JPH06127923A - Fluidized bed reactor for producing polycrystalline silicon - Google Patents

Abstract

PURPOSE:To prevent impurities from being mixed in silicon particles over a long period of time by specifying the total content of impurity elements in a fluidized reactor construction material in depth up to the prescribed surface of the fluidized bed reactor construction material to a prescribed value. CONSTITUTION:In a fluidized bed reactor for producing polycrystalline silicon particles, a reactor where impurity elements (group Ia, group IIa, transition metal elements, boron, phosphorus and arsenic) are contained by <=10ppm altogether in the material of a reactor construction member with which silicon particles come into contact, in depth of at least 20mum from the surface of the reactor construction member is used, causing the contamination due to the diffusion of the impurity elements to be prevented. Heat resistant materials of good workability, such as SiC, SiC/Si, alumina, mullite, graphite and silicon nitride are used as the reactor construction member. In the production process of the materials and that of the formed parts, the impurity elements are prevented from being mixed. And the surface of the reactor construction member thus produced may be coated with a silicon film of >=10mum thickness.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, polycrystalline silicon has been mainly produced by a so-called Siemens method in which silicon produced by thermal decomposition of a silane compound such as halogenated silane or monosilane is deposited on a silicon rod. In this method, a silane compound is brought into contact with a silicon rod that has been electrically heated, and silicon produced by thermal decomposition of the silane compound is deposited on the silicon rod. In the case of halogenated silane, the silicon rod is heated to about 1100 to 1200 ° C. by resistance heating, and silicon is deposited on it, but the inner wall of the quartz glass bell jar reactor is cooled to about 300 ° C. Of silicon is prevented. Therefore, the Siemens method is a process in which most of the energy required for heating is lost due to cooling, resulting in large heat loss. In addition, this method has a drawback in that the amount of silicon produced per unit time is small because the deposition area is small, and from this point also the amount of energy consumed per unit amount of silicon produced is large. Furthermore, this method is a batch method in which when a silicon rod becomes thick to a certain extent, it is collected and replaced again with a new one, and therefore equipment has to be increased for mass production, resulting in a large equipment cost. It has the disadvantage.

In order to overcome these drawbacks, a method has been proposed in which a silane compound-containing gas is brought into contact with fluidized silicon particles to deposit silicon on the particles. According to this method, there are advantages that the deposition area is large, the energy cost can be suppressed low, and the silicon particles can be continuously produced and recovered, so that the facility cost can be reduced.

As described above, the production of polycrystalline silicon by the fluidized bed method has an advantage in terms of production cost.
In the Siemens method, the silicon does not directly contact the reaction vessel, whereas in the fluidized bed method, silicon particles come into direct contact with the reactor and are rubbed against each other, which is a disadvantage that impurities are often mixed. There is a point. The inclusion of impurities not only decreases the yield when producing single crystal silicon from polycrystalline silicon, but also seriously affects the characteristics of semiconductors, and thus cannot provide polycrystalline silicon that can be used for semiconductor applications. there is a possibility.

Therefore, in the production of polycrystalline silicon by the fluidized bed method, various materials have been proposed for the fluidized bed reactor in order to prevent impurities from being mixed into silicon particles. For example, a liner in which the surface of ceramics is coated with silicon is used as a reaction vessel (Japanese Patent Laid-Open No. SHO 6-96).
No. 3-225512), a dense, high-purity silicon carbide sintered body having substantially no porosity is used as a reaction vessel (Japanese Patent Laid-Open No. 62-182162), and the surface of a ceramic base is made high. A reaction tube coated with dense silicon carbide having a purity and a porosity of substantially zero is used (JP-A-62-62).
No. 7620), a reactor made of silicon is used (Japanese Patent Laid-Open No. 64-65010), and a reactor of high-purity graphite coated with high-purity silicon is used (Japanese Patent Laid-Open No. 167811/1990). ), Using a reactor having a gas-impermeable Si ₃ N ₄ film having a film thickness of 10 μm or more on the inner surface of the substrate (Japanese Patent Laid-Open No. 63-117906).

[0006]

However, even when a reaction tube made of the above-mentioned material is used, there is a problem that when the reaction is carried out for a long time, impurities are mixed into the silicon particles from the reaction tube. However, there is a problem that it is difficult to manufacture a reaction tube from the viewpoint of the material used, and the conventional reactor is not yet sufficiently satisfactory.

