JPH0840717A - Fluidized bed reactor for monosilane decomposition - Google Patents

Abstract

PURPOSE:To improve a silane conversion rate by constructing a wall of a reactor in a shape of a cone expanding upward and making the wall to incline with a specific angle against a vertical line. CONSTITUTION:A reactor 1 is constructed with a wall which forms a cone expanding upward having an angle of 1.3-3.9 degree against a vertical line. Seed particles consisting of polycrystal Si having a particle size distribution of about 250-1000mum in particle diameters are packed in the reactor 1 to about 1000mm in a stationary layer height. While the inside of the reactor vessel 1 is heated with a heater, a raw material gas and hydrogen gas are blown into the reactor vessel 1 through a raw material gas-introducing tube 4 and a H2-introducing tube 5, respectively in the conditions that a monosilane concentration is about 10mol.% and each of the gas line velocity of 2<=U/Umf<=8 (U is a gas linear velocity; Umf is a minimum fluidizing velocity for the particles in use). The introduced gas ascends through the reactor vessel 1, the Si seed particles are fluidized to form a fluidizing layer and Si precipitates on the surface of the Si seed particle to make it grow. After a specified precipitation period, Si particles are taken out through a granular Si-discharging tube 6 to the outside of the reactor vessel in a sequential manner and, in return for it, new seed crystals are introduced into the reactor vessel through a Si-supplying tube 3. The gas which has completed the reaction is discharged through a gas-purging tube 7.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fluidized bed reactor for monosilane decomposition for producing polycrystalline silicon by thermal decomposition of monosilane.

[0002]

2. Description of the Related Art Conventionally, polycrystalline silicon has been manufactured by depositing it on a silicon rod by a thermal decomposition reaction of monosilane (silane). In this manufacturing method, a reaction furnace called a bell jar is used, and the furnace wall is cooled in order to prevent silicon from precipitating on the wall surface of the reaction furnace. In addition, this method has the disadvantages that the deposition area is small and thus the deposition rate of silicon is slow, and that the productivity is poor because it is a batch system. In order to overcome the drawbacks of this technique, a method (fluidized polycrystalline silicon production method) of depositing silicon on fluidized fine silicon granules having a substantially large deposition area has been proposed.

In Japanese Patent Laid-Open No. 58-204814, a fluidized bed reactor in which the diameter of the reaction tube is changed depending on the location is used and the flow rate of the gas containing monohalosilane flowing from the bottom to the top in the reaction tube is changed. A method for producing polycrystalline silicon particles is disclosed, in which silicon is deposited on high-purity silicon granules and the size range of the silicon granules floating in a fluidized bed is widened.

Further, in Japanese Patent Application Laid-Open No. 57-145021, chlorosilane and hydrogen gas are introduced from a plurality of nozzles at the bottom into a fluidized bed reactor having a taper opening upward so that silicon microparticles are introduced into the reactor. Disclosed is a method of producing granular polycrystalline silicon particles by flowing and depositing silicon on the particles. The above methods are all methods for producing polycrystalline silicon particles using monohalosilane or monochlorosilane as a raw material. On the other hand, a method for producing polycrystalline silicon particles by thermal decomposition of monosilane in a heating fluidized bed reactor is also known. However, in the conventional heating fluidized bed reactor used for producing polycrystalline silicon by thermal decomposition of monosilane, depending on the reactor diameter and the particle size used, fluidized silicon particles are condensed and closed in the reactor. Or, the bubbles of the decomposition gas (silane and hydrogen) formed in the fluidized bed become larger than the reactor diameter and become slug flow, which does not occur in the production method using halosilane as a raw material that a high silane conversion rate cannot be obtained. There was no problem.

[0005]

The gas linear velocity in the method of depositing silicon produced by thermal decomposition of monosilane on fluidized silicon granules is usually 2 × Umf ≦ U ≦ 8.
It is known that × Umf (U: gas linear velocity, Umf: minimum fluidization velocity of used particles) is preferable. The reason is U
When ≦ 2 × Umf, silicon is condensed and 8 × Umf
This is because when ≦ U, the gas bubbles formed in the fluidized bed have a size larger than the reactor diameter and become slug flow, and a high conversion rate of silane cannot be obtained. Depending on the reactor diameter and the particle size used, even at a gas linear velocity in this range, silicon condenses and bubbles of the decomposition gas (silane and hydrogen) formed in the fluidized bed become larger than the reactor diameter. It will be a slug flow. 1000μ in a normal cylindrical reactor
When fluidized polycrystalline silicon is produced by using m silicon particles, the diameter of gas bubbles formed in the fluidized bed reaches 200 mm even if the gas linear velocity is U = 6 × Umf, and the reactor diameter is less than 200 mm. However, there was a problem that the entire fluidized bed became slug flow and a high conversion rate of silane could not be obtained. Further, some methods for producing fluidized polycrystalline silicon using a cone-shaped reactor have been proposed.
Since the purpose is to keep the silicon particles having a wide particle size distribution up to granules of mm in a good flow state, the cone angle is too wide and the silicon particles having the particle size distribution are used to Monosilane concentration of 10mo
When it was carried out at 1%, there was a problem that even if the gas linear velocity was U = 6 × Umf, the silicon particles were condensed at the portion where the gas linear velocity in the upper part of the fluidized bed became small and the reaction could not be continued.

