DE3842099A1 - Fluidised-bed reactor for producing polycrystalline silicon - Google Patents

Abstract

Fluidised-bed reactor for producing polycrystalline silicon of high purity by introducing a silane-containing gas stream into a reaction zone comprising fluidised silicon particles, in which the silane-containing gas is heterogeneously decomposed in the reaction zone 14 to give silicon which deposits on the silicon particles 12, whereby the silicon particles 12 are enlarged and the enlarged silicon particles are deposited out as silicon product particles 16 in the vicinity of the bottom of the reaction zone 14 in a collection zone 17, and in which there is a discharge zone 10 arranged above the reaction zone 14, which discharge zone 10 has a cross-sectional area at right angles to the direction of the fluidising gas stream which is smaller than or equal to the cross-sectional area of the reaction zone 14 at right angles to the direction of the fluidising gas stream, with the fluidising gas velocity being sufficient to discharge and remove a substantial part of the silicon powder particles 20 formed by homogeneous decomposition of the silane-containing gas, but not sufficient to discharge appreciable amounts of the silicon particles 12, 16 of the fluidised bed 14, and also a process for producing polycrystalline silicon. <IMAGE>

Description

The invention relates to a fluidized bed reactor, in particular a fluidized bed reactor and a process for its production of high purity polycrystalline silicon.

The use of silicon for electronic purposes is required the manufacture of ultra high purity silicon materials. Silicon material is commonly used in semiconductors with contamination levels of less than 1 part per trillion (ppb) demands. Continuing progress in electronic Industry and the development of many new products this area have become an expanding market for silicon ultra high purity. High purity silicon continues to be for the production of solar cell fields for direct Conversion of sunlight into electricity required. For All of these applications are in urgent need to improve existing ones Silicon technology used to increase silicon purity and quality at reduced costs. The production of high purity polycrystalline silicon on a continuous or semi-continuous basis Using a fluidized bed reaction zone is an important one Aspect of the overall process for the production of silicon single crystals ultra high purity.

The production of polycrystalline silicon from silane and / or halosilane-containing gases is obtained by pyrolysis of the silane-containing Gases to high-purity silicon reached.  

The pyrolysis step makes use of a fluidized bed reaction zone, in which the silane-containing gases are heated by a Fluidized bed of silicon particles are passed. Within In this fluidized bed, the silane becomes silicon of high purity and decomposes hydrogen as a by-product. The silicon higher Purity is deposited on the silicon particles in the fluidized bed. The deposition of the silicon on the silicon seed particles causes these particles to grow in size. The larger silicon product particles are then on removed from the fluidized bed in a conventional manner. Such manufacturing processes are in US-A 39 79 490, 30 12 861 and 3 0 12 862.

The decomposition of silane to silicon is both heterogeneous as well as homogeneous. The homogeneous decomposition results in the generation of silicon powder in the submicron and / or micron range. The powdered silicon has high surfaces, so all the particles in the fluidized bed tend to be a lot grow slower compared to the rate of growth if the powder particles are not present in the fluidized bed are. As the process progresses, the little ones start Particles begin to accumulate in the reactor because they are homogeneously produced will. As the silicon powder increases, are becoming product size silicon particles with an increasing slower speed as a result of the decrease in the number the silicon particles available for growth generated. As pyrolysis progresses, the layer begins to separate, with the smaller particles at the top and the larger particles are at the bottom. Because the bigger ones Product particles are withdrawn from the bottom of the reactor, only large particles are removed. With continued distance the large particles become the entire fluidized bed reactor finally essentially a layer of small silicon powder particles.

The presence of silicon powder particles during the subsequent Single crystal pulling is undesirable because of the part  do not melt readily, but rather on the surface drive and disadvantageously around the newly formed Deposit the single crystal rod. Silicon is also subject to in powder form because of its increased surface area during the Manufacturing process to a greater extent of contamination. Another problem is the difficulty of silicon powder to handle in the micron to submicron size range.

The homogeneous decomposition of silane can be reduced by lowering the Temperature at which the fluidized bed reaction zone operated is pushed back. Nevertheless, this has the disadvantage connected that the efficiency of heterogeneous decomposition by a significant decrease in the silane pyrolysis temperature as well is affected. Another measure requires maintenance of low silane and / or halosilane concentrations in the reaction zone to ensure homogeneous decomposition limit. However, this measure has the disadvantage that that a low silane / halosilane concentration becomes a low silicon production speed. There is therefore a need for a fluidized bed reactor that Pyrolyze gases containing silane and / or halosilane at temperatures can, which leads to the efficient heterogeneous decomposition of Silane gases leads and in that through the homogeneous decomposition silicon powder generated in the fluidized bed is removed before it accumulates and the silicon powder particles occur gain supremacy in the fluidized bed.

Other objects, advantages and features of the invention will become apparent the description below and the preferred ones explained therein Embodiments in connection with the accompanying Drawings clearly. The invention relates to a fluidized bed reactor for the production of polycrystalline silicon high purity by introducing a gas stream containing silane into a reaction zone made of fluidized silicon particles. The gas containing silane becomes heterogeneous to silicon in the reaction zone decomposes, the resulting silicon on the  Precipitates silicon particles. The deposit of silicon on the silicon particles increases the silicon particles and leads to the fact that the enlarged silicon particles as Silicon product particles near the bottom of the reaction zone deposit in a collection zone. According to the invention Arrangement of a discharge zone is provided above the reaction zone. The discharge zone has a cross-sectional area perpendicular to the direction of the silane-containing gas flow, which is smaller than or equal to the cross-sectional area of the reaction zone perpendicular to the direction of the silane-containing gas flow. The host zone is by a fluidizing gas velocity featured that suffices a substantial amount of through the homogeneous decomposition of the silane-containing gas produced silicon powder particles discharge and remove, but not sufficient amount of silicon particles from the Discharge fluidized bed.

