JPH06127927A - Production of granular polycrystalline silicon - Google Patents

Abstract

PURPOSE:To provide a method capable of stably and continuously effecting reaction over a long period of time with a long reactor service life by effectively preventing the deposition of silicon on the walls of the reactor and effectively suppressing the generation of the fine powder silicon by decomposition of a silane compd. in a gaseous phase in the process for production of the granular polycrystalline silicon by a fluidized bed method. CONSTITUTION:Seed silicon is heated up to its reaction temp. or near this temp. and is supplied into a fluidized bed reactor where silicon particles are fluidized at the time of producing the granular polycrystalline silicon by thermally decomposing the silane compd. on these fluidized silicon particles by using the above reactor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing granular polycrystalline silicon by a fluidized bed method.

[0002]

2. Description of the Related Art High-purity polycrystalline silicon is used as a raw material for semiconductor devices, solar cells, and the like, which have become extremely popular in recent years, and is mainly manufactured by the Siemens method. In this method, a thin silicon rod having a diameter of about 5 mm installed in a bell jar type reactor is electrically heated, and a mixed gas of a gaseous silane compound and hydrogen is introduced into the silicon rod to deposit silicon on the surface of the silicon rod. It is a method to let. This method is suitable for producing high-purity silicon,
Since the reaction surface area is small, the productivity is low, and the heat dissipation from the surface of the bell jar type reactor is large, so the power consumption is large, and the silicon rod is collected every time the silicon rod grows to a certain thickness, and another new However, it is not suitable for mass production because of the drawbacks such as the need to stop the reaction for exchanging the product.

On the other hand, the fluidized bed method has recently been drawing attention as an energy-saving method for producing granular polycrystalline silicon. In this method, a silane compound-containing raw material gas is introduced to the surface of fluidized silicon particles, silicon produced by thermal decomposition of the silane compound is deposited on the surface of the fluidized silicon, and high-purity granular polycrystalline silicon is obtained. Is a method of manufacturing. In this method, since the reaction is carried out on the fluidized particle surface, the area of the reaction surface is large and the productivity is high, the continuation is easy, and the heat dissipation amount is significantly smaller than that of the Siemens method. is there. Furthermore, since this method is easy to scale up, it can be said to be the most suitable method for industrialization. The fluidized bed method polycrystalline granular silicon is more advantageous than the rod-shaped silicon obtained by the Siemens method in terms of transportation, crushing, packing, etc. because the product is granular, and when it is remelted in a crucible for single crystal production. It has many advantages such as easy supply and easy melting.

In the method for producing granular crystalline silicon by the fluidized bed method, the reaction heat is generally supplied from a heat source external to the reactor through a reactor wall or by a heat supplier arranged in the reactor. Done. When the reaction heat is supplied from the external heat source of the reactor, the temperature distribution in the reactor has the highest temperature on the wall surface of the reactor, so that a large amount of silicon is also decomposed on the wall surface of the reactor and a large amount of silicon is generated. It deposits on the wall of the vessel. Such deposition of silicon on the reactor wall surface reduces the internal volume of the reactor and the yield of product silicon particles. Furthermore, the thermal expansion coefficient of the reactor and that of the deposited silicon are different, so the reactor cooling This sometimes causes inconvenience such as damage to the reactor. Further, in the vicinity of the wall surface of the reactor, the silane compound is decomposed in the gas phase due to the high temperature, and silicon fine powder is also generated. Such fine powder accumulates in the pipe connected to the reactor and causes a problem such as a pipe clogging trouble.

