JP2000119024A - Production of tungsten hexafluoride - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the corrosion of pipes with produced metallic tungsten and the deterioration of the gas purity accompanying the corrosion and produce high-purity tungsten hexafluoride by bringing the metallic tungsten into contact with nitrogen trifluoride gas at a specified moisture concentration in a reactional vessel at a specific temperature. SOLUTION: The moisture concentration in NF3 gas is <=1 vol.ppm and a vessel made of nickel or Monel metal is used as a reactional vessel. The contact temperature is 200-400 deg.C. Two methods i.e., a method for condensing moisture at a low temperature and a method for chemically or physically adsorbing the moisture with a drying agent are used as a method for removing the moisture in the NF3 gas. Furthermore, the NF3 gas is passed through a flocculator cooled to -78 to -130 deg.C temperature to remove the moisture. Otherwise, moisture absorbing operations are carried out by using concentrated sulfuric acid. A bubbler type or a scrubber type is used as an apparatus and the moisture is absorbed by subjecting the concentrated sulfuric acid to gas-liquid contact with the NF3 gas. The concentration of the sulfuric acid is >=80%. A method for using a dehydrated synthetic zeolite is industrially suitable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing high-purity tungsten hexafluoride (WF ₆ ). In particular, high-purity tungsten hexafluoride has attracted attention as a wiring material for semiconductor manufacturing.

[0002]

2. Description of the Related Art Nitrogen trifluoride (NF ₃ ) used as a raw material
As a gas, an NH ₄ F · χHF (χ = 1 to 2) electrolytic solution is used, and NH ₃ is brought into contact with F ₂ gas generated by electrolysis using an electrolytic solution or HF as an electrolytic solution. Can be obtained by chemical methods. However, since NF ₃ obtained by these methods contains many impurities, it is necessary to remove it.

[0003] Therefore, it is difficult to obtain by direct electrolysis or chemical methods.
NF₃HF and OF contained in₂, N₂F₂, N
₂F₄, CO₂, N₂Impurities such as O
Liquid removal method, N₂O for sodium thiosulfate
Using aqueous solution (Japanese Patent Publication No. 5-05372)
No. 5 gazette) and the like.₃Using metal
When reacting with Ngustene, also collected from the reaction tube
Reacts with the metal gas piping provided between
A blue product is observed. WF collected ₆inside
Also contains trace amounts of metal components used in gas piping
Becomes

[0004]

OBJECTS OF THE INVENTION It is an object of the present invention to produce high purity WF ₆ stably.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on a method for stably purifying WF ₆ to a high purity, and as a result, a small amount of water has been found in the NF ₃ gas after the cleaning treatment. Paying attention to the fact that it is contained, it has been found that by removing this water to the limit, WF ₆ with high purity can be obtained, and the present invention has been completed.

That is, according to the present invention, the concentration of water in the nitrogen trifluoride gas is 1 ppm by volume or less.
The present invention relates to a method for producing high-purity tungsten hexafluoride, which is characterized by contacting at a temperature of ℃.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. The present invention is a method for obtaining high-purity WF6 by a main reaction between NF ₃ gas and metal tungsten (W). If expensive metal materials such as platinum, nickel, and monel are used for all the parts that come into contact with the gas, there is no problem, but the equipment cost is enormous. Since the reaction portion between NF ₃ gas and metal tungsten (W) is relatively high at 200 to 400 ° C., platinum, nickel, and monel must be used in the reactor. It is preferable to use inexpensive stainless steel metal for the gas contact part such as a collecting container.