[0006]

The object of the present invention is to provide a fluidized bed reactor for monosilane decomposition capable of solving all of these problems, suppressing the condensation of silicon particles, and achieving a high silane conversion rate. To do. Another object of the present invention is to select a specific shape for the heated fluidized bed reactor used for the production of polycrystalline silicon by the thermal decomposition of monosilane to suppress the condensation of silicon particles and to achieve a high silane conversion rate. It is to provide a fluidized bed reactor for decomposing monosilane.

Further objects and advantages of the present invention will be apparent from the following description. According to the present invention, the above objects and advantages of the present invention are to have a wall forming an upwardly-opening cone and the angle between this wall and the vertical being in the range of 1.3 to 3.9 °. Is achieved by a monosilane decomposition fluidized bed reactor.

The gas linear velocity in the method of depositing silicon on fluidized silicon granules is usually 2≤U / Umf≤8.
It is known that (U: linear velocity of gas, Umf: minimum fluidization velocity of particles used) is preferable, but the present inventors have found that the easiness of condensation of silicon particles depends on the silane concentration in the decomposition gas and the gas. The relationship between the linear velocity of gas and the silane concentration in the decomposition gas when silicon is condensed was investigated, considering that it is governed by the correlation of linear velocity. FIG. 1 shows the relationship between the silane concentration in the decomposition gas and the linear gas velocity when the silicon particles cause condensation and when they do not. The experimental data in FIG. 1 has various reaction temperatures, silane concentrations, fluidized bed heights, particle diameters, and the like. From FIG. 1, in order to prevent silicon from condensing, a large gas linear velocity is required when the silane concentration in the decomposition gas is high, but when the silane concentration in the decomposition gas is low. , It was found that silicon condensation does not occur even at a small gas linear velocity. While the decomposition gas flows from the bottom to the top, the silane in the decomposition gas is converted into silicon, and the silane concentration decreases, paying attention to the decrease in the silane concentration while the decomposition gas flows from the bottom to the top. In addition, it was found that the gas linear velocity can be reduced within the limit that does not cause the condensation, that is, the reactor diameter can be increased. In this way, by increasing the reactor diameter from the bottom to the top, the bubbles of gas formed in the fluidized bed temporarily become larger than the reaction diameter, and even if the slug flow occurs, the bubbles will rise from the bottom. As it goes up, it becomes smaller than the reactor diameter, the slug flow is eliminated, the contact efficiency between the silicon particles and the decomposition gas is improved, the silane conversion rate is improved, and the condensation of silicon also occurs. It was found that there is a reactor shape that does not exist.

If there is a wall forming an upwardly-opened cone and the angle between the wall and the vertical line is 0 ° (that is, straight copper type) or less than 1.3 °, silicon particles of 1000 μm are generated. When using a linear gas velocity of U = 6 × Umf, the gas bubbles formed in the fluidized bed become slug flow with a size larger than the reactor diameter, and the bubbles flow from bottom to top in the reactor. Since the diameter is not smaller than the diameter, the slug flow is not eliminated, and the high conversion rate of monosilane cannot be obtained.

On the other hand, it has a wall made of an upwardly-opening cone, and if the angle between the wall and the vertical line is larger than 3.9 °, it is 250.
When the monosilane concentration in the source gas is 10 mol% using silicon particles having a wide particle size distribution ranging from fine particles of up to 500 μm to granules of 1 to 2 mm, the linear gas velocity is U.
= 6 × Umf, the gas linear velocity in the upper part of the fluidized bed becomes small and silicon condenses.

