitting reutilization. Effective utilization of expensive NF3 has become possible.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing highly pure arsenic nitrogen suitable for use as a dry etching gas for ultra-LS.

More specifically, dinitrogen difluoride (N2F2) or nitrogen fluoride (NF), which includes dinitrogen difluoride and nitrous oxide (N20),
The present invention relates to a method for purifying nitrogen fluoride by removing dinitrogen difluoride or dinitrogen difluoride and arsenite ffi in one step by contacting 3) with activated carbon.

Nitrogen is used as a fluorine source for chemical lasers or as a cleaning gas for CVD equipment, and in recent years, it has been used as a dry etching agent for VLSIs to remove deposits on silicon substrates compared to fluorocarbon-based etching agents. It is a useful gas that is attracting attention because of its excellent etching rate and selectivity. When used as a dry etching gas, especially high purity
Arsenic nitrogen is required.

The types and composition of impurities contained in nitrogen fluoride vary somewhat depending on the method for producing nitrogen fluoride, but generally dinitrogen difluoride and nitrous oxide are mainly included.

Traditionally, there are several methods for purifying nitrogen fluoride.

(1) Method of dividing crude nitrogen fluoride gas after liquid ripping it at liquid nitrogen temperature (NF3B, P, -129°C, N2F2B, P, -1
06~-111℃.

N20BP, -89°C) (2) An adsorption method using a zeolite adsorbent was used.

By the way, method (1) requires a relatively complicated device and requires complicated low-flow operations, and method (2) requires insufficient performance of the zeolite adsorbent, and the adsorbent's performance is insufficient. In order to extend the service life, it is necessary to reduce the concentration of dinitrogen difluoride to a very low level in the previous step (Japanese Patent Application Laid-open No. 161588/1983).

Problems to be Solved by the Invention In consideration of the above circumstances, the present invention solves the problem of using dinitrogen difluoride or dinitrogen fluoride containing dinitrogen difluoride and arsenite, which requires complicated operations. The purpose of the present invention is to provide a method for purifying nitrogen fluoride, which has the feature of removing dinitrogen difluoride or dinitrogen difluoride and arsenite nitrous oxide in one step continuously for a long period of time without the need for purification. .

Means for Solving the Problems In order to achieve the above object, as a result of repeated studies, the present inventors discovered that dinitrogen difluoride or dinitrogen difluoride contained in nitrogen fluoride as a main impurity We have discovered that activated carbon is uniquely superior in removing dinitrogen fluoride and nitrous oxide.

That is, the gist of the present invention is to contact dinitrogen difluoride or dinitrogen difluoride and nitrogen containing nitrous oxide with activated carbon, and to The present invention provides a method for purifying nitrogen fluoride, which is characterized by removing nitrogen, nitrous acid, and arsenic nitrogen in one step.

The activated carbon used in the present invention may be any type of activated carbon, such as coconut shell carbon, petroleum-based activated carbon, or coal-based activated carbon, and may be in a crushed form as long as it has a shape that is easy to handle.

Any granular form can be used. The adsorption temperature may be room temperature.

By the way, activated carbon usually contains 50% relative humidity.
An equilibrium amount of water of 15 to 10 parts is adsorbed on a dry basis.

Normally, use it as is or leave it for 10 minutes to dry.
It is used after being heated and dehydrated at a temperature of about 0 to 120°C.

As a result of repeated studies on improving adsorption performance, the inventors of the present invention found that in the above-mentioned normal dehydration treatment, activated carbon still contains
It has been found that about 5 stripes of adsorbed water remain, and by reducing the amount of this remaining adsorbed water to 1% or less, the specific adsorption capacity of activated carbon can be dramatically increased.

As a method for activating activated carbon so as to reduce the amount of residual adsorbed water to 1% or less, for example, under an atmosphere of an inert gas such as dry nitrogen gas, or under reduced pressure, preferably at 120 to 550°C,
When heated and dehydrated at a temperature of 50 to 400°C, the water content in the activated carbon becomes 1 weight or less, and 06 weight or less.

The heat treatment conditions can be appropriately selected taking into consideration the amount of activated carbon, the treatment temperature, etc., but when the temperature exceeds 550°C, the effect reaches an equilibrium even when heated, and the necessity thereof becomes less.

'i! i:'The amount of residual adsorbed water on activated carbon was measured by heating a sample to 550°C in dry nitrogen and taking the loss on ignition as specified in the Japanese Industrial Standards.

Nitrogen fluoride which can be treated by the method of the invention may vary considerably in the type and composition of impurities contained.