However, in the case of this stainless steel, if water is contained in the WF ₆ obtained by the reaction, the stainless steel is eroded, and the metal component of the stainless steel becomes contaminated with the WF ₆ , thereby causing a decrease in purity. It became. WF ₆
The cause of water contamination is one of the causes, such as water adhering to metallic tungsten, insufficient purging of the reaction tube, piping, and valve, and leakage of air, and requires careful attention.
Most importantly, however, the amount of water in the raw material NF ₃ should be 1 ppm by volume or less, preferably 0.1 ppm by volume or less. When the water content in NF ₃ exceeds 1 ppm by volume, the metal component of stainless steel is WF as described above.
No. ₆ , which is not preferable because it causes contamination and lowers the purity.

Although it is possible to remove contaminated metals by using precision distillation or a high-performance filter, it is not a preferable method because the cost is increased. Rather, the materials used for precision distillation columns,
Depending on the material of the filter, the purity may be further reduced.

Next, a method of removing water from the NF ₃ will be described. There are various methods for removing water, and roughly classified into two methods: a method of condensing at a low temperature and a method of chemical moisture absorption or physical adsorption using a desiccant. The present invention can be carried out by any of these methods. However, the following method having particularly excellent removal effect is suitably employed.

One method is to condense at a low temperature.
To remove moisture by bubbling the agglomerator was cooled F ₃ at a temperature of -78 to-130 ° C.. Cooling temperature is -78
When the temperature exceeds ℃, the water concentration cannot be reduced to 1 ppm by volume or less. Cooling the aggregator at a temperature lower than -130 ° C is not preferable because NF ₃ is liquefied.

Another method is a method using a desiccant. As the desiccant, phosphorus pentoxide, magnesium perchlorate, concentrated sulfuric acid and synthetic zeolite having excellent hygroscopicity are preferably used. Among them, concentrated sulfuric acid is an industrially advantageous method because it is liquid and can constantly maintain a high concentration using a circulation pump.

The concentrated sulfuric acid used in the present invention is a chemical or a reagent having a sulfuric acid concentration of 80% or more. It is desirable that concentrated sulfuric acid does not contain H ₂ S or SO ₃ . Various types of devices are used in the moisture absorption operation using concentrated sulfuric acid. In general, a bubbler system or a scrubber system is used generously, and NF ₃ is brought into contact with gas and liquid to absorb moisture.

As a material for these devices, a metal material such as stainless steel or Hastelloy, or a resin material such as polypropylene or Teflon can be used. The temperature at which concentrated sulfuric acid is brought into contact with NF ₃ is not particularly limited as long as the concentrated sulfuric acid does not freeze, but is usually performed at room temperature. In winter,
Since concentrated sulfuric acid may freeze, it is necessary to take measures such as keeping the temperature at about 20 ° C. Further, a method using a dehydrated synthetic zeolite is industrially suitable, and a method using these together is also possible.

As described above, a nickel or monel vessel is used as the reaction vessel to be brought into contact with metal tungsten, and the water content in NF ₃ is adjusted to 1 ppm by volume or less, preferably 0.1 ppm by volume or less. This made it possible to produce high-purity tungsten hexafluoride by bringing the NF ₃ and metal tungsten into contact at 200 to 400 ° C.

[0016]

The present invention will be described below with reference to examples and comparative examples. In addition,% is based on weight and ppm and ppb are based on volume. Example 1 Metal tungsten was placed in a 1 L nickel reaction vessel.
00g was charged and heated to 300 ° C. On the other hand, 6.5 ppm
NF ₃ gas containing water at a rate of -12 at 100 cc / min.
The water was reduced to 0.3 ppm by ventilating a 500 cc dehydration trap cooled to 0 ° C. This gas is passed through the above-mentioned reaction tube and reacted with metallic tungsten to form WF.
₆ was produced. This generated gas is supplied to the electrolytically polished SU
Using the stainless steel pipe of S316 as a conduit, it was led to a Teflon absorption bottle. In the absorption bottle, 100 g of ultrapure water was used as an absorption liquid, and absorbed into the absorption bottle for 2 hours. After the absorbent was heated to dryness to precipitate WO ₃ ↓, the treated liquid extracted with diluted nitric acid was analyzed by ICP-MS. The results are shown in Table 1. No corrosion was observed in the stainless steel pipe of SUS316, and the analysis results showed that the metal component caused by the corrosion was 10 ppb or less.

