WO2012143867A1 - An arrangement for manufacturing crystalline silicon ingots - Google Patents

An arrangement for manufacturing crystalline silicon ingots Download PDF

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Publication number
WO2012143867A1
WO2012143867A1 PCT/IB2012/051941 IB2012051941W WO2012143867A1 WO 2012143867 A1 WO2012143867 A1 WO 2012143867A1 IB 2012051941 W IB2012051941 W IB 2012051941W WO 2012143867 A1 WO2012143867 A1 WO 2012143867A1
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WO
WIPO (PCT)
Prior art keywords
crucible
circumferential
frame structure
hood
arrangement according
Prior art date
Application number
PCT/IB2012/051941
Other languages
French (fr)
Inventor
Egor VLADIMIROV
Alexandre TEIXEIRA
Kai Johansen
Pouria Homayonifar
Original Assignee
Rec Wafer Pte. Ltd.
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 Rec Wafer Pte. Ltd. filed Critical Rec Wafer Pte. Ltd.
Publication of WO2012143867A1 publication Critical patent/WO2012143867A1/en

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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
    • 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
    • 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
    • C30B11/002—Crucibles or containers for supporting the melt
    • 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
    • C30B28/00—Production of homogeneous polycrystalline material with defined structure
    • C30B28/04—Production of homogeneous polycrystalline material with defined structure from liquids
    • C30B28/06—Production of homogeneous polycrystalline material with defined structure from liquids by normal freezing or freezing under temperature gradient
    • 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
    • C30B35/00—Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure
    • 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
    • C30B35/00—Apparatus not otherwise provided for, specially adapted for the growth, production or after-treatment of single crystals or of a homogeneous polycrystalline material with defined structure
    • C30B35/002—Crucibles or containers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27D—DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS, IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KIND OF FURNACE
    • F27D7/00—Forming, maintaining, or circulating atmospheres in heating chambers
    • F27D7/06—Forming or maintaining special atmospheres or vacuum within heating chambers

