JPH06247708A - Purifying method of hydrosilicofluoric acid - Google Patents

Abstract

(57) [Summary] [Structure] 100 kg of hydrosilicofluoric acid (hydrogen fluoride 7.8 mol / liter, silicon tetrafluoride 3.9 mol / liter)
While stirring potassium permanganate, which is an oxidizer, is added until the liquid color becomes pale purple, the liquid is introduced into a distillation apparatus made of fluororesin and heated and distilled, and the sulfur contained in the aqueous solution is added. Compounds, phosphorus compounds, boron compounds and arsenic compounds are oxidized and removed. [Effect] It is possible to remove impurities, which have been difficult to purify only by the conventional distillation method, to an ultratrace amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying hydrosilicofluoric acid.

[0002]

2. Description of the Related Art Conventionally, a technique of depositing silicon dioxide on a substrate in hydrosilicofluoric acid is known (for example, JP-A-57-196744 and 61-12034).
No. 61-28104, No. 62-20876, and JP-A No. 1-367770).

This technique is used for coating silicon dioxide on optical disks and liquid crystal glass substrates and for forming insulating films on semiconductor elements. The chemicals used in the above fields are required to have extremely high purity.
In particular, in the semiconductor device manufacturing process, since impurities such as sulfur compounds, phosphorus compounds, boron compounds and arsenic compounds are extremely disliked, there is an increasing demand for supplying high-purity hydrosilicofluoric acid. Further, commercially available hydrosilicofluoric acid is an ordinary semiconductor chemical (for example, hydrofluoric acid,
It contains a large amount of impurities as compared with hydrogen peroxide water, etc., and there is a problem in terms of the content of impurities for use in the above application fields.

Under such circumstances, it is desired to industrially establish a method for purifying hydrosilicofluoric acid, and the necessity of supplying high-purity hydrosilicofluoric acid is increasing.

This hydrosilicofluoric acid has a temperature of 100 to 140 ° C.
Since it is decomposed into silicon tetrafluoride, hydrogen fluoride and water by heating to a certain degree and gasified, it is conventionally known that impurities can be removed to some extent by distillation (see Japanese Patent Publication No. 43-17412). .

[0006]

However, in the case of refining hydrosilicofluoric acid, high-boiling metal impurities can be purified to the ppb level, which is a chemical grade for semiconductors, by the above-mentioned method. ,
Regarding impurities such as boron compounds and arsenic compounds, in addition to the compounds having various boiling points, the impurities themselves react with fluorine in hydrosilicofluoric acid to form fluorine compounds having considerable boiling points. There is a problem that it is very difficult to purify these impurities to the ppb level only by distillation because they are likely to be generated only by devising the device such as increasing the number of stages of the distillation column. .

[0007]

As a result of earnest studies, the present inventors have found that, in order to solve the above problems, sulfur is obtained by adding an oxidizing agent such as potassium permanganate to hydrosilicofluoric acid and subjecting it to heat distillation. It has been found that impurities such as compounds, phosphorus compounds, boron compounds and arsenic compounds can be removed in an extremely small amount, and the present invention has been completed.

That is, according to the present invention, in purifying hydrosilicofluoric acid, 0.3 to 1.3 times the molar number of silicon tetrafluoride is contained with respect to hydrogen fluoride, both of which are 20 to 65 weight percent. An oxidizing agent such as potassium permanganate is added to a certain aqueous solution and heated and distilled to oxidize and remove sulfur compounds, phosphorus compounds, boron compounds and arsenic compounds contained in the aqueous solution.

The object of the present invention is to purify hydrosilicofluoric acid by adding an oxidizing agent to an aqueous solution containing hydrogen fluoride and silicon tetrafluoride, and heating and distilling the solution.
Impurities that were difficult to purify by the above-mentioned distillation method alone,
It is to remove to a very small amount.

The oxidizing agent which can be used in the present invention is not limited to potassium permanganate, but may be one which has an oxidizing action on impurities such as sulfur compounds, phosphorus compounds, boron compounds and arsenic compounds in hydrosilicofluoric acid. Good. For example, potassium dichromate, potassium persulfate, hydrogen peroxide, fluorine gas, chlorine gas, ozone and the like can be used. Also,
The addition method may be such that it is added to the liquid of hydrosilicofluoric acid before distillation, or it may be added to a distillation can or a distillation column at the time of distillation.

[0011]

It is presumed that the impurities which were difficult to purify by the above-mentioned distillation method can be purified by the present invention as follows. 1 Impurities such as sulfur compounds, phosphorus compounds, boron compounds, and arsenic compounds are oxidized by an oxidant, and the boiling point of the resulting compound shifts to a remarkably higher side than the boiling point of hydrosilicofluoric acid, or conversely low. The shift to the side facilitates separation by distillation. 2 Impurities such as sulfur compounds, phosphorus compounds, boron compounds and arsenic compounds in hydrosilicofluoric acid are oxidatively decomposed by an oxidant, and the boiling point of the resulting compound is significantly higher than that of hydrosilicofluoric acid. Shifting or vice versa facilitates separation by distillation.

