JP3341314B2 - Polycrystalline silicon manufacturing method - Google Patents

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 high-purity polycrystalline silicon, and more particularly to a method for producing polycrystalline silicon from monosilane by a fluidized bed method.

[0002]

2. Description of the Related Art A typical production method of polycrystalline silicon includes a Siemens method and a Komatsu method. These methods energize and heat a silicon rod placed in a bell jar furnace, and distribute gaseous chlorosilane (Siemens method) or monosilane (Komatsu method) (hereinafter, referred to as "silanes") therethrough. is there. The silanes supplied into the furnace generate silicon by thermal decomposition and reduction, and are deposited on a silicon rod. The silicon rod grows to a predetermined size and is recovered to be a product.

Currently, most polycrystalline silicon is manufactured by these methods because of the feature that it is relatively easy to maintain high purity. However,
These methods are basically batch operations, have poor production efficiency, and have the disadvantage of increasing the number of bell jars when mass production is required, and increasing equipment costs.
The reaction is carried out at 1,050 to 1,150 ° C., but the bell jar is cooled in order to prevent deposition on the wall, so that it has a drawback that most of the applied energy is dissipated as heat. .

Under these circumstances, the development of polycrystalline silicon by a fluidized bed method has been recently developed. This is a seed particle made of polycrystalline silicon in a cylindrical fluidized bed reactor (hereinafter referred to as "seed silicon particle").
Is used as a raw material to deposit silicon on the surface. In this method, seed silicon particles are usually supplied from above a reactor heated by an external heater. A gas containing silanes as a raw material is supplied from below. The supplied particles are fluidized by the gas rising in the reactor to form a fluidized bed. The raw material gas is heated by the heater and the particles while passing through the reactor, thermally decomposes to generate silicon, and precipitates on the surface of the fluidized seed silicon particles.

[0005] The production of polycrystalline silicon by the fluidized bed method is continuous and is easy to scale up, so it is not only suitable for industrialization but also uses an insulated reactor. The heat dissipation is 1/10 or less of that of the Siemens method or Komatsu method, which is energy saving, and the surface area of the granules is remarkably large as compared with the rods.

Furthermore, the granular polycrystalline silicon produced by this method requires less labor for transportation, crushing, packing, etc., as compared with rods produced by the Siemens method or the Komatsu method.
Furthermore, since it has fluidity, it can be easily supplied to a crucible when monocrystalline silicon is produced from the obtained polycrystalline silicon. There are many advantages in single crystal production, such as the ability to increase the packing density in the crucible and the ease of continuous supply.

[0007]

On the other hand, granular polycrystalline silicon produced by a fluidized-bed method has a large deposition area, so that even a product is easily contaminated and particles react. Since it is in constant contact with the inner wall of the vessel, it is more susceptible to contamination, and ensuring the purity of the product has become a major technical issue.

In addition, when polycrystalline silicon is produced by this method, the reaction is carried out at 600 to 850 ° C. to decompose silanes to produce silicon. Heating from the outside and a method of installing a heating element inside are generally performed. Therefore, it is inevitable that the temperature of the wall and the heating element becomes higher than that of the seed silicon particles from which silicon is to be deposited. Obstacles such as obstruction were inevitable.

This precipitation phenomenon prevents smooth particle flow,
Not only has the fatal effect on the reaction, but also causes the following troubles. That is, when high-purity silicon is obtained by a fluidized bed reaction, in order to prevent contamination from the reactor wall,
It is common to use a ceramic material such as quartz, but since it is inferior in strength to a metal material or the like, it is easy for these ceramics to be damaged by precipitation of silicon having a different coefficient of thermal expansion.

[0010] For stable continuation of the reaction, prevention of breakage due to the precipitation is also a major problem. In order to avoid this, various devices have been proposed.
In 9-45917, the inside of the reactor is doubled of an inner cylinder and an outer cylinder, and the seed silicon particles in the inner cylinder are fluidized by the dispersion plate at the lower part of the inner cylinder, and the particles that have risen with the gas flow are dispersed in the inner cylinder and the outer cylinder. In this case, particles are heated by a heater provided outside the outer cylinder. By utilizing the circulation of the silicon particles, a silicon-containing gas is supplied into the inner cylinder while keeping the inside of the reactor at the reaction temperature to prevent the deposition on the wall. In this method, the particles are heated as they descend the annulus and pass through and circulate between the inner cylinder and the bottom plate,
Since the temperature of the contacting dispersion plate is increased, the silicon-containing gas is thermally decomposed near the dispersion plate. Therefore, the deposited silicon may adhere to the dispersion plate and cause clogging. Precipitation on the inner cylinder wall surface cannot be ignored. In addition, there is a disadvantage that such a complicated reactor is difficult to manufacture.

