KR100795693B1 - Method for the purification of monosilane - Google Patents

Abstract

The present invention relates to a method for purifying monosilane, and according to the present invention, a method for purifying monosilane with washing water having a pH greater than 7 and less than 10 and then drying with an absorbent includes B ₂ H ₆ , PH ₃ , and AsH _3. Trace impurities, such as H ₂ O, can be removed at low cost with high efficiency to provide ultra-high purity monosilane.

Description

Method for Purifying Monosilane {METHOD FOR THE PURIFICATION OF MONOSILANE}

The present invention relates to a method for purifying monosilane, and in particular, removes trace impurities such as B ₂ H ₆ , PH ₃ , AsH ₃ , H ₂ O contained in the monosilane at low cost and with high efficiency to prepare an ultra high purity monosilane. It is about how to.

Monosilane (SiH ₄ ) is widely used as a chemical vapor deposition (CVD) gas for semiconductor thin films, a TFT manufacturing gas for liquid crystal displays (LCD), a gas for solar cells, etc. In recent years, its purity is important due to high density and high performance of electronic components. It is becoming.

Monosilane is usually prepared by the disproportionation reaction of chlorosilanes such as SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl or reduction by hydrogenating agent, or reduction reaction of Mg ₂ Si and then by fractional distillation. In order to separate, it usually contains a trace amount of B ₂ H ₆ , PH ₃ , AsH ₃ , H ₂ O as an impurity, it is necessary to remove the trace impurities when high purity is required.

Distillation purification is generally known as a method of removing these impurities (see US Pat. Nos. 4,340,574, 4,676,967 and US Patent Application Publication No. 20028167), which require very high theoretical singularity and reflux ratios and cost. Not only this, but also a disadvantage that impurities cannot be completely removed.

On the other hand, Japanese Patent Application Laid-Open No. 2001-131187 discloses a method of obtaining a purified monosilane by contacting pure water with a monosilane prepared by disproportionating alkoxysilane as a raw material. However, the impurities to be treated in this method are hydrocarbons.

It is an object of the present invention to provide a new and simple purification method that can be purified with higher purity by removing B ₂ H ₆ , PH ₃ , AsH ₃ , H ₂ O and the like present as trace impurities in monosilane.

The present invention provides a method for purifying monosilane, which comprises washing the monosilane with washing water of pH 7 or more and 10 or less and then drying it with an absorbent.

Hereinafter, the present invention will be described in more detail.

Monosilane which can be used in the purification method of the present invention is prepared by disproportionation of halogenated silanes such as chlorosilanes, for example, SiHCl ₃ , SiH ₂ Cl ₂ , SiH ₃ Cl according to a conventional method, and then fractionated. It is preferable to isolate | separate by the distillation method.

The disproportionation of halogenated silanes involves the starting silanes into two types: silanes with more hydrogen and fewer halogen atoms and silanes with fewer hydrogen and more halogen atoms. Refers to the reaction to convert, in the case of chlorosilane can be represented by the following scheme.

SiH₂Cl₂ ＋ SiCl₄ 2 SiHCl ₃

SiH ₂ Cl ₂ + SiCl ₄

SiH₃Cl ＋ SiHCl₃ 2 SiH ₂ Cl ₂

SiH ₃ Cl + SiHCl ₃

SiH₄ ＋ SiH₂Cl₂ 2 SiH ₃ Cl

SiH ₄ + SiH ₂ Cl ₂

Fractional distillation of monosilane after the disproportionation reaction may be carried out at a pressure of 0 to 50 kg / cm ² G using a single column or packed column distillation column according to a conventional method.

According to the present invention, with respect to the monosilane separated as described above (typically the specific resistance is in the range of 1,000 to 3,000 ohm · cm), an alkali of high purity (up to 100 ppb of impurity) such as NaOH, KOH or LiOH is pure (impurity). It is characterized in that gas-liquid contact washing is performed using washing water having a pH of 7 or more and 10 or less prepared by dissolving in 100 ppb or less).