In order to avoid the above problems, various methods have been conventionally proposed. For example, JP-A-59-45
Japanese Patent No. 917 describes a reactor having a double-tube structure having an inner cylinder and an outer cylinder in the fluidized bed reactor, and a dispersion plate arranged at the bottom of the inner cylinder. In this device, a silane compound is ejected through the dispersion plate into the inner cylinder to fluidize the silicon particles filled in the inner cylinder, and a part of the fluidized silicon particles is mixed with the outer cylinder. The gap between the cylinder and the cylinder is moved from the top to the bottom, and the silicon particles moved to the bottom are circulated again in the inner cylinder together with the raw material gas ejected from the dispersion plate. In this case, the heat required for the reaction moves from the external heat source to the bottom direction between the outer cylinder and the inner cylinder via the outer cylinder wall, and is transferred to the circulating flow of silicon particles circulating in the inner cylinder. . Then, the inside of the inner cylinder is maintained at a predetermined reaction temperature by the circulating flow of the silicon particles. In such a fluidized bed method, since the raw material gas is supplied into the inner cylinder and the amount of unreacted raw material gas existing in the gap between the outer cylinder and the inner cylinder is small, the silicon deposition on the inner wall surface of the outer cylinder is prevented. Can be effectively prevented, and since the temperature of the inner cylinder inner wall surface is lower than the outer cylinder inner wall surface temperature and almost equal to the silicon particle temperature in the inner cylinder, a large amount of silicon is deposited on the inner cylinder inner wall surface. Can be prevented. However, in the case of such a conventional method, since the dispersion plate arranged at the bottom of the inner cylinder is heated to a high temperature by the high-temperature silicon particle circulation flow, the raw material silane compound is thermally decomposed in the vicinity of the dispersion plate, and the generated silicon is generated. There is a problem that it adheres to the dispersion plate and causes clogging of the dispersion plate, which makes it difficult to operate the device stably over a long period of time.

In Japanese Patent Laid-Open No. 2-279512, in order to reduce the concentration of the silane compound contacting the wall surface of the reactor, hydrogen is circulated along the wall surface of the reactor to seal the wall surface with hydrogen, and the inside thereof is sealed. A method of preventing the deposition of silicon on the wall surface of the vessel by passing the raw material gas is disclosed. However, in this method, the hydrogen that is circulated to seal the vessel wall is quickly mixed with the source gas, so the sealing effect is not sufficient, and it is not possible to sufficiently prevent the deposition of silicon on the vessel wall. Can not.

[0007]

SUMMARY OF THE INVENTION The present invention effectively prevents precipitation of silicon on a reactor wall in a method for producing granular polycrystalline silicon by a fluidized bed method, and
It is an object of the present invention to provide a method capable of effectively suppressing the generation of fine silicon powder due to the decomposition of a silane compound in a gas phase, having a long reactor life, and performing a reaction continuously for a long time stably. To do.

[0008]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. That is, according to the present invention, when a silane compound is thermally decomposed on the fluidized silicon particles using a fluidized bed reactor in which the silicon particles are fluidized to produce granular polycrystalline silicon, the seed silicon is reacted. Provided is a method for producing granular polycrystalline silicon, which comprises heating to a temperature at or near a temperature and supplying the same into a reactor.

The silane compound used in the present invention may be any gaseous silane compound which is thermally decomposed by heating to precipitate silicon, and various conventionally known compounds are used. Examples of such silane compounds include monosilane,
Other than disilane, etc., monochlorosilane, dichlorosilane,
Examples thereof include halogenated silane compounds such as trichlorosilane. The silane compound is thermally decomposed at a temperature of 500 to 900 ° C, preferably 600 to 750 ° C to generate silicon. On the other hand, halogenated silane is 900 to 1350 ° C.
Preferably, it is thermally decomposed at a temperature of 1050-1150 ° C. to produce silicon.

The silane compound is advantageously used in the form of a mixed gas with a gas that does not react with silicon, for example, a diluent gas such as hydrogen, neon, helium, or argon. In this case, the concentration of the silane compound in the mixed gas is usually 5 to 10
It is 0 vol%, preferably 10 to 50 vol%. When halogenated silane is used as the silane compound, 40 to 90 vol% of hydrogen is contained in the mixed gas.
Preferably, it is present at a ratio of 50 to 80 vol%.

Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an example of a fluidized bed reactor used for carrying out the present invention. In FIG. 1, reference numeral 1 is a cylindrical reactor, and an upper part of the reactor is connected to an expanded empty column 3 equipped with a gas discharge pipe 11 and a seed silicon supply pipe 12. In addition, a gas dispersion plate 13 is provided at the bottom of the reactor 1.
Is provided, and the dispersion plate communicates with the product silicon particle extracting pipe 10 and the raw material gas introducing pipe 9. Further, an annular heater 2 for heating the reactor 1 is provided around the reactor above the position of the gas dispersion plate 13. At the central portion of the top plate 16 of the expansion tower 3, a silicon particle supply pipe 1
2, the heating pipe 8 and the measuring pipe 7 are sequentially connected, and the silicon particle filling drum 5 is connected to the upper end of the measuring pipe 7. The outer peripheral surface of the filling drum 5 is surrounded by a jacket 6 with a space therebetween, and a void portion formed by the outer peripheral surface of the filling drum and the jacket 6 is formed in the gas flow passage. A heater 4 for heating the silicon particle heating tube 8 is arranged around the silicon particle heating tube 8. Opening / closing valves 18 and 19 are provided above and below the silicon particle measuring pipe 7, and an opening / closing valve 20 is also provided below the heating pipe 8. The top plate 16 of the expansion empty tower 3 and the jacket 6 of the filling drum 5 are connected by a pipe 11 so that the exhaust gas discharged from the expansion empty tower 3 forms a space between the outer peripheral surface of the drum 5 and the jacket 6. After passing through, it is designed to be discharged through the pipe 15. The pipe 21 communicating with the dispersion plate 13 is a diluent gas introduction pipe for diluting the raw material silane compound.

The apparatus shown in FIG. 1 can be modified in various ways. For example, an inner cylinder can be inserted into the reactor 1 to form a double-cylinder structure reactor. The heating method of can also be an internal heating method. Further, the supply system of the seed silicon filled in the drum 5 to the reactor may be a continuous supply system in which a fixed amount of the seed silicon continuously flows down without using a measuring tube. By pressurizing the inside of the drum 5, the exhaust gas from the expanded empty column 3 is transferred to the drum 5 via the seed silicon heating pipe 8 and the seed silicon measuring pipe.
It is also possible to have a structure that does not flow into. Furthermore, a cylindrical body can be inserted as a liner in the reactor 1.

In order to produce granular polycrystalline silicon using the fluidized bed reactor shown in FIG.
Further, the diluting gas is introduced into the dispersion plate 13 through the pipe 21, from which it is jetted into the reactor 1 to fluidize the polycrystalline silicon particles filled in the reactor to form the fluidized bed 14 and by the annular heater 2. The inside of the reactor is heated to maintain a predetermined reaction temperature (average temperature of the fluidized bed), that is, a temperature at which the silane compound is thermally decomposed, and silicon generated from the silane compound is deposited on the fluidized silicon particles.

As described above, when the silane compound is pyrolyzed on the fluidized silicon particles to generate silicon and the silicon is deposited on the fluidized silicon particles, the silicon particles grow and the fluidized bed height increases. , The seed silicon with a small particle size is fed into the reactor to keep the average particle size of the fluidized bed constant, and the silicon particles are extracted from the reactor to set the fluidized bed height to a predetermined height. It is necessary to hold. The present invention is characterized in that seed silicon is supplied into the reactor in a preheated state.

That is, in the apparatus shown in FIG. 1, the seed silicon composed of polycrystalline silicon particles filled in the drum 5 through the pipe 17 passes through the pipe 11 from the expanded empty column 3 to the outer periphery of the drum 5. It is preheated by heat exchange with the heated exhaust gas discharged from the pipe 15 through the gap between the surface and the jacket 6. The temperature of the seed silicon preheated in the drum 5 is at least 50 ° C., preferably 8 ° C.
It is 0 ° C or higher. The seed silicon preheated in the drum 5 is
After closing the valve 19 and opening the valve 18 and transferring a certain amount thereof into the measuring pipe 7, the valve 20 and the valve 18
Is closed and the valve 19 is opened to transfer the seed silicon into the heating tube 8 where it is heated by the heater 4. The heating temperature of the seed silicon in the heating pipe 8 is a temperature around the reaction temperature (fluidized bed average temperature) in the reactor 1. For example,
Assuming that the reaction temperature is T (R), the temperature T (S) of the seed silicon in the heating tube 8 is preferably regulated to fall within the following range. T (R) −200 ≦ T (S) ≦ T (R) +200 (1) The more preferable range of T (S) is as follows. T (R) -50 ≦ T (S) ≦ T (R) +50 (2)