Definitions

  • the present invention relates to an arrangement for manufacturing of crystalline silicon ingots by directional solidification.
  • the invention relates to a gas shield arrangement alleviating or preventing contamination of molten silicon through the gas phase in crystallization furnaces producing high quality crystalline silicon ingots for photovoltaic applications.
  • the bulk volume of the world production of photovoltaic elements comprising solar panels is based on multicrystalline silicon wafers cut from ingots that are cast by directional solidification (DS) based on the Bridgeman method in electrically heated furnaces.
  • the crucible being employed is usually made of silica Si0 2 , and the furnaces have heating elements above, below and/or sidewise with respect to the crucible to provide the heat for melting and control of heat extraction during the directional solidification.
  • the process may be described as follows:
  • a crucible open at the top made of Si0 2 is covered in its interior with silicon nitride containing coating and filled with a silicon feedstock to a predetermined height.
  • the crucible is then placed on the floor of the heating compartment of the furnace.
  • a circumferential support structure of graphite plates is attached along the outer crucible walls to provide mechanical support at elevated temperatures when the Si0 2 -crucible sags.
  • the furnace compartment is then closed, evacuated and the inert purge gas is supplied during the period the heating elements are engaged in melting/solidification of silicon feedstock. When the silicon is melted, the heating is adjusted to obtain a directional solidification.
  • An inert purge gas usually argon, is flushed onto the surface of the silicon to protect against gaseous contamination and to remove effectively SiO- gas at least as long as the silicon is in a liquid phase.
  • a main challenge in these processes is to maintain the purity of molten silicon material during melting and solidification.
  • the melt is usually protected from gaseous
  • the amount of purge gas may be insufficient to prevent back flows of CO generated inside the furnace chamber (due to release of SiO from the melt with subsequent contact with graphite parts of the hot zone) resulting in formation of SiC impurities in the melt.
  • Build-up of carbon in the silicon melt leads to formation of SiC precipitates responsible for shunting effects (short circuit of pn-junctions) in solar cells leading to drastic degradation of efficiencies of photovoltaic cells.
  • Especially high amounts of CO are generated in cases where the furnace is subject to leakages of ambient air into the interior of the hotzone.
  • Another drawback of low purge gas flow resulting in a reduced evaporation of SiO from the melt is a reduction of cell efficiencies due to light induced degradation related to higher oxygen content in silicon. Meanwhile, utilization of higher amounts of gas flows leads to degradation of silicon nitride coating with subsequent sticking of silicon to silica crucible walls, which causes loss of ingots due to their cracking.
  • the oxygen leads to formation of SiO gas evaporating from the melt, and the SiO gas will subsequently react with graphite in the hot zone forming CO gas.
  • Typical values associated with the Bridgman method is interstitial oxygen levels of 2- 10 17 - 6- 10 17 /cm 2 and 2 ⁇ 10 17 - 6 ⁇ 10 17 /cm 2 of substitutional carbon.
  • SiC-particles cause wire breakage in sawing machines and cause appearance of saw marks on the wafers in their vicinity.
  • a way to avoid the formation of precipitates in the melt is to shift carbon saturation level towards the top of the block beyond the ingot zone used for wafer cutting.
  • WO 2007/148985 it is known device and method for production of ingots of semiconductor grade silicon, including solar grade silicon, where the presence of oxygen in the hot zone is substantially reduced or eliminated by employing materials void of oxides in the hot zone of the melting and crystallisation process.
  • the method may be employed for any known process including for crystallising semiconductor grade silicon ingots, including solar grade silicon ingots, such as the Bridgman process, the block- casting process, and the CZ-process for growth of mo no crystal line silicon crystals.
  • the invention also relates to devices for carrying out the melting and crystallisation processes, where the materials of the hot zone are void of oxides.
  • DE 10 2006 017 622 discloses manufacturing multi-crystalline silicon by vertical- gradient- freeze procedure, which comprises placing a lid resting upon a crucible to build a container structure, filling the container structure with silicon filling made of particulate or granular silicon up to a predetermined height, heating the container structure for melting the silicon fillings to liquid silicon, and cooling the container structure and solidifying the liquid silicon.
  • the container has an inlet and an outlet for flushing gas to isolate the interior of the container structure from the exterior
  • the lid has a contour corresponding to that of a crucible and is resting on the brackets posed on a crucible sides.
  • a directional solidification furnace which includes a crucible for holding molten silicon and a lid covering the crucible and forming an enclosure over the molten silicon.
  • the crucible also includes an inlet in the lid for introducing inert gas above the molten silicon to inhibit contamination of the molten silicon.
  • the furnace further comprises an inlet in the lid for introducing inert gas above the molten silicon.
  • a first gap and a second gap are disposed adjacent the lid. The first and second gaps define a nonlinear flow path for facilitating removal of contaminants from the enclosure and allowing the inert gas to exit the enclosure.
  • WO 2009/014963 it is known a method and apparatus for casting silicon for photovoltaic cells and other applications able to form an ingot low in carbon and whose crystal growth is controlled to increase the cross-sectional area of seeded material during casting.
  • the invention utilizes a lid and/or flowing of an inert gas to improve the purity of cast silicon, such as silicon having very low carbon concentrations.
  • Lower impurities reduce the number of foreign particles included in the ingots (termed inclusions) and improve yields of the wafers and/or solar cells.
  • An additional benefit to silicon having increased purity includes more and/or greater monocrystalline material from the same ingot. Less impurities in the silicon also allows for faster crystal growth. Additionally, low carbon content enables a greater variety of thermal processes for turning the wafer into a solar cell.
  • a material known to have extreme resistance towards thermal shock and mechanical wear is ceramic composites comprising carbon fibre-reinforced silicon carbide ceramics (C-C/SiC or C/SiC composites). These materials have presently found use as friction linings in braking systems of automotive applications, in aero-space applications, as combustor chamber linings, in turbine blades, in jet engine nozzles, etc.
  • C-C/SiC or C/SiC composites may be produced by forming an intermediate body of carbon fibre-reinforced polymer (CRFP), heating the CRFP until the polymer is pyrolysed to form a porous green body of carbon fibre- reinforced carbon (C/C-body), contacting the green C/C-body with molten silicon and allow the silicon to infiltrate the green C/C-body (often termed Liquid Silicon
  • EP 1 547 992 discloses a method for manufacturing C-C/SiC composites from a mixture of resin and carbon fibres which is pyrolysed to a green body directly without first hardening the resin. Then the green body is infiltrated with silicon to form the C-C/SiC composite.
  • the main objective of the invention is to provide an apparatus for manufacturing ingots of crystalline photovoltaic grade silicon which substantially reduces/eliminates the problem of carbon contamination of silicon, reduces number of precipitates (crucial for fast wafer cutting), and which substantially reduces consumption of purge gas and effectively protects heating elements and the hot zone of furnace from deterioration.
  • the invention is based on the realisation that a more operationally flexible and applicable solution for shielding the melt in a crucible from a back flow of contaminated purge gas in industrial production lines is obtained by forming the gas shield as an integral part of the hot zone of the crystallisation furnace.
  • the present invention relates to an arrangement for manufacturing a crystalline silicon ingot by directional solidification, comprising:
  • thermo zone able to house a crucible and which is sealed against the ambient atmosphere, where the hot zone comprises:
  • the gas shield arrangement comprises:
  • the inlet for purge gas is positioned to supply purge gases under the hood.
  • the term "hot zone” as used herein means a compartment of the furnace where the heating is taking place and which is having thermally insulating walls, floor and ceiling.
  • the hot-zone is usually a compartment shaped as a parallelepiped, but may have other geometries.
  • the hot zone needs some form of heating means in order to perform the melting and solidification required to make crystalline silicon ingots.
  • the invention may apply any known or conceivable heating means for melting and directionally solidifying the silicon in the crucible.
  • a suited example of heating means is electric resistance heaters which may be placed in the bottom, the upper part, on the sides, or in any combination of these places of the hot zone.
  • bottom support structure means a load carrying structure of graphite or another heat conductive and mechanically rigid material for supporting the crucible and other structures/devices placed in the hot zone.
  • the bottom support structure may form a horizontally oriented partition wall or floor covering the entire cross-section area of the hot zone and thus dividing the lower part of the hot zone into two chambers: one upper chamber where the crucible is to be placed and one lower chamber containing the heating means for heating from below.
  • This provision has the advantage of protecting the lower heating means from deteriorative gases stemming from the melt.
  • the present invention may also be applied for furnaces with any type of conceivable load carrying support structure for carrying the crucible, including furnaces where the crucible is placed directly on the bottom of the heat insulating wall of the hot zone.
  • top shield means the upper closure of the compartment if the hot zone containing the crucible, and will usually be an upper substantially horizontally oriented partition wall or ceiling dividing the upper compartment of the hot-zone into two horizontally separated chambers: the lower becoming the chamber housing the crucible and the upper chamber containing upper heating elements.
  • This provision has the advantage of protecting the top heating elements from deteriorative gases stemming from the melt.
