JP2014141409A - Thermal plasma treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a high-purity polysilicon at a high speed.SOLUTION: The provided thermal plasma treatment apparatus I is furnished with: a reaction vessel 100 possessing a high-frequency plasma torch 10 in the interior thereof; a raw ingredient gas feeder 50 for feeding, into the high-frequency plasma torch 10, a raw ingredient gas including a silicon halide; a cooler 70 for cooling and solidifying droplets of molten polysilicon generated as a result of the thermal plasma treatment of the raw ingredient gas; and a silicon particle recovery device 80 for recovering the polysilicon particles cooled and solidified by the cooler 70.

Description

  The present invention relates to a thermal plasma processing apparatus.

  In recent years, as a manufacturing method for obtaining a polycrystal (polysilicon) of silicon (Si), for example, Patent Document 1 describes a method of forming a polysilicon film by a CVD method (Chemical Vapor Deposition). Has been. Patent Document 2 describes a method for producing acicular crystalline silicon by a gas phase synthesis reaction of silicon tetrachloride and zinc (Zn). Furthermore, Patent Document 3 describes a method for producing high-purity silicon in which a gas phase reaction between silicon tetrachloride and zinc metal is performed in zinc chloride gas.

Japanese Patent Application Laid-Open No. 07-183529 JP 2006-290645 A Japanese Patent Laid-Open No. 2004-210594

By the way, the conventional CVD method is usually performed under a reduced pressure of several tens to several hundreds of pascals, so that there is a problem that the concentration of the source gas is extremely low and the crystal growth rate of polysilicon is slow. In addition, in the gas phase synthesis reaction using the silicon tetrachloride reduction method, the recovery of the product and the separation of the by-product zinc chloride are insufficient, and the purity of the resulting polysilicon is insufficient. There's a problem.
An object of the present invention is to provide a method for obtaining high-purity polysilicon at high speed.

According to the present invention, a reaction vessel provided with a high frequency plasma torch inside, a raw material gas supply device for supplying a raw material gas containing silicon halide in the high frequency plasma torch, and a thermal plasma treatment of the raw material gas. There is provided a thermal plasma processing apparatus comprising: a cooling device that cools and solidifies molten polysilicon droplets; and a silicon particle recovery device that recovers and solidifies polysilicon particles cooled and solidified by the cooling device.
Here, it is preferable that the thermal plasma processing device further includes an exhaust gas purification device that purifies a halide generated as a by-product during the thermal plasma processing of the source gas.
The thermal plasma processing apparatus is provided between the high-frequency thermal plasma torch and the cooling device, receives the molten polysilicon droplets generated and dropped by the thermal plasma processing in the high-frequency thermal plasma torch, and It is preferable to provide a melting tube that is allowed to flow down.

  According to the present invention, high-purity polysilicon can be obtained at high speed.

It is a figure explaining an example of a thermal plasma processing apparatus. It is a figure explaining a melting tube.

  Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention. The drawings used are for explaining the present embodiment and do not represent the actual size.

(Thermal plasma processing equipment)
FIG. 1 is a diagram illustrating an example of a thermal plasma processing apparatus.
As shown in FIG. 1, a thermal plasma processing apparatus I is connected to a reaction vessel 100 having a high-frequency plasma torch 10 inside and a bottom portion of the reaction vessel 100 via a connecting pipe 60, and later described source gas thermal plasma. Cooling device 70 for cooling molten polysilicon droplets generated by the treatment, silicon particle recovery device 80 for recovering the solidified polysilicon particles cooled by cooling device 70, and halides by-produced during thermal plasma processing And an exhaust purification device 90 for purifying gas. Furthermore, the thermal plasma processing apparatus I includes a gas supply device 40 that supplies a plasma gas into the high-frequency plasma torch 10 and a source gas supply device 50 that supplies a source gas into the high-frequency plasma torch 10 in a thermal plasma state. ing. In the present embodiment, the inside of the reaction vessel 100 is sealed with an inert gas such as argon.