Further, in Japanese Patent Application Laid-Open No. 2-279512, in order to reduce the silicon-containing gas concentration on the reactor wall,
A proposal has been made to prevent deposition by allowing hydrogen to flow along the inner surface of the reactor wall and passing the source gas through the inside. The reactor used here is described in JP-A-59-4591.
Although it does not use a reactor with a complicated structure such as 7, hydrogen and the raw material gas are rapidly mixed in the reactor. Therefore, to prevent deposition on the wall only by the sealing effect of hydrogen. Not enough.

[0012]

Means for Solving the Problems The present inventors have studied the method of preventing the deposition on the wall without contaminating the inside of the system, and as a result, have reached the present invention. According to the present invention, it is very easy to solve this problem, it is possible to suppress the deposition of silicon on the vessel wall without using a means such as the use of an inner cylinder that causes a decrease in the purity of the product, and high purity of the product And stable operation can be achieved at the same time.

That is, according to the present invention, in the production of high-purity polycrystalline silicon by a fluidized bed reactor, the reactor inner diameter (Dt
), The height of the static layer (Ls) of the silicon particles is made three times or more to prevent silicon deposition on the wall. Conventionally, increasing the ratio of the height of the stationary bed to the inner diameter of the column, Ls / Dt, increases the proportion of the bed that does not contribute to the reaction, and causes slugging such as plug flow. It has been considered a harmful operation.

However, the present inventors have studied the method of suppressing the deposition of silicon on the wall, and have found the following new fact. That is, the superficial velocity of the fluidized gas inside the reactor is
If a certain value or more is given to the average particle size of the particles and the minimum fluidization speed, increasing Ls / Dt is nothing.
This is very effective in preventing the silicon from being deposited on the wall portion without obstructing the reaction of the fluidized bed.

The structure of the present invention is as described in the claims, and the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing one embodiment of the present invention. The cylindrical reactor 1 is provided with a gas discharge pipe 2 at the upper part and a feed pipe 3 for feeding seed silicon particles into the reactor. The bottom of the reactor is doubled by a gas distribution plate 5 provided at a distance from the bottom plate 4. A raw material monosilane gas or a mixed gas of monosilane and a diluent gas is supplied from a raw material gas supply pipe 6 connected to the bottom plate 4. A product extraction pipe 7 is connected to the dispersion plate 5 through the bottom plate 4. A heating heater 8 is provided above the gas dispersion plate 5 so as to surround the reactor 1.

A predetermined amount of polycrystalline silicon particles is charged into the reactor 1. The particle size of the polycrystalline silicon particles is 300 to 2,
000 μm is preferred. The pressure inside the reactor is preferably from normal pressure to about 5 atm. The inside of the container is heated by a heater 8, and a source gas mixed with a diluent gas is blown from a source gas supply pipe 6 as necessary. The polycrystalline silicon particles flow violently by these gas flows to form a fluidized bed 9. The heated raw material gas is decomposed and silicon is deposited on the particle surface and grows. The polycrystalline silicon particles for which a predetermined precipitation reaction has been completed are withdrawn from the reactor through a product withdrawing pipe 7. Withdrawal amount and frequency are usually extracted in order to keep the height of the fluidized bed constant. As a method for measuring the bed height, a method of measuring the differential pressure of the fluidized bed can be used simply and accurately. .

Additional seed silicon particles are supplied from the charging pipe 3 into the reactor to supply the growing particles in the fluidized bed. The additional seed silicon particles are as efficient as possible to obtain a product if the particle size is as small as possible.However, if the flow velocity of the fluidized bed exceeds the terminal velocity of the particles, it will not be retained in the fluidized bed and will be discharged out of the system. It does not work effectively. Therefore, the particle size is 50 to 3
It is customary to use a size of about 50 μm. The raw material gas and the diluent gas after being used for the silicon deposition reaction are discharged out of the system through the gas discharge pipe 2. The exhaust gas may be compressed and circulated for use. There is no problem in using it for another system.

The preferred reaction temperature of the present invention is from 600 to 8
50 ° C. If the temperature is lower than 600 ° C., a precipitation reaction hardly occurs, and if the temperature exceeds 850 ° C., an improvement in the reaction rate cannot be expected, which is not only economically disadvantageous but also increases the generation of fine powder, which is not preferable. The concentration of the silane gas in the mixed gas is 5 to 40.
Vol% is preferred, and more preferably 10 to 30 Vol%. If the amount is less than 5 Vol%, the deposition of silane on the surface of the seed silicon particles is extremely small, resulting in poor productivity. The particle diameter of the granular polycrystalline silicon obtained by the reaction is 300 to
It is preferably in the range of 3,000 μm, of which 500 μm
m or more is particularly preferred. As a diluting gas, an inert gas such as nitrogen or argon or a hydrogen gas can be used. However, hydrogen is generated during the production of polycrystalline silicon, and hydrogen is used because the diluting gas does not need to be separated when circulated. The use of gas is preferred.

