JPH0692618A - Production of granular polycrystalline silicon - Google Patents

Abstract

PURPOSE:To stably obtain high-purity granular polycrystalline silicon by setting up a heater at a specified position to a fluidized bed in a reactor and by specifying the temperature of the inner wall coming into contact with a silane-contg. mixed gas to suppress silicon deposition on the inner wall. CONSTITUTION:A heater 8 is set up >=100mm apart above the lower end 5 of a fluidized bed and seed silicon particles 3 are fed into a reactor 1. Feedstock silane is diluted with a gas into a mixed gas 6 with a silane concentration of >=1vol.% and this mixed gas is also fed into the reactor 1. The temperature of the inner wall 10 of the reactor coming into contact with the mixed gas 6 is set at <=720 deg.C. Thus, silicon deposition on the inner wall 10 can be suppressed and the objective high-purity granular polycrystalline silicon 300-3000mum in granule diameter can stably be obtained in a continuous manner.

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 from silane as a raw material by a fluidized bed method.

[0002]

2. Description of the Related Art Siemens method and Komatsu method are typical methods for producing polycrystalline silicon. In these methods, a silicon rod placed in a bell jar furnace is electrically heated, and gaseous chlorosilane (Siemens method) or monosilane (Komatsu method) is circulated through the silicon rod to generate silicon by thermal decomposition and reduction of the silanes. Then, polycrystalline silicon is deposited on the silicon rod. After the silicon rod grows to a predetermined size, it is recovered and used as a product. Currently, most of polycrystalline silicon is manufactured by these methods, and it is relatively easy to maintain high purity of products. However,
These methods are basically batch operations, have poor production efficiency, and in the case of mass production, the number of bell jars must be increased to deal with the increase in equipment cost, and the reaction is generally 1,050 to 1 , 150 ° C., but cooling is performed to prevent the deposition of silicon on the wall surface, so most of the energy supplied is dissipated as heat.

Under these circumstances, the recent development is the production of granular polycrystalline silicon by the fluidized bed method. In this method, granular silicon particles are used as seed crystals, and silicon is deposited on the surface of the particles in a cylindrical fluidized bed reactor. In this method, the reactor is usually heated by an external heater, seed silicon particles are supplied from the upper part of the reactor, and a mixed gas composed of the raw material silanes and a diluent gas is supplied from the lower part of the raw material gas supply line. . The silicon particles in the reactor are fluidized by the mixed gas rising in the reactor to form a fluidized bed. The mixed gas is heated by the silicon particles while passing through the reactor, is thermally decomposed to generate silicon, and is deposited on the surface of the fluidized silicon particles.

The production of granular polycrystalline silicon by the fluidized bed method is not only suitable for industrialization because it can be continuously operated and is easy to scale up, but also uses an adiabatic reactor. The heat dissipation is 1/10 or less of the Siemens method, which is energy saving.
Further, since the surface area of the granular polycrystalline silicon particles is remarkably larger than that of the rod, it is an extremely advantageous method in terms of productivity. In addition, the granular polycrystalline silicon produced by this method is less likely to be transported, crushed, packed, etc., as compared with the rod-shaped one produced by the Siemens method, and has fluidity, so that it is a single crystal. It has a number of advantages in single crystal production, such as the fact that it can be easily supplied to the crucible, the packing density in the crucible can be increased, and that it can be continuously supplied, which is performed during silicon production. .

[0005]

However, since the granular polycrystalline silicon produced by the fluidized bed method has a large deposition area, the product is easily contaminated, and seed crystals and generated granular polycrystalline silicon are not easily produced. Since it is in constant contact with the inner wall of the reactor, it is more susceptible to contamination, and ensuring the purity of the product is a major technical issue. In addition, in producing granular polycrystalline silicon by this method, a reaction of 600
It is necessary to carry out at ˜800 ° C. to decompose silanes to generate silicon. As a heating method for this, a method of installing a heater from outside the reactor or a heating element inside the reactor is used. Although the method is generally performed, in either method, it is inevitable that the inner wall of the reactor and the heating element have a higher temperature than the seed crystal on which silicon is to be deposited. Therefore, decomposition of silanes is promoted in these high temperature parts, and problems such as deposition of silicon on the inner wall of the reactor and blockage of the inside of the reactor occur. This phenomenon of silicon deposition on the inner wall of the reactor hinders the smooth particle flow of the seed crystal and has a fatal effect on the reaction. As a material for the inner wall of the reactor, a ceramic material such as quartz is generally used for the purpose of preventing contamination from the inner wall, but these ceramic materials have higher strength than metal materials. Therefore, the precipitation of silicon with a different coefficient of thermal expansion is likely to cause damage to the ceramic material, and in order to operate stably and continuously, prevention of damage to the inner wall ceramic material due to this precipitation is also a major issue. is there.