Therefore, an object of the present invention is to prevent the mixing of impurities into silicon particles from a fluidized bed reactor for a long time in a fluidized bed reactor for producing polycrystalline silicon, and to use it. It is an object of the present invention to provide a fluidized bed reactor which is advantageous in terms of manufacturing reaction tubes.

[0008]

As a result of intensive studies to solve the above problems, the present inventors have used a material containing only a specific amount or less of an impurity element on the inner surface on the fluidized bed side of a fluidized bed reactor. The inventors have found that the above problems can be solved by carrying out a silicon deposition reaction in a fluidized bed reactor, and have completed the present invention.

That is, according to the present invention, in a fluidized bed reactor for fluidizing silicon particles, a depth of 20 μm from at least the surface of the reactor constituent member with which the silicon particles come into contact.
A fluidized bed reactor for producing polycrystalline silicon, characterized in that the total content of the impurity elements in the above materials is 10 ppm or less.

In the fluidized bed reactor for producing polycrystalline silicon according to the present invention, impurity elements (group Ia, group IIa, transition) are contained in a material at a depth of at least 20 μm from at least the surface of a reactor constituent member with which silicon particles come into contact. The total content of metal elements, boron, phosphorus and arsenic is 10 ppm or less. By using such a reactor,
It is possible to prevent the impurity elements in the reactor components from diffusing and contaminating the surface with which the silicon particles come into contact. Also, the fluidized bed reactor of the present invention is easy to manufacture.

The reactor constituting member in the fluidized bed reactor of the present invention includes a reaction cylinder when the reactor is composed of one reaction cylinder, and the reactor includes an outer cylinder and a liner inside thereof. When the inner cylinder is inserted as, the inner cylinder is included, and further, the reactor is composed of the outer cylinder and the inner cylinder inserted therein, and the lower end surface of the inner cylinder is the outer cylinder. The double-cylinder structure reactor (Japanese Patent Laid-Open No. 59-45917) located above the lower end surface includes the outer cylinder and the inner cylinder. On the surface of these reactor components,
Silicon particles come into contact during the reaction. When a large amount of the impurity element is contained in these constituent members, the impurity element is mixed in the silicon particles.

The material used for the reactor constituent member of the present invention is a heat-resistant material having good workability, such as SiC or S.
Examples thereof include iC / Si, alumina, mullite, graphite, silicon nitride and the like. These heat-resistant materials, in the material manufacturing process and the molded product manufacturing process from the material,
By controlling the content of the impurity element to obtain a molded product having a total content of the impurity elements of 10 ppm or less, particularly 5 ppm or less, the molded article can be used as it is as a reactor constituent member.

In the present invention, the impurity element in the material at a depth of at least 20 μm from the surface is 10 p.
If necessary, a silicon film can be coated on the surface of the reactor constituent member controlled to pm or less. The thickness of this silicon film is 10 μm or more, preferably 20 to 2000 μm. As a method for coating the silicon film, any method such as a chemical vapor deposition method (CVD method) using a silicon compound or a dipping method in a silicon melt can be used as long as it can coat a high-purity silicon film. In this case, the purity of the silicon film is, of course, equal to or higher than that of polycrystalline silicon for semiconductors.

Next, the method for producing granular polycrystalline silicon using the fluidized bed reactor of the present invention will be described in detail. Figure 1
1, 1 is a fluidized bed reactor, 2 is an inner cylinder inserted as a liner into the reactor, 3 is a seed silicon particle introduction pipe, 4
Is a source gas introduction pipe, 5 is a gas dispersion plate, 6 is a heater for heating, 7 is a product silicon particle extraction pipe, and 8 is a waste gas extraction pipe. In the present invention, when the inner cylinder 2 constituting the liner is provided, the inner cylinder 2 is made of a heat-resistant material having a total impurity element content of 10 ppm or less, or a silicon film coating on the inner surface of the cylinder. Or the heat-resistant material is coated on the inner surface of the cylinder with a high-purity heat-resistant material film, and then coated with a silicon film.

In order to produce granular polycrystalline silicon using this fluidized bed reactor, silicon particles are charged into the fluidized bed reactor through the introduction pipe 3, and then the raw material gas introduction pipe 4 is used.
A silane compound-containing gas is blown from the bottom of the fluidized bed reactor 1 through the gas dispersion plate 5 into the fluidized bed reactor 1 to fluidize the silicon particles on the gas dispersion plate 5, and then flow with the heater 6 for heating. The silicon oxide particles are heated to a predetermined temperature. The silane compound undergoes thermal decomposition in the fluidized bed, and the produced silicon is deposited on the fluidized silicon particles. Since particles grow due to silicon precipitation and the height of the fluidized bed increases, small seed silicon particles are introduced through the introduction tube 3 to keep the average particle diameter in the fluidized bed constant and the extraction tube 7
By extracting some of the product silicon particles, the height of the fluidized bed is kept constant. The average particle size of the seed silicon particles is 50 to 300.
μm is preferable, and the fluidized bed temperature is preferably 600 to 800 ° C.

