JPS6090810A - Manufacture of gaseous fluorosilane - Google Patents

Abstract

PURPOSE:To obtain gaseous fluorosilane of high purity by passing crude gaseous fluorosilane contg. silane compounds contg. chlorine as impurities through an activated carbon layer to remove said impurities. CONSTITUTION:Crude gaseous fluorosilane represented by formula I (where (n) is an integer of >=1, and (m) is 0-2n+1) contains silane compound contg. chlorine such as chlorosilane and partially fluorinated fluorochlorosilane in large quantities as impurities. The gaseous fluorosilane is passed through a column packed with activated carbon. Said impurities are removed by adsorption on the activated carbon to reduce the impurity content to <= several ppm, and gaseous fluorosilane of high purity for forming a thin film of amorphous silicon fluoride is obtd. Any of SiHF3, SiH2F2 and Si2F6 can be purified by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high-purity fluorosilane, and more particularly, to a method for producing high-purity fluorosilane suitable for forming a fluorinated amorphous silicon thin film.

Fluorosilan has recently attracted attention as a raw material for fluorinated amorphous silicon thin films. Currently, we are using tetrafluorosilane (silicon tetrafluoride (Si)).
F4)) is used as a raw material for amorphous silicon thin films, but silicon tetrafluoride alone does not form a thin film, so it must be mixed with hydrogen or silane, and it also has poor film formability. There are problems in that the film formation rate and uniform film formation are not necessarily satisfactory.

We have found that a uniform film can be easily formed by glow discharge decomposition of H-containing fluorosilanes such as 5iHFs and SiH2F2 or higher fluorosilanes such as Si2Fg.

However, these fluorosilanes are usually combined with chlorosilane/(or chlorohigher silane) and 5bF8, TiF4,
The fluorosilane gas obtained by this method contains impurities such as unreacted chlorosilane and partially fluorinated fluorochlorosilane and other chlorinated silane compounds. It is mixed as.

The content of these impurities varies depending on the reaction conditions, but is usually between 20,000 ppm and several thousand ppm (in terms of chlorine content), and when such fluorosilane is used as a thin film raw material, a large amount of chlorine is introduced into the thin film, which impairs the thin film properties. This has a negative impact on

That is, especially as the fluorosilane gas for forming a thin film, it is desirable to use a highly pure fluorosilane gas containing only a few ppn of chlorine impurities as described above.

The present inventors first tried the cooling condensation removal method and the liquefaction distillation method, which are commonly used methods for removing trace impurities present in gases, but fluorosilane containing chlorosilane and fluorochlorosilane as impurities was Because the boiling point difference between the silane compound and fluorosilane is small, and the boiling points of these components are very low, it has been found that it is difficult to effectively remove trace impurities down to the order of ppm using this method.

We have also attempted to adsorb and remove impurities using adsorbents such as silica gel and alumina, but these compounds have very similar physical properties to each other. It was found that it is difficult to selectively adsorb and remove only chlorosilane and fluorochlorosilane.

The present inventors investigated various methods for removing the above-mentioned chlorine-based impurities from fluorosilane, and as a result, discovered that activated carbon adsorbs chlorosilane and fluorochlorosilane extremely selectively, and completed the present invention. It's arrived.

That is, the present invention is directed to general formula (1)% formula %[) (where n is an integer such that n≧1, and m is an integer such that 0≦m≦20) containing a chlorinated silane compound as a main impurity.
The present invention provides a method for producing high-purity fluorosilane gas, which is characterized by passing crude fluorosilane gas represented by +1 (integer +1) through an activated carbon layer.

The fluorosilane gas in the present invention has the general formula (1) % formula % (1) (where n is an integer such that n≧1, and m is 0≦m≦2n
+1 integer), for example, SiF4, SiH
Fg, SiH2F2, SiHaF, 5i2Fe,
S i2HFs, 5i2H2F4.5izHsFs.

S 12H4F2.5i2HsFs SIs Fs,
Examples include 5isHF7 and SiH2F2.

The crude fluorosilane gas to which the present invention is directed is one containing a chlorine-based silane compound as a main impurity in the above-mentioned compound in an amount of about 20,000 ppm to several thousand ppm.

