JPS604125B2 - Manufacturing method of high purity silicon tetrafluoride - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high purity silicon tetrafluoride suitable for producing amorphous silicon semiconductors for electronic materials, solar cell elements, etc.

It is well known that silicon tetrafluoride can be obtained by the reaction of silicon oxide and hydrogen fluoride according to the formula {1), and it is also well known that it is produced by the sulfuric acid decomposition of phosphate rock during wet phosphoric acid production. It is also well known that in the presence of water produced by or other moisture, it is easily hydrolyzed to produce silicic acid and silicic acid gel as shown in formula (2).

Si02 14HF → SiF4 12th 20
{1} $iF4 12th 20 → 2nd day 2SiF6 10Si0
2. Therefore, in order to suppress the reaction of formula (■), methods are used to separate SiF4 and SiF4 by maintaining the temperature at a high temperature to prevent water condensation, or by washing the generated gas with a water-absorbing medium such as sulfuric acid. .

The present inventors suspended and dispersed amorphous or crystalline silicon oxide in sulfuric acid as a silicon oxide raw material, added hydrofluoric acid or anhydrous hydrogen fluoride to this, and simultaneously reacted to generate silicon tetrafluoride. It has been found that in a method in which SiF4 is isolated by immediately absorbing the generated water in a medium of sulfuric acid, hexafluorodisiloxane is often mixed as an impurity in the obtained silicon tetrafluoride.

Hexafluorodisiloxane (SiF3-○-SiF3)
If SiF4 contains siloxane bonds, the siloxane bonds will enter the bond lattice of silicon during the production of an amorphous silicon thin film due to glow discharge, etc., and this will have a significant adverse effect on the optical characteristics. The object of the present invention is to obtain highly pure SiF4 containing extremely little hexafluorodisiloxane.

Although the formation mechanism of hexafluorodisiloxane is not necessarily clear, it is presumed that the reaction between Sj02 and HF proceeds as a sequential reaction as follows. AiF4 Toka 201 SjF3
10-SiF3 Jugonghua {8}'5-, The day 20 produced in the reaction of {6) is absorbed into the sulfuric acid medium and produces SiF4, but the sulfuric acid concentration gradually decreases.

On the other hand, the reaction [7] also occurs in competition with the chemical reaction, and once SiF4 is absorbed into sulfuric acid, it reacts with water corresponding to the water vapor pressure corresponding to the sulfuric acid concentration8).
It is thought that hexafluorosiloxane is produced as shown in the figure. Based on the above findings, the present inventors brought silicon tetrafluoride gas (containing a small amount of hexafluorosiloxane) obtained in advance into contact with aqueous sulfuric acid solutions of various concentrations, and found that the amount of hexafluorodisiloxane produced was significantly different depending on the sulfuric acid concentration. This was confirmed by observing the infrared absorption spectrum of the gas. That is, the infrared absorption spectrum of SiF4 is strongest at 1031 skin-1, 391, 1191, 1294
"1827, 2057 has strong absorption to skin-1, and SiF
31○-SiF3 is strong against 839, 1205 enemy-1, 9
84, 1032, 1040, 1242, 12 porridge-1,
shows a spectrum with medium absorption, but “2 of SjF4
057 Fox-1 (Si-F expansion/contraction), SiF3-0-SiF
Since the 839 arc-1 of 3 (stretching and contraction of Si-F) exists independently, it is possible to estimate the amount of SiF3 101 SiF3 in SiF4 by comparing the magnitude of absorption at this wave number. It is. When the amount of SjF3-○-SiF3 at various sulfuric acid concentrations was measured using this method, it was found that "at sulfuric acid concentration of 85% or more, SiF3-○- in the raw material SjF4
It was confirmed that while the amount of SjF3 hardly changes, it increases rapidly below 80%. Table 1 and Figure 1 show the infrared absorption peak of 2057-1 of SiF4 and SiF3
-○- The change in the ratio of the infrared absorption peak of 839 skin-1 of SiF3 is shown with respect to the sulfuric acid concentration (SiF4 flow rate constant, temperature at room temperature, day 04 trap 250'). Table 1 Various sulfuric acid concentrations and (SiF3)20 production amount Raw material Si
(SiF3)20 peak ratio in R gas.