Next, the seed silicon heated to the predetermined temperature in the heating pipe 8 as described above opens the valve 20, introduces this into the expanded empty column 3 through the supply pipe 12, and downward from there. And dropped into the reactor 1 to be supplied. The product silicon particles are extracted from the extraction pipe 10 in accordance with the amount of the heated seed silicon supplied and the amount of silicon deposited on the fluidized silicon particles, and the fluidized bed height is kept constant. The average particle size of the seed silicon used in the present invention is preferably 50 to 300.
.mu.m, and the silicon particles forming the fluidized bed are preferably 300-1500 .mu.m. Further, the deposition rate of silicon on the fluidized silicon particles is 100
10 to 300 g / min, preferably 20 to 100 per g
g / min.

In the fluidized bed reactor shown in FIG. 1, the seed silicon is intermittently supplied to the reactor. However, the seed silicon is made to flow down at a constant rate in the heating pipe, so that the seed silicon is continuously supplied. It can also be supplied. The amount of seed silicon supplied is determined depending on the amount of fluidized silicon particles and the deposition rate of silicon on the particles, but generally 1 to 2 per hour with respect to the amount of fluidized silicon particles.
The proportion is 0% by weight, preferably 5 to 10% by weight.

[0018]

According to the present invention, the seed silicon is supplied to the reactor in a state of being preheated to a temperature around the reaction temperature, so that silicon is deposited on the reactor wall and silane in the gas phase is used. It is possible to effectively prevent generation of fine powder due to decomposition of the compound. That is, when the seed silicon is heated to or near the reaction temperature and supplied to the reactor,
Since a considerable amount of heat possessed by such silicon is supplied into the reactor, the load of the heating source for heating the fluidized bed in the reactor to the reaction temperature is reduced accordingly. As a result, when the amount of heat is transferred from the external heat source through the reactor wall to the inside of the reactor, the temperature of the inner wall surface of the reactor is significantly lowered,
Since the temperature approaches the reaction temperature, the deposition of silicon on the inner wall of the reactor can be effectively prevented, and the gas temperature near the inner wall of the reactor also drops significantly. Therefore, it exists near the inner wall of the reactor. Excessive heating of the silane compound is avoided, and generation of fine silicon powder due to decomposition of the silane compound in the gas phase can be effectively prevented. Therefore, according to the present invention, it is possible to solve all kinds of apparatus troubles caused by the deposition of silicon on the wall surface of a reactor and the generation of fine silicon powder, which are seen in the conventional method.

Further, according to the present invention, when the seed silicon is heated to the reaction temperature or a temperature in the vicinity thereof and supplied to the reactor, the temperature condition (reaction condition) of the fluidized bed due to the supply of the seed silicon is extremely changed. Since it is very small, there is no rapid change in the decomposition rate of the silane compound, and silicon can be deposited on the fluidized silicon particles at a stable rate while avoiding the generation of fine silicon powder. Moreover, unlike the case of the conventional method, since there is no sudden temperature drop when supplying the seed silicon, the reactor is not subjected to any thermal shock, and the reactor is damaged by the thermal shock as seen in the case of the conventional method. There is no problem. Furthermore, when increasing the amount of seed silicon supplied to increase the production of product silicon, or when replacing the silicon in the reactor, the amount of seed silicon supplied can be increased without the reactor being shut down or the heating conditions changing significantly. Can be increased.

[0020]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 In a quartz outer cylinder having an inner diameter of 100 mm and a height of 1200 mm,
Granular polycrystalline silicon was produced using a fluidized bed reactor equipped with a fluidized bed reactor 1 having a two-cylinder structure in which a quartz tube having an inner diameter of 80 and a height of 1100 mm was inserted. In the apparatus used in this example, the annular heater 2 was installed in the reactor portion at a distance of 0 to 1000 mm from the horizontal plane of the dispersion plate of the reactor 1. Furthermore, the particle diameter of the reactor inner cylinder is 300 to 20.
Silicon particles having an average particle size of 750 μm were distributed in the range of 00 μm. The stationary layer height of the filled silicon particles was 240 mm.