  • the present invention may also be applied for furnaces without an upper two-chamber construction (no partition wall) such that the top shield becomes the upper thermal insulating wall of the hot-zone.
  • circumferential means that the structure, i.e. the support structure, the frame structure, or the hood, surrounds the outer walls of the crucible to form a continuous structure extending along the entire periphery of the crucible.
  • the structure, except for the hood, may be in contact with the crucible wall, or it may be at a distance from the crucible wall.
  • circumferential support structure means a mechanically support structure functioning as the load carrying structure or suspension point for the circumferential frame structure.
  • the circumferential support structure will often be rectangular plates of graphite or another heat resistant mechanically rigid material that is placed or mounted alongside the outer walls of the crucible to provide mechanical strength at elevated temperatures when the crucible sags.
  • the circumferential support structure may be any conceivable structure able to suspend the circumferential frame structure at its intended position, such as i.e. a protruding section of the crucible, arms extending from the heat insulating walls of the hot zone etc.
  • the term “circumferential frame structure” as used herein means the lower part of the gas shield arrangement.
  • the circumferential frame structure should form a substantially horizontally oriented continuous planar platform projecting from the outer wall of the crucible along the entire periphery of the crucible at a specific height above the bottom support structure.
  • the planar platform should surround the outer wall of the crucible with a maximum clearance of a few millimetres. That is, the horizontal cross-section area of the circumferential frame structure should have a length and width of at least 40 mm larger than the length and width of the crucible's horizontal cross-section area and have a centred void with a length and width in the range of 1 to 10 mm larger as the complementary shape and dimension of the crucible's cross-section area.
  • the frame will when being thread over the crucible and placed onto the circumferential support structure define a horizontally oriented continuous planar platform projecting from the outer wall of the crucible along the entire periphery of the crucible at the top of the graphite support structure.
  • the distance from the inner to the outer edge of the platform along the side sections, that is the width of the circumferential frame structure, should be at least 20 mm. There is no upper limit to this width; the invention may apply any size of the frame's width as long as it fits inside the furnace compartment.
  • the width of the circumferential frame will be in the range from 20 to 200 mm, leading to a length and width of the horizontal cross-section area of the circumferential frame structure in the range from 40 to 400 mm larger than the length and width of the crucible's horizontal cross-section area.
  • the circumferential frame structure may be simply resting on the circumferential support structure, or made to be an integral part of the circumferential support structure by being attached or fastened to the circumferential support structure.
  • the dimensioning and/or positioning of the circumferential support structure may advantageously be such that when the circumferential frame structure is laid onto or attached to the upper face of the support structure, the upper surface of the circumferential frame structure is at a level in the range of 10 to 100 mm below the upper edge of the crucible wall (measured at standard conditions, STP).
  • the circumferential frame structure may advantageously include a "skirt" in the form of a peripheral perpendicularly downwardly oriented lip at the distal end (furthest away from the crucible) of the planar platform. This feature provides mechanical rigidity of the circumferential frame structure with respect to bending, and will also function as a deflection wall preventing outgoing gases exiting the circumferential slot from deteriorating the graphite support structure.
  • hood as used herein means the upper part of the gas shield.
  • the hood is gas tight structure attached to the top shield (or directly to the upper heat insulating wall of the hot zone in cases with no upper partition wall or ceiling) and thus integrated with the upper part of the hot zone.
  • the hood may be given any conceivable shape and
  • the slot or opening should be going all way around the crucible; there should be no contact between the hood and the crucible and circumferential frame structure at any point.
  • the minimum distance between the crucible wall and the hood 16 may advantageously be in the range from 10 to 100 mm.
  • the minimum distance between the crucible wall and the lower edge of the hood may advantageously be at least half of the width of the circumferential frame structure. This feature provides the advantage of forming a longer flow path for the purge gas inside the gas shield towards the circumferential slot formed between the hood and the
  • the slot between the platform of circumferential frame structure and the upper hood is defined by the vertical distance or gap between them.
  • the width of the gap should preferably be in the range from 1 - 50 mm, depending on gas pressure, temperature and gas flow volume of the purge gas being supplied to the hot zone.
  • the gap width should preferably be in the range of 2 - 10 mm, or more preferably or 4 - 6 mm.
  • vertical distance or gap as used herein means the shortest distance between the upwardly facing surface (flat planar surface) of the circumferential frame structure and the lowest point of the hood.
  • the hood may for instance be made by joining together four planar trapezoidal sheets of a heat conductive, preferably chemically resistant and rigid material to form an
  • the hood may advantageously be tapered outwardly to form a shape resembling a truncated pyramid suspended from the top shield with an angle, related to the surface of the top shield, in one of the following ranges; from 30° to 75°, from 45° to 70°, or from 55° to 65°.
  • the feature of having an outwardly tapered hood that encompasses the top section of the crucible and forms a circumferential slot together with the circumferential frame structure at a distance below and outside of the upper edge of the crucible, is that this structure defines an open volume (gas pocket) between the slot and the crucible which allows to accommodate small accidental backflow of the purge gas without exposing the entire liquid silicon under the hood.
  • This feature is suitable for furnaces with
  • the hood may also include a planar sheet or plate covering the upper partitioning ceiling. This plate may be of the same chemically inert material as the hood, and will protect the top shield and the upper heating means from the fumes from the melt.
  • the feature of having a hood which is integrated with the top shield and which extends down towards the circumferential frame provides the advantage of avoiding physical contact between the crucible and the hood of the gas shield, and thus elimination of any damages of the construction resulting from operations (loading/unloading of crucibles into furnace, closing/opening the furnace), which necessary require existence of clearance to preserve the desired width of circumferential slot for the purge gas coming out.
  • the upwardly facing flat planar surface of the circumferential frame structure with a width in the range from 20 to 200 mm allows to accommodate a certain extent of arbitrary tilts and shifts of the crucible positioning (arising from loading/unloading operations) meanwhile preserving the desired width of the slot.
  • the slot realized below and beyond the periphery of the crucible alleviates the chemical wear of the release coating of the crucible (thus avoiding loss of ingots due to coating destruction resulting in sticking of silicon to silica walls with subsequent cracking of ingots) by purge gas by means of reducing the exposure of the coating to the high flow velocities in the vicinity of the circumferential slot.
  • a further advantage is that the arrangement according to the invention reduces the consumption of purge gas by a factor of 4 - 5 as compared to similar arrangements without the gas shield.
  • Another advantage is that it becomes possible to utilize larger volume of the crucible by accommodating higher loads of silicon under the hood.
  • the gas shield should be made of a material which is able to withstand the high temperatures associated with the melting of silicon without decomposing or in other way releasing (by gassing, perspiration, flaking, etc.) contaminating compounds.
  • the material should also withstand the temperatures without loss of its desired mechanical rigidity.
  • the gas shield material preferably should be chemically inert in the chemical environment encountered in crystallisation furnaces for manufacturing mono- and multi- crystalline silicon ingots.
  • the temperature profile and heat fluxes inside the hot-zone of the furnace should not be detrimentally affected by the introduction of the gas-shield in order to preserve the intended heat extraction rates and control of the directional solidification process. That is, the heat resistance across the gas-shield should not hinder heat extraction through the bottom of the crucible.
  • the gas-shield should be made of a material with sufficient mechanical rigidity to form a rigid gas-shield with a plate thickness of the gas-shield elements in the range of 1 - 20 mm, which is preferably chemically inert with respect to the chemical environment in the furnace during process conditions, and which optionally has a thermal conductivity of at least 1 W/mK or higher.
  • Examples of suited materials for use in the gas-shield includes, but is not limited to, ceramic materials with a SiC-coating, such as i.e. carbon fibre-reinforced carbon (known as CFRC, C/C, CFC etc) with a SiC-coating, graphite coated with SiC, silicon carbide ceramics (C-C/SiC or C/SiC composites), silicon carbide fibre composite (SiC/SiC). These materials will have sufficient thermal conductivity, the necessary mechanical rigidity to allow forming the circumferential hood and circumferential frame structure with a sheet thickness in the range of 1 - 10 mm, preferably 2 - 8 mm, 2 - 5 mm, or 2 - 3 mm.
  • ceramic materials with a SiC-coating such as i.e. carbon fibre-reinforced carbon (known as CFRC, C/C, CFC etc) with a SiC-coating, graphite coated with SiC, silicon carbide ceramics (C-C/S
  • the SiC-coating may be applied on the inner side and optionally on the outer side of the gas shield to form a coating with a thickness in the range of 10 - 200 ⁇ , preferably 20 - 150 ⁇ , 40 - 120 ⁇ , or 60 - 100 ⁇ .
  • the CFRC may advantageously be given a coating of SiC with thickness from about 10 to about 200 ⁇ SiC on one or both sides of the CFRC in order to make the gas shield more chemically inert towards the compounds of the gases in the hot zone.