The invention further relates to a method of manufacture high purity polycrystalline silicon by pyrolysis of gas containing silane in a fluidized bed reaction zone made of silicon particles. As a step, the method comprises the introduction a gas stream containing silane into the reaction zone from fluidized Silicon particles. The silane-containing gas becomes heterogeneous decomposes under conditions under which the product silicon which precipitates heterogeneous decomposition on the silicon particles, whereby the silicon particles enlarge and deposit as silicon product particles in a collection zone. The Silicon product particles are extracted from the collection zone. Formed by the homogeneous decomposition of the silane-containing gas stream Silicon powder particles are made from the silicon particles the fluidized bed by passing the fluidizing gas stream separated by a discharge zone. The discharge zone has a cross-sectional area perpendicular to the direction of the silane-containing Gas flow that is less than or equal to Cross-sectional area of the reaction zone perpendicular to the direction of the  gas stream containing silane. The discharge zone is through a Gas velocity marked, which is sufficient, an essential Remove and remove the amount of silicon powder particles, however, an appreciable amount of the silicon particles is not sufficient to carry out.

According to the invention, a device and a means are thus provided, from a fluidized bed reaction zone over a Discharge zone through the homogeneous decomposition of silane To remove gas generated silicon powder.

From the attached drawings shows

Fig. 1 shows schematically a flow chart of a silicon manufacturing method using a fluidized bed reactor for the pyrolysis of silane-containing gases;

2 shows a cross section through a particular embodiment of a device according to the invention.

Fig. 3 shows a further embodiment of this device according to the invention; and

Fig. 4 shows the relationship between the gas velocity to the maximum size of the exiting particles.

The term "heterogeneous decomposition" as used herein relates to the reduction of silane or halosilane to silicon, which occurs in two or more phases, such as when the decomposition occurs at the boundary between a gas and a solid phase. This heterogeneous decomposition leads to the deposition of silicon either on suspended silicon particles in the fluidized bed or on the inner surfaces of the fluidized bed reactor. "Homogeneous decomposition" occurs in a single phase on, such as the gas phase, and produces silicon powder or dust with a high surface area in the micron to submicron size range. in the  decomposition is generally at a given temperature of gases containing silane either heterogeneous and / or homogeneous, depending on the concentration of the silane-containing gas. In general a low silane feed concentration is desirable, about the decomposition of the silane-containing gas and halosilane to perform silicon in a heterogeneous manner. However can have a very low feed concentration of gas containing silane to a slow silicon production rate to lead.

The term "silicon seed particles" refers to such particles in the fluidized bed, which have a size in the range of 50 µ to 400 µm. Such particles enlarge in the desired Way, when silicon is deposited on it, eventually it to be obtained as silicon product particles. "Silicon product particles" are those seed particles that have a size of at least 400 µm, preferably in the range of 400 µm to 1300 µm, have enlarged. Such particles separate nearby the bottom of the reaction zone and are in a collection zone won, which allows removal in a conventional manner. The term "silicon particle" refers to both silicon seed particles as well as on product particles in the fluidized bed.

The term "silicon powder" generally refers to Silicon particles in the micron to submicron range with high Surface resulting from the homogeneous decomposition of the silane and / or result in gas containing halosilane.

The term "silane-containing gas" as used herein refers to gases containing silane and or halosilane, if not displayed differently.

The term "fluidizing gas" or "fluidizing gas" as related here, refers to the combination of silane Gas and any other additional inert carrier gas that is added to the fluidized bed reactor to aid in fluidization to help the silicon particles.  

Polycrystalline silicon can be introduced by introducing a current a gas containing silane into the fluidized bed in one Reaction zone suspended silicon particles are made. These silicon particles are directed upwards Flow of a fluidizing gas in a reaction zone suspended. The fluidizing gas velocity through the Reaction zone is at a value above the minimum fluidizing gas velocity the silicon particles held. The Temperature in the reaction zone is within a range between the decomposition temperature of the gas containing silane and the melting temperature of silicon. The silane-containing Gas is decomposed to form silicon that is on the Precipitation surface of the silicon particles. If that Silicon deposits on the silicon particles enlarge these particles and separate near the bottom of the Fluidized bed arranged in a below the reaction zone Collection zone. The collecting zone can be any known collecting device to obtain finely divided material. The Product particles are removed from the collection zone in a conventional manner won.

The silane-containing gas can be used in accordance with conventional Practices introduced across the floor into the fluidized bed reaction zone will. The gas containing silane can be introduced without dilution or with an inert carrier gas, such as hydrogen, Argon, helium or the like can be diluted. While The decomposition of silane becomes hydrogen as a by-product generated and can be used as a carrier gas for additional quantities on silane feed gas in semi-continuous or continuous Operation of a fluidized bed.

Any suitable silane-containing gas stream that is thermally in the Gas phase can be pyrolyzed or reduced to silicon, can be used as feed gas for the fluidized bed. Examples for such gases are chlorine silane and halosilanes,  Bromine, fluorine and iodine. Although the chlorosilanes, such as trichlorosilane, Tetrachlorosilane and dichlorosilane can be used are special advantages associated with the use of silane. The slightly exothermic silane pyrolysis reaction runs essentially completely, is irreversible and will, in comparison to those for pyrolysis of halosilane gases and the like required temperatures, at a slightly lower temperature initiated by about 200 ° C. In addition, this is silane and its Decomposition products, d. H. Silicon and hydrogen, not corrosive and harmless to the environment. In comparison, the chlorosilane decomposition a reversible and incomplete reaction that leads to the production of by-products that are corrosive in nature are. Accordingly, this is the silane in the execution of the Invention preferred gas, although related to other silane-containing gases can be.