  The high-frequency plasma torch 10 includes an inner tube 13 that forms a plasma chamber 12 that generates a thermal plasma (plasma soot) 11 inside, a high-frequency transmission coil 14 that is attached to the outside of the inner tube 13, and a high-frequency transmission coil. 14 includes a cooling pipe 15 that cools the plasma chamber 12 with cooling water (W), and an outer pipe 16 that is provided further outside the cooling pipe 15. Further, gas supply ports 17 a and 17 b for supplying a raw material gas and the like into the plasma chamber 12 are provided in the upper part of the plasma chamber 12.

  In addition, although the high frequency plasma torch 10 is the structure which arrange | positions the coil 14 for a high frequency transmission between them with the double tube | pipe of the inner tube | pipe 13 and the outer tube | pipe 16, it is not limited to this. For example, the high frequency transmission coil 14 may be wound outside the outer tube 16. The size of the capacity is not particularly limited. Further, the ejection direction of the raw material gas and the like supplied from the gas supply ports 17a and 17b is not limited and may be ejected in various directions.

  The inner tube 13 and the outer tube 16 of the high-frequency plasma torch 10 are made of a heat resistant material such as quartz glass and silicon nitride. A high frequency current of about 4 MHz normally flows through the high frequency transmission coil 14. Cooling water (W) flows through the cooling pipe 15 provided between the inner pipe 13 and the outer pipe 16.

A funnel-shaped member 20 is provided below the high-frequency plasma torch 10. The funnel-shaped member 20 is connected to a cooling device 70 provided outside the reaction vessel 100 via a connecting pipe 60. The droplets of molten polysilicon 200 generated by the thermal plasma process in the plasma chamber 12 are guided to the lower part of the reaction vessel 100 by the funnel member 20.
Examples of the material constituting the funnel member 20 and the reaction vessel 100 include stainless steel. In this embodiment, in consideration of corrosion caused by a halogen gas or the like generated during thermal plasma treatment of a raw material gas, a corrosion resistant alloy (for example, Hastelloy C (registered) having nickel as a main component and molybdenum, chromium, iron, etc. added thereto. Trademark)).

  In addition, a melt tube 30 is provided at the middle portion of the funnel-shaped member 20 to receive and drop the molten polysilicon 200 droplets generated and dropped by the thermal plasma process. The melting tube 30 is held at an intermediate portion of the funnel member 20 by a predetermined holder (not shown). The melting tube 30 is heated to a temperature higher than the melting point of polysilicon by a predetermined heating device (not shown). In the present embodiment, the melting tube 30 is heated to about 1,700 K (1,427 ° C.) to about 2000 K (1,727 ° C.). The molten polysilicon 200 dropped on the melting tube 30 is further heated by the melting tube 30 and flows downward while maintaining the molten state. The material constituting the melting tube 30 is not particularly limited as long as it can be maintained at a temperature higher than the melting point of polysilicon. In the present embodiment, high-purity graphite is used.

  FIG. 2 is a diagram illustrating the melting tube 30. As shown in FIG. 2, the melting tube 30 has a funnel-like shape composed of a conical body portion 30a and a tubular portion 30b. A plurality of heating wires 30 c made of silicon carbide (SiC) are embedded in the melting tube 30. The melting tube 30 is energized by using a predetermined power source (not shown) to the plurality of heating wires 30c, whereby a temperature higher than the melting point of polysilicon (about 1,687 K (1,414 ° C.)) (usually, About 1,800 K (1,527 ° C. or higher). The molten polysilicon 200 dropped on the melting tube 30 held at a temperature higher than about 1,800 K (1,527 ° C.) higher than the melting point of polysilicon (about 1,687 K (1,414 ° C.)) The state is maintained and flows downward through the main body portion 30a and the tubular portion 30b.