In order to avoid the above problems, various methods have been proposed. For example, in Japanese Patent Laid-Open No. 59-45917, a double tube type reactor having an inner cylinder and an outer cylinder and having a space between the inner cylinder and a dispersion plate is used, and a mixture of silanes and hydrogen is introduced from the lower part of the inner cylinder. Gas is supplied and the seed silicon particles are circulated between the inner cylinder and the outer cylinder, and the seed silicon particles are heated by a heater installed outside the outer cylinder, and the inside of the inner cylinder is maintained while maintaining the reaction temperature inside the reactor. A method for preventing silicon deposition on the wall surface has been proposed. However, in this method, the seed silicon particles are heated when they descend between the inner cylinder and the outer cylinder, and pass through between the inner cylinder and the bottom plate and circulate. The silanes therein may be thermally decomposed in the vicinity of the dispersion plate, and the deposited silicon may adhere to the dispersion plate to cause clogging, and the prevention of silicon deposition on the inner wall surface of the inner cylinder is not sufficient. In addition, the reactor used in this method has a double tube structure with a space between the inner cylinder and the dispersion plate, and a reactor having such a complicated structure is difficult to manufacture.

Further, in JP-A-2-279512, in order to reduce the concentration of the silicon-containing gas on the inner wall of the reactor, hydrogen is circulated along the inner wall of the reactor, and the raw material gas is passed through the inside of the reactor, whereby the reaction is performed. A method of preventing silicon deposition on the inner wall of the container has been proposed. However, in this method, since hydrogen and the raw material gas are rapidly mixed in the reactor, the sealing effect of hydrogen on the wall surface is insufficient, and it cannot be said to be sufficient to prevent silicon deposition.

The present inventors can suppress precipitation of silicon on the inner wall of a reactor without using a reactor having a complicated structure, and stably and continuously produce high-purity granular polycrystalline silicon. We conducted a thorough study in order to find a way to achieve this.

[0009]

In order to solve the above-mentioned problems, the present inventors have set a heater at a specific position of a reactor and brought it into contact with a mixed gas containing silane at a specific concentration or more. The present invention has been completed by finding that it is effective to set the inner wall temperature of the reactor to a specific temperature or lower.

That is, according to the present invention, when producing granular polycrystalline silicon by a fluidized bed method using silane as a raw material, a heater is installed above the lower end of the fluidized bed by 100 mm or more, and the silane concentration is 1% by volume or more. The temperature of the inner wall of the reactor contacting the mixed gas of the silane and the diluent gas at 720 ° C
The present invention relates to a method for producing granular polycrystalline silicon characterized by the following.

The present invention will be described in detail below. In the present invention, the raw material silane is diluted with a diluting gas such as nitrogen, argon or hydrogen gas and supplied to the reactor as a mixed gas. The silane concentration in the supplied mixed gas is preferably 5 to 40% by volume, more preferably 10 to 40% by volume.
It is 30% by volume. If the amount is less than 5% by volume, the amount of silicon deposited on the seed silicon particles will be small and the productivity will be poor. If the amount is more than 40% by volume, the mixed gas having a silane concentration of 1% by volume or more in the present invention will be contacted. Since it becomes difficult to control the temperature of the inner wall of the reactor to 720 ° C. or less, silicon deposition on the inner wall of the reactor is increased and fine powder is also generated. The flow rate of the mixed gas may be such that the flow rate in the reactor is a suitable flow rate that is equal to or higher than the minimum fluidization rate in the average particle size of the polycrystalline silicon particles in the fluidized bed. Supply 10 times.