[0016]

EXAMPLES The present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

Example 1 Granular silicon was produced using a fluidized bed reactor having a structure shown in FIG. 1 in which a SiC pipe having an inner diameter of 100 mm was incorporated inside the fluidized bed reactor. Impurities in SiC used as a liner material are Fe: 3 ppm or less, Cr: 1
ppm or less, Ni: 2 ppm or less, and others (BP and As) were 1 ppm or less. As the gas dispersion plate 5, a silicon plate was added so that there was no fear of contamination, and then acid cleaning was sufficiently performed.

3.5 kg of silicon particles having an average particle diameter of 700 μm were charged in the reaction vessel, and 120 liter / min of hydrogen gas and 29 liter / min of monosilane gas were introduced from the raw material gas inlet 4. The particle temperature was maintained at 660 ° C. by the heater 6. Silicon having an average particle size of 170 μm was introduced at a rate of 35 g / hour from the seed silicon introduction tube 3, and product silicon was extracted from the extraction tube 7 at a rate of 1700 g / hour at intervals of 15 minutes.
The product silicon particles were cooled in the extraction line 7, and then received in a Teflon bin that had been sufficiently acid-washed and pure-water washed.

The impurity analysis of the obtained product was performed as follows. Regarding the metals, the solution after removing silicon with HF / HNO ₃ was analyzed by ICP-MS and atomic absorption method. B, P and C were measured by FT-IR after being single crystallized by the FZ method. The impurities in the product after operating for 100 hours were the values shown in Table 1.

[0020]

[Table 1]

Examples 2 to 5 Granular polycrystalline silicon was produced under the same conditions as in Example 1 except that the various ceramics shown in Table 2 were used in place of the SiC pipe used in Example 1. Regarding the content of impurities in the product silicon particles at the time when the reaction was carried out for 100 hours, metals were below the detection limit in any case, and B: 0.07 to 0.15 (ppba),
P: 0.04 to 0.20 (ppba), C: 0.15
It was 0.25 (ppma). The impurities in the SiC coating film applied to the surface of the liner are 10 ppm or less for all the elements.

[0022]

[Table 2]

Comparative Example 1 The reaction was carried out in the same manner as in Example 2 except that the SiC used in Example 2 was used as it was without being coated with high-purity SiC. Impurities in the product after 100 hours were Fe: 25 ppb and Ni: 10 ppb.

[0024]

INDUSTRIAL APPLICABILITY According to the use of the fluidized bed reactor for producing polycrystalline silicon according to the present invention, it is possible to sufficiently prevent the impurity element from being mixed into the silicon particles from the fluidized bed reactor for a long time, High-purity polycrystalline silicon that can be used for semiconductor applications can be produced for a long time.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a fluidized bed reactor for carrying out the present invention.

[Explanation of symbols]

 1 Fluidized Bed Reactor 2 Liner (Inner Cylinder) 3 Type Silicon Particle Introducing Tube 4 Raw Material Gas Introducing Tube 5 Gas Dispersion Plate 6 Heating Heater-7 Product Silicon Particle Extracting Tube 8 Waste Gas Extracting Tube

 ─────────────────────────────────────────────────── ─── 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 Town No. 3-1, Tonen Kagaku Co., Ltd. Technical Development Center (72) Inventor Nobuhiro Ishikawa 1 in the first place of Funami-cho, Minato-ku, Aichi Prefecture Nagoya City Toagosei Chemical Industry Co., Ltd. Nagoya Research Institute (72) Invention Person Hirohiro Tasuke 23 Nagoya Toagosei Chemical Industry Co., Ltd., 23, Showa-cho, Minato-ku, Nagoya City, Aichi Prefecture

Claims (1)

[Claims] 1. In a fluidized bed reactor for fluidizing silicon particles, the total content of impurity elements in the material at least 20 μm deep from the surface of the reactor constituent member with which silicon particles come into contact is 10 ppm or less. And a fluidized bed reactor for producing polycrystalline silicon.