  From the gas supply device 40, a plasma gas that generates thermal plasma in the plasma chamber 12 is supplied. Examples of the plasma gas include rare gases such as argon and helium, gases such as hydrogen and nitrogen, and mixed gases thereof.

From the source gas supply device 50, a mixed gas of silicon halide and carrier gas is supplied into the high-frequency plasma torch 10. Examples of the silicon halide compound used in the present embodiment include silicon fluoride, silicon chloride, silicon bromide, and silicon iodide. Among these, silicon chloride and silicon bromide are preferable.
Examples of silicon chloride include silicon tetrachloride (SiCl ₄ ), hexachlorodisilane, octachlorotrisilane, decachlorotrisilane, dodecachloropentasilane, and the like. Further, silane derivatives such as chlorosilane (SiH ₃ Cl), dichlorosilane (SiH ₂ Cl ₂ ), and trichlorosilane (SiHCl ₃ ) can be given. Examples of silicon bromide include silicon tetrabromide (SiBr ₄ ), disilicon hexabromide, trisilicon octabromide, tetrasilicon decabromide and the like. Furthermore, silicon bromide trichloride, silicon dibromide dichloride, silicon tribromide chloride, silicon iodide trichloride, silicon chlorosulfide, hexachlorodisiloxane and the like can be mentioned.
Among these, silicon tetrachloride (SiCl ₄ ) is particularly preferable.

In the present embodiment, when the silicon halide compound used as a raw material is solid, a solution in which the raw material is dissolved in a predetermined solvent is prepared in advance, and this solution is gasified and supplied to the reaction vessel 100. You can also The solvent that can be used is not particularly limited as long as it can dissolve the silicon halide compound. Specific examples include, for example, trifluoromethane (fluoroform), ethane, propane, butane, benzene, methyl ether, chloroform and the like.
The carrier gas is preferably inert to the silicon halide compound used as a raw material, and examples thereof include helium, neon, and argon. In this embodiment, argon is used as the carrier gas.

(Polysilicon production method)
Next, a method for manufacturing polysilicon using the above-described thermal plasma processing apparatus I will be described. In this embodiment, an example in which silicon tetrachloride (SiCl ₄ ) is used as a silicon halide compound and argon is used as a carrier gas to produce polysilicon will be described.

  First, plasma gas is supplied from the gas supply device 40 through the supply pipe 41 to the plasma chamber 12 of the high-frequency plasma torch 10 from the gas supply port 17a. The plasma gas supplied into the plasma chamber 12 is turned into plasma by a high-frequency transmission coil 14 to which a high-frequency voltage is applied from a predetermined high-frequency (RF) power source (not shown), and the plasma chamber 12 of the high-frequency plasma torch 10. A thermal plasma 11 is formed inside. The supply amount of the plasma gas supplied from the gas supply port 17 is appropriately selected according to the capacity of the plasma chamber 12, the properties of the thermal plasma 11, the processing amount of the source gas, and the like, and is not particularly limited.

The high frequency (frequency) and voltage (or power) of the high frequency voltage applied to the high frequency transmission coil 14 are appropriately selected according to properties such as the temperature of the thermal plasma 11 and are not particularly limited. In the present embodiment, the high frequency (frequency) of the high frequency voltage applied to the high frequency transmission coil 14 is 4 MHz, and the power consumption is 35 kW.
Although the temperature of the thermal plasma 11 formed in the plasma chamber 12 is not particularly limited, in the present embodiment, for example, it reaches a range of about 6,000 ° C. to 10,000 ° C.

Next, a source gas composed of silicon tetrachloride (SiCl ₄ ) and argon is supplied from the source gas supply device 50 through the supply pipe 51 into the plasma chamber 12 of the high-frequency plasma torch 10 through the gas supply port 17b. Silicon tetrachloride (SiCl ₄ ) is introduced into the thermal plasma 11 formed in the plasma chamber 12 together with the carrier gas argon (raw material gas introduction step).
Silicon tetrachloride (SiCl ₄ ) introduced into the thermal plasma 11 is subjected to thermal plasma treatment, heated by the heat of the thermal plasma 11, and decomposed in an instant to produce molten polysilicon (thermal plasma process).