However, the effect of this oxidizing method and the refining method by heat distillation is practically sufficiently satisfactory, and has been confirmed by many experiments. Moreover, the purification method according to the present invention is such that the crude hydrosilicofluoric acid contains 0.3 to 1.3 times the molar number of silicon tetrafluoride with respect to hydrogen fluoride,
The effect is exhibited in a wide concentration range such as an aqueous solution in which both are 20 to 65% by weight.

[0013]

EXAMPLES The effects of the present invention will be described below with reference to examples, but the method of the present invention is not limited to these examples.

Example 1 100 kg of a raw material hydrosilicofluoric acid (hydrogen fluoride 7.8 mol / liter, silicon tetrafluoride 3.9 mol / liter) containing impurities shown in Table 1 was mixed with potassium permanganate to obtain a liquid color. It was charged until it showed a light purple color. The liquid was introduced into a distillation apparatus made of fluororesin, and heated and distilled to purify hydrosilicofluoric acid to obtain 80 kg of purified hydrofluorosilicic acid.
Then, the content of impurities in the purified hydrofluorosilicic acid
The results shown in Table 1 were obtained by the ICP-MS method and the ICP-AES method.

[0015]

[Table 1]

Example 2 200 kg of a raw material hydrosilicofluoric acid (hydrogen fluoride: 3.3 mol / liter, silicon tetrafluoride: 3.9 mol / liter) containing impurities shown in Table 2 was mixed with potassium permanganate to obtain a liquid color. It was charged until it showed a light purple color. The solution was introduced into a distillation apparatus made of fluororesin, and subjected to heat distillation to purify hydrosilicofluoric acid to obtain 170 kg of purified hydrofluorosilicic acid. Then, the content of impurities in the purified hydrofluorosilicic acid was examined by the ICP-MS method and the ICP-AES method, and the results shown in Table 2 were obtained.

[0017]

[Table 2]

Example 3 150 kg of raw material hydrosilicofluoric acid (hydrogen fluoride: 3.3 mol / liter, silicon tetrafluoride: 4.0 mol / liter) containing impurities shown in Table 3 was introduced into a distillation apparatus made of a fluororesin and distilled. The fluorohydrofluoric acid was purified by performing distillation at an evaporation rate of 15 kg / hour while introducing 100 ml / min of fluorine gas into the column to obtain 120 kg of purified hydrofluoric acid.
Then, the content of impurities in the purified hydrofluorosilicic acid
The results shown in Table 3 were obtained by an ICP-MS method and an ion chromatography method.

[0019]

[Table 3]

Raw material hydrosilicofluoric acid (hydrogen fluoride 7.8 mol / liter, silicon tetrafluoride 3.9 mol / liter) containing impurities shown in Table 4 was added to 100 kg of potassium dichromate.
200 g was added while stirring. The liquid was introduced into a distillation apparatus made of fluororesin, and heated and distilled to refine hydrosilicofluoric acid to obtain 70 kg of purified hydrosilicofluoric acid. And
The content of impurities in the purified hydrosilicofluoric acid was examined by the ICP-MS method and the ion chromatography method, and the results shown in Table 4 were obtained.

[0021]

[Table 4]

Comparative Experiment 100 kg of a raw material hydrosilicofluoric acid (hydrogen fluoride: 7.8 mol / liter, silicon tetrafluoride: 3.9 mol / liter) containing impurities shown in Table 5 was introduced into a distillation apparatus made of a fluororesin, and heated and distilled. Was performed to purify hydrosilicofluoric acid to obtain 65 kg of purified hydrosilicofluoric acid. Then, the content of impurities in the purified hydrofluorosilicic acid was examined by the ICP-MS method and the ion chromatography method, and the results shown in Table 5 were obtained.

[0023]

[Table 5]

[0024]

As is apparent from the above, the method for purifying hydrosilicofluoric acid according to the present invention is extremely effective in removing impurities such as sulfur compounds, phosphorus compounds, boron compounds and arsenic compounds in hydrosilicofluoric acid. It is valid.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tomokatsu Okada 2-6-10 Koraibashi, Chuo-ku, Osaka City, Osaka Prefecture Morita Chemical Industry Co., Ltd.

Claims (1)

[Claims] 1. An aqueous solution containing 0.3 to 1.3 times the number of moles of silicon tetrafluoride with respect to hydrogen fluoride, both of which is 20 to 65 weight percent, is added with an oxidizing agent such as potassium permanganate. A method for purifying hydrosilicofluoric acid, which comprises heating and distilling to oxidize and remove sulfur compounds, phosphorus compounds, boron compounds and arsenic compounds contained in the aqueous solution.