JPH0411486B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a method of producing high purity silicon hydride. More specifically, when silicon hydride is produced by reducing silicon halide with alkyl aluminum hydride, a specific amount of alkyl aluminum halide is added to the alkyl aluminum hydride in advance before they are reacted, and then , is a method characterized in that it is used for reaction with silicon halide. By this method, the amount of by-product impurities in monosilane is significantly reduced, and the ability to reduce the alkyl aluminum hydride per certain period of time is also improved. A method of adding a halide to the production of monosilane, which is a type of silicon hydride, has been conventionally known. For example, German Patent No. 1117090 exemplifies the addition of diethylaluminum monochloride when silicon tetrachloride is reduced with sodium hydride. However, this diethylaluminium monochloride is used for the purpose of activating sodium hydride, which is practically insoluble in the solvent, by solubilizing it. This is completely different from the purpose of activating alkyl aluminum hydride or reducing by-products as in the present invention. Also, French Patent No. 1499032 describes the reduction of silicon halide with an alkyl aluminum hydride. However, compared to the present invention, the present invention:
A specific amount of alkyl aluminum halide is added to the alkyl aluminum hydride, which is a reducing agent.
They differ in that they are added and used. In fact, when silicon halide is reduced with an alkyl aluminum hydride, a large amount of silicon hydride, which is thought to have been produced due to insufficient reduction of silicon halide, is produced as a by-product along with the desired silicon hydride. For example, when silicon tetrachloride is reduced, monochlorosilane and especially monochlorosilane are by-produced together with monosilane, and in the case of hexachlorodisilane, monochlorodisilane is produced as a by-product together with disilane. These by-products limit the applications of silicon hydrides such as monosilanes. It is extremely harmful, especially when used in semiconductor manufacturing. Its removal requires complicated operations, large-scale equipment, and a large amount of cost. Therefore, it is absolutely necessary to prevent the generation of by-products during synthesis as much as possible. In order to solve the above problem, as a result of intensive studies, we surprisingly found that by adding a specific amount of alkyl aluminum halide to the alkyl aluminum hydride prior to the reaction, the action of the alkyl aluminum hydride was not impaired in any way. We succeeded in significantly reducing the amount of silicon hydrogenation halide, which is a by-product impurity, without causing any
We have arrived at the present invention. That is, the present invention is characterized in that when silicon hydride is produced by reducing a silicon halide with an alkyl aluminum hydride, the alkyl aluminum halide is added in an amount of 3 mol % or more of the alkyl aluminum hydride. This is a method for producing high purity silicon hydride. The present invention will be explained in more detail below. The silicon halide that is a raw material in the present invention is a compound represented by the general formula SinX _2o+2 . In this formula, X is a substituent, at least one of which is a halogen atom, but the other part may be a hydrogen atom, an alkoxy group, an alkyl group, an aryl group, or a vinyl group, and n is 1 , 2 or more, but the larger n becomes, the more difficult it becomes to handle, and the more difficult it becomes to implement the present invention. The substituents represented by X include methyl group, ethyl group, propyl group, n-butyl group, i-butyl group, pentyl group, vinyl group, phenyl group, p-methylphenyl group, methoxy group,
It is an ethoxy group, etc., and the halogen may be chlorine or bromine. Among the compounds represented by the above general formula, particularly preferred examples for carrying out the present invention include silicon tetrachloride,
hexachlorodisilane, tetraethoxysilane,
These are diethyldichlorosilane and trichlorosilane. The alkyl aluminum hydride used in the present invention is a compound having a reducing ability represented by the general formula R ₁ R ₂ AlH. Both R ₁ and R ₂ are alkyl groups having 1 to 10 carbon atoms, such as ethyl, n-propyl, and isobutyl.
R ₁ and R ₂ may be the same or different.
Among the compounds represented by the above general formula, preferable examples include diethyl aluminum hydride,
Diisobutylaluminum hydride.
The alkyl aluminum halide in the present invention is a compound represented by the general formula AlR _o X _3-o .
X is a halogen, such as chlorine or bromine. R
is an alkyl group having 1 to 10 carbon atoms, such as ethyl group, n-propyl group, isobutyl group,
It is. However, since the presence of an alkyl group is not essential, n can be any number among 0, 1, and 1.5. Among the compounds represented by the above general formula, preferred examples include ethylaluminum dichloride,
These are ethylaluminum sesquichloride, isobutylaluminum dichloride, and aluminum chloride. The present invention can also be carried out by using a mixture of these compounds. The amount of alkyl aluminum halide added in the present invention is at least 3 mol % or more, preferably 5 mol % of the alkyl aluminum hydride.
