KR960014593B1 - Method for deposition of high purity silicon on silicon particles from silicon source gases in fluidized bed reactor - Google Patents

Abstract

In the method of manufacturing granular-type polycrystal silicone using fluidized-bed reactor, the silicone containing gas is injected in the reaction region of the reactor and the silicone elements are flowed by carrier gas in the reactor, and the silicone elements are heated by microwave in the heating region of the reactor. The silicone elements in the reaction region and the silicone elements in the heating region, are mixed together, and the carrier gas is controlled so as to prevent the returning gas from the reaction region to the heating region.

Description

Method for producing high purity granular polycrystalline silicon by fluidized bed heating method by microwave

FIG. 1 shows one embodiment of an apparatus for the preparation of high purity granular polycrystalline silicon by a fluidized bed heating method by microwaves.

2 is a cross-sectional view of another embodiment of a device for the production of high purity or higher polysilicon by the fluidized bed heating method by microwaves.

* Explanation of symbols for main parts of the drawings

1: quartz reactor 2: microwave heating furnace

3: upper extension area 4: gas barrier plate

5: silicon seed particle 8: carrier gas

9: reaction gas 10: heating zone

11 Reaction zone 13 Separation means

14,15: gas distribution means 1617: gas supply means

18,19: chamber 20: product outlet

23: microwave generator 24: waveguide

25: microwave 27: insulation

28: outflow mixed gas 29: gas outlet pipe

30: seed particle supply means 31: infrared thermometer

33,34: Gasket 36: Granular Silicon Products

This patent relates to a method for producing high purity polycrystalline silicon by a fluidized bed heating method by microwaves. In particular, a method for producing high-purity polycrystalline silicon by an improved heating method of microwaves in the precipitation of silicon by pyrolysis or hydrogen reduction of a reaction gas containing a silicon element in a CVD (chemical vapor deposition) fluidized bed reactor will be.

High-purity polycrystalline silicon, which is used as a raw material for semiconductors and solar cells, is produced by a CVD process by pyrolysis or hydrogen reduction of a reaction gas containing a silicon element. Globally, commercial production of high-purity polycrystalline silicon is in Siemens reactors. The reactor is equipped with a seed rod (Slim rod) is heated by the electrical resistance inside, the silicon is precipitated by contacting the mixed gas of hydrogen and the reaction gas on the heated seed rod surface. The fixed region by this reactor had a problem of low productivity and high power source unit by batch.

Recently, there have been attempts to use fluidized bed CVD reactors as a new method for the production of high purity polycrystalline silicon. Fluidized bed reactors have attracted a lot of attention because many silicon particles flowing not only provide a large surface area to which a reaction gas containing silicon element can contact, but also provide economical continuous operation. In order to use the rod-shaped product produced by the existing Siemens reactor in the production of a single crystal, which is a subsequent process, there is a problem in that it needs to be broken into blocks. However, the high-purity polycrystalline silicon produced in the fluidized bed reactor is produced as a nearly spherical granular (particulate form) product, which allows continuous quantitative supply to a subsequent polycrystalline growth process. As a result, the sequential growth of the single crystal growth process is possible, which not only reduces the investment cost but also greatly improves the productivity.

There are many advantages to the use of fluidized bed reactors, but there are also many problems instead. In particular, high temperature heating of the fluidized bed reactor is a problem. Commonly known methods for heating fluidized bed reactors include external heating using resistance heaters (USP 4 207 360, 4 748 052). In these cases, it is inevitable that the reactor wall is hotter than the silicon particles in the reaction zone. Therefore, when resistive heating is used on the outer wall of the fluidized bed CVD reactor, the deposition rate of silicon on the inner wall of the reactor is increased, and heat transfer from the wall to the flowing silicon particles is poor due to the deposited silicon. In addition, the design of the reactor and the selection of materials becomes difficult. In this heating method, the operation must be interrupted periodically to remove silicon deposited on the inner wall of the reactor or to replace the reactor itself, and thus it cannot be operated continuously and is inefficient. And when using a quartz reactor, which is the recommended material for the production of high-purity polycrystalline silicon, thermal shock occurs due to the difference in thermal expansion between the silicon deposited on the inner wall of the reactor and the reactor material. And due to the precipitated silicon, the quartz reactor is crushed or easily broken when cooling the reactor.

