JP3162588B2 - Method for producing high-purity nitrogen trifluoride gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing high purity nitrogen trifluoride (NF ₃ ). More specifically, industrially, the present invention relates to a manufacturing method for providing high-purity nitrogen trifluoride at a low cost, by reacting hydrofluoric acid gas and ammonia gas of a predetermined purity, and using the obtained ammonium acid fluoride as an electrolyte. Further, the present invention is characterized in that electrolysis is performed by a molten salt electrolysis method using nickel electrodes of a predetermined purity for the anode and the cathode. The high-purity nitrogen trifluoride (NF ₃ ) in the present invention refers to one having a purity of 99.99% by volume (hereinafter referred to as 4N) or more.

[0002]

2. Description of the Related Art Nitrogen trifluoride is used for electronic materials, in particular, as a cleaning gas for CVD equipment, and for cleaning dry etching agents for semiconductors and single-wafer devices in the liquid crystal field for TFTs. In recent years, it has attracted attention and its production has increased significantly.

[0003] NF ₃ gas used in these applications is
In recent years, there has been an increasing demand for higher purity.

Conventionally, various methods have been proposed as methods for producing NF ₃ by molten salt electrolysis. For example, for an electrode to be used, a method using nickel for the anode is widely used industrially because it does not generate impurities, for example, CF ₄ .

As a raw material for performing molten salt electrolysis, a method according to the present applicant; a method according to Japanese Patent Application Laid-Open No. 4-56789 or the like is a preferable method because it has less impurities compared to the prior art. . However, in recent years, with the progress of technology, there has been a need for high-purity NF ₃ gas.
Higher purity of the product gas was required.

[0006] As a method of purifying the crude gas, a crude gas obtained by electrolysis (hereinafter referred to as a crude gas) is led to a purifying apparatus together with a carrier gas, and is adsorbed by, for example, zeolite, activated alumina, silica gel or the like. Gas purification has been performed by chemical cleaning treatment and / or plasma decomposition and / or cryogenic separation and / or liquefaction rectification of gas.

[0007] As impurities in the crude gas, nitrous oxide (N ₂ O), carbon dioxide (CO ₂ ), carbon monoxide (C ₂ ) except for the carrier gas component and water (H ₂ O).
O), dinitrogen difluoride (N ₂ F ₂ ), oxygen difluoride (O
F ₂ ), sulfur hexafluoride (SF ₆ ), carbon tetrafluoride (CF
₄ ), etc., so that purification was necessary, and the purification of the crude gas was carried out by the above-mentioned purification apparatus.

In the case of using these refining devices, it is necessary to control the performance depending on the content and dispersion of impurities. For example, when an adsorbent is used, the adsorption speed,
It is necessary to change parameters of various conditions, such as renewal of the adsorbent and change of the regeneration frequency, which requires labor, and it is also necessary to examine the purity of the obtained purified gas with considerable frequency. However, quality control, such as the presence of a product, is difficult, which has led to an increase in manufacturing costs.

Further, 4N (purity 99.99%), 5N
(Purity 99.999%) or higher
When F ₃ gas is produced industrially, the level of impurities in the crude gas, that is, the amount of trace components, becomes a problem. Purifying a crude gas, increasing its purity, and achieving high purity have a limit in terms of equipment and economy when performing the purification, and it is necessary to economically produce high-purity gas. Was practically difficult.

[0010]

The object of the present invention means to solve] In view of the above problems, relates to economically process for producing high-purity NF _3, which is characterized in that the electrode is used, raw materials and predetermined component The present inventors have found that high-purity NF ₃ gas can be industrially and economically produced by greatly reducing the impurity level in the crude gas, and have completed the present invention.