The present invention relates to a reactor having an inner diameter (Dt),
An obstacle to the reaction is eliminated by increasing the ratio (Ls / Dt) of the height of the stationary bed (Ls) of the fluidized bed. Specifically, Ls / Dt is set to 3 or more. Ls / Dt
There is no particular upper limit to the value of, but since the reaction occurs only in the lower part of the reactor, it is not economical to make this ratio too large,
0 or less is preferable.

Further, the present invention provides a method for measuring the superficial velocity in a reactor of a fluidizing gas containing monosilane, that is, a mixed gas of a diluent gas such as monosilane and hydrogen, by measuring a body area average particle diameter of silicon particles in a fluidized bed. The fluidized bed reaction is carried out within the range of the value represented by the following equation with respect to the “average particle size” and the minimum fluidization rate. U ₀ > (80 · Dp) ^1/2 + Umf If U ₀ is equal to or less than (80 · Dp) ^1/2 + Umf, particles are easily coagulated in the reactor fluidized bed and silicon is easily deposited on the wall.
Improper.

Here, Umf is the minimum fluidization rate at the average particle size of silicon particles in the fluidized bed, and is expressed by the following equation. Umf = (ρp -ρf) · g · Dp 2 / 1650μ Umf; minimum fluidization velocity (m / s) .rho.p, .rho.f; density of the silicon particles and the gas (kg / m ³⁾ g; gravitational acceleration (m / s ² ) Dp; average particle diameter of silicon particles (m) μ; viscosity of gas (Pa · s)

The superficial velocity is obtained by the following equation, and is usually adjusted by the supply amount of the fluidizing gas. U ₀ = (Q _SiH4 + Q _H2 + Q _X ) · (P _initial / P _r )
(T _r / T _initial ) / A _r U ₀ ; superficial velocity (m / s) Q _SiH4 , Q _H2 , Q _X ; gas (SiH ₄ , H ₂ , etc.) flow rate at supply (m ³ / s) ) P _initial , _Pr ; pressure (at the time of supply, inside the reactor) (kg /
cm ² ) T _initial , T _r ; temperature (at the time of supply, in the reactor) (K) _Ar ; reactor cross-sectional area (m ² )

The average particle diameter of the silicon particles is the body area average diameter represented by Dp = Σw / Σ (w / dp). Dp: average particle diameter of silicon particles (m) w; mass (kg) dp: measured value of particle diameter (m)

[0024]

According to the present invention, deposition of silicon on a wall, particularly a wall heated by a heater, which has conventionally been a major problem in the production of silicon by a fluidized bed, is suppressed to an almost negligible level. It is possible to do. This is because the superficial velocity in the reactor is given a certain value for the average particle diameter and the minimum fluidization velocity, and the ratio of the height of the fluidized bed to the inner diameter (Dt) of the fluidized bed (Ls). It is presumed that by setting (Ls / Dt) to 3 or more, silicon precipitated on the wall portion is peeled off by the silicon particles in the fluidized bed to prevent adhesion of a certain amount or more.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these embodiments. Example 1 According to the embodiment shown in FIG. 1, granular polycrystalline silicon was produced under the following conditions. Inner diameter 100mm to prevent silane leakage when quartz tube is broken by mistake,
Stainless steel outer cylinder of 2,000mm height, inner diameter 8
A fluidized bed reactor comprising a quartz reaction tube having a height of 0 mm and a height of 1,800 mm was used. The heater was installed outside the outer cylinder in a range up to 1,000 mm above the dispersion plate. A hydrogen mixed gas containing 15% by volume of monosilane was supplied and fluidized. Polycrystalline silicon particles having an average particle diameter of 750 μm in a particle diameter range of 300 to 2,000 μm are placed in a quartz reaction tube such that the ratio of the particle layer height at rest to the tower diameter is 1: 3.3. Filled. The reaction was performed at a reaction temperature of 650 ° C. and a flow rate (superficial velocity) of the raw material gas of 0.58 m / s. The minimum fluidization speed at this time is 0.30 m / s,
The value of (80 · Dp) ^1/2 + Umf is 0.54 m / s. The pressure inside the reactor is 1.3 atm.