In order to prevent this, the use of a graphite (graphite) reactor is proposed (US Patent 4,092,44). In this case, silicon was deposited on the inner wall of the reactor made of gparite. Graphite has similar thermal expansion difference to precipitated silicon, which is effective for increasing the use time of the reactor. However, silicon products sanded up from such a reactor have a problem of contamination of carbon which is a main component of graphite. Moreover, thick silicon precipitation on the inner wall of the reactor causes periodic shutdowns. Therefore, the production of granular polysilicon using a fluidized bed reactor requires an effective heating method other than conventional wall heating.

For this purpose, a method of heating fluidized bed silicon particles by microwaves, which is a kind of electromagnetic waves, has been proposed (Patent Publication No. 88-618). Here, the ultrashort waves have a frequency range of 300 MHz to 300 GHz in the electrical spectrum. In general, microwaves with a frequency of 915 MHz or 2,450 MHz are commonly used. Since silicon is one of materials that absorb microwaves and is easily heated, heating by microwaves may be effectively used for fluid bed heating of silicon particles. In this heating method, since the microwaves pass through the quartz reactor within the reaction temperature range, only the silicon particles inside the reactor are heated, and the temperature of the reactor wall is kept lower than that of the silicon particles, so that impurity contamination from the reactor wall and silicon precipitation on the reactor inner wall are maintained. It has the advantage of minimizing the phenomenon. However, since the inner wall surface of the reactor keeps in contact with the hot silicon particles, it is difficult to maintain the inner wall temperature of the reactor below the initial decomposition temperature of the reaction gas in which the precipitation of silicon is fundamentally prevented. As a result, precipitation of silicon on the inner wall of the reactor cannot be completely avoided. If silicon precipitates on the inner wall of the reactor to which microwave is supplied, the deposited silicon layer will absorb most of the microwave and be heated. As the temperature increases, the silicon absorbs more and more microwaves, causing rapid heating in the silicon layer deposited on the wall to be heated, and some melting will occur. If the flowing silicon particles adhere to the molten portion, the absorption of microwaves will occur at the same time, and the surface of the silicon particles will melt, and the sintering phenomenon of the new particles will be repeated. Eventually, there will be an accident that the reactor wall and the silicon particles melt down bent. In this case, the advantages over the microwave heating method will disappear. In the conventional microwave heating method, in order to solve these problems, cooling of the outer wall of the reactor with a refrigerant without disturbing microwave projection in the reaction region has been described.

Monosilane with a CVD reaction temperature of 700 ° C also described the importance of wall cooling when used as a reaction gas. In the case of pyrolysis of monosilane, the precipitation of silicon selectively occurs in the silicon particles that are hotter than the cooled reactor wall, thereby reducing the precipitation of silicon on the inner wall surface. On the other hand, when trichlorosilane is used as the reaction gas, silicon precipitation occurs simultaneously not only on the surface of silicon particles in flow by hydrogen reduction or pyrolysis at a reaction temperature of 900 ° C. or higher but also on the inner wall surface of the reactor in which the reaction gas contacts. In order to prevent the precipitation of silicon on the reactor wall, it should be kept below 400 ° C., which is the temperature at which silicon precipitation is prevented. As a result, excessive cooling of the outer wall of the reactor causes huge heat loss and increases the energy of microwaves required for heating, which is inefficient. Therefore, as a way to improve this phenomenon, it has been proposed to fundamentally solve the silicon deposition on the inner wall of the reactor and to reduce the heat loss.

