JP2931660B2 - Purification method of silicon tetrafluoride gas - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for purifying silicon tetrafluoride (SiF ₄ ) gas.

More specifically, carbon dioxide (CO) in silicon tetrafluoride gas
₂ ) The removal method.

[Problems to be solved by conventional technology and invention]

Silicon tetrafluoride gas has recently attracted attention as a raw material for amorphous silicon thin film semiconductors and as a dry etching agent, but high purity silicon tetrafluoride gas for these uses is required.

Silicon tetrafluoride gas is produced by various methods, but in most cases contains carbon dioxide as an impurity. Silicon tetrafluoride gas is produced by various methods such as an acid decomposition method of an acid of silicofluoric acid or a silicofluoride compound, a pyrolysis method of a silicofluoride compound, or a synthesis method by a reaction between hydrogen fluoride and silicon dioxide. Have been.

However, since the silicon tetrafluoride gas obtained by these production methods contains several hundred ppm of CO ₂ , it must be removed. Especially when used as a raw material of amorphous silicon thin film semiconductor, the presence of CO ₂ causes a large amount of oxygen to be mixed into the generated silicon thin film,
Since it has a bad influence on semiconductor characteristics, it must be particularly removed.

Regarding the removal of CO ₂ , there is known a method of removing by adsorption using activated carbon, activated alumina, zeolite, or the like. However, when these adsorbents are used, the main gas, silicon tetrafluoride, is also adsorbed at the same time, so that there is a problem that the yield is reduced. For the adsorption removal method using zeolite, see JP-A-59-50016.
There is a strong demand for a method of reducing high-purity silicon tetrafluoride gas, which is required for amorphous silicon thin film semiconductor raw materials, ie, impurities, particularly CO _2, to about several ppm.

[Means for solving the problem]

In view of such a situation, the present inventors consider that CO 2 in silicon tetrafluoride
As a result of intensive studies using various adsorbents on the removal method of ₂ , as a result of heat treatment of the hydrotalcite-like compound, CO ₂ of silicon tetrafluoride gas was extremely efficiently removed, and silicon tetrafluoride was removed. They have found that they can be removed without reducing the yield, and have completed the present invention.

That is, the present invention provides a hydrotalcite that has been previously dehydrated, in a state where water is not substantially mixed therein, from -10 to -90.
Aeration in the temperature range of 100 ° C.
The present invention relates to a method for purifying silicon tetrafluoride gas which is heat-treated in the range of ° C.

[Detailed Disclosure of the Invention]

 Hereinafter, the present invention will be described in detail.

Hydrotalcite is a natural mineral that is produced as a mixture with penitrate, muskovite, etc. in limited areas, such as Norway's Sunalm and the Soviet Ural. However, synthetic products that are more stable than natural products are preferably used.

The hydrotalcite-like compound (hereinafter referred to as hydrotalcite) used in the present invention is a compound having a MOL of [15,
2, 31 (1977) and 15, 10, 32 (1977)].

^{_{[M 1-X 2+ M X}} 3+ (OH) 2] X + [A x / n n- · mH 2 O] in ^x-, M ²⁺
Is a divalent metal, Mg ²⁺ , and M ³⁺ is a trivalent metal, Al ³⁺ . A ^n- is an n-valent anion such as Cl ⁻ , Fe (CN) ₆
^4- . x is in the range of 0 <x <0.33.

As a production method, an aqueous solution of aluminum chloride, an aqueous solution of magnesium chloride, an aqueous solution of sodium carbonate and an aqueous solution of sodium hydroxide are continuously supplied to a reaction vessel at normal temperature and normal pressure and mixed. The feed rates of these mixtures are adjusted with sodium hydroxide to maintain pH = 10-11. The obtained suspension is filtered, washed with water, dried, formed into a spherical shape of about 2 mm by a granulator, further immersed in a K ₄ Fe (CN) ₆ solution, filtered, and dried.

Since the obtained hydrotalcite contains several percent of water, it is subjected to a dehydration treatment.

The dehydration treatment is performed at a temperature of 100 to 300 ° C. 100
If the temperature is lower than ℃, desorption of interlayer water becomes insufficient, and the amount of adsorbed CO ₂ decreases. If the temperature exceeds 300 ° C., desorption of the structural water in the hydrotalcite starts, causing a structural change and a decrease in the amount of adsorption.

The heating time depends on the processing temperature, but is preferably about 1 to 5 hours.

Purification of the silicon tetrafluoride gas is performed by a method in which the gas is passed through a hydrotalcite layer filled in a column or the like. The ventilation temperature at this time is preferably from -10 to -95C.

If the aeration temperature exceeds −10 ° C., the ability to adsorb CO ₂ decreases. Therefore, there is a problem that the amount of the adsorbent must be increased and the container to be filled must be enlarged. If the temperature is lower than −90 ° C., the sublimation temperature of silicon tetrafluoride is −95 ° C.
Therefore, operation is practically difficult below this temperature.

The ventilation rate of the silicon tetrafluoride gas to the hydrotalcite layer depends on the filling amount of the hydrotalcite, but it is 0.3 to 0.6.
m / min is preferred.

