JP4801601B2 - Method for producing silicon - Google Patents

Description

  The present invention relates to a method for producing silicon. More specifically, the present invention is suitably used as silicon for solar cells, and can increase the reaction surface area while simultaneously increasing the reaction temperature of silicon. The present invention relates to a silicon manufacturing method capable of manufacturing silicon efficiently at a low cost at a low unit.

  Conventionally, as a method of producing eleven nine-class high-purity silicon used as a silicon wafer for semiconductors, a seed crystal silicon rod is generally placed in a bell jar type reactor, and trichlorosilane or the like is placed in the reactor. A Siemens method in which silane-based gas is introduced and silicon is deposited on the silicon rod by a CVD method is used. The biggest problem with this Siemens method is that the growth reaction rate of silicon is slow, the power intensity is remarkably high and not economical. For example, even when an efficient large reactor is used, an electric power consumption unit of 100 kWh / kgSi or more is required.

On the other hand, in the case of silicon used for solar cells, silicon for solar cell grades (SOG-Si) does not require as high purity as silicon for semiconductors and is required in large quantities. It has become a very important issue to lower. In view of this, development of a technology for manufacturing silicon for a solar cell grade (SOG-Si) having a small electric power consumption rate is underway in Japan and overseas.
The flow of these developments can be broadly divided into a method for producing silane-based gases such as trichlorosilane and monochlorosilane as a starting material, and a method for producing metal grade inexpensive silicon (MG-Si) directly as a starting material. There are two ways.

  Conventionally, for example, it has a heating zone and a reaction zone. In the heating zone, silicon particles are fluidized by an inert silicon-free carrier gas to form a fluidized bed and heated by microwave energy. There has been proposed a method for producing silicon particles in which elemental silicon is deposited on the silicon particles in a fluidized bed in which the silicon particles are exposed to a reaction gas containing gas and an average temperature of less than 900 ° C. and the carrier gas ( For example, see Patent Document 1).

In addition, in the conventional Siemens method, a silicon-containing gas such as trichlorosilane is used as a main raw material, and a rod-shaped silicon seed crystal is energized and heated to keep the surface temperature at about 1000 ° C., so that silicon is decomposed and precipitated. In addition, the productivity of batch processes is poor and the power consumption rate is extremely high. To solve this drawback, a cylindrical reaction tube is heated to a temperature higher than the melting point of silicon, and chlorosilanes are added to the reaction tube. And hydrogen are supplied, and these chlorosilanes and hydrogen are reacted to generate melted silicon and dripped to continuously recover the melted silicon (for example, patents). Reference 2).
This method enables continuous production of polycrystalline silicon. Furthermore, heating the reaction temperature above the melting point of silicon (1414 ° C.) can significantly increase the reaction rate and reduce the power consumption rate. It is possible.

Further, as an improvement of this method, while heating and holding the surface of the reaction substrate at a temperature below the melting point of silicon, silanes are contacted with the substrate surface to deposit silicon, and then the substrate is A method has been proposed in which the surface temperature of a material is raised to melt part or all of the deposited silicon, and the molten silicon is dropped from the surface of the base material and recovered (see, for example, Patent Document 3).
In this method, contamination from the reaction substrate can be minimized by reducing the contact time between the reaction substrate and the silicon melt.
Japanese Patent Laid-Open No. 11-139817 JP 2002-29726 A Republished 2002-100777

By the way, the conventional various silicon manufacturing methods have the following problems.
(1) In the method for producing silicon particles, although the power unit is low and the reaction surface area can be increased, since the reaction temperature of silicon is 700 ° C. at the maximum, the decomposition rate of the reaction gas is slow, It is difficult to increase productivity any more.
(2) In the method of melting the precipitated silicon once and recovering the molten silicon, the reaction temperature is increased by increasing the reaction temperature, but it is difficult to increase the reaction area, and it is established as a mass production process. More ingenuity is needed to make it happen.
In addition, problems such as contamination of silicon during reaction may occur.