The newly proposed patent relates to an improved method of microwave heating in an induction bed reactor for the preparation of granular polycrystalline silicon. This can be achieved by separating the fluidized bed by means of separation means into the reaction zone and the heating zone. Separation means free exchange of silicon particles by fluidization of both regions. The silicon particles in the heating zone are fluidized by a carrier gas which does not contain the reaction gas supplied by the independent gas distribution means, and is heated by the microwaves supplied to the heating zone. On the other hand, the silicon particles in the reaction zone are fluidized by a mixed gas of a gas supplied by an independent gas distribution means and a reaction gas containing elemental silicon. The contact of the silicon particles between the two zones naturally occurs, which occurs at the top of the heating zone. Here, the silicon particles heated in the heating zone and the silicon particles in the reaction zone are mixed vigorously with each other, and heat transfer takes place effectively, so that the temperature difference between the two zones is almost insignificant. The reaction temperature in the reaction zone is maintained by the mutual contact of the particles between the two zones and the radiant heat transfer. Therefore, no direct projection of microwaves into the reaction zone is required for heating the reaction zone. The flow rate of the carrier gas supplied to the heating zone is controlled in such a range that sufficient fluidization of the silicon particles heated by microwaves in the heating zone and essentially blocking back flow of the reaction gas from the reaction zone. As a result, it is possible to fundamentally avoid the phenomenon of silicon deposition on the inner wall surface of the supply port through which microwaves are supplied to the heating zone.

In addition, since the outer wall of the reactor surrounding the heating zone is not cooled by the supply of the refrigerant, the amount of microwaves required to maintain the reaction temperature can be reduced. This energy saving can reduce the energy density per unit area of microwave energy supplied to the heating zone, thereby improving operation stability and effectively transferring the heat supplied by the microwave to the reaction zone so that it can be effectively used for the CVD reaction. In addition, in order to minimize the heat loss of the outer wall surface of the reactor it was also possible to insulate with a heat insulating material, in this case, it is possible to use a heat insulating material (usually silicon based) with a low absorption rate of energy per second.

1 shows one embodiment of an apparatus for the production of high purity granular polycrystalline silicon by an improved heating method of a fluidized bed reactor according to the proposed patent. The quartz reactor 1 is installed inside the microwave furnace 2 made of stainless steel and silver metal capable of reflecting microwaves without loss. The upper part of the reactor is provided with an upper expansion region 3 made of metal, and is fixed by the gas barrier plate 4 with a gasket 33 of graphite type to reduce vibration of the quartz reactor 1 due to fluidization. . Silicon seed particles 5 are supplied to the quartz reactor 1 by the seed particle supply means 30 in order to provide the silicon precipitation area by the CVD reaction. The hopper filled with inert gas or reducing gas is in communication with the seed particle supply means 30. The silicon seed particles 5 are supplied by the seed particle supply means 30, and fall down by their own weight to the bottom of the reactor. The injection amount of the silicon seed particles 5 required for forming the fluidized bed inside the CVD reaction quartz reactor 1 is predetermined by silum. The lower end of the quartz reactor 1 is fixed to the microwave furnace 2 by means of a gasket 34 of a heating zone type. The silicon filling layer filled in the quartz reactor 1 is supported by gas distribution means 14 and 15 made of silicon, quartz or a material lined with silicon. When the quartz reactor 1 is heated for the CVD reaction, both ends thereof are fixed in the microwave furnace 2 by the gaskets 33 and 34 of the heating zone type so as to withstand horizontal and vertical thermal expansion. .

The silicon filling layer of the quartz reactor 1 is separated by the separating means 13 into the heating zone 10 and the reaction zone 11. The silicon particles in the heating zone 11 are fluidized by a reducing gas or a carrier gas 8 such as hydrogen, which does not contain a reaction gas containing silicon. The carrier gas 8 is supplied by the gas distribution means 16 and the water distribution means 14 surrounded by a chamber 18 made of metal such as stainless steel or silicon lining material. The silicon particles in the reaction zone 11 on the other side of the heating zone 10 are fluidized by a reaction gas containing a silicon element. In the quartz reactor 1, a carrier gas or a reducing gas may be added to the reaction gas 9, if necessary, in order to adjust the concentration of the reaction gas containing a silicon element. The reaction gas is supplied by the gas distribution means 15 and the gas supply means 17 surrounded by the chamber 19 made of metal such as stainless steel or silicon lining material. Preheating of the reaction gas 9 is limited to below the temperature at which the precipitation of silicon is prevented before it is introduced into the quartz reactor 1. In the upper portion of the heating zone 10, the carrier gas 8 and the reaction gas 9 are mixed with each other, and the upper particle layer of the separating means 13 is fluidized by the mixed gas 35. Therefore, the silicon particles not included in the heating zone 10 are utilized as the reaction zone 11 required for the precipitation of silicon.