The supply amount of the source gas supplied from the gas supply port 17b and the supply amount of the carrier gas are appropriately selected according to the capacity of the plasma chamber 12, the properties of the thermal plasma 11, the processing amount of the source gas, and the like, and are not particularly limited. In the present embodiment, silicon tetrachloride (SiCl ₄ ) is preferably heated to a predetermined temperature before being supplied to the reaction vessel 100. Although the temperature of the heated silicon tetrachloride is not particularly limited, in the present embodiment, it is usually in the range of 300 K (27 ° C.) to 570 K (297 ° C.), preferably 330 (57 ° C.) to 520 K (247 ° C.). It is.

Moreover, the ratio of silicon tetrachloride (SiCl ₄ ) and argon in the raw material gas supplied to the reaction vessel 100 is not particularly limited, but usually, silicon tetrachloride (SiCl ₄ ) 0.1 ml to 100 ml with respect to 50 ml of argon. 000 ml, preferably 10 ml to 5,000 ml, more preferably 10 ml to 200 ml. If the ratio of silicon tetrachloride (SiCl ₄ ) to argon is too small, the production rate of polysilicon tends to be slow. If the ratio of silicon tetrachloride (SiCl ₄ ) to argon is excessively large, the formation of the thermal plasma 11 tends to become unstable.

In the present embodiment, it is preferable to supply hydrogen into the plasma chamber 12 at the same time when the source gas containing silicon tetrachloride (SiCl ₄ ) is introduced into the plasma chamber 12 of the high-frequency plasma torch 10. By supplying hydrogen into the plasma chamber 12, chlorine generated from silicon tetrachloride (SiCl ₄ ) decomposed by thermal plasma treatment can be captured. The amount of hydrogen supplied into the plasma chamber 12 is appropriately selected according to the supply amount of silicon tetrachloride (SiCl ₄ ) and is not particularly limited. In the present embodiment, 2 mol or more, preferably 4 mol or more, more preferably 8 mol or more of hydrogen is supplied into the plasma chamber 12 with respect to 1 mol of silicon tetrachloride (SiCl ₄ ).

Moreover, the pressure of the reaction vessel 100 including the high-frequency plasma torch 10 is appropriately adjusted and is not particularly limited. However, in the present embodiment, it is usually adjusted in the range of 3 MPa to 20 MPa, preferably 5 MPa to 10 MPa.
In the present embodiment, the thermal plasma treatment can be performed in a supercritical fluid state of a mixed gas of silicon tetrachloride (SiCl ₄ ) and argon by adjusting the pressure of the reaction vessel 100. Here, the supercritical fluid state is defined as a non-condensable fluid that exceeds the gas-liquid critical temperature inherent to the substance. That is, when gas and liquid are present in the sealed container, the liquid thermally expands as the temperature rises, and its density decreases. On the other hand, the density of gas increases as the vapor pressure increases. And finally, the density of both becomes equal, and it becomes a uniform state indistinguishable from gas and liquid. In the temperature-pressure diagram (not shown) of the substance, the point at which such a state is reached is called the critical point, the critical point temperature is called the critical temperature (Tc), and the critical point pressure is called the critical pressure (Pc). A supercritical fluid state means that the temperature and pressure of a substance exceed a critical point.

In the present embodiment, silicon tetrachloride has a critical temperature (Tc) of 506.75 K (233.6 ° C.) and a critical pressure (Pc) of 3.73 MPa. The critical temperature (Tc) of argon is 87.45K (-185.7 ° C.), and the critical pressure (Pc) is 4.86 MPa.
In the case of a mixture of silicon tetrachloride and argon, the critical temperature (Tc) and critical pressure (Pc) of the mixture depend on the composition of silicon tetrachloride and argon, and the critical temperature (Tc) and critical pressure (Pc) of each substance. ) Can be adjusted accordingly.