The pressure of silicon tetrafluoride at the time of ventilation is not particularly limited. For example, the pressure can be set within a range from a vacuum of about 1 torr to a pressure of about 10 atm.

The method for analyzing carbon dioxide in silicon tetrafluoride gas is performed by gas chromatography.

The present invention provides a method for adsorbing and removing carbon dioxide in silicon tetrafluoride gas in this manner, by dehydrating the adsorbent,
The carbon dioxide is completely removed by a very simple method of using under specific conditions, and there is no adsorption amount of silicon tetrafluoride as a main component, so that it can be purified in a good yield. It is possible to provide high-purity silicon tetrafluoride used as a raw material for an amorphous silicon thin film semiconductor and a dry etching agent.

Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples. In the following,% and ppm are on a volume basis unless otherwise specified.

Example 1 A 10-neck four-neck separable flask equipped with a stirrer, a thermometer, and a reflux condenser was charged with an aqueous solution of aluminum chloride 3 (0.2 m
ol), an aqueous solution of magnesium chloride 3 (10.6 mol) and an aqueous solution of sodium carbonate 3 (0.15 mol) were added and, after stirring well, sodium hydroxide was added so as to maintain the pH at 10 to 11,
The reaction was performed for 3 hours. The obtained suspension was filtered, thoroughly washed with water, dried, and pulverized well.
The shape was spherical. Thereafter, it was further immersed in a K ₄ Fe (CN) ₆ solution, filtered, and dried to obtain spherical hydrotalcite.

Thereafter, a stainless steel column having an inner diameter of 15 mm was filled with hydrotalcite granulated to 2 mm (filling height: 400 mm), and then dehydration treatment and aeration of silicon tetrafluoride gas were performed under the conditions shown in Table 1.

As a result of measuring the content of CO ₂ before and after aeration of the silicon tetrafluoride gas into the hydrotalcite layer by gas chromatography, it was found that the CO ₂ content was favorably removed. Also, as a result of calculating the yield from the weight of silicon tetrafluoride before and after aeration,
It was found that silicon tetrafluoride had a small amount of adsorption on the hydrotalcite layer.

Examples 2 to 3 The hydrotalcite produced in Example 1 was treated under the heating conditions shown in Table 1 and aerated under the conditions shown in Table 1.

As a result, as in Example 1, it was found that the amount of silicon tetrafluoride adsorbed on the hydrotalcite layer was small.

Examples 4 and 5 Using the hydrotalcite manufactured in Example 1, the temperature in the column under the aeration conditions performed in Example 1 was changed to the conditions shown in Table 1 and aeration was performed.

As a result, as in Example 1, it was found that the amount of silicon tetrafluoride adsorbed on the hydrotalcite layer was small.

Comparative Examples 1-2 Using the hydrotalcite produced in Example 1, heat treatment was performed under the heating conditions shown in Table 2 and ventilation was performed under the conditions shown in Table 2. As a result, it was found that CO ₂ was not sufficiently removed depending on the heat treatment conditions of hydrotalcite.

Comparative Examples 3 to 5 Using the same apparatus as in Example 1, heat treatment was performed using the adsorbents shown in Table 2 under the heating conditions shown in Table 2, and aeration was performed under the conditions shown in Table 2. As a result, although CO ₂ was sufficiently removed by the adsorbent, it was found that silicon tetrafluoride adsorbed a large amount on the hydrotalcite layer, and the yield was reduced.

[Effects of the Invention] As described in detail above, the present invention provides a method of removing CO _{2 in} silicon tetrafluoride gas, in which hydrotalcite as an adsorbent is heated to a specific temperature in advance and dehydrated. -10 to -90 ° C. and a state in which substantially no water is mixed in, which is a very simple method of passing silicon tetrafluoride gas.

That is, in Comparative Examples 3 to 5 in which the adsorbent was other than hydrotalcite, the yield of silicon tetrafluoride was reduced, and in Comparative Examples 1 and 2, in which the dehydration treatment of silicon tetrafluoride was out of the range. The yield of silicon fluoride decreases, and improvement in yield is not achieved. On the other hand, the examples using hydrotalcite and the use conditions within the range are capable of removing only CO ₂ without lowering the yield of silicon tetrafluoride, and these performances are poor. It is clear that all are excellent, and the significance of the present invention is great.

Claims (2)

(57) [Claims] The present invention is characterized in that the hydrotalcite compound represented by the general formula (1) is subjected to a dehydration treatment in advance and aerated in a temperature range of -10 to -90 ° C in a state in which substantially no water is mixed. A method for purifying silicon tetrafluoride gas. [M _1-X ²⁺ M _X ³⁺ (OH) ₂ ] ^{X +} [A _{X / n} ⁿ⁻ · mH ₂ O] ^x− (1) (where M ²⁺ is a divalent metal Mg ²⁺ , M ³⁺ is trivalent metal Al ³⁺ , ^An-
N-valent anion, for example Cl ^-, Fe (CN) shows ₆ ^4-. x
Indicates 0 <x <0.33. ) 2. The method according to claim 1, wherein the dehydration treatment is performed by heating at a temperature in the range of 100 to 300 ° C.