Therefore, the chlorinated silane compound contained as an impurity has a close relationship with the fluorosilane, for example, trifluorosilane is trichlorosilane (SiHCIg).
Fluorochlorosilane (Si HCl2F 1Si
HCI F2 ) and unreacted trichlorosilane are mixed in as impurities. Similarly, difluorosilane uses dichlorosilane (Si H2CI2) as a raw material, so the impurities include Si H2CI F and 5iH2C1□.
Furthermore, monofluorosilane (Si HgP ) contains monochlorosilane (Si HsCl ), which is a raw material, as an impurity.

The present invention is a method for obtaining high-purity fluorosilane gas by passing the crude fluorosilane gas through an activated carbon layer to selectively adsorb and remove the chlorine-based impurities on the activated carbon.

In the present invention, the activated carbon used is not particularly limited and can be used for all purposes such as gas purification, liquid phase, catalyst support, deodorization, and gas treatment. In the present invention, activated carbon is preferably packed in a layered column and crude fluorosilane gas is passed through the column, so activated carbon is preferably in the form of granules.

Of course, if it is in granular form, the activated carbon after aeration can be regenerated at an appropriate frequency and used repeatedly.

Incidentally, it is preferable that the activated carbon is pretreated by a commonly known method such as heat treatment or depressurization treatment prior to aeration of the fluorosilane gas.

In particular, by removing residual moisture in the activated carbon in advance by heat treatment or the like, it is possible to prevent the formation of siloxane due to the reaction between fluorosilane and water and prevent loss of fluorosilone.

In the present invention, there is no particular restriction on the temperature at which crude fluorosilane gas is vented to the activated carbon layer (processing temperature), but if the venting temperature is too low, the processing equipment will be expensive, while if it is too high, the adsorption effect of impurities will be reduced. A range of 0 to -75°C is preferred.

Of course, in this temperature range, the treatment temperature is preferably as low as possible, as long as it is above the dew point of the fluorosilate, which is determined by the operating pressure. There is no particular restriction on the pressure of fluorosilane during ventilation, and it may be increased pressure, normal pressure, or reduced pressure, and can be carried out, for example, in the range of reduced pressure of about I Torr to increased pressure of about 10 atmospheres.

Next, the present invention will be explained in more detail based on examples.

Examples 1-3 The apparatus shown in FIG. 1 was used.

Stainless steel column IK with inner diameter 1511J, average particle size 0
．． Filled with 7 sweetfish granular activated carbon (coconut husk charcoal for gas purification) (
After the filling height was 40 crn), it was set in the refrigerant 2 maintained at a constant temperature. Various crude fluorosilane gases were passed through the column from cylinder 3 under the conditions shown in Table 1. The obtained gas was placed in a cylinder 5 filled with liquid nitrogen 4. Note that 6 is a vacuum pump for exhausting the inside of the system.

The concentration of the chlorinated silane compound in the gas was determined by absorbing the gas into an HF aqueous solution, followed by chlorine analysis, and expressed as the chlorine content. It can be seen that the chlorine concentration in the purified gases is 3 ppm or less in all cases, and that high-purity fluorosilane that can be used for forming thin films can be obtained.

Table 1 Examples 4 to 6 Using the apparatus shown in Fig. 1, using a column packed with activated carbon (for gas purification and liquid phase), 5iH was obtained under the conditions shown in Table 2.
An attempt was made to purify F1.

As a result of analyzing the gas at the column outlet, it was found that all of the gases were purified to a chlorine density of 3 ppm or less. Instead of granular activated carbon, the adsorbents shown in Table 3 were filled and salt 'lI! An attempt was made to purify 5iHFs containing impurities consisting of 1200 ppm of chlorinated silane compounds at 4y11%.

The ventilation conditions were the same as in Examples 1 to 3, and the gas flow rate was 70 M1.
/a111% temperature was -40°C.

The results show that the obtained 5iHFa contains a large amount of chlorine compounds as impurities and has almost no tlJ effect.

Table 3

Claims (5)

[Claims] (1) Contains chlorine-based sila/compound as the main impurity, general formula (1) % formula % (1) (where n is an integer such that n≧1, m is 0≦m≦20
A method for producing high-purity fluorosilane gas, which comprises passing crude fluorosilane gas represented by +1 (integer +1) through an activated carbon layer. (2) The method according to claim 1, wherein the high purity fluorosilane gas is 5iHFa. (3) The method according to claim 1, wherein the high purity fluorosilate/gas is SiHgFz. (4) The method according to claim 1, wherein the high purity fluorosilane gas is Si2Fg. (5) The method according to any one of claims 1 to 4, wherein the high-purity If fluorosilane gas is a gas for forming a fluorinated amorphous silicon thin film.