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
  • C01B33/037—Purification
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
  • C30B15/34—Edge-defined film-fed crystal-growth using dies or slits
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
  • C30B29/02—Elements
  • C30B29/06—Silicon

Definitions

• the present invention relates to a method of removing nonmetallic impurities from metallurgical silicon.
• metallurgical silicon as used herein is intended to cover all Si quality grades, ie metallurgical silicon, upgraded metallurgical grade silicon, solar grade silicon and electronic grade silicon, and the associated raw material grade silicon. Silicon and the corresponding precursors of the Si quality grades and the corresponding raw silicon The term “metallurgical silicon” is therefore to be interpreted in the broadest sense.
• UMG unidirectional metallurgical-grade
• UMG's raw silicon often still has relatively high levels of impurities that are undesirable and must be removed to produce high quality solar cells can.
• German patent application 10 2008 025 263.8 describes a process for purifying metallurgical silicon, in which silicon containing halogenide has been added, a melt has been produced from the substances, and the impurities have been removed from the melt and sublimated in the form of metal halide. be removed. This method therefore relates to the removal of metals from the metallurgical silicon.
• the method is also suitable for further purification of UMG raw silicon. Removed metals include semimetals, alkaline earth metals, etc. It has also been shown that very good results can be achieved on primary products of UMG raw silicon with this method. Such • precursors are also referred to as raw UMG silicon.
• US Pat. No. 4,312,849 discloses a process for removing phosphorus contaminants.
• a silicon melt is produced, through which a gas is blown containing a chlorine source.
• a vacuum treatment of the melt is performed.
• Yet another known method involves the simultaneous removal of boron and phosphorus by a plasma cleaning process.
• the present invention has for its object to provide a method for removing nonmetallic impurities from metallurgical silicon, which can be carried out in a particularly simple and effective manner.
• This object is achieved in a first variant by a method for removing nonmetallic impurities from metallurgical silicon, comprising the following steps:
• halide-containing silicon used according to the invention is preferably EG-silicon (EG: electronic-grade).
• the solid halide-containing silicon is mixed in the first variant of the method according to the invention with the metallurgical silicon to be cleaned, after which a melt is produced.
• the halide-containing silicon is introduced directly into a melt from the metallurgical silicon to be purified.
• halo-containing compounds are released by the melting of the added halogen-containing silicon and distributed in a homogeneous manner in the melt.
• the halogen-containing compounds convert the non-metallic impurities into volatile compounds (non-metal halides) that escape from the melt, thus achieving the desired cleaning effect.
• the melt is fed in with halide-containing silicon.
• melt is meant the melt consisting of the mixture of halide-containing silicon and the silicon to be purified, or the melt consisting solely of silicon to be cleaned
• the appropriate refining process can be set by the "post-feeding", for example re-greasing - be liert or started again.
• the melt is homogenized. This can be done, for example, via an agitation of the melt, in particular by crucible rotation, use of an agitator, etc.
• the melt can also be homogenized solely by allowing it to stand for a sufficient time so that a suitable homogenization results through convection ,
• the halide-containing silicon used is preferably chloride-containing silicon.
• the halide-containing silicon used may preferably be one which contains halosilane components in a mixture with Si components.
• halosilanes Si n X 2n + 2f where X is halogen and n is 1-10, preferably 1-3
• X is halogen and n is 1-10, preferably 1-3
• the corresponding halide content can be determined quantitatively by titration with silver nitrate (according to Mohr). IR spectroscopic measurements (ATR technique, diamond single reflection) of chlorine-containing silicon show a signal at 1029 cm -1 . The strength depends on the halide content and increases with increasing halide content.
• the halide-containing silicon is preferably used with a halide content of 1 at% to 50 at%.
• a halide content of 1 at% to 50 at%.
• the grain size is expediently 50 microns to 20,000 microns.
• the halide-containing silicon preferably has a bulk density of 0.2 g / cm 3 to 1.5 g / cm 3 .
• the halide content depends on the grain size. With increasing grain size, the halide content increases.
• the purification process according to the invention can be used in particular in Si crystallization processes using UMG crude Si, for example in block casting or Bridgman processes, Czochralsky process, EFG process, string-ribbon process, RSG process.
• the process according to the invention is used for purifying the Si melt from which the ingots (in the case of multicrystalline Si) or crystals (in the case of monocrystalline Si) are produced.
• the Bridgman process multicrystalline ingots are made by passing through controlled directional solidification creates monocrystalline areas of up to several centimeters in diameter.
