JP3389619B2 - Manufacturing method of polycrystalline silicon - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polycrystalline silicon by a fluidized bed method. 2. Description of the Related Art There are a Siemens method and a Komatsu method as typical production methods of polycrystalline silicon. 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. In addition, the granular polycrystalline silicon produced by this method requires less time for transportation, crushing, packing, etc., compared to the rod 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. However, the granular polycrystalline silicon produced by the fluidized bed method has a large deposition area, so that even the product is apt to be contaminated, and the particles are formed in the reactor. Since it is in constant contact with the inner wall, it is more susceptible to contamination, and ensuring the purity of the product is 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. In addition, even if such a method is used, it is not possible to prevent a phenomenon in which particles in the fluidized bed aggregate. This particle agglomeration is important for the fluidized bed reaction.
This is a more serious problem than the deposition of silicon on a wall, and no knowledge has been shown on solving this problem. On the other hand, in view of this reaction from the viewpoint of effective silicon production, the largest cause of the decrease in yield is due to fine powder produced as a by-product. In the decomposition reaction of silane, a reaction on the surface of silicon particles and a nucleation reaction in a gas phase occur in concert. Although this ratio is determined by the reaction temperature, it is also true that the ratio is greatly affected by the flow state. How to suppress the by-product of fine powder and improve the yield is also a major issue in silicon production by the fluidized bed method. Means for Solving the Problems The present inventors have intensively studied means for solving this particle aggregation and fine powder by-product and maintaining a high purity of the product. They have found that both can be solved and that the deposition of silicon on the reactor wall can be prevented, and the present invention has been completed. That is, the present invention provides a method for producing high-purity polycrystalline silicon using a fluidized-bed reactor through a gas dispersion plate.
To supply the fluidized gas containing monosilane uniformly into the fluidized bed
While maintaining the superficial velocity of the fluidized gas containing silane in the reactor within a certain range with respect to the average particle diameter and the minimum fluidization velocity of the particles in the fluidized bed, the reactor wall In addition to preventing precipitation of silicon on the surface and aggregation of particles, by-products of fine powder can be suppressed, and stable operation of the fluidized bed can be performed. The configuration is as described in the claims. Hereinafter, the present invention will be described 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 ,
The fluidizing gas containing monosilane flows through the gas distribution plate 5.
Ru is uniformly supplied to the dynamic layer. 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. . To supply the growing particles in the fluidized bed, additional seed silicon particles are supplied from the charging tube 3 into the reactor. The additional seed silicon particles should be as small as possible,
Although the efficiency of obtaining the product is high, if the flow velocity of the fluidized bed exceeds the terminal velocity of the particles, the product is not retained in the fluidized bed and is discharged out of the system, so that it does not work effectively. Therefore, a particle size of 50 to 350
It is customary to use a size of about 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 present invention provides a fluidizing gas containing monosilane,
Generally, the superficial velocity in the reactor of a mixed gas comprising a diluent gas such as monosilane and hydrogen is determined by the body area average particle size of the silicon particles in the fluidized bed (hereinafter simply referred to as “average particle size”).
The fluidized bed reaction is performed within the range of the value shown by the following equation with respect to the minimum fluidization rate. ^{(400 · Dp) 1/2 + Umf} > U 0> (80 · Dp) 1/2 + Umf [0020] Here Umf is the minimum fluidizing velocity in the average particle size of the silicon particles in the fluidized bed, the following equation Indicated by 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. 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 (as supplied, reactor) (K) A _r; average particle diameter of the reactor cross-sectional area (m ²⁾ [0022] Silicon particles, Dp =? w /
It is the body area average diameter indicated by Σ (w / dp). Dp: average particle size (m) of silicon particles w; mass (kg) dp: measured value of particle size (m) If U ₀ is less than (80 · Dp) ^1/2 + Umf, the reactor fluidized bed Aggregation and precipitation on the wall are liable to occur, while if it is more than (400.Dp) ^1/2 + Umf, fine powder is liable to be generated, and both are unsuitable. For reference 6
Tables 1 and 2 show values such as the minimum fluidization speed (m / s) when the average particle size is variously changed at 50 ° C. and a silane concentration of 10%. [Table 1] [Table 2] The superficial velocity is usually adjusted by the supply amount of the fluidizing gas. 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. If the amount exceeds 40 Vol%, the amount of silicon deposited on the inner wall of the reactor increases. 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 are particularly preferred. As the diluent gas, an inert gas such as nitrogen or argon or a hydrogen gas can be used.However, when the diluent gas is circulated and used, it is not necessary to separate hydrogen generated during the production of polycrystalline silicon. The use of hydrogen gas is preferred. The use of the present invention not only prevents the agglomeration of particles, but also effectively suppresses the deposition of silicon on the reactor wall, which is not preferably deposited, and maintains a stable fluidized bed reaction. Becomes possible. In addition, fine powder by-products that cause a reduction in the reaction yield can be suppressed, and highly efficient silicon can be produced. The reason for this is that, in the production method of the present invention, the superficial velocity in the reactor of the fluidized gas containing the raw material silane is set to a value within a certain range with respect to the average particle diameter and the minimum fluidization velocity of the particles in the reactor. By keeping the particle motion in the reactor above the critical value, it is possible to overcome the cohesive force, and the motion of the particles makes it possible to exfoliate the silicon deposited on the wall appropriately. It is estimated that 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 1 to prevent monosilane from leaking if quartz tube is accidentally damaged