A mixed gas of monosilane having a monosilane concentration of 20 wt% and hydrogen is introduced from the source gas introduction pipe 9 into the dispersion plate 1.
3 and jetted into the inner cylinder of the reactor 1 to fluidize the silicon particles. The flow rate of the mixed gas passing upward in the inner cylinder was 0.5 m / sec, and the height of the fluidized bed was 4.5 times (360 mm) the diameter of the inner cylinder. With the annular heater 2, the fluidized bed average temperature (reaction temperature) in the inner cylinder is 700 ° C.
Held in. The seed silicon has a particle size of 100 to 3
The particles having an average particle size of 150 μm were used in the range of 00 μm. This kind of silicon is 8 in the drum 5.
It is preheated to 0 ° C., and a certain amount thereof is transferred into the measuring pipe 7 and then transferred to a heating pipe 8, where it is heated to about 700 ° C. which is almost the same temperature as the reaction temperature, and this heated seed silicon is expanded to an empty space. Feed to Reactor 1 via 3. The heating seed silicon was intermittently supplied every 30 minutes at a rate of 3 wt% of the amount of silicon particles with which the reactor was charged once. Further, in accordance with the supply of this type of silicon, product silicon particles were extracted through the extraction tube 10.

When the reaction was continued for 100 hours as described above, no problem occurred in continuing the reaction. Further, the reaction temperature during the supply of seed silicon did not substantially change, and the reaction could proceed smoothly. 10
After continuing for 0 hours, all the silicon in the reactor was extracted, and 3.2 kg of charged silicon was charged from the seed silicon charging drum 5 at a supply temperature of 700 ° C. for a supply time of about 8 minutes. After that, the reaction was continued for 72 hours,
No problems occurred, and there was no fluctuation in the reaction temperature during the seed silicon supply, and the results were favorable. After the reaction was stopped, no cracks were observed in the quartz inner tower, and the deposits were inspected after cooling, but the precipitation of silicon was extremely small and the thickness was 2 mm at the maximum.

Example 2 A continuous experiment was conducted for 120 hours in the same manner as in Example 1 except that the reaction temperature and the temperature of the seed silicon to be supplied were set to 750 ° C. However, as in Example 1, no trouble was found. Also,
The state of silicon deposition on the inner cylinder wall surface and the dispersion plate after the 120-hour experiment was almost the same as in Example 1 and was very slight.

Example 3 In Example 1, after the reaction was continued for 24 hours, the seed silicon supply rate was 2.0 times (6 wt% of the silicon particles in the reactor).
(Corresponding to the above), the silicon particle withdrawing speed was adjusted accordingly, and the reaction was further continued for 150 hours. Also in this case, the reaction temperature and the decomposition rate of monosilane did not substantially change, and the reaction proceeded smoothly. The state of silicon deposition on the inner cylinder wall surface and the dispersion plate was almost the same as in Example 1, and was extremely small.

Comparative Example 1 The reaction was continued for 98 hours in the same manner as in Example 1 except that the seed silicon temperature was 25 ° C. In this case, no special trouble occurred while the reaction was continued, but the reaction temperature was greatly reduced when the seed silicon was supplied, and the decomposition rate of monosilane was also greatly reduced. Also, when the state of silicon deposition on the inner cylinder wall was inspected after the reaction was stopped, the maximum thickness was 3 mm, while the silicon deposition amount on the dispersion plate was 2 mm at maximum.
Showed the thickness of.

