JPS6163514A - Method of purifying monosilane - Google Patents

Abstract

PURPOSE:To produce a high-purity monosilane in high yield, by reducing specific chlorosilane, separating an unreduced substance and an impurity through condensation, condensing an uncondensed gas, evaporating the condensed solution to give a gas, and subjecting it to adsorption treatment. CONSTITUTION:One or more chlorosilanes shown by the formula SiHnCl4-n (n is 0, 1, 2, or 3) are reduced by a well-known means, to give a crude monosilane gas containing an unreduced chlorosilane and a hydrocarbon im purity. The crude monosilane gas is introduced into the first condenser, treated at about -10--80 deg.C, the greater part of unreduced chlorosilane and hydrocar bon are condensed and separated. Then, a remaining uncondensed gas is intro duced into the second condenser, treated at -112--100 deg.C, and the all condensa ble gas is condensed. The condensed solution is partially evaporated, to give a monosilane gas containing a very small amount of unreduced substance and hydrocarbon, and subjected to adsorption treatment with an adsorbent, to give a monosilane having >=about 99.9998% purity.

Description

[Detailed description of the invention] 〔Technical field〕 The present invention relates to a method for purifying monosilane.

(Prior Art) With the rapid growth and growth of the electronics industry market, the demand for monosilane as a raw material gas for forming semiconductor thin films in IC1 solar cells, photosensitive drums, etc. has increased rapidly in recent years. The method for producing monosilane gas is as follows:
A common method is to reduce chlorosilanes such as silicon tetrachloride or silicon trichloride with an alkali metal hydride or alkyl aluminum hydride. Monosilane as a raw material gas used in the electronics field described above is required to have extremely high purity.

For this reason, high purity monosilane has conventionally been produced by cooling at a low temperature of -20° C. or lower, by treating with an adsorbent such as activated carbon or synthetic zeolite, or by combining these treatments.

However, the purification method described above requires a large amount of adsorbent and has a short life. For example, even if crude monosilane gas is cooled to temperatures below -20°C, a considerable amount of unreacted chloro-7ranes and hydrocarbons with 3 or more carbon atoms remain in the treated gas, which is then directly transferred to activated carbon. When treating with adsorbents such as , large amounts of activated carbon are required. Activated carbon adsorbs monosilane as well as chlorosilanes, which are impurities, so not only is the product monosilane lost when activated carbon is regenerated, but activated carbon that has adsorbed these can easily ignite when exposed to air, making it difficult to handle. It is very time consuming and dangerous.

[Purpose of the invention]

An object of the present invention is to provide a purification method that uses as little amount of adsorbent as possible to produce high-purity monosilane safely and in high yield.

[Disclosure of the invention]

The above object of the present invention is based on the general formula 5iHC1! (n
4-n Here, n represents 0.1.2 or 3. ) In purifying the crude monosilane gas obtained by reducing one or more types of chlorosilanes, the crude monosilane gas is introduced into a first condenser to condense and separate most of the unreduced substances and impurities, The uncondensed gas obtained from the first condenser is introduced into a second condenser to condense substantially all of the condensable gas to obtain a condensate, and then a portion of the condensate is reevaporated to substantially This is achieved by obtaining a gas consisting of monosilane and adsorbing the gas with an adsorbent.

The present invention will be explained in detail below.

Chlorosilane n 4 represented by the general formula SiHC1
-n groups are silicon tetrachloride, trichlorosilane, dichlorosilane, and monochlorosilane. Crude monosilane gas is obtained by reducing these chlorosilanes by a known method using an alkali metal hydride or an alkyl aluminum hydride. This crude monosilane gas contains n, 1 to 40% of unreduced chlorosilanes and 0.0% of hydrocarbons.
It contains 1 to 5%. This crude monosilane gas is introduced into the first condenser. In the first condenser, the treatment is performed at a temperature such that most of the unreduced chlorosilanes and hydrocarbons are condensed, for example, from -10°C to -80°C. The condensate condensed and separated in the first condenser can be recycled to the reduction reaction system either as it is or after separating the hydrocarbons.