  • Both the hood and the frame structure may be made of sheet materials of CFRC with a SiC coating. The feature of low thermal resistance is less relevant for the frame structure as for the hood, such that the thickness of the sheet material being applied for the circumferential frame structure may be a factor 2 or 3 higher than for the hood.
  • the invention may apply any known or conceivable crucible for production of crystalline silicon by directional solidification.
  • crucibles include one of: silicon carbide, silicon nitride coated crucibles of quartz, reaction bonded silicon nitride, C-C/SiC, etc.
  • the arrangement according to the invention is not tied to Bridgeman type furnaces or processes, but may be applied for any known or conceivable process for forming mono- or multi-crystalline silicon ingots.
  • the gas pressure inside the hot zone of the furnace during melting and directional solidification may advantageously be lowered in order to enhance oxygen evaporation from the melt.
  • Lowered pressure conditions as used herein means any gas pressure in the range from 10 3 to 10 5 Pa, from 10 4 to 10 5 Pa, from 3 - 10 4 to 9- 10 4 Pa, or from 6- 10 4 to 9- 10 4 Pa.
  • the purge gas may be any known or conceivable gas suitable as cover gas for silicon melts, such as noble gases or any other gas acting as chemically inert gas in the actual environment or an inert gas mixed with a reactive gas.
  • the applied flow ranges may be from 2 to 50 Nl/min, from 2 to 30 Nl/min, from 5 to 25 Nl/min, or from 5 to 15 Nl/min.
  • Figure 1 is a schematic drawing of a cross-section seen from the side of an example embodiment of the invention.
  • Figure 2 is an expanded view of the section within the box marked with a dashed line in Figure 1.
  • Figure 3 a is a schematic drawing of the circumferential frame structure according to the invention seen from above, and figure 3 b) is a cross-section seen from the side.
  • Figure 4 a) and b) is a schematic drawing of the hood according to the invention seen from below and from the side, respectively.
  • Figure 5 is a truncated schematic drawing of a cross-section seen from the side of the material employed in an example embodiment of the circumferential frame structure or circumferential hood according to the invention.
  • Figure 6 is a schematic drawing of a cross-section seen from the side of a second example embodiment of the invention.
  • Figure 7 a) is a photograph of a multicrystalline silicon ingot manufactured according to the present invention
  • b) is a photograph of a multicrystalline silicon ingot manufactured without use of the gas shield arrangement.
  • Figure 8 is a curve diagram showing reduction of CO concentration (arb. units) above silicon melt as a function of Ar flow (arb. units) for prior art gas supply (upper black line, crosses) as compared with gas supply according to the present invention (lower line, full circles).
  • Figure 9 is a curve diagram showing the carbon concentration (arb. units) as a function ingot height (arb. units) as found by SIMS analysis for ingots produced without gas shield arrangement (upper grey line, circles) and with the gas shield of the present invention (lower line, crosses).
  • Figure 10 a) is a diagram summarising sawing mark depth for wafering process as a function of ingot height for ingots produced without the gas shield arrangement
  • b) is a diagram summarising sawing mark depth for cutting wafers process as a function of ingot height for ingots produced with the gas shield according to the present invention.
  • Figure 1 1 is a diagram indicating the 16 blocks being cut from one ingot and showing typical distribution of loss reduction (in %) in the wafer production line obtained by the present invention compared with prior art baseline manufacturing without the gas shield arrangement.
  • Figure 12 is a diagram showing the cell efficiency distribution of solar cells produced from mono crystalline silicon ingot, which was crystallized in a vertical gradient freeze furnace according to prior art baseline manufacturing without employing the gas guiding device according to the invention.
  • Figure 13 is a diagram showing the cell efficiency distribution of solar cells produced from mono crystalline silicon ingot, which was crystallized in a vertical gradient freeze furnace employing the gas guiding device according to the present invention.
  • the example embodiment, shown in Figure 1 comprises an inner furnace space or hot- zone for performing melting and solidification of silicon 1 in a crucible 2 by the
  • the hot zone is the inner compartment confined by the heat insulating walls 3.
  • the crucible 2 is a conventional silica crucible coated with a slip coating of silicon nitride.
  • the crucible 2 is placed onto a graphite floor 4 which divides the inner compartment of the hot zone into one bottom chamber 5 housing electric resistance heaters 6 made of graphite for heating the bottom of the crucible 2 and one mid chamber 7 housing the crucible 2.
  • the sides of the crucible 2 are mechanically supported by graphite plates 8.
  • the hot zone is equipped with a top shield in the form of a horizontal partition wall 9 dividing the compartment of the hot zone further to form one upper chamber 10 housing electric resistance heaters 1 1 made of graphite for heating the crucible 2 from above.
  • Purge gas is supplied to the hot zone via inlet 12 and extracted together with the gases evaporating from the melt via gas outlets 13, towards a pump (not shown) for maintaining desired pressure and flow conditions.
  • a circumferential frame structure 14 is made of a planar sheet of CFRC of thickness 3 - 4 mm and which is coated with 80 - 100 ⁇ thick layer of SiC.
  • the width of the upwardly facing flat planar surface 15 is about 100 mm.
  • the circumferential frame 14 is also drawn schematically in Figure 3 a) and 3 b), where 3 a) is seen from above and 3 b) from the side.
  • the distance marked by arrow C on Figure 3 is the width of the opening or the void where the crucible 2 is to enter. This distance is 4 mm larger than the width of the horizontal cross-section of the crucible 2.
  • the width of the circumferential frame is marked by arrow D.
  • the hood 16 is made of a planar sheet of CFRC of thickness 2 mm and which is coated with 80 - 100 ⁇ thick layer of SiC on both sides, as shown schematically in Figure 5.
  • the thermal conductivity of the SiC-coated CFRC is about 20 W/mK.
  • the hood 16 is made of four planar trapezoidal sheets joined together to form an "umbrella" (hollow truncated pyramid) resembling structure which is suspended from the top shield 9 of the hot-zone of the furnace, as may be seen in Figure 4 a) which is a view from below and 4 b) which is a side view.
  • FIG. 2 An expanded view of the area inside the box marked with a dashed line in Figure 1 is shown in Figure 2.
  • the vertical distance defining the slot between the circumferential frame structure 14 and the circumferential hood 16 is marked on the figure by arrow A, and is in the range of 4 - 6 mm.
  • the distance between the lower edge of the hood 16 and the wall of the crucible 2 is marked by arrow B. This distance is half of the width D of the circumferential frame.
  • the gas flow inside the hot-zone is indicated by the arrows and is 5 - 7 Nl/min and the pressure is 9 ⁇ 10 4 Pa (900 mbar).
  • the cross-section of the CFRC material coated with SiC from both sides and used both for manufacturing of the top shield 9 and the hood 16 is illustrated in Figure 5, where reference number 20 is the CFRC and 21 is the SiC-coating.
  • the second example embodiment illustrated on Figure 6 is similar to the first example embodiment shown on Figure 1 except that the top shield 9 is made of a 2 mm thick sheet of CFRC which is coated with one 80 - 100 ⁇ thick layer of SiC on the lower side facing the mid chamber 7.
  • the hood 16 is attached to the top shield 9.
  • the circumferential frame structure 14 is constructed from four L-pro files forming a "skirt" 17 at the distal end of the frame to provide increased mechanical rigidity with respect to bending during operations of loading/unloading of the crucibles into the furnace.
  • the hot zone is also shown encompassed in a steel casing 18 defining the vacuum sealing of the furnace. Otherwise, the second example embodiment is equal to the first example embodiment.
  • Figure 7 a) is a photograph of a multi-crystalline silicon ingot made with a gas shield arrangement according to the present invention, and Figure 7 b) without.
  • the surface of the ingot in Figure 7 b) is considerably more dull and grey due to formation of SiC resulting from a reaction with CO that is transported to the melt inside the furnace chamber.
  • This result is supported by measurements of CO concentration above the silicon melt at the beginning of the crystallization as a function of argon supply demonstrated on Figure 8.
  • the figure shows that CO-concentration above the melt is much more efficiently reduced by lower amounts of purge gas in case of application of the gas shield arrangement.
  • the results obtained for ingots produced without the gas shield arrangement is the upper black line with crosses, and the results for the ingots made with the gas shield arrangement according to the present invention is the lower line with full circles.
  • the carbon concentration of the produced ingots is also measured across the ingot height.
  • the results shown on Figure 9 are typical averages of SIMS analysis for carbon distribution for one of the 32 ingots.
  • the ingots produced with the gas shield arrangement according to the present invention have a carbon concentration of a factor 3 or more at ingot heights from 60 % and below, and a carbon concentration of about 25 % lower at the upper part of the ingot.
  • the results obtained for ingots produced without the gas shield arrangement is the upper grey line with circles, while the results for the ingots produced with the gas shield arrangement of the present invention is the lower line with crosses.
  • Figure 1 1 is a diagram showing typical distribution of loss reduction (%) (achieved by application of gas shield arrangement according to the present invention) for each of 16 blocks cut from one ingot resulting in average reduction of wafer losses about 58 % compared to the factory baseline without gas shield arrangement.
  • Crystallized silicon ingot is cooled down and cut vertically into 16 equivalent bricks of approximately 245 mm height. Then the square wafers are produced by slicing the bricks in horizontal direction into wafers of size 156 mm x 156 mm and 200 ⁇ thick. After slicing, the wafers are subsequently washed, dried and then go through the standard process of solar cell preparation: etching to texture the surface, chemical vapor deposition (CVD) of n-dopant (phosphorous), in-diffusion of phosphorous at elevated temperatures, deposition of anti-reflective coating of silicon nitride on a front surface of the wafer. Finally, the metallic electrical contacts are applied on a front and back sides of the wafer.
  • CVD chemical vapor deposition