  The present invention has been made to solve the above-described problems, and it is possible to increase the reaction surface area while increasing the reaction temperature of silicon. As a result, the power unit is low and the cost is low. An object of the present invention is to provide a silicon manufacturing method capable of efficiently manufacturing silicon.

  As a result of intensive studies on a method for producing silicon using powder, lump, flakes, etc., the present inventors have found that the powder in a reaction vessel having a lid attached to the open end of the bottom of the cylindrical body. Generated by the decomposition or reduction of the silane-based gas by introducing silicon, lump-like or flake-shaped silicon, heating it, and passing one of silane-based gas, silane-based gas and hydrogen gas through the heated silicon If silicon is grown on the surface of the powdery, lump or flake silicon, and then the silicon is heated to a temperature equal to or higher than its melting point, it is recovered by melting, dropping, It has been found that silicon can be efficiently produced at low cost and at low cost, and the present invention has been completed.

  That is, in the method for producing silicon according to the present invention, powdery, lump or flake silicon is charged into a reaction vessel having a lid attached to the open end of the bottom of the cylindrical body, and then the silicon is heated to 1000 ° C. or higher. And heated to a temperature not higher than the melting point of silicon, and through the heated silicon, a reaction gas of silane-based gas, silane-based gas and hydrogen gas is passed through the raw material gas introduction pipe provided in the lid portion. The silicon produced by the decomposition or reduction of the silane-based gas is grown on the surface of the powdery, lump or flake silicon, and then the lid is removed from the reaction vessel, and the silicon in the reaction vessel is removed. It is characterized by being recovered by melting and dropping by heating to a temperature equal to or higher than its melting point.

The silane-based gas is preferably one or more selected from the group consisting of monosilane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane.
The reaction vessel is a quartz reaction vessel, graphite is disposed so as to surround the reaction vessel, a high-frequency induction heating coil for heating the graphite by high-frequency induction heating is disposed, and the reaction vessel is radiated by the radiant heat generated by the graphite. It is preferable to heat the silicon inside.
It is preferable that a slit is formed in the graphite in a direction substantially orthogonal to the high frequency induction heating coil.

The reaction vessel may be a quartz reaction vessel, a graphite heater may be disposed so as to surround the reaction vessel, and the silicon in the reaction vessel may be heated by the graphite heater.
Further, the reaction vessel is a graphite reaction vessel, and a high frequency induction heating coil for heating by high frequency induction heating is disposed in the graphite reaction vessel, and the inside of the reaction vessel is radiated by the graphite reaction vessel. Silicon may be heated.
Further, the reaction vessel may be a graphite reaction vessel, a graphite heater may be disposed so as to surround the reaction vessel, and silicon in the reaction vessel may be heated by the graphite heater.

  According to the method for producing silicon of the present invention, powdery, lump or flake silicon is charged into a reaction vessel having a lid attached to the open end of the bottom of the cylindrical body, and then the silicon is heated to 1000 ° C. or higher. And heated to a temperature not higher than the melting point of silicon, and caused by decomposition or reduction of the silane-based gas by passing one of the silane-based gas, silane-based gas, and hydrogen gas through the heated silicon. Since the grown silicon is grown on the surface of the powdery, lump or flake silicon, the reaction surface area can be increased simultaneously with increasing the reaction temperature of silicon. Accordingly, it is possible to efficiently produce silicon at a low cost by reducing the power consumption rate.

  Also, after removing the lid from the reaction vessel, the silicon in the reaction vessel is melted, dropped and recovered by heating to a temperature above its melting point, so that the molten silicon is recovered efficiently and in a short time Therefore, the production efficiency of silicon can be increased.