Example 2 100 cc / m of NF ₃ gas containing 6.5 ppm of water
The water was reduced to 0.7 ppm by bubbling 500 cc of 98% sulfuric acid in. This gas was passed through the reaction tube in the same manner as in Example 1, and the product gas was electropolished to S
US316 stainless steel tubing was used as a conduit and led to a Teflon absorption bottle. In the absorption bottle, 100 g of ultrapure water was used as an absorption liquid, and absorbed into the absorption bottle for 2 hours. The treatment solution obtained by the same operation as in Example 1 was used for this absorption solution, and then treated with ICP-M.
The analysis was performed at S. Table 1 shows the results.
No corrosion was observed in the stainless steel pipe of No. 6, and the analysis result showed that the metal component caused by the corrosion was 10 ppb or less.

Example 3 100 cc / m of NF ₃ gas containing 6.5 ppm of water
The solution was bubbled through 500 cc of 98% sulfuric acid, and then passed through 100 cc of dehydrated synthetic zeolite (4%) to reduce the water content to 0.08 ppm. This gas was passed through the reaction tube in the same manner as in Example 1, and the produced gas was led to a Teflon-made absorption bottle using a stainless steel SUS316 pipe electropolished as a conduit. Ultrapure water 10 in the absorption bottle
0 g was used as the absorbing solution and absorbed into it for 2 hours. The treated solution obtained by the same operation as in Example 1 was
Analysis was performed by CP-MS. The results are shown in Table 1, where S
No corrosion was observed in the stainless steel pipe of US316, and the analysis result showed that the metal component caused by the corrosion was 10 ppb or less.

Comparative Example 1 NF ₃ gas containing 6.5 ppm of water was passed through the above-mentioned reaction tube in the same manner as in Example 1, and the produced gas was subjected to electrolytically polished SU.
Using the stainless steel pipe of S316 as a conduit, it was led to a Teflon absorption bottle. In the absorption bottle, 100 g of ultrapure water was used as an absorption liquid, and absorbed into the absorption bottle for 2 hours. The processing solution obtained by the same operation as in Example 1 was subjected to ICP-MS
Was analyzed. The results are shown in Table 1. SUS316
Corrosion was observed in the stainless steel pipe, and the analysis results showed that the concentration of the metal component caused by the corrosion was high.

[0020]

[Table 1]

[0021]

According to the present invention, the control value of moisture in NF ₃ gas used as a raw material for producing metal tungsten is 1 pp.
By setting the value to m or less, it is possible to manufacture high-purity metal tungsten by preventing the conventional corrosion of piping caused by the generated metal tungsten itself and the accompanying decrease in gas purity.

Claims (6)

[Claims] 1. The method according to claim 1, wherein the concentration of water in the nitrogen trifluoride gas is 1
A method for producing high-purity tungsten hexafluoride having a capacity of not more than ppm and contacting metal tungsten at 200 to 400 ° C. in a reaction vessel using said nitrogen trifluoride gas. 2. The concentration of water in nitrogen trifluoride gas is as follows:
2. The method according to claim 1, wherein the amount is 0.1 ppm by volume or less. 3. The method according to claim 1, wherein a container made of nickel or monel is used as a reaction container for bringing the nitrogen trifluoride gas into contact with the metal tungsten. 4. A nitrogen trifluoride gas of -78 to -130.
The method according to claim 1, wherein the gas is passed through a coagulator cooled at a temperature of ° C. 5. The method according to claim 1, wherein the nitrogen trifluoride gas is brought into contact with concentrated sulfuric acid having a sulfuric acid concentration of 80% or more at room temperature. 6. The method of claim 1 wherein nitrogen trifluoride gas is passed through the dehydrated synthetic zeolite.