The silane feed gas streams and the inert carrier gas streams can using a conventional gas distributor under the Reaction zone to form the fluidizing gas stream in the Reaction zone are introduced. The fluidizing gas velocity through the reaction zone is generally on a Speed kept one to eight times, preferably two to five times, the minimum for fluidization the average diameter particles in the fluidized bed required fluidization rate corresponds. The term "average diameter," as used here, denotes the sum of the quotients of a given Particle diameter and that of the respective particles with the weight fraction assigned to given diameter. Preferably the fluidization rate is about four times the minimum fluidization rate of the silicon particles in the fluidized bed. The minimum fluidization rate can be determined in a conventional and known manner with the equation

wherein

V ₀ = minimum surface gas velocity for fluidization (m / s)
D _p = average particle diameter in the layer (m)
ρ = density of the fluidizing gas (kg / m³)
ρ _p = density of the particles (kg / m³)
Φ _S = sphericity of the particles
ε = empty fraction in the particle layer with minimal fluidization
µ = absolute viscosity of the fluidizing gas (kg / ms)
g = gravitational acceleration (m / s²)

The minimum fluidization rate is strict Function of gas velocity and gas density, as well as the average particle diameter, particle shape and the empty fraction. Thus, the minimum fluidization rate with minor changes in these factors cover a wide area.

The minimum fluidization rate is preferred calculated for conditions such as those near the gas distributor exist. When using such conditions that the Include temperatures that are usually lower than in the rest of the reaction zone, it is possible to ensure that the calculated minimum fluidization speed is sufficient, fluidize the entire layer. At elevated temperatures in the reaction zone are those concerning viscosity and density Variables in the equation given above are temperature sensitive and can at a minimal fluidization rate lead, which is not sufficient, the layer at the lesser Fluidize temperatures in the lower part of the layer. When calculating the minimum fluidization rate However, based on the cooler conditions, it is possible to do the calculation to ensure the lowest fluidizing gas velocity, which fluidizes the entire layer. The invention is  not to specific minimum fluidization rates limited; usable minimum fluidization rates are, however, in the range from 12.2 cm / s to 42.7 cm / s (0.4 ′ / s up to 1.4 ′ / s), preferably from 18.3 cm / s to 36.6 cm / s (0.6 ′ / s to 1.2 '/ s), and most preferably from 27.4 cm / s to 33.5 cm / s (0.9 ′ / s to 1.1 ′ / s). Although the pyrolysis of silane Gas volume in the reaction zone increased (1 mol of silane gas gives 2 Mole of hydrogen gas), the increase in volume caused by the Reaction zone led gas at least partially through the Control of volumetric flow of feed gases balanced will. Depending on the respective in the discharge zone required gas velocity, the required gas volume, that leaves the reaction zone can be determined. Considering the volume of the additional generated in the pyrolysis reaction Gases it is possible to add the desired volume Feed gas, which is used to obtain the gas leaving the reaction zone desired volume is required to determine. It should be noted that the ratio of carrier gas to reaction gas in the feed gases have an impact on the total amount in the pyrolysis step generated by-product gas. If less by-product gas is desirable, the ratio of silane Gas can be reduced to inert gas. If more by-product gas is desirable, the ratio of gas containing silane to Inert gas can be increased.

As discussed, the temperature in the reaction zone is within the decomposition range of the silane-containing gas and the Melting temperature kept by silicon. The lowest temperature at which the decomposition of silane occurs is approximately 200 ° C. The melting temperature of silicon is around 1400 ° C. It is therefore preferred to have the reaction zone at a Temperature in the range of 200 ° C to 1400 ° C, preferably from 550 ° C to 1000 ° C to operate. The temperature that needed to keep the reaction zone at such temperatures can be generated with conventional heating systems, for example by electrical resistance heaters located on the outside of the reactor wall are arranged.  

The production of polycrystalline silicon in a fluidized bed reactor depends on the supply of the layer with silicon seed particles with an average diameter in Range from 50 µm to 400 µm. These silicon seed particles form the substrate on which the heterogeneous decomposition of the silane originating silicon is deposited. In this scale, in which the silane decomposes and the silicon particles in the Growing in size, the enlarged product particles separate with an average diameter of at least about 400 µm near the bottom of the reaction zone in a collection zone from. These enlarged particles preferably have an average diameter in the range of 400 microns to 1300 µm and more preferably about 1000 µm. The silicon product particles are then collected and can either be continuous or periodically withdrawn from the collection zone. The product particles are of a sufficient size that they simple and without unwanted contamination of the high-purity material can be handled.

It is possible to supply the fluidized bed with replacement Silicon seed particles make up a small proportion of the product material branch off and this material using suitable methods To crush or grind particles of seed size. The seed-sized particles can then enter the fluidized bed again be introduced. After the introduction, such small Silicon seed particles growth sites of silane decomposition, such as previously, and slowly increase in size to serve as product particles to be pulled out of the layer.