That is, the method for producing high-purity NF ₃ in the present invention refers to a method for producing high-purity nitrogen trifluoride by a molten salt electrolysis method using a metal electrode. As a raw material for the liquid, a method characterized by reacting hydrofluoric acid gas and ammonia gas to form ammonium acid fluoride and using the ammonium acid fluoride as an electrolytic solution, wherein nickel as a metal electrode used is nickel Purity is more than 98.5wt%,
The method is characterized in that the hydrofluoric acid gas used has a purity of 99.8 wt% or more, and the ammonia gas used has a purity of 99.5 wt%.

[0012]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a view showing a flow sheet of an embodiment suitable for carrying out the present invention. In FIG. 1, predetermined amounts of hydrofluoric acid gas (HF) and ammonia gas (NH ₃ )
It is led to a raw material preparation tank, reacted, and made into ammonium acid fluoride. The ammonium acid fluoride is supplied to an electrolytic cell,
NF ₃ gas is generated on the anode side of the electrode by a molten salt electrolysis method. The raw material preparation tank 3 is preferably sealed with an appropriate amount of nitrogen gas, argon gas, helium gas or the like for the purpose of not being affected by outside air.

[0014] The hydrofluoric acid gas (HF) used may be
99.8 wt% or more, the purity of ammonia gas (NH ₃ ) used is 99.5 wt% or more, and nickel (N
The purity of i) is preferably 98.5 wt% or more. If the purity of hydrofluoric acid gas is 99.8 wt% or less and / or the ammonia gas is 99.5 wt% or less and / or the purity of nickel used as an electrode is 98.5 wt% or less, a highly pure product with a purity of nitrogen trifluoride of 4 N or more can be obtained. Becomes difficult,
Not suitable.

The reaction between hydrofluoric acid gas and ammonia gas is as follows:
Because it proceeds very quickly, there is no need for sufficient stirring, etc.
There is no particular limitation as long as the hydrofluoric acid gas and the ammonia gas can contact each other. The reaction conditions are HF / NH
_{The 4} F molar ratio is preferably about 1.5 to 2.0.

The electrodes, hydrofluoric acid gas, and ammonia gas used contain various kinds of impurities. For example,
The hydrofluoric acid gas contains moisture, sulfur represented by sulfur dioxide and sulfuric acid, silicon represented by hydrofluoric acid, carbon dioxide, carbon monoxide, other carbon, oxygen, and other trace components. Ammonia gas has moisture, sulfur represented by sulfur dioxide and sulfuric acid, carbon dioxide, carbon monoxide and other carbon, oxygen and other trace components.Nickel electrode contains traces of moisture and carbon. Metal Mn, Fe,
It contains trace components such as S, Si, Cu, Mo, Cr, P, Al, Ti, Na, K, Co, and W.

According to the study of the present inventors, the main impurities in nitrogen trifluoride gas are N ₂ O, CO ₂ , CO, N ₂ F ₂ , OF ₂ , SF ₆ and CF _4.
The components are N, O, C, F, and S. Excluding the components of nitrogen trifluoride (NF ₃ ), the components become O, C, and S. It is only necessary to control the constituents composed of O, C, and S among the impurity components.
However, it is very difficult to identify what the impurities are due to the small amount. Thus, as an alternative, the present invention specifies the purity of the electrode, hydrofluoric acid gas and ammonia gas.

The influence on the purity of the obtained nitrogen trifluoride gas varies depending on the content of each impurity, but according to the study of the present inventors, the purity of nickel, hydrofluoric acid gas, and ammonia gas used as electrodes is determined. Is measured, and if the purity is within the range described in the present invention, the obtained crude gas is led to a purification device similar to the conventional one, whereby a high-purity nitrogen trifluoride gas can be easily obtained. . .

In the present invention, the term "purity" refers to the purity of nickel as nickel (Ni), and each of the impurities in the hydrofluoric acid gas and the ammonia gas, excluding water, is a hydrofluoric acid (HF) and an ammonia gas. It refers to the purity of (NH ₃ ). However, unlike the other impurities in the refining process, the water in both gases can be easily removed and does not pose a major problem in obtaining high-purity nitrogen trifluoride gas. In view of the above, according to the study by the present inventors, H ₂ O is preferably 0.01% by volume or less.