That's all. Although the upper limit of the amount added is not particularly limited, adding too much will lower the concentration of alkyl aluminum hydride and increase the total amount of alkyl aluminum compounds, resulting in a decrease in the reaction rate and an increase in the volume of the reaction vessel. This is not preferable because it increases industrial disadvantages such as an increase in the amount of heat used. The alkyl aluminum halide has a halogen to aluminum ratio of X/
There are four types of compounds with Al ratios of 1.5, 2, and 3, and when compared with the same number of moles, the larger the X/Al ratio, the greater the effect of their addition. Specifically, trihaloaluminum > alkyl aluminum dihalide >
The order is aluminum alkyl sesquihalides. However, since trihaloaluminum is a solid, it is difficult to handle and mix. Therefore, alkyl aluminum dihalides are most preferred. X/
The higher the Al ratio, for example, the Cl/Al ratio, the more
The reason for the large addition effect is the solvent effect, catalytic effect,
Furthermore, changes in the intermolecular ring structure formed by the alkyl aluminum compound in the solvent are considered, but this is not clear. In the reaction of the present invention, dialkyl aluminum halide is produced as the 4AlR ₂ H + SiX ₄ → 4AlR ₂ X + SiH ₄ reaction progresses, as illustrated below. That is, except at the initial stage of the reaction, alkyl aluminum halide coexists with alkyl aluminum hydride, which is the gist of the present invention. However, surprisingly, as in the present invention,
If the alkyl aluminum halide is added to the alkyl aluminum hydride before the start of the reaction, it will have an effect that goes beyond simply correcting the initial period of the reaction, that is, it will improve the yield and, in particular, reduce impurities. This has the effect of significantly reducing The alkyl aluminum halide may be added to the alkyl aluminum hydride by directly mixing the two, or by diluting them with a solvent and mixing them. In most cases, heat is generated by mixing, so
It is necessary to be careful about overheating. The reaction for reducing silicon halide in the present invention refers to all reactions for producing silicon hydride from silicon halide as defined in the present invention. That is, for example, the reaction of SiCl ₄ +4AlEt ₂ H →SiH ₄ +4AlEt ₂ Cl as well as the reaction of Si(OEt) ₄ +4AlEt ₂ H →4AlEt ₂ (OEt) are also reactions for reducing silicon halide in the present invention. In the present invention, silicon tetrachloride is reduced with a mixture of alkyl aluminum hydride and alkyl aluminum halide in order to obtain monosilane with less impurities. Although it is not essential to use a reaction solvent, it is generally preferable to use one because the reaction becomes slower. Regarding the reaction solvent, in order to recover the alkyl aluminum present in the reaction system after the reduction reaction, a solvent that does not react with the alkyl aluminum and does not form a complex is preferable. Particularly preferred are aliphatic saturated hydrocarbons and aromatic hydrocarbons. Specifically, heptane, octane, liquid paraffin, benzene, and toluene are preferred. On the other hand, in order to carry out the reaction faster and at a lower temperature, polar solvents such as diethyl ether and tetrahydrofuran are preferably used. However, in this case, the polar solvent forms a complex with the alkyl aluminum, so the alkyl aluminum cannot be separated and recovered by simple operations such as distillation.
The separation operation becomes difficult. Do not use solvents that react with alkylaluminiums, such as carbon tetrachloride. If the reaction temperature is too low, the reaction will not proceed, and if it is too high, the alkyl aluminum will self-decompose and side reactions will occur.