The particle size of seed silicon particles forming a fluidized bed in the reactor and serving as nuclei for silicon precipitation is 50 to 350 μm.
It is preferably m. The temperature of the fluidized bed in the reactor is
600-800 degreeC is preferable, More preferably, it is 620-
750 ° C. If the temperature is less than 600 ° C, the silicon deposition reaction on the seed silicon particles does not proceed sufficiently, and
When the temperature exceeds 00 ° C, it becomes difficult to satisfy the conditions of the present invention, so that the deposition of silicon on the inner wall of the reactor increases and the generation of fine powder increases.

In the present invention, the temperature of the inner wall of the reactor that contacts the mixed gas having a silane concentration of 1% by volume or more needs to be 720 ° C or lower, preferably 680 ° C or lower, and more preferably 650 ° C or lower. It is to be. Here, the inner wall of the reactor refers to a wall forming the inside of the reaction tube, a dispersion plate, and the like. When the temperature of the inner wall of the reactor contacting with the mixed gas having a silane concentration of 1% by volume or more exceeds 720 ° C., the amount of silicon deposited on the inner wall of the reactor increases, and stable operation cannot be achieved, or the reactor is preferably broken. There is also a phenomenon that does not occur.
In order to satisfy the conditions of the present invention in the reactor, a thermometer is installed on the inner wall of the reactor, and at the same time, the silane gas concentration at this point is measured to determine the fluidized bed temperature, the silane concentration in the mixed gas, and the mixture. The gas supply rate is adjusted within the range of preferable conditions.

Heating is performed from the outside by a heater, but in the present invention, the heater is 100 mm above the lower end of the fluidized bed.
It is necessary to install them separately. Thereby, the temperature of the inner wall of the reactor at the lower end of the reactor having a high silane concentration can be lowered. Place the heater above the bottom of the fluidized bed 1
When installed at a position of less than 00 mm, the temperature of the inner wall of the reactor becomes high in the lower part of the reactor having a high silane concentration, and the temperature of the inner wall of the reactor which comes into contact with a mixed gas having a silane concentration of 1% by volume or more, which is the condition of the present invention It becomes difficult to maintain the temperature below 720 ° C., and more silicon is deposited on the inner wall of the reactor.

By the above method, it is possible to suppress the deposition of silicon on the inner wall of the reactor and to produce granular polycrystalline silicon having a particle diameter of 300 to 3000 μm.

FIG. 1 is a schematic view showing an embodiment of the present invention. The cylindrical reactor 1 is provided with a gas discharge line 2 and a seed silicon supply line 3 for charging seed silicon particles into the reactor at the top of the reactor, and a mixed gas supply line 6 at the bottom of the reactor. I have it. The bottom of the reactor is doubled by a gas distribution plate 5 provided at a distance from the bottom plate 4. A product withdrawing line 7 is connected to the center of the dispersion plate 5 through the bottom plate 4. Also, at least 100 mm above the dispersion plate 5, which is the lower end of the fluidized bed.
As described above, the heater 8 is provided so as to surround the reactor 1. The dispersion plate can be cooled if necessary. The temperature of the inner wall of the reactor is measured by the temperature sensor 11, the concentration of silane gas is appropriately sampled from the sampling port 12, and the silane concentration is measured by a gas chromatograph. When a fluidized bed is formed with only seed silicon particles and reacted, the particles have a small particle diameter and are discharged out of the system. Therefore, a predetermined amount of polycrystalline silicon particles are initially charged in the reactor 1. The particle size of the polycrystalline silicon particles is 30
0 to 3000 μm is preferable. The reactor is heated by the heater 8, and the mixed gas of silane and the diluent gas is blown from the mixed gas supply line 6. In this case, the silane or the mixed gas of silane and the diluent gas and the diluent gas can be separately supplied, or these gases can be preheated and supplied. The polycrystalline silicon particles vigorously flow due to the mixed gas flow to form a fluidized bed 9 whose lower end is in contact with the upper surface of the dispersion plate. Silicon is deposited and grows on the surfaces of the polycrystalline silicon particles. After the prescribed reaction is completed,
The granular polycrystalline silicon of the product is the product extraction line 7
The seed silicon particles are further extracted from the reactor, and at the same time, the seed silicon particles are supplied from the seed silicon particle supply line 3 into the reactor to replenish the particles in the fluidized bed. Exhaust gas composed of unreacted silane and hydrogen gas after the silicon deposition reaction is discharged from the system through the gas discharge line 2. The discharged gas can be discarded as it is, or can be circulated for use.
It can also be used in another reaction system.