The microwave generator 23 converts electricity into the microwave 25. Atmospherically useful microwave generators generate microwaves with a frequency determined in pulse or continuous wave mode. The generated microwave 25 is transmitted through the waveguide 24 communicated with the microwave heating furnace 2 and passes through the wall surface of the quartz reactor 1 on the side of the heating zone 10. Waveguide 24 is made of a metal or alloy, such as aluminum, copper, which is effective for microwave transmission. The heating zone 10 is located in front of the outlet of the waveguide 24, and the silicon particles flowing in the heating zone 10 are located in the microwave heating furnace 2 and the quartz reactor 1 except the heating zone 10. Absorbs most of the microwaves 25 that penetrate other spaces without formation of electromagnetic fields. In the heating zone 10, the silicon particles subjected to the radiation of the microwaves 25 are heated by themselves by thermal conversion of absorbed microwave energy.

Between the upper portion of the heating zone 10 and the reaction zone 11 in a fluidized state, a large amount of heat generated in the heating zone 10 is instantaneously transferred to the reaction zone 11 by virtuous mixing of silicon particles. The flow of fluidizing gas serves as an important function for the rapid particle contact between the two zones. The flow of the carrier gas 8 flows at a flow rate sufficient to allow rapid contact between the heating zone 10 and the reaction zone 11 as well as fluidization of the silicon particles in the heating zone. Carrier gas 8 is purified in a plateau before being introduced into quartz reactor 1 and preheated to 200-400 ° C. in a preheater. In consideration of the possibility of contamination and energy efficiency inside the preheater, preheating of the carrier gas 8 is not necessarily required for the reaction temperature. The flow rate of the reaction gas 9 is previously determined by experiment and is sufficient for the fluidization of the silicon particles in the reaction zone 11 at the reaction temperature. The silicon element-containing liquid is vaporized before being introduced into the reactor 1 and preheated with the reaction gas 9. On the other hand, the reaction gas 9 may be supplied in a gas / liquid mixed state by spraying a silicon element-containing liquid into a reducing gas such as hydrogen at a predetermined ratio. Preheating of the reaction gas 9 is maintained below the initial decomposition temperature of the silicon element-containing gas in order to prevent the deposition of silicon on the inner wall surfaces of the gas chamber 19 and the gas supply means 17 as well as the gas decomposition means 15. do. When the gas distribution means 15 or the reaction gas 9 of the reaction gas 9 in contact with the fluidized silicon particles is heated above the initial decomposition temperature, silicon is precipitated in the gas distribution means 15, 17. This blocks the flow of gas. Therefore, the temperature of the reaction gas 9 and the surface temperature of the gas distribution means 15 should be kept below the initial decomposition temperature of the reaction gas.

In a fluidized bed reactor, the fluidized gas is heated toward the top, so that the upper portion of the fluidized bed has a higher average linear velocity and degree of fluidization than the lower portion. Silicon particles grown sufficiently than the size of the silicon seed particles 5 have a property to sink to the bottom of the fluidized bed. They flow out into the granular silicon product 36 through the product outlet means 20. In the continuous production of granular silicon, the inflow rate of the seed particles 5 and the outflow rate of the ideal silicon product 36 are determined in correlation with the mass balance equation based on the operating parameters of the fluidized bed.

The rise of the carrier gas 8 prevents the backflow of the reaction gas containing silicon elements from the reaction zone to the heating zone, and provides rapid particle contact between the heating zone 10 and the reaction zone 11. The diffusion of the reaction gas containing silicon into the heating zone is prevented by the separating means 13. The carrier gas 8 rises from the gas distribution means 14, and the gas expands and plasticizes by raising the temperature by direct contact with the silicon particles heated by microwaves. The phenomenon in which the reaction gas containing silicon flows back into the heating region 10 can be easily prevented by the collected technique. This fact means that the precipitation of silicon is prevented inside the heating zone 10, especially in the reactor inner wall surface where microwaves are injected. In the fluidized bed reactor of the prior art, microwaves do not have this capability because they are introduced directly into the reaction zone. Precipitation of silicon on the inner wall of the reactor is an unavoidable problem in the reaction zone. In the previous technique, the outer wall of the reactor was cooled with a cooling fluid to prevent silicon precipitation from occurring on the reactor walls where microwaves were injected.