Uncondensed gas obtained from the first condenser is introduced into the second condenser. In the second condenser, the process is carried out at -1126C to -100C, and substantially all of the unreduced substances, hydrocarbons and monosilane are condensed. Note that inert gases such as nitrogen and hydrogen that are entrained in the second condenser are separated and removed without being condensed here. Of the condensate in the second condenser, a portion containing unreduced substances is transferred to the first condenser and/or the reduction reaction system.
It can be recycled as is or after being subjected to appropriate treatment.

A portion of the condensate in the second condenser is then reevaporated. Re-evaporation is carried out, for example, by heat absorption in the second condenser, or by heating with steam, heat medium, or the like.

The gas substantially consisting of monosilane obtained by the re-evaporation contains trace amounts of unreduced substances and hydrocarbons. In order to remove this, adsorption treatment is performed using an adsorbent. As the adsorbent, for example, activated carbon is used to remove unreduced substances, and molecular sieve is used to remove hydrocarbons. Usually, an adsorption tower filled with activated carbon and an adsorption tower filled with molecular sheep are installed in series to perform adsorption treatment.

The highly purified monosilane gas is filled into a cylinder or the like either as it is or after being condensed.

The purity of Mono7 run obtained by the method of the present invention is substantially 99.9998% or higher.

[Effects of the Invention] According to the method of the present invention, in which condensation is carried out in two stages and then adsorption treatment is carried out, extremely high purity mono 7 run can be obtained without increasing the amount of adsorbent used. Since most of the impurities such as unreduced substances and hydrocarbons are removed in advance from the adsorption treatment zone, the life of the adsorbent is extended, and the regeneration and disposal of the adsorbent is also safe and efficient. It has the effect of being able to be carried out.

(Example) The water invention will be specifically explained below with reference to Examples.

Example 1 Using a 1 m2 reactor, silicon tetrachloride was reduced using aluminum diethyl hydride as a reducing agent, and 2ON
Crude monosilane gas of rIL' was obtained. The volume composition of this crude monosilane gas is 69% monosilane, 30% chlorosilanes, 200 ppm ethane, 1 butane, 40 fl Opp
It was m. This crude monosilane gas was introduced into the first condenser using 5ONm3 of hydrogen as carrier gas.

Unreduced substances and impurities such as ethane and butane were condensed and separated at -25°C, and the condensate was recycled to the reactor. The volumetric composition of the uncondensed gas obtained from the first condenser is 90.3% monosilane, 8.7% chlorosilanes, and 19% ethane.
0 ppm, butane 3000 ppm. This uncondensed gas was introduced into the second condenser. The condensable gas was completely condensed and recovered at -175°C. The condensate is monosilane 19.
0 to 9, and unreduced substances and impurities 2.5 to 9.

Then, when 80% of this condensate was evaporated, the composition of the evaporated gas was monosilica/L7. okg, unreduced substances and impurities were 0.2 Jc9. This operation removed 92% of impurities. Next, an adsorption tower filled with activated carbon and an adsorption tower filled with molecular sheep were introduced for adsorption treatment. The purity of the obtained mono 7 run was 99
．． It was 9998%.

Example 2 Purification was carried out in the same manner as in Example 1, except that 90% of the condensate obtained from the second condenser was evaporated.

The evaporated gas was 18.31c9 of monosilane, 1.1 kg of unreduced substances and impurities, and 56% of the unreduced substances and impurities were removed by the evaporation operation.

Adsorption treatment was performed in the same manner as in Example 1, and the purity was 99.9.
998% monosilane was obtained.

Claims (1)

[Claims] (1) General formula SiH_nCl_4_-_n (where n
represents 0, 1, 2 or 3) When purifying crude monosilane gas containing unreduced chlorosilanes and hydrocarbons as main impurities obtained by reducing one or more chlorosilanes represented by Crude monosilane gas is introduced into a first condenser to condense and separate most of the unreduced chlorosilanes and hydrocarbon impurities, and the uncondensed gas obtained from the first condenser is introduced into a second condenser to reduce condensability. Substantially the entire amount of the gas is condensed to obtain a condensate, a portion of the condensate is then re-evaporated to obtain a gas consisting essentially only of monosilane containing extremely small amounts of impurities, and the gas is absorbed by an adsorbent. A method for purifying monosilane characterized by adsorption treatment.