[0017]

As a result of various studies, the present inventors have found that silicon deposition on the inner wall of the reactor has a silane concentration of 1% by volume or more in the mixed gas in the reactor and is in contact with the mixed gas. The present invention has been made by finding that the temperature of the inner wall becomes particularly intense when the temperature exceeds 720 ° C. The temperature of the inner wall of the reactor is relatively low in the portion located below the fluidized bed,
As the temperature approaches the heater, the temperature gradually rises and reaches the maximum in the central part of the heater. On the other hand, the silane in the mixed gas is
Since the seed silicon particles in the lower part of the reactor are sequentially reacted, the silane concentration in the mixed gas is high in the lower part of the reactor and gradually decreases as it goes to the upper part of the reactor. In the present invention, the heater is moved upward from the lower end of the fluidized bed by 10
By installing them at a distance of 0 mm or more, it is possible to lower the reactor inner wall temperature in the lower part of the reactor where the silane concentration in the mixed gas is high, and the condition of the present invention, that is, the mixed gas having a silane concentration of 1% by volume or more. The temperature of the inner wall of the reactor which comes into contact can be maintained below 720 ° C. In the region where the silane concentration in the mixed gas is less than 1% by volume, there is no particular restriction on the temperature of the inner wall of the reactor.

[0018]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. {Example-1} Using the apparatus shown in FIG. 1, polycrystalline silicon was manufactured under the following conditions. To prevent silane from leaking when the quartz tube is accidentally broken, the inner diameter is 100m
A reactor in which a quartz reaction tube having an inner diameter of 80 mm and a height of 1,800 mm was installed inside a stainless steel tube having a height of m and a height of 2,000 mm was used. The heater is 120 ~ above the dispersion plate.
It was installed at a position of 620 mm. Particle size is 300-2,0
Polycrystalline silicon particles having an average particle diameter of 500 μm and a diameter of 00 μm were filled in a quartz reaction tube from a dispersion plate to a height of 200 mm so that the ratio of the height of the stationary layer to the inner diameter of the reactor was 1: 2.5. . The fluidized bed temperature was 650 ° C., and the silane concentration was 15% by volume diluted with hydrogen so that the temperature of the inner wall of the reactor and the concentration of the mixed gas at that position satisfied the conditions of the present invention.
The mixed gas of was supplied to the reactor at a flow rate of 0.33 m / s.
In order to keep the height of the fluidized bed during the reaction constant, the amount of granular polycrystalline silicon particles increased by the reaction was taken out of the system. Further, in order to keep the average particle size similar to the initial state, seed silicon particles having an average particle size of 200 μm were additionally charged. In this case, the temperature of the inner wall of the reactor and the silane concentration in the mixed gas are shown in Table 1.

[0019]

[Table 1] The reaction was continued for 50 hours, but no problem occurred in the reaction. After the reaction was stopped, deposits in the quartz reactor were inspected, but the deposition of silicon was 3 mm at maximum.

Comparative Example-1 As a mixed gas diluted with hydrogen, a mixed gas having a silane concentration of 25% by volume was added at a flow rate of 0.3.
A test was conducted under the same conditions as in Example 1 except that the reactor was supplied at 3 m / s, and the temperature of the inner wall of the reactor was 750 ° C. at a position 120 mm above the lower end of the fluidized bed. Was 1.2 to 2% by volume. After reacting for 6 hours, the temperature distribution in the reactor was disturbed due to the precipitation of silicon, so the reaction was stopped. When inspecting the deposits inside the quartz reaction tube,
Silicon was deposited on the inner wall of the reactor with a thickness of 15 mm.