• the Czochralsky method is a method of producing silicon single crystals by pulling a crystal from the silicon melt. Under pulling and turning movements, a cylindrical silicon monocrystal is deposited on a crystallization seed.
• the process according to the invention preferably uses a halide-containing silicon obtained by thermal decomposition of halogenated polysilane.
• WO 2006/125425 A1 discloses a process for producing silicon from halosilanes, in which, in a first step, the halosilane is reacted to produce a plasma discharge to form a halogenated polysilane, which subsequently decomposes to silicon in a second step with heating becomes.
• the halide-containing silicon used according to the invention can be prepared, for example, by such a process, wherein the silicon used according to the invention should preferably have a relatively high halide content of 1 at% -50 at%.
• This relatively high halide silicon is characterized by relatively low temperatures and relatively high Pressures in the thermal decomposition (pyrolysis) made possible.
• the silicon obtained by thermal decomposition of halogenated polysilane directly precipitates in granular form.
• the granular halide-containing silicon used in the invention is preferably prepared so that the halogenated polysilane is thermally decomposed with continuous addition in a reactor.
• the halogenated polysilane is preferably added dropwise to the reactor.
• This continuous approach achieves the desired relatively high halide content.
• the thermal decomposition preferably takes place in a temperature range of 350 0 C instead of 0 CI.200, wherein the temperature preferably for the decomposition of the halogenated polysilane less than 400 0 C.
• the thermal decomposition is preferably carried out at a pressure of 10 ⁇ 3 mbar to 300 mbar above atmospheric pressure, with pressures> 100 mbar being preferred.
• an inert gas atmosphere in particular argon atmosphere, can be maintained.
• the adjustment of the desired halide content is possible by varying a number of parameters, for example setting a desired time profile, temperature profile and pressure profile.
• the halide-containing silicon is preferably obtained directly in granular form.
• this does not exclude that the final product obtained by further mechanical measures, As mechanical crushing, screening, etc., can be modified accordingly to achieve desired material properties in certain areas.
• a further process variant for adjusting the halide content of the halide-containing silicon used according to the invention relates to an after-treatment of the silicon obtained.
• the halide content can be reduced by heating.
• a specific silicon places (particle size 50 .mu.m to 20,000 .mu.m, chloride content 15%) was reduced by heating at 1150 0 C for four hours up to 4%, for example, the ridge CHIO halt.
• a suitable aftertreatment may be mentioned, for example, baking, baking under vacuum, crushing or sieving.
• the inventive method can be used in particular for removing non-metallic impurities from precursors of UMG silicon.
• precursors relate, for example, UMG materials with reduced cleaning costs, so that by using the method according to the invention, the overall process for the production of "solar grade" materials is cheaper.
• the quality of the corresponding materials can be improved in a controlled manner so that overall solar cells can be produced with higher efficiency at a reduced total cost.
• a mixture of 106.8 g of UMG silicon and 106.5 g of granular silicon obtained by thermal decomposition of halogenated polysilane having a grain size of about 800 ⁇ m and a halide content of about 30 at% was prepared.
• the resulting mixture was placed on an alumina crucible with a coating of Si 3 N 4 and melted in a tube furnace under a pressure of 1 atm and an air atmosphere with a temperature gradient of 4.8 ° C / cm sample volume.
• the heating phase from 20 0 C to 1510 0 C lasted 8 h.
• the melt was held for 2 hours at a temperature of 1,510 0 C.
• By lowering the temperature for 10 h from 1510 0 C to 1280 0 C was followed by crystallization, followed by a cooling process of 1280 0 C to 20 0 C for 12 h followed.
• the present process is particularly suitable for removing metallurgical silicon nonmetallic impurities, UMG raw silicon or UMG silicon precursors. It is preferably used for controlling and / or adjusting the specific resistance of UMG raw silicon or of ingots or crystals of UMG raw silicon or precursors of UMG raw Si.
• the present invention further relates to a metallurgical silicon (as defined at the outset) obtained by a method as described above.
• the metallurgical silicon can be present in multicrystalline or monocrystalline form. It is preferably used for the production of solar cells or semiconductor devices. According to the invention, therefore, improved Si materials from ingots (multi- crystalline Si) and crystals (monocrystalline Si).

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Inorganic Chemistry (AREA)
• Silicon Compounds (AREA)

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• 2008
  • 2008-08-01 DE DE102008036143A patent/DE102008036143A1/de not_active Withdrawn
• 2009
  • 2009-07-29 JP JP2011520323A patent/JP5635985B2/ja not_active Expired - Fee Related
  • 2009-07-29 EP EP09771469.5A patent/EP2321220B1/de not_active Not-in-force
  • 2009-07-29 WO PCT/DE2009/001059 patent/WO2010012273A2/de not_active Ceased
  • 2009-07-29 US US13/057,084 patent/US9327987B2/en not_active Expired - Fee Related

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