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Abstract

The present invention relates to an arrangement for manufacturing of crystalline silicon ingots by directional solidification which comprises a furnace with a hot zone able to house at least one crucible and which is sealed against the ambient air atmosphere, where the hot zone comprises: i) heating means for heating the crucible, ii) an outlet for evacuating gas from the hot zone of the furnace, iii) an inlet for supplying purge gas, iv) a bottom support structure for carrying the crucible, v) a top-shield, vi) a circumferential support structure, and vii) a gas shield arrangement within the hot zone of the furnace, wherein the gas shield arrangement comprises: a circumferential frame structure with a flat horizontal planar upper surface facing the top shield, and which is placed on top of the circumferential support structure, and a circumferential hood attached to and extending downward from the top shield to a distance above the flat planar upper surface of the circumferential frame structure and thus forming a continuous slot along the periphery of the circumferential hood at a distance from the crucible wall, and the inlet for purge gas is positioned to supply purge gases under the hood.

Description

AN ARRANGEMENT FOR MANUFACTURING CRYSTALLINE SILICON INGOTS
The present invention relates to an arrangement for manufacturing of crystalline silicon ingots by directional solidification. In particular, the invention relates to a gas shield arrangement alleviating or preventing contamination of molten silicon through the gas phase in crystallization furnaces producing high quality crystalline silicon ingots for photovoltaic applications.
Background
Presently, the bulk volume of the world production of photovoltaic elements comprising solar panels is based on multicrystalline silicon wafers cut from ingots that are cast by directional solidification (DS) based on the Bridgeman method in electrically heated furnaces. The crucible being employed is usually made of silica Si02, and the furnaces have heating elements above, below and/or sidewise with respect to the crucible to provide the heat for melting and control of heat extraction during the directional solidification. The process may be described as follows:
A crucible open at the top made of Si02 is covered in its interior with silicon nitride containing coating and filled with a silicon feedstock to a predetermined height. The crucible is then placed on the floor of the heating compartment of the furnace. Next, a circumferential support structure of graphite plates is attached along the outer crucible walls to provide mechanical support at elevated temperatures when the Si02-crucible sags. The furnace compartment is then closed, evacuated and the inert purge gas is supplied during the period the heating elements are engaged in melting/solidification of silicon feedstock. When the silicon is melted, the heating is adjusted to obtain a directional solidification. An inert purge gas, usually argon, is flushed onto the surface of the silicon to protect against gaseous contamination and to remove effectively SiO- gas at least as long as the silicon is in a liquid phase.
A main challenge in these processes is to maintain the purity of molten silicon material during melting and solidification. The melt is usually protected from gaseous
contaminants by a combination of evacuating the atmosphere in the hot zone of the furnace and flushing a cover of inert purge gas over the surface of the liquid silicon phase. However, the amount of purge gas may be insufficient to prevent back flows of CO generated inside the furnace chamber (due to release of SiO from the melt with subsequent contact with graphite parts of the hot zone) resulting in formation of SiC impurities in the melt. Build-up of carbon in the silicon melt leads to formation of SiC precipitates responsible for shunting effects (short circuit of pn-junctions) in solar cells leading to drastic degradation of efficiencies of photovoltaic cells. Especially high amounts of CO are generated in cases where the furnace is subject to leakages of ambient air into the interior of the hotzone. Another drawback of low purge gas flow resulting in a reduced evaporation of SiO from the melt is a reduction of cell efficiencies due to light induced degradation related to higher oxygen content in silicon. Meanwhile, utilization of higher amounts of gas flows leads to degradation of silicon nitride coating with subsequent sticking of silicon to silica crucible walls, which causes loss of ingots due to their cracking. The oxygen leads to formation of SiO gas evaporating from the melt, and the SiO gas will subsequently react with graphite in the hot zone forming CO gas. Typical values associated with the Bridgman method is interstitial oxygen levels of 2- 1017 - 6- 1017/cm2 and 2· 1017 - 6· 1017/cm2 of substitutional carbon.
With regard to the downstream processing, silicon carbide (SiC) inclusions lead to productions losses in process of sawing wafers out of the blocks cut from the solidified ingots: SiC-particles cause wire breakage in sawing machines and cause appearance of saw marks on the wafers in their vicinity. A way to avoid the formation of precipitates in the melt is to shift carbon saturation level towards the top of the block beyond the ingot zone used for wafer cutting.
Thus, there is a need for controlling/eliminating the intrusion of carbon and sufficient evaporation of oxygen from the silicon metal during formation of the multi-crystalline ingots in a manner avoiding decomposition of the silicon nitride coating of the crucible, which is illustrated in the present invention.
Prior art
From WO 2007/148985, it is known device and method for production of ingots of semiconductor grade silicon, including solar grade silicon, where the presence of oxygen in the hot zone is substantially reduced or eliminated by employing materials void of oxides in the hot zone of the melting and crystallisation process. The method may be employed for any known process including for crystallising semiconductor grade silicon ingots, including solar grade silicon ingots, such as the Bridgman process, the block- casting process, and the CZ-process for growth of mo no crystal line silicon crystals. The invention also relates to devices for carrying out the melting and crystallisation processes, where the materials of the hot zone are void of oxides.
DE 10 2006 017 622 discloses manufacturing multi-crystalline silicon by vertical- gradient- freeze procedure, which comprises placing a lid resting upon a crucible to build a container structure, filling the container structure with silicon filling made of particulate or granular silicon up to a predetermined height, heating the container structure for melting the silicon fillings to liquid silicon, and cooling the container structure and solidifying the liquid silicon. The container has an inlet and an outlet for flushing gas to isolate the interior of the container structure from the exterior
atmosphere in order to avoid contamination of molten silicon with impurities of the furnace atmosphere. The lid has a contour corresponding to that of a crucible and is resting on the brackets posed on a crucible sides.
From WO 2010/033885 it is known a directional solidification furnace which includes a crucible for holding molten silicon and a lid covering the crucible and forming an enclosure over the molten silicon. The crucible also includes an inlet in the lid for introducing inert gas above the molten silicon to inhibit contamination of the molten silicon. The furnace further comprises an inlet in the lid for introducing inert gas above the molten silicon. A first gap and a second gap are disposed adjacent the lid. The first and second gaps define a nonlinear flow path for facilitating removal of contaminants from the enclosure and allowing the inert gas to exit the enclosure.
From WO 2009/014963 it is known a method and apparatus for casting silicon for photovoltaic cells and other applications able to form an ingot low in carbon and whose crystal growth is controlled to increase the cross-sectional area of seeded material during casting. The invention utilizes a lid and/or flowing of an inert gas to improve the purity of cast silicon, such as silicon having very low carbon concentrations. Lower impurities reduce the number of foreign particles included in the ingots (termed inclusions) and improve yields of the wafers and/or solar cells. An additional benefit to silicon having increased purity includes more and/or greater monocrystalline material from the same ingot. Less impurities in the silicon also allows for faster crystal growth. Additionally, low carbon content enables a greater variety of thermal processes for turning the wafer into a solar cell.
A material known to have extreme resistance towards thermal shock and mechanical wear is ceramic composites comprising carbon fibre-reinforced silicon carbide ceramics (C-C/SiC or C/SiC composites). These materials have presently found use as friction linings in braking systems of automotive applications, in aero-space applications, as combustor chamber linings, in turbine blades, in jet engine nozzles, etc.
From US 7 238 308 it is known that C-C/SiC or C/SiC composites may be produced by forming an intermediate body of carbon fibre-reinforced polymer (CRFP), heating the CRFP until the polymer is pyrolysed to form a porous green body of carbon fibre- reinforced carbon (C/C-body), contacting the green C/C-body with molten silicon and allow the silicon to infiltrate the green C/C-body (often termed Liquid Silicon
Infiltration, LSI in the literature) such that at least some of the silicon reacts with the carbon phase of the C/C-body and forms silicon carbide, and thus providing a carbon fibre-reinforced composite ceramic having a matrix comprising SiC, Si, and C. Similar techniques and materials are known from US 6 030 913 and EP 0 915 070.
EP 1 547 992 discloses a method for manufacturing C-C/SiC composites from a mixture of resin and carbon fibres which is pyrolysed to a green body directly without first hardening the resin. Then the green body is infiltrated with silicon to form the C-C/SiC composite. By varying the relative amounts of the ingredients, it is possible to produce composites with tailored amounts of C/C and C/SiC, and thus make composites with different thermal conductivities.
Objective of the invention
The main objective of the invention is to provide an apparatus for manufacturing ingots of crystalline photovoltaic grade silicon which substantially reduces/eliminates the problem of carbon contamination of silicon, reduces number of precipitates (crucial for fast wafer cutting), and which substantially reduces consumption of purge gas and effectively protects heating elements and the hot zone of furnace from deterioration.
The objective of the invention may be realised by the features as set forth in the description of the invention below, and/or in the appended patent claims.
Description of the invention
Design consideration
The invention is based on the realisation that a more operationally flexible and applicable solution for shielding the melt in a crucible from a back flow of contaminated purge gas in industrial production lines is obtained by forming the gas shield as an integral part of the hot zone of the crystallisation furnace.
Thus, the present invention relates to an arrangement for manufacturing a crystalline silicon ingot by directional solidification, comprising:
- a furnace with a hot zone able to house a crucible and which is sealed against the ambient atmosphere, where the hot zone comprises:
i) heating means for heating the crucible,
ii) an outlet for evacuating gas from the hot zone of the furnace,
iii) an inlet for supplying purge gas,
iv) a bottom support structure for carrying the crucible,
v) a top-shield separating an upper part of the hot zone into two over-laid chambers,
vi) a circumferential side support structure for the crucible, and
vii) a gas shield arrangement within the hot zone of the furnace,
characterized in that
- the gas shield arrangement comprises:
- a circumferential frame structure with a horizontal planar upper surface facing the top shield, and which is placed on top of the circumferential support structure, and
- a circumferential hood attached to and extending downward from the top shield to a distance above the horizontal planar upper surface of the
circumferential frame structure and thus forming a continuous slot along the periphery of the circumferential hood at a distance from the crucible wall, and
- the inlet for purge gas is positioned to supply purge gases under the hood.
The term "hot zone" as used herein means a compartment of the furnace where the heating is taking place and which is having thermally insulating walls, floor and ceiling. The hot-zone is usually a compartment shaped as a parallelepiped, but may have other geometries. There is often a steel shell or other type of mechanically rigid and gas-tight structure enclosing the hot zone to be used for forming the vacuum in the hot zone. The hot zone needs some form of heating means in order to perform the melting and solidification required to make crystalline silicon ingots. The invention may apply any known or conceivable heating means for melting and directionally solidifying the silicon in the crucible. A suited example of heating means is electric resistance heaters which may be placed in the bottom, the upper part, on the sides, or in any combination of these places of the hot zone.