{Comparative Example-2} The reaction was carried out under the same conditions as in Example 1, except that the position of the heater was lowered to 50 to 550 mm above the lower end of the fluidized bed.
The temperature of the inner wall of the reactor at a position 70 mm above the lower end of the fluidized bed was 780 ° C., and the silane concentration at this position was 1.5 to 2.5% by volume. Although the reaction was continued for 14 hours, the precipitation of silicon on the inner wall of the upper part of the dispersion plate became remarkable and the reaction could not be continued. The quartz reaction tube was also damaged.

{Comparative Example-3} In Example 1, the position of the heater was further lowered to 0 to 500 above the lower end of the fluidized bed.
When the reaction was carried out under the same conditions except that the reactor was installed at a position of mm, the temperature of the inner wall of the reactor at a position of 60 mm above the lower end of the fluidized bed was 780 ° C., and the silane concentration at this position was 2-3% by volume. Met. Although the reaction was continued for 10 hours, the precipitation of silicon on the inner wall of the upper part of the dispersion plate became remarkable and the reaction could not be continued. The quartz reaction tube was also damaged.

{Example-2} Inner diameter 200 mm, height 2,
A reactor was used in which a quartz reaction tube having an inner diameter of 160 mm was installed inside a 000 mm stainless steel tube. The heater was installed at a position of 200 to 1,000 mm above the lower end of the fluidized bed. Polycrystalline silicon particles having a particle diameter of 300 to 2,000 μm and an average particle diameter of 500 μm were added from the dispersion plate to a height of 400 mm so that the ratio of the stationary layer height to the inner diameter of the reactor was 1: 2.5. Filled. Fluidized bed temperature 650
C., the temperature of the inner wall of the reactor and the concentration of the mixed gas at that position satisfy the conditions of the present invention, and a mixed gas having a silane concentration of 20% by volume diluted with hydrogen is supplied to the reactor at a flow rate of 0.33 m / s. Other conditions were the same as in Example 1. At this time, the pressure in the reactor was 1.02 atm. Table 2 shows the temperature of the inner wall of the reactor and the silane concentration in the mixed gas in this case.

[0024]

[Table 2] The reaction was continued for 30 hours, but there was no problem in the reaction. After the reaction was stopped, the deposit in the quartz reaction tube was inspected, but the deposition of silicon had a maximum thickness of 2 mm.

[0025]

According to the present invention, without using a reactor having a complicated structure, silicon deposition on the inner wall of the reactor has been a factor that hinders stable operation in the conventional granular polycrystalline silicon production by the fluidized bed method. It is possible to prevent the occurrence of abnormal conditions such as damage to the reactor due to silicon precipitation, insufficient fluidization of the fluidized bed, and blockage, and to enable stable and continuous production of granular polycrystalline silicon. Become.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention.

[Explanation of symbols]

 1; Reactor 2; Gas discharge line 3; Seed silicon particle supply line 4; Bottom plate 5; Dispersion plate 6; Mixed gas supply line 7; Product withdrawing line 8; Heater 9; Fluidized bed 10; Quartz reaction tube 11; Temperature sensor 12; Gas sampling port

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Komatsu 3-1, Chidori-cho, Kawasaki-ku, Kanagawa Prefecture Tonen Chemical Co., Ltd. Technology Development Center (72) Masaaki Ishii 3 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 Tonen Chemical Co., Ltd. Technology Development Center (72) Inventor Kazutoshi Takatsuna 3-1, Chidori-cho, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Tonen Chemical Co., Ltd. Technical Development Center (72) Inventor Yasuhiro Saruwatari Kawasaki, Kanagawa Prefecture 3-1, Chidori-cho, Kawasaki-ku, Tonen Chemical Co., Ltd. Technology Development Center

Claims (1)

[Claims] 1. When producing granular polycrystalline silicon by a fluidized bed method using silane as a raw material, a heater is installed 100 mm or more above the lower end of the fluidized bed, and diluted with silane having a silane concentration of 1% by volume or more. A method for producing granular polycrystalline silicon, characterized in that the temperature of the inner wall of the reactor in contact with the mixed gas with the gas is set to 720 ° C. or lower.