JPS604126B2 - Purification method of silicon tetrafluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the production of high purity silicon tetrahydride suitable for the production of amorphous silicon semiconductors such as electronic materials and solar cell elements.

More specifically, the present invention provides SiOF2, (SiF3)2
The present invention relates to a method for purifying silicon tetrafluoride containing oxygen-containing silicon fluorides such as 0, (SiF3)2SjF202, and optionally sulfur compounds such as S02, S03, and 2S. Generally, silane gas is used as a raw material for manufacturing amorphous silicon semiconductor films, but in recent years, the properties of amorphous silicon containing fluorine have attracted attention, and high-purity silicon tetrafluoride gas is used as its raw material.

The type of impurities in this gas differs depending on the manufacturing method, but
Silicon tetrafluoride currently on the market contains many impurities, and the physical properties of amorphous silicon semiconductors obtained from it are not necessarily satisfactory. As a result of various studies conducted by the present inventors regarding these impurities,
General silicon tetrafluoride gas contains oxygen-containing silicon fluoride, mainly (SiF3) containing only a few hundred units of 20.
S02, S03, and H2S are mainly found in dozens of sulfur compounds.
It turned out that the side degree was included.

These impurities are added to the Si skeleton during the process of manufacturing an amorphous silicon film by glow discharge decomposition of silicon tetrafluoride.
This causes the introduction of and ○ atoms, which has an adverse effect on the physical properties of the semiconductor. The use of adsorbents as a means of removing impurities present in gases has long been known, but there are no examples of using adsorbents to remove impurities from silicon tetrafluoride gas. Not yet known.

The present inventors researched various adsorbents to remove oxygen-containing fluorides such as (SiF3)20 and sulfur compounds such as S02, S03, and Hibu, and found that only activated carbon showed a specific effect. This discovery led to the completion of the present invention.

That is, the present invention is a method for purifying silicon tetrafluoride, which comprises bringing silicon tetrafluoride containing an oxygen-containing silicon fluoride and optionally a sulfur compound as impurities into contact with activated carbon. Zeolite, activated alumina, silica gel, activated carbon, etc. are generally known adsorbents and are widely used for purposes such as purification and drying. Among these adsorbents, zeolite-based adsorbents, such as molecular sieves, etc. It is well known that sulfur compounds such as S02, S03, and Hb can be removed by selecting appropriate pore conditions.
It has been found that zeolite-based adsorbents are not suitable for removing these impurities from silicon tetrafluoride. The reason for this is that silicon tetrafluoride reacts with the components in the zeolite, producing a large amount of oxygen-containing silicon oxides, their polymers, silicon oxides, etc., and rather contaminating the silicon tetrafluoride. This also applies to activated alumina or silica gel. In contrast, the present inventors found that (Si in silicon tetrafluoride)
F3) Oxygenated silicon fluoride such as 20 and S02, S03
It was discovered that activated carbon is uniquely superior in removing sulfur compounds such as Ni2S, and it can remove oxygen-containing silicon fluoride extremely well, even when sulfur compounds are present. It was confirmed that this was almost completely removed.

Silicon tetrafluoride from any process is applicable to the present invention, and for example, silicon tetrafluoride obtained by contacting silicon oxide and hydrogen fluoride with sulfuric acid as a medium is used.

In this case, the higher the sulfuric acid concentration is, for example, 80% or more, the more significantly (SiF3)20 is reduced (separately proposed by the present inventors); When applied to silicon tetrafluoride, even higher purity silicon tetrafluoride can be obtained. Furthermore, it has been found that if it is necessary to further remove (SiF3)20, this can be done extremely well by reducing the amount of water in the activated carbon as much as possible.

In general, activated carbon has an equilibrium adsorption amount of water of less than 2-3% on a dry basis at a temperature of 40% or less, and is often used as is unless there is a particular need, or if it has already been adsorbed before use. Even when used after drying to remove moisture etc., this drying is usually carried out to about 120 to 180 oo. However, with this level of drying treatment, it is normal for the activated carbon to still contain more than 0.7% moisture on a dry basis, and this very small amount of moisture remaining in the activated carbon causes the m-type reaction. Since (SiF3)20 is generated in . *AiF4 10th 201st (SiF3) 20th is F [
1} (Sip3) It is difficult to completely remove 20, and if further purification is necessary, use activated carbon whose moisture content is at least 0.7% or less on a dry weight basis. It is necessary.

In order to obtain such a moisture content, it is difficult to achieve such a moisture content by ordinary drying as described above, and specific activation conditions are required. The conditions include, for example, in order to prevent the combustion of activated carbon and the influence of moisture in the atmosphere, in an inert gas such as nitrogen gas under increased pressure or reduced pressure, or in a vacuum of 180 to 500 ton.
There is a method of heating at a temperature of 200 to 350 degrees. Heating time varies depending on equipment, temperature, etc.
For example, in the case of an adsorption layer with an inner diameter of 3 mm and a layer height of 20 mm,
0000 and requires heating for about 4 hours. After heating, it is necessary to either leave it to cool or forcibly cool it, and be especially careful not to let it come into contact with moisture during this time.
For example, when coming into contact with air, it is necessary to sufficiently and completely remove moisture from the air. Regardless of the type of activated carbon used in the present invention, such as chassis shell carbon, animal bone carbon, or coal-based carbon, and regardless of its shape, when activated under the conditions described above,
Oxygen-containing silicon fluoride is adsorbed extremely well, and highly pure silicon tetrafluoride can be obtained.

