WO2008034576A1 - PRODUCTION DE Si PAR RÉDUCTION DE SiCl4 AU MOYEN DE Zn LIQUIDE, ET PROCÉDÉ DE PURIFICATION - Google Patents

PRODUCTION DE Si PAR RÉDUCTION DE SiCl4 AU MOYEN DE Zn LIQUIDE, ET PROCÉDÉ DE PURIFICATION Download PDF

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Publication number
WO2008034576A1
WO2008034576A1 PCT/EP2007/008089 EP2007008089W WO2008034576A1 WO 2008034576 A1 WO2008034576 A1 WO 2008034576A1 EP 2007008089 W EP2007008089 W EP 2007008089W WO 2008034576 A1 WO2008034576 A1 WO 2008034576A1
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WO
WIPO (PCT)
Prior art keywords
sicl
process according
contacting
metal phase
chloride
Prior art date
Application number
PCT/EP2007/008089
Other languages
English (en)
Inventor
Eric Robert
Tjakko Zijlema
Original Assignee
Umicore
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from EP06019822A external-priority patent/EP1903005A1/fr
Application filed by Umicore filed Critical Umicore
Publication of WO2008034576A1 publication Critical patent/WO2008034576A1/fr

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
    • C01B33/033—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by reduction of silicon halides or halosilanes with a metal or a metallic alloy as the only reducing agents
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/037—Purification

