WO2017075108A1 - Procédé et appareil pour la production de silicium de qualité solaire - Google Patents

Procédé et appareil pour la production de silicium de qualité solaire Download PDF

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Publication number
WO2017075108A1
WO2017075108A1 PCT/US2016/058952 US2016058952W WO2017075108A1 WO 2017075108 A1 WO2017075108 A1 WO 2017075108A1 US 2016058952 W US2016058952 W US 2016058952W WO 2017075108 A1 WO2017075108 A1 WO 2017075108A1
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WO
WIPO (PCT)
Prior art keywords
container
reacting
walls
elemental
temperature
Prior art date
Application number
PCT/US2016/058952
Other languages
English (en)
Inventor
Angel Sanjurjo
Xiaobing Xie
Jianer BAO
Jordi Perez-Mariano
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Sri International
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Publication date
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Publication of WO2017075108A1 publication Critical patent/WO2017075108A1/fr

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B14/00—Crucible or pot furnaces
    • F27B14/08—Details peculiar to crucible or pot furnaces
    • F27B14/10—Crucibles
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/02—Silicon
    • C01B33/021—Preparation
    • C01B33/027—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material
    • C01B33/033—Preparation by decomposition or reduction of gaseous or vaporised silicon compounds other than silica or silica-containing material by reduction of silicon halides or halosilanes with a metal or a metallic alloy as the only reducing agents
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • 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
    • 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
    • C30B35/007—Apparatus for preparing, pre-treating the source material to be used for crystal growth
    • 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
    • F27D11/00—Arrangement of elements for electric heating in or on furnaces
    • F27D11/06—Induction heating, i.e. in which the material being heated, or its container or elements embodied therein, form the secondary of a transformer
    • 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
    • F27D99/00—Subject matter not provided for in other groups of this subclass
    • F27D99/0001—Heating elements or systems
    • F27D99/0006—Electric heating elements or system
    • F27D2099/0015—Induction heating
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the field of the invention relates to a method and an apparatus for producing silicon with high purity and low cost for solar cell manufacture, and more specifically, for producing solar grade silicon with a multi-step process including reducing silicon tetrafluoride (S1F4) gas with pure elemental magnesium.
  • S1F4 silicon tetrafluoride
  • Another industrial production path is the selective purification of metallurgical- grade Si.
  • the need to combine several steps to achieve a minimum desired purity has resulted in a high cost-to-purity ratio process. Therefore, a need exists to produce solar grade silicon with a highly efficient (consuming less energy), low cost- to-purity ratio, reliable, and high yield process.
  • a new design for a high throughput apparatus for producing solar grade silicon is desired.
  • Embodiments of Applicants' disclosure describes a method for making high purity elemental silicon, comprising: pressurizing a first reacting container with silicon tetrafluoride (S1F4); adding elemental magnesium (Mg°) to the container to generate Si 0 and MgF2; and separating the Si 0 and the MgF2.
  • S1F4 silicon tetrafluoride
  • Mg° elemental magnesium
  • the pressure of SiF4 in the first reacting container could be between about 0.1 standard atmosphere and about 10 standard atmospheres; the pressure of S1F4 in the first reacting container could also be between about 0.5 standard atmosphere and about 1.5 standard atmospheres; and the pressure of S1F4 in the first reacting container could be between about 0.8 standard atmosphere and about 1.2 standard atmospheres.
  • the method further comprises heating the first reacting container to a first temperature, wherein the first temperature could be between about 800°C and about 2000°C; the first temperature could be between about 1200°C and about 1600°C; and the first temperature could be between about 1250°C and about 1450°C.
  • the method further comprises injecting elemental magnesium in a form that is selected from the group consisting of elemental magnesium particles, elemental magnesium bricks, elemental magnesium sponge, and liquid elemental magnesium.
  • the liquid elemental magnesium is added at a temperature between about 662°C and about 725°C.
  • the elemental magnesium is added in amounts such that when melted a pool of molten elemental magnesium comprises a height less than about 10 cm.
  • the elemental magnesium can also be added in amounts such that when melted a pool of molten elemental magnesium comprises a height less than about 3 cm.
  • the method comprises providing a first reacting container comprising a reaction zone and one or more first reacting container walls; and adding the elemental magnesium at a rate to control a temperature of the reaction zone and a temperature of one or more first reacting container walls.
  • the providing further comprises providing a first reacting container comprising one or more first reacting container walls and providing the first reacting container comprising an insulating layer, which may have a heating unit disposed therein, disposed between the one or more external walls and the one or more internal walls.
  • the one or more first reacting container walls comprises an external portion comprising Inconel and the one or more first reacting container walls an internal portion comprising Graphite.
  • the insulation material is selected from the group consisting of silicon dioxide (S1O2), silicon nitride (Si3N 4 ), and silicon carbide (SiC).
