JP3187544B2 - Production method of ammonium cryolite - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a manufacturing method of an ammonium cryolite used as a raw material for producing useful NF ₃ as a gas or the like for gas cleaning in a semiconductor manufacturing device or the like.

[0002]

2. Description of the Related Art NF ₃ is usually a colorless gas having a boiling point of about -1.
It has a melting point of about −208 ° C. and a temperature of 29 ° C., and has recently attracted attention as a gas for cleaning semiconductor devices.

Various methods for producing NF ₃ have been proposed. For example, US Pat. No. 3,304,248 discloses that gaseous nitrogen is passed through a plasma arc at a temperature exceeding 1000 ° C., and gaseous fluorine is anoded. A method for obtaining NF ₃ by introducing it into the post-arc region as close as possible to US Pat.

[0004] In addition, gas phase reactions such as a reaction between hydrazoic acid gas and oxygen difluoride and a direct fluorination of ammonia are known. Also, molten salt electrolysis of ammonium oxyfluoride is known. However, in any of these methods, since the reaction is in a gas phase, it is necessary to prevent the reaction from being difficult to control and to prevent generation of an atmosphere containing flammable or explosive hydrogen.

Furthermore, Japanese Patent Publication No. 55-8926 discloses a method of reacting ammonium oxyfluoride with gaseous fluorine in a molten state. However, since this method is a gas-liquid reaction, the control of the reaction is not always easy, the corrosion of the apparatus is remarkable, and the yield of NF ₃ is low, which is not industrially sufficient. is there.

As a solution to such a disadvantage, Japanese Patent Application Laid-Open No. Sho 60-71503 discloses a solid metal fluoride such as ammonium cryolite [(NH ₄ ) ₃ Al].
F ₆ ] and elemental fluorine are reacted at room temperature or higher.

Although the industrial production of ammonium cryolite is not common, the production of small quantities of ammonium cryolite involves boiling fresh aluminum hydroxide in an aqueous solution of ammonium fluoride, or adding an aqueous solution of ammonium fluoride to water. It is known that aluminum oxide is obtained by mixing with aluminum oxide dissolved in hydrofluoric acid.

However, the ammonium cryolite thus obtained has a small particle size and a low bulk density,
Not necessarily sufficient in the production of F _3. Specifically, if the particle size is small, the reaction with elemental fluorine proceeds rapidly, the control of the reaction system temperature becomes difficult, and the reaction temperature rises significantly, causing ammonium cryolite to self-decompose. , NF ₃ is reduced. Further, there is a problem in handling such as generation of dust. Also,
If the bulk density is small, the volumetric efficiency of the device will be poor.

[0009]

[Specific means for solving the problem]
The particle size and the bulk density are large, specifically, the average particle size is 25
As a result of intensive studies to obtain ammonium cryolite having a bulk density of about 0 to 350 μm and a bulk density of about 1 to 1.2 g / cm ³ , such a purpose is achieved by selecting a specific reaction method and a limited pH range. It has been found that the present invention can be achieved.

That is, in the present invention, the reaction pH is 6 to 8.5 by simultaneously adding hexafluoroaluminic acid and ammonia.
The method for producing ammonium cryolite, characterized by crystallizing in the range of

The ammonia may be a gas or a liquid, and the pH during the reaction is preferably in the range of 6 to 8.5. The selection of the pH is important because the bulk density and the particle size are small even if it is less than or exceeds this range. This p
Preferably, the H range is maintained throughout the reaction. Therefore, as the reaction mode, it is preferable to simultaneously add the raw materials hexafluoroaluminic acid and ammonia.

To obtain hexafluoroaluminic acid as a raw material, 6F / A when dissolving aluminum hydroxide in hydrofluoric acid is used.
The molar ratio is preferably in the range of 0.9 to 1.1. When the molar ratio is low, the powder properties are improved, but NH ₄ AlF ₄
And the like. On the other hand, when the molar ratio is high, the particle size and the bulk density are small, and the loss of NH ₃ and hydrofluoric acid increases.

The reaction temperature is not particularly limited. However, since the reaction is exothermic, the amount of raw materials added is limited in order to carry out the reaction at a low temperature, and the productivity cannot be said to be good. In consideration of these conditions, the reaction at 30 ° C. or higher is generally preferred.

The thus obtained reaction slurry is solidified.
NF is separated by liquid separation and drying. _ThreeSuitable for gas production
Ammonium cryolite with high bulk density and large average particle size
Can be NF_ThreeIn the manufacture of
Is a reaction between element cryolite and elemental fluorine.
NH as the reaction residue_FourAlF_FourRemains. 2
5% ammonia water and 55% hydrofluoric acid are reacted at about pH 8.
To obtain ammonium cryolite
Therefore, such a recycling process should be taken industrially.
Is preferred.

[0015]

The present invention will be described below in detail with reference to examples. Examples 1 to 3 and Comparative Examples 1 to 6 25% ammonia water and 3
The reaction was carried out at a reaction temperature of 60 ° C. while adjusting the pH to a predetermined value while stirring 0% H ₃ AlF ₆ . The reaction slurry was dried at 150 ° C. after solid-liquid separation. The results are shown in Table 1.

[0016]

[Table 1]

Example 4 (NH) prepared in Example 1_Four)_ThreeAlF₆And elemental
NF _ThreeWas manufactured. 100l tephro
The reaction residue NH_FourAlF_FourAnd 25%
Reaction at pH 8 with ammonia water and 55% hydrofluoric acid
(NH_Four)_ThreeAlF₆Was manufactured. Reaction slurry
Was dried at 150 ° C. after solid-liquid separation. Average particle size 120μ
m, bulk density 0.95g / cm^Three(NH_Four)_ThreeAlF
₆was gotten.

COMPARATIVE EXAMPLE 7 25% aqueous ammonia was charged into a 100 l Teflon reaction tank, and a 30% H ₃ AlF ₆ solution was added to the slurry p with stirring.
After H was added to 8, the reaction slurry was solid-liquid separated and dried at 150 ° C. The obtained (NH ₄ ) ₃ Al
The average particle size of F ₆ is 13 μm, and the bulk density is 0.25 g / cm.
^{Was 3} .

Comparative Example 8 A 30% H ₃ AlF ₆ solution was charged into a 100 l Teflon reaction tank, and 25% aqueous ammonia was added to the slurry p with stirring.
After H was added until H was 8, the reaction slurry was solid-liquid separated and dried at 150 ° C. The obtained crystals are (NH ₄ ) ₃
NH ₄ AlF ₄ in addition to the 10-15% of AlF ₆ were included. The results are shown in Table 2.

[0020]

[Table 2]

Example 5 (NH ₄ ) ₃ AlF ₆ was produced in the same manner as in Example 1 except that the reaction temperature was changed at a reaction pH of 8. The results are shown in Table 3.

[0022]

[Table 3]

[0023]

According to the present invention, it is possible to easily obtain ammonium cryolite, which is extremely suitable as a raw material for producing NF _{3 which} is useful as a gas for gas cleaning in a semiconductor manufacturing apparatus or the like.

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Claims (1)

(57) [Claims] 1. A process for producing ammonium cryolite, characterized by simultaneously adding hexafluoroaluminic acid and ammonia to crystallize the mixture at a reaction pH in the range of 6 to 8.5.