The term "bottom support structure" as used herein means a load carrying structure of graphite or another heat conductive and mechanically rigid material for supporting the crucible and other structures/devices placed in the hot zone. The bottom support structure may form a horizontally oriented partition wall or floor covering the entire cross-section area of the hot zone and thus dividing the lower part of the hot zone into two chambers: one upper chamber where the crucible is to be placed and one lower chamber containing the heating means for heating from below. This provision has the advantage of protecting the lower heating means from deteriorative gases stemming from the melt. However, the present invention may also be applied for furnaces with any type of conceivable load carrying support structure for carrying the crucible, including furnaces where the crucible is placed directly on the bottom of the heat insulating wall of the hot zone.
The term "top shield" as used herein means the upper closure of the compartment if the hot zone containing the crucible, and will usually be an upper substantially horizontally oriented partition wall or ceiling dividing the upper compartment of the hot-zone into two horizontally separated chambers: the lower becoming the chamber housing the crucible and the upper chamber containing upper heating elements. This provision has the advantage of protecting the top heating elements from deteriorative gases stemming from the melt. However, the present invention may also be applied for furnaces without an upper two-chamber construction (no partition wall) such that the top shield becomes the upper thermal insulating wall of the hot-zone.
The term "circumferential" as used herein means that the structure, i.e. the support structure, the frame structure, or the hood, surrounds the outer walls of the crucible to form a continuous structure extending along the entire periphery of the crucible. The structure, except for the hood, may be in contact with the crucible wall, or it may be at a distance from the crucible wall.
The term "circumferential support structure" as used herein means a mechanically support structure functioning as the load carrying structure or suspension point for the circumferential frame structure. The circumferential support structure will often be rectangular plates of graphite or another heat resistant mechanically rigid material that is placed or mounted alongside the outer walls of the crucible to provide mechanical strength at elevated temperatures when the crucible sags. However, the circumferential support structure may be any conceivable structure able to suspend the circumferential frame structure at its intended position, such as i.e. a protruding section of the crucible, arms extending from the heat insulating walls of the hot zone etc. The term "circumferential frame structure" as used herein means the lower part of the gas shield arrangement. The circumferential frame structure should form a substantially horizontally oriented continuous planar platform projecting from the outer wall of the crucible along the entire periphery of the crucible at a specific height above the bottom support structure. The planar platform should surround the outer wall of the crucible with a maximum clearance of a few millimetres. That is, the horizontal cross-section area of the circumferential frame structure should have a length and width of at least 40 mm larger than the length and width of the crucible's horizontal cross-section area and have a centred void with a length and width in the range of 1 to 10 mm larger as the complementary shape and dimension of the crucible's cross-section area. Thus the frame will when being thread over the crucible and placed onto the circumferential support structure define a horizontally oriented continuous planar platform projecting from the outer wall of the crucible along the entire periphery of the crucible at the top of the graphite support structure. The distance from the inner to the outer edge of the platform along the side sections, that is the width of the circumferential frame structure, should be at least 20 mm. There is no upper limit to this width; the invention may apply any size of the frame's width as long as it fits inside the furnace compartment. In practice the width of the circumferential frame will be in the range from 20 to 200 mm, leading to a length and width of the horizontal cross-section area of the circumferential frame structure in the range from 40 to 400 mm larger than the length and width of the crucible's horizontal cross-section area. The circumferential frame structure may be simply resting on the circumferential support structure, or made to be an integral part of the circumferential support structure by being attached or fastened to the circumferential support structure. The dimensioning and/or positioning of the circumferential support structure may advantageously be such that when the circumferential frame structure is laid onto or attached to the upper face of the support structure, the upper surface of the circumferential frame structure is at a level in the range of 10 to 100 mm below the upper edge of the crucible wall (measured at standard conditions, STP).
The circumferential frame structure may advantageously include a "skirt" in the form of a peripheral perpendicularly downwardly oriented lip at the distal end (furthest away from the crucible) of the planar platform. This feature provides mechanical rigidity of the circumferential frame structure with respect to bending, and will also function as a deflection wall preventing outgoing gases exiting the circumferential slot from deteriorating the graphite support structure.
The term "hood" as used herein means the upper part of the gas shield. The hood is gas tight structure attached to the top shield (or directly to the upper heat insulating wall of the hot zone in cases with no upper partition wall or ceiling) and thus integrated with the upper part of the hot zone. The hood may be given any conceivable shape and
dimensioning as long as it forms an upper enclosure of the crucible extending from the top shield down to a small distance above the flat planar surface of the circumferential frame structure, and which is located at a distance apart from the crucible such that purge gas will be allowed to flow between the crucible and the inner surface of the hood towards the slot or opening that is being made between the hood and the flat planar surface of the circumferential frame structure. The slot or opening should be going all way around the crucible; there should be no contact between the hood and the crucible and circumferential frame structure at any point. The minimum distance between the crucible wall and the hood 16 may advantageously be in the range from 10 to 100 mm. The minimum distance between the crucible wall and the lower edge of the hood may advantageously be at least half of the width of the circumferential frame structure. This feature provides the advantage of forming a longer flow path for the purge gas inside the gas shield towards the circumferential slot formed between the hood and the
circumferential frame structure, and thus eliminates the occurrence of back- flow zones inside the gas-shield. The slot between the platform of circumferential frame structure and the upper hood is defined by the vertical distance or gap between them. The width of the gap should preferably be in the range from 1 - 50 mm, depending on gas pressure, temperature and gas flow volume of the purge gas being supplied to the hot zone. The gap width should preferably be in the range of 2 - 10 mm, or more preferably or 4 - 6 mm. The term "vertical distance or gap" as used herein means the shortest distance between the upwardly facing surface (flat planar surface) of the circumferential frame structure and the lowest point of the hood.
The hood may for instance be made by joining together four planar trapezoidal sheets of a heat conductive, preferably chemically resistant and rigid material to form an
"umbrella" resembling structure which is suspended from the top shield of the hot-zone of the furnace. Other embodiments of the hood may also be employed. The hood may advantageously be tapered outwardly to form a shape resembling a truncated pyramid suspended from the top shield with an angle, related to the surface of the top shield, in one of the following ranges; from 30° to 75°, from 45° to 70°, or from 55° to 65°. The feature of having an outwardly tapered hood that encompasses the top section of the crucible and forms a circumferential slot together with the circumferential frame structure at a distance below and outside of the upper edge of the crucible, is that this structure defines an open volume (gas pocket) between the slot and the crucible which allows to accommodate small accidental backflow of the purge gas without exposing the entire liquid silicon under the hood. This feature is suitable for furnaces with
intermittent operation of the vacuum pump since there is often formed a small fluctuations of the pressure (below 1 - 2 mbar) and thus resulting in a short fluctuating deviations of the purge gas flow in the vicinity of the slot. In case the top shield is not made of chemically inert material, the hood may also include a planar sheet or plate covering the upper partitioning ceiling. This plate may be of the same chemically inert material as the hood, and will protect the top shield and the upper heating means from the fumes from the melt.
The feature of having a hood which is integrated with the top shield and which extends down towards the circumferential frame provides the advantage of avoiding physical contact between the crucible and the hood of the gas shield, and thus elimination of any damages of the construction resulting from operations (loading/unloading of crucibles into furnace, closing/opening the furnace), which necessary require existence of clearance to preserve the desired width of circumferential slot for the purge gas coming out. The upwardly facing flat planar surface of the circumferential frame structure with a width in the range from 20 to 200 mm allows to accommodate a certain extent of arbitrary tilts and shifts of the crucible positioning (arising from loading/unloading operations) meanwhile preserving the desired width of the slot. Furthermore, in a particular case of the silica crucible, the slot realized below and beyond the periphery of the crucible alleviates the chemical wear of the release coating of the crucible (thus avoiding loss of ingots due to coating destruction resulting in sticking of silicon to silica walls with subsequent cracking of ingots) by purge gas by means of reducing the exposure of the coating to the high flow velocities in the vicinity of the circumferential slot. A further advantage is that the arrangement according to the invention reduces the consumption of purge gas by a factor of 4 - 5 as compared to similar arrangements without the gas shield. Another advantage is that it becomes possible to utilize larger volume of the crucible by accommodating higher loads of silicon under the hood.
Material consideration
The gas shield should be made of a material which is able to withstand the high temperatures associated with the melting of silicon without decomposing or in other way releasing (by gassing, perspiration, flaking, etc.) contaminating compounds. The material should also withstand the temperatures without loss of its desired mechanical rigidity. Further, the gas shield material preferably should be chemically inert in the chemical environment encountered in crystallisation furnaces for manufacturing mono- and multi- crystalline silicon ingots.
Another consideration that advantageously may be taken into account is that the temperature profile and heat fluxes inside the hot-zone of the furnace should not be detrimentally affected by the introduction of the gas-shield in order to preserve the intended heat extraction rates and control of the directional solidification process. That is, the heat resistance across the gas-shield should not hinder heat extraction through the bottom of the crucible. Thus, in summary, the gas-shield should be made of a material with sufficient mechanical rigidity to form a rigid gas-shield with a plate thickness of the gas-shield elements in the range of 1 - 20 mm, which is preferably chemically inert with respect to the chemical environment in the furnace during process conditions, and which optionally has a thermal conductivity of at least 1 W/mK or higher.
Examples of suited materials for use in the gas-shield includes, but is not limited to, ceramic materials with a SiC-coating, such as i.e. carbon fibre-reinforced carbon (known as CFRC, C/C, CFC etc) with a SiC-coating, graphite coated with SiC, silicon carbide ceramics (C-C/SiC or C/SiC composites), silicon carbide fibre composite (SiC/SiC). These materials will have sufficient thermal conductivity, the necessary mechanical rigidity to allow forming the circumferential hood and circumferential frame structure with a sheet thickness in the range of 1 - 10 mm, preferably 2 - 8 mm, 2 - 5 mm, or 2 - 3 mm. The SiC-coating may be applied on the inner side and optionally on the outer side of the gas shield to form a coating with a thickness in the range of 10 - 200 μιη, preferably 20 - 150 μιη, 40 - 120 μιη, or 60 - 100 μιη. The CFRC may advantageously be given a coating of SiC with thickness from about 10 to about 200 μιη SiC on one or both sides of the CFRC in order to make the gas shield more chemically inert towards the compounds of the gases in the hot zone. Both the hood and the frame structure may be made of sheet materials of CFRC with a SiC coating. The feature of low thermal resistance is less relevant for the frame structure as for the hood, such that the thickness of the sheet material being applied for the circumferential frame structure may be a factor 2 or 3 higher than for the hood.