Evening (1-T, /〆TO) 839 佽-1ノ〃. Evening (1-T
No r. ) 2057 ghost 120,101'/〇,848
=〇,119 Based on the above results, the present inventors further conducted the following experiment to confirm the influence of the sulfuric acid concentration in the reaction system. ■Sj02/day2 in 95% sulfuric acid
The silicon oxide raw materials were mixed and suspended so that the S04 molar ratio was 0.33, and anhydrous hydrofluoric acid was reacted in an equivalent amount with Si02.The sulfuric acid concentration after the reaction was measured and was 85%, indicating that the amount of sulfuric acid generated during this time was 85%. Most of SjF4 contains SiF3-
It was found that SiF3 does not exist. ■Si02 and Ni2S04 are mixed so that the molar ratio is 0.5,
The SjF4 gas generated when an equivalent amount of HF is reacted with Si02 is stored in a trap at a liquid N2 temperature, and the gas is vaporized using a 100° C.
SiF3-0-
It was confirmed that a minute peak of SiF3 existed. The final sulfuric acid concentration at this time was 80.3%. ■90% day 2 When Si02 is added so that the Sj02/ratio S04 molar ratio is 0.7 during S04 and reacted with hydrofluoric anhydride, SjF4 is generated with the addition of hydrofluoric anhydride, but at the start of the reaction,
It was confirmed that at the end of the reaction, the amount of SiF3--SiF3 produced in the generated gas was very different and increased as the reaction progressed. The final sulfuric acid concentration in this case was 73%. Figure 2 shows the Si02/ratio S04 molar ratio 0.7, day 2S0
4 shows the infrared absorption spectra of the produced gas at the start and end of the reaction when the concentration is 90%.

These results show that the production of hexafluorodisiloxane is overwhelmingly based on the shelf method, and the medium sulfuric acid concentration must be 80% or more, preferably 85% or more to produce hexafluorodisiloxane. The present invention was achieved by confirming that the conditions do not allow this. That is, the present invention is characterized in that when producing silicon tetrafluoride through a contact reaction between crystalline or amorphous silicon oxide and hydrogen fluoride using sulfuric acid as a medium, the concentration of sulfuric acid in the medium is maintained at 80% or more. This is a method for producing high-purity silicon tetrafluoride. In the present invention, the reaction concentration is not particularly limited, but when the reaction is carried out at room temperature, the reaction solution temperature increases with the addition of hydrofluoric anhydride to 65 to 70°C. The pressure is not particularly important, but it is best to keep it below 2 to 3 degrees of mercury to avoid excessive decompression. When carrying out the method of the present invention, it is important to take measures to prevent the concentration of sulfuric acid in the medium from becoming less than 80%. It is also possible to add sulfuric acid separately to compensate for the decrease in sulfuric acid concentration. Alternatively, a slurry in which SiQ is uniformly dispersed and suspended in sulfuric acid at a predetermined concentration is continuously introduced into the reactor, and at the same time, anhydrous hydrofluoric acid or anhydrous fluoric acid is added. It is also possible to introduce a mixed acid obtained by absorbing an acid into sulfuric acid at a predetermined concentration into an equivalent reactor to continuously generate SjF4, and to keep the medium sulfuric acid concentration constant at 85% or more.

Examples of silicon oxide raw materials that can be used in the present invention include crystalline silicon oxide such as silica sand, quartz, and crystal powder, silica gel or its powder, ferrosilicon dust, and silicon oxide by-produced during the manufacturing process of chemical industrial products. Examples include amorphous silicon oxide. Hydrofluoric acid and anhydrous hydrogen fluoride (hydrogen fluoride gas) can both be used as raw materials for presentation, but in order to maintain the medium sulfuric acid concentration at 80% or higher, they must contain as little water as possible. Also, from the viewpoint of handling, it is advantageous to use hydrogen fluoride gas or lacrimal acid absorbed in sulfuric acid.The present invention will be described in more detail with reference to Examples.Example 1 Inside coated with polyethylene A mixed slurry of 189 ml of finely ground frog sand containing 95% 2S04,600 ml and 999% Si, which is crystalline silicon oxide, was placed in the closed reactor.

