WO2007094607A1 - Method for preparing granular polycrystalline silicon using fluidized bed reactor - Google Patents

Abstract

The present invention relates to a method for mass preparation of granular polycrystalline silicon in a fluidized bed reactor, comprising (a) a reactor tube, (b) a reactor shell encompassing the reactor tube, (c) an inner zone formed within the reactor tube, where a silicon particle bed is formed and silicon deposition occurs, and an outer zone formed in between the reactor shell and the reactor tube, which is maintained under an inert gas atmosphere, and (d) a controlling means to keep the pressure difference between the inner zone and the outer zone being maintained within the range of 0 to 1 bar, thereby capable of maintaining physical stability of the reactor tube and efficiently preparing granular polycrystalline silicon even at a relatively high reaction pressure.

Description

METHOD FOR PREPARING GRANULAR POLYCRYST ALLINE SILICON USING FLUIDIZED BED REACTOR

[TECHNICAL FIELD]

The present invention relates to a method for mass production of granular

polycrystalline silicon using a fluidized bed reactor that can be maintained stable

during a long-term operation even at a relatively high pressure.

[TECHNICAL PROBLEM]

Generally, high-purity polycrystalline silicon is used as a basic material for

manufacturing semiconductor devices or solar cells. The polycrystalline silicon is

prepared by thermal decomposition and/ or hydrogen reduction of a highly-purified

silicon atom-containing reaction gas, thereby allowing continuous deposition of

silicon on silicon particles.

For mass production of polycrystalline silicon, a bell-jar type reactor has been

mainly used, which provides a rod-type polycrystalline silicon product with a

diameter of about 50-300 mm. However, the bell-jar type reactor, which consists

fundamentally of the electric resistance heating system, cannot be operated

continuously due to inevitable limit in extending the maximum rod diameter

achievable. This reactor is also known to have serious problems of low deposition

efficiency and high electrical energy consumption because of limited silicon surfaces

and high heat loss.

Alternatively, a fluidized bed reactor has recently been developed to prepare granular polycrystalline silicon with a size of 0.5-3 mm. According to this method,

a fluidized bed of silicon particles is formed by the upward flow of a gas and the size

of the silicon particles increases as the silicon atoms deposit on the particles from the

silicon atom-containing reaction gas supplied to the heated fluidized bed.

As in the conventional bell-jar type reactor, the fluidized bed reactor also uses

a silane compound of Si-H-Cl system such as monosilane (SiH₄), dichlorosilane

(SiHaQ₂), trichlorosilane (S1HCI3), silicon tetrachloride (SiCl₄) or its mixture as the

silicon atom-containing reaction gas, which usually further comprises hydrogen,

nitrogen, argon, helium, etc.

For the silicon deposition, the reaction temperature (i.e., temperature of the

silicon particles) should be maintained high. The temperature should be about

600-850 °C for monosilane, and about 900-1,100 °C for trichlorosilane, which is most

widely used.

The process of silicon deposition, which is caused by thermal decomposition

and/ or hydrogen reduction of a silicon atom-containing reaction gas, includes

various elementary reactions, and there are complex routes where silicon atoms

grow into granular particles depending on the reaction gas. However, regardless

of the kind of the elementary reaction and the reaction gas, the operation of the

fluidized bed reactor is able to provide a granular polycrystalline silicon product.

Here, smaller silicon particles, i.e., seed crystals become bigger in size due to

continuous silicon deposition or the agglomeration of silicon particles, thereby

losing fluidity and moving downwards eventually. The seed crystals may be prepared or generated in situ in the fluidized bed itself, or supplied into the reactor

continuously, periodically or intermittently. Thus prepared bigger particles, i.e.,

polycrystalline silicon product, may be discharged from the lower part of the reactor

continuously, periodically or intermittently.

Due to the relatively high surface area of the silicon particles, the fluidized

bed reactor system provides a higher reaction yield than that by the bell-jar type

reactor system. Further, the granular product may be directly used without a

further processing for the following-up processes such as single crystal growth,

crystal block or film production, surface treatment and modification, preparation of

chemical materials for reaction or separation, or molding or pulverization of silicon

particles. Although these follow-up processes have been operated in a batchwise

manner, the manufacture of the granular polycrystalline silicon allows the processes

to be performed in a semi-continuous or continuous manner.

The increase in the productivity of the fluidized bed reactor is required for

low-cost manufacture of granular polycrystalline silicon. For this purpose, it is

most effective to increase the silicon deposition rate with low specific energy

consumption, which can be obtained by continuous operation of the fluidized bed

reactor under high pressures. For continuous operation of the process with the

fluidized bed reactor, it is essential to secure the physical stability of the reactor

components.

Unlike conventional fluidized bed reactors for preparing common chemical

products, serious limitations are encountered in material selection of the components of the fluidized bed reactor for preparing polycrystalline silicon.

Especially, considering the desired high purity of the polycrystalline silicon, the

material selection of the fluidized bed wall is important. The reactor wall is weak

in physical stability because it is always in contact with silicon particles fluidizing at

high temperatures, and is subject to the irregular vibration and severe shear stress

caused by the fluidized bed of the particles. However, it is very difficult to select

an appropriate material among the high-purity non-metallic inorganic materials that

are capable of enduring a relatively high pressure condition, because a metallic

material is not appropriate because of high reaction temperature and chemical

properties of the reaction gas. For this reason, the fluidized bed reactor for

manufacture of polycrystalline silicon inevitably has a complex structure. It is

therefore common that a reactor tube made of quartz is positioned in an electrical

resistance heater for heating the silicon particles, and both the reactor tube and the

heater are surrounded by a metallic shell. It is preferred to fill an insulating

material in between the heater and the reactor shell or outside the reactor shell to

reduce heat loss.

For example, U.S. patent no. 5,165,908 discloses a reactor system where an

electric resistance heater encloses a reactor tube made of quartz, both of which are

protected by a jacket-shaped stainless-steel shell and an insulating material is

installed outside the shell.

U.S. patent no. 5,810,934 discloses a fluidized bed reactor for manufacture of

polycrystalline silicon, comprising a reactor vessel, i.e., the reactor tube defining a fluidized bed; a shroud, i.e., a protection tube surrounding the reactor tube; a heater

installed outside the shroud; and an outer containment surrounding the heater and

an insulating material. This patent emphasizes that the protection tube made of

quartz be installed in between the reactor tube and the heater to prevent the crack of

the reactor tube and the contamination of its inner space.

Meanwhile, the fluidized bed reactor for manufacture of polycrystalline

silicon may have a different structure depending on the heating method.

For example, U.S. patent no. 4,786,477 discloses a method of heating silicon

particles with microwave penetrating through the quartz reactor tube instead of

applying a conventional heater outside the tube. However, this patent still has a

problem of a complex structure of the reactor and fails to disclose how to increase

the reaction pressure inside the quartz reactor tube.

To solve the above problem, U.S. 5,382,412 discloses a simple-structured

fluidized bed reactor for manufacture of polycrystalline silicon, wherein a

cylindrical reactor tube is hold vertically by a metallic reactor shell. However, this

patent still has problems that the inner pressure cannot be increased beyond

atmospheric pressure and the microwave supplying means should be combined

with the reactor shell, thus failing to provide ways to overcome the mechanical

weakness of the reactor tube that is anticipated at high-pressure reaction.

[TECHNICAL SOLUTION]

Therefore, an object of the present invention is to provide an improved method for preparing polycrystalline silicon by stable, long-term operation of a

fluidized bed reactor without being restrained by increase in reaction pressure.

In this respect, the present inventors completed the present invention based

on the experimental result that, if the pressure difference between both sides of the

reactor tube is maintained within a predetermined range, the fluidized bed reactor

might be operated with long-term stability even at high pressures, satisfying various

conditions required for preparing polycrystalline silicon based on the the fluidized

bed process.

Another object of the present invention is to provide a method for preparing

an improved of the fluidized bed reactor which can be applied to high-pressure

operations although being composed of the material acceptable to

atmospheric-pressure operation for preparing polycrystalline silicon.

Still another object of the present invention is to provide a method for

preparing polycrystalline silicon, which allows easy installation of a heating means

for heating silicon particles to a high reaction temperature required for preparing

polycrystalline silicon.

A further object of the present invention is to provide a method for preparing

polycrystalline silicon, which may secure a long-term stability while enduring a

physical stress exerted on the reactor tube by the fluidization of silicon particles.

A still further object of the present invention is to provide a method for

preparing polycrystalline silicon, wherein the stability of a reactor may be secured

despite the exposure of the reactor tube to continuously fluidizing silicon particles at high temperature and pressure.

The present invention also aims to provide a method which can be

conveniently applied to preparing high-purity polycrystalline silicon granules while

minimizing impurity contamination.

[MODE FOR INVENTION]

For accomplishing the aforementioned purposes, the present invention

provides a method for preparing polycrystalline silicon using a fluidized bed reactor,

comprising the following procedures: (a) employing a fluidized bed reactor wherein

a reactor tube is vertically placed within a reactor shell so as to be encompassed by

the reactor shell, whereby dividing an inner space of the reactor shell into an inner

zone formed within the reactor tube and an outer zone formed in between the

reactor shell and the reactor tube, wherein a silicon particle bed is formed and silicon

deposition occurs in the inner zone while a silicon particle bed is not formed and

silicon deposition does not occur in the outer zone; (b) directly or indirectly

measuring and/ or controlling an inner zone pressure using an inner pressure

controlling means, directly or indirectly measuring and/ or controlling an outer zone

pressure using an outer pressure controlling means, and maintaining the difference

between the inner zone pressure and the outer zone pressure within 1 bar using a

pressure-difference controlling means; (c) introducing a fluidizing gas into the

silicon particle bed using a fluidizing gas inlet means; (d) introducing a silicon

atom-containing reaction gas into the silicon particle bed using a reaction gas inlet

means; (e) introducing an inert gas into the outer zone, whereby maintaining a substantially inert gas atmosphere in the outer zone; (f) heating the silicon particle

bed using a heating means installed in the inner zone and/ or the outer zone; (g)

discharging polycrystalline silicon particles prepared within the inner zone to the

outside of the fluidized bed reactor; (h) discharging an off-gas including a fluidizing

gas that passes through the silicon particle bed, a non-reacted reaction gas and a

byproduct gas to the outside of the fluidized bed reactor.

In a preferred embodiment, the reaction gas is a silicon atom-containing gas

selected from the group consisting of monosilane, dichlorosilane, trichlorosilane,

silicon tetrachloride and a mixture thereof.

Optionally, the reaction gas further comprises at least one gas selected from

the group consisting of hydrogen, nitrogen, argon, helium, hydrogen chloride and a

mixture thereof.

In a preferred embodiment, the fluidizing gas is a gas selected from the group

consisting of hydrogen, nitrogen, argon, helium, hydrogen chloride, silicon

tetrachloride and a mixture thereof.

In a preferred embodiment, the inert gas comprises at least one gas selected

from the group consisting of hydrogen, nitrogen, argon and helium.

In a preferred embodiment, the outer zone pressure (Po) or the inner zone

pressure (Pi) is maintained within the range of 1-15 bar.

In particular, the outer zone pressure (Po) may be controlled in the range of

between maximum and minimum pressure values measurable in the inner zone.

Meanwhile, the difference between the outer zone pressure (Po) and the inner zone pressure (Pi) is maintained to satisfy the condition of 0 bar < (Pi - Po) < 1 bar,

when the inner pressure controlling means is spatially connected to the inner zone

through at least one means selected from the group consisting of a fluidizing gas

inlet means, a reaction gas inlet means, a silicon particle outlet means and an inner

zone connecting means, which are spatially connected to the the silicon particle bed.

In contrast, the difference between the outer zone pressure (Po) and the inner

zone pressure (Pi) is maintained so as to satisfy the condition of 0 bar < (Po - Pi) ≤ 1

bar, when the inner pressure controlling means is spatially connected to the inner

zone through at least one means selected from the group consisting of a gas outlet

means, a silicon seed crystals inlet means and an inner zone connecting means,

which are spatially connected to an upper part of the inner zone instead of the

silicon particle bed.

In a preferred embodiment, a pressure controlling condition of the

pressure-difference controlling means comprised in the inner pressure controlling

means and/ or the outer pressure controlling means is determined based on gas

analysis of the gas that is present within or discharged out of the inner zone and/ or

the outer zone by using a gas analyzing means.

