WO2008026931A1 - Procédé et équipement pour la fabrication d'un silicium multicristallin de grade solaire à partir de silicium métallurgique - Google Patents

Procédé et équipement pour la fabrication d'un silicium multicristallin de grade solaire à partir de silicium métallurgique Download PDF

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Publication number
WO2008026931A1
WO2008026931A1 PCT/NO2007/000296 NO2007000296W WO2008026931A1 WO 2008026931 A1 WO2008026931 A1 WO 2008026931A1 NO 2007000296 W NO2007000296 W NO 2007000296W WO 2008026931 A1 WO2008026931 A1 WO 2008026931A1
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WO
WIPO (PCT)
Prior art keywords
silicon
boat
housing
heater
refining
Prior art date
Application number
PCT/NO2007/000296
Other languages
English (en)
Inventor
Dag ØVREBØ
William George Clark
Original Assignee
Norsk Hydro Asa
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
Application filed by Norsk Hydro Asa filed Critical Norsk Hydro Asa
Publication of WO2008026931A1 publication Critical patent/WO2008026931A1/fr

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Classifications

    • 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
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/16—Heating of the molten zone
    • C30B13/20—Heating of the molten zone by induction, e.g. hot wire technique
    • 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
    • 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 and apparatus for manufacturing multi- crystalline solar grade silicon from metallurgical silicon.
  • Multi-crystalline silicon wafers for photovoltaic solar cells are predominantly produced by melting refined silicon into blocks which is cut into wafers.
  • the starting material for this process is metallurgical silicon, a typically 99% pure material made from carbo-thermal reduction of silicon oxide (silica).
  • Metallurgical silicon has to be purified before it can be used for PV wafer production. This is now commonly done via the so-called silane route which was developed by Union Carbide and others in the 80's.
  • the silicon is chlorinated with hydrogen and made into trichlorosilane and then further processed into silane (SiH 4 ).
  • the silane is then thermally decomposed into poly silicon - a silicon powder/granule with less than 25 ppm metallic impurity.
  • This process is both capital and energy intensive, and the yield is only 20%, the rest comes off as oxidised silicon (SiCI 2 ), which will have to be disposed or sold as a low value by-product.
  • the refined poly silicon (also called Solar Grade Silicon- SGS) is then shipped to wafer producers, who melt the metal in large blocks and who subsequently cut the large blocks into smaller blocks suitable for wafer sawing by wire.
  • the wafer manufacturing process has a yield of 35% (Si into the plant vs. Si out as wafer). Approx 30% is further lost in wafer cutting and the remaining is lost as scrap and off cuts in melting and block preparation.
  • Si yield in the total process from metallurgical silicon to wafer is only 7% which is partly the reason for the high cost. Due to the above low yield process, a number of attempts have been made to find alternative routes, the most common one being some sort of metallurgical refining, i.e. avoiding the silane gas phase.
  • the method according to the invention is characterized in that the silicon, being provided in a boat in a closed housing, is subjected to horizontal refining in a repeatable process where one or more zones of the silicon at a time is heated by a heater at preferably constant speed along the total length of the boat, whereby a purging gas under the refining is passed along the boat from one inlet end of the housing to an outlet end of the housing purging off any impurities generated under the refining operation, as defined in the attached independent claim 1.
  • the apparatus is characterised in that the equipment is of the horizontal refining type and includes a boat for the silicon to be provided in a closable housing, which housing at one end is provided with an inlet for purge gas and an outlet for purge gas together with any impurities being purged off the silicon during refining, a heater provided around the boat or around the housing for heating a zone or zones of the silicon, and that the boat or heater is movable in relation to one another in the longitudinal direction of the boat along its total length, as defined in the independent claim 6.
  • the molten metal will circulate within the slice due to the temperature gradient and magnetic field from the RF coil, and thereby continuously bring impurities to the top where it comes in contact with a gas thereby enabling continuous gas purification. It is known that a small amount of water in argon or another inert gas will oxidise carbon and boron, which can then be flushed away as boron and carbon oxide gas. Phosphorous will evaporate if the gas is at slight vacuum and thereby be removed as a volatile gas. • The rate of purification can be increased by placing several induction coils, say four coils which travel together. When VA of the bar is done, they are all shifted back VA distance and coil no 2 takes over where coil no 1 left and the process is repeated.
  • Fig. 1 shows a schematic view of a horizontal zone refining apparatus according to the present invention
  • Fig. 2 shows in larger scale part of the apparatus according to the invention shown in Fig. 1
  • a travelling heater unit 1 positioned at one end of a boat (metal basin) 2, melts a narrow 'X' section of the charge.
  • the boat is provided in a closable housing 3 to obtain a controlled atmosphere in a space 7 surrounding the boat.
  • Purge gas is provided to be supplied through an inlet 4 at one end of the housing 3 and is further provided to be purged together with impurities from an outlet 5 at the other end of the housing.
  • the housing may preferably be of cylindrical shape and made of a suitable material such as quartz.
  • the heater 1 in the form of an electromagnetic coil, is provided on the outside of the housing.
  • the conducting threads of the electromagnetic coil 1 form an angle to the boat and direction of travel (arrow 6 in Fig. 2), thereby providing a vertical (transversal relative to the boat) zone refining effect in addition to the horizontal effect. Further, the magnetic field of the coil induce a rotation in the molten zone obtained by the coil and thereby makes gas purging more effective as impurities continually are being are being brought to the gas/liquid interface by the rotation.
  • metallurgical silicon is provided in the boat 2, which in turn is provided in the housing 4 being closed off from the surroundings.
  • the heater is switched on and a purge gas in the form of Ar, O 2 H 2 O or other suitable gasses, or combination of gasses, is admitted to the space 7 between the housing and boat.
  • the heater unit 1 is traversed along the length of the boat at a constant speed.
  • the first 'pass' is usually quicker, with high heat, to consolidate the material.
  • Subsequent passes are slower to accomplish purification. Two or three passes may be required to achieve desired purity.
  • Purification is carried out by the act of crystallization: as the narrow molten zone travels along the bar, impurities are pushed forward and carried with the melt. The molten metal will circulate within the slice due to the temperature gradient and magnetic field from the coil, and thereby continuously bring impurities to the top where it comes in contact with the flush gas thereby enabling combined gas purification.
  • the rate of purification can be increased by placing, in stead of one, several induction coils, say four coils which travel together. When V ⁇ of the bar is done, they are all shifted back 14 distance and coil no 2 takes over where coil no 1 left and the process is repeated.
  • a silicon bar with rectangular cross section may be made, say with a height and width of 15 x 15 cm directly by zone refining.
  • This zone-refined bar, combined with gas purification would have the required purity for wafer production.
  • the bar can be cut into wafers directly. In this way one will save a number of process steps like crushing, re-melting and cutting of silicon blocks into bars suitable for wafer cutting.
  • the overall process will also be more efficient and increase the overall Si yield from 7% to 60%.
  • the coil may instead of being provided on the outside of the housing, be provided inside the housing.
  • the electromechanical coil may be stationary and the boat moving, instead of vice versa.