Oxygenated silicon fluoride in silicon tetrafluoride, especially (SiF3)2
As a guideline for the degree of purification of 0, the infrared absorption spectrum of silicon tetrafluoride gas is measured using a gas cell with a length of 10 relative length equipped with a KB window plate.
Absorption derived from stretching vibration and SiF3 of (SiF3)20
The absorption ratio of 83-1 due to the stretching vibration is (2)
It can be determined relatively by calculating the absorption ratio using the formula and comparing the absorption ratio between both the raw material gas and the purified gas. Absorption ratio=-log(・-person)839ｽ-・/-log
(・-person) 2o57佽-1'21 In order to describe the present invention in more detail, Examples will be shown below. Examples 1 to 7 The blood of S022Q Misaki and S034 contains (SiF3)20 as an oxygen-containing silicon fluoride, and the absorption ratio of the 2057 arc-1 and Isokika-1 of this infrared absorption spectrum is 1.5 Silicon tetrafluoride gas was purified under the activation conditions shown in Table 1, water content in activated carbon, layer height, SiF4 flow rate, etc.

As a result of analyzing S02 and S03 in the purified gas and observing the infrared absorption spectrum, both S020.1 to 0.
．． 24 "S031~3 legs, indicating that it is removed well, and the absorption ratio of the infrared absorption spectrum indicating the presence of (SiF3)20 is also 0.15 or less, and in the case of raw material silicon tetrafluoride. The absorption ratio is significantly reduced compared to the absorption ratio of 1.5.Especially in Examples 4 to 7, the absorption ratio was 0.03 or less, and extremely pure silicon tetracide gas was obtained.Also, the amount of water in the activated carbon was heated to 500°C in vacuum), and the amount of weight loss until it reached a constant weight was regarded as the moisture content.Comparative Examples 1 to 4 Using the same silicon tetrafluoride gas used in Examples 1 to 7, Under the conditions shown in 1, molecular sieve (5A) (comparative example 1), molecular sieve (1iso) (comparative example 2), activated alumina (comparative example 3), and silica gel (comparative example 4) were used as zeolite-based adsorbents. Purification was performed using

As shown in Table 1, the results show that although some adsorption effects are observed for S02 and S03, both (SjF3)2
0 on the contrary, and white powder was produced, making it impossible to use it for refining tetrasilicone.・ Funato! Steam Fusuma Tomb Ken S Climber * Climber KQ ◎Misakizen to Hajime Gyoto** Example 8 S02 ■ Wind, S0310 Wind, Sun 2 S ■ Blood and (SiF3
) 20, and the absorption ratio of 2057-1 to 839-1 in the infrared absorption spectrum is 1.8. (crushed coal)
Inner diameter 25mm filled with 200mm, length 300w/
Purification was carried out by connecting the adsorbent to an adsorption layer and passing it through at a flow rate of 150/min.

This purified gas was stored in a -17000 pressure-resistant cooling trap and then completely gasified. The analysis result of this gas is S0
20.2 legs, S031 legs, Hibu 0.0 Yanagi, and a sample of this gas was collected at a gas pressure of 1 atm in a 100mm gas cell with a KBr window plate, and the infrared absorption As a result of measuring the spectrum, a highly purified silicon tetrafluoride gas was obtained in which almost no infrared absorption peak of Satoshikiji-1, which indicates the presence of (SiF3)20, was observed. The activated carbon in this example was activated as follows. 2 in nitrogen stream
After heating at 90°C to 110°C for 4 hours, the mixture was forcibly cooled to room temperature by sucking and circulating air dehydrated and decarboxylated with sulfuric acid and KOH using a vacuum pump. Example 9 S0220 skin,
Silicon tetrafluoride gas containing S083 wind and having an absorption ratio of 839 arc-1 of (SiF3) 20 and 2057 arc-1 of SiF4 of 0.078 is heated at a rate of 100 per minute.
Passed at a flow rate of 'S020.1 willow, S031.8
A silicon tetrafluoride gas having an infrared absorption ratio of (SiF3)20 to SiF4 of 0.15 was obtained.

This gas was further heat-treated in another vacuum for 300,004 hours to obtain an adsorbed moisture content of 0.10% (dry weight basis) in a column with an inner diameter of 35 mm and a height of 25 mm filled with granulated chassis shell activated carbon. Purification was carried out by passing at a flow rate of 100 min/min. After storing this purified gas in a pressure-resistant cooling tube at -170°C for about 200 days, the entire amount is gasified, and the SO0 in this gas is
2. The result of S03 analysis is SQO. Bow legs, S031. The gas was collected in a 100-cell gas cell equipped with a KBr window plate at a pressure of 1 or 1 atm, and the infrared absorption spectrum was measured.
)20 absorption ratio was 0.013. Example 10 Finely powdered amorphous silicic acid created in the process of producing Na3NFs from Na2SiF6 was suspended and dispersed in 85% purified Hibu 04, and anhydrous hydrogen fluoride gas was poured into the suspended system while stirring. By injecting the impurity composition into S021.5 legs,
A silicon tetrafluoride gas was obtained which was on the S03■ side, contained a small amount of (SiF3)20 as determined by infrared absorption spectrum measurement, and had an absorption ratio of 0.15.

Claims (1)

[Claims] 1. A method for purifying silicon tetrafluoride, which comprises bringing silicon tetrafluoride containing oxygen-containing silicon fluoride into contact with activated carbon.