At this time, the Sj02/day ○4 molar ratio is 0.534. This slurry is heated at 2pm), 98% day 2S
The air dehumidified in Q was flowed through the entire reaction system including the reactor for about 5 hours at a flow rate of 10 Z'min, and after replacing the air in the reaction system, the air was stopped and the hydrogen fluoride gas was heated for 40 T'Hr. The reaction was started by blowing into the reactor at a rate of . The temperature of the liquid in the reactor was 20 qC before the start of the reaction, and started to rise with the start of the reaction, reaching 6.0 qC after 1 hour, and maintained an almost equilibrium state thereafter. The reaction lasted for 6 hours, and the gas generated during this time was -15
It was collected as a solid in a pressure-resistant cooling trap at 0°C. Later, this trap is kept at room temperature and the entire amount is gasified, and this is converted into Na
The absorption peak of 839 arc-1 of hexafluorodisiloxane was obtained by measuring the infrared absorption spectrum using a Hitachi EPI-G21 model infrared spectrophotometer using a 100% gas cell with a CI window plate. is SiF4 2057 skin-1
It was confirmed that the SiF4 gas was of high purity with an absorption peak of 0.0. The final sulfuric acid concentration in the reactor under these conditions was 81%. Example 2 A slurry prepared by adding 200% of SJ02 crystal powder, which is crystalline silicon oxide, with a purity of 99.8% to 41,000 liters of 95% water was placed in a closed reactor with an internal volume of 8 and heated from the outside. After the liquid temperature was maintained at 60 oo, and the entire reaction system was replaced with N2 gas, the hydrogen fluoride gas was replaced with 60 oo.
It was introduced into the slurry at a rate of 0 pm/Hr to start the reaction.

As the liquid temperature rises as the addition of hydrogen fluoride gas begins, it is cooled externally to keep the reaction temperature within the range of 70 to 8,000 ℃, allowing the reaction to continue for 5 hours. During this time, the entire amount of gas generated is placed in a pressure trap cooled with liquid nitrogen. After storing the gas at
The absorption ratio of 839ka-1 between 057ka-1 and (SiF3)20 was 0.04, confirming that it was SiF4 gas with extremely low content of (SiF3)20. At this time, the 2S04 concentration in the reactor on the last day was 85%. Example
3 90% Sunshine 04 N from NabuiF6 in 100 parts by weight
A slurry in which parts by weight (Si02 component 93%) of the amorphous powder produced in the process of manufacturing AIF6 is suspended and HF: 4: 20 weight ratio is 28.6: 6
7.8:3.6 sulfuric acid-oxygen acid was continuously added to a closed reactor with an inner volume of 3 covered with polyethylene at a weight ratio of slurry and mixed acid of 1:0.75. The medium sulfuric acid concentration in the reaction system was maintained in the range of 85 to 87% by injecting the reactor and carrying out the reaction across the ocean, removing the reaction-completed liquid from the bottom of the reactor, and simultaneously generating Sip4 gas continuously.

This generated gas was passed through a 98% day 2S04 cleaning trap to absorb and remove unreacted HF, then compressed and filled into a pressure container, and then subjected to infrared spectrometry using a Hitachi EPI-G21 type gas cell with a 100% NaCI window plate. The result of measuring the infrared absorption spectrum with a multimeter was 83 of hexafluorodisiloxane.
The absorption of 9Hada-1 was extremely small, confirming that it was a high purity SiF4 gas.

[Brief explanation of drawings]

Of the attached drawings, Figure 1 shows the infrared absorption peak of 2057 arc-1 of SiF4 and the 839 arc-1 of SiF3-○-SiF3.
FIG. 2 is a graph showing the relationship between the change in the ratio of the infrared absorption peak of 1 and the sulfuric acid concentration.
．． 7. Day 2 Shows the infrared absorption spectra of the produced gas at the start and end of the reaction when the S04 concentration is 90%. 1 diagram ice 2 diagram

Claims (1)

[Claims] 1 When silicon oxide and hydrogen fluoride are subjected to a contact reaction using sulfuric acid as a medium to produce silicon tetrafluoride, the concentration of sulfuric acid in the medium is 80%.
A method for producing high-purity silicon tetrafluoride, characterized by maintaining the above-mentioned purity.