In a fluidized bed reactor, the homogeneous decomposition of gases containing silane, which are used to form silicon powder high surface area, undesirable for several reasons. Mainly reduces the high surface area of the unwanted Silicon powder in the fluidized bed reactor the speed with which the silicon particles grow in the fluidized bed. By doing Dimensions of how the silicon powder increases in the fluidized bed,  the growth rate of the silicon particles drops. As pyrolysis increases, the layer begins to become smaller Separate particles at the top and larger particles at the bottom. As the larger particles are pulled off the bottom of the reactor only large particles are removed. The amount of Silicon particles in the fluidized bed is getting smaller, while the amount of silicon powder particles is becoming more and more dominant. This has the effect of depleting silicon particles, so that finally the entire fluidized bed reactor in the essentially to a layer of small silicon powder particles becomes. It follows that the removal of these silicon powder particles the operation of the process for producing high purity Silicon from gases containing silane in a fluidized bed reactor useful.

In practice it has been found that by arranging a discharge zone, which are characterized by a certain gas velocity is one above the fluidized bed reaction zone substantial amount due to the homogeneous decomposition of silane generated silicon dust particles from the fluidized bed reactor can be removed without a significant amount of in the Fluid bed to remove existing silicon particles. The The discharge zone preferably has a smaller cross-sectional area than the fluidized bed reaction zone. The speed of the fluidizing gas flowing through the discharge zone must be such that for a given cross-sectional area of the discharge zone the silicon powder particles discharged and through the upper part of the reactor are carried out. However is ideally, the fluidizing gas velocity is not so great that they lead to a significant loss Amount of silicon particles from the fluidized bed. It was generally found to be a suitable one to achieve these goals Fluidizing gas velocity through the discharge zone is in the range of 3 cm / s to 146 cm / s (0.1 ′ / s to 4.8 ′ / s).

As soon as a desired gas velocity through the discharge zone is set up, the respective dimensions  the discharge zone can be determined in a conventional manner. For example, as the diameter of the discharge zone decreases the gas velocity through the discharge zone at a given gas velocity through the reaction zone to. Accordingly, with an increase in diameter the discharge zone the gas velocity through the discharge zone at a given gas velocity in a reaction zone from. This represents the diameter of the discharge zone is a variable used to achieve the desired gas velocity be set by the discharge zone can.

A fluidized bed reactor constructed according to the invention is in the generally a vertical vessel. Although a cylindrical vessel and such a reaction zone is preferred, of course that any one suitable for fluid bed operation Configuration can be used. The special dimensions the reaction zone and the reaction vessel depends primarily depends on the economy of the design. The reaction zone is allowed the result is not too tight or low production. Accordingly, it must not be too far, or inadequate heat transfer and fluidization difficulties arise.

As generally mentioned above, the diameter of the discharge zone depends on the desired fluidization rate of the fluidizing gas flowing through the discharge zone, as well as the size of the silicon powder particles whose removal is desired and the size of the silicon particles whose retention is desired. For a given fluidization gas velocity through the reaction zone, the relationship is illustrated by the straight line in FIG. 4 for discharge zones with a diameter less than or equal to the diameter of the reaction zone. In the plot, straight line 1 shows the relationship between the maximum size of the emerging particles and the gas velocity in the reaction zone for a discharge zone with a diameter of 20 cm. Line 2 shows the same relationship for a discharge zone with a diameter of 25 cm and line 3 shows the same for a discharge zone diameter of 30 cm. This straight line explains that as the diameter of the discharge zone (lines 1 , 2 and 3 ) increases, the maximum size of the exiting particles (y axis) for a given fluidizing gas velocity (x axis) decreases. This follows because the gas velocity through the discharge zone decreases with increasing diameter with a given reaction zone flow velocity.

Lines C - 1 and C - 2 illustrate an expanded head conventionally used in silane production and located above the reaction zone and which has a diameter which is larger than the diameter of the reaction zone and which does not correspond to the invention. Lines C - 1 and C - 2 are only shown for comparison purposes. The enlarged head generally results in a gas velocity that is insufficient to carry silicon particles over. However, the enlarged head also leads to a gas velocity which is insufficient to carry out a substantial part of the silicon powder particles. In contrast, the discharge zone of line 1 , 2 or 3 gives a gas velocity through the discharge zone which is sufficient to remove a substantial part of the silicon powder particles without discharging any significant amount of silicon particles.

The discharge of silicon powder is also dependent on the length of the Discharge zone influenced. The length of the discharge zone is again depending on the fluidization gas velocity, the Discharge zone diameter and average particle size, to be carried out. The discharge zone height for a given discharge zone diameter can be by the equation can be determined as follows:

E = 3.43 ( µ _c / µ ₀) (V ² / gZ) ^1.42

wherein

E = discharge in kg solid / kg gas
µ _c = gas viscosity under operating conditions (kg / ms)
µ ₀ = air viscosity at 25 ° C (kg / ms)
V = gas velocity (m / s)
g = gravitational acceleration (m / s²)
Z = height of the discharge zone (m)

The height of the discharge zone is preferably for the purpose of Invention in the range of 71 cm to 710 cm (2 'to 20'), stronger preferably at 152.5 cm to 305 cm (5 ′ to 10 ′).

The height of the discharge zone is particularly important if the discharge zone has a diameter which is equal to the diameter of the reaction zone. Because of the equivalent diameter, the gas velocities through the reaction zone (V ₁) and the discharge zone (V ₂) are the same, unless an external gas source is connected to the discharge zone. The desired separation of silicon powder particles from silicon particles can be achieved by having a discharge zone of sufficient height that the fluidizing gas velocity removes a substantial amount of the silicon powder particles without removing a significant amount of the larger silicon particles. If the discharge zone is sufficiently high, the larger silicon particles lose their upward velocity and thus fall back into the fluidized bed reaction zone due to gravity, while the smaller silicon powder particles are discharged and are carried out through the upper part of the discharge zone as a result of the fluidizing gas velocity.