The invention may apply any known or conceivable crucible for production of crystalline silicon by directional solidification. Examples of crucibles include one of: silicon carbide, silicon nitride coated crucibles of quartz, reaction bonded silicon nitride, C-C/SiC, etc. The arrangement according to the invention is not tied to Bridgeman type furnaces or processes, but may be applied for any known or conceivable process for forming mono- or multi-crystalline silicon ingots.
Gas flow conditions
The gas pressure inside the hot zone of the furnace during melting and directional solidification may advantageously be lowered in order to enhance oxygen evaporation from the melt. Lowered pressure conditions as used herein means any gas pressure in the range from 103 to 105 Pa, from 104 to 105 Pa, from 3 - 104 to 9- 104 Pa, or from 6- 104 to 9- 104 Pa. The purge gas may be any known or conceivable gas suitable as cover gas for silicon melts, such as noble gases or any other gas acting as chemically inert gas in the actual environment or an inert gas mixed with a reactive gas. The applied flow ranges may be from 2 to 50 Nl/min, from 2 to 30 Nl/min, from 5 to 25 Nl/min, or from 5 to 15 Nl/min.
List of figures
Figure 1 is a schematic drawing of a cross-section seen from the side of an example embodiment of the invention.
Figure 2 is an expanded view of the section within the box marked with a dashed line in Figure 1.
Figure 3 a) is a schematic drawing of the circumferential frame structure according to the invention seen from above, and figure 3 b) is a cross-section seen from the side.
Figure 4 a) and b) is a schematic drawing of the hood according to the invention seen from below and from the side, respectively. Figure 5 is a truncated schematic drawing of a cross-section seen from the side of the material employed in an example embodiment of the circumferential frame structure or circumferential hood according to the invention.
Figure 6 is a schematic drawing of a cross-section seen from the side of a second example embodiment of the invention.
Figure 7 a) is a photograph of a multicrystalline silicon ingot manufactured according to the present invention, and b) is a photograph of a multicrystalline silicon ingot manufactured without use of the gas shield arrangement.
Figure 8 is a curve diagram showing reduction of CO concentration (arb. units) above silicon melt as a function of Ar flow (arb. units) for prior art gas supply (upper black line, crosses) as compared with gas supply according to the present invention (lower line, full circles).
Figure 9 is a curve diagram showing the carbon concentration (arb. units) as a function ingot height (arb. units) as found by SIMS analysis for ingots produced without gas shield arrangement (upper grey line, circles) and with the gas shield of the present invention (lower line, crosses).
Figure 10 a) is a diagram summarising sawing mark depth for wafering process as a function of ingot height for ingots produced without the gas shield arrangement, and b) is a diagram summarising sawing mark depth for cutting wafers process as a function of ingot height for ingots produced with the gas shield according to the present invention.
Figure 1 1 is a diagram indicating the 16 blocks being cut from one ingot and showing typical distribution of loss reduction (in %) in the wafer production line obtained by the present invention compared with prior art baseline manufacturing without the gas shield arrangement.
Figure 12 is a diagram showing the cell efficiency distribution of solar cells produced from mono crystalline silicon ingot, which was crystallized in a vertical gradient freeze furnace according to prior art baseline manufacturing without employing the gas guiding device according to the invention.
Figure 13 is a diagram showing the cell efficiency distribution of solar cells produced from mono crystalline silicon ingot, which was crystallized in a vertical gradient freeze furnace employing the gas guiding device according to the present invention.
Example embodiments of the invention
The invention will now be described in greater detail by way of example embodiments. These example embodiments should not be interpreted as a limitation of the general inventive idea of employing a gas shield made of a circumferential frame structure and a circumferential hood for protecting molten silicon from gaseous contaminants during melting and solidification. First example embodiment
The example embodiment, shown in Figure 1 , comprises an inner furnace space or hot- zone for performing melting and solidification of silicon 1 in a crucible 2 by the
Bridgeman method. The hot zone is the inner compartment confined by the heat insulating walls 3. The crucible 2 is a conventional silica crucible coated with a slip coating of silicon nitride.
The crucible 2 is placed onto a graphite floor 4 which divides the inner compartment of the hot zone into one bottom chamber 5 housing electric resistance heaters 6 made of graphite for heating the bottom of the crucible 2 and one mid chamber 7 housing the crucible 2. The sides of the crucible 2 are mechanically supported by graphite plates 8. Above the crucible 2, the hot zone is equipped with a top shield in the form of a horizontal partition wall 9 dividing the compartment of the hot zone further to form one upper chamber 10 housing electric resistance heaters 1 1 made of graphite for heating the crucible 2 from above. Purge gas is supplied to the hot zone via inlet 12 and extracted together with the gases evaporating from the melt via gas outlets 13, towards a pump (not shown) for maintaining desired pressure and flow conditions.
A circumferential frame structure 14 is made of a planar sheet of CFRC of thickness 3 - 4 mm and which is coated with 80 - 100 μιη thick layer of SiC. The width of the upwardly facing flat planar surface 15 is about 100 mm. The circumferential frame 14 is also drawn schematically in Figure 3 a) and 3 b), where 3 a) is seen from above and 3 b) from the side. The distance marked by arrow C on Figure 3 is the width of the opening or the void where the crucible 2 is to enter. This distance is 4 mm larger than the width of the horizontal cross-section of the crucible 2. The width of the circumferential frame is marked by arrow D.
The hood 16 is made of a planar sheet of CFRC of thickness 2 mm and which is coated with 80 - 100 μιη thick layer of SiC on both sides, as shown schematically in Figure 5. The thermal conductivity of the SiC-coated CFRC is about 20 W/mK. The hood 16 is made of four planar trapezoidal sheets joined together to form an "umbrella" (hollow truncated pyramid) resembling structure which is suspended from the top shield 9 of the hot-zone of the furnace, as may be seen in Figure 4 a) which is a view from below and 4 b) which is a side view.
An expanded view of the area inside the box marked with a dashed line in Figure 1 is shown in Figure 2. The vertical distance defining the slot between the circumferential frame structure 14 and the circumferential hood 16 is marked on the figure by arrow A, and is in the range of 4 - 6 mm. The distance between the lower edge of the hood 16 and the wall of the crucible 2 is marked by arrow B. This distance is half of the width D of the circumferential frame. The gas flow inside the hot-zone is indicated by the arrows and is 5 - 7 Nl/min and the pressure is 9 · 104 Pa (900 mbar). The cross-section of the CFRC material coated with SiC from both sides and used both for manufacturing of the top shield 9 and the hood 16 is illustrated in Figure 5, where reference number 20 is the CFRC and 21 is the SiC-coating.
Second example embodiment
The second example embodiment illustrated on Figure 6 is similar to the first example embodiment shown on Figure 1 except that the top shield 9 is made of a 2 mm thick sheet of CFRC which is coated with one 80 - 100 μιη thick layer of SiC on the lower side facing the mid chamber 7. The hood 16 is attached to the top shield 9. Also, the circumferential frame structure 14 is constructed from four L-pro files forming a "skirt" 17 at the distal end of the frame to provide increased mechanical rigidity with respect to bending during operations of loading/unloading of the crucibles into the furnace. The hot zone is also shown encompassed in a steel casing 18 defining the vacuum sealing of the furnace. Otherwise, the second example embodiment is equal to the first example embodiment.
Verification of the invention
The effect of the invention on silicon ingots
A series of comparison experiments where silicon has been melted and solidified according to the Bridgeman method using the arrangement according to the second example embodiment with and without the gas shield (circumferential hood and circumferential frame structure) have been performed to verify the effect of the invention.
The tests were conducted with exactly the same heating and solidifying procedure, same flow of the purge gas and pressure. The only difference between the tests was that one series of ingots was produced with the gas shield arrangement according to the invention and another without the gas shield arrangement.
Figure 7 a) is a photograph of a multi-crystalline silicon ingot made with a gas shield arrangement according to the present invention, and Figure 7 b) without. As can be clearly seen on the photographs, the surface of the ingot in Figure 7 b) is considerably more dull and grey due to formation of SiC resulting from a reaction with CO that is transported to the melt inside the furnace chamber. This result is supported by measurements of CO concentration above the silicon melt at the beginning of the crystallization as a function of argon supply demonstrated on Figure 8. The figure shows that CO-concentration above the melt is much more efficiently reduced by lower amounts of purge gas in case of application of the gas shield arrangement. The results obtained for ingots produced without the gas shield arrangement is the upper black line with crosses, and the results for the ingots made with the gas shield arrangement according to the present invention is the lower line with full circles. The carbon concentration of the produced ingots is also measured across the ingot height. The results shown on Figure 9 are typical averages of SIMS analysis for carbon distribution for one of the 32 ingots. As can be seen from the Figure 9, the ingots produced with the gas shield arrangement according to the present invention have a carbon concentration of a factor 3 or more at ingot heights from 60 % and below, and a carbon concentration of about 25 % lower at the upper part of the ingot. The results obtained for ingots produced without the gas shield arrangement is the upper grey line with circles, while the results for the ingots produced with the gas shield arrangement of the present invention is the lower line with crosses.
The results shown in Figure 10 a) and b) demonstrate the level of sawing marks across the ingot height (accumulated for 512 wafer blocks cut from 32 ingots) indicating that the blocks being sawn out of the ingots made with the gas shield should contain much less SiC-inclusions which are known to cause wire-breaks and reduce wafer production output in the process of wire-sawing (wafering) of the blocks into wafers. One of the problems is that the wire when reaching hard SiC-inclusion produces sawing wire defects (sawing marks) causing rejection of the wafer for further downstream
processing.
Finally, Figure 1 1 is a diagram showing typical distribution of loss reduction (%) (achieved by application of gas shield arrangement according to the present invention) for each of 16 blocks cut from one ingot resulting in average reduction of wafer losses about 58 % compared to the factory baseline without gas shield arrangement.
The effect of the invention on the solar cells
The effect of the invention on the downstream processing of the wafers to solar cells has been investigated as follows:
Crystallized silicon ingot is cooled down and cut vertically into 16 equivalent bricks of approximately 245 mm height. Then the square wafers are produced by slicing the bricks in horizontal direction into wafers of size 156 mm x 156 mm and 200 μιη thick. After slicing, the wafers are subsequently washed, dried and then go through the standard process of solar cell preparation: etching to texture the surface, chemical vapor deposition (CVD) of n-dopant (phosphorous), in-diffusion of phosphorous at elevated temperatures, deposition of anti-reflective coating of silicon nitride on a front surface of the wafer. Finally, the metallic electrical contacts are applied on a front and back sides of the wafer.
The solar cells produced from wafers went through the cell tester, where the wafers with different cell efficiencies, but having resistance below the threshold of 30 ohm are sorted out as "shunted" i.e. of inappropriate quality. As it could be seen from
comparison of cell distribution shown on Figure 12 (crystallization process without gas guiding device) and Figure 13 (crystallization process with gas guiding device), the employment of gas guiding device reduces the fraction of shunted solar cells by a factor of 10 due to reduced precipitation of SiC particles.