The best mode for carrying out the method for producing silicon of the present invention will be described.
This embodiment is specifically described for better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

FIG. 1 is a cross-sectional view showing a silicon manufacturing apparatus used in the silicon manufacturing method of one embodiment of the present invention, FIG. 2 is a vertical cross-sectional view thereof, and in the figure, 1 is a reaction vessel, and is in powder form A crucible body 2 in which the bottom of a cylinder (cylindrical body) in which silicon A for bulk or flake material is stored is an open end 2a, and a lid 3 made of graphite that can be attached to and detached from the open end 2a. It is comprised by.
The crucible body 2 may be a cylindrical heat insulating member that is less affected by contamination of silicon. For example, a quartz tube, graphite, or the like is preferably used.
The lid 3 may be a disk-like heat insulating member having a diameter equal to or larger than that of the opening end 2a. For example, a quartz plate, a graphite plate, or the like is preferably used.

Further, 4 is a quartz raw material provided in the central portion of the lid portion 2 so as to penetrate therethrough, and allows a reaction gas G of any one of silane-based gas, silane-based gas and hydrogen gas to flow through the reaction vessel 1. A gas introduction tube 5 is a cylindrical graphite tube disposed so as to surround the outer peripheral surface of the reaction vessel 1, and a heat insulating cylindrical alumina tube 6 is disposed so as to surround the outer peripheral surface of the graphite tube 5. Is a high frequency induction heating coil wound around the outer peripheral surface of the alumina tube 6 and heating the graphite 5 by high frequency induction heating.
The graphite tube 5 may be simply a cylindrical graphite tube, or as shown in FIG. 1, a plurality of vertically long slits 5a may be formed along the axis. When the slit 5 a is formed, the extending direction of the slit 5 a is substantially orthogonal to the winding direction of the high frequency induction heating coil 7.

  As the raw material silicon A used here, silicon wafer scraps obtained by crushing silicon wafers, polysilicon crushed products obtained by crushing polysilicon (polycrystalline silicon), etc. are preferably used. The product can be used in various shapes and sizes, such as powder, lump or flake.

Further, as the reaction gas G, any one of silane-based gas, silane-based gas and hydrogen gas is used. As the silane-based gas, monosilane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, One selected from the group of tetrachlorosilane is preferably used. In addition, it is good also as mixed gas which mixed 2 or more types of these gas as needed.
The above monosilane, disilane, and trisilane can be used alone, but monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane are preferably mixed with hydrogen gas because they contain chlorine.

Next, a method for manufacturing silicon using this silicon manufacturing apparatus will be described.
First, powdery, lump-like or flake-like silicon A is charged into the reaction vessel 1 in which the lid 3 is attached to the open end 2b of the crucible body 2. Next, a predetermined high frequency voltage is applied to the high frequency induction heating coil 7 by a high frequency power source (not shown) to heat the graphite tube 5 by high frequency induction heating, and silicon A is heated to 1000 ° C. by the radiant heat generated by the heated graphite 5. Heat to above and below the melting point of silicon.

After the temperature of the silicon A reaches a predetermined temperature within the range of 1000 ° C. or more and below the melting point of silicon, any of silane-based gas, silane-based gas, and hydrogen gas is supplied to the silicon A through the source gas introduction pipe 4. The reaction gas G is allowed to flow.
When the reaction gas G is passed through the silicon A, silane-based gases such as monosilane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane contained in the reaction gas G are decomposed or reduced. Silicon generated in the process grows on the surface of silicon A. Thus, silicon grows on the surface of silicon A by the CVD method.
When a predetermined amount of silicon grows on the surface of silicon A, the pressure loss of the reaction gas G inside the source gas introduction pipe 4 starts to increase.

  After confirming that this pressure loss has started to increase, the lid 3 is removed from the open end 2b of the crucible body 2, and a predetermined high frequency power is applied to the high frequency induction heating coil 7 so that the graphite tube 5 is subjected to high frequency induction heating. The silicon A is heated to a temperature equal to or higher than the melting point of silicon by the radiant heat generated by the heated graphite tube 5 and melted. This molten silicon A falls down below the crucible body 2 and is recovered.