The generated NF ₃ gas, which is a crude gas, is led to a purification device to remove a trace amount of impurities to obtain a high-purity nitrogen trifluoride gas.

FIG. 2 is a diagram showing details of the electrolytic cell in FIG. 1 according to the present invention. In FIG. 2, the reacted ammonium ammonium fluoride is led to the electrolytic cell main body 1 to be used as an electrolytic solution 2. The supply of the electrolytic solution may be either a continuous type or a batch type. However, when it is desired to continuously obtain a fixed amount of nitrogen trifluoride, the continuous type is preferable. Electrolytic cell body 1
Is partitioned by the partition plate 7 into the anode chamber 3 and the cathode chamber 5. The anode chamber 3 has a nickel anode 4 having a predetermined purity, and the cathode chamber 5 has a cathode 6 having the same purity as the anode 4. It should be noted that there is no particular problem even if the electrolytic cell main body 1 has a plurality of anodes and cathodes, and a plurality of structures are generally used industrially from the viewpoint of production efficiency and the like.

The electrolysis conditions are as follows: a molten salt electrolysis method of nitrogen trifluoride is carried out at a temperature of about 110 to 140 ° C., and a direct current is applied to the electrodes 4 and 6 in the electrolytic cell main body 1 so that I do.

The voltage during electrolysis is 5 to 10 V, and the current density is 1
Approximately 15 A / dm ² .

By this molten salt electrolysis, N
F ₃ gas is generated, and H ₂ gas is generated from the cathode. still,
In the electrolytic cell 1, a partition plate 7 is provided between the anode 4 and the cathode 6 in order to avoid mixing of the generated NF ₃ gas and H ₂ gas.

The NF ₃ gas and the H ₂ gas generated from the electrodes are taken out through separate conduits 8 and 9 so as not to mix. The crude NF ₃ gas taken out through the conduit 8 is led to a purification device. Further, the H ₂ gas generated from the cathode 6 is discharged into the atmosphere via an elimination device (not shown) or the like.

The purifying apparatus (method) may be, for example, a purifying apparatus comprising a gas cleaning apparatus for cleaning with a chemical solution, an adsorption tower using an adsorbent, a rectifying tower, and the like which have been generally used.

At the time of electrolysis, nitrogen gas, argon gas, and the like are used in order to make the electrolysis reaction proceed mildly and to maintain the pressure in the anode chamber 3 and the cathode chamber 5 as uniform as possible.
An appropriate amount of a gas such as helium gas is introduced as a carrier gas to the anode chamber 3 and the cathode chamber 5 through the conduits 10 and 11, respectively.

The carrier gas has a purity of NF
The purity which does not affect the purity of ₃ is preferable, and in the study of the present inventors, the purity is preferably 4N or more, and more preferably 6N or more. As the carrier gas, it is preferable to use nitrogen gas, which is industrially inexpensive and easily obtains a high-purity product.

[0029]

The present invention will be described more specifically with reference to the following examples.

Example 1 NF ₃ was produced by a molten salt electrolysis method using the flow sheet and the electrolytic cell shown in FIGS.

First, 2.00 kg / hr of hydrofluoric acid gas having a purity of 99.90 to 99.95 wt% and ammonia gas having a purity of 99.6 to 99.7 wt%.
And 71 kg / hr at reactor 500l lined with PFA in SS-400, is reacted with a seal of a purity of 99.9999% of the N ₂ gas, the molar ratio of HF / NH ₄ F is 1.7 mole acid fluoride Ammonium chloride was obtained.

Next, the temperature was adjusted to 120 ° C. while continuously supplying ammonium acid fluoride to a 450-liter electrolytic bath (three sets of electrodes) in which PSA was lined with SUS-304. Next, while introducing nitrogen gas into the anode chamber at a flow rate of 0.11 / min, a current of 5 amperes (A) was passed from the anode to the cathode to perform electrolysis. At this time, the anode and the cathode were made of nickel having a purity of 99.0 wt%. The electrolysis was carried out continuously for 3,000 hours.