The gas velocities through the reaction zone (V ₁) and the discharge zone (V ₂) are chosen so that an effective fluidized bed is maintained and at the same time an effective removal of the silicon powder particles is achieved. The respective dimensions of the discharge zone therefore vary with the size of the silicon particles and the desired fluidizing gas velocity through the reaction zone. The combination of the variables relating to the height of the discharge zone and the diameter of the discharge zone makes it possible to provide a gas velocity (V ₂) which discharges silicon powder particles, but not a significant amount of the larger silicon particles.

In a particular embodiment of the invention, it is preferred that the planar cross-sectional area of the discharge zone is smaller than a similar planar cross-sectional area the reaction zone. In a typical cylindrical reaction zone the reaction zone diameter is about 30.5 cm (12 ″). Therefore, the discharge zone is preferably not larger than 30.5 cm (12 ″) in diameter. Is more preferred the discharge zone diameter in the range from 17.8 cm to 25.4 cm (7 ″ to 10 ″), and most preferably about 20.3 cm (8th"). However, it is understood that the invention is not based on this Dimensions is limited as long as the removal of the silicon powder particles is achieved without a significant Amount of silicon particles is discharged.

In the practice of the invention, those skilled in the art can make substantial amounts of silicon powder from the reaction zone of a fluidized bed for the production of polycrystalline silicon by pyrolysis remove from gas containing silane. Preferably, the Invention the removal of at least 50% by the homogeneous Decomposition of silane-containing gas produced silicon powder. According to a most preferred embodiment at least about 90% removed. Furthermore, the practice of Invention limit the loss of carryout to less than about 70% of the fluidized bed silicon particles, stronger preferably less than about 10% and most preferred to less than about 1%.

Practical embodiments of the invention are described in description below in conjunction with the accompanying  Drawings made clear. It is understood that the description refer to the explanation of more preferred and alternative Embodiments of the invention relate to and not limitative is to be understood.

Fig. 1 shows schematically the overall process of the decomposition of silane, in which the discharge zone of the fluidized bed can be used advantageously. The method includes a reactor 48 , a heat exchanger 42 , a filter 38 , a compressor 37 and a gas separator 36 . The fluidized bed reactor 48 is heated by a heating device, generally designated 49 . The silane feed material in line 32 is combined with the recycle hydrogen and / or inert carrier gas in line 34 and forms the direct fluidizing gas stream through line 33 into the bottom of reactor 48 . Silicon seed particles of conventional size are introduced into reactor 48 through line 30 . These silicon seed particles are suspended as a fluidized bed in the reactor 48 and moved through the fluidizing feed gas stream entering the reactor 48 through line 33 . The silicon product particles resulting from the deposition of silicon on the silicon particles of the fluidized bed reactor 48 are withdrawn from the reactor 48 through line 31 near the bottom. Such product particles have the size and density suitable for direct handling, without the consolidation processes necessary in other processes in which fine silicon powder or fine dust are produced in significant amounts.

As stated above, the use of silane as a silane-containing gas is advantageous because silane and its decomposition products, ie silicon and hydrogen, are not corrosive and environmentally friendly. The by-product hydrogen formed during the decomposition of silane is withdrawn from the reactor 48 through line 43 together with any inert carrier gas which may be present and excess silane fed to the reactor 48 via line 33 . The top gas of line 43 is returned via line 45 . The returned hydrogen in line 45 can be used to dilute the silane-containing feed gas in line 32 , which is fed through line 33 into the reactor 48 . If the amounts of inert carrier gas used are used in the process according to the invention, it is possible for both hydrogen and the inert carrier gas to be present in lines 33, 43, 45, 46, 47, 50, 35 and 34 .

The return gas stream 45 passes through a heat exchanger 42 for cooling in countercurrent with a coolant which enters through line 40 through exchanger 42 and leaves via line 41 . The recycle gas stream 45 is cooled to lower the temperature, to protect downstream devices from damage, as well as to avoid gas contamination by recycle devices. The recycle gas stream 45 is cooled to a temperature that prevents the recycle gas 45 from causing premature heterogeneous decomposition on the silane-containing gas 32 if the two are mixed prior to entering the reactor 48 . The cooled recycle gas stream leaves exchanger 42 through line 46 and enters filter device 38 . The filter device 38 removes the silicon powder from the cooled recycle gas stream 46 from the silane pyrolysis reaction. The filtered silicon powder leaves the filter through line 39 . The filtered recycle gas stream leaves filter 38 through line 47 and is recompressed in line 50 using compressor 37 . Line 50 enters separator 36 , where the recycle gas in line 35 and line 34 is separated. Line 35 primarily contains hydrogen and trace amounts of other inert carrier gases. Such hydrogen can be used in other processes within the system. The recycle gas stream in line 34 containing hydrogen and other fluidizing gases is recombined with the silane feed stream in line 32 and makes up the fluidizing gas feed stream in line 33 .

Fig. 2 shows an embodiment of the invention, according to which the fluidizing gas velocity V ₂ through the discharge zone 10 is equal to the fluidizing gas velocity V ₁ through the reaction zone 14th The silane feed gas in line 32 is combined with a hydrogen / inert carrier gas feed stream 34 and forms the feed stream in line 33 to the bottom of the reactor 48 . The fluidization feed gas enters the fluidized bed reaction zone 14 through the perforations of a conventional gas distributor plate 15 . The silane gas of the feed stream is decomposed in the fluidized bed 14 made of silicon particles 12 to form silicon which is deposited on the silicon particles 12 in the fluidized bed 14 to form enlarged silicon product particles 16 . The enlarged silicon product particles 16 deposit near the bottom of the reactor 48 and are collected in the collection chamber 17 . The product particles 16 obtained are then withdrawn from the collection chamber 17 in a conventional manner (not shown). The fluidized bed reactor 48 is characterized by a fluidizing gas velocity sufficient Sieren 12 the silicon particles to fluidic.