According to the silicon manufacturing method of this embodiment, the reaction temperature of silicon can be increased, and the reaction surface area of silicon can be increased. Accordingly, the reaction time can be shortened, the power consumption can be reduced, and silicon can be manufactured at low cost.
Also, after removing the lid from the reaction vessel, the silicon in the reaction vessel is melted, dropped and recovered by heating to a temperature above its melting point, so that the molten silicon is recovered efficiently and in a short time Therefore, the production efficiency of silicon can be increased.

In the silicon manufacturing apparatus, instead of the above configuration, a graphite heater is disposed so as to surround the outer peripheral surface of the reaction vessel 1, and the silicon A in the reaction vessel 1 is heated by the graphite heater. Also good.
Further, the reaction vessel 1 is made of graphite, and a high frequency induction heating coil 7 for heating by high frequency induction heating is disposed in the graphite reaction vessel, and the reaction vessel 1 is generated by radiant heat generated by the graphite reaction vessel by this high frequency induction heating. The silicon A inside may be heated.
Further, the reaction vessel 1 may be made of graphite, a graphite heater may be disposed so as to surround the outer peripheral surface of the reaction vessel, and the silicon A in the reaction vessel 1 may be heated by the graphite heater.
Even if the silicon manufacturing apparatus having such a configuration is used, the same effects as those of the silicon manufacturing method described above can be obtained.

  Hereinafter, although the manufacturing method of the silicon | silicone of this invention is demonstrated concretely according to an Example, this invention is not limited by these Examples.

"Example 1"
A quartz crucible with a graphite lid 3 attached to the open end 2b of a crucible body 2 made of a transparent quartz tube having an inner diameter of 300 mm is used as the reaction vessel 1, and a source gas introduction pipe 4 is attached to the lid 3 of the quartz crucible. In order to surround the outer periphery of the quartz crucible, a simple graphite graphite tube 5 having no slit 5a is disposed, and a high-frequency induction heating coil 7 is wound around the outer peripheral surface around the graphite tube 5. An alumina tube 6 was arranged.
Next, 30 kg of silicon wafer scraps for solar cells that have been crushed so that the outer shape of the precipitation nuclei as raw material silicon is approximately 10 mm or less and 1 mm or more are introduced into the quartz crucible, and argon gas is allowed to flow from the raw material gas introduction pipe 4. After expelling residual air between the silicon wafer scraps, the graphite tube 5 is heated by high frequency induction heating from the outside of the alumina tube 6 by the high frequency induction heating coil 7, and the silicon wafer scraps in the quartz crucible are radiated by the radiant heat of the graphite tube 5. Was heated.

After confirming that the temperature of the silicon wafer scraps began to rise to 600 ° C. or more from the outer peripheral side, monosilane was passed through the source gas introduction pipe 4 at a flow rate of 250 g / min. Here, during the flow of monosilane, the temperature in the quartz crucible is controlled so that it does not exceed 1350 ° C. with a margin lower than the melting point of silicon, 1414 ° C., and does not fall below 1250 ° C. did.
After 3 hours from the start of temperature control, it was confirmed that the pressure loss began to increase, the monosilane flow was stopped, the lid 3 was removed, and the unreacted silicon in the quartz crucible was dropped and removed. Thereafter, the power load of high-frequency induction heating was increased to heat and melt the silicon in the quartz crucible to a temperature equal to or higher than the melting point of silicon, and the molten silicon was dropped and recovered.

As a result of measuring the weights of the unreacted silicon and the recovered silicon, it was found that the increase in the weight of silicon grown by the decomposition reaction of monosilane was 26.6 kg. Further, the purity of the recovered silicon was 6 nine class, which was a purity level that could be used sufficiently as silicon for solar cells.
In addition, the power consumption is 7.6 kWh per kg of silicon for the weight increase, which is significantly lower than the Siemens power unit of 100 to 200 kWh / kg, which is a typical method for producing semiconductor grade polysilicon. It was confirmed that the basic unit was also excellent.