At the top of the heating zone 10, the carrier gas 8 is mixed with the reaction gas 9, and these mixed gases are in contact with the heated silicon particles to perform the CVD reaction. Precipitation of silicon is caused by the reaction gas injected in the lower part of the reaction zone, and the CVD reaction is dominant in the upper part where the temperature of the mixed gas and the silicon particles is sufficiently higher than the lower part. The chemical equilibrium of the CVD reaction is obtained within several cm of the packed bed height in the fluidized state of 90 ° C. or higher for trichloride silane, and the CVD reaction almost reaches the equilibrium at the top of the reaction zone 11. Outflow mixed gas 26 of unreacted gas, by-product gas, and carrier gas is discharged out of the fluidized bed reactor through the gas outlet pipe 29 through the upper expansion region 3. The effluent mixed gas 28 discharged to the gas outlet pipe 29 is recovered and reprocessed and reused under the scope of this patent. The maximum packed bed height in the reaction zone relative to the reaction yield required for the precipitation of silicon at the reaction temperature is already determined by chemical composition analysis of the effluent mixed gas 28.

The heat generated in the heating zone 10 by the microwave projection includes the heat required for the CVD reaction, the heat required for heating the fluidized gases 8 and 9, and the quartz reactor through the wall of the microwave heating furnace 2 ( The amount of heat lost in 1) and the amount of heat lost in the extended region 3 are covered. In CVD operations, calorie loss must be minimized for energy accumulation. Under the proposed patent environment, the heat loss through the wall of the quartz reactor 1 is gradually reduced by the insulation of the heat insulator 27 on the outer wall of the reactor. Various inorganic materials with low thermal conductivity are useful as insulation materials. The heat insulating material around the heating zone 10 through which microwaves penetrate is limited to materials such as opaque quartz, high purity fibrous silica, and the like, which have almost no loss of microwaves therein. The heat loss to the bottom of the fluidized bed reactor is already offset by the fluidized gases 8 and 9 injected from the bottom of the fluidized bed and is utilized as the release of the heat required for preheating the injected gas. The amount of microwave energy is adjusted according to the temperature of the reaction zone 11 measured by the infrared thermometer 31 which is a sensing means communicated with the top of the quartz reactor 1.

2 is another embodiment of a fluidized bed reactor according to this patent, wherein a heating zone is formed in an annular zone in the lower zone of the fluidized bed reactor. The same reference numerals as in FIG. 1 are given here.

In the lower region of the silicon fluidized bed inside the quartz reactor 1, a separation means 13 made of silicon, quartz or a high-purity material lined with silicon is installed, and the two means of the heating zone 10 and the reaction zone 11 are bordered thereon. It is divided into areas. The reaction gas 9 is introduced into the quartz reactor 1 by the gas distribution means 15 and ascends through the separation means 13. The inside of the separating means 13 may be fluidized by filling with silicon, and sometimes the operation is performed without the filling of silicon. The annular heating zone 10 is formed around the separating means 13. The carrier gas 8 is injected through the gas distribution means 14 along the annular region where the reaction gas 9 containing silicon element is prevented from being diffused into the heating region 10 by the separating means. The reaction zone 11 for the CVD reaction is formed in the silicon fluidized bed except for the heating zone. The inflow rate of the carrier gas 8 and the reactant gas 9 has a flow rate sufficient to fluidize the silicon particles in the two regions as described in the aspect of electricity.

The amount of heat required for the CVD operation is supplied to the reaction zone where heat is indirectly transferred from the heating zone to the heating zone, and the heat of the heating zone is made by microwave heating. The silicon particles in the heating zone 10 are heated by microwaves penetrating through the waveguides 24a and 24b and the reactor wall in front of the waveguide. In the proposed embodiment, two separate microwave generators 23a, 23b are used to convert from a commercial power source to microwaves 25a, 25b. In addition, instead of using two microwave generators, the required microwaves are generated by one high power generator, and the generated microwaves may be supplied separately by a separating means in the heating zone.