Claims

1. An arrangement for manufacturing a crystalline silicon ingot by directional solidification, comprising:
- a furnace with a hot zone able to house a crucible and which is sealed against the ambient atmosphere, where the hot zone comprises:
i) heating means for heating the crucible,
ii) an outlet for evacuating gas from the hot zone of the furnace,
iii) an inlet for supplying purge gas,
iv) a bottom support structure for carrying the crucible,
v) a top-shield separating an upper part of the hot zone into two over-laid chambers,
vi) a circumferential side support structure for the crucible, and
vii) a gas shield arrangement within the hot zone of the furnace,
characterized in that
- the gas shield arrangement comprises:
- a circumferential frame structure with a horizontal planar upper surface facing the top shield, and which is placed on top of the circumferential support structure, and
- a circumferential hood attached to and extending downward from the top shield to a distance above the horizontal planar upper surface of the
circumferential frame structure and thus forming a continuous slot along the periphery of the circumferential hood at a distance from the crucible wall, and
- the inlet for purge gas is positioned to supply purge gases under the hood.
2. Arrangement according to claim 1 , wherein the circumferential frame structure and the hood are made of one the following materials: carbon fibre-reinforced carbon, silicon carbide ceramics such as C-C/SiC or C/SiC-composites, silicon carbide fibre composite SiC/SiC, carbon fibre-reinforced carbon with a SiC-coating, or graphite coated with SiC.
3. Arrangement according to claim 1 , wherein the circumferential frame structure and the circumferential hood are made of planar and/or L-profile sheets of carbon fibre- reinforced carbon with a SiC-coating, where
- the thickness of the carbon fibre-reinforced carbon sheets is in the range of 1 - 10 mm, and
- the SiC-coating is applied to both sides of the sheet and given a thickness in the range of 10 - 200 μπι.
4. Arrangement according to claim 3, wherein
- the thickness of the planar and/or L-profile sheets is within one of the following ranges; 2 - 8 mm, 2 - 5 mm, or 2 - 3 mm, and - the thickness of the coating is within one of the following ranges; 20 - 150 μηι, 40 - 120 μηι, or 60 - 100 μηι.
5. Arrangement according to claim 1 , wherein
- the width of the circumferential frame structure is in the range from 20 to 200 mm, and
- the circumferential frame structure is
i) given a complementary shape as the horizontal cross-section area of the crucible,
ii) a length and width of the horizontal cross-section area of the
circumferential frame structure in the range from 40 to 400 mm larger than the length and width of the crucible's horizontal cross-section area, and
iii) a length and width of the horizontal cross-section area of a centred void in the range from 1 to 10 mm larger than the length and width of the crucible's horizontal cross-section area.
6. Arrangement according to claim 5, wherein the circumferential frame structure is made of L-profile sheets of carbon fibre-reinforced carbon with a SiC-coating.
7. Arrangement according to claim 5, wherein the circumferential frame structure is resting on the circumferential support structure.
8. Arrangement according to claim 5, wherein the circumferential frame structure is made an integral part of the circumferential support structure by being attached or fastened to the circumferential support structure.
9. Arrangement according to claim 1 , wherein the circumferential frame structure is positioned such that the upper surface of the circumferential frame structure is at a level in the range from 10 to 100 mm below the upper edge of the crucible wall.
10. Arrangement according to claim 1 , wherein the hood is tapered outwardly to form a shape resembling a hollow truncated pyramid suspended from the top shield forming an angle with respect to the surface of the top shield in one of the following ranges: from 30° to 75°, from 45° to 70°, or from 55° to 65°.
1 1. Arrangement according to any of claims 1 - 10, wherein the vertical distance between the lower edge of the hood and upward facing flat planar surface of the circumferential frame structure is in the range from 2 to 50 mm.
12. Arrangement according to claim 1 1 , wherein the vertical distance is either in the range of 2 - 10 mm, or in the range of 4 - 6 mm.
13. Arrangement according to claim 10, wherein the distance between the lower edge of the hood and the crucible wall is in the range from 10 to 100 mm.
14. Arrangement according to any of claims 1 to 13, wherein the circumferential frame structure includes a "skirt" in the form of a peripheral perpendicularly
downwardly oriented lip at the distal end of the frame structure.
15. Arrangement according to any of claims 1 to 14, wherein
- the top shield is a substantially horizontally oriented partition wall or ceiling dividing the upper section of the hot-zone in two horizontally separated chambers, and
- the surface of the top shield facing the crucible is covered by a sheet of one of the materials of claim 2.
16. Arrangement according to claim 15, wherein the sheet covering the top shield is coated on the side facing the crucible with a layer of SiC.
PCT/IB2012/051941 2011-04-19 2012-04-18 An arrangement for manufacturing crystalline silicon ingots WO2012143867A1 (en)

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GB1106558.8A GB2490129A (en) 2011-04-19 2011-04-19 Directional solidification furnace
US201161480969P 2011-04-29 2011-04-29
US61/480,969 2011-04-29

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111850673A (en) * 2020-07-27 2020-10-30 江苏协鑫硅材料科技发展有限公司 Gas stirring device, ingot furnace and using method thereof
CN113802181A (en) * 2020-06-11 2021-12-17 苏州阿特斯阳光电力科技有限公司 Silicon material charging method

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0915070A2 (en) 1997-11-10 1999-05-12 Deutsches Zentrum für Luft- und Raumfahrt e.V. Method of making carbon fibre reinforced ceramified shaped body and use of such a shaped body
US6030913A (en) 1997-03-12 2000-02-29 Sgl Technik Gmbh Silicon carbide articles reinforced with short graphite fibers
EP1547992A1 (en) 2003-12-18 2005-06-29 Deutsches Zentrum für Luft- und Raumfahrt e.V. Process for producing a fibre reinforced composite material and the fibre reinforced composite material
US7238308B2 (en) 2002-03-19 2007-07-03 Audi Ag Process for the infiltration of porous carbon composites
DE102006017622A1 (en) 2006-04-12 2007-10-18 Schott Ag Manufacturing multi-crystalline silicon comprises placing detachable upper section at an upper edge of crucible furnace to build container structure, filling the container structure with silicon filling, and heating the container structure
WO2007148985A1 (en) 2006-06-23 2007-12-27 Rec Scanwafer As Device and method for production of semiconductor grade silicon
WO2009014963A1 (en) 2007-07-20 2009-01-29 Bp Corporation North America Inc. Methods and apparatuses for manufacturing cast silicon from seed crystals
WO2010033885A1 (en) 2008-09-19 2010-03-25 Memc Electronic Materials, Inc. Directional solidification furnace for reducing melt contamination and reducing wafer contamination

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6030913A (en) 1997-03-12 2000-02-29 Sgl Technik Gmbh Silicon carbide articles reinforced with short graphite fibers
EP0915070A2 (en) 1997-11-10 1999-05-12 Deutsches Zentrum für Luft- und Raumfahrt e.V. Method of making carbon fibre reinforced ceramified shaped body and use of such a shaped body
US7238308B2 (en) 2002-03-19 2007-07-03 Audi Ag Process for the infiltration of porous carbon composites
EP1547992A1 (en) 2003-12-18 2005-06-29 Deutsches Zentrum für Luft- und Raumfahrt e.V. Process for producing a fibre reinforced composite material and the fibre reinforced composite material
DE102006017622A1 (en) 2006-04-12 2007-10-18 Schott Ag Manufacturing multi-crystalline silicon comprises placing detachable upper section at an upper edge of crucible furnace to build container structure, filling the container structure with silicon filling, and heating the container structure
WO2007148985A1 (en) 2006-06-23 2007-12-27 Rec Scanwafer As Device and method for production of semiconductor grade silicon
WO2009014963A1 (en) 2007-07-20 2009-01-29 Bp Corporation North America Inc. Methods and apparatuses for manufacturing cast silicon from seed crystals
WO2010033885A1 (en) 2008-09-19 2010-03-25 Memc Electronic Materials, Inc. Directional solidification furnace for reducing melt contamination and reducing wafer contamination

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN113802181A (en) * 2020-06-11 2021-12-17 苏州阿特斯阳光电力科技有限公司 Silicon material charging method
CN111850673A (en) * 2020-07-27 2020-10-30 江苏协鑫硅材料科技发展有限公司 Gas stirring device, ingot furnace and using method thereof

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