Definitions

  • the invention relates to the manufacture of solar grade silicon as a feedstock material for the manufacture of crystalline silicon solar cells.
  • the Si metal is obtained by direct reduction of SiCl 4 , a precursor that is commonly available in high purity grades.
  • Silicon suitable for application in solar cells is commonly manufactured by the thermal decomposition of SiHCl 3 according to the Siemens process or its variants. The process delivers very pure silicon, but it is slow, highly energy consuming, and requires large investments.
  • SiCl 4 An alternative route towards the formation of Si for solar cells is the reduction of SiCl 4 with metals such as Zn. This process has the potential for significant cost reduction because of lower investment costs and reduced energy consumption.
  • the Si chloride is preferably SiCl 4 , i.e. the same compound as used in the contacting step.
  • the contacting and the separating steps are performed in a single reactor. This is rendered possible by the fact that a major part (more than 50% by weight) of the formed Si is retained in the liquid metal phase.
  • the Si-bearing metal phase as obtained in the contacting step can advantageously contain, besides Si as solute, also at least some Si in the solid state, e.g. as suspended particles. Formation of particular Si may indeed occur during the contacting step, when the Zn metal gets saturated in Si.
  • Solid state Si can also be obtained by cooling the Si- bearing metal phase as obtained in the contacting step, preferably to a temperature of between 420 and 600 0 C.
  • the solid state Si can preferably be separated from the bulk of the molten phase, e.g. after settling. This Si metal phase is however still impregnated with Zn and has to be further processed in the purification step.
  • SiCl 4 it is advantageous to perform the contacting step by injecting SiCl 4 into a bath comprising molten Zn at a flow rate adapted to limit the loss of Si by entrainment with evaporating Zn-chloride, to less than 15% (weight).
  • Flow rates of SiCl 4 up to 50 kg/min per m 2 of bath surface are compatible with the abovementioned low Si losses.
  • the gaseous SiCl 4 is adequately dispersed in the bath, e.g. by using multiple submerged nozzles, a submerged nozzle equipped with a porous plug, a rotating gas injector, or any other suitable mean or combination of means.
  • the SiCl 4 can be injected along with a carrier gas such as N 2 .
  • a flow rate over 10, and preferably 12 or more kg/min per m 2 of bath surface is advised to perform the process in a more economical way.
  • the obtained Zn-chloride can be subjected to molten salt electrolysis, thereby recovering Zn, which can be recycled to the SiCl 4 reduction step, and chlorine, which can be recycled to a Si chlorination process for the production of SiCl 4 ;
  • - Zn that is vaporised in the purification step can be condensed and recycled to the SiCl 4 contacting step; and/or- the fraction of SiCl 4 that exits the contacting and the purification steps un-reacted can be recycled to the SiCl 4 contacting step, e.g. after condensation.
  • SiCl 4 is reduced with liquid Zn.
  • the technology for this process is therefore much more straightforward than that required for the gaseous reduction process.
  • a Si-bearing alloy containing both dissolved and solid Si can be obtained, while the chlorinated Zn either forms a separate liquid phase, containing most of the solid Si, or is formed as a vapour.
  • Zn can be retrieved from its chloride, e.g. by molten salt electrolysis, and reused for SiCl 4 reduction.
  • the Si-bearing alloy is purified at high temperatures, above the melting point of Si, which is well above the boiling points of both Zn and Zn-chloride.
  • the evaporated Zn can be retrieved and reused for SiCl 4 reduction. Any other volatile element is also removed in this step. It is thus possible to close the loop on Zn, thereby avoiding the introduction of impurities into the system through fresh additions.
  • gaseous SiCl 4 is contacted with liquid Zn at atmospheric pressure, at a temperature above the boiling point OfZnCl 2 (732 °C) and below the boiling point of Zn (907 0 C).
  • the preferred operating temperature is 750 to 880 0 C, a range ensuring sufficiently high reaction kinetics, while the evaporation of metallic Zn remains limited.
  • the molten Zn is placed in a reactor, preferably made of quartz or of another high purity material such as graphite.
  • the SiCl 4 which is liquid at room temperature, is injected in the zinc via a submerged tube. The injection is performed in the lower part of the Zn-containing vessel.
  • the SiCl 4 which is heated in the tube, is actually injected as a gas. It can also be vaporized in a separate evaporator, and the obtained vapours are then injected in the melt.
  • the end of the injection tube can be provided with a dispersion device such as a porous plug or fritted glass. It is indeed important to have a good contact between the SiCl 4 and the Zn to get a high reduction yield.
  • the reduction process produces ZnCl 2 . It has a boiling point of 732 0 C, and is gaseous at the preferred operating temperature. It leaves the Zn-containing vessel via the top. The vapours are condensed and collected in a separate crucible.
  • the process also produces reduced Si.
  • the Si dissolves in the molten Zn up to its solubility limit.
  • the Si solubility in the Zn increases with temperature and is limited to about 4% at 907 °C, the atmospheric boiling point of pure Zn.
  • the amount of SiCl 4 injected is such that the solubility limit of Si in Zn is exceeded.
  • Solid, particulate Si is produced, which may remain in suspension in the molten Zn bath and/or aggregate so as to form dross. This results in a Zn metal phase with a total (dissolved, suspended and drossed) mean Si concentration of preferably more than 10%, i.e. considerably higher than the solubility limit, and thus in a more efficient and economic Si purification step.