The cleaning can be carried out at a pressure of 0 to 50 kg / cm ² G using a conventional cleaning tower such as a single column, packed column or spray tower. When the pH of the washing water is 7 or less, the monochlorosilane contained in a small amount in the purified monosilane may not only hydrolyze to generate HCl but also impurities such as B ₂ H ₆ , PH ₃ , and AsH ₃ may not be sufficiently removed. In addition, when the pH exceeds 10, the monosilane may cause a hydrolysis reaction, which may lower the product yield.

The monosilane from which trace impurities B ₂ H ₆ , PH ₃ , AsH _3, and the like have been removed by the cleaning process is then removed using an absorbent to remove the H ₂ O component. Moisture adsorbents that can be used in the present invention are conventional dry absorbers such as dry molecular sieves 3A, 4A, 5A, silica gel, alumina and the like.

According to the present invention, B ₂ H ₆ , PH ₃ , AsH ₃ , water, and the like, which are present as trace impurities in the monosilane, are completely removed, thereby obtaining ultra high purity monosilane having a specific resistance of 4,500 ohm · cm or more.

The invention is illustrated by the following examples, but the invention is not so limited.

Example 1

Reaction of 4% by weight of SiH ₄ (monosilane), 12% by weight of SiH ₃ Cl, 42% by weight of SiH ₂ Cl ₂ , 41% by weight of SiHCl ₃ and 1% by weight of SiCl ₄ , obtained by disproportionation of dichlorosilane (DCS) The liquid was continuously supplied at a flow rate of 1 kg / hr at a pressure of 20 kg / cm ² G to a packed distillation column (10 mm polling) with a tower diameter of 100 mm and a tower height of 10 m. (MS) was obtained at a flow rate of 0.037 kg / hr (yield 92.5%, crude monosilane).

This crude monosilane was then pH-adjusted with NaOH at a pressure of 3 kg / cm ² G continuously at a pressure of 3 kg / cm ² G to a 100 mm top and 1 m top packed scrubber (10 mm polling charge). Contact washing with 25 ° C washing water, taking out from the tower at a temperature of 25 ° C, and drying again by passing through a packed dehydration column of the same size (3L charge of molecular sieve 3A previously dried with high purity nitrogen at 150 ° C). , Indirectly cooled with liquid nitrogen and collected in a vessel (purified monosilane A).

Examples 2 and 3

In Example 1, purified monosilane B and C were obtained in the same manner except that the crude monosilane was washed with washing water of pH 7.5 and pH 9, respectively.

Comparative Examples 1 and 2

In Example 1, purified monosilanes D and E were obtained in the same manner except that crude monosilane was washed with washing water of pH 6.5 and pH 10.5, respectively.

Test Example

Table 1 shows the results of measuring the specific resistance of the crude silane and the purified monosilane A to E obtained in Examples 1-3 and Comparative Examples 1-2. The specific resistance value is a measure of the purity evaluation of monosilane, and a silicon thin film was grown using monosilane and then measured by Schottky diode method for the thin film. This means low.

 As can be seen from Table 1, the monosilane purified by washing with a washing water of a predetermined pH range according to the method of the present invention and then dried with an absorbent is very high compared to the monosilane purified only by distillation or out of the pH range. Purity (resistance value) is shown.

According to the present invention, monosilane can be obtained in a very high purity by a simple method, and it can be usefully used as a thin film raw material of various devices.

Claims (6)

The monosilane is washed with washing water of pH 7 or more and 10 or less containing an alkali component and then dried with an absorbent to remove impurities selected from B ₂ H ₆ , PH ₃ , AsH ₃ and mixtures thereof from the monosilane. A method for purifying monosilane, including the above. The method of claim 1, Wherein the monosilane used for purification is prepared by disproportionation of halogenated silanes and then separated by fractional distillation. The method of claim 2, The monosilane used for purification has a specific resistance in the range of 1,000 to 3,000 ohmcm. delete The method of claim 1, The absorbent is selected from dry molecular sieves 3A, 4A, 5A, silica gel, alumina and mixtures thereof. The method of claim 1, The monosilane after purification has a resistivity of 4,500 ohm · cm or more.