According to Fig. 2 and 3, a competing reaction for the heterogeneous decomposition of Silaneinspeisung in the reaction zone 14 is the homogeneous decomposition of silane. The homogeneous decomposition leads to the formation of silicon powder particles 20 , which accumulate near the upper end of the fluidized bed reaction zone 14 . It is necessary to remove these silicon powder particles 20 in order to make the process for producing the silicon product particles 16 efficient. The smaller size of the silicon powder particles 20 permits the discharge of such particles 20 with the upward flowing fluidizing gases when they flow through the discharge zone 10 directly above the upper end of the fluidized bed reaction zone 14 . The fluidizing gas velocity through the discharge zone 10 must be such that it does not lead to the discharge of the silicon particles 12 . The by-product hydrogen gas, the fluidizing gases and the silicon powder particles chen 20 exit through the upper part of the discharge zone 10 through the outlet 43 . The gas stream from 43 is further processed downstream to separate the individual gases and the silicon powder particles 20 .

It should be noted that in the particular embodiment of FIG. 2, the discharge zone 10 and the reaction zone 14 have the same diameter, which is why the fluidizing gas velocities through the discharge zone 10 and the reaction zone 14 are the same. By appropriately selecting the fluidization gas velocity, the desired separation of the silicon powder particles 20 and the silicon particles 12 can be achieved by providing a discharge zone 10 of the correct height at the upper end of the fluidized bed reaction zone 14 . For example, as soon as a desired gas velocity is selected that effectively fluidizes the layer of silicon particles 12 , the gas velocity through the discharge zone 10 is determined. The height of the discharge zone 10 directly above the upper end of the fluidized bed 14 is such that the fluidizing gas velocity is sufficient to discharge a significant amount of silicon powder particles 20 , but is not sufficient to discharge a significant amount of silicon particles 12 . If too many of the silicon particles 12 are discharged, the height of the discharge zone 10 must be increased. On the other hand, if not enough silicon powder particles 20 are removed, the height of the discharge zone 10 must be reduced to a height that allows removal of a desired amount of silicon powder particles 20 without removing a significant amount of silicon particles 12 .

Because the silicon seed particles in the fluidized bed 14 grow into silicon product particles 16 that are ultimately withdrawn from the system, it is necessary to add the amount of silicon seed particles via line 30 . The new seed particles are provided by crushing or grinding the product particles 16 obtained. Heat is supplied to the fluidized bed reaction zone 14 by a suitable heating device 49 , such as a resistance heater, which is arranged on the outer reactor wall.

Fig. 3 shows an embodiment of the invention in which the fluidizing gas velocity V ₂ through the discharge zone 10 is greater than the fluidizing gas velocity V ₁ through the reaction zone 14th The higher speed V ₂ is achieved by using a discharge zone 10 , the diameter of which is smaller than the diameter of the reaction zone 14 . At a given gas velocity V ₁ through the reaction zone 14 , it is possible to increase this velocity V ₁ in the discharge zone 10 to V ₂ by the diameter of the discharge zone 10 being smaller than the diameter of the reaction zone 14 . Such an increased speed V ₂ is desirable if the speed V ₁ is not sufficient to discharge silicon powder particles 20 .

The following example serves to explain a special one Embodiment of the invention and is not intended to be limiting be understood.

example

There are the reactor of the invention and the inventive Method as in the above description based on the Drawings described for the thermal decomposition of silane Gas related to silicon.

The fluidized bed reaction zone has a bed diameter of 30 cm. The layer contains silicon particles with an average Diameter of about 1000 µm. Gas containing silane and fluidizing gases become the bottom of the fluidized bed reaction zone fed through a conventional gas distributor. The Feed gases enter the reaction zone at a temperature of about 25 ° C and a pressure of about 2.07 bar (30 psig) into the  Reaction zone. The feed current contains 56 vol .-% silane and 44 vol% fluidizing gases. The volumetric amount of feed gases, which enters the fluidized bed reaction zone is so adjustable that the gas velocity through the reaction zone can also be set.

A discharge zone is located above the fluidized bed reaction zone arranged, which has a diameter of 30 cm. The Discharge zone has a height that is essentially equivalent to the height of the fluidized bed reaction zone. Feed gas, which on Soil enters the reaction zone, flows up and through the reaction zone into the discharge zone and at the top of the Discharge zone.

The gas velocity through the reaction zone is adjusted to be approximately 10, 15, 20, 25, 30, 35 and 40 cm / s. At each different gas velocity in the reaction zone, the particles that are discharged from the discharge zone are collected. The collected particles are conventionally sized, such as sieve sets, and the maximum size of the particles that emerge. The maximum size of the emerging particles is determined for each gas velocity of the reaction zone. The relationship is illustrated as straight line 3 in FIG. 4.

Additional measurements of the maximum size of the exiting particles are carried out in the manner described above for discharge zones which have a diameter of 25 cm and 20 cm. The relationships for these discharge zones are shown in FIG. 4 as straight lines 2 and 1 , respectively.