The silicon particles and the carrier gas heated in the heating zone 10 are in fluid contact with the silicon particles in the reaction zone 11 at the upper end of the reaction gas and the separation means 13 and fluidize smoothly. The contact of the particles is naturally caused by the rise of gas bubbles formed by the fluidizing gases 8, 9. These contacts dominate indirect heating in which the heat of the heating zone heated by the microwaves is transferred to the reaction zone. Radiative heat transfer between particles governs heat transfer in high temperature reaction systems. The temperature of the reactor wall in contact with the reaction zone 11 is lower than the silicon particles in the heating zone 10. Furthermore, as long as the flows of the fluidizing gases 8, 9 are in contact at the top of each of the annular heating zones, the concentration of the reaction gas containing silicon in the mixed gas 35 is close to the inner wall surface of the reactor 1. low. This is because a significant amount of carrier gas 8 rises along the inner wall surface despite contact with the reaction gas in the reaction zone. Therefore, precipitation of silicon on the reactor wall in the reaction zone is not a problem. On the other hand, the concentration of the reaction gas is highest in the axial direction, so that the CVD reaction occurs predominantly on the surface of the silicon particles in the direction of the central axis of the reaction zone rather than the wall surface of the reaction zone. The grown particles, that is, the granular silicon product, flow out through the product outlet means 20 and the mixed gas after the reaction is discharged out of the reactor through the gas outlet tube 29.

The rate of gas flow, that is, the rate of carrier gas, is adjusted so that heat transfer from the heating zone 10 to the reaction zone 11 is effective. In the above-mentioned embodiment, the minimum flow rate of the carrier gas 8 is determined at a rate at which the backflow phenomenon of the reaction gas containing silicon element from the reaction zone 11 to the heating zone 10 is prevented. The minimum flow rate is predetermined by gas sample analysis in the annular heating zone. Precipitation of silicon on the inner wall surface of the reactor through which the microwaves 25a and 25b penetrate is prevented. When a small particle size silicon fluidized bed forms a high fill height, the excess gas flow rate grows as the bubbles rise and become larger than the cross-sectional area of the reactor, resulting in a slugging state in which the silicon particle layer separates up and down. . Operation in the slugging state not only reduces the reaction yield, but also causes the silicon particles to stick. The speed of the carrier gas 8 is controlled in an extinction range in which a slugging state is prevented and a backflow phenomenon of the reaction gas containing silicon element is prevented.

Insulating material was installed between the outer wall surface of the quartz reactor (1) and the microwave heating furnace (2) to reduce the heat loss and detract energy. The heat insulating material 27b surrounding the heating area uses various types of materials having low absorption of microwaves such as high purity silica. Unlike the heating zone, the heat insulating material 27a surrounding the outer wall surface of the reaction zone is selected from not only silica but also useful heat insulating materials conventionally used. These materials are used in various forms such as felts, wools, fabrics, tubes, blocks, and the like.

An example of a process for the preparation of high purity polycrystalline silicon according to the proposed patent is described below.

Example 1

Two kinds of CVD operations were conducted to test the effectiveness of the proposed patent compared to the conventional microwave heating method, and trichlorosilane was used as the reaction gas.

As an example of the CVD operation to test the proposed patent, an inner diameter of 104 mm, a thickness of 3 mm, and a height of 1060 mm were used to install a cylindrical quartz reactor inside the microwave furnace 2 of FIG. A square plate made of quartz having a width of 80 mm, a height of 200 mm, and a thickness of 5 mm was installed at the bottom of the quartz reactor 1 to separate the reactor into the heating zone 10 and the reaction zone 11. 3.4 kg of silicon particles having an average particle diameter of 335 μm having a particle size range of 177-590 μm were supplied by forming a silicon particle filling layer. The height of the filling layer was maintained at 300 mm based on the gas distribution means 14 and 15. Microwaves with a frequency of 2450 MHz were supplied to the heating zone through the waveguide 24 communicated with the microwave heating furnace 2. A 20 mm thick insulation made of high purity silica was installed between the outer wall of the reactor and the inner wall of the microwave furnace. Typical operating conditions for this demonstration are:

(1) Carrier gas (hydrogen)

Flow rate 0.5mol / min

Preheating temperature 350 ℃

(2) reactive gases (trichlorosilane and hydrogen)

Flow rate 0.35mol / min for trichlorosilane

Flow rate of hydrogen 0.45mol / min

Preheating temperature 100 ℃

(3) CVD operating temperature 960 ° C

(4) reaction pressure atmospheric pressure

The operation is maintained by a control means in which a series of silicon seed particles 5 is supplied to the reactor, and the height of the silicon packed layer inside the reaction is kept constant. The sufficiently grown granular silicon 33 was carried out by the method of continuously flowing out by the product outlet means 20.

When operating according to this method, 1140 g of silicon precipitate was obtained by CVD operation for 10 hours. Microwave energy of about 3.2KW was required before the injection of trichlorosilane, and when the CVD reaction occurred by injection of trichlorosilane, 4.3KW of microwave energy was required. The temperatures of the gas dispersion plates of the carrier gas and the reactant gas were maintained at 625 and 342 ° C. during the CVD operation. No precipitation of silicon on the reactor wall surrounding the heating zone after the CVD operation was observed, and no local rupture or deformation was observed with the quartz reactor. There was no phenomenon in which the silicon particles were entangled with each other in the silicon particles remaining in the reactor after operation and the granular silicon products leaked out. In addition, no precipitation of silicon was found on the surface of the dispersion plate into which the reaction gas was introduced.

CVD operations were also conducted to test the traditional microwave heating method. For example, the apparatus used in the above experiment was retrofitted as described below. The separator was removed from the reactor and the silicon particle packed layer was used as the reaction zone without separation of the heating zone. In order to minimize the precipitation of silicon on the inner wall of the reactor, a gas injection nozzle for injecting the cooling gas was installed in the lower part of the microwave heating furnace 2, and the outer wall of the reactor was cooled with nitrogen gas. Furthermore, the porous dispersion plate with the water cooling means interposed. The cooling gas was discharged through the hole made in the gas barrier plate 4 in FIG. The reaction gas 9 preheated to the gas chambers 18 and 19 separated by the two gas supply means 16 and 17 is modified to be injected through the gas distribution means 14 and 15. In this traditional process, it was the same as the first example, except that the injection rate of the carrier gas and the reaction gas were premixed and preheated to 150 ° C. under operating conditions with microwave supplied. Nitrogen injection rates for wall cooling and coolant flow in the dispersion plate were 8.5 mol / min and 9 L / min.

When operating in the traditional way, more microwave energy was needed to maintain the same reaction temperature as the electrical embodiment of this patent. This is a necessary result of cooling the reactor wall. The microwave energy required to maintain the CVD operating temperature before and after the injection of trichlorosilane was 6.1 kW and 7.6 kW. However, after the introduction of the trichlorosilane, the microwave energy required to maintain the reaction temperature gradually increased at 7.6 KW. This phenomenon increased over time and reached the limit of microwave output, so no further operation was possible. This increase in microwave energy was mainly due to the precipitation of silicon on the inner wall of the quartz reactor into which microwave was introduced. This is because the heat transfer rate is faster at the outer wall surface where the hot silicon particles are in contact with the outer wall surface of the quartz reactor than the cooling by the cooling fluid, so that the silicon precipitation occurs without effective cooling.

The thickness of the layer in which the silicon precipitated on the inner wall of the reactor gradually increased, and part of the microwave energy supplied therein was absorbed and lost, thereby increasing the energy of the microwave required to maintain the reaction temperature. When the device was dismantled after the operation, it was observed that some silicon particles were entangled with each other on the inner wall of the reactor in front of the outlet of the waveguide 24. It was observed that more than 120g of silicon particles in 3920g of total products were entangled inside the reactor, including 420kg of pure silicon deposition. This phenomenon seems to be due to the supply of excessive microwaves for the supply of heat loss of the cooling loss of the wall to increase the energy density per unit area of the region to which the microwaves are supplied, resulting in an unwanted overheating section. In the subsequent CVD operation and other operating conditions, the CVD operation by the conventional microwave heating method was inefficient, unstable, and had problems of silicon deposition on the inner wall.