Comparative Example 2 In Comparative Example 1, after the reaction was continued for 24 hours, the seed silicon supply rate was 2.0 times (6 wt% of silicon particles in the reactor).
(Corresponding to the above), the silicon particle extraction speed was adjusted accordingly, and the reaction was continued for a further 72 hours. In this case, in the latter half of the experiment in which the seed silicon supply rate was increased, the reaction temperature and the monosilane decomposition rate were significantly reduced during seed silicon supply. When the reaction was stopped 96 hours (4 days) from the start of the reaction and the inner cylinder wall surface was inspected, hair cracks were found at a distance of 400 to 650 mm from the horizontal plane of the dispersion plate of the quartz inner cylinder. Next, when the amount of deposited silicon on the inner wall surface was inspected, silicon having a thickness of 5 mm was deposited at the place where the deposited amount was the largest. Further, the amount of silicon deposited on the dispersion plate showed a maximum thickness of 6 mm.

Example 4 An experiment was conducted in the same manner as in Example 1 except that the inner cylinder was not installed. Even in this case, no trouble occurred even if the reaction was continued for 96 hours, and the deposition of silicon on the inner wall of the reactor and the dispersion plate was extremely small, and was about 2 mm at the maximum.

Comparative Example 3 An experiment was conducted in the same manner as in Example 4, except that the temperature of the seed silicon supplied was 25 ° C. In this case, the reaction is 72
Although no special trouble occurred even after continuing the time, the reaction temperature dropped significantly when the seed silicon was supplied. Further, after the reaction was continued for 72 hours, when the inside of the reactor was inspected, it was confirmed that the amount of silicon deposited on the wall of the reactor was remarkable, and that silicon was deposited at a maximum thickness of 4 mm, and the amount of fine silicon powder was large. It was confirmed.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an example of a fluidized bed reactor used for producing granular polycrystalline silicon of the present invention.

[Explanation of symbols]

1 Cylindrical Reactor 11 Gas Discharge Pipe 2 Annular Heater 12 Type Silicon Supply Pipe 3 Expanded Empty Tower 13 Gas Dispersion Plate 4 Heater 14 Fluidized Bed 5 Type Silicon Packing Drum 15 Piping 6 Jacket 16 Expanded Empty Tower Top Plate 7 Type Silicon Metering Pipe 17 Pipe 8 type Silicon heating pipe 18, 19, 20
Valve 9 Raw material gas introduction pipe 21 Dilution gas introduction pipe 10 Silicon particle extraction pipe

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[Procedure amendment]

[Submission date] May 11, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

Next, the seed silicon heated to the predetermined temperature in the heating pipe 8 as described above opens the valve 20, introduces this into the expanded empty column 3 through the supply pipe 12, and downward from there. And dropped into the reactor 1 to be supplied. The product silicon particles are extracted from the extraction pipe 10 in accordance with the amount of the heated seed silicon supplied and the amount of silicon deposited on the fluidized silicon particles, and the fluidized bed height is kept constant. The average particle size of the seed silicon used in the present invention is preferably 50 to 300.
.mu.m, and the silicon particles forming the fluidized bed are preferably 300-1500 .mu.m. Further, the deposition rate of silicon on the fluidized silicon particles is 100
10 to 300 g / hour, preferably 20 to 100 per g
g / hour.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kazutoshi Takatsuna 3-1, Chidori-cho, Kawasaki-ku, Kanagawa Prefecture Tonen Kagaku Co., Ltd. Technology Development Center (72) Inventor Yasuhiro Saruwatari Chidori, Kawasaki-ku, Kawasaki-shi, Kanagawa 3-1, Machi Tonen Kagaku Co., Ltd. Technology Development Center (72) Inventor Nobuhiro Ishikawa 23, Toagosei Kagaku Kogyo Co., Ltd. Nagoya Plant, 23, 17 Showa-cho, Minato-ku, Nagoya, Aichi Prefecture (72) Inventor ▲ Hirota Tasuke 23 Toagosei Chemical Industry Co., Ltd. Nagoya Factory, 23, 17 Showa-cho, Minato-ku, Nagoya, Aichi Prefecture

Claims (1)

[Claims] 1. When producing a granular polycrystalline silicon by thermally decomposing a silane compound on the fluidized silicon particles using a fluidized bed reactor in which the silicon particles are fluidized, seed silicon is used at a reaction temperature or A method for producing granular polycrystalline silicon, which comprises heating to a temperature in the vicinity and supplying the same into a reactor.