JPH0443845B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for purifying monosilane. More specifically, the present invention relates to a method for obtaining monosilane that does not contain gases having a boiling point lower than monosilane, such as oxygen, nitrogen, hydrogen, argon, helium, and methane.

[Prior art]

With the rapid growth of the electronics industry market, demand for monosilane has increased rapidly in recent years as a raw material gas for forming semiconductor thin films in ICs, solar cells, photoreceptor drums, etc. Common methods for producing monosilane gas include reducing it with chlorosilanes such as silicon tetrachloride or silicon trichloride, alkali metal hydrides or alkyl aluminum hydrides, or reacting Mg ₂ Si with hydrochloric acid or ammonium chloride. .

Monosilane gas obtained by these methods has been purified by adsorption using an adsorbent such as activated carbon or molecular sieve, purified by distillation, or purified by a combination of these methods for practical use. These purification methods have a sufficient purification effect on impurities with a boiling point higher than that of monosilane (-112°C), but impurities with boiling points higher than monosilane, such as oxygen, nitrogen, hydrogen, argon, helium, and methane, A sufficient purification effect cannot be obtained for impurities with low . Therefore, it has been filled into containers such as cylinders and used for various purposes with such trace amounts of impurities mixed in.

[Purpose of the invention]

However, for applications such as semiconductors, solar cells, and photoreceptor drums that require high purity, contamination of low-boiling point substances such as oxygen, nitrogen, hydrogen, argon, helium, and methane in the product monosilane gas is a problem. It has a significant impact on the quality of the product in its application. The present inventors have found that, in particular, for amorphous silicon solar cells, the presence of very small amounts of impurities such as oxygen and nitrogen in the raw material monosilane significantly affects the performance of the cell, especially its aging characteristics. found that it has an effect.

Therefore, an object of the present invention is to provide a method for filling and storing a container with high-purity monosilane gas so that it can be suitably used in fields that require particularly high quality, such as amorphous silicon solar cells. be.

[Disclosure of the Invention] That is, the above objects of the present invention are achieved by maintaining monosilane under reflux in a storage tank of liquid monosilane. The present invention will be explained in detail below.

Monosilanes to which the present invention can be applied include those produced by reducing chlorosilanes using a reducing agent;
It may also be manufactured by combining an alloy such as Mg ₂ Si with hydrochloric acid or ammonium chloride. Regardless of the manufacturing process, the monosilane entrained with purified hydrogen is condensed and stored in the product holder.

In the present invention, purification is carried out by maintaining monosilane under reflux in this storage tank, preferably at around -112°C, which is the boiling point of monosilane. Thereafter, it is extracted from the storage tank, preferably from the lower part of the storage tank, with a pump, heated with a vaporizer, and filled into a container such as a cylinder. When extracting monosilane with a pump, it is possible to extract it in liquid form, but
Alternatively, monosilane may be extracted from the gas phase of a storage tank held under reflux using a compressor and filled into a container.

(Example) The present invention will be specifically explained below using examples.

(Example 1) 3 m ² in a liquid silane holder with 40 jackets
A countercurrent condenser with a heat transfer area of The counterflow condenser was cooled with liquid nitrogen at a pressure of 5 Kg/cm ² G. The holder part was kept cool with 75mm thick urethane foam. Do not pour liquid nitrogen into the jacket. This holder is supplied with a carrier gas of ^10Nm3 per hour (1500ppm nitrogen, oxygen and argon).
Hydrogen containing 100 ppm was used to supply 1.2 Kg of silane per hour for 10 hours, and 12 Kg of liquid silane was stored. The silane in the holder is kept at boiling point and refluxed in a counterflow condenser. Liquid silane was extracted from the bottom of the storage tank using a pump, vaporized, and then filled into two 47 cylinders with silane gas.
Analysis of impurities in the cylinder revealed that nitrogen
0.7ppm, sum of oxygen and argon 0.3ppm, hydrogen
5ppm, no methane detected.

Comparative Example 1 Pass liquid nitrogen through the jacket of the holder and -
A cylinder was filled with monosilane in the same manner as in Example 1 except that the temperature was maintained at 120°C. As a result, the impurities in the cylinder were 12 ppm of nitrogen and 4 ppm of oxygen and argon.
It was hot.

[Effects and industrial applicability of the invention]

For example, when monosilane purified by the method of the present invention is filled into a 47 cylinder, the amount of nitrogen mixed in can be reduced to 1 ppm or less, the mixed amount of oxygen can be reduced to 0.5 ppm or less, hydrogen is also reduced to 10 ppm or less, and It becomes possible to fill a container with ultra-high purity silicon that does not detect argon, helium, methane, etc. Therefore, the monosilane filled into the container in this way can be effectively used for applications such as ICs, solar cells, and photosensitive drums.

Claims (1)

[Claims] 1. A method for purifying monosilane, which comprises maintaining monosilane under reflux in a liquid monosilane storage tank.