In a preferred embodiment, a packed bed of packing materials, which are not

fluidized by the flow of the fluidizing gas, is formed in a lower part of the silicon

particle bed with the height of the packed bed being positioned below the outlet of

the reaction gas inlet means through which the reaction gas is introduced into the

silicon particle bed. Referring to the Drawings herein there is provided a detailed description of

the present invention hereunder.

For preparing polycrystalline silicon according to the present invention it is

required to employ a fluidized bed reactor as schematically shown in Figure 1,

wherein a reactor tube is encompassed by a reactor shell so that the space inside the

reactor shell can be divided into an inner zone and an outer zone by the reactor tube.

In accordance with the primary aspect of the present invention, the pressure

difference between the two zones is maintained within 1 bar during the operation of

the reactor.

That is, a reactor tube 2 is vertically placed within a reactor shell 1 to be

encompassed by the reactor shell 1, whereby dividing an inner space of the reactor

shell 1 into an inner zone 4 formed within the reactor tube 2 and an outer zone 5

formed in between the reactor shell 1 and the reactor tube 2, wherein a bed of silicon

particles 3, i.e., a silicon particle bed is formed and silicon deposition occurs in the

inner zone while a silicon particle bed is not formed and silicon deposition does not

occur in the outer zone. Then, polycrystalline silicon is prepared according to the

present invention by emplying the fluidized bed reactor and maintaining the

difference between the inner zone pressure and the outer zone pressure within 1 bar.

Based on this method, granular polycrystalline silicon may be prepared by

directly or indirectly measuring and/ or controlling an inner zone pressure using an

inner pressure controlling means, directly or indirectly measuring and/ or

controlling an outer zone pressure using an outer pressure controlling means, and maintaining the difference between the inner zone pressure and the outer zone

pressure within 1 bar by means of controlling pressure difference.

In addition, granular polycrystalline silicon may be prepared by introducing

a fluidizing gas into the silicon particle bed using a fluidizing gas inlet means;

introducing a silicon atom-containing reaction gas into the silicon particle bed using

a reaction gas inlet means; introducing an inert gas into the outer zone 5, whereby

maintaining a substantially inert gas atmosphere in the outer zone 5; discharging

polycrystalline silicon particles prepared within the inner zone 4 to the outside of the

fluidized bed reactor; and discharging an off-gas including a fluidizing gas that

passes through the silicon particle bed, a non-reacted reaction gas and a byproduct

gas to the outside of the fluidized bed reactor.

First, hereunder is provided a detailed description about how to constitute

the fluidized bed reactor to be employed for the process according to the present

invention.

Figures 2 and 3 are cross-sectional views of the high-pressure fluidized bed

reactor for preparing granular polycrystalline silicon, in which some of the

embodiments according to the present invention are illustrated in a comprehensive

way.

The structure of the fluidized bed reactor employed in to the present

invention is composed of a reactor tube and a reactor shell. An inner space of the

fluidized bed reactor here is separated from an outer space. The reactor shell 1

encompasses the reactor tube 2 that is substantially vertically placed within the reactor shell 1. The reactor tube 2 divides an inner space of the reactor shell 1 into

an inner zone 4 formed within the reactor tube 2 and an outer zone 5 formed in

between the reactor shell 1 and the reactor tube 2, wherein a silicon particle bed is

formed and silicon deposition occurs in the inner zone 4 while a silicon particle bed

is not formed and silicon deposition does not occur in the outer zone 5.

The reactor shell 1 is preferably made of a metallic material with reliable

mechanical strength and processability such as carbon steel, stainless steel or other

alloy steels. The reactor shell 1 may be divided into a plurality of components such

as Ia, Ib, Ic and Id as set forth in Figures 2 and 3 for convenience in fabrication,

assembly and disassembly.

It is important to assemble the components of the reactor shell 1 by using

gaskets or sealing materials for complete sealing. The components may have

various structures of a cylindrical pipe, a flange, a tube with fittings, a plate, a cone,

an ellipsoid and a double-wall jacket with a cooling medium flowing in between the

walls. The inner surface of each component may be coated with a protective layer

or be installed with a protective tube or wall, which may be made of a metallic

material or a non-metallic material such as organic polymer, ceramic and quartz.

Some of the components of the reactor shell 1, illustrated as Ia, Ib, Ic and Id

in Figures 2 and 3, are preferably maintained below a certain temperature by using a

cooling medium such as water, an oil, a gas and air for protecting the equipment or

operators, or for preventing any thermal expansion in equipment or a safety

accident. Although not set forth in Figures 2 and 3, the components that need to be cooled may preferably be equipped with a coolant-circulating means at their inner

or outer walls. Instead of cooling, the reactor shell 1 may comprise an insulating

material on the outer wall.

The reactor tube 2 may be of any shape only if it can be hold by the reactor

shell 1 in such a manner that it can separate the inner space of the reactor shell 1 into

an inner zone 4 and an outer zone 5. The reactor tube 2 may be of a structure of a

simple straight tube as in Figure 2, a shaped tube as in Figure 3, a cone or an

ellipsoid, and either one end or both ends of the reactor tube 2 may be formed into a

flange shape. Further, the reactor tube 2 may comprise a plurality of components

and some of these components may be installed in the form of a liner on the inner

wall of the reactor shell 1.

The reactor tube 2 is preferred to be made of an inorganic material, which is

stable at a relatively high temperature, such as quartz, silica, silicon nitride, boron

nitride, silicon carbide, graphite, silicon, glassy carbon or their combination.

Meanwhile, a carbon-containing material such as silicon carbide, graphite,

glassy carbon may generate carbon impurity and contaminate the polycrystalline

silicon particles. Thus, if the reactor tube 2 is made of a carbon-containing material,

the inner wall of the reactor tube 2 is preferred to be coated or lined with materials

such as silicon, silica, quartz or silicon nitride. Then, the reactor tube 2 may be

structured in a multi-layered form. Therefore, the reactor tube 2 is of one-layered or

multilayered structure in the thickness direction, each layer of which is made of a

different material. Sealing means 41a, 41b may be used for the reactor shell 1 to safely hold the

reactor tube 2. The sealing means are preferred to be stable at a temperature of

above 200 ⁰C and may be selected from organic polymer, graphite, silica, ceramic,

metal or their combination. However, considering the vibration and thermal

⁵ expansion during reactor operation, the sealing means 41a, 41b may be installed less

firmly to lower the possibility of cracking of the reactor tube 2 in the course of

assembly, operation and disassembly.

The partition of the inner space of the reactor shell 1 by the reactor tube 2 may

prevent the silicon particles in the inner zone 4 from leaking into the outer zone 5

^w and differentiate the function and condition between the inner zone 4 and the outer

zone 5.

In addition to the process for preparing granular polycrystalline silicon

according to present invention as described above, it is required for carrying out a

high-temperature silicon deposition reaction to heat silicon particles in the silicon

¹^ bed by a heating means installed in the inner zone 4 and/ or the outer zone 5. One or

a plurality of heating means 8a, 8b may be installed in the inner zone 4 and/ or the

outer zone 5 in various manner. For example, a heating means may be installed

only in the inner zone 4 or in the outer zone 5 as illustrated in Figure 2 in a

comprehensive manner. Meanwhile, a plurality of heating means may be installed in

²⁰ both zones, or only in the outer zone 5 as illustrated in Figure 3. Besides, although

it is not illustrated in Drawings, a plurality of heating means 8a, 8b may be installed

only in the inner zone 4. Otherwise, a single heating means may be installed in the outer zone 5 only.

The electric energy is supplied to the heating means 8a, 8b through an electric

energy supplying means 9a-9f installed on or through the reactor shell 1. The

electric energy supplying means 9a-9f, which connects the heating means 8a, 8b in

the reactor and an electric source E outside the reactor, may comprise a conductive

metallic component in the form of a cable, a bar, a rod, a shaped body, a socket or a

coupler. Otherwise the electric energy supplying means 9a-9f may comprise an

electrode that is made of a material such as graphite, ceramic (e.g., silicon carbide),

metal or a mixture thereof, and is fabricated in various shapes for connecting the

electric source E with the heating means. Alternatively, the electric energy

supplying means can be prepared by extending a part of the heating means 8a, 8b.

In combining the electric energy supplying means 9a-9f with the reactor shell 1,

electrical insulation is also important besides the mechanical sealing for preventing

gas leak. Further, it is desirable to cool down the temperature of the electric energy

supplying means 9 by using a circulating cooling medium such as water, an oil and

a gas.

Meanwhile, a gas inlet means should be installed at the fluidized bed reactor

to form a fluidized bed, where silicon particles can move by gas flow, within the

reactor tube 2, i.e., in a lower part of the inner zone 4, for preparation of

polycrystalline silicon by the silicon deposition on the surface of the fluidizing

silicon particles.

The gas inlet means comprises a fluidizing gas inlet means 14, 14' for introducing a fluidizing gas 10 into the silicon particle bed and a reaction gas inlet

means 15 for introducing a silicon atom-containing reaction gas the silicon particle

bed, both of which are installed in combination with the reactor shell Ib.

In this respect, granular polycrystalline silicon may be prepared according to

the present invention by introducing a fluidizing gas 10 into the silicon particle bed

using a fluidizing gas inlet means 14, 14', and introducing a silicon atom-containing

reaction gas 11 into the silicon particle bed using a reaction gas inlet means 15.

As used herein, "a fluidizing gas" 10 refers to a gas introduced to cause some

or most of the silicon particles 3 to be fluidized in the fluidized bed formed within

the inner zone 4. In the present invention, hydrogen, nitrogen, argon, helium,

hydrogen chloride (HCl), silicon tetrachloride (SiC14) or a mixture thereof may be

used as the fluidizing gas 10.

As used herein, "a reaction gas" 11 refers to a source gas containing silicon

atoms, which is used to prepare the polycrystalline silicon particles. In the present

invention, monosilane (SiH₄), dichlorosilane (SiH₂Cb), trichlorosilane (SiHCIs),

silicon tetrachloride (SiCl₄) or a mixture thereof may be used as the

silicon-containing reaction gas 11. The reaction gas 11 may further comprise at

least one gas selected from hydrogen, nitrogen, argon, helium and hydrogen

chloride. Further, in addition to serving as a source for silicon deposition, the

reaction gas 11 contributes to the fluidization of the silicon particles 3 as the

fluidizing gas 10 does.

The fluidizing gas inlet means 14, 14' and the reaction gas inlet means 15 may comprise a tube or nozzle, a chamber, a flange, a fitting, a gasket, etc, respectively.

Among these components, the parts exposed to the inner space of the reactor shell 1,

especially to the lower part of the inner zone 4, where the parts are likely to contact

the silicon particles 3, are preferred to be made of a tube, a liner or a shaped article

the material of which is selected from those applicable to the reactor tube 2.

Optionally, the lower part of the fluidized bed 4a in the inner zone 4 may

comprise an additional gas distributing means 19 for distributing the fluidizing gas

10 in combination with the fluidizing gas inlet means 14, 14' and the reaction gas

inlet means 15. The gas distributing means 19 may have any geometry or structure

including a multi-hole or porous distribution plate, a packed bed of packing

materials submerged in the particle bed, a nozzle or a combination thereof. When

the gas distributing means 19 is additionally employed, its component, like the

upper surface of the gas distributing means 19, which is likely to contact the silicon

particles 3, is preferably made of an inorganic material that can be used for the

reactor tube 2. To prevent silicon deposition on the upper surface of the gas

distributing means 19, the outlet of the reaction gas inlet means 15, through which a

reaction gas 11 is injected into the interior of the fluidized bed, is preferably

positioned higher than the upper part of the gas distributing means 19.

In the reactor inner zone 4, the fluidizing gas 10, which is required to form the

fluidized bed 4a of silicon particles, may be supplied in various ways depending on

how the fluidizing gas inlet means 14, 14' is constituted. For example, as illustrated

in Figure 2, the fluidizing gas 10 may be supplied by a fluidizing gas inlet means 14, 14' coupled with the reactor shell 1 so that a gas chamber may be formed in lower

part of the distribution plate-shaped gas distributing means 19. Alternatively, as

illustrated in Figure 3, a fluidizing gas 10 may be supplied by a fluidizing gas inlet

means 14 coupled with the reactor shell 1 so that one or a plurality of fluidizing gas

^ nozzle outlet may be positioned in between the gas distributing means 19 that

comprises a third packed bed of packing materials other than those fluidizing silicon

particles. Meanwhile, the gas distributing means 19 and the fluidizing gas inlet

means 14, 14' may be constituted by using both the distribution plate and the

packing materials.

¹⁰ As an example, in addition to the distribution plate and/ or the nozzle (s) for

introducing the fluidizing gas 10, it is possible to employ a packed bed of packing

materials other than the silicon particles 3 to be included in the silicon product

particles 3b. The packing materials may have a sufficient size or mass, so as not to be

fluidized by the flow of the fluidizing gas 10, and may be shaped like a sphere, an

^I^ ellipsoid, a pellet, a nugget, a tube, a rod, or a ring, etc. The packing materials

composition may be selected from those applicable to the reactor tube 2 as well as

high-purity silicon, with their average size being within the range of 5-50 mm.

When employed as a gas distributing means 19, the packed bed of packing

materials, which are not fluidized by the flow of the fluidizing gas 10, may

²⁰ preferably be formed in a lower part of the silicon particle bed with the height of the

packed bed being positioned below the outlet of the reaction gas inlet means 15

through which the reaction gas 11 is introduced into the silicon particle bed. In this case, the movement of silicon particles and the flow of the fluidizing gas may occur

in the space formed between the packing materials, while the heat transferred

downward from the fluidized bed of silicon particles 3 heated by the heating means

being utilized for preheating the upcoming fluidizing gas 10.

In the present invention, the polycrystalline silicon particles are prepared in

the inner zone 4 of the reactor based on the silicon deposition. Following the supply

of the reaction gas 11 through the reaction gas inlet means 15, the silicon deposition

occurs on the surface of the silicon particles 3 heated by the heating means 8a, 8b.

In addition, granular polycrystalline silicon may be prepared by discharging

polycrystalline silicon particles prepared within the inner zone 4 to the outside of the

fluidized bed reactor.

A particle outlet means 16 is also required to be combined with the reactor

shell 1 to discharge thus prepared silicon particles from the inner zone 4 to the

outside of the fluidized bed reactor.

An outlet pipe, which constitutes the particle outlet means 16, may be

assembled with the reaction gas inlet means 15 as illustrated in Figure 2.

Alternatively, it may be installed independently of the reaction gas inlet means 15 as

illustrated in Figure 3. Through the particle outlet means 16 the silicon particles 3b

may be discharged when required from the fluidized bed 4a in a continuous,

periodic, or intermittent way.

As illustrated in Figure 2, an additional zone may be combined with the

reactor shell 1. The additional zone can be provided at some part or a lower part of the fluidizing gas inlet means 14', allowing a space for the silicon particles 3b to

reside or stay with an opportunity of cooling before being discharged from the

reactor.

Silicon particles 3, i.e., silicon particles 3 discharged from the inner zone 4 to

the outside of the reactor according to the present invention, may be delivered to a

storage member or a transfer member of the polycrystalline silicon product, which is

directly connected to the reactor. Meanwhile, thus-prepared silicon product

particles 3b may have a particle-size distribution due to nature of the fluidized bed

reactor, and smaller particles included therein may be used as seed crystals 3a for

the silicon deposition. It is thus possible that the silicon product particles 3b

discharged from the inner zone 4 to the outside of the reactor may be delivered to a

particle separation member where the particles can be separated by size. Then the

larger particles may be delivered to the storage member or the transfer member,

while the smaller particles are used as seed crystals 3a.

Otherwise, considering the relatively high-temperature of the silicon particle

bed 4a within the inner zone 4, the silicon particles 3b are preferred to be cooled

down while being discharged through the particle outlet means 16. For this

purpose, a cooling gas such as hydrogen, nitrogen, argon, helium, or a mixture

thereof may flow in the particle outlet means 16, or a cooling medium such as water,

oil or gas may be circulated through the wall of the particle outlet means 16.

Alternatively, although it is not illustrated in Drawings, the particle outlet

means 16 may be constituted in combination with the inner space of the reactor shell 1 (e.g. 14' in Figure 2) or a lower part of the reactor shell (e.g., Ib in Figures 2 and 3),

allowing a sufficient space for the silicon particles 3b to reside or stay with an

opportunity of cooling for a certain period of time before being discharged to the

outside of the reactor.

It is necessary to prevent the silicon product particles 3b from being

contaminated while discharged from the reactor through the the particle outlet

means 16. Therefore, in constituting the particle outlet means 16, the elements that

may contact high-temperature silicon product particles 3b may be made of a tube, a

liner or a shaped product that is made of or coated with an inorganic material

applicable to the reactor tube 2. These elements of the particle outlet means 16 are

preferred to be coupled to the metallic reactor shell and/ or a protection pipe.

The components of the particle outlet means 16, which are in contact with the

relatively low-temperature product particles or comprise a cooling means on their

wall, may be made of a metal-material tube, a liner or a shaped product, the inner

wall of which is coated or lined with a fluorine-containing polymer material.

As mentioned above, the silicon product particles 3b may be discharged from

the inner zone 4 in the reactor through the particle outlet means 16 to a storage

member or a transfer member of the polycrystalline silicon product in a continuous,

periodic, or intermittent way.

Meanwhile, a particle separation member may be installed in between the

reactor and the product storage member, to separate the silicon product particles 3b

by size and use small-sized particles as seed crystals 3a. Various commercial devices may be used as the particle separation member in the present invention.

It is desirable to constitute the elements of the particle separation member,

which may be in contact with the silicon product particles 3b, by using the same

material as the one used in the particle outlet means 16, or pure polymer material

that does not contain either an additive or a filler.

For continuous operation of the fluidized bed reactor, it is necessary to

combine the reactor shell Id with a gas outlet means 17 which is installed for

discharging an off-gas from the fluidized bed reactor. The off-gas 13 comprises a

fluidizing gas that passes through the silicon particle bed, a non-reacted reaction gas

and a byproduct gas, passes through the upper part of the inner zone, 4c, and is

finally discharged to the outside of the fluidized bed reactor.

Fine silicon particles or high-molecular-weight byproducts entrained in the

off-gas 13 may be separated from an additional off-gas treating means 34.

As illustrated in Figures 2 and 3, an off-gas treating means 34, which

comprises a cyclone, a filter, a packed column, a scrubber or a centrifuge, may be

installed outside the reactor shell 1 or at the upper zone 4c of the inner zone within

the reactor shell 1.

Fine silicon particles, thus separated from the off-gas treating means 34, may

be used for another purpose, or as seed crystals 3a for preparing silicon particles

after being recycled into the fluidized bed 4a at the inner zone of the reactor.

When manufacturing silicon particles in a continuous manner, it is preferred

to maintain the number and the average particle size of the silicon particles, which forms the fluidized bed 4a, within a certain range. This may be obtained by

supplementing nearly the same number of the seed crystals within the fluidized bed

4a as that of the discharged silicon product particles 3b.

As mentioned above, the fine silicon particles or powders separated from the

off-gas treating means 34 may be recycled as seed crystals, but their amount can not

be sufficient. It is then required to further yield, generate or prepare additional

silicon seed crystals for continuous preparation of the silicon particles as required in

the fluidized bed.

In this regard, it may be necessary to further separate the smaller silicon

particles among the silicon product particles 3b and use them as seed crystals 3a.

However, the additional process for separating seed crystals 3a from the product

particles 3b outside the fluidized bed reactor has drawbacks of high chances of

contamination and difficulties in operation.

Instead of the additional separation of product particles 3b, it is also possible

to separate smaller particles out of them and to recycle the smaller particles as seed

crystals into the fluidized bed. To this purpose an additional particle separation

member may be installed in the middle of a discharge path included in the particle

outlet means 16. Supplying a gas into the pathway in a counter-current manner

leads to cooling of the product particles 3b, separatioin of smaller particles out of

them and recycling of the smaller particles into the fluidized bed 4a. This reduces the

burden of preparing or supplying seed crystals, and increases the average particle

size of the final silicon product particles 3b while decreasing their particle size distribution.

As another embodiment, the silicon seed crystals may be prepared by

pulverizing some of silicon product particles 3b discharged through the particle

outlet means 16 into seed crystals in a separate pulverizing apparatus. Thus

prepared seed crystals 3a may be introduced into the inner zone 4 of the reactor in a

continous, periodic or intermittently way as required. One example when seed

crystals 3a is downwardly introduced into the inner zone 4 is illustrated in Figure 2,

where a seed crystals inlet means 18 is combined with the topside of the reactor shell

Id. This method allows an efficient control in the average size and the feeding rate

of seed crystals 3a as required, while it has a drawback of requiring an additional

pulverizing apparatus.

On the contrary, silicon particles may be pulverized into seed crystals inside

fluidized bed 4a by using an outlet nozzle of a reaction gas inlet means 15 combined

with the reactor shell or an additionally installed gas nozzle for a high-speed gas jet

inside the fluidized bed allowing particle pulverization. This method has an

economic advantage because it needs no additional pulverizing device, while having

a drawback that it is difficult to control the size and the amount of the seed crystals

being generated in the reactor within a predetermined acceptable range.

In the present invention, the inner zone 4 comprises all spaces required for

forming a silicon particle bed 4a, introducing a fluidizing gas 10 and a reaction gas

11 into the silicon particle bed 4a, allowing silicon deposition, and discharging the

off-gas 13 containing a fluidizing gas, a non-reacted reaction gas and a byproduct gas. Therefore, the inner zone 4 plays a fundamental role for silicon deposition in

the fluidized bed of silicon particles 3 and preparation of polycrystalline silicon

product particles.

In contrast to the inner zone 4, the outer zone 5 is an independently formed

^ space in between the outer wall of the reactor tube 2 and the reactor shell 1, where a

silicon particle bed 3 is not formed and silicon deposition does not occur because the

reaction gas is not supplied therein. Therefore, the outer zone 5 may be defined as

the inner space within the reactor shell 1 excluding the inner zone or the space

formed in between the reactor shell 1 and the reactor tube 2.

0 In addition to the above-mentioned embodiments according to the present

invention, granular polycrystalline silicon may be prepared by introducing an inert

gas into the outer zone 5, whereby maintaining a substantially inert gas atmosphere

in the outer zone 5.

The importance and roles of the outer zone 5 maintained in an inert gas

5 atmospher according to the present invention may be summarized as follows.

First, the outer zone 5 provides a space for protecting the reactor tube 2 by

maintaining pressure difference between the inner zone 4 and the outer zone 5

within a certain range.

Second, the outer zone 5 provides a space for installing an insulating material

^ 6 that prevents or decreases heat loss from the reactor.

Third, the outer zone 5 provides a space for a heater to be installed around the

reactor tube 2. Fourth, the the outer zone 5 provides a space for maintaining a substantially

inert gas atmosphere outside the reactor tube 2 to prevent dangerous gas containing

oxygen and impurities from being introduced into the inner zone 4, and for safely

installing and maintaining the reactor tube 2 inside the reactor shell 1.

Fifth, the outer zone 5 allows a real-time monitoring of the status of the

reactor tube 2 during operation. The analysis or measurement of the outer-zone gas

sample from the outer zone connecting means 28 may reveal the presence or

concentration of a gas component that may exist in the inner zone 4, the change of

which may indirectly reveal an accident at the reactor tube.

Sixth, the outer zone 5 provides a space for installing a heater 8b surrounding

the reactor tube 2, as illustrated in Figure 3, for heating up and chemically removing

the silicon deposit layer accumulated on the inner wall of the reactor tube 2 due to

silicon deposition operation.

Lastly, the outer zone 5 provides a space required for efficient assembly or

disassembly of the reactor tube 2 and the inner zone 4.

According to the present invention, the outer zone 5 plays many important

roles as mentioned above. Thus, the outer zone may be partitioned into several

sections in an up-and-down and/ or a radial or circumferential direction, utilizing

one or more of tubes, plates, shaped articles or fittings as partitioning means.

When the outer zone 5 is further partitioned according to the present

invention, the divided sections are preferred to be spatially communicated with each

other while having substantially the same atmospheric condition and pressure. An insulating material 6, which may be installed in the outer zone 5 for

greatly reducing heat transfer via radiation or conduction, may be selected from

industrially acceptable inorganic materials in the form of a cylinder, a block, fabric, a

blaneket, a felt, a foamed product, or a packing filler material.

The heating means 8a, 8b, connected to an electric energy supplying means 9,

which is connected to the reactor shell for maintaining reaction temperature in the

fluidized bed reactor, may be installed in the outer zone 5 only, or installed alone

within the inner zone 4, especially within the silicon particle bed 4a. The heating

means 8a, 8b, may be installed in both the inner zone 4 and the outer zone 5, if

required, as illustrated in Figure 2. Figure 3 illustrates an example when a plurality

of independent heating means 8a, 8b are installed in the outer zone 5.

When a plurality of heating means 8a, 8b are installed in the fluidized bed

reactor, they may be electrically connected in series or parallel relative to an electric

source E. Alternatively, the power supplying system comprising an electric source

E and an electric energy supplying means 9a-9f may be constituted independently as

illustrated in Figures 2 and 3.

As illustrated in Figure 2, the heater 8a installed within the silicon particle

bed 4a may have an advantage of directly heating silicon particles in the fluidized

bed. In this case, to prevent accumulative silicon deposition on the surface of the

heater 8a, the heater 8a is preferably positioned lower than the reaction gas outlet of

a reaction gas inlet means 15.

In the present invention, an inert gas connecting means 26a, 26b is installed on the reactor shell, independently of the inner zone 4, to maintain a substantially

inert gas atmosphere in the outer zone 5 precluding silicon deposition. The inert

gas 12 may be one or more selected from hydrogen, nitrogen, argon and helium.

An inert gas connecting means 26a, 26b, which is installed on or through the

reactor shell and spatially connected to the outer zone 5, has the function of piping

connection for supplying or discharging an inert gas 12, and may be selected from a

tube, a nozzle, a flange, a valve, a fitting or a combination thereof.

Meanwhile, apart from the inert gas connecting means 26a, 26b, a reactor

shell, which is spatially exposed to the outer zone 5 directly or indirectly, may be

equipped with an outer zone connecting means 28. Then, the outer zone connecting

means 28 may be used to measure and/ or control temperature, pressure or gas

component. Although even a single inert gas connecting means 26a, 26b may allow

to maintain a substantially inert gas atmosphere in the outer zone 5, the supply or

discharge of an inert gas may be independently performed by using a double-pipe

or a plurality of inert gas connecting means 26a, 26b.

Further, the inert gas connecting means 26a, 26b maintains an independent

inert gas atmosphere in the outer zone 5, and may also be used for measuring

and/ or controlling flow rate, temperature, pressure or gas component, which can

also be performed by using the outer zone connecting means 28.

Figures 2 and 3 provide various examples in a comprehensive way where the

outer zone pressure (Po), i.e., pressure in the outer zone 5 is measured and/ or

controlled by using the inert gas connecting means 26a, 26b or outer zone connecting means 28.

The outer zone connecting means 28 may be installed to measure and/ or

control the maintenance of the outer zone 5, independently of or on behalf of the

inert gas connecting means 26a, 26b. The outer zone connecting means 28 has the

function of piping connection, and may be selected from a tube, a nozzle, a flange, a

valve, a fitting or their combination. If the inert gas connecting means 26a, 26b is not

installed, the outer zone connecting means 28 may be used to supply or discharge an

inert gas 12 as well as to measure or control temperature, pressure or gas component.

Therefore, it is not necessary to differentiate the inert gas connecting means 26a, 26b

from the outer zone connecting means 28 in respect of shape and function.

Meanwhile, unlike the outer zone 5 where pressure may be maintained nearly

constant irrespective of position and time, there exists inevitably a pressure

difference within the inner zone 4 according to the height of the fluidized bed 4a of

silicon particles 3. Thus, the inner zone pressure (Pi), i.e., pressure in the inner zone

4 changes according to the height in the inner zone 4.

Although the pressure drop imposed by the fluidized bed of solid particles

depends on the height of the fluidized bed, it is common to maintain the pressure

drop by fluidized bed less than about 0.5-1 bar unless the height of the fluidized bed

is excessively high. Further, irregular fluctuation of the pressure is inevitable with

time due to the nature of the fluidization of solid particles. Thus, pressure may

vary in the inner zone 4 according to position and time.

Considering these natures, the pressure controlling means for the inner zone pressure (Pi), i.e., the inner pressure controlling means 30 for directly or indirectly

measuring and/ or controlling pressure in the inner zone 4 may be installed at such a

point among various positions that it may be spatially connected to the inner zone 4.

Pressure controlling means according to the present invention, i.e., the inner

pressure controlling means 30 and the outer pressure controlling means 31 may be

installed on or through various positions depending on the details of the reactor

assembly as well as on the operational parameters to be controlled.

The the inner pressure controlling means 30 may be spatially connected to the

inner zone 4 through an inner zone connecting means 24, 25, a fluidizing gas inlet

means 14, a reaction gas inlet means 15, a particle outlet means 16, or a gas outlet

means 17, which are spatially exposed directly or indirectly to the inner zone 4.

Meawhile, the pressure controlling means for the outer zone pressure (Po),

i.e., the outer pressure controlling means 31 may be spatially connected to the outer

zone 5 through an outer zone connecting means 28 or an inert gas connecting means

26a, 26b, etc., which are installed on or through the reactor shell 1 and spatially

exposed directly or indirectly to the outer zone 5.

According to a preferable embodiment of the present invention for preparing

granular poly crystalline silicon, the inner pressure controlling means 30 and/ or the

outer pressure controlling means 31 comprise the components necessary for directly

or indirectly measuring and/ or controlling pressure.

Either of the pressure controlling means, 30 and 31, comprises at least one

selected from the group consisting of: (a) a connecting pipe or fitting for spatial connection; (b) a manually-operated, semi-automatic, or automatic valve; (c) a

digital- or analog-type pressure gauge or pressure-difference gauge; (d) a pressure

indicator or recorder; and (e) an element constituting a controller with a signal

converter or an arithmetic processor.

The inner pressure controlling means 30 is interconnected with the outer

pressure controlling means 31 in the form of a mechanical assembly or a signal

circuit. Further, either of the pressure controlling means may be partially or

completely integrated with a control system selected from the group consisting of a

central control system, a distributed control system and a local control system.

Although the inner pressure controlling means 30 and/ or the outer pressure

controlling means 31 may be independently constituted in terms of pressure, either

of the pressure controlling means may be partially or completely integrated with a

means for measuring and/ or controlling a parameter selected from the group

consisting of flow rate, temperature, gas component and particle concentration, etc.

Meanwhile, either of the controlling means, 30 or 31, may further comprise a

separation device such as a filter or a scrubber for separating particles, or a container

for buffering pressure. This protects the component of the pressure controlling

means from contamination by impurities, and also provides a means to buffer

pressure changes.

As an example, the inner pressure controlling means 30 may be installed at or

connected to the inner zone connecting means 24, 25, which is installed on or

through the reactor shell and is spatially exposed directly or indirectly to an inner zone 4 for measurement of pressure, temperature or gas component or for viewing

inside the reactor. By constituting the inner pressure controlling means 30 so that it

may be connected to the inner zone connecting means 24, 25, pressure in an upper

part of the inner zone 4c may be stably measured and/ or controlled although it is

difficult to detect the time-dependent pressure fluctuation due to the fluidized bed

of silicon paricles. For more accurate detection of the time-dependent pressure

fluctuation related with the fluidized bed, the inner zone connecting means may be

installed so that it may be spatially connected to the inside of the fluidized bed.

The inner pressure controlling means 30 may also be installed at or connected

to other appropriate positions, i.e., a fluidizing gas inlet means 14 or a reaction gas

inlet means 15 or a particle outlet means 16 or a gas outlet means 17, etc., all of

which are combined with the reactor shell thus being spatially connected to the

inner zone 4.

Further, a plurality of inner pressure controlling means 30 may be installed at

two or more appropriate positions which ultimately allow spatial connection with

the inner zone 4 through the inner zone connecting means 24, 25 and/ or those at

other positions.

As mentioned above, the presence of silicon particles affects the inner zone

pressure, Pi. Thus, the measured value of Pi varies according to the position where

the inner pressure controlling means 30 is installed. Following observations by the

present inventors, the value of Pi is influenced by the characteristics of the fluidized

bed and by the structure of a fluidizing gas inlet means 14 or a reaction gas inlet means 15 or a particle outlet means 16 or a gas outlet means 17, but its positional

deviation according to pressure measurement point is normally observed to be not

greater than 1 bar.

Then, the present invention permits to carry out directly or indirectly

measuring and/ or controlling an inner zone pressure using the inner pressure

controlling means 30, directly or indirectly measuring and/ or controlling an outer

zone pressure using an outer pressure controlling means 31, and maintaining the

difference between the inner zone pressure and the outer zone pressure within 1 bar

using the pressure-difference controlling means.

In a preferred embodiment, the outer pressure controlling means 31, for

directly or indirectly measuring and/ or controlling the outer zone pressure, i.e.,

pressure in the outer zone 5, is preferred to be installed so that it may be spatially

connected to the outer zone 5. The position where the outer pressure controlling

means 31 may be connected or installed includes, for example, an outer zone

connecting means 28 or an inert gas connecting means 26a, 26b installed on or

through the reactor shell, which is spatially connected to the outer zone 5 directly or

indirectly. In the present invention, the outer zone 5 is required to be maintained in a

substantially inert gas atmosphere. Thus, the outer zone connecting means 28 may

also comprise the function of an inert gas connecting means 26a that may be used for

introducing an inert gas 12 to the outer zone 5 or an inert gas connecting means 26b

that may be used for discharging an inert gas 12 from the outer zone 5. This means

that the inert gas inlet means 26a or the inert gas outlet means 26b may be used as the inert gas connecting means 26 and the outer zone connecting means 28. Further,

the inert gas inlet means 26a and the inert gas outlet means 26b may be installed

separately at those connecting means 26, 28, or be connected to either of those

connecting means 26, 28 as an integrated double tube-type structure. Therefore, it is

⁵ possible to spatially connect the outer zone 5 to the outer pressure controlling means

31 for directly or indirectly measuring and/ or controlling pressure in the outer zone

5 through an inert gas connecting means 26a, 26b or an outer zone connecting means

28.

In the present invention, the inner pressure controlling means 30 and/ot the

⁰ outer pressure controlling means 31 may be used to maintain the value of | Po - Pi

I , i.e. the difference between the pressure in the inner zone 4, i.e., the inner zone

pressure (Pi) and the pressure in the outer zone 5, i.e., the outer zone pressure (Po)

within 1 bar. However, it should be noted in constituting the inner pressure

controlling means 30 that Pi may vary depending on the position selected for

^ connection to the inner zone.

The value of Pi measured through an inner zone connecting means 24, 25, a

fluidizing gas inlet means 14, a reaction gas inlet means 15, or a particle outlet means

16, etc., which are installed at the positions spatially connected to an inner or lower

part of the fluidized bed, is higher than the value of Pi measured through an inner

⁰ zone connecting means, a gas outlet means 17 or silicon seed crystals inlet means 18,

etc., which are installed at the positions spatially connected to a space like an upper

part of the inner zone 4c and are not in direct contact with the fluidized bed of silicon particles.

Especially, the pressure value, measured through an inner zone connecting

means, a fluidizing gas inlet means 14 or a particle outlet means 16, which is

spatially connected to a lower part of the fluidized bed of silicon particles, shows a

maximum inner zone pressure value, Pi_maχ. On the contrary, a minimum inner zone

pressure value, Pimin, may be obtained when measured through a gas outlet means

17 or an inner zone connecting means 24, 25, which is not in direct contact with the

fluidized bed. This is because there is a pressure difference depending on the height

of the fluidized bed of silicon particles 4a and the value of Pi is always higher in the

lower part as compared to that in the upper part of the fluidized bed.

This pressure difference increases with the height of the fluidized bed. An

excessively high bed with the pressure difference being 1 bar or higher is not

preferred because the height of the reactor becomes too high to be used. In contrast,

a very shallow bed with the pressure difference of 0.01 bar or lower is not preferred

either, because the height and volume of the fluidized bed is too small to achieve an

acceptable minimum productivity of the reactor.

Therefore, the pressure difference in the fluidized bed is preferred to be

within the range of 0.01-1 bar. That is, pressure differences between maxium

pressure value (Pi_max) and minimum pressure value (Pimin) in the inner zone 4 is

preferred to be within 1 bar.

When maintaining the value of I Po - Pi | , i.e., pressure difference between

inside and outside the reactor tube 2 within the range of 0 to 1 bar, it should be noted that the pressure difference may vary depending on the height of the reactor

tube 2.

It is preferred to meet the requirements of Po < Pi and 0 bar < (Pi - Po) < 1 bar,

when the inner pressure controlling means 30 is spatially connected to the inner

zone 4 through an inner zone connecting means, a fluidizing gas inlet means 14, a

reaction gas inlet means 15 or a particle outlet means 16, etc., which is connected to

an inner or lower part of the fluidized bed of silicon particles, the pressure of which

is higher than that of the upper part of the inner zone 4c.

In contrast, it is preferred to meet the requirements of Pi < Po and 0 bar < (Po -

Pi) < 1 bar, when the inner pressure controlling means 30 is spatially connected to

the inner zone 4 through a gas outlet means 17, a silicon seed crystals inlet means 18,

or an inner zone connecting means 24, 25, etc., which is not spatially connected to

the silicon particle bed but connected to an upper part of the inner zone 4c, the

pressure of which is lower than that of the inner or lower part of the fluidized bed.

It may also be permissible to constitute the inner pressure controlling means

30 and/ or the outer pressure controlling means 31 in such manner that Pi or Po is

represented by an average of a plurality of pressure values measured at one or more

positions. Especially, because there may be pressure difference in the inner zone 4

depending on the connection position, the inner pressure controlling means 30 may

comprise a controlling means with an arithmetic processor that is capable of

estimating an average value of pressure from those values measured with two or

more pressure gauges. Therefore, when maintaining the value of I Po - Pi I , i.e., the pressure

difference value between inside and outside the reaction tube, within 1 bar, it is

preferred to maintain the pressure value at outer zone 5, Po, in between Pimax and

Pimm, which are maximum and minimum values, respectively, that can be measured

by the spatial connection of those pressure controlling means to the inner zone 4.

The inner pressure controlling means 30 and/ or outer pressure controlling

means 31 according to the present invention should comprise a pressure-difference

controlling means that maintains the value of I Po - Pi I within 1 bar.

The pressure-difference controlling means may be comprised in only one of

the inner pressure controlling means 30 or the outer pressure controlling means 31,

or in both of the controlling means independently, or in the two controlling means

30, 31 in common.

However, it is preferred to apply and maintain a pressure-difference

controlling means with consideration that pressure value varies depending on the

position selected for measuring the pressure in the inner zone 4, Pi. When Pi is

measured through a fluidizing gas inlet means 14, a reaction gas inlet means 15, a

particle outlet means 16, or an inner zone connecting means, etc., which are spatially

connected to inner part of the fluidized bed, especially to the lower part of the

fluidized bed, where the pressure is higher than that in an upper part of the inner

zone 4c, the pressure-difference controlling means may preferably be operated so

that the requirements of Po < Pi and 0 bar < (Pi - Po) < 1 are satisfied. Then, the

pressure-difference controlling means enables the outer zone pressure (Po) and inner zone pressure (Pi) to satisfy the requirement of 0 bar < (Pi - Po) < 1 bar, with

the inner pressure controlling means 30 being spatially connected to an inner part of

the fluidized bed through a fluidizing gas inlet means 14 or a reaction gas inlet

means 15 or a particle outlet means 16 or an inner zone connecting means.

In contrast, it is preferred to apply and maintain a pressure-difference

controlling means so that the requirements of Pi ≤ Po and 0 bar < (Po - Pi) < 1 bar

may be satisfied if Pi is measured at a position that is spatially connected to the

upper part of the inner zone 4c among various parts of the inner zone 4. Then, the

pressure-difference controlling means enables the requirement of 0 bar < (Po - Pi) < 1

bar to be satisfied, with the inner pressure controlling means 30 being spatially

connected to the inner zone 4 through a gas outlet means 17, a silicon seed crystals

inlet means 18, or an inner zone connecting means 24, 25, which are not in direct

contact with the fluidized bed of silicon particles.

In the present invention, being comprised in only one of the inner pressure

controlling means 30 or the outer pressure controlling means 31, in both of the two

controlling means 30, 31 independently, or in the two controlling means 30, 31 in

common, the pressure-difference controlling means maintains the value of I Po - Pi

I within 1 bar.

When the difference between Po and Pi is maintained within 1 bar by using

the pressure-difference controlling means, very high or low values of Pi or Po do not

influence on the reactor tube 2 because the pressure difference is small between the

inner zone and the outer zone of the reactor tube 2. It is preferred in terms of productivity to maintain the reaction pressure

higher than at least 1 bar instead at a vacuum state less than 1 bar, if pressure is

expressed in absolute unit in the present invention.

The feeding rates of fluidizing gas 10 and reaction gas 11 increase with

pressure in a nearly proportional manner, based on mole number or mass per unit

time. Thus, the heat duty in the fluidized bed 4a for heating the reaction gas from an

inlet temperature to the temperature required for reaction also increases with the

reaction pressure, i.e., Po or Pi.

In case of the reaction gas 11, it is impossible to supply the gas into the reactor

after preheating up to higher than about 350-400 ⁰C, i.e., incipient decomposition

temperature. Meanwhile, it is inevitable to preheat the fluidizing gas 10 up to

lower than the reaction temperature because impurity contamination is highly

probable during a preheating step outside the fluidized bed reactor, and the

fluidizing gas inlet means 14 can hardly be insulated to achieve a gas preheating to

above the reaction temperature. Therefore, difficulties in heating increase with

pressure. When the reaction pressure exceeds about 15 bar, it is difficult to heat the

fluidized bed 4a as required although a plurality of heating means 8a, 8b are

additionally installed at the inner space of the reactor shell. Considering these

practical limitations, the outer zone pressure (Po) or the inner zone pressure (Pi) is

preferred to be maintained within the range of about 1-15 bar based on the absolute

pressure.

According to the pressure within the reactor, the inner pressure controlling means 30 and/ or the outer pressure controlling means 31 may comprise a

pressure-difference controlling means that can reduce the pressure difference

between inside and outside the reactor tube 2. This can be practised in various ways,

some examples of which are described hereinafter.

The reaction pressure may be set to a high level by using the

pressure-difference controlling means without deteriorating the stability of the

reactor tube 2, thus enabling to increase both the productivity and stability of the

fluidized bed reactor.

For example, irrespective of the position of installation of the inner pressure

controlling means 30 for ultimate connection to the inner zone 4, both of the inner

pressure controlling means 30 and the outer pressure controlling means 31 may

comprise respective pressure-difference controlling means so that the inner zone

pressure (Pi) in the inner zone 4 and the outer zone pressure (Po) in the outer zone 5

may be controlled at predetermined values of pressure, i.e. Pi* and Po*, respectively,

satisfying the requirement of | Po* - Pi* I < 1 bar.

For this purpose, the inner pressure controlling means 30 may comprise a

pressure-difference controlling means that maintains Pi at a predetermined value,

Pi*. At the same time, the outer pressure controlling means 31 may also comprise a

pressure-difference controlling means that maintains Po at such a predetermined

value, Po*, that the requirement of | Po* - Pi* | < 1 bar is satisfied independently of

the height. Likewise, the outer pressure controlling means 31 may comprise a

pressure-difference controlling means that maintains Po at a predetermined value, Po*. At the same time, the inner pressure controlling means 30 may also comprise a

pressure-difference controlling means that maintains Pi at such a predetermined

value, Pi*, that the requirement of I Po* - Pi* I < 1 bar is satisfied independently of

the height.

As an another embodiment, irrespective of the position of installation of the

inner pressure controlling means 30 for ultimate connection to the inner zone 4, the

inner pressure controlling means 30 may comprise a pressure-difference controlling

means that maintains Pi at a predetermined value, Pi*, while the outer pressure

controlling means 31 may comprise a pressure-difference controlling means that

controls the outer zone pressure, Po, in accordance with the change of the real-time

inner zone pressure so that the requirement of I Po - Pi | < 1 bar is satisfied

independently of the height.

Meanwhile, when determining the values of the control parameters, Pi* and

Po*, which are predetermined for maintaining the difference between Po and Po

within 1 bar, it may be necessary to consider whether or not impurity components

can possibly migrate through a sealing means 41a, 41b of reactor tube 2.

In assemblying the fluidized bed reactor for operation according to the

present invention, there exists a practical limit that a sufficient degree of gas-tight

sealing may not be obtained at sealing means 41a, 41b for reactor tube 2. Further, its

degree of sealing can be reduced by the shear stress imposed on reactor tube 2 due

to fluidization of silicon particles 3. In the present invention, the problem of possible

migration of impurity components between the inner zone 4 and the outer zone 5 through the sealing means 41a, 41b may be solved by properly presetting the values

of control parameters, i.e., Pi* and Po*, for the pressure-difference controlling means.

According to the present invention, the pressure control parameters to be

used at the pressure-difference controlling means for controlling pressures in the

inner zone and the outer zone, respectively, may be predetermined based on the

analysis of the composition of off-gas 13 or the gas present in outer zone 5. For

example, the pattern of impurity migration between inner zone 4 and outer zone 5

through the sealing means 41a, 41b may be deduced based on the component

analysis on off-gas 13 sampled through the gas outlet means 17 or off-gas treating

means 34, or that on the gas present in outer zone 5 sampled through an outer zone

connecting means 28 or an inert gas connecting means 26b. If off-gas 13 is verified to

comprise the constituent of inert gas 12, which is not supplied into the inner zone,

the influx of impurity elements from outer zone 5 into inner zone 4 may be

decreased or prevented by presetting the value of Pi* higher than that of Po*, i.e., Pi*

> Po*. In contrast, if the gas discharged out of outer zone 5 is verified to comprise the

constituent of off-gas 13 of inner zone 4 besides that of inert gas 12, the influx of the

impurity elements from inner zone 4 into outer zone 5 may be decreased or

prevented by presetting the value of Po* higher than that of Pi*, i.e., Po* > Pi*.

As metioned above, although the sealing means 41a, 41b of reactor tube 2

may not be installed or maintained in a satisfactory manner during the assembly or

operation of the fluidized bed reactor, an undesirable migration of impurity

components between the two zones through the sealing means may be minimized or prevented by appropriate selection of the control parameters for the pressure

controlling means. Here, at whatever values Pi* and Po* may be preset in the

pressure-difference controlling means, the requirement of I Po* - Pi* I < 1 bar should

be satisfied according to the present invention.

⁵ As another example to accomplish the object of the present invention, the

pressure difference, i.e., ΔP = | Po - Pi | may be measured by interconnecting the

inner pressure controlling means 30 and the outer pressure controlling means 31,

whereby the pressure-difference controlling means may maintain the value of ΔP

within the range of 0 to 1 bar, irrespective of the position of inner zone 4 selected for

¹⁰ measurement of Pi, by controlling the inner pressure controlling means 30 and/ or

the outer pressure controlling means 31 in a manual, semi-automatic or automatic

way.

As still another example to accomplish the object of the present invention, the

pressure-difference controlling means may comprise an equalizing line, which

^⁵ spatially interconnects a connecting pipe comprised in the inner pressure controlling

means 30 and a connecting pipe comprised in the outer pressure controlling means

31. A connecting pipe, which is comprised in the the inner pressure controlling

means 30 and constitutes the equalizing line 23, may be installed at a position

selected for spatial connection with inner zone 4, including but not limited to an

²⁰ inner zone connecting means 24, 25; a fluidizing gas inlet means 14, 14'; a reaction

gas inlet means 15; a particle outlet means 16; a gas outlet means 17; or a seed

crystals inlet means 18, all of which are spatially exposed to the inner zone in a direct or indirect manner. Meanwhile, a connecting pipe, which is comprised in the

outer pressure controlling means 31 and constitutes an equalizing line 23, may be

installed at a position selected for spatial connection with outer zone 5, including but

not limited to an outer zone connecting means 28 or an inert gas connecting means

26a, 26b comprising the inert gas inlet means and the inert gas outlet means, all of

which are coupled with the reactor shell and spatially exposed to the outer zone in a

direct or indirect manner.

The equalizing line 23, which interconnects spatially the inner pressure

controlling means 30 and outer pressure controlling means 31, may be referred to as

a simplest form of the pressure-difference controlling means because it may always

maintain the pressure difference between two interconnected zones 4, 5 at nearly

zero.

Despite this advantage, when constitutuing the pressure-difference

controlling means by the equalizing line 23 alone, gas and impurity components

may undesirably be interchanged between two zones 4, 5. In this case, the impurity

elements generated or discharged from an insulating material or a heating means

installed in outer zone 5 may contaminate the inner zone 4, especially the

polycrystalline silicon particles. Likewise, silicon fine powders or components of

residual reaction gas or reaction byproduct discharged from the inner zone 4 may

contaminate the outer zone 5.

Therefore, when the equalizing line 23 is used as the pressure-difference

controlling means, a pressure equalizing means, which can decrease or prevent the possible interexchange of gas and impurity components between two zones 4, 5,

may be further added to the equalizing line 23. The pressure equalizing means may

comprise at least one means selected from a check valve, a pressure equalizing valve,

a 3-way valve, a filter for separating particles, a damping container, a packed bed, a

piston, an assistant control fluid, and a pressure compensation device using

separation membrane, which, respectively, is able to prevent the possible

interexchange of gas and impurity components without deteriorating the effect of

pressure equalization.

Besides, the pressure-difference controlling means may comprise a manual

valve for controlling pressure or flow rate, or may further comprise a(n)

(semi-) automatic valve that performs a(n) (semi-)automatic control function

according to a predetermined value of pressure or pressure difference. These valves

may be installed in combination with a pressure gauge or a pressure indicator that

exhibits a pressure or pressure difference.

The pressure gauge or the pressure indicator is available commercially in the

form of either analogue, digital or hybrid device, and may be included in an

integrated system of data acquisition, storage and control, if combined with a data

processing means such as a signal converter or a signal processor, etc., and/ or with a

local controller, a distributed controller or a central controller including a circuit for

performing an arithmetic operation.

Illustrative embodiments according to the Drawings herein are explained

hereinafter in terms of the application of the pressure-difference controlling means for decreasing the pressure difference between inside and outside the reactor tube 2

in the the fluidized bed reactor for preparing granular polycrystalline silicon.

[DESCRIPTION OF DRAWINGS]

Figure 1 schematically shows the characteristics of the method for preparing

granular polycrystalline silicon according to the present invention.

Figure 2 is a cross-sectional view of a high-pressure fluidized bed reactor for

preparing granular polycrystalline silicon, in which several embodiments of the

present invention are illustrated in a comprehensive way.

Figure 3 is a cross-sectional view of a high-pressure fluidized bed reactor for

preparing granular polycrystalline silicon, in which some other embodiments

according to the present invention are illustrated in a comprehensive way.

Code Explanation of the Drawings

1: Reactor shell 2: Reactor tube

3: silicon particles 3a: Silicon seed crystals

3b: Silicon product particles 4: Inner zone

5: Outer zone 6: Insulating material

7: Liner 8: Heater

9: Electric energy supplying means 10: Fluidizing gas

11: Reaction gas 12: Inert gas

13: Off-gas 14: Fluidizing gas inlet means

15: Reaction gas inlet means 16: Particle outlet means 17: Gas outlet means 18: Silicon seed crystals inlet means

19: Gas distributing means 23: Equalizing line

24, 25: Inner zone connecting means 26: Inert gas connecting means

27: On/ off valve 28: Outer zone connecting means

30: Inner pressure controlling means 31: Outer pressure controlling means

32: Pressure-difference gauge 33: Fluctuation reducing means

34: Off-gas treating means 35: Gas analyzing means

36: Filter 41: Sealing means

E: Electric source

[BEST MODE]

The present invention is described more specifically by the following

Examples. Examples herein are meant only to illustrate the present invention, but in

no way to limit the scope of the claimed invention.

Example 1

Hereunder is provided a description of one embodiment where the inner

zone pressure (Pi) and the outer zone pressure (Po) are independently controlled at

predetermined values, Pi* and Po*, respectively, and the difference between the

values of the inner zone pressure and the outer zone pressure is thereby maintained

within the range of 0 to 1 bar.

As illustrated in Figures 2 and 3, an inner pressure controlling means 30 may

be constituted by interconnecting a first pressure control valve 30b with a gas outlet means 17 through an off-gas treating means 34 for removing fine silicon particles,

which are interconnected with each other by a connecting pipe. The pressure of the

upper part of the inner zone 4 may be controlled at a predetermined value, Pi*, by

using the first pressure control valve 30b which behaves as an element of a

pressure-difference controlling means.

Meanwhile, as illustrated in Figure 2, an outer pressure controlling means 31

may be constituted by interconnecting an inert gas connecting means 26a, a fourth

pressure gauge 31a' and a fourth pressure control valve 31b'. Although being

separately installed in Figure 2, the fourth pressure gauge 31a' and the fourth

pressure control valve 31b' may be integrated with each other by a circuit, and thus

be constituted as a single device that can measure and control pressure at the same

time.

When the inner pressure controlling means 30 is connected to an upper part

of the inner zone 4c, the pressure of which is lower than those in or below the

fluidized bed, it is preferred to preset Pi* and Po* so that the condition of Po* > Pi*

may be satisfied.

In this Example, the outer zone pressure may be controlled at a

predetermined value, Po*, so that the condition of 0 bar < (Po* - Pi*) < 1 bar may be

satisfied, by using the fourth pressure gauge 31a' and the fourth pressure valve 31b'

both of which behave as elements of a pressure-difference controlling means.

However, when an inert gas 12 component is detected in the off-gas 13 by a

gas analyzing means 35, which may be installed as illustrated in Figure 3, Po* may be preset at a lower value so that the condition of Pi* ≥ Po* may be satisfied.

Meanwhile, the inner pressure controlling means 30 and the outer pressure

controlling means 31 may further comprise their own pressure-difference controlling

means, respectively, thus enabling the condition of 0 bar < | Po - Pi | < 1 bar to be

satisfied, where Po and Pi are values of pressure measured in connection with the

outer zone 5 and any position in the inner zone 4, respectively.

Example 2

Hereunder is provided a description of another embodiment where the inner

zone pressure (Pi) and the outer zone pressure (Po) are independently controlled at

the predetermined values, Pi* and Po*, respectively, and the difference between the

values of the inner zone pressure and the outer zone pressure is thereby maintained

within the range of 0 to 1 bar.

As illustrated in Figures 2 and 3, an inner pressure controlling means 30 may

be constituted by interconnecting a first pressure control valve 30b with the gas

outlet means YJ through the off-gas treating means 34 for removing fine silicon

particles, which are interconnected with each other by a connecting pipe. The

pressure of the upper part of the inner zone 4 may be controlled at a predetermined

value, Pi*, by using the first pressure control valve 30b which behaves as an element

of a pressure-difference controlling means.

Meanwhile, as illustrated in Figure 2, an outer pressure controlling means 31

may be constituted by interconnecting an inert gas connecting means 26b, an on/ off valve 3Ic₇ a third pressure gauge 31a and a third pressure control valve 31b.

Although being separately installed in Figure 2, the third pressure gauge 31a and the

third pressure control valve 31b may be integrated with each other by a circuit, and

thus be constituted as a single device that can measure and control pressure at the

same time.

Unlike in Example I₇ the supply of an inert gas 12 may be controlled by the

third pressure control valve 31b in combination with the Po control, instead of

connecting the inert gas connecting means 26a to a pressure-difference controlling

means such as the fourth pressure gauge 31a' and the fourth pressure valve 31b'

When the inner pressure controlling means 30 is connected to an upper part

of the inner zone 4c, the pressure of which is lower than those in or below the

fluidized bed, it is preferred to preset Pi* and Po* so that the condition of Po* > Pi*

may be satisfied.

In this Example, the outer zone pressure may be controlled at a

predetermined value, Po*, so that the condition of 0 bar ≤ (Po* - Pi*) ≤ 1 bar may be

satisfied, by the third pressure gauge 31a and the third pressure control valve 31b

both of which behave as elements of a pressure-difference controlling means.

However, when an inert gas 12 component is detected in the off-gas 13 by a

gas analyzing means 35, which may be installed as illustrated in Figure 3, Po* may

be preset at a lower value so that the condition of Pi* > Po* may be satisfied.

Meanwhile, the inner pressure controlling means 30 and the outer pressure

controlling means 31 may further comprise their own pressure-difference controlling means, respectively, thus enabling the condition of 0 bar < I Po - Pi I ≤ 1 bar to be

satisfied, where Po and Pi are values of pressure measured in connection with the

outer zone 5 and any position in the inner zone 4, respectively.

Example 3

Hereunder is provided a description of one embodiment where the inner

zone pressure (Pi) is controlled according to the change of the outer zone pressure

(Po), and the difference between the values of the inner zone pressure and the outer

zone pressure is thereby maintained within the range of 0 to 1 bar.

As illustrated in Figures 2 and 3, a gas outlet means 17, an off-gas treating

means 34 for removing fine silicon particles and a first pressure control valve 30b are

interconnected with each other by a connecting pipe. Then an inner pressure

controlling means 30 may be constituted by interconnecting the connecting pipe

with an on/ off valve 27e and a pressure-difference gauge 32.

Meanwhile, as illustrated in Figure 2, an outer pressure controlling means 31

may be constituted by interconnecting an inert gas connecting means 26b and a

pressure-difference gauge 32, which are interconnected with each other by the

connecting pipe. Here an inert gas 12 may be supplied to the outer zone through an

inert gas connection means 26a.

In the present example, the pressure-difference gauge 32 is be a common

element for both the inner pressure controlling means 30 and the outer pressure

controlling means 31. Besides the pressure control valve 31b, 31b' may be omitted. When the inner pressure controlling means 30 and the outer pressure

controlling means 31 are constituted as described above, the difference between the

outer zone pressure (Po) and the inner pressure (Pi) in upper part of the inner zone

can be maintained to be lower than 1 bar independently of the change of the outer

zone pressure (Po) by using the pressure-difference gauge 32 and the first pressure

control valve 30b both of which behave as elements of a pressure-difference

controlling means.

Further, the inner pressure controlling means 30 may be connected to an

upper part of the inner zone 4c, the pressure of which is lower than those in or

below the fluidized bed, and it is preferred to control the first pressure control valve

30b so that the condition of Po > Pi may be satisfied.

However, when an inert gas 12 component may be detected in the off-gas 13

by a gas analyzing means 35, which may be installed as illustrated in Figure 3, the

first pressure control valve 30b may be controlled so that the condition of Pi > Po

may be satisfied.

Following the aforementioned constitution and operation of the fluidized bed

reactor, the condition of 0 bar < | Po - Pi I < 1 bar may be satisfied at any position in

the inner zone 4.

Meanwhile, the object of the present Example may be accomplished either by

automatic control of the integrated circuit of the pressure-difference gauge 32 and

the first pressure control valve 30b, or by manual operation of the first pressure

control valve 30b in accordance with the values of ΔP measured with the pressure-difference gauge 32.

Instead of the pressure-difference gauge 32, only a first pressure gauge 30a

and a third pressure gauge 31a may be installed as the inner pressure controlling

means 30 and the outer pressure controlling means 31, respectively. Alternatively,

the pressure-difference controlling means may be further corrected or improved by

equipping a first pressure gauge 30a and a third pressure gauge 31a in the inner

pressure controlling means 30 and the outer pressure controlling means 31,

respectively, in addition to the pressure-difference gauge 32.

Example 4

Hereunder is provided a description of another embodiment where the inner

zone pressure (Pi) is controlled according to the change of the outer zone pressure

(Po), and the difference between the values of the inner zone pressure and the outer

zone pressure is thereby maintained within the range of 0 to 1 bar.

As illustrated in Figures 2 and 3, an inner pressure controlling means 30 may

be constituted by interconnecting a first pressure control valve 30b with the gas

outlet means 17 through the off-gas treating means 34 for removing fine silicon

particles, which are interconnected with each other by a connecting pipe.

Meanwhile, as illustrated in Figure 2, an outer pressure controlling means 31

may be constituted by interconnecting an inert gas connecting means 26a for

supplying an inert gas 12 and a fourth pressure gauge 31a', which are

interconnected with each other by the connecting pipe. Here, an inert gas 12 may be discharged through an inert gas connection means 26b. Besides the pressure control

valve 31b, 31b' in Figure 2 may be omitted.

When the inner pressure controlling means 30 and the outer pressure

controlling means 31 are constituted as described above, the difference between the

outer zone pressure (Po) and the inner pressure (Pi) in the upper part of the inner

zone 4c can be maintained to be lower than 1 bar independently of the change of the

outer zone pressure (Po) by using the fourth pressure gauge 31a' and the first

pressure control valve 30b both of which behave as elements of a pressure-difference

controlling means.

Further, since the inner pressure controlling means 30 may be connected to an

upper part of the inner zone 4c, the pressure of which is lower than those in or

below the fluidized bed, it is preferred to control the first pressure control valve 30b

so that the condition of Po > Pi may be satisfied.

However, when an inert gas 12 component is detected in an off-gas 13 by a

gas analyzing means 35, which may be installed as illustrated in Figure 3, the first

pressure control valve 30b may be controlled so that the condition of Pi > Po may be

satisfied.

Following the aforementioned constitution and operation of the fluidized bed

reactor, the condition of 0 bar < | Po - Pi I < 1 bar may be satisfied at any position in

the inner zone 4.

Meanwhile, the object of the present Example may be accomplished either by

automatic control of the integrated circuit of the fourth pressure gauge 31a' and the first pressure control valve 30b, or by manual operation of the first pressure control

valve 30b in accordance with the pressure value measured with the fourth pressure

gauge 31a'.

Instead of connecting a fourth pressure gauge 31a' to the inert gas connecting

means 26, the outer pressure controlling means 31 may also be constituted by

connecting a fifth pressure gauge 31p to an outer zone connecting means 28 as

illustrated in Figure 2 or a fifth pressure gauge 31p connected to the outer zone

connecting means 28a as illustrated in Figure 3 or a third pressure gauge 31a

connected to an inert gas connecting means 26b as illustrated in Figure 3. Then, the

respective pressure gauge employed in the outer pressure controlling means 31 may

also behave as another element of the pressure-difference controlling means.

Accordingly, the object of the present Example may be accomplished by regulating

the first pressure control valve 30b, which behaves as an element of the

pressure-difference controlling means that is comprised in the inner pressure

controlling means 30, in accordance with the other element of the

pressure-difference controlling means that is comprised in a variety of outer

pressure controlling means 31.

Example 5

Hereunder is provided a description of one embodiment where the outer

zone pressure (Po) is controlled according to the change of the inner zone pressure

(Pi), and the difference between the values of the inner zone pressure and the outer zone pressure is thereby maintained within the range of 0 to 1 bar.

As illustrated in Figures 2 and 3, an inner pressure controlling means 30 may

be constituted by interconnecting an on/ off valve 27 ά and a pressure-difference

gauge 32 with an outer zone connecting means 25 instead of the gas outlet means 17,

which are interconnected with each other by a connecting pipe.

Meanwhile, as illustrated in Figure 2, the outer pressure controlling means 31

may be constituted by interconnecting a third pressure control valve 31b and

pressure-difference gauge 32 with an inert gas connecting means 26b, which are

interconnected with each other by the connecting pipe. This case corresponds to the

case of constitution where the on/ off valves 27c, 27e are closed. In the present

example, the pressure-difference gauge 32 is a common element for both the inner

pressure controlling means 30 and the outer pressure controlling means 31.

When the inner pressure controlling means 30 and the outer pressure

controlling means 31 are constituted as described above, the difference between the

outer zone pressure (Po) and the inner pressure (Pi) in the upper part of the inner

zone 4c can be maintained to be lower than 1 bar independently of the change of the

inner zone pressure (Pi) by using the pressure-difference gauge 32 and the third

pressure control valve 31b both of which behave as elements of a pressure-difference

controlling means.

Further, since the inner pressure controlling means 30 may be connected to an

upper part of the inner zone 4c the pressure of which is lower than those in or below

the fluidized bed, the third pressure control valve 31b may be controlled so that the condition of Po ≥ Pi may be satisfied.

However, when an inert gas 12 component is detected in an off-gas 13 by a

gas analyzing means 35 which may be installed as illustrated in Figure 3, the first

pressure control valve 30b may be controlled so that the condition of Pi ≥ Po may be

satisfied.

Following the aforementioned constitution and operation of the fluidized bed

reactor, the condition of 0 bar < | Po - Pi I ≤ 1 bar may be satisfied at any position in

the inner zone 4.

Meanwhile, the object of the present Example may be accomplished either by

automatic control of the integrated circuit of the pressure-difference gauge 32 and

the third pressure control valve 31b, or by manual operation of the third pressure

control valve 31b in accordance with the ΔP value measured with the

pressure-difference gauge 32.

Instead of the pressure-difference gauge 32, only a first pressure gauge 30a

and a third pressure gauge 31a may be installed as the inner pressure controlling

means 30 and the outer pressure controlling means 31, respectively. Alternatively,

the pressure-difference controlling means may be further corrected or improved by

equipping a first pressure gauge 30a and a third pressure gauge 31a in the inner

pressure controlling means 30 and the outer pressure controlling means 31,

respectively, in addition to the pressure-difference gauge 32.

The outer pressure controlling means in this Exmaple may be constituted in

another form. For example, instead of interconnection of the pressure control valve 31b and pressure-difference gauge 32 with the inert gas connecting means 26b in

Figure 2, the outer pressure controlling means may also be constituted by

interconnecting the fourth pressure valve 31b' and the pressure-difference gauge 32

with the inert gas connecting means 26a for supplying the inert gas, which are

interconnected with each other by a connecting pipe. If corresponding elements of

the pressure-difference controlling means is further replaced together with such

modification of the outer pressure controlling means, the object of the present

Example may also be accomplished thereby.

Example 6

Hereunder is provided a description of another embodiment where the outer

zone pressure (Po) is controlled according to the change of the inner zone pressure

(Pi), and the difference between the values of the inner zone pressure and the outer

zone pressure is thereby maintained within the range of 0 to 1 bar.

As illustrated in Figure 3, the inner pressure controlling means 30 may be

constituted by interconnecting a second pressure gauge 30a' and a

pressure-difference gauge 32 with a fluidizing gas inlet means 14, which are

interconnected with each other by a connecting pipe and/ or by electrical integration.

Meanwhile, as illustrated in Figure 3, the outer pressure controlling means 31

may be constituted by interconnecting a third pressure gauge 31a and a

pressure-difference gauge 32, both of which are connected to an inert gas connecting

means 26b, with a second pressure control valve 30b' which is connected to an inert gas connecting means 26a. Here, the interconnection may be achieved by the

connecting pipe and/ or by electrical integration.

In the present example, the pressure-difference gauge 32 is a common

element for both the inner pressure controlling means 30 and the outer pressure

controlling means 31. The pressure-difference gauge 32 exhibits a physical and/ or

electrical signal for the difference between Pi and Po, which are measured with the

second pressure gauge 30a' and the third pressure gauge 31a, respectively.

A fluctuation reducing means 33 may further be applied to the

pressure-difference gauge because the fluidization of silicon particles in the

fluidized bed naturally introduces fluctuation in the value of Pi measured by the

second pressure gauge 30a'. The fluctuation reducing means 33 may comprise a

pressure fluctuation damping (or buffering) means such as a physical device or a

software-based device that transforms the fluctuating signals into an average Pi

value for a predetermined short period of time (e.g., one second).

Then, by using the pressure-difference gauge 32 and the second pressure

control valve 30b' both of which behave as elements of a pressure-difference

controlling means, the difference between the outer zone pressure (Po) and the inner

zone pressure (Pi) is maintained to be lower than 1 bar independently of the change

of the inner zone pressure (Pi) measusred through the fluidizing gas inlet means 14

in connection with the inner zone.

Further, since the inner pressure controlling means 30 may be connected to a

lower part of the fluidized bed, the pressure of which is higher than that in upper part of the inner zone 4c, the second pressure control valve 30b' may be controlled so

that the condition of Po < Pi may be satisfied.

However, when an off-gas 13 component is detected in an inert gas 12' by a

gas analyzing means 35, which may be installed as illustrated in Figure 3, the second

pressure control valve 30b' may be controlled so that the condition of Po > Pi may be

satisfied.

Following the aforementioned constitution and operation of the fluidized bed

reactor, the condition of 0 bar < I Po - Pi I < 1 bar may be satisfied at any position in

the inner zone 4.

Meanwhile, the object of the present Example may be accomplished either by

automatic control of the integrated circuit of the pressure-difference gauge 32 and

the second pressure control valve 30b', or by manual operation of the second

pressure control valve 30b' in accordance with the ΔP value measured with the

pressure-difference gauge 32.

Further, on behalf of the third pressure gauge 31a in connection with the inert

gas connecting means 26b, another outer pressure gauge may be connected to the

pressure-difference gauge 32 for achieving the object of the present Example. For

example, the outer pressure gauge may also be selected from the fifth pressure

gauge 31p in connection with the outer zone connecting means 28a or a sixth

pressure gauge 31q in connection with the inert gas connecting means 26a.

Example 7 Hereunder is provided a description of one embodiment where the difference

between the values of the inner zone pressure and the outer pressure is maintained

within the range of 0 to 1 bar by using an equalizing line spatially interconnecting

the inner zone and the outer zone.

As illustrated in Figure 2, the equalizing line 23 may be composed of a

connecting pipe which spatially interconnects an inner zone connecting means 25

with an inert gas connecting means 26b.

In this case, the inner pressure controlling means 30 may be basically

composed of the inner zone connecting means 25 and the connecting pipe, and may

further comprise an on/ off valve 27d and a first pressure gauge 30a as illustrated in

Figure 2. Meanwhile, the outer pressure controlling means 31 may be basically

composed of a connecting means, which is selected from an inert gas connecting

means 26a or an outer zone connecting means 28, and the connecting pipe, and may

further comprise an on/ off valve 31c and a third pressure gauge 31a as illustrated in

Figure 2.

In the present Example, an equalizing line 23 is composed of the two

connecting pipes that constitute the inner pressure controlling means 30 and the

outer pressure controlling means 31, respectively. Therefore, the equalizing line 23

behaves, by itself, as a pressure-difference controlling means. Spatially

interconnecting the upper part of the inner zone 4c with the outer zone 5, the

equalizing line 23 naturally prevents an apparent pressure difference between these

two zones. The pressure difference between Pi, measured at a lower part of the fluidized

bed 4a where Pi is highest in the bed, and Po, measured at an upper part of the inner

zone 4c, is usually below 1 bar. Thus, if the equalizing line 23 is used as the

pressure-difference controlling means, the pressure difference between Pi and Po,

i.e., between inside and outside of the reactor tube 2 may be maintained below 1 bar

irrespective of the measurement point of Pi.

The object of the present Example may also be accomplished by selecting a

space in connection with a gas outlet means 17, instead of the inner zone connecting

means 25, for constituting the inner pressure controlling means 30.

Meanwhile, the effect of pressure equalization of Pi and Po attributed to the

equalizing line 23, which is a pressure-difference controlling means in the present

Example, may also be obtained when a pressure equalizing valve 27c is further

equipped at the equalizing line 23 enabling spatial partition of the inner zone and

the outer zone.

Example 8

Hereunder is provided a description of another embodiment where the

difference between the values of the inner zone pressure and the outer zone pressure

is maintained within the range of 0 to 1 bar by using an equalizing line spatially

interconnecting the inner zone and the outer zone

As illustrated in Figure 3, the equalizing line 23 may be composed of a

connecting pipe which spatially interconnects an inner zone connecting means 25 and an outer zone connecting means 28b. In this case, the inner pressure controlling

means 30 may be basically composed of the inner zone connecting means 25 and the

connecting pipe. Meanwhile, the outer pressure controlling means 31 may be

basically composed of the outer zone connecting means 28b and the connecting pipe.

In the present Example, an equalizing line 23 is composed of the two

connecting pipes that constitute the inner pressure controlling means 30 and the

outer pressure controlling means 31, respectively. Therefore, the equalizing line 23

behaves, by itself, as a pressure-difference controlling means. Spatially

interconnecting the upper part of the inner zone 4c with the outer zone 5, the

equalizing line 23 naturally prevents an apparent pressure difference between these

two zones.

The pressure difference between Pi, measured at a lower part of the fluidized

bed 4a where Pi is highest in the bed, and Po, measured at an upper part of the inner

zone 4c, is usually below 1 bar. Thus, if the equalizing line 23 is used as the

pressure-difference controlling means, the pressure difference between Pi and Po,

i.e., between inside and outside of the reactor tube 2 may be maintained below 1 bar

irrespective of the measurement point of Pi.

Meanwhile, to prevent the migration of impure particles and components

through the equalizing line 23, a filter 36 and/ or an on/ off valve 27d may be further

equipped at the equalizing line 23 as illustrated in Figure 3.

Example 9 Hereunder is provided a description of still another embodiment where the

difference between the values of the inner zone pressure and the outer zone pressure

is maintained within the range of 0 to 1 bar by using an equalizing line spatially

interconnecting the inner zone and the outer zone.

As illustrated in Figure 3, the equalizing line 23 may be composed of a

connecting pipe which spatially interconnects a gas outlet means 17 with an inert

gas connecting means 26b.

In this case, the inner pressure controlling means 30 may be basically

composed of the gas outlet means 17, an off-gas treating means 34 and the

connecting pipe, and may further comprise a first pressure gauge 30a, an on/ off

valve 31d, a filter 36, etc., as illustrated in Figure 3. Meanwhile, the outer pressure

controlling means 31 may be basically composed of a connecting means, which is

selected among an inert gas connecting means 26a or an outer zone connecting

means 28, and the connecting pipe, and may further comprise an on/ off valves 31b,

31e, 31f, 31g, a gas analyzing means 35 and a third pressure gauge 31a, etc., as

illustrated in Figure 3.

In the present Example, an equalizing line 23 is composed of the two

connecting pipes that constitute the inner pressure controlling means 30 and the

outer pressure controlling means 31, respectively. Therefore, the equalizing line 23

behaves, by itself, as a pressure-difference controlling means. Spatially

interconnecting the upper part of the inner zone 4c with the outer zone 5, the

equalizing line 23 naturally prevents an apparent pressure difference between these two zones.

The pressure difference between Pi, measured at a lower part of the fluidized

bed 4a where Pi is highest in the bed, and Po, measured at an upper part of the inner

zone 4c, is usually below 1 bar. Thus, if the equalizing line 23 is used as the

pressure-difference controlling means, the pressure difference between Pi and Po,

i.e., between inside and outside of the reactor tube 2 may be maintained below 1 bar

irrespective of the measurement point of Pi.

The object of the present Example may also be accomplished when a raction

gas inlet means 15 is interconnected with the outer zone 5 by selecting a space in

connection with a raction gas inlet means 15, instead of the gas outlet means 17, for

constituting the inner pressure controlling means 30.

Meanwhile, the effect of pressure equalization of Pi and Po attributed to the

equalizing line 23, which is a pressure-difference controlling means in the present

Example, may also be obtained when a pressure equalizing valve 27c in Figure 3 is

further equipped at the equalizing line 23 enabling spatial partition of the inner zone

and the outer zone.

Example 10

Hereunder is provided a description of still another embodiment where the

outer zone pressure (Po) is controlled according to the change of the inner zone

pressure (Pi), and the difference between the values of the inner zone pressure and

the outer zone pressure is thereby maintained within the range of 0 to 1 bar. In the present Example, an average value of the inner zone pressure, Pi(avg),

may be estimated from the two values of pressure measured at two spaces which are

in spatial connection with a fluidizing gas inlet means 14 and a gas outlet means 17

independently. Then, Po may be controlled according to the estimated value of

Pi(avg), thus maintaining the difference between the values of Pi and Po within 1 bar,

preferably 0.5 bar.

In the present Example, a second pressure gauge 30a' and a first pressure

gauge 30a are installed in connection with a fluidizing gas inlet means 14 and a gas

outlet means 17, respectively. The inner pressure controlling means 30 may be

constituted as an integrated circuit of a pressure-difference gauge 32 of Figure 3 and

a controller comprising an arithmetic processor, where the controller generates an

estimated value of Pi(avg) based on the real-time measurements of the two pressure

gauges 30a', 30a. Meanwhile, as illustrated in Figure 3, an outer pressure controlling

means 31 may be constituted as an integrated circuit of the pressure-difference

gauge 32 as well as a second pressure control valve 30b' and a third pressure gauge

31a which are connected to an inert gas connecting means 26a and an inert gas

connecting means 26b, respectively. Here, the pressure-difference gauge 32 exhibits

the difference between Pi(avg) and Po, and generates an electric signal

corresponding to the difference, thus operating the second pressure control valve

30b'. Therefore, being a common element for both the inner pressure controlling

means 30 and the outer pressure controlling means 31, the software-based function

of the pressure-difference gauge 32 may be coupled into the controller for estimation of Pi(avg).

Because the value of Pi measured by the second pressure gauge 30a'

fluctuates depending on the fluidization state of the fluidized bed, the controller

comprising an arithmetic processor for estimation of Pi(avg) may further comprise a

software-based damping means that generates time-averaged values of pressure,

Pi*(avg), at an interval of, for example, 10 seconds or 1 minute based on the

fluctuating real-time values of Pi. This damping means may allow a smooth

operation of the second pressure control valve 30b' based on the time-averaged

value instead of the fluctuating Pi.

Using the controller comprising an arithmetic processor and the second

pressure control valve 30b' as a pressure-difference controlling means, it is possible

to control the outer zone pressure (Po) according to the change of the time-average

of Pi values measured at different positions in connection with the inner zone, and

then to maintain the difference of Po from and Pi(avg) or Pi*(avg) within the range

of 0 to 1 bar.

The manipulation of the second pressure control valve 30b' for controlling the

outer zone pressure according to the average value of the inner zone pressure may

be adjusted following a gas-component analysis on the off-gas through a gas outlet

means 17 or the off -gas treating means 34 and/ or on the gas dischargd from the

outer zone through the outer zone connecting means 28 or an inert gas connecting

means 26b. If a large amount of an inert gas component is detected in the off-gas, it

is preferred to lower Po, thus decreasing the migration of impurity into the inner zone 4 from the outer zone 5. On the contrary, if an off-gas 13 component is

detected in the gas from the outer zone besides an inert gas 12, it is preferred to raise

Po, thus decreasing the migration of impurity into the outer zone 5 from the inner

zone 4. Nontheless, according to the present Example, the condition of I Po -

Pi*(avg) I < 1 bar should be satisfied irrespective of conditions for controlling Po. If

the impurity component is not detected, it is preferred to manipulate the second

pressure control valve 30b' so that Po may be substantially the same with Pi*(avg).

Therefore, it is possible to minimize or prevent the undesirable migration of

impurity by controlling the pressure difference between the inner zone 4 and the

outer zone 5, although the sealing means 41a, 41b for reactor tube 2 are not

maintained perfect during the operation of the fluidized bed reactor.

The object of the present Example may also be accomplished by constituting

the outer pressure controlling means 31 in a different way. For example, instead of

the third pressure gauge 31a connected to the inert gas connecting means 26b, a fifth

pressure gauge 31p or a sixth pressure gauge 31q, which are connected to an outer

zone connecting means 28a or an inert gas connecting means 26a, respectively, may

be selected as the pressure gauge to be connected to the the pressure-difference

gauge 32. Further, instead of the second pressure control valve 30b' connected to the

inert gas connecting means 26a, a third pressure control valve 31b connected to the

inert gas connecting means 26b may be selected as the pressure control valve.

Meanwhile, the object of the present Example may also be accomplished by

constituting the inner pressure controlling means 30 in a different way. For example, instead of the second pressure gauge 30a' connected to the fluidizing gas inlet means

14, a pressure gauge in spatial connection with a silicon product particle outlet

means 16 may be selected for measurement of Pi(avg) together with the first

pressure gauge 30a connected to the gas outlet means 17.

Besides the aforementioned Examples, the inner pressure controlling means

30, the outer pressure controlling means 31 and the pressure-difference controlling

means may be constituted in a variety of manners for preparation of granular

polycrystalline silicon according to the present invention.

[INDUSTRIAL APPLICABILITY]

As set forth above, the method according to the present invention for

preparing granular polycrystalline silicon using the fluidized bed reactor have the

superiority as follows.

1. Bulk production of granular polycrystalline silicon can be carried out

according to the process using the fluidized bed reactor as set forth herein.

2. The pressure difference between both sides of the reactor tube is

maintained so low that a high-pressure silicon deposition is possible without

deteriorating the physical stability of the reactor tube, thus enabling to

fundamentally prevent the damage of the reactor tube due to the pressure difference,

and to improve long-term stability of the reactor.

3. The pressure difference between the inner zone and the outer zone may be

maintained within a predetermined range at a relatively low cost without continuously providing a large amount of inert gas into the outer zone of the reactor.

4. High reaction temperature required for silicon deposition can be easily

maintained by the heating means employed for heating the silicon particle bed.

5. The process as set forth herein can be utilized for economical and

energy-efficient production of high-purity polycrystalline silicon with minimized

impurity contamination and enhanced productivity.

6. The outer zone of the reactor is maintained under an inert gas atmosphere

and the inert gas may be discharged through a separate exit. Thus, although an

insulating material and optionally a heater are installed in the outer zone and the

outer zone may comprise additional partitioning means in a radial or vertical

direction, it is possible to decrease remarkably the possibility that impurity from

these components can migrate into the inner zone and deteriorate the quality of

polycrystalline silicon product.

7. The long-term stability of the reactor may be improved remarkably because

any thermal degradation in terms of chemical and physical properties of those

additional components in the outer zone is less probable under the inert gas

atmosphere.

Claims

CLAIMSWhat is claimed is:

1. A method for preparing poly crystalline silicon using a fluidized bed reactor,

comprising:

(a) employing a fluidized bed reactor wherein a reactor tube is vertically placed

within a reactor shell so as to be encompassed by the reactor shell, whereby

dividing an inner space of the reactor shell into an inner zone formed within the

reactor tube and an outer zone formed in between the reactor shell and the

reactor tube, wherein a silicon particle bed is formed and silicon deposition

occurs in the inner zone while a silicon particle bed is not formed and silicon

deposition does not occur in the outer zone;

(b) directly or indirectly measuring and/ or controlling an inner zone pressure

using an inner pressure controlling means, directly or indirectly measuring

and/ or controlling an outer zone pressure using an outer pressure controlling

means, and maintaining the difference between the inner zone pressure and the

outer zone pressure within 1 bar using a pressure-difference controlling means;

(c) introducing a fluidizing gas into the silicon particle bed using a fluidizing gas

inlet means;

(d) introducing a silicon atom-containing reaction gas into the silicon particle

bed using a reaction gas inlet means;

(e) introducing an inert gas into the outer zone, whereby maintaining a substantially inert gas atmosphere in the outer zone;

(f) heating the silicon particle bed using a heating means installed in the inner

zone and/ or the outer zone;

(g) discharging polycrystalline silicon particles prepared within the inner zone

to the outside of the fluidized bed reactor;

(h) discharging an off-gas including a fluidizing gas that passes through the

silicon particle bed, a non-reacted reaction gas and a byproduct gas to the

outside of the fluidized bed reactor

2. The method of claim 1, wherein the reaction gas is a silicon atom-containing gas

selected from the group consisting of monosilane, dichlorosilane, trichlorosilane,

silicon tetrachloride and a mixture thereof.

3. The method of claim 2, wherein the reaction gas further comprises at least one gas

selected from the group consisting of hydrogen, nitrogen, argon, helium, hydrogen

chloride and a mixture thereof.

4. The method of claim 1, wherein the fluidizing gas is a gas selected from the group

consisting of hydrogen, nitrogen, argon, helium, hydrogen chloride, silicon

tetrachloride and a mixture thereof.

5. The method of claim 1, wherein the inert gas comprises at least one gas selected from the group consisting of hydrogen, nitrogen, argon and helium.

6. The method of claim 1, wherein the outer zone pressure (Po) or the inner zone

pressure (Pi) is maintained within the range of 1-15 bar.

7. The method of claim 1, wherein the outer zone pressure (Po) may be controlled in

the range of between maximum and minimum pressure values measurable in the

inner zone.

8. The method of claim 1, wherein the difference between the outer zone pressure

(Po) and the inner zone pressure (Pi) is maintained so as to satisfy the condition of 0

bar < (Pi - Po) < 1 bar, when the inner pressure controlling means is spatially

connected to the inner zone through at least one means selected from the group

consisting of a fluidizing gas inlet means, a reaction gas inlet means, a silicon

particle outlet means and an inner zone connecting means, which are spatially

connected to the the silicon particle bed.

9. The method of claim 1, wherein the difference between the outer zone pressure

(Po) and the inner zone pressure (Pi) is maintained so as to satisfy the condition of 0

bar < (Po - Pi) ≤ 1 bar, when the inner pressure controlling means is spatially

connected to the inner zone through at least one means selected from the group

consisting of a gas outlet means, a silicon seed crystals inlet means and an inner zone connecting means, which are spatially connected to an upper part of the inner zone

instead of the silicon particle bed.

10. The method according to any of claims 1, 8 or 9, wherein a pressure controlling

condition of the pressure-difference controlling means comprised in the inner

pressure controlling means and/ or the outer pressure controlling means is

determined based on gas analysis of the gas that is present within or discharged out

of the inner zone and/ or the outer zone by using a gas analyzing means.

11. The method of claim 1, wherein a packed bed of packing materials, which are not

fluidized by the flow of the fluidizing gas, is formed in a lower part of the silicon

particle bed with the height of the packed bed being positioned below the outlet of

the reaction gas inlet means through which the reaction gas is introduced into the

silicon particle bed.