Next, a detailed description of the present invention will be given with reference to the drawings. FIG. 2 is a cross-sectional view of the reaction container 1 according to one embodiment of the present invention, which has a wall forming a cone that opens upward,
The angle between the wall and the vertical line is 3.0 °. The reaction vessel 1 has a bottom diameter of 200 mm and an upper diameter of 514 mm.
The upper part is provided with a gas vent pipe 7 and a supply pipe 3 for inserting silicon seed particles into the container. Reaction vessel 1
At the bottom of the column, there is provided a raw material monosilane gas introduction pipe 4 and a hydrogen gas introduction pipe 5 for extracting granular silicon 6 made of granular silicon. The extraction tube 6 for granular silicon is provided at the center of the gas dispersion plate 8. A heater 2 is provided above the gas dispersion plate 8 so as to surround the reaction container 1. The gas vent pipe 7 is provided with a gas sampling port 9. The reaction vessel 1 was filled with seed particles made of polycrystalline silicon and having a wide particle size distribution from 250 to 500 μm fine particles to 1000 μm granules so that the static bed height was 1000 mm, and the inside of the vessel was heated by the heater 2. Raw material gas introduction pipe 4
And the concentration of monosilane from the hydrogen introducing pipe 5 is 10 mol%,
Gas is blown into the reaction vessel 1 so that the gas linear velocity is U = 6 × Umf. The gas blown into the reaction vessel 1 rises in the reaction vessel 1, and in this process physically fluidizes the silicon particles in the vessel to form a fluidized bed, and chemically forms a fluidized bed. Silicon is deposited on the surface of the silicon particles to grow the silicon particles. During this period, the concentration of monosilane in the gas is measured online from the successive gas sampling port 9 by the gas chromatograph 10. The silicon that has undergone the predetermined deposition reaction is sequentially withdrawn from the reaction container 1 through the granular silicon withdrawal pipe 6, and seed particles are inserted into the reaction container from the supply pipe 3 instead. The gas used for the silicon deposition reaction is discharged from the reaction vessel 1 through the gas vent pipe 7.

[0012]

In the reactor of the present invention, even if the bubbles of the cracking gas (silane and hydrogen) formed in the fluidized bed are larger than the diameter of the reaction vessel, the reactor diameter increases as the bubbles rise. Above a certain height, the bubbles are below the reactor diameter, slug flow is eliminated and a high conversion of silane is obtained. Moreover, the gas linear velocity in the upper part of the fluidized bed is 2 ×
Since Umf ≦ U, the silicon particles are not condensed due to the decrease in the gas linear velocity. The shape of the reactor has a wall that forms a cone that opens upward, and the angle between the wall and the vertical line is 1.
There is no problem if it is 3 ° or more and 3.9 ° or less, but it is more preferable that this angle is 3.0 ° or more and 3.9 ° or less in order to make the conversion rate of monosilane higher.

[0013]

As can be understood from the above description, according to the present invention, even if the particle diameter is in a considerably wide range, or even if the reactor diameter is considerably small, the silicon particles are not condensed. It is possible to exert the effect that a high conversion rate of silane to silicon can be obtained without any occurrence.

[0014]

【Example】

Example 1 Polycrystalline silicon was manufactured under the following conditions according to the embodiment shown in FIG. Shape of reactor: It has a wall that forms an upward-opening cone, and the angle between the wall and the vertical line is 3.0 ° Particle average diameter: 1000 μm Reaction temperature: 650 ° C. Concentration of monosilane in the source gas: 10 mol% Raw material gas (monosilane and hydrogen) Linear velocity: 2 m / sec In silicon production, silicon particles do not coagulate and the reactor is not clogged, and the conversion rate of monosilane to silicon is steadily 99 mol% or more. It has been operating continuously for a month.

Comparative Example 1 The shape of the reaction tube had a wall forming an upwardly-opened cone, but the angle formed by the wall and the vertical line was 4.0 °. Other than that, when the reaction was carried out in the same manner as in Example 1, the silicon silane was condensed in the upper part of the fluidized bed at the same time when monosilane was introduced into the reactor, and the reactor was blocked.

Example 2 The reaction was carried out in the same manner as in Example 1 except that the shape of the reaction tube had a wall forming an upward-opening cone and the angle between the wall and the vertical line was 1.6 °. However, the conversion rate of monosilane to silicon was 70 mol%.

[Brief description of drawings]

FIG. 1 is a diagram showing a correlation between a silane concentration in a decomposition gas and a decomposition gas linear velocity when condensation of silicon particles occurs and when condensation does not occur.

FIG. 2 is a schematic cross-sectional view of one embodiment of the fluidized bed reactor of the present invention.

[Explanation of symbols]

 ○: No condensation of silicon particles ★: Condensation of silicon particles 1: Reaction vessel 2: Heater 3: Silicon particle supply pipe 4: Monosilane gas inlet port 5: Hydrogen gas inlet pipe 6: Granular silicon extraction pipe 7: Gas Vent pipe 8: Gas dispersion plate 9: Gas sampling port 10: Gas chromatograph

Claims (1)

[Claims] 1. A fluidized bed for decomposing monosilane, characterized in that it has a wall forming an upward-opening cone, and the angle between this wall and a vertical line is in the range of 1.3 to 3.9 °. Reactor.