As described above, silicon tetrachloride (SiCl ₄ ) is decomposed by the thermal plasma treatment, and the generated molten polysilicon 200 becomes droplets, and the surface of the melting tube 30 provided in the funnel-shaped member 20 of the reaction vessel 100. Fall into. As described above, the melting tube 30 is heated to a temperature higher than the melting point of polysilicon (about 1,687 K (1,414 ° C.)) by energizing a plurality of heating wires 30 c (see FIG. 2) embedded therein. The temperature is maintained at about 1,800K or higher. Therefore, the molten polysilicon 200 that has dropped onto the surface of the melting tube 30 passes through the conical body portion 30a (see FIG. 2) and the tubular portion 30b (see FIG. 2) at the top of the melting tube 30 while remaining in a liquid state. To flow downward.

Subsequently, the droplets of the molten polysilicon 200 flowing down below the melting tube 30 are cooled and solidified in the cooling device 70 provided outside the reaction vessel 100 via the connecting tube 60 connected to the funnel member 20 (cooling). Process). The cooling device 70 is cooled by cooling water (W).
In the present embodiment, the polysilicon cooled by the cooling device 70 is usually in the form of particles having a diameter of about 0.5 mm to 1 mm, and is recovered in the silicon particle recovery device 80.
Further, chlorine decomposed by thermal plasma treatment of silicon tetrachloride (SiCl ₄ ) is recovered by a predetermined exhaust purification device 90, and carrier gas such as argon is exhausted (B). Further, unreacted silicon tetrachloride (SiCl ₄ ) is recovered by a predetermined recovery device (not shown) and recycled to the source gas supply device 40.

The granular polysilicon recovered in the silicon particle recovery device 80 is transferred into a predetermined heat-resistant container such as a crucible, for example, and is higher in temperature than the melting point of polysilicon (about 1,687 K (1,414 ° C.)). Is melted at a temperature of about 1,800 K or higher, and is formed into, for example, an ingot.
As described above in detail, in this embodiment, high-purity polysilicon is formed at high speed by performing thermal plasma treatment on silicon tetrachloride (SiCl ₄ ).

DESCRIPTION OF SYMBOLS 10 ... High frequency plasma torch, 11 ... Thermal plasma, 12 ... Plasma chamber, 13 ... Inner pipe, 14 ... High frequency transmission coil, 15 ... Cooling pipe, 16 ... Outer pipe, 17a, 17b ... Gas supply port, 20 ... Funnel shape 30 ... Melting tube, 40 ... Gas supply device, 50 ... Raw material gas supply device, 60 ... Connecting pipe, 70 ... Cooling device, 80 ... Silicon grain recovery device, 90 ... Exhaust gas purification device, 100 ... Reaction vessel, 200 ... Molten polysilicon

Claims (3)

A reaction vessel with a high frequency plasma torch inside;
A source gas supply device for supplying a source gas containing silicon halide in the high-frequency plasma torch;
A cooling device for cooling and solidifying molten polysilicon droplets generated by thermal plasma treatment of the source gas;
A silicon particle recovery device for recovering and solidifying polysilicon particles cooled and solidified by the cooling device;
A thermal plasma processing apparatus comprising:   The thermal plasma processing apparatus according to claim 1, further comprising an exhaust purification device that purifies a halide generated as a by-product during the thermal plasma processing of the source gas.   A melting tube that is provided between the high-frequency thermal plasma torch and the cooling device and that receives and drops the molten polysilicon droplets generated and dropped by the thermal plasma treatment in the high-frequency thermal plasma torch; The thermal plasma processing apparatus according to claim 1, wherein the apparatus is a thermal plasma processing apparatus.

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