CN101563290B - Method and apparatus for improving the efficiency of purification and deposition of polycrystalline silicon - Google Patents

Abstract

Methods and apparatus for the commercial-scale production of purified polycrystalline silicon granules with one or more tailored levels of n- and p- type impurities from an impure silicon source such as, for example, metallurgical-grade silicon. Purification systems and methods involve: (1) one or more series of temperature controlled reactors or vessels provided with dual fluidized beds wherein solids and gases are transported so that varying degrees of purification and deposition of solid silicon is accomplished by strict control of temperature and residence time; (2) separation and recoveryof the compounds of high-melting-point impurities such as, for example, FeSi and FeI2; (3) purification, separation, and recycling of silicon tetraiodide; (4) separation and recovery of iodide compounds of lower-boiling-point liquid impurities such as for example, AlI3, in a continuous fractional distillation column, facilitated by an iodine reflux; (5) separation and recovery of very fine solidparticles including impurity iodides and elemental silicon in a liquid mixture downstream of a fractional distillation column; (6) recovery of input iodine from the oxidation of both solid and liquidiodide impurity waste streams from the process.

Description

Improve the purifying of polysilicon and the method and apparatus of sedimentation effect

The intersection document

The right of priority that No. the 60/838th, 479, the U.S. Provisional Application that the application requires to submit on August 18th, 2006, this paper is with its complete being incorporated herein by reference.

Invention field

The present invention relates to produce the method for silicon raw material, more particularly, relate to the method for purification of impure silicon, it is used to make the pure silicon feedstock of photovoltaic device and other semiconducter device with generation through means of iodine chemical vapor transport.

Background of invention

Owing to comprise soaring oil prices and government factors such as policy to environmental problems such as Global warmings, for the market requirement of the solar energy collecting system of sensitive cell (PV) form in the whole world just with every year above 25% speed increment.The main substrate material of PV is a silicon, account for present installation business equipment about 90%.But, be there is not direct method at present with competitive price production PV level polysilicon (PV-Si) based on a critical defect in the PV value chain of silicon.The major cause of this situation is that in history, PV industry mainly depends on the discarded silicon materials that from microelectronics industry, reclaim.Recently, the whole world has surpassed the supply of the electronic-grade silicon (REG-Si) that reclaims for the demand of PV-Si, and thinks that this silicon source no longer can satisfy the demand of PV industry.

Many PV producers are considering that now direct purchase also is the electronic-grade silicon (EG-Si) that is in nervous supply, but its price exceeds 10 times more than than the historical average price of REG-Si.The high price of EG-Si mainly is because the complicacy and the cost with high investment of at present leading this industrial trichlorosilane and silane process.In many cases, the EG-Si producer also by forward integration in the microelectronics value chain, so optimize these technology for terminal user market (end-user market).PV industry is needed to be simpler, more economical and move safer technology than prevailing EG-Si technology.

At USP 6,712, in 908 and 6,468,886, people such as Wang disclose the three step process of a kind of PV-of production silicon and EG-silicon.The first step, impure metallurgical grade silicon (MG-Si) are under the temperature of T＜900 ℃ and Iod R, and this helps silicon tetraiodide SiI ₄Formation.Produce the SiI of capacity then by this way ₄To fill storage tank.In case produce the SiI of aequum ₄, just be recycled to the initial reactor stage (stage), wherein, temperature has been increased to and has been higher than 1200 ℃, and SiI ₄Produce a large amount of unsettled silicon diiodide vapor compound SiI with the MG-Si reaction ₂SiI ₂Transfer to the colder zone of " cold wall " reactor drum through natural convection, in this zone, its decompose and as polysilicon deposition on the solid substrate that can be inertia or high purity silicon rod.

But, have many problems relevant with the record of this invention and with prior art relevant other problem, but these problems have hindered the realization of method mass-producing, economy of producing PV-silicon and EG-silicon together.Describe these shortcomings below in detail.

1. in the reaction of silicon and deposition, using " cold wall " container is crucial for the method and apparatus of disclosed these inventions of people such as Wang.But because following 3 factors, this will cause for the control of the spatial distribution of siliceous deposits relatively poor: the SiI that 1) forms silicon ₂Decomposition reaction is the function of temperature; 2) SiI ₂Be easy to decompose, do not need solid substrate just can in vapor phase, form solid silicon; 3) at the SiI of reactor drum ₂Form zone (that is, T～1200 ℃) and be at least 500 ℃ with thermograde between the wall regional (that is, T=200-700 ℃).In addition, owing to formed by SiI at reactor bottom ₂Saturated product steam, some steams be to colder move, thereby produced the thermodynamic driving force for the meticulous silica flour nucleogenesis in the vapor phase.Any number between the 10-50% of total silicon amount that the amount of silica flour can produce for any specified time.This silica flour will produce equably, and when being injected into beer still, with liquid silicon tetraiodide SiI ₄Stream is carried secretly together.Because the silica flour of offhand separate entrained, the operation of distillation tower is affected, and for frequent cleaning need stop technology, thereby make that this technology is more infeasible.And the silicon that produces like this is very thin, and because it has the trend of oxidation by air in terminal user's ingot and wafer mfr's facility, generally is not available form.In a word, the interaction of above-mentioned three kinds of factors causes producing a large amount of silicon products that not only is inappropriate for sale but also is difficult to from technology, shift out, thereby has reduced the economic feasibility of people's such as Wang technology.

2.MG-Si in surpass half weight impurity generally form by the Fe atom.Although in bottom, Leng Bi chamber, under about 1250 ℃ temperature, Fe and SiI ₄Reaction forms FeI ₂Steam, but along with vapour temperature is reduced to 700-800 ℃ near cold wall, Fe changes solid FeSi into.Because relatively poor to the cold wall reactor temperature controlling, along with liquid flow flows to the distillation unit, most Fe atom possibly be entrained in the silicon tetraiodide liquid flow as solid.

In addition, under the situation that gas-phase silicon forms, these impurity are because pollution recirculation flow and the inside pipe fitting that stops up distillation tower influence the operation of distillation tower.Do not remove these impurity because people's such as Wang record provides, they will increase during the course, and recycling gets back in the cold wall reactor, greatly reduce the total efficiency of purifying.

3. cold wall reactor is as the operation of natural convection drive system, and this causes near the uppermost areas of reactor drum, forming vaporous cloud.Because the existence of this vaporous cloud can not preferentially be removed boron (B) and phosphorus (P) at the top end part of reactor drum, because remove the iodide of these elements in offhand preferentially other main compound from vaporous cloud such as silicon tetraiodide, iodine and other impurity.And according to people's such as Wang record, any elemental silicon removed unintentionally from this part of reactor drum or iodate silicon can not reclaim and obtain.

4.Wang put down in writing the method and apparatus of purifying silicon tetraiodide in distillation tower Deng the people, this distillation tower moves with batch mode, uses the input SiI that introduces the bottom ₄Stream.This system type is called as " batch distillation that does not have backflow ".In this operational mode, level of purification generally is not very good, can not satisfy the effective required SiI of technology in the circulation loop certainly ₄In 10,000: 1 or higher impurity reduce level.In addition since with startup and out of service relevant expensive, the extensive use of batch distillation is generally infeasible.

5. the iodine raw material that in this technology, adds is generally more expensive than MG-Si.Therefore, need make in the technology use of iodine reduce to minimum and from the impurity output stream, reclaim iodine, but this is an integral part guaranteeing the technology of mass-producing economically.People's such as Wang method and apparatus do not have instruction how from the solid that forms and liquid iodide (like, FeI ₂And AlI ₃) the middle iodine that reclaims.In addition, people such as Wang do not have explanation how the use of iodine in the technology to be reduced to minimum, so that the working cost of initial outlay and business equipment minimizes.

6.Wang Deng people's method and apparatus hypothesis, in case the subordinate phase of operation begins, and silicon tetraiodide recycling gets in the cold wall reactor, just do not have free-iodine (that is, I or I ₂) stay in the system.But, the calculation of thermodynamics demonstration, under 1100-1300 ℃, at reactor bottom, solid Si and SiI ₄Reaction between the steam has produced the compound that following stoichiometric calculation shows: ${\mathrm{Si}}_{\left(s\right)}+2.5\mathrm{Si}{I}_4\⇔3.4\mathrm{Si}{I}_2+2.3I+0.3I_2+0.1\mathrm{Si}{I}_3.$ Owing to ignored the existence of free-iodine, the needs to the raw material of condensation, purifying and this costliness of recycling have been ignored in the distillation tower design, because do not reflux ability at the top of tower.

7. in business-like technology, the iodine raw material contains the impurity that need remove.If propiodal is the caliche mineral reserve, these impurity are generally water, nonvolatile solid and chloro-bromine compounds so.Openly do not remove the method for these impurity people such as Wang.

8.Wang the method for the economy of producing EG-Si is not provided Deng the people.For example, for wherein there not being purifying SiI ₄The situation of recycling, the experimental result of record show that the purity level of B and P is respectively 4 and the 7ppm atom.In order to reduce the level of B and P, even further reduce to the EG-Si specification of ppb-, need SiI ₄Be in 100-1 with the recycle ratio of input MG-Si, in 000 the scope.This recirculation volume is surprisingly expensive in business system, therefore needs a kind of method to come to reduce greatly SiI ₄The size of recycle ratio and distillation tower is so that this chemical process is more more economical than the trichlorosilane and the silane method of the competition of discussing in the past.

9. natural convection is the main pattern of substance transportation in " cold wall " reactor drum.The method of this mixed reactant can not cause high yield, generally avoids the use of in the chemical process system in commercial applications, because it causes the unnecessary cost with high investment of plant and equipment.

10. do not remove the beer still mid-boiling point and be higher than CI ₄The means of liquid iodide impurity.

In a word, the defective of foregoing invention makes its extremely difficult silicon of producing purifying with commercial size economically.

Other relevant prior art comprises: USP 3,006,737, people such as Moates; USP3,020,129, Herrick; USP 4,910,163, Jain; With USP 6,281,098, people such as Wang.

Relevant publication comprises: Herrick, people such as C.S., " High-purity Silicon froman Iodide Process Pilot Plant, " J.Electrochem.Soc., Vol.107, No.2, Feb.1960, pp.111-117; Glang, people such as R., " Silicon ", in The Art andScience of Growing Crystals, John Wiley and Sons, New York, 1963, pp.80-87; Szekely, G., " Preparation of Pure Silicon by Hydrogen Reductionof Silicon Tetraiodide, " J.Electrochem.Soc., Vol.104, No.11, Nov.1957, pp.663-667; Litton, F.B. waits the people, " High Purity Silicon, " J.Electrochem.Soc., Vol.101, No.6, June 1954, pp.287-292; Glang R. waits the people, " Impurity Introduction during Epitaxial Growth of Silicon, " IBMJournal, July 1960, pp.299-301; And Hillel, people such as R., " Stabilit é Thermique et Propri é t é s Thermodynamiques des Iodures de Phosphore al ' é tat Condens é et Gaseux; " J.Chimie Physique, Vol.73, No.9-10; 1976, pp.845-848.

Summary of the invention

Correspondingly, the invention provides the method and system of the silicon that material produce or purifying by multiple source be used for many commercial applications.But the present invention further provides the technology of mass-producing to the commercial ability (that is, annual 500-5,000 ton) of producing PV-level silicon and EG-level silicon by originating such as impure silicon such as metallurgical grade or chemical grade silicon (being generally the silicon of 98-99.5% purity).

Another aspect of the present invention also provides method economy, high-throughput that deposits pure silicon grain, and said pure silicon grain can be used for the main PV producer and uses the application in the continuous processing of being with silicon (stringribbon) or ball shaped unit (spherical cells).

The present invention also provides the device of producing pure granular silicon feedstock.

Embodiments more of the present invention provide through inciting somebody to action not pure silicon and the circulation SiI that comprises purifying ₄And I ₂Flow direction of material first module (two-step fluidized bed reactor assembly) in continuously feeding and produce the method for pure granular silicon feedstock.The first fluidized bed can contain the inert solid material such as silicon-dioxide, and the first fluidized bed maintains constant temp in the whole reactor volume, and from the mixture of wherein letting off steam, this steam mixture contains steam SiI ₂, SiI ₄, I, I ₂, the iodide vapors of the impurity element that in MG-Si, comprises and comprise the entrained solid particulate of unreacted MG-Si.Under the situation that does not have tangible temperature to descend; This vapor/solids mixture is transferred in the separation vessel like cyclonic separator (cyclone); Solid and vapor phase are separated basically in separation vessel, make to comprise that most of entrained particulates of pure silicon is not recovered, and remaining vapor phase are guided into the fluidized-bed that maintains lower in fact temperature and when beginning, in suspension-s, contain some pure silicon seed particles; In this fluidized-bed, SiI ₂Reaction produces pure solid silicon nuclear in vapor phase, and reaction forms film on pure solid silicon seed particles.

Can control the ratio of gas phase and the formation of seed particles silicon through the amount that changes fluidized-bed temperature, steam composition and seed particles.By this way, the size of fluidized bed seed particles is grown in time, and new silicon nuclear forms in gas phase to replenish fluidized-bed.But the high surface area of second fluidized-bed allows high silicon production rate and mass commercial working method.The controllability and the optimization of whole technology have further been improved for the excellent control of fluidized-bed temperature.

The steam flow that leaves second fluidized-bed reactor mainly comprises SiI ₄, I, I ₂And SiI ₃Steam, the iodide vapors of the element impurity of MG-Si and the pure silicon of carrying secretly the nuclear that in the vapor phase deposition reaction process, forms.This vapor/solids mixture is transferred in the solid/gas separation device like cyclonic separator; The solid/gas separation device maintains the temperature more lower slightly than second fluidized-bed, thereby makes that further silicon nucleogenesis minimizes in the vapor phase in the second fluidized-bed downstream.In cyclonic separator, catch pure silicon nuclear, make it turn back to fluidized-bed then, as the seed particles of further siliceous deposits.Can take out with the pure silicon particle in second fluidized-bed or from technology and sell, perhaps be transferred to the further purification step in Unit second, in Unit second, another double-fluidized-bed reactor assembly repeats aforesaid reaction/deposition process.

By this way, the purity of the silicon grain of generation can customize (tailor) through the unit that the n-type and the p-type impurity that use in one or more change grain silicon products are formed.Second unit deposition fluidized bed has the silicon purity range doubly than the high 10-100 of silicon grain that gets into from first module.Further the repeating and in other unit, to take place of this process, but the maximum unit number of economics general requirement.

In first module; The steam flow that leaves the gas/solid separator is quickly cooled to 700-800 ℃ temperature to catch the solid like FeSi through heat exchanger network subsequently; Be transferred to the high-temperature gas filter system then, this filter system is removed these and other solid in the air-flow.

The residuum of steam mixture is caused in another heat exchanger system; In this heat exchanger system; Temperature further is reduced to 200-300 ℃; Thereby condensation part steam, then with this liquid/vapor mixture near near the introducing continuous fractionation tower of two positions (the long mid point of tower with the bottom of tower).The liquid in the distillation tower and the component of steam mainly are SiI ₄Because in technology, need supplementing iodine, iodine vapor/flow that therefore will be pure is relatively more being introduced in the separation column near the top of tower, and further purifying in tower.In distillation tower, product and outgoing position thereof are following: the iodide of higher (that is AlI, ₃, TiI ₄, CI ₄And PI ₃) near bottom, take out; SiI ₄Near the middle level, take out; More lower boiling compound (that is BI, ₃) near the upper strata, take out; The iodine of purifying takes out from the top, and as the backflow to this tower, thereby steady-state operation is provided.With the pure iodine liquid and the SiI that produce by this way ₄Be transferred in the liquid/solid strainer, this liquid/solid strainer is removed any particulate that possibly be entrained into distillation tower or in distillation tower, form.Part contains iodine and SiI ₄Filterable liquid flow and then be circulated back to the first module fluidized-bed reactor, and if final silicon purity target need, then guide this part into Unit second double-fluidized-bed reactor drum with the ratio that helps further silicon purifying.Whole technology is generally moved under the absolute pressure that only is slightly higher than 100kPa, but distillation tower also can move under vacuum condition.

All impurity iodides of in Unit first or second, collecting (for example, solid FeI ₂, liquid A lI ₃With liquid PI ₃) be mixed together with the form of liquid/solid slurry, and inject reactor drum 400-900 ℃ of heating, that have oxygen containing dry atmosphere continuously.Under these conditions, the oxide compound of most of impurity element is more stable than its corresponding iodide, thereby can be with the iodine of the transformation efficiency disengaged vapor form of 90-95%.The air-flow that is loaded with iodine is cooled to the fusing point that is lower than iodine then by stages, and the neat liquid iodine of generation is recycled in the pure iodine streams at the distillation tower upper reaches.By this way, the iodine that is fed in the production of polysilicon technology of major part is recycled and reused.

Consider in conjunction with following description and accompanying drawing, can further understand other purpose of the present invention and advantage.Although following description possibly contain the detail of describing embodiment of the present invention, this should not be construed as the restriction for scope of the present invention, but as the example of preferred implementation.For each aspect of the present invention, many variations that those of ordinary skills knew that this paper proposes are possible.Can under the situation that does not deviate from spirit of the present invention, make many variations and modification within the scope of the invention.

Description of drawings

Add this paper and constitute the accompanying drawing of the part of specification sheets, the preferred embodiment of the present invention has been described, and has been explained principle of the present invention with describing part.

Fig. 1 is the device synoptic diagram that shows the streams that is used for commercial prodn PV-silicon and EG-silicon.

Fig. 2 shows the device synoptic diagram that from the waste streams of technology shown in Figure 1, reclaims the streams of iodine.

Fig. 3 has the integrated silicon purification of dual-reaction chamber or the synoptic diagram of depositing system.

With reference to quoting

This paper is introduced in all publications of mentioning in the specification sheets and patented claim as a reference, as each independent publication or patented claim especially, be incorporated herein by reference individually.

Preferred implementation details

The invention provides the method and apparatus of the polycrystalline silicon raw material product of producing one or more n-types that contain tailored levels and p-type impurity.Can use the disclosed technology of this paper and install high yield and produce various other silicon of level at low cost.

Referring to Fig. 1, impure silicon materials is introduced in the densifications mutually as the first fluidized bed 10 in the unit 1 of double-fluidized-bed system through piping 11.To comprise circulating liquid SiI ₄With 52 vaporizations of the liquid mixture of iodine, and be with or without down auxiliary such as the rare gas element 10a of argon, the bottom through fluidized-bed 10 pumps in the unit 1.The mol ratio of circulating liquid and impure silicon materials generally is not more than about 20: 1.

Fluidized-bed 10 maintains the 1200-1350 ℃ of steady temperature in the scope in its whole volume, and can contain the inert particulate such as high-purity quartz, promoting suitable mixing behavior, and the ratio of adjustment MG-Si and circulating liquid 52.Be appreciated that; Reactor drum provided by the invention or container; The reactor drum or the container that comprise the fluidized- bed 10,20,60,70 that is used for unit 1 and 2; Can be processed by structured material, said structured material generally comprises provides the internal layer ceramic shell of the outer layer metal of structural strength alloy housing with the high temperature corrosion that is exposed to a particulate, the halogen-containing steam that wherein contains of opposing.

Impure silicon materials mainly comprises silicon, but also contains p-type and n-type impurity such as boron or phosphorus, and possibly contain the extensive combination of metallic element and non-metallic element.Quartz particle has suitable size, and generally is retained in the densification mutually, basically not with vapor reaction.Impure silicon materials particulate and iodine and SiI in the fluidized-bed 10 ₄Vapor reaction, mainly produce vapor species SiI ₂, SiI ₄, I, SiI ₃Iodide vapors with some impurity element.Under isothermal condition, this steam flow migrates out the fine and close phase of fluidized-bed 10, gets into separator 14 through piping 13, like cyclonic separator (cyclone separator).Along with impure pasc reaction; Its particle diameter and quality are reduced to a certain degree; Fluidizing medium this moment (fluidizing medium) has to be enough to remaining small-particle is transported to the momentum in the separator 14, through piping 16 they is shifted out from technology from separator 14.Usually, can to remove diameter be 1 micron or littler particulate to separator 14.The bigger particulate that removes unintentionally from fluidized-bed can separate from particulate, and turns back to fluidized-bed 10 through piping 12.

Can separate the steam flow that deducts the particulate that removes like this, be used for further handling according to the present invention.The steam of the preferred free from dust that forms like this leaves separator, and is transported to heat exchanger 25 through pipeline 15, and heat exchanger 25 makes temperature reduce several Baidu in short range.Because steam cools off by this way, silicon have in gas phase with very little nuclear or on heat-exchanger surface with the trend of thin film deposition.The residence time of the weak point in the heat exchanger and flow pattern minimize these trend basically.The refrigerative steam that forms like this gets into the bottom of second fluidized-bed 20 that maintains the 800-1000 ℃ of steady temperature in the scope through piping 24.Perhaps, heat exchanger 25 can be positioned within second fluidized-bed 20 the direct upper reaches with break plate.Another selection scheme that proposes is, second fluidized-bed 20 on its shell or densification contain heat exchange chuck (jacket) mutually.In this case, the steam 15 of free from dust remains on the operating temperature of the first fluidized bed 10, gets into the fine and close phase of second fluidized-bed 20 until it, is cooled off by the particulate of a large amount of lesser tempss thereafter.

In the starting period of this process, second fluidized-bed 20 can comprise the fine and close phase of the initial seed particles with high purity silicon.Can regard fluidized-bed 20 as two different phases---contain the fine and close phase of the well-mixed suspended particulates that are soaked in the steam, with comprise the vapour bubble that mainly moves up in vertical direction second mutually.The benefit of bubble formation is to provide extra high solid mixing velocity, causes having homogeneous temp in the whole bed volume.Shortcoming is that bubble causes steam to walk around reaction zone and productive rate totally descends.In this case, the steam that contains in the bubble tends to mainly in gas phase, produce silicon, and the steam in the densification mutually then tends on particulate with the form of film depositing silicon.Thereby dense phase particles is grown in this process, and new silicon particle nuclear then passes through SiI ₂Even gas-phase reaction in vapor phase and adding.Because this performance in the operational process of fluidized-bed 20, generally need not add new high-purity seed silicon particles.Because dense phase silicon particles reaches bigger size, it is useful from fluidized-bed 20, taking out them through piping 22.These particulates can be by sale 23 or the fluidized-bed 70 in piping 21 pilot units 2, as the parent material that is similar to aforesaid second purification sequence.

Some silicon nuclears that will in the gas phase of fluidized-bed 20, form shift through piping 29, get in the separator 27 like cyclonic separator, and in separator 27, they separate with steam, and leave through separator, turn back to fluidized-bed through piping 26.Separator 27 remains below about 800 ℃ temperature, minimizes so that any residual silicon in fluidized-bed 20 downstream forms.

The steam that leaves separator 27 is transported in the heat exchanger 32 through piping 28; Heat exchanger 32 is reduced to 500-700 ℃ with vapour temperature; Steam arrives high-temperature filter 30 through pipeline 31 then, and high-temperature filter 30 is caught the impurity fine particles like FeSi and HMP iodide, as filter residue.Impurity is regularly removed from strainer 30, and be collected in the container 33.

Filterable steam is transported to heat exchanger 35 through piping 34, causes SiI thereby heat exchanger 35 is reduced to 200-300 ℃ with vapour temperature ₄Condensation.The vapour-liquid mixture that obtains is divided into two plumes, and the part material pumps into the middle portion of through-plate tower (tray-tower) distillation tower 40 through piping 36, and the part material pumps into reboiler part 46 through piping 36a.The iodine of commercial grade iodine raw material or recycling from waste recovery process (as shown in Figure 2) is vaporized, and be fed in the distillation tower through pipeline 82 through pipeline 81 and condensing surface 80.The continuous output stream of distillation tower 40 comprises liquid SiI ₄(boiling point, 288 ℃) 44, liquid iodine (boiling point, 183 ℃) 51 and (if existence) argon gas 49.At the top of tower, continuous backflow 42 mainly is an iodine, its condensation in reflux exchanger unit 41.If in technology, use rare gas element, then, from iodine vapor, separate, and, turn back in technique unit 1 and 2 through piping 10a and pipeline 70a respectively through piping 49 with its cooling like argon.In the bottom of tower, reboiler 46 is used for controlling the temperature of boiling thing 47 continuously, and boiling thing 47 mainly comprises the high-boiling-point impurity like aluminum iodide (boiling point, 382 ℃) and titanium iodide (boiling point, 377 ℃).In the operational process of distillation tower, a certain amount of impurity liquid shifts out from following column plate (column trays) in batches: boron iodide (boiling point, 210 ℃) 43, iodate phosphorus (boiling point; 316 ℃) and iodate carbon (boiling point; 320 ℃) 45, and aluminum iodide, and the liquid iodide 48 of higher.These liquid flow are sent to useless iodine as shown in Figure 2 then and reclaim technology.From the liquid iodine of recirculation loop through piping 51 transhipments, with liquid SiI through the purifying of piping 44 ₄Merge, and in liquid-solid strainer 50, filter, to shift out any particulate that floats on a liquid.These solia particles comprise impurity iodides and other impurity compound of not caught by gas-solid filter 30, purifying silicon with other with raw material introduce in the technology or because the solid pollutant that the corrosive nature of process vessel wall produces.Its downstream from distillation tower are shifted out guaranteed that the solid the recirculation flow can not pollute technique unit 1 and 2.Regularly from technology, remove filter residue 53.The liquid iodine of purifying and SiI ₄Mixture be recycled in the unit 1 and 2 of this technology through pipeline 52 or 54 respectively.

In unit 2, double-fluidized-bed system equally repeats as unit 1.But, the flow velocity that should be noted that size and the material of the equipment in this part of technology be not must with unit 1 in identical.In addition, the silicon of the purifying that this unit obtains can mix with the purifying silicon that last unit obtains in varing proportions, thereby the final silicon product that further customizes n-type and p-type impurity is formed.

The silicon particle of purifying that is in the temperature of fluidized-bed 20 is continuously fed in the densification mutually of the fluidized-bed 70 that remains on 1200-1350 ℃ of temperature through feeding screw or other mechanical means.Heating liquid SiI ₄With the circulating mixture of iodine, and the bottom of introducing fluidized-beds through piping 54.If need in the technology, also inert gas 70a can be provided.As the same in unit 1, generally be not more than about 20: 1 through the circulating liquid of piping 54 and mol ratio through the purifying silicon material of piping 21.Fluidized-bed 70 is kept the 1200-1350 ℃ of constant temp in the scope in its whole volume, and can contain the inert particulate just like high-purity quartz.Because the process step through list the front has been removed most of metal and other non-metallic element, the silicon particle of the purifying in the fluidized-bed 70 and iodine and SiI ₄Vapor reaction, mainly produce vapor species SiI ₂, SiI ₄, I, SiI ₃It mainly is the iodide impurities steam of B, P and carbon.Under isothermal condition, this steam flow migrates out the fine and close phase of fluidized-bed 70, is transferred to separator 72 through piping 74.Silicon particle reaction along with previous purifying; Its particle diameter and quality are reduced to a certain degree; Fluidizing medium has at this moment is enough to remaining small-particle is transported to the momentum in the cyclonic separator 72, from cyclonic separator 72, catches them, and turns back to fluidized-bed 70 through piping 71.The silicon particle of the too little and previous purifying that is difficult to remove with steam from separator 72 in piping 73 is transported to heat exchanger 62, heat exchanger 62 reduces several Baidu with temperature in short range.These particulates finish as seed particles in fluidized-bed 60.When this vapor/solids mixture is cooled off by this way, exist silicon in gas phase with very little nuclear deposition or on heat-exchanger surface and the purifying silicon particulate of carrying secretly with the trend of thin film deposition.The residence time of the weak point in the heat exchanger and flow pattern minimize these trend basically.Perhaps, heat exchanger 62 can be positioned within second fluidized-bed 60 and the direct upper reaches that are positioned at break plate.The refrigerative steam that forms like this gets into the bottom of second fluidized-bed 60 that maintains the 800-1000 ℃ of steady temperature in the scope through piping 61.As stated, if heat-eliminating medium is provided on chuck or in the densification mutually, this temperature reduction also can occur in the fluidized-bed 60.In the starting period of this process, the densification of fluidized-bed 60 comprises the seed particles of high purity silicon mutually, but for above-mentioned reasons in operational process generally without any need for replenishing.Because dense phase silicon particles reaches bigger size, it is useful from fluidized-bed 60, shifting out them through piping 63.These particulates can be used as the silicon sale of higher degree or guide to Unit the 3rd etc., are used for producing more highly purified product.

Some silicon nuclears that in the gas phase of fluidized-bed 60, form shift through piping 66 and get in the separator 65, and in separator 65, they separate with steam, and turn back to fluidized-bed through piping 67.Separator 65 remains below about 800 ℃ temperature, minimizes so that any residual silicon in fluidized-bed 60 downstream forms.The steam that leaves separator 65 is transported to heat exchanger 32 through piping 64, and therefore gets into described last process step again.

Fig. 2 has shown the process flow sheet that reclaims iodine in the waste streams from Fig. 1.The flux that should be noted that this technology generally is about 1/100 of an aforementioned technology, and along with the amount of equipment corrosion product final in the amount of impurity among the MG-Si and the waste streams and change.

From the liquid flow 43,45,48 of the distillation tower among Fig. 1 40 individually or mix ground warp piping 11 and get in the mixing vessel 10 of 200-300 ℃ of temperature.From the filter residue efflux of solids 33,53 of the said technology of Fig. 1 individually or mix ground warp piping 12 and get in the mixing vessels 10.The relative proportion of stream 11 and 12 changes according to the level of the composition of pollutent, especially boron, phosphorus, lead, arsenic and mercury.Too high and can not realize under the situation that enough iodine reclaims at the content of these concrete impurity, contain the specific stream of impurity with mode individual curing described below.

Liquid/solid mixtures is transferred to well heater 30 through piping 13, and well heater 30 is elevated to the temperature of streams about 400 ℃.Then the slurries of heating are ejected into through piping 31 and contain just like the inert particulate of silicon-dioxide and be lower than the bottom of the fluidized-bed reactor 50 that moves under the absolute pressure of about 1000kPa.According to the composition of the impurity element in the streams in the pipeline 31, fluidized-bed 50 remains on 400-900 ℃ temperature.Oxygen containing gas gets into through piping 21 and contains in the tower of silica gel or other absorption agent, and water cut is reduced to ppm.This step is useful for reducing big water gaging with the possibility that recycled iodine gets into the technology of Fig. 1.Then oxygen containing dry gas is pumped in the combustion heater 40 through piping 22, combustion heater 40 is elevated to 500-900 ℃ with the temperature of air-flow 41, imports the bottom of fluidized-bed 50 then with the speed that is enough to the thorough mixing inert particulate.

In fluidized-bed 50, solid that oxygen in the air-flow 41 and streams 31 contain and the reaction of liquid impurity iodide produce soild oxide and contain I ₂Steam with I.The impurity iodides that surpasses 95 weight % is reacted by this way.Under 700 ℃, the stabilization of solid oxide compound that containing the key element that reclaims fully in the atmosphere of the excessive oxygen of stoichiometry is following: Fe ₂O ₃, Al ₂O ₃, VO ₂, TiO ₂, CaO, NiO, Mn ₂O ₃, Cr ₂O ₃, MgO, ZrO ₂, CuO, CdO, SnO ₂, Bi ₂O ₃, SbO ₂, SrO, TeO ₂, In ₂O ₃, Co ₃O ₄And Ga ₂O ₃In fluidized-bed, produce the soild oxide of these impurity elements on silica particle surface or in the gas phase.The oxide compound B of boron ₂O ₃Oxide compound As with arsenic ₂O ₅In fluidized-bed, can be solid or liquid, this depends on that temperature is higher than respectively or is lower than about 450 ℃ and 600 ℃.Owing to existing the liquid oxidation thing to go under the fluidised situation, two-stage oxidation is suitable, and perhaps, fluidized-bed 50 can be by the operation of fast fluidized scheme to eliminate this potential problem effectively.

If oxide compound forms on silicon dioxide microparticle, the size of these particulates increases in time so, and finally shifts out from fluidized-bed through piping 53.Similarly, if the oxide core that in gas phase, forms is suspended in the fluidized-bed even as big as keeping, they also increase in time and finally shift out through piping 53 so.But some gaseous oxidation things forms particulate or small droplets, said particulate or small droplets too little thereby can be from fluidized-bed 10 elutriation and getting in the separator 51, in separator 51, they are separated from the gas in stream 54.Because operating temperature is lower, gets into the boron of separator 51 and the liquid oxidation thing of arsenic and can change solid into.

Temperature is that 300-400 ℃ the steam flow that does not contain particulate is discharged from separator 51, and introduces in one or more heat exchangers 60 through piping 52.Heat exchanger 60 is reduced to the temperature of steam flow about 200 ℃ in the exit, and steam is transferred in the condensing surface 70 through piping 61 then, and condensing surface 70 makes the temperature of steam be slightly higher than the fusing point (that is, 113 ℃) of iodine.In condensing surface, near the inlet of condensing surface 70, iodine vapor is in about 183 ℃ of beginning condensations.Along the length of prolong, the dividing potential drop of pure iodine vapor is reduced near the about 80mm Hg of outlet from the 760mm Hg of ingress.By this way, approximately the iodine of the introducing condensing surface 70 of 80-90 weight % is converted into liquid form.In piping 71 pumping liquids-solid filter 72, strainer 72 is removed any residual particulate of not caught by cyclonic separator 51 to the liquid iodine of condensation then.In addition, strainer 72 is also removed the phosphorous oxides (P that in the time of about 200 ℃, in condensing surface 70, is formed by the same steam of forming ₂O ₅) ₂Remove the filter residue that produces in the strainer 72 through piping 73, and filterable liquid iodine is delivered in the iodine material of purifying as shown in Figure 1.

From the steam flow of condensing surface 70 then through piping 74 pumps to cooling water heat exchanger 80,, to refrigeration unit 90, then be transported to and be lower than about 10 ℃ down in the cloth filters 100 of operation through piping 81 pumps through piping 91.In these process steps, iodine vapor is converted into solid form, and reclaims as filter residue, is recycled in the iodine material of the purifying in the technology of Fig. 1.Because under these temperature, the dividing potential drop of the pure iodine in the air-flow is reduced to and is lower than about 0.1mm Hg, has reclaimed most of residual iodine so by this way.Contain aerobic and a small amount of CO ₂Filterable air-flow shift through piping 101 then and get in the splitters (splitter), some gas is recycled in the air-flow 21 that iodine reclaims technology through 102 thus, and some gaseous emissions are in surrounding environment.

Fig. 3 has explained another aspect of the present invention, and it provides a series of one or more silicon processing module.Based on concrete application, this module can dispose and be used for silicon purifying, siliceous deposits or the processing of other silicon.A kind of processing module of the silicon with dual-reaction chamber that preferred embodiment provides of the present invention.For example, reaction chamber #1 can be thermoregulator, is used for being created in the silicon iodide vapor product of operation in first TR.Input or the material that one or more various silicon are handled material can be accepted in this chamber, like other local described impure silicon materials of this paper, inert gas/solid materials and iodine or silicon iodide vapor mixture.Of the present invention a kind of preferred embodiment in, each chamber can dispose the performance two kinds of effects device: the pasc reaction device of fluidized-bed according to a further aspect in the invention with silicon and inert material; With the separator that is used to separate silicon iodide vapor product (like cyclonic separator).In alternate embodiments of the present invention, can in the equipment that separates, exercise every kind of function, like the reactor drum and the separator (see figure 1) of a series of thermal controls and fluid connection.The silicon iodide vapor product that in reaction chamber #1, produces can be delivered among the reaction chamber #2 that in second TR, moves through thermoswitch.Owing to have thermograde between the reaction chamber, in reaction chamber #2, there is or do not exist the silicon seeds particulate, therefore can form the solid silicon product of purity with selection level according to the present invention.Thermoswitch can be any device that produces or keep the intermediate temperature range that needs.A kind of heat exchanger that preferred embodiment comprises between the first and second temperature regulation containers of the present invention so that selectable thermograde to be provided, thereby helps the formation of solid silicon product between them.A kind of preferred embodiment in, in the fluidized-bed among silicon iodide vapor product can transfer to and maintain relatively lower temp, can contain at least some pure silicon seed particles in suspension-s the reaction chamber #2.Thereby, like SiI ₂Silicon iodide vapor product not only can in vapor phase, react producing pure solid silicon product, and can on seed particles, react the film that can from reaction chamber #2, take out to form.Because silicon particle reaches bigger size, they itself can be used as commercial end product and take out, or as parent material or system's input thing, and being used for can be in another continuous silicone processing module another processing of multiple or purification sequence as stated.As other embodiment of the present invention, shown silicon processing module can connect with series system.Further handle or purifying can be realized through silicon iodide vapor and/or other input thing are delivered in the successive module.

Can regard aforementioned part as the just example of the principle of the invention.Further; Because those skilled in the art can expect many modifications and variation; With described concrete structure and operation, thereby all suitable modifications and equivalence can drop in the following scope of the present invention that claims limited shown in it be not desired to limit the invention to.

Claims (21)

1. the method for a purifying silicon comprises:

(a) with the recycling of impure solid silicon raw material and purifying contain silicon vapor input first class bed bioreactor, the recycling of wherein said purifying contains silicon vapor and comprises SiI ₄And I ₂Steam;

(b) make the said impure solid silicon raw material and the siliceous vapor reaction of recycling of said purifying, to generate steam mixture, wherein said steam mixture comprises SiI ₂, SiI ₄, I ₂, I and from the iodine vapor that contains of the impurity of said impure solid silicon raw material;

(c) comprise the excessive impure solid silicon and the output of steam mixture from said first class bed bioreactor output;

(d) said output is transferred in the solids-gases separator;

(e) said output is separated into solid separated and isolating steam;

(f) from the solids-gases separator, shift out the fine powder part of said solid separated, and the coarse fraction of said solid separated is turned back to said first class bed bioreactor;

(g) with said isolating vapor transfer to second fluidized-bed reactor;

(h) when initial, pure silicon seeds particulate is provided to said second fluidized-bed reactor;

(i) said second fluidized-bed reactor, form pure silicon grain from said isolating steam; With

(j) from the pure silicon grain of second fluidized-bed reactor output.

2. the method for claim 1, wherein said second fluidized-bed reactor maintains 800-1000 ℃ temperature.

3. method as claimed in claim 2, wherein, said first class bed bioreactor maintains 1200-1350 ℃ temperature.

4. method as claimed in claim 3, wherein, said solids-gases separator maintains and the similar temperature of said first class bed bioreactor.

5. method as claimed in claim 4, wherein, said second fluidized-bed reactor maintains the temperature lower in fact than first class bed bioreactor.

6. method as claimed in claim 5, wherein, in said second fluidized-bed reactor, the SI in the isolating steam ₂Reaction forms pure solid silicon nuclear in steam, and reacts with said initial silicon seeds particulate, on said seed particles, forms said pure silicon particulate film.

7. method as claimed in claim 6, wherein, SiI ₄, I ₂, I, SiI ₃With the mixture that contains iodine vapor from the impurity of said not pure silicon feedstock be the output of said second fluidized-bed reactor.

8. method as claimed in claim 7 wherein, offers the second solids-gases separator with said mixture and said pure silicon particle.

9. method as claimed in claim 8, wherein, the said second solids-gases separator maintains than the lower temperature of said second fluidized-bed reactor, so that the silicon nucleogenesis in the gas phase in the said second fluidized-bed downstream minimizes.

10. method as claimed in claim 9 wherein, turns back in said second fluidized-bed reactor from the pure solid silicon nuclear of the said second solids-gases separator.

11. the method for a purifying silicon comprises:

The silicon raw material and the input of iodo steam that will have the initial purity level are set in the first temperature regulation reaction chamber of first temperature;

Silicon raw material and iodo steam are reacted in the first temperature regulation reaction chamber so that silicon iodide vapor product to be provided;

Silicon iodide vapor product is transferred in the second temperature regulation reaction chamber that is set at second temperature; With

Silicon iodide vapor product is reacted in the second temperature regulation reaction chamber, and in the second temperature regulation reaction chamber, to form solid silicon product, the purity level of this solid silicon product surpasses the initial purity level of silicon raw material.

12. method as claimed in claim 11, wherein, the said first and second temperature regulation reaction chambers comprise the fluidized-bed that is used for the auxiliary temperature adjusting.

13. method as claimed in claim 12, wherein, said fluidized-bed is formed by silicon materials and inert material.

14. method as claimed in claim 13, wherein, said silicon materials are made up of the silicon seeds particulate.

15. wherein, there is thermograde in method as claimed in claim 11 between the temperature of the first and second temperature regulation reaction chambers.

16. method as claimed in claim 11, wherein, the said second temperature regulation reaction chamber maintains than the lower in fact temperature of the first temperature regulation reaction chamber.

17. method as claimed in claim 11, wherein, said vapor product comprises following at least a: SiI ₂, SiI ₄, I ₂, I, impurity the SiI that contains iodine vapor, recycling ₄, recycling I ₂Steam or its combination.

18. method as claimed in claim 11 wherein, before transferring to the second temperature regulation reaction chamber, uses solid-vapour separator to separate said silicon iodide vapor product.

19. method as claimed in claim 11, wherein, said silicon iodide vapor product is transferred to the second temperature regulation reaction chamber through over-heat-exchanger under the thermal control condition.

20. method as claimed in claim 11, wherein, said solid silicon product forms in the second temperature regulation reaction chamber, in the presence of the silicon seeds particulate.

21. a silicon processing module contains:

Be used for producing the first temperature regulation reaction chamber of silicon iodide vapor product, the said first temperature regulation reaction chamber moves in first TR;

Accept silicon iodide vapor product and produce the second temperature regulation reaction chamber of solid silicon product by silicon iodide vapor product, the said second temperature regulation reaction chamber moves in second TR; With

Heat exchanger between first and second temperature conditioning chambers, it is used between first and second temperature conditioning chambers, providing selectable thermograde, to help the formation of solid silicon product.

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