  • the particulate Si can be subject to losses by entrainment with the ZnCl 2 gaseous stream, however, in practice the Si loss by entrainment is less than 15% of the total Si input, and this is to be considered as acceptable.
  • the Si-bearing alloy is allowed to cool down to a temperature somewhat above the melting point of the Zn, e.g. 600 °C.
  • a major part of the initially dissolved Si crystallizes upon cooling, and accumulates together with any solid Si that was already present in the bath, in an upper solid fraction.
  • the lower liquid fraction of the metal phase is Si-depleted, and can be separated by any suitable means, e.g. by pouring. This metal can be directly re-used for further SiCl 4 reduction.
  • the upper Si-rich fraction is then subjected to the purification as mentioned above, with the advantage that the amount of Zn to be evaporated is considerably reduced.
  • the molten silicon can be solidified in a single step, chosen from the methods of crystal pulling such as the Czochralski method, directional solidification and ribbon growth.
  • the ribbon growth method includes its variants, such as ribbon-growth-on-substrate (RGS), which directly yields RGS Si wafers.
  • the molten silicon can be granulated, the granules being fed to a melting furnace, preferably in a continuous way, whereupon the molten silicon can be solidified in a single step, chosen from the methods of crystal pulling, directional solidification and ribbon growth.
  • the solid material obtained can then be further processed to solar cells, directly or after wafering, according to the solidification method used.
  • the Zn can be separated from the Si-bearing alloy by vaporisation at a temperature above the boiling point of Zn (907 °C). Si with a purity of 5N to 6N is then obtained.
  • a special high temperature sparging or bubbling step with Cl 2 and/or a gaseous Si chloride typically leads to Si with even superior purity.
  • the temperature is further increased above the melting point (1414 °C) but below the boiling point (2355 0 C) of Si.
  • Some of the elements that can be eliminated efficiently by this process step are Cr, Cu, Mn, Al, Ca, B and P.
  • a further advantage of the invention is that the Si can be recovered in the molten state at the end of the purification process.
  • the Si is produced as a solid that has to be re-melted to be fashioned into wafers by any of the commonly used technologies (crystal pulling or directional solidification).
  • Directly obtaining the Si in the molten state allows for a better integration of the feedstock production with the steps towards wafer production, providing an additional reduction in the total energy consumption of the process as well as in the cost of the wafer manufacturing.
  • the liquid Si can indeed be fed directly to an ingot caster or a crystal puller. Processing the Si in a ribbon growth apparatus is also possible.
  • Example 1 The following example illustrates the invention. 8500 g of metallic Zn is heated to 850 0 C in a graphite reactor. The height of the bath is about 19 cm and its diameter is 9 cm. A MinipulsTM peristaltic pump is used to introduce SiCl 4 in the reactor via a quartz tube. The immersed extremity of the tube is fitted with a porous plug made of quartz. The SiCl 4 , which has a boiling point of 58 °C, vaporises in the immersed section of the tube and is dispersed as a gas in the liquid Zn. The SiCl 4 flow rate is ca. 250 g/h, and the total amount added is 5200 g. The flow rate corresponds to 0.66 kg/min per m 2 of bath surface.
  • the ZnCl 2 which evaporates during the reaction, is condensed in a graphite tube connected to the reactor and is collected in a separate vessel. Any un- reacted SiCl 4 is collected in a wet scrubber connected to the ZnCl 2 vessel.
  • the Si losses can be attributed to the entrainment of particles of Si with the escaping ZnCl 2 vapours, and to the incomplete reduction of SiCl 4 into Si metal. Of the remaining Si, 62 g is found in the ZnCl 2 and about 10 g in the scrubber.
  • the Zn-Si alloy is separated in two fractions of about equal weight. Each fraction is heated to 1550 °C for 1 h in a quartz crucible, in order to evaporate the Zn and melt the Si. A quartz tube is dipped into the molten bath corresponding to a first alloy fraction, and SiCl 4 is bubbled at a flow rate of 200 g/h. The second alloy fraction is not sparged. Both fractions are allowed to cool down to room temperature, under inert atmosphere. Two samples are taken from each fraction, and analysed by Glow Discharge Mass Spectrometry (GDMS). The average impurity levels are reported in the Table below. The concentration of most impurities is significantly reduced by the SiCl 4 sparging step. Table: Impurities in Si after thermal treatment with and without SiC14 bubbling
  • any un-reacted SiCl 4 is collected in a wet scrubber connected to the ZnCl 2 vessel.
  • About 99 kg of Zn-Si phase is obtained.
  • the total Si content of this phase is about 16.5%.
  • the Si reaction yield is thus about 90%.
  • the Si losses can be attributed to the entrainment of particles of Si with the escaping ZnCl 2 vapours, and to the incomplete reduction of SiCl 4 into Si metal. Of the remaining Si, about 1.4 kg are found in the ZnCl 2 arid about 0.4 kg in the scrubber.
  • the Zn-Si phase is separated in two fractions of about equal weight. Each fraction is heated to 1550 °C for 2 h in a silica crucible, in order to evaporate the Zn and melt the Si. A quartz tube is dipped into the molten bath corresponding to a first fraction, and SiCl 4 is bubbled at a flow rate of 1000 g/h during 1 hour. The second alloy fraction is not sparged. Both fractions are allowed to cool down to room temperature, under inert atmosphere. As in the previous example, the concentration of most impurities is significantly reduced by the SiCl 4 sparging step.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Silicon Compounds (AREA)