In order to keep the height of the fluidized bed constant during the fluidized bed reaction, particles increasing in weight by the reaction were continuously taken out of the system. In order to keep the average particle size the same as in the initial state, seed silicon having an average particle size of 200 μm was periodically added. Although the operation was continued for 50 hours, the phenomenon that the particles in the fluidized bed aggregated did not occur. After the completion of the reaction, an inspection of the inside of the reactor revealed that silicon deposition on the wall was 1 mm or less.

(Examples 2 to 6) Reaction was performed under the same conditions as in Example 1 except that the average particle diameter of silicon particles in the fluidized bed, the superficial velocity, the height of the stationary bed, and the reaction time were changed as shown in Table 1. I let it. The results are shown in Table 1.

[0028]

[Table 1]

Comparative Example 1 A hydrogen mixed gas containing 15% by volume of monosilane was supplied to the same reactor as in Example 1 and fluidized. Seed silicon particles having a particle diameter range of 300 to 2,000 μm and an average particle diameter of 750 μm were packed so that the ratio of the height of the fluidized bed to the tower diameter was 1: 2. Reaction temperature 6
50 ° C., flow rate of raw material gas (superficial velocity) is 0.58 m / s
As a reaction. The minimum fluidization rate at this time is 0.
30 m / s. The pressure inside the reactor is 1.3 atm.

In order to keep the height of the fluidized bed constant during the fluidized bed reaction, particles increasing in weight by the reaction were continuously taken out of the system. In order to keep the average particle size the same as in the initial state, seed silicon having an average particle size of 200 μm was periodically added. The reaction was continued for 30 hours, but no phenomenon in which the particles in the fluidized bed aggregated occurred. However, when the inside of the reactor was inspected after the completion of the reaction, 2 to 10 mm of silicon was deposited on the wall.

(Comparative Examples 2 to 6) Except that the average particle size, the superficial velocity, the height of the stationary layer, and the reaction time were changed as shown in Table 2,
The reaction was carried out under the same conditions as in Example 1. The results are shown in Table 2.

[0032]

[Table 2]

(Examples 7 to 11) Average particle diameter, superficial velocity,
The reaction was carried out under the same conditions as in Example 1 except that the height of the stationary layer and the reaction time were changed as shown in Table 3. The results are shown in Table 3.

[0034]

[Table 3]

(Comparative Examples 7 to 11) Average particle diameter, superficial velocity,
The reaction was carried out under the same conditions as in Example 1 except that the height of the stationary layer and the reaction time were changed as shown in Table 4. In addition, there was particle aggregation in the fluidized bed and silicon deposition on the wall, and the reaction was abandoned on the way. The results are shown in Table 4.

[0036]

[Table 4]

(Comparative Example 12) A reaction was carried out under the same conditions as in Comparative Example 1 except that the flow rate (superficial velocity) of the raw material gas was changed to 0.40 m / s. When the reaction was continued for 1 hour, particles were deposited on the wall, and it was impossible to continue the reaction.

[0038]

The production method of the present invention provides a method for preventing silicon deposition on walls, which has been a factor hindering stable operation in the conventional production of polycrystalline silicon by a fluidized bed method.

As a result, a stable reaction can be achieved without an abnormal situation such as blockage or breakage of the reactor or insufficient fluidization due to precipitation. In addition to the fact that the method of the present invention can be carried out easily without requiring any special device, and that the method of the present invention can be carried out without inserting any insert into the reactor, contamination from those materials is taken into consideration. This is a very advantageous method for obtaining high-purity silicon without the necessity.

[Brief description of the drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reactor 2 Gas discharge pipe 3 kind silicon particle input pipe 4 Bottom plate 5 Gas dispersion plate 6 Raw material gas supply pipe 7 Product extraction pipe 8 Heating heater 9 Fluidized bed

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masaaki Ishii 3-1 Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Pref. No.3-1, Tonencho Co., Ltd., Technology Development Center (72) Inventor Yasuhiro Saruwatari No.3-1, Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Pref. 63-225516 (JP, A) JP-A-2-279512 (JP, A) JP-A-2-6392 (JP, A) JP-A-2-31833 (JP, A) JP-A-63-69708 (JP, A A) JP-A-2-30611 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 33/00-39/54

Claims (1)

(57) [Claims] 1. A method for producing granular polycrystalline silicon by a fluidized bed method using monosilane, wherein the height of the stationary layer of silicon particles is at least three times the inner diameter of the reactor and the inside of the reactor is a fluidized gas. The superficial velocity U ₀ (m / s) is defined as U ₀ > (80 · Dp) with respect to the body area average particle diameter Dp (m) and the minimum fluidization velocity Umf (m / s) of the silicon particles in the fluidized bed. ^A method for producing polycrystalline silicon, characterized by ^1/2 + U _mf .