"Example 2"
The silicon manufacturing method of the second embodiment is different from the silicon manufacturing method of the first embodiment in that the reaction vessel 1 is heated by a high-frequency induction heating coil 7 and a cylindrical graphite tube 5 having an inner diameter of 300 mm and a vertically long slit. This is in that 24 pieces of 5a formed at equal intervals in the circumferential direction were used. In addition, the type, shape, quantity, etc. of silicon were the same as those in Example 1.
Here, similarly to Example 1, argon gas was first flowed and heating was started. Compared with Example 1, it was difficult to apply a power load at the beginning of heating, and it took time to raise the temperature.

After confirming that the temperature of the silicon wafer scrap started to rise to 600 ° C. or more from the outer peripheral side, monosilane was passed through the source gas introduction pipe 4 at a flow rate of 370 g / min. As the temperature rose, the silicon wafer scraps were also directly loaded with power, and the subsequent heating was faster than in Example 1. Here, the temperature in the quartz crucible was controlled under the same conditions as in Example 1 during the flow of monosilane.
After 2 hours from the start of temperature control, the pressure loss began to increase, so the monosilane flow was stopped, the lid 3 was removed, unreacted silicon in the quartz crucible was dropped and removed, and then high frequency induction heating was performed. The silicon load in the quartz crucible was heated to a temperature equal to or higher than the melting point of silicon and melted, and the melted silicon was dropped and recovered.

As a result of measuring the weights of unreacted silicon and recovered silicon, it was found that the increase in weight of silicon grown by monosilane decomposition reaction was 27.2 kg. Further, the purity of the recovered silicon was 6 nine class, which was a purity level that could be used sufficiently as silicon for solar cells.
The amount of power consumption was 6.8 kWh per kg of silicon corresponding to the weight increase, and the power consumption rate was further improved from that in Example 1.

"Example 3"
The silicon production method of Example 3 is different from the silicon production method of Example 1 in that, as the reaction vessel 1, a graphite tube having a diameter of 300 mm and purified with a halogen gas was attached to a graphite lid. A high frequency induction heating coil is arranged on the outer periphery of the graphite tube, and the graphite tube is directly heated by the high frequency induction heating coil. As raw material silicon, silicon wafer scrap for solar cells and polysilicon This is a point using trichlorosilane as the reaction gas G using a mixture of crushed products.

First, silicon wafer scraps crushed to 1 to 10 mm as raw material silicon and 15 kg of a crushed polysilicon product obtained by pulverizing semiconductor grade polysilicon to 1 mm or less were put into a graphite tube, for a total of 30 kg.
Next, in the same manner as in Example 1, argon gas was flowed and heating was started.
After confirming that the surface temperature of the graphite tube began to rise to 600 ° C. or higher, 900 g / min of trichlorosilane and 450 NL / min of hydrogen gas were passed through the raw material gas introduction tube 4. After the start of the flow of these gases, the temperature inside the graphite tube was controlled under the same conditions as in Example 1.

  After 4 hours from the start of temperature control, pressure loss began to increase, so the gas flow was stopped, the lid 3 was removed, unreacted silicon in the graphite tube was dropped and removed, and then high frequency induction heating was performed. The power load was increased to heat and melt the silicon in the graphite tube to a temperature equal to or higher than the melting point of silicon, and the molten silicon was dropped and recovered.

As a result of measuring the weights of unreacted silicon and recovered silicon, it was found that the increase in weight of silicon grown by the decomposition reaction of trichlorosilane was 26.2 kg. Further, the purity of the recovered silicon was slightly high at 3 ppm of carbon (C), but the other components were 6-nine class, which was a purity level that could be sufficiently used as silicon for solar cells.
In addition, the amount of power consumption is 13.4 kWh per kg of silicon corresponding to the weight increase, and it was confirmed that the power consumption rate was extremely low in comparison with the Siemens method.

Example 4
The silicon manufacturing method of the fourth embodiment is different from the silicon manufacturing method of the third embodiment in that a graphite heater is disposed on the outer periphery of the graphite tube, and the graphite tube is directly heated by this graphite heater. As G, tetrachlorosilane is used.

