JP2927914B2 - Method for producing nitrogen trifluoride gas - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing nitrogen trifluoride (NF ₃ ) gas. More specifically, NF by electrolysis of NH ₄ F ・ HF molten salt
₃ Related to gas production method.

(Problems to be Solved by the Prior Art and the Invention) NF ₃ is a colorless chemically stable gas having physical properties of a boiling point of −129 ° C. and a melting point of −207 ° C.

In recent years, NF ₃ gas has attracted attention as a dry etching agent in semiconductor manufacturing processes and as a cleaning gas for CVD equipment. However, high purity NF ₃ gas is required for these applications.

NF ₃ gas is produced by various methods. For example, a method of electrolyzing a molten salt of ammonium oxyfluoride, a method of reacting ammonium oxyfluoride with gaseous fluorine in a molten state, a method of reacting an ammonium complex of solid metal fluoride with elemental fluorine, NH ₄ F ・ HF made from ammonium fluoride or ammonium acid fluoride and hydrogen fluoride
And, further potassium fluoride or acidic potassium fluoride to this, there is such a molten salt electrolysis method in KF · NH ₄ F · HF system was added to the raw material.

However, most of the gases obtained by either method are nitrogen (N ₂ ), oxygen (O ₂ ), oxygen difluoride (OF ₂ ),
High-purity NF ₃ gas for the above applications because it contains relatively large amounts of impurities such as nitrous oxide (N ₂ O), carbon dioxide (CO ₂ ), and nitrogen difluoride (N ₂ F ₂ ) Purification is required to obtain.

The following method is known as a purification method for removing these impurities in the NF ₃ gas.

That is, 1) a method in which N ₂ F ₂ is brought into contact with an aqueous solution of KI, Na ₂ S, Na ₂ S ₂ O _3, etc. [J. Massonne, Chemie Ingeneur Techinil (Chem. Ing. Techn.) 41, ( 12), 695, (196
9)] or by contacting with metal at a temperature of 148.9 to 537.8 ° C (Japanese Patent Publication No. 59-15081).
2) OF ₂ can be removed by a method of contacting with an aqueous solution of Na ₂ S ₂ O ₃ , KI, Na ₂ SO ₃ , HI, Na ₂ S or the like. 3) N ₂ O or C
Components having a relatively high boiling point, such as O _2, can be efficiently removed by contact with an adsorbent such as zeolite [Chem. Eng., 84, 116, (1977), etc.].

On the other hand, low-boiling components such as N ₂ and O ₂ are limited in the method of removing by utilizing reaction or adsorption because NF ₃ gas is the main component of the composition, and a method of obtaining high-purity NF ₃ gas Is not preferred. Further, since N ₂ has a strong affinity for liquefied NF ₃ , generally, the NF ₃ gas is cooled to a temperature of −150 to −190 ° C. to liquefy the NF ₃ gas, and further evacuated to obtain N ₂ , O _2.
Was being removed.

However, even in the above method, N ₂ and O ₂ have high purity.
The NF ₃ gas quality could not be removed to a satisfactory degree. In addition, it is difficult to supply and treat NF ₃ gas during the removal work due to the vacuum evacuation, which inevitably results in batch operation, which complicates the process and work. doing.

(Means for Solving the Problems) In view of such a situation, the present inventors have conducted intensive studies and, as a result, supplied NF ₃ gas to the backflow-type condensing heat exchanger and continuously liquefied NF ₃ gas. it is, the reservoir of liquefied NF ₃ which is connected to the inverse-flow aggregation heat exchanger, and a liquid storage and NF ₃ obtained by liquefied by said reverse-flow condenser heat exchanger, further liquefaction NF ₃ in該貯tank To the boiling state, and NF ₃
The inventors have found that low-boiling components such as N ₂ and O ₂ can be removed from the exhaust port by refluxing the gas, thereby completing the present invention.