The crude gas generated from the anode chamber is sent to a purifying device comprising a gas washing device for washing water, sodium sulfite and potassium hydroxide with a chemical solution, an adsorption tower filled with natural zeolite and a rectification column, and the outlet of the device The gas amount was measured with a gas meter. Outlet gas purity analysis was performed using online gas chromatography. as a result,
The gas amount was 10 to 11 l / min, and the purity of the obtained NF ₃ gas was as shown in Table 1.

[0034]

[Table 1]

Example 2 The same apparatus as in Example 1 was used to adjust the purity of hydrofluoric acid gas to 99.90.
~ 99.95wt%, purity of ammonia gas 99.6 ~ 99.7wt%,
The same conditions as in Example 1 were used except that the purity of the electrode was 99.0 wt%. The purity of the obtained NF ₃ was analyzed.
The result shown in FIG. The electrolysis was performed for 2,000 hours.

[0036]

[Table 2]

Comparative Example 1 An experiment was carried out under the same conditions as in Example 1 except that the purity of the electrode was 98.3 wt% in the same apparatus as in Example 1. N obtained
When the purity of F ₃ was analyzed, the results shown in Table 3 were obtained.
Purity was below 4N. The electrolysis was stopped after 1,000 hours due to the low purity of the obtained product.

[0038]

[Table 3]

Comparative Example 2 Using the same apparatus as in Example 1, the purity of hydrofluoric acid gas was 97.5-9.
The test was performed under the same conditions as in Example 1 except that the content was 8.0 wt%. When the purity of the obtained NF ₃ was analyzed, the results shown in Table 4 were obtained, and the purity was lower than 4N. In addition, electrolysis was stopped after 600 hours because the obtained product purity was low.

[0040]

[Table 4]

Comparative Example 3 Using the same apparatus as in Example 1, the purity of ammonia gas was adjusted to 97.0
The procedure was performed under the same conditions as in Example 1 except that the content was set to 998.5 wt%. When the purity of the obtained NF ₃ was analyzed, the result shown in Table 5 was obtained, which was lower than 4N. In addition, electrolysis was stopped in 700 hours because the obtained product purity was low.

[0042]

[Table 5]

[0043]

As described above, the present invention provides:
Industrially, in a method of producing high-purity nitrogen trifluoride gas (NF ₃ ) at low cost, a hydrofluoric acid gas and an ammonia gas having a predetermined purity are reacted, and the obtained ammonium ammonium fluoride is used as an electrolytic solution. Further, it is a very simple method of performing electrolysis by a molten salt electrolysis method using nickel electrodes of a predetermined purity for the anode and the cathode.

By specifying the purity of the electrode and the raw material to be used, it is possible to easily produce NF ₃ of high purity, which was difficult to achieve conventionally, by the method of the present invention. .

Further, the effects of the present invention can be easily obtained without changing the conventional equipment by changing to the predetermined electrode and changing to the predetermined raw material disclosed in the present invention. The industrial and economic effects of the invention are extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a flow sheet suitable for carrying out the present invention.

FIG. 2 shows an example of an electrolytic cell suitable for carrying out the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyzer main body 2 Electrolyte 3 Anode chamber 4 Anode 5 Cathode chamber 6 Cathode 7 Separator 8 Conduit 9 Conduit 10 Carrier gas conduit 11 Carrier gas conduit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C25B 1/00-15/08 C01B 21/083

Claims (1)

(57) [Claims] 1. A method for producing high-purity nitrogen trifluoride by molten salt electrolysis using ammonium acid fluoride as an electrolytic solution using a nickel electrode, wherein the nickel electrode has a purity of 98.5% by weight or more, A method for producing high-purity nitrogen trifluoride gas, characterized in that ammonium fluoride is obtained by reacting hydrofluoric acid gas having a purity of 99.8% by weight or more with ammonia gas having a purity of 99.5% by weight or more.