JPS59121109A - Production of high purity silicon - Google Patents

Abstract

PURPOSE:To produce high-purity Si in molten state, in an extremely high yield, by thermally cracking a high-purity monosilane gas at a specific high temperature. CONSTITUTION:A high-purity monosilane (SiH4) gas 4 is supplied and decomposed in the reaction zone of the reactor 1 maintained at >=1,400 deg.C by the graphite heater 2 to obtain high purity molten Si and H2 gas. The H2 gas is exhausted from the outlet pipe 6, and the high-purity Si is collected in the receiver 3 in molten state, and sent through the delivery pipe 5 to the process for the production of Si single crystal. The used SiH4 gas can be thermally decomposed to the high-purity Si in an extremely high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing high purity silicon from monosilane. Since high-purity silicon is a raw material for devices such as semiconductors and solar power generation, the demand for it is expected to increase in recent years, and there is a need for a method for efficiently manufacturing it in large quantities. Various methods for producing high-purity silicon have been proposed. For example, (1) A mixed gas of high-purity notorichlorosilane and hydrogen or a mixed gas of high-purity monosilane and hydrogen is sent to a penger containing a high-purity seed silicon rod heated by electricity, and a high-purity variant silicon rod is There is a so-called seanonce method in which silicon is deposited and grown on top. In addition to requiring a large amount of electricity, this method requires depositing a certain amount of silicon on a seed silicon rod, taking it out, attaching the seed silicon rod again and depositing silicon, and the operation is batch-type. Therefore, even if mass-produced, the manufacturing cost is high.

(2) High-purity inorganic silane compounds such as tetrawarm silicon, trichlorosilane, dichlorosilane, monochlorosilane, and monosilane are supplied to a fluidized bed reactor in which seed silicon particles with a particle size of 50 to 500 μm are present and heated to a temperature of 4000 μm. ~
There is a fluidized bed method in which reduction and thermal decomposition reactions are carried out at 1,200° C. and a pressure of 1 to 3 atmospheres to deposit silicon on the surface of seed silicon present in a reactor.

Since this method uses seed silicon grains, the reaction surface area is large, so the rate of silicon precipitation and growth is very high.This has the advantage that high productivity can be obtained with a small reaction vessel. The disadvantage is that continuous operation is not possible. In addition, in this method, if quartz, silicon carbide, silicon nitride, etc. are used as the reactor material, the reaction will be delayed due to the difference in the coefficient of expansion due to temperature of the reactor material and the thermal expansion coefficient of the precipitated silicon. A fatal drawback is that the reactor breaks down when the reactor rises or cools.

To further explain these methods, the Siemens method and the fluidized bed method use a mixed gas of hydrogen and silanes such as high-purity trichlorosilane, dichlorosilane, and hismonosilane as a raw material gas, but hydrogen chlorination of trichlorosilane, dichlorosilane, etc. When silicon is precipitated from silicon, there is a thermodynamic equilibrium value between the reaction product gas and the precipitated silicon solid, and it is not possible to convert all of the raw material gas into silicon. In order to fully improve this conversion efficiency, hydrogen must be mixed with the raw material gas to reduce the ratio of chlorine atoms to hydrogen atoms in the raw material gas.

Therefore, in general, 3 parts per 100 parts of raw material hydrogenated silicon chloride.
About 0.00 to 5.000 parts of hydrogen is mixed. In the case of monosilane, there is no chlorine atom in its molecule, so there is no restriction on thermodynamic equilibrium values, and it converts almost 100% to silicon, but when analyzed in the gas phase, it becomes an amorphous powder and no seeds are formed. It does not precipitate and grow on the solid surface of silicon. To avoid this, it is necessary to completely suppress the gas phase decomposition reaction by mixing hydrogen with the raw material gas.Generally, 1,000 to 10,000 parts of hydrogen is mixed with 100 parts of monosilane gas as the raw material for precipitation. There is. In this way, producing high-purity silicon using silane gases as raw materials requires the use of large amounts of hydrogen gas, which is not economical, and even if the hydrogen gas used in the reaction can be recovered and reused. The reaction temperature is 700-1. ``Hydrogen gas had to be heated to 00°C, which required a large amount of energy.

The purpose of the present invention is to solve these drawbacks by introducing high-purity monosilane into a reaction zone at a temperature of 1.400°C or higher, decomposing it, and using the resulting high-purity silicon as a melt. The purpose is to provide a method for producing high-purity silicon that can completely convert the raw material gas into silicon by discharging it outside the reaction system and without mixing hydrogen gas with the raw material gas, and moreover economically. be.

That is, in the present invention, when monosilane is thermally decomposed to obtain silicon, monosilane is supplied to a reaction zone of a reactor at a temperature of 1400° C. or higher, thermally decomposed to form a silicon melt, and this is discharged from the system. It is characterized by

The present invention will be explained in more detail below. The present invention is a method of obtaining silicon as a melt produced by thermally decomposing high-purity monosilane at a temperature of 1400° C. or higher. The reaction is carried out according to the following formula.

5jH4--9Si+2H2 The reaction of this formula starts at a temperature of about 500°C, and it has been known that the melting point of silicon is 1400°C, but the present invention uses monosilane as a raw material without adding hydrogen. Monosilane is thermally decomposed by supplying monosilane to a reactor in which the temperature of the reaction zone is maintained at 1400°C or higher,
This is a method for producing high-purity silicon in which the produced silicon is immediately obtained as a melt.

In the present invention, monosilane is used as the raw material gas, but as mentioned above, it is not preferable to mix a large amount of hydrogenated chlorinated silane such as trichlorosilane or dichlorosilane because the thermodynamic equilibrium yield of the precipitation reaction is low. If it exists, it can be used as a raw material gas in the present invention.