That is, in the production of nitrogen trifluoride gas, the present invention relates to a nitrogen trifluoride gas backflow type condensation heat exchanger, a liquid nitrogen trifluoride storage tank connected thereto, and a storage tank connected to the other end. And collecting and / or storing the nitrogen trifluoride using a device having a low-boiling component exhaust port.

(Detailed Disclosure of the Invention) Hereinafter, the present invention will be described in detail.

As described above, NF ₃ gas is produced by various methods, but the present invention is not limited to the type of the production method, and what is the aspect before the present invention is carried out. It can also be implemented.

Next, the NF ₃ gas backflow condensation heat exchanger 1 used in the present invention
The liquefied NF ₃ storage tank 2 will be described.

One end of the NF ₃ gas reverse-flow condensing heat exchanger 1 on the process side is connected to a liquefied NF ₃ storage tank 2, and a liquefied NF ₃ gas outlet 3 is provided. It is preferable that the NF ₃ condensed in the NF ₃ gas backflow type condensation heat exchanger 1 be arranged and structured so that it can easily flow into the liquefied NF ₃ storage tank 2. Also the NF
_{Since the} low-boiling component contained in the NF ₃ gas is discharged from the other end of the _three- gas backflow-type condensing heat exchanger 1, a low-boiling component exhaust port 4 is provided so as not to hinder the discharge. There is. In general, there is no problem in releasing to the atmosphere, but it is preferable to apply a gas seal 5 with mercury or the like so that the air does not flow backward and flow into the NF ₃ gas backflow type condensation heat exchanger 1 side. preferable.

The NF ₃ gas backflow-type heat exchanger for condensation 1 used here is preferably a multi-tube heat exchanger.

The outside of the liquefied NF ₃ storage tank 2 is covered with a cold insulating material such as urethane foam 6, but it is not necessary to completely cool the NF ₃ because a small amount of heat is required to bring NF ₃ into a boiling state. The degree of cooling is appropriately selected depending on the capacity of the NF ₃ gas backflow condensation heat exchanger 1. By these, NF ₃
Gas recirculation becomes possible. In addition, in collection and / or storage that does not require the recirculation of NF ₃ gas, strong cold preservation such as storage in a vacuum double structure like a Dewar bottle may be performed.

NF ₃ into the NF ₃ gas backflow-type condenser heat exchanger 1 from the outside
The gas is supplied from the NF ₃ gas supply port 7 connected to the NF ₃ storage tank. As a result, most of the low-boiling components contained in the NF ₃ gas are removed and then stored in the liquefied NF ₃ storage tank 2.

Refrigerant is supplied to the conjugate side of the NF ₃ gas reverse-flow condensing heat exchanger 1, and a refrigerant supply port 8 and a refrigerant discharge port 9 are provided. As the refrigerant, petroleum ether or the like cooled to an arbitrary temperature with liquid nitrogen or the like can be used in addition to liquid air (−186 to −196 ° C.) and liquid nitrogen (−196 ° C.). However, liquid nitrogen, which is easy to handle and the like, is generally used as the refrigerant.

The collected NF ₃ gas is extracted from the liquefied NF ₃ storage tank 2. Specifically, NF ₃ is extracted from the gas phase using a compressor, or NF ₃ is extracted from the lower part of the liquefied NF ₃ storage tank 2 in a liquefied state. Thereafter, it is filled into cylinders or is subsequently transferred to some process.

In addition, as described above, in the semiconductor manufacturing process, the gas filled in the cylinder is a dry etching gas or CV.
Used as cleaning gas for D chamber.

(Examples) Hereinafter, the present invention will be described more specifically with reference to examples.
In the following,% and ppm are based on the capacity unless otherwise specified.

Example 1 Using the apparatus shown in FIG. 1, NF ₃ gas containing low-boiling components was collected. The equipment is NF ₃ with a heat transfer area of 2 m ²
Gas backflow type heat exchanger for condensation 1 and one end of it about 10cm thick
A liquefied NF ₃ storage tank 2 having a capacity of about 20 liters covered with urethane foam is connected.

First, NF ₃ conjugate side of the gas backflow-type condenser heat exchanger 1, while controlled by the temperature controller to supply liquid nitrogen at a pressure of about 5 kg / cm ^2, the NF ₃ gas backflow-type condenser heat exchanger Was kept at -180 ° C.

Next, NF ₃ gas containing about 20% of N ₂ gas and about 1% of O ₂ gas as impurities is supplied from the external NF ₃ gas supply port 7 at 5 l / min.
NF ₃ gas of about 5 kg was liquefied and collected.

During this time, the thermometer installed near the lower part of the liquefied NF ₃ storage tank 2 always indicated the boiling point of NF ₃ at −129 ° C. Also,
When the gas released to the atmosphere from the NF ₃ gas backflow type condensation heat exchanger 1 was sampled and analyzed, almost all of the gas was nitrogen and oxygen.

Next, gas was extracted from the NF ₃ gas extraction port 10 of the liquefied NF ₃ storage tank 2 and analyzed by gas chromatography. As a result, N ₂ gas was about 20 ppm and O ₂ gas was 5 ppm.

Example 2 The NF ₃ gas containing impurities used in Example 1 was continuously supplied for 7 hours, and liquefied NF was supplied 5 hours after the start of the supply.
_{3 A} small amount of liquefied NF ₃ was withdrawn from the lower part of the storage tank 2 into a cylinder, vaporized, and analyzed by gas chromatography in the same manner as in Example 1.

As a result, N ₂ gas was about 25 ppm, and O ₂ gas was 5 ppm.

In apparatus in Comparative Example 1 Example 1 Remove the urethane foam liquefaction NF ₃ storage tank 2, except that the liquid of NF ₃ storage tank 2 was immersed in Dewar filled with liquid nitrogen was carried out in the same manner as in Example 1.

As a result, N ₂ gas was about 280 ppm and O ₂ gas was 120 ppm.

(Effect of the Invention) With the combination of liquefaction of NF ₃ gas and evacuation, which has been conventionally performed, the removal of low-boiling components was not satisfactory. In addition, since liquefaction and collection of NF ₃ gas cannot be performed during vacuum evacuation, gas must be collected in batch operation, and if gas is to be continuously collected, it is necessary to provide two or more collection facilities. Was.

However, according to the present invention, since the low-boiling components are efficiently removed by bringing the liquefied NF ₃ into a boiling state, the content of O ₂ and N ₂ contained in the collected NF ₃ as compared with the conventional method is reduced. The amount is significantly reduced. It also has the advantage that gas can be continuously collected and purified.

[Brief description of the drawings]

FIG. 1 is a diagram showing a NF ₃ gas reverse flow type heat exchanger for condensation and a liquefied NF ₃ condenser used in Examples and Comparative Examples. In the figure, 1 ... NF ₃ gas backflow type heat exchanger for condensation 2 ... Liquefied NF ₃ storage tank 3 ... Liquefied NF ₃ gas outlet 4 ... Low boiling point component exhaust port 5 ... Gas seal 6 ... Urethane foam 7 NF ₃ gas supply port 8… Refrigerant supply port 9… Refrigerant discharge port 10… Indicates liquefied NF ₃ gas discharge port.

Claims (1)

(57) [Claims] In a process for producing a nitrogen trifluoride gas, a heat exchanger for backflow-type condensation of nitrogen trifluoride gas and a liquid heat exchanger connected to the heat exchanger for backflow-type condensation of nitrogen trifluoride gas are provided. Nitrogen trifluoride gas characterized by collecting and / or storing nitrogen trifluoride gas using a device comprising a storage tank for nitrogen fluoride and a low-boiling component exhaust port connected to the storage tank and the other end. Manufacturing method.