For comparison purposes, an expanded head with a diameter of 35 cm and 40 cm, compared to a reaction zone diameter of 30 cm, was arranged above the reaction zone. The maximum size of the exiting particles is determined as described above and the relationships are shown as straight lines C - 1 and C - 2 in FIG. 4. The straight lines C - 1 and C - 2 are for comparison purposes only and do not represent examples according to the invention.

Figure 4 shows that for a given discharge zone diameter, as the gas velocity through the reaction zone increases, the maximum size of the exiting particles also increases. If the discharge zone has a diameter that is less than or equal to the diameter of the reaction zone for a given reaction zone velocity (lines 1 to 3 ), the maximum size of the exiting particles is larger than the maximum size of the exiting particles at the same reaction zone gas velocity, if the discharge zone has a larger diameter than the reaction zone (straight lines C - 1 and C - 2 ). This is a result of the increased gas velocity V ₂ through the discharge zone compared to the gas velocity through the expanded head. The invention therefore, as explained by lines 1 , 2 and 3 , allows the maximum size of the exiting particles to be increased for a given reaction zone gas velocity when compared with the maximum size of the exiting particles in a discharge zone having a larger diameter than in the reaction zone .

Claims (31)

1. A fluidized bed reactor for producing high purity polycrystalline silicon by introducing a silane-containing gas stream into a reaction zone of fluidized silicon particles, wherein the silane-containing gas in the reaction zone 14 is heterogeneously decomposed into silicon, which is deposited on the silicon particles 12 , whereby the silicon particles 12 enlarge and the enlarged silicon particles separate out as silicon product particles 16 near the bottom of the reaction zone 14 in a collecting zone 17 , and in which a discharge zone 10 is arranged above the reaction zone 14 , which discharge zone 10 has a cross-sectional area perpendicular to the direction of the fluidizing gas stream, which is smaller is equal to or equal to the cross-sectional area of the reaction zone 14 perpendicular to the direction of the fluidizing gas flow, characterized in that the fluidizing gas velocity is sufficient, a substantial part of that due to homogeneous decomposition of the silane To discharge and remove silicon gas particles 20 formed by gas, but it is not sufficient to discharge significant amounts of the silicon particles 12 , 16 of the fluidized bed 14 . 2. fluidized bed reactor according to claim 1, characterized, that the fluidizing gas from that of silane, halosilane, hydrogen and mixtures thereof existing group selected is.   3. Fluidized bed reactor according to claim 1 or 2, characterized in that the discharge zone is designed so that a gas velocity results, which effectively prevents the discharge of silicon particles 12 , 16 with an average diameter in the range from 50 to 400 µm. 4. fluidized bed reactor according to claim 3, characterized in that the discharge zone 10 is designed so that a gas velocity results, which effectively prevents the discharge of silicon particles 12 , 16 of more than about 100 microns in size. 5. Fluidized bed reactor according to one of claims 1 to 4, characterized in that the discharge zone 10 is designed so that a gas velocity results which causes the removal of at least about 50% of the silicon powder 20 produced by the homogeneous decomposition of the silane-containing gas stream. 6. Fluidized bed reactor according to one of claims 1 to 5, characterized in that the discharge zone 10 is designed so that a gas velocity results which causes the removal of at least about 90% of the silicon powder 20 produced by the homogeneous decomposition of the silane-containing gas stream. 7. fluidized bed reactor according to one of claims 1 to 6, characterized in that the discharge loss of silicon particles 12 , 16 from the fluidized bed 14 makes up less than 70% of the silicon particles in the fluidized bed. 8. fluidized bed reactor according to claim 7, characterized in that the discharge loss of silicon particles 12 , 16 from the fluidized bed 14 makes up less than 10% of the silicon particles of the fluidized bed. 9. fluidized bed reactor according to one of claims 1 to 8, characterized in that the discharge zone 10 has a diameter in the range of 17.8 cm to 25.4 cm (7 "to 10"). 10. fluidized bed reactor according to claim 9, characterized in that the discharge zone 10 has a diameter of about 20.3 cm (8 ″). 11. Fluidized bed reactor according to claim 9 or 10, characterized in that the length of the discharge zone 10 is in the range from 61 cm to 6.1 m (2 'to 20'). 12. fluidized bed reactor according to one of claims 1 to 11, characterized, that the average diameter of the silicon powder particles 20 is up to about 100 microns. 13. fluidized bed reactor according to claim 12, characterized, that the average diameter of the silicon powder particles 20 is up to about 50 microns. 14. Fluidized bed reactor according to one of claims 1 to 13, characterized in that the average diameter of the silicon product particles 16 is in the range from 400 µm to 1300 µm. 15. Fluidized bed reactor according to one of claims 1 to 14, characterized in that the gas velocity through the discharge zone 10 is in the range from 3 cm / s to 146 cm / s (0.1 '/ s to 4.8' / s). 16. fluidized bed reactor according to one of claims 1 to 15, characterized, that the silane-containing gas from that of silane, halosilanes and Mixtures of which existing group is selected. 17. A process for producing polycrystalline silicon of high purity by pyrolysis of a gas containing silane in a fluidized bed reaction zone comprising silicon particles, which comprises

• (a) introducing a silane-containing gas stream into the reaction zone 14 made of fluidized silicon particles 12 ;
• (b) the heterogeneous decomposition of the silane-containing gas under conditions in which the product silicon of the heterogeneous decomposition is deposited on the silicon particles 12 , whereby the silicon particles 12 enlarge and deposit as silicon product particles 16 in a collection zone 17 ;
• (c) recovering the silicon product particles 16 from the collection zone 17 ; and
• (d) separating the silicon powder particles 20 formed by the homogeneous decomposition of the silane-containing gas stream from the silicon particles 12 , 16 by passing the fluidizing gas stream through a discharge zone 10 having a cross-sectional area perpendicular to the direction of the silane-containing gas stream that is less than or equal to the cross-sectional area of the reaction zone 14 perpendicular to the direction of the silane-containing gas stream, the discharge zone 10 being characterized in that it has a gas velocity which is sufficient to discharge and remove a substantial amount of the silicon powder particles 20 , but is not sufficient, a significant amount of the silicon particles 12 , 16 to carry out.