Next, the thermal decomposition temperature is a temperature higher than the melting point of silicon, preferably 1400 to 2000°C.

At temperatures below 1400°C, it is difficult to obtain a silicon melt, and at high temperatures exceeding 2000°C, corrosion of the reactor material and contamination with impurities from the reactor material are undesirable.

The type of reactor used in the present invention is not restricted in any way as long as the reaction temperature can be maintained at 1.400° C. or higher. A specific example of the reactor is a cylindrical vertical reactor equipped with a receiver at the bottom for collecting precipitated and melted silicon. As the material for the reactor, a material that can withstand temperatures of 1.40'O<0>C or higher, such as graphite or carporundum, is used.

The misfiring BA will be explained in more detail below with reference to the drawings. The drawing is a sectional view of a reactor used in an example of the present invention.

In the drawings, reference numeral 1 is a reactor, 2 is a graphite heating element, 3 is a silicon receiver, 4 is a monosilane supply pipe, 5 is a silicon extraction pipe, and 6 is an exhaust pipe.

First, as shown in the drawing, raw material monosilane is supplied to the reactor 1 through the monosilane supply pipe 4.

Monosilane is heated to a temperature of 1400 by graphite heating element 2.
Silicon is thermally decomposed in the reaction zone heated to temperatures above 0.degree. C., and silicon is precipitated and becomes a melt. It is collected in a silicon receiver 3 heated by a graphite heating element 2, and the temperature is 1400.
It is discharged out of the system through a silicon extraction pipe 5 made of a U-shaped tube heated to a temperature above .degree. Further, the exhaust gas is discharged from the exhaust pipe 6 to the outside of the system. Note that when the exhaust gas is passed through a monosilane abatement device, such as a device completely filled with an aqueous caustic soda solution, trace amounts of unreacted raw material gas contained in the exhaust gas are absorbed and removed.

As explained above, the present invention is a method in which monosilane is supplied to a reaction zone heated to a temperature of 1400° C. or higher in a reactor, thermally decomposed to form a silicon melt, and this is discharged from the reaction system.

According to the method of the present invention, (1) since the reactor is heated to a temperature higher than the melting point of silicon, silicon does not precipitate and grow on the surface of the reactor, and smooth long-term operation is possible. (2
) There is no need to dilute the raw material monosilane with large amounts of hydrogen,
Not only is the reactor smaller than the Siemens method and fluidized bed method mentioned above, but a large amount of hydrogen gas is introduced into the reactor.
There is no need to raise the reaction temperature to 700 to 1,200°C, resulting in significant energy savings. (3) Polycrystalline silicon produced by the Siemens method or fluidized bed method is cooled to room temperature, and then heated to a temperature of 1.400 to produce single crystal silicon.
Although it must be melted at a temperature of .degree. C. or higher, in the present invention, it is obtained as a melt in the high-purity silicon production process, so it can be sent directly to the single-crystal silicon production process.

The present invention will be described in more detail below with reference to Examples.

Example 1 Monosilane gas was thermally decomposed using the reactor shown in the drawing. The reactor 1 was a graphite cylinder with an inner diameter of 50 ports and a height of 1000 mm, and the silicon receiver 2 provided at the bottom of the reactor had an inner diameter of 300 mm.

First, the inside of the reactor 1 is sufficiently replaced with argon gas, and then the graphite heating element 2 attached to the reactor 1 is heated with high frequency in an argon gas stream to raise the temperature inside the reactor to 60 kl.
Heated to 0°C. After confirming that the temperature has stabilized,
High purity monosilane gas was continuously introduced into the reactor 1 from the monosilane gas supply pipe 4 at a rate of 3 t/min at room temperature. The exhaust gas from the reactor was sent to the abatement device through the exhaust pipe 6.

After 3 hours of operation, the graphite heating element 2 attached to the silicone receiver 3 and the U-shaped silicone extraction pipe 5 was heated to 1,500°C by high-frequency heating to precipitate and melt. Silicon was continuously extracted and the operation was continued for 100 hours. As a result, high purity silicon averages 215.9/hr
Obtained with.

After cooling this, single crystal silicon was manufactured using the single crystal pulling method and its resistivity was measured and found to be 100 ohm.
It was found that z is a raw material that can be fully used for semiconductors.

Example 2 Highly purified duchlorosilane 3.1% and trichlorosilane 1, which were purified by thoroughly removing all impurity metal compounds other than silicon.
．． Example 1 was carried out in the same manner as in Example 1, except that monosilane gas containing 2% was continuously fed to reactor 1 at a rate of 3 mL.

As a result, high purity silicon was obtained at an average rate of 205 g/hr. After cooling this, a single crystal silicon was completely produced by a single crystal pulling method, and its resistivity was measured], and it was found that it was 00 ohmα, and was a raw material that could be sufficiently used for semiconductors.

[Brief explanation of the drawing]

The drawing is a cross-sectional view of an apparatus used in an embodiment of the present invention. Number 1... Reactor 2... Graphite heating element 3.
...Silicon receiver 4...Monosilane gas supply pipe 5
...Silicon extraction pipe 6...Exhaust pipe Procedure Amendment 1, Indication of matter A 1, 1982 Patent No. 19A No. 228985 2, Title of invention Process for manufacturing high purity silicon 3, Case of person making amendment Relationship with Patent applicant 4, Detailed explanation of the invention column 5 of the specification subject to amendment, Contents of the amendment, page 1, line 20, "Benger" is replaced with "Pelger"
I am corrected.

Claims (1)

[Claims] When obtaining silicon by thermally decomposing high-purity monosilane, monosilane is supplied to the reaction zone of the reactor at a temperature of 1,400°C or higher and is thermally decomposed to form a silicon melt, which is then completely discharged from the reaction system. A method for producing high-purity silicon characterized by: