CN101146743A - Process for the production of si by reduction of siclj with liquid zn - Google Patents

Abstract

The invention relates to the manufacture of high purity silicon as a base material for the production of e.g. crystalline silicon solar cells. SiCU is converted to Si metal by contacting gaseous SiCU with liquid Zn, thereby obtaining a Si-bearing alloy and Zn-chloride, which is separated. The Si-bearing alloy is then purified at a temperature above the boiling point of Zn. This process does not require complicated technologies and preserves the high purity of the SiCU towards the end product, as the only reactant is Zn, which can be obtained in very high purity grades and continuously recycled.

Description

By reduce SiCl with liquid zn 4The method for preparing Si

The present invention relates to as the preparation that is used to make raw-material solar battery grade (solar grade) silicon (Si) of solar cells made of crystalline silicon.Described Si metal is by directly reducing SiCl ₄, a kind of precursor that can obtain with high purity usually, and obtain.

The silicon that is applicable to solar cell passes through SiHCl usually according to Siemens method or its process variant ₃Thermolysis production.This method can be produced very pure silicon, but its speed is slow, energy consumption is high and require big investment.

The another kind of approach that is formed for the silicon of solar cell is to use metal, for example Zn reduction SiCl ₄Owing to reduced investment cost and reduced energy expenditure, this method can significantly reduce cost.

At US2, described Zn by vapor phase in 773,745, US2,804,377, US2,909,411 or US3,041,145 and directly reduced SiCl ₄When using Zn steam, in fluid bed-type of reactor, form granulous silicon product, this makes the separation of Si easier.Yet, based on the complex process of the production process of this theory.

In JP11-092130 and JP11-011925, described with liquid zn and directly reduced SiCl ₄Si forms fine powder, and passes through by gaseous state ZnCl ₂Byproduct is taken out of and is separated with liquid zn.Yet this technology is not too practical, and this is because the selection of the operational condition that the major part that causes described Si is taken out of along with described gas stream is obviously too harsh.Equally, with described thin Si powder from ZnCl ₂In separate subsequently and handle and melt this thin Si powder and all be a problem.ZnCl ₂Must be evaporated twice in addition, this causes the integral energy efficient of this technology to reduce.

The purpose of this invention is to provide the method that solves the prior art problem.

In order to reach this purpose, according to the present invention, highly purified Si metal passes through SiCl ₄Be transformed into the technology of Si metal and obtain, it may further comprise the steps:

-with gaseous state SiCl ₄Contact with the liquid metal that contains Zn, thereby acquisition contains metallographic phase and the zinc chloride of Si;

-described zinc chloride is separated from the metallographic phase of the described Si of containing; With

-the metallographic phase of the described Si of containing of purifying under the temperature of the boiling point that is higher than Zn, thus evaporate zinc and obtain the Si metal.

Described contact and separating step carry out in single reactor.This becomes possibility by most of (surpassing 50 weight %) formed Si being retained in the fact of described liquid metal in mutually.

By carrying out described contact procedure under the temperature more than the boiling point of the zinc chloride that is higher than evaporation, it is useful that contact and separating step are united.Allow described zinc chloride to discharge, so that its collection is used for further processing.

As the siliceous metal phase that in described contact procedure, obtains, except that Si, some solid-state Si can advantageously also be contained at least, for example as suspended particles as solute.When described Zn metal is saturated in Si, during described contact procedure even can form special Si.Can also by will as described in the Si metallographic phase that contains that obtains in the contact procedure preferably be cooled to 420 to 600 ℃ and obtain solid-state Si.Preferably, for example at post precipitation, can from the body of fusion phase, isolate solid state si.Yet still infiltration has Zn in this Si metallographic phase, and must further handle in purification step.

Advantageously, by under the flow velocity that is suitable for to be limited in along with the loss amount of the Si that takes away of evaporation zinc chloride less than 15 weight %, with SiCl ₄Be blown in the groove that contains molten state Zn and carry out contact procedure.For this purpose, suitable SiCl ₄Flow velocity for being lower than 0.8kg/min/m ²Rooved face is long-pending to be suitable.Yet, if with gasiform SiCl ₄Be dispersed in the described groove, higher speed is high to 10kg/min/m ²Rooved face is long-pending, but preferably is limited to 2kg/min/m ², be matched with the low loss of above-mentioned Si.Use as a plurality of immersion nozzles and can obtain sufficient dispersion, this immersion nozzle has the combination of porous plug, rotation diverting device or these devices.SiCl ₄Can with carrier gas such as N ₂Inject together.

Under the pressure that under the temperature that is higher than the Si fusing point and especially reduces or to carry out described purification step under vacuum be favourable.Can advantageously in same reactor, purify once more as preceding two processing steps.

Recirculation is one or more not to be that the materials flow of finished product also is favourable:

-zinc chloride that obtains can be carried out fused salt electrolysis, can be recycled to SiCl thereby reclaim ₄Zn in the reduction step and can be recycled to and be used to prepare SiCl ₄The Si chloridization process in chlorine;

-Zn that evaporates in purification step can be concentrated, and be recycled to SiCl ₄Conversion process in; And/or for example after condensation, can be with the unreacted SiCl that from contact procedure, discharges ₄Part be recycled to SiCl ₄Conversion process in.

According to the present invention, SiCl ₄Reduce with liquid zn.Therefore it is needed simpler to be compared to gaseous reduction technology for the technology of this technology.What can obtain to contain dissolving and solid Si contains the Si alloy, and chlorating Zn or formation simultaneously contains the separation liquid phase of the overwhelming majority's solid Si, perhaps forms steam.Zn can for example obtain from its muriate by fused salt electrolysis again, and is used for SiCl once more ₄Reduction.At high temperature purifying contains the Si alloy, and this temperature is more than the boiling point of Zn and Zn muriate, but below the boiling point (2355 ℃) of Si itself.Can reclaim the Zn of evaporation and be used to reduce SiCl once more ₄In this step, remove any other volatile constituent.Therefore this can finish the circulation of Zn, thereby avoids by adding new additive impurity being incorporated in the described system.

Should be noted that except Zn, can also use the muriate of formation to compare SiCl ₄More stable, be easy to other metal that from Si, separates and be easy to from its muriate, reclaim.

In a preferred specific embodiments of the present invention, with gaseous state SiCl ₄Under atmospheric pressure, be higher than ZnCl ₂Contact with liquid zn under boiling point (732 ℃) and the temperature that is lower than Zn boiling point (907 ℃).Preferred service temperature is 750 to 880 ℃, and this scope is guaranteed sufficiently high reaction kinetics, limits the evaporation of Metal Zn residuum simultaneously.

In a typical specific embodiments, the Zn that melts is placed in the reactor, this reactor preferably by quartzy or other high purity material as, graphite is made.To under the room temperature be liquid SiCl ₄Be injected in the zinc by dipping tube.Inject at the container bottom that contains Zn.Heated SiCl in the pipe ₄Be actually and inject with gaseous state.End at described injection tube is equipped with diverting device, for example porous plug or sintered glass.At SiCl ₄Good to contact for obtaining high reduction ratio be very important with having between the Zn.The SiCl that can have if not so, partial reduction ₂, perhaps SiCl ₄Described Zn is not reacted.Along with SiCl ₄-Zn full contact can be observed the conversion near 100%.Verified, the described SiCl of good distribution ₄It is the important factor that the restriction air-flow is taken away the Si of good distribution.

Reduction process produces ZnCl ₂Its boiling point is 732 ℃, is gas under preferred working temperature.It leaves the described Zn of containing container by the top.Described steam can concentrate in isolating fusion pot and collect.

Described technology also produces reductive Si.Described Si dissolves the solubleness until it in fusion Zn.Described Si in Zn solubility with temperature and increase, and under 907 ℃ of the atmospheric boiling points of pure Zn, be restricted to about 4%.

In first advantageous embodiment of the present invention, the SiCl of injection ₄Amount surpasses the solubleness of Si in Zn.Produce solid particulate Si, it can be retained in the suspension in fused Zn groove and/or assemble and form dregs.That this causes having in the Zn metallographic phase is total (dissolved, suspension with molten slag), and average Si concentration is preferably and surpasses 10%, promptly is significantly higher than described solubleness, and thereby causes more efficient and more economical Si purification step.Yet any Si particle all may be along with ZnCl ₂Air-flow is taken away and is lost.This risk can be by using enough low SiCl ₄Air-flow and/or guarantee SiCl ₄The method that is dispersed in the Zn melt minimizes.The Si that is pulled away and loses accounts for being lower than of the Si total amount that joins described technology and 15% thinks acceptable.

In second advantageous embodiment of the present invention, allow to contain the temperature that the Si alloy is cooled to be higher than a little the Zn fusing point, for example 600 ℃.The Si of most of initial dissolution crystallization under cooling, and the solid Si that has existed in the chamber in the solid part of top accumulates in.The liquid part that metallographic phase is lower is a scrap silicon, can be with any suitable method, as topple over its separation.This metal can directly be used for further SiCl once more ₄Reduction.The top part that is rich in Si is carried out aforesaid purifying subsequently, and its advantage is significantly to have reduced the amount of the Zn that is evaporated.

Above-mentioned the first and second two embodiments certainly combine.

When carrying out purification step more than the Si fusing point, fused silicon can solidify in an independent step, and this step is selected from as the Czochralski method of Czochralski method, orientation solidification method and ribbon growth method.Described ribbon growth method comprises its deformation method, and as on-chip belt crystal growth (RGS), it will directly make RGS Si wafer.

Perhaps, the molten silicon granulation preferably can be supplied to melting furnace in a continuous manner with described particle, thereby molten silicon can solidify in an independent step, this step is selected from Czochralski method, orientation solidification method and ribbon growth method.

The solid material that is obtained can directly or further be processed into solar cell according to used clotting method after making wafer.

Can separate the Si alloy and typical trace impurity, for example Tl, Cd and Pb Zn together from described containing by evaporation.Obtaining purity then is the Si of 5N to 6N.For these operations, temperature is brought up to the boiling point (907 ℃) that is higher than Zn, and preferably be higher than the fusing point (1414 ℃) of silicon but be lower than the boiling point (2355 ℃) of silicon.Operation is favourable under pressure that reduces or vacuum.Therefore Zn and its volatile impunty are removed from alloy, stay fused Si.The nonvolatile impurity that only exists in Zn in Si keeps.The example of this impurity is Fe and Cu.Their concentration or can pass through fore-distillation Zn, by at the formed ZnCl of electrolysis ₂Repeatedly described Zn is recycled to SiCl afterwards ₄The Zn amount that the Si evaporation of every kg is required drops to minimumly in the reduction step or in described purification step, and drops to minimum.Under this optimized condition, can obtain the Si that purity surpasses 6N.

Further advantage of the present invention is can molten state reclaim Si in the later stage of described purifying process.In fact, in Simens method and its deformation method, described silicon is produced as solid, and described solid must melt it to make wafer again by any technology commonly used (Czochralski method, orientation solidification method).The Si that directly obtains molten state can further reduce the total energy consumption of described technology and the cost of manufacturing wafer better in conjunction with feedstock production and wafer fabrication steps.Described liquid Si can be fed directly in blank casting machine or the crystal puller.Processing Si also is possible in ribbon growth apparatus.

If do not wish the wafer material that manufactures a finished product, and just want the intermediate solid raw material, the purified Si of granulation is favourable.With for example, the bulk that obtains in the technology based on the Simens method is compared, the particle of acquisition is easier to handle and be easy to batching.Under the situation of ribbon growth technologies, this particularly important.The production of free flowing powder can be to CZ smelting furnace or ribbon growth apparatus continuously feeding.

Embodiment 1

The present invention will be described with the following example.The Metal Zn of 4192g is heated to 850 ℃ in graphiote reactor.About 15cm of the height of groove and diameter are 7cm.Minipuls ^TMPeristaltic pump is used for introducing SiCl by silica tube in reactor ₄The immersion end of described pipe is equipped with the porous plug that aluminosilicate is made.Boiling point is 58 ℃ SiCl ₄Gasification in the submergence of described pipe part, and as gas dispersion in liquid zn.Described SiCl ₄Flow velocity is about 150g/h, and the total amount of adding is 1625g.Flow velocity is equivalent to 0.65 kg/min/m ²Rooved face is long-pending.The ZnCl of Xing Chenging during reaction ₂With carbon tube that reactor is connected in evaporation and being concentrated, and in separation vessel, collect.Any unreacted SiCl ₄With described ZnCl ₂Collect in the wet scrubber that container connects.Obtained the Zn-Si alloy, it reaches capacity in Si under general temperature of reactor, and contains other Si solid particulate.The silicon total content is 9% in the mixture.Under the flow velocity of identical 150g/h,, improve SiCl in order to be increased in the amount of Si in the described Zn-Si alloy ₄Addition be enough.This Zn-Si alloy that contains solid Si is heated to 1500 ℃ with an evaporation Zn that concentrated and reclaimed.Then with the Si cool to room temperature; Reclaim the Si of 229g.

Therefore si reaction yield is about 85%.The loss of silicon is because along with the ZnCl that overflows ₂Steam has been taken away the Si particle, and SiCl ₄Incomplete reduction become the Si metal.In remaining Si, at ZnCl ₂In the 40g that has an appointment, 3g is arranged in washer.

Embodiment 2

This embodiment has illustrated the granulating of molten silicon, and when the temperature more than described purification step is fusing point at Si was carried out, this technology was especially suitable.One kilogram molten silicon is remained in the smelting furnace under 1520 ℃.The fusion pot that will comprise this molten metal places inert atmosphere (Ar).This smelting furnace allows fusion pot to tilt, at room temperature molten silicon is poured in the container that contains ultrapure water.Silicon is easy to form the particle of size between 2 to 10mm.

Claims (16)

1. with SiCl ₄Change into the technology of Si metal, it may further comprise the steps:

-usefulness contains the liquid metal and gaseous state SiCl of Zn ₄Contact, thus obtain to contain Si metallographic phase and zinc chloride;

-described zinc chloride is separated from contain the Si metallographic phase; With

-described the Si of the containing metallographic phase of purifying under the temperature of the boiling point that is higher than Zn, thus evaporate zinc and obtain the Si metal,

It is characterized in that described contact and described separating step carry out in single reactor.

2. technology as claimed in claim 1, wherein said contact and described separating step by operation under the temperature of the boiling point of the zinc chloride that is higher than evaporation they and carry out simultaneously.

3. as claim 1 or 2 described technologies, the Si metallographic phase that contains that wherein obtains in described contact procedure comprises to the solid-state Si of small part.

4. as each described technology among the claim 1-3, wherein before described purification step, insert the described Si of containing metallographic phase is cooled to the cooling step of preferred 420 to 600 ℃ temperature, thereby will change into solid-state as the part Si at least that solute is present in the described Si of the containing metallographic phase that obtains in described contact procedure.

5. as claim 3 or 4 described technologies, wherein will separate with the solid-state Si that exists, formation contains the Si metallographic phase, and it is further processed in described purification step.

6. as the described technology of claim 1 to 5, wherein said contact procedure is passed through SiCl ₄Be blown in the groove that contains molten state Zn and carry out, the loss that used flow velocity is suitable for the silicon that will take away along with the evaporation zinc chloride is limited in less than 15%.

7. technology as claimed in claim 6, wherein SiCl ₄Flow velocity be lower than 0.8kg/min/m ²Rooved face is long-pending.

8. as each described technology in the claim 1 to 7, wherein said purification step is to carry out under the temperature that is higher than the silicon fusing point, thereby forms the liquid Si of purifying.

9. technology as claimed in claim 8, wherein said purification step are under the pressure that reduces or carry out under vacuum.

10. as each described technology in the claim 1 to 9, further may further comprise the steps:

-make institute's isolating zinc chloride experience fused salt electrolysis, thus Zn and chlorine reclaimed;

-described Zn is recycled to described SiCl ₄In the reduction step; With

-described chlorine is recycled in the chlorination process of Si, be used to prepare SiCl ₄

11. as each described technology in the claim 1 to 10, wherein the Zn that will in described purification step, evaporate its concentrate and it be recycled to SiCl ₄In the conversion process.

12. as each described technology in the claim 1 to 11, the unreacted SiCl that will in described contact procedure, overflow wherein ₄Part be recycled to SiCl ₄In the conversion process.

13. technology as claimed in claim 8 or 9 comprises the independent curing schedule of purified liquid Si, the method for use is selected from Czochralski method, orientation solidification method and ribbon growth method.

14. technology as claimed in claim 8 or 9 comprises the granulation of purified liquid Si.

15. technology as claimed in claim 14 may further comprise the steps:

-with described particulate charge in melting furnace; With

-carry out independent curing schedule, used method is selected from Czochralski method, orientation solidification method and ribbon growth method.

16., wherein solid materials is made wafer and further is processed into solar cell as claim 13 or 15 described technologies.