18. The method according to claim 17, characterized in that the discharge zone 10 is designed so that a gas velocity results which effectively prevents substantial discharge of silicon particles 12 , 16 with an average diameter in the range of 50 to 400 microns. 19. The method according to claim 18, characterized in that the discharge zone 10 is designed so that a gas velocity results which effectively prevents a substantial loss of discharge of silicon particles 12 , 16 with a size of more than about 100 microns. 20. The method according to any one of claims 17 to 19, characterized in that the discharge zone 10 is designed so that a gas velocity results which causes the removal of at least 50% of the silicon powder 20 produced by the homogeneous decomposition of the silane-containing gas stream. 21. The method according to any one of claims 17 to 20, characterized in that the loss of discharge of silicon particles 12 , 16 from the fluidized bed 14 makes up less than 10% of the silicon particles of the fluidized bed. 22. The method according to any one of claims 17 to 21, characterized in that the discharge zone 10 has a diameter in the range of 17.8 cm to 25.4 cm (7 "to 10"). 23. The method according to any one of claims 17 to 22, characterized in that the fluidizing gas velocity through the discharge zone 10 is in the range of 3 cm / s to 146 cm / s (0.1 '/ s to 4.8' / s). 24. Fluidized bed reactor for the production of polycrystalline silicon of high purity by introducing a silane-containing gas stream into a reaction zone of fluidized silicon particles with an average diameter in the range from 50 μm to 400 μm, the silane-containing gas at a temperature in the range from 550 ° C. to 1000 ° C is decomposed in the reaction zone 14 to silicon, which is deposited on the silicon particles 12 , whereby the silicon particles 12 enlarge and the enlarged silicon particles 16 with an average diameter in the range of 400 microns to 1300 microns as silicon product particles 16 near the bottom of the Separate reaction zone 14 in a collecting zone 17 , and in which a discharge zone 10 is arranged above reaction zone 14 , which discharge zone has a cross-sectional area perpendicular to the direction of the silane-containing gas stream which is smaller than or equal to the cross-sectional area of reaction zone 14 perpendicular t to the direction of the silane-containing gas flow, characterized in that the fluidizing gas velocity is in the range from 3 cm / s to 146 cm / s (0.1 ′ / s to 4.8 ′ / s), the fluidizing gas velocity being the distance of at least 50% of the silicon powder 20 produced by the homogeneous decomposition of the silane-containing gas stream is effected, but is not sufficient to discharge a significant amount of silicon particles 12 , 16 . 25. fluidized bed according to claim 24, characterized, that the silane-containing gas is silane. 26. Fluidized bed according to claim 24, characterized in that the discharge loss on silicon particles 12 , 16 of the fluidized bed 14 makes up less than 70% of the silicon particles of the fluidized bed. 27. A process for producing high purity polycrystalline silicon by pyrolysis of gas containing silane in a fluidized bed reaction zone from silicon particles, which process comprises:

• (a) introducing a silane-containing gas stream into the reaction zone 14 made of fluidized silicon particles 12 with an average diameter in the range from 50 µm to 400 µm;
• (b) the heterogeneous decomposition of the silane-containing gas at a temperature in the range of 550 ° C to 1000 ° C, wherein the product silicon of the heterogeneous decomposition is deposited on the silicon particles 12 , whereby the silicon particles 12 enlarge and as silicon product particles 16 with an average diameter deposit in the range from 400 µm to 1000 µm in a collection zone 17 ;
• (c) recovering the silicon product particles 16 from the collection zone 17 ; and
• (d) separating silicon powder particles 20 produced by the homogeneous decomposition of the silane-containing gas stream and having an average diameter of up to approximately 1 μm from the silicon particles 12 , 16 by passing the fluidizing gas stream through a discharge zone 10 with a cross-sectional area perpendicular to the direction of the silane-containing gas stream, which is less than or equal to the cross-sectional area of the reaction zone perpendicular to the direction of the silane-containing gas stream; The discharge zone 10 is characterized by a fluidization gas velocity in the range from 3.0 cm / s to 146 cm / s (0.1 ′ / s to 4.8 ′ / s) and the fluidization gas velocity by the removal of at least 50% of the causes the homogeneous decomposition of the silane-containing gas stream generated silicon powder 20 , but is not sufficient to discharge a significant amount of silicon particles 12 , 16 .

28. The method according to claim 27, characterized, that the silane-containing gas is silane. 29. The method according to claim 27 or 28, characterized in that the discharge loss on silicon particles 12 , 16 of the fluidized bed 14 makes up less than 70% of the silicon particles of the fluidized bed. 30. The method according to claim 17 or 27, characterized in that the discharge zone 10 has a cross-sectional area perpendicular to the direction of the silane-containing gas stream, which is smaller than the cross-sectional area of the reaction zone perpendicular to the direction of the silane-containing gas stream. 31. Fluidized bed reactor according to claim 1 or 24, characterized in that the discharge zone 10 has a cross-sectional area perpendicular to the direction of the silane-containing gas stream, which is smaller than the cross-sectional area of the reaction zone 14 perpendicular to the direction of the silane-containing gas stream.