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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)

Abstract

L'invention concerne un procédé et un appareil pour la fabrication d'un silicium multicristallin de grade solaire à partir de silicium métallurgique. Le silicium est disposé dans une nacelle (2) dans un boîtier clos (3), et est soumis à un raffinage horizontal par un procédé répétable selon lequel une ou plusieurs zones (X) du silicium sont chauffées en même temps par un dispositif de chauffage (1), de préférence à une vitesse constante le long de la longueur totale de la nacelle (2), un gaz de purge étant circulé pendant l'opération de raffinage le long de la nacelle (2) entre un orifice d'entrée (4) à une extrémité du boîtier et un orifice de sortie (5) à l'autre extrémité du boîtier, éliminant ainsi toutes les impuretés générées par l'opération de raffinage.
PCT/NO2007/000296 2006-08-30 2007-08-22 Procédé et équipement pour la fabrication d'un silicium multicristallin de grade solaire à partir de silicium métallurgique WO2008026931A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NO20063862 2006-08-30
NO20063862 2006-08-30

Publications (1)

Publication Number Publication Date
WO2008026931A1 true WO2008026931A1 (fr) 2008-03-06

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NO2007/000296 WO2008026931A1 (fr) 2006-08-30 2007-08-22 Procédé et équipement pour la fabrication d'un silicium multicristallin de grade solaire à partir de silicium métallurgique

Country Status (1)

Country Link
WO (1) WO2008026931A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008119330A1 (fr) * 2007-03-30 2008-10-09 Solmic Gmbh Procédé et dispositif de purification de masses fondues

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2739088A (en) * 1951-11-16 1956-03-20 Bell Telephone Labor Inc Process for controlling solute segregation by zone-melting
US2901325A (en) * 1955-07-22 1959-08-25 Bell Telephone Labor Inc Method of preparing silicon
US2935386A (en) * 1956-01-03 1960-05-03 Clevite Corp Method of producing small semiconductor silicon crystals
US3093456A (en) * 1958-09-02 1963-06-11 Texas Instruments Inc Method for recovery and reuse of quartz containers
US3222217A (en) * 1959-09-23 1965-12-07 Siemens Ag Method for producing highly pure rodshaped semiconductor crystals and apparatus
EP0264045A2 (fr) * 1986-10-15 1988-04-20 Bayer Ag Procédé de raffinage de silicium et silicium purifié de cette façon
EP0530567A1 (fr) * 1991-08-27 1993-03-10 Bayer Ag Procédé de fabrication de silicium et appareil pour sa mise en oeuvre

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2739088A (en) * 1951-11-16 1956-03-20 Bell Telephone Labor Inc Process for controlling solute segregation by zone-melting
US2901325A (en) * 1955-07-22 1959-08-25 Bell Telephone Labor Inc Method of preparing silicon
US2935386A (en) * 1956-01-03 1960-05-03 Clevite Corp Method of producing small semiconductor silicon crystals
US3093456A (en) * 1958-09-02 1963-06-11 Texas Instruments Inc Method for recovery and reuse of quartz containers
US3222217A (en) * 1959-09-23 1965-12-07 Siemens Ag Method for producing highly pure rodshaped semiconductor crystals and apparatus
EP0264045A2 (fr) * 1986-10-15 1988-04-20 Bayer Ag Procédé de raffinage de silicium et silicium purifié de cette façon
EP0530567A1 (fr) * 1991-08-27 1993-03-10 Bayer Ag Procédé de fabrication de silicium et appareil pour sa mise en oeuvre

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008119330A1 (fr) * 2007-03-30 2008-10-09 Solmic Gmbh Procédé et dispositif de purification de masses fondues

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