Generally, the range is -30°C to 100°C, preferably,
A range of 0°C to 50°C is used. A reaction pressure of room temperature or 2 kg/cm ² (gauge pressure) is sufficient, but depending on the reaction temperature or equipment, the reaction may be carried out under reduced pressure or increased pressure. The raw materials and products used in this reaction are active, and most of them decompose or ignite when they react with oxygen and moisture, so the reaction must be carried out in an atmosphere that is inert to the raw materials and products. It must be done. For example, it must be in an atmosphere of an inert gas such as helium argon, nitrogen, or hydrogen that has been sufficiently deoxidized and dehydrated. This reaction can be carried out in any of the batch, semi-batch and continuous methods. Now, the silicon hydride produced by the method of the present invention is, for example, monosilane, disilane, diethyldihydrosilane, etc., and includes organic and inorganic synthetic raw materials,
It has many uses such as fuel and catalyst, and is an industrially important compound. Furthermore, monosilane produced using the method of the present invention has particularly low impurities, so
Through simple purification, it can be used as a raw material for various semiconductors. EXAMPLES Next, examples will be shown in order to concretely invent the present invention, but the present invention is not limited to these examples only. Example 1 A 500 ml stainless steel gas collection trap was connected to a 500 ml stainless steel induction stirring autoclave with a gas flow meter interposed therebetween. Further, a metering pump for charging silicon tetrachloride dissolved in liquid paraffin from the outside was connected to the autoclave. The charging tube was a dip tube. These entire systems were placed in a helium atmosphere before the reaction. The gas collection trap was cooled with liquid nitrogen. 34.4 g (0.4 mol) of diethyl aluminum hydride was diluted in 40 g of liquid paraffin. Then, 14.9 g of ethylaluminum sesquichloride (AlEt _1.5 Cl _1.5 )
(0.12 mol) was dissolved in 50 g of liquid paraffin and added dropwise. The molar ratio to diethylaluminium hydride is 30 mol%. This mixture was charged into an autoclave, brought to room temperature and degassed for 20 minutes under a vacuum of 2 mmHg, then
The atmosphere was changed back to helium gas. On the other hand, 17.0 g (0.1 mol) of silicon tetrachloride was dissolved in 30 g of liquid paraffin. Do this with a metering pump
It was press-fitted into an autoclave kept at 45°C for 1.5 hours. The generated monosilane gas was collected in a trap. After the reaction was completed, residual monosilane gas in the reaction system was sent to a trap using helium and collected. The gas composition of the trap was determined by gas chromatography. The amount of monosilane gas produced is 1.93N−
The yield was 86%. Amount of by-product monochlorosilane contained in monosilane (SiH ₃ Cl/
SiH ₄ ) was 90 ppm. Comparative Example 1 Synthesis was carried out in exactly the same manner as in Example 1, except that diethylaluminum chloride was not added. The amount of monosilane produced was 1.59N-, and the yield was 71%. The amount of by-product monochlorosilane (SiH ₃ Cl/SiH ₄ ) was 6300 ppm. Example 2 The same raw materials and equipment as in Example 1 were used, except that the reaction temperature was 43°C and 10.2 g (0.08 mol) of ethyl aluminum dichloride was dissolved in liquid paraffin instead of ethyl aluminum sesquichloride. Synthesis was carried out using In this case, the molar ratio of ethylaluminum dichloride to diethylaluminum hydride was 20%. The amount of monosilane produced was 2.02N-, and the yield was 90%. The amount of by-products (SiH ₃ Cl/SiH ₄ ) is
It was 50ppm. Examples, 3.4.5, Comparative Example 2 Using the same raw materials and equipment as in Example 2, the amount of alkyl aluminum halide to be added to the alkyl aluminum hydride was investigated. It is clear from Table 1 that unless the amount of ethylaluminum dichloride added is 3 mol % or more of diethylaluminum hydride, the yield of monosilane will be low and a large amount of by-products will be produced. Example 6 A study was conducted to synthesize disilane using hexachlorodisilane as a raw material in the same manner as in Example 2. However, in order to collect disilane after the reaction into a trap, the reaction solution was bubbled with helium gas, and the gas was sent to the trap to collect disilane. 3.1 g (0.05 mol) of disilane was obtained from 18.0 g (0.067 mol) of hexachlorodisilane. The yield was 75%. Comparative Example 3 The same procedure as Example 6 was carried out except that ethylaluminum dichloride was not added. 2.3 g (0.037 mol) of disilane was obtained. Yield is 55
It was %. Example 7 In the same manner as in Example 2, a study was conducted to synthesize monosilane using tetraethoxysilane as a raw material. From 20.8g (0.1mol) of tetraethoxysilane,
Monosilane 1.90N- was obtained. The yield was 85%. Example 8 An experiment was conducted using the same equipment as in Example 1. Diisobutyl aluminum hydride 89.1g
(0.45 mol) was diluted in 40 g of liquid paraffin.
Thereafter, 2.9 g (0.02 mol) of aluminum chloride was added, and the mixture was heated and stirred at 60° C. for 2 hours. The molar ratio of aluminum chloride to diisobutylaluminum hydride is 4.5%. The mixture was placed in an autoclave, brought to room temperature and degassed for 20 minutes under a vacuum of 2 mm Hg, after which the atmosphere was replaced with helium. On the other hand, 43.4 g (0.4 mol) of trimethylchlorosilane was dissolved in 50 g of liquid paraffin. This was pressurized into an autoclave maintained at 50°C using a metering pump for 2 hours. Thereafter, helium gas was bubbled through the autoclave, and the reaction solution in the autoclave and trimethylsilane gas generated in the space were collected in a trap. The amount of trimethylsilane produced was 22.9 g (0.31 mol). The yield was 78%.

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Claims (1)

[Claims] 1. When producing silicon hydride by reducing silicon halide with an alkyl aluminum hydride, 3 of the alkyl aluminum hydride
% by mole or more of the general formula _{AIR o} A method for producing high-purity silicon hydride, which comprises adding an alkyl aluminum halide to perform the reduction reaction.