Example 2

As another example of the CVD operation to test the proposed patent, a cylindrical quartz reactor of cooling 204 mm, thickness 4.5 mm and height 1700 mm was installed inside the microwave furnace 2 of FIG. After separating the tube-shaped separator tube 13 made of a sex tube having an inner diameter of 80 mm, a height of 350 mm, and a thickness of 5 mm into a heating zone 10 and a reaction zone 11, it was installed under the quartz reactor 1. 33 kg of silicon particles having an average particle diameter of 647 μm having a particle size range of 297-1000 μm were supplied by forming a silicon particle filling layer. Based on the gas distribution means 14, 15, the height of the packed bed was maintained at 700 mm. The microwave at the frequency of 915 MHz was supplied to the heating region through waveguides 24a and 24b connected to the microwave heating furnace 2. 20 mm thick insulating materials 27a and 27b made of high purity silica were installed between the outer wall surface of the Sung Young reactor 1 and the inner wall surface of the microwave heating furnace 2. Typical operating conditions for this experiment are:

(1) Carrier gas (hydrogen)

Flow rate 4.0mol / min

Preheating temperature 250 ℃

(2) reactive gases (trichlorosilane and hydrogen)

Flow rate 3.1mol / min for trichlorosilane

Flow rate of hydrogen 6.0mol / min

Preheating temperature 100 ℃

(3) CVD operation temperature 930 ° C

(4) reaction pressure atmospheric pressure

The operation is maintained by a control means in which a series of silicon seed particles 5 is supplied to the reactor, and the height of the silicon packed layer inside the reaction is kept constant. The sufficiently grown granular silicon 33 was carried out by the method of continuously flowing out by the product outlet means 20.

When operating according to the method according to the proposed patent, a net silicon precipitation of 30.4 kg was obtained by CVD operation for 30 hours. Microwave energy of about 17KW was needed before the injection of trichlorosilane and 28KW of energy was required when the CVD reaction occurred by injection of trichlorosilane. After the CVD operation, no silicon precipitation shape was observed on the reactor wall surrounding the heating zone, and no local rupture or deformation was observed in the quartz reactor. After the operation, the silicon particles remaining in the reactor and the granular silicon leaked did not exhibit the tangling of the silicon particles.

Claims (3)

In a method for producing a daily polycrystalline silicon using a fluidized bed reactor, a reaction region for depositing silicon metal on a surface of an electrosilicon particle in which a gaseous or vaporous silicon element-containing gas is maintained at a reaction temperature and a part of the battery silicon particles are above an electrical reaction temperature. The electric fluidized bed reactor is separated into a heating zone to be heated by heating, and a reaction gas containing an electrosilicon element is introduced into the electrical reaction zone. Therefore, the electrical silicon is fluidized in the electrical reaction zone and the carrier gas is introduced into the electrical heating zone. By fluidizing the silicon particles in the zone and introducing microwave energy into the electric heating zone, the electric silicon particles in the electric heating zone are heated, and the electro-silicon particles in the electric reaction zone and the electric silicon particles in the top of the electric heating zone are mixed. Therefore Method for fluidized bed heating by microwaves by adjusting the speed of the carrier gas of electricity in the electric heating zone to heat transfer from the heating zone to the electric reaction zone and fundamentally prevent backflow of the reaction gas from the electrical reaction zone to the heating zone. Method for producing high purity granular polycrystalline silicon by 2. The microwave according to claim 1, wherein the microwave energy is heated to at least one side of the electric fluidized bed reactor having the electric heating zone so that the temperature of the electric heating zone is at least the electric reaction temperature. Method for producing high purity granular polycrystalline silicon by fluidized bed heating method. The method for producing high purity granular polycrystalline silicon according to claim 1, wherein the outer wall surface of the electrically fluidized bed reactor is insulated with a heat insulating material made of a material having a low permeation loss of microwaves.