In the same manner as in Example 1, argon gas was flowed and heating was started.
After confirming that the surface temperature of the graphite tube started to rise to 600 ° C. or higher, 900 g / min of tetrachlorosilane and 500 NL / min of hydrogen gas were passed through the raw material gas introduction tube 4. After the start of the flow of these gases, the temperature inside the graphite tube was controlled under the same conditions as in Example 1.

  After 5 hours from the start of temperature control, the pressure loss began to increase, so the gas flow was stopped, the lid 3 was removed, unreacted silicon in the graphite tube was dropped and removed, and the graphite heater power was removed. The load was increased and the silicon in the graphite tube was heated to a temperature equal to or higher than the melting point of silicon and melted, and the melted silicon was dropped and recovered.

As a result of measuring the weights of unreacted silicon and recovered silicon, it was found that the increase in weight of silicon grown by the decomposition reaction of tetrachlorosilane was 25.3 kg. Further, although the purity of the recovered silicon was slightly high at 4 ppm in carbon (C), the other components were 6-nine class, which was a purity level that could be used sufficiently as silicon for solar cells.
In addition, the amount of power consumption is 16 kWh per kg of silicon corresponding to the weight increase, and it was confirmed that the power consumption rate was extremely low in comparison with the Siemens method.

It is a cross-sectional view which shows the silicon manufacturing apparatus used for the silicon manufacturing method of one Embodiment of this invention. It is a longitudinal cross-sectional view which shows the silicon manufacturing apparatus used for the silicon manufacturing method of one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reaction container 2 Crucible body 2a Open end 3 Cover part 4 Raw material gas introduction tube 5 Graphite tube 5a Slit 6 Alumina tube 7 High frequency induction heating coil A Raw material silicon G Reaction gas

Claims (7)

Powdered, lump or flake silicon is put into a reaction vessel with a lid attached to the open end of the bottom of the cylindrical body,
Next, the silicon is heated to a temperature of 1000 ° C. or higher and lower than the melting point of silicon, and silane-based gas, silane-based gas, and hydrogen gas are added to the heated silicon by a source gas introduction pipe provided on the lid. Any reactive gas is allowed to flow to grow silicon produced by decomposition or reduction of the silane-based gas on the surface of the powdery, lump or flake silicon,
Next, the method for producing silicon is characterized in that the lid portion is removed from the reaction vessel, and the silicon in the reaction vessel is heated to a temperature equal to or higher than the melting point thereof to be melted, dropped and recovered.   2. The silicon according to claim 1, wherein the silane-based gas is one or more selected from the group consisting of monosilane, disilane, trisilane, tetrasilane, monochlorosilane, dichlorosilane, trichlorosilane, and tetrachlorosilane. Manufacturing method. The reaction vessel is a quartz reaction vessel,
Graphite is arranged so as to surround the reaction vessel, a high-frequency induction heating coil for heating the graphite by high-frequency induction heating is arranged, and silicon in the reaction vessel is heated by radiant heat generated by the graphite. The method for producing silicon according to claim 1 or 2.   4. The method for producing silicon according to claim 3, wherein a slit is formed in the graphite in a direction substantially orthogonal to the high frequency induction heating coil. The reaction vessel is a quartz reaction vessel,
3. The method for producing silicon according to claim 1, wherein a graphite heater is disposed so as to surround the reaction vessel, and the silicon in the reaction vessel is heated by the graphite heater. The reaction vessel is a graphite reaction vessel,
The high-frequency induction heating coil for heating by high-frequency induction heating is disposed in the graphite reaction vessel, and silicon in the reaction vessel is heated by radiant heat generated by the graphite reaction vessel. 2. The method for producing silicon according to 2. The reaction vessel is a graphite reaction vessel,
3. The method for producing silicon according to claim 1, wherein a graphite heater is disposed so as to surround the reaction vessel, and the silicon in the reaction vessel is heated by the graphite heater.

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