That is, even if impurities other than dinitrogen difluoride and nitrous oxide, such as tetrafluorocarbon, silicon tetrafluoride, etc., are present in nitrogen fluoride, its performance is not affected at all. In particular, if the composition is less than 4 parts by volume of dinitrogen difluoride or less than 3 parts by volume of nitrous oxide, the life of the adsorbent is preferably long.

According to the method of the present invention, either crude nitrogen fluoride produced by a known method or relatively low-purity nitrogen fluoride, which is provided on the market as a general-purpose product, can be treated. It is possible and high purity can be achieved.

Furthermore, if nitrogen fluoride is used as a cleaning gas for a CVD device, by treating the waste gas with this method, the nitrogen fluoride contaminated with impurities can be purified and reused. This makes it possible to effectively utilize expensive nitrogen fluoride.

Example EXAMPLES The present invention will be specifically explained below with reference to Examples.

〔Example]〕

32 pieces of crushed coconut shell activated carbon were placed in an adsorption tower with an inner diameter of 20 mm.
The system was heated at 250° C. for 6 hours while maintaining the inside of the system at 1 torr or less using a vacuum pump.

The moisture content in the activated carbon after treatment was 007 on a dry basis.

To the adsorption tower treated in this way, N2F21. ．． 5 vo
1%.

NF3 gas containing 0.4 vol % of N2 as an impurity was introduced at room temperature at a flow rate of 20 me/min. As a result of analyzing the adsorption tower outlet gas over time (gas chromatography), the time (breakthrough time) at which these impurity components were detected was 93 hours for N2F2 and 12 hours for N20.
It was time.

[Example 2] The same adsorption tower as in Example 1 was filled with 40.9 kg of petroleum pinch activated carbon in the form of pellets, and heated at 200°C under a stream of dry nitrogen.
The mixture was heat-treated for 10 hours.

The moisture content in the activated carbon after treatment was 0.15 on a dry basis. - To the adsorption tower subjected to the above treatment, as in Example 1, N2F2 ], 5 vol%, N20 o,
4 20me of NF6 gas containing 1% of VO as an impurity
It was introduced at room temperature at a flow rate of /min.

As a result of analyzing the gas at the mouth of the adsorption tower over time, the breakthrough time was 7 hours for N2F2 near and 11 hours for N20.

[Example 3] Commercially available granular coconut husk charcoal was placed in the same adsorption tower as in Example 1.
32.9 was filled.

The moisture content in the activated carbon was 1.50% on a dry basis.

"N2F21, 5 to the adsorption tower 2, as in Example 1.
NF and gas containing impurities (7) were introduced at room temperature at a flow rate of 20 ml/min.

As a result of analyzing the gas at the outlet of the adsorption tower over time, the breakthrough time was 48 hours for N2F2 and 0 hours for N20. In the adsorption tower, 24
g, and heat-treated at 290° C. for 8 hours under a stream of dry nitrogen.

The moisture content in the activated carbon after treatment was 0.08% on a dry basis. To the adsorption tower subjected to the above treatment, N2F21. Qv
20 rne of NF3 gas containing o1% as an impurity
It was introduced at room temperature at a flow rate of /min.

Adsorption Bath Exit 1] As a result of analyzing the gas over time, the breakthrough time was 113 hours for N2F2.

[Comparative Example] In an adsorption tower similar to that in Example 1, a pellet-shaped Molequilla was added.
Filled with 65 g of sieve 5A,
Heat treatment was performed at ℃ for 10 hours.

” 1.5 vol of N2F to the adsorption tower subjected to the above treatment.
, Ne.

20m of NF3 gas containing O,4vol as an impurity
It was introduced at room temperature at a flow rate of e/min.

As a result of analyzing the gas at the outlet of the adsorption tower over time, the breakthrough time was 9 hours for N2F2 and 11 hours for N20.

Effects of the Invention As described above, the method for purifying nitrogen fluoride according to the present invention uses an extremely simple method to purify nitrogen fluoride at room temperature for an extremely long time.
Furthermore, the present invention provides a method for removing dinitrogen difluoride or dinitrogen difluoride and nitrous oxide contained as impurities in nitrogen fluoride at a rate of -2''.

Claims (2)

[Claims] (1) Removal of dinitrogen difluoride or dinitrogen difluoride and nitrous oxide by bringing dinitrogen difluoride or dinitrogen difluoride and nitrogen fluoride containing dinitrogen difluoride and nitrous oxide into contact with activated carbon. A method for purifying nitrogen trifluoride, characterized by: (2) The purification method according to claim 1, wherein the activated carbon is treated at 120°C to 550°C and has a moisture content of 1% by weight or less.