A fluidized bed reactor comprising a quartz reaction tube having an inner diameter of 80 mm and a height of 1,800 mm provided with a stainless steel outer cylinder having a thickness of 00 mm and a height of 2,000 mm was used. The heater is outside the outer cylinder,
It was installed in a range up to 1,000 mm above the dispersion plate. A hydrogen mixed gas containing 10% 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 were filled in a quartz reaction tube such that the ratio of the particle layer height at rest to the tower diameter was 1: 2. . The reaction was performed at a reaction temperature of 650 ° C. and a flow rate (superficial velocity) of the raw material gas of 0.59 m / s.
The minimum fluidization speed at this time is 0.32 m / s,
The value of (400 · Dp) ^1/2 + Umf is 0.87 m / s, and the value of (80 · Dp) ^1/2 + Umf is 0.56 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 of increasing weight due to the reaction were continuously taken out of the system. In order to keep the average particle diameter the same as in the initial state, seed silicon particles having an average particle diameter of 180 μm were intermittently added. Although it continued for 50 hours, no phenomenon such as aggregation of particles in the fluidized bed occurred. After the completion of the reaction, the inside of the reactor was inspected. As a result, silicon deposition on the wall was about 5 mm at the maximum, and there was no obstacle to the continuation of the reaction. The by-product fine powder was 6% by weight based on the total reacted monosilane. Examples 2 to 6 The reaction was carried out under the same conditions as in Example 1 except that the average particle diameter of the silicon particles in the fluidized bed, the superficial velocity and the reaction time were changed as shown in Table 3. The results are shown in Table 3. [Table 3] (Examples 7 to 11) Further, the reaction was carried out under the same conditions as in Example 1 except that the average particle diameter, the superficial velocity and the reaction time of the silicon particles in the fluidized bed were changed as shown in Table 4. . The results are shown in Table 4. [Table 4] (Examples 12 to 16) Further, the average particle size of the silicon particles in the fluidized bed, the height of the stationary layer, the silane concentration and the reaction time were changed as shown in Table 5, and the other conditions were the same as in Example 1. I let it. The results are shown in Table 5. [Table 5] (Comparative Examples 1 to 5) The reaction was carried out under the same conditions as in Example 1 except that the average particle diameter, the superficial velocity and the reaction time of the silicon particles in the fluidized bed were changed as shown in Table 6.
In addition, there was agglomeration of particles in the fluidized bed of the reactor and silicon deposition on the wall, and the reaction was abandoned halfway. The results are shown in Table 6. [Table 6] (Comparative Examples 6 to 10) Furthermore, the average particle size of the silicon particles in the fluidized bed, the superficial velocity and the reaction time were changed as shown in Table 7, and the reaction was carried out under the same conditions as in Example 1 except for that. Was. In addition, the upper part of the reactor was blocked by fine powder, and the reaction was abandoned halfway. The results are shown in Table 7. [Table 7] According to the production method of the present invention, in the conventional production of polycrystalline silicon by the fluidized bed method, the most important factors that hinder stable operation are particle aggregation in the fluidized bed and silicon on the wall. An object of the present invention is to provide a method of preventing precipitation and suppressing the rate of generation of by-product fine powder, which is the greatest inhibitor of productivity improvement. Thus, a stable reaction can be achieved without causing an abnormal situation such as blockage or breakage of the reactor or insufficient fluidization due to precipitation, and by suppressing by-product fine powder,
It is possible to avoid clogging by fine powder and improve the yield, and to achieve both stable operation and high efficiency operation. 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] 1 reactor 2 Gas exhaust pipe Three kinds of silicon particle injection tube 4 Bottom plate 5 Gas dispersion plate 6 Source gas supply pipe 7 Product extraction tube 8 heater for heating 9 Fluidized bed

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masaaki Ishii 3-1, Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the R & D Center (72) Inventor Kazutoshi Takazuna Chidori, Kawasaki-ku, Kawasaki-shi, Kanagawa No.3-1, Tonencho Co., Ltd. Technology Development Center (72) Inventor Yasuhiro Saruwatari No.3-1, Chidori-cho, 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) (58) Field surveyed (Int. Cl. ⁷ , DB name) C01B 33/00-39/54

Claims (1)

(57) [Claim 1] In a method for producing granular polycrystalline silicon by a fluidized bed method using monosilane, a method comprising the steps of:
The fluidized gas containing monosilane uniformly in the fluidized bed.
While supplying , the superficial velocity U ₀ (m / s) of the fluidized gas in the reactor
Is the average particle diameter Dp (m) of the body area of the silicon particles in the fluidized bed.
And the minimum fluidization speed U _mf (m / s), the range is (400 · Dp) ^1/2 + U _mf > U ₀ > (80 · Dp) ^1/2 + U _mf. Manufacturing method of crystalline silicon.