Abstract

L'invention concerne la production de silicium à degré de pureté élevé qui est utilisé en tant que matériau de base pour produire, par exemple, des cellules solaires à base de silicium cristallin. Le composé SiCl4 est converti en métal Si par contact de SiCl4 gazeux avec du Zn liquide, ce qui permet d'obtenir un alliage comportant du Si et du chlorure de Zn, cet alliage et ce composé étant ensuite séparés. Puis, l'alliage comportant du Si est purifié par chauffage à une température supérieure au point de fusion du Si et par injection de Cl2 et/ou de chlorure de Si gazeux dans la masse en fusion. Ce procédé n'exige pas une technologie compliquée, et permet de conserver le degré de pureté élevé du composé SiCl4 jusqu'a l'obtention du produit final. Le seul autre réactif employé est Zn, qui peut être obtenu à des degrés de pureté très élevés et qui peut être recyclé après l'électrolyse du chlorure de Zn.
PCT/EP2007/008089 2006-09-22 2007-09-18 PRODUCTION DE Si PAR RÉDUCTION DE SiCl4 AU MOYEN DE Zn LIQUIDE, ET PROCÉDÉ DE PURIFICATION WO2008034576A1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
EP06019822.3 2006-09-22
EP06019822A EP1903005A1 (fr) 2006-09-22 2006-09-22 Procédé de production de silicium par réduction du tétrachlorure de silicium par du zinc liquide, et procédé de purification
US84674006P 2006-09-25 2006-09-25
US60/846,740 2006-09-25
EP07010410 2007-05-25
EP07010410.4 2007-05-25

Publications (1)

Publication Number Publication Date
WO2008034576A1 true WO2008034576A1 (fr) 2008-03-27

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WO (1) WO2008034576A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103241742A (zh) * 2013-05-13 2013-08-14 杨恺 高纯度SiCl4提纯方法

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0007063A1 (fr) * 1978-07-11 1980-01-23 COMPAGNIE GENERALE D'ELECTRICITE Société anonyme dite: Procédé et dispositif d'élaboration de silicium polycristallin
JPH1111925A (ja) * 1997-06-25 1999-01-19 Sumitomo Metal Ind Ltd 多結晶シリコンおよび塩化亜鉛の製造方法
JPH1160228A (ja) * 1997-08-12 1999-03-02 Sumitomo Shichitsukusu Amagasaki:Kk 亜鉛還元による高純度シリコンの製造方法
JPH1192130A (ja) * 1997-09-11 1999-04-06 Sumitomo Sitix Amagasaki:Kk 高純度シリコンの製造方法
WO2002016265A1 (fr) * 2000-08-21 2002-02-28 Astropower, Inc. Procede et appareil permettant de purifier le silicium
WO2006100114A1 (fr) * 2005-03-24 2006-09-28 Umicore Procede de fabrication de si par reduction de sicu a l’aide de zn liquide
WO2007013644A1 (fr) * 2005-07-28 2007-02-01 Sumitomo Chemical Company, Limited Procédé servant à produire du silicium polycristallin

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0007063A1 (fr) * 1978-07-11 1980-01-23 COMPAGNIE GENERALE D'ELECTRICITE Société anonyme dite: Procédé et dispositif d'élaboration de silicium polycristallin
JPH1111925A (ja) * 1997-06-25 1999-01-19 Sumitomo Metal Ind Ltd 多結晶シリコンおよび塩化亜鉛の製造方法
JPH1160228A (ja) * 1997-08-12 1999-03-02 Sumitomo Shichitsukusu Amagasaki:Kk 亜鉛還元による高純度シリコンの製造方法
JPH1192130A (ja) * 1997-09-11 1999-04-06 Sumitomo Sitix Amagasaki:Kk 高純度シリコンの製造方法
WO2002016265A1 (fr) * 2000-08-21 2002-02-28 Astropower, Inc. Procede et appareil permettant de purifier le silicium
WO2006100114A1 (fr) * 2005-03-24 2006-09-28 Umicore Procede de fabrication de si par reduction de sicu a l’aide de zn liquide
WO2007013644A1 (fr) * 2005-07-28 2007-02-01 Sumitomo Chemical Company, Limited Procédé servant à produire du silicium polycristallin

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Week 200719, Derwent World Patents Index; AN 2007-192504, XP002462659 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103241742A (zh) * 2013-05-13 2013-08-14 杨恺 高纯度SiCl4提纯方法
CN103241742B (zh) * 2013-05-13 2015-02-18 杨恺 高纯度SiCl4提纯方法

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