  • One or more internal walls can be coated with pure MgF2.
  • the method further comprises removing unreacted S1F4 gas from the first reacting container; filling the first reacting container with an inert gas; opening the first reacting container; and discharging the elemental Si and the MgF2.
  • the method comprises providing a first reacting container formed to include one or more apertures extending through a bottom portion thereof; disposing a second container adjacent to the first reacting container; and discharging MgF2 from the first reacting container into a second container.
  • the method comprises melting the elemental Si and discharging molten elemental Si into the second container and forming the one or more apertures to comprise a diameter of between about 0.5 mm and about 1 cm.
  • the method comprises after discharging the elemental Si from the first reacting container, crystallizing the molten element Si to form an elemental Si ingot.
  • Embodiments of Applicants' disclosure further describe an apparatus for preparing high purity elemental Si.
  • the apparatus comprises a container having an outer container surface and defining an enclosed space, wherein the container is capable of withstanding temperature greater than about 1400°C; and a lid removably attached to the container.
  • the apparatus further comprises a cooling coil comprises a spiral wound, tubular member to circulate a coolant therethrough.
  • the container comprises one or more container walls.
  • the one or more container walls comprise an external portion comprising Inconel.
  • the one or more container walls comprise an internal portion comprising Graphite and the one or more container walls comprise an insulating layer disposed between the external portion of the one or more external walls and the internal portion of the one or more internal walls.
  • the apparatus further comprises a thermocouple capable of monitoring a temperature of the reaction zone and the one or more container walls; a pressure sensor in fluid communication with the enclosed space; a pressure-gauging port extending through the one or more container walls to communicate with the pressure sensor; a vacuum port extending through the one or more container walls to communicate with the enclosed space; a material input tube extending through the one or more container walls to communicate with the enclosed space; and a gas inlet extending through the one or more container walls to communicate with the enclosed space.
  • a thermocouple capable of monitoring a temperature of the reaction zone and the one or more container walls
  • a pressure sensor in fluid communication with the enclosed space
  • a pressure-gauging port extending through the one or more container walls to communicate with the pressure sensor
  • a vacuum port extending through the one or more container walls to communicate with the enclosed space
  • a material input tube extending through the one or more container walls to communicate with the enclosed space
  • a gas inlet extending through the one or more container walls to communicate with the enclosed space.
  • the apparatus comprises one or more second containers, wherein at least one second container is located below or adjacent to the first reacting container such that a reaction product can be disposed into the second container from the first reacting container.
  • the patent or application file contains at least one drawing executed in color.
  • FIG. 1 A illustrates an embodiment of a reacting container 100 used to carry out the reaction of elemental magnesium (Mg) and S1F4;
  • FIGS. IB and 1C illustrate reacting container 101;
  • FIG. ID shows yet another embodiment of the reacting container 101;
  • FIG. IE shows different layers of one or more walls of the reacting container
  • FIG. IF illustrates reacting container 102
  • FIGS. 2A-2C show XRD phase analysis of the reaction product after S1F4 and
  • FIG. 3 A is a top view of an open container 130 during Mg ignition showing a bright color
  • FIG. 3B is the reaction product showing both brown particles and fracture areas with metallic appearance
  • FIG. 4 is phase diagram of Mg-Silicon
  • FIGS. 5A-5D are flowcharts summarizing a method for making high purity elemental silicon (Si 0 );
  • FIGS. 6A and 6B show cross-section views of the reaction product in a graphite crucible under optical microscope and the product in the crucible after melt separation;
  • FIGS. 7 A and 7B illustrate Si 0 after the melt and separation process
  • FIG. 8 is a diagram of solubility of Mg in silicon.
  • Embodiments of the disclosure solve the issue of manufacturing solar grade silicon with high purity at a large scale with a lost cost.
  • the photovoltaic industry In order to be suitable for use in the photovoltaic industry, the photovoltaic industry generally requires that metallurgical grade silicon that has a purity level of about 98-99% by weight, be further purified to a purity level of 99.99-99.9999% by weight.
  • the reacting container 100 comprises an outer container surface 1 10, which defines a first enclosed space 120; an induction coil 140, which wraps around the outer reacting container surface 110; and an open cup 130, which is disposed within the first enclosed space 120.
  • the outer reactor surface 110 comprises a first wall 102 and a second wall 104.
  • the first and the second walls 102 and 104 comprise Quartz with cooling coolant running in between.
  • the walls 102 and 104 comprise high temperature enduring and corrosion resistant alloys, such as, molybdenum, stainless steel, tungsten, tantalum, titanium, or nickel.
  • the first and the second walls 102 and 104 define a second enclosed space 106.
  • the second enclosed space 106 can be used to circulate liquid coolant, for example, water, to cool the outer reactor surface 1 10 and the reacting container 100.
  • the first wall 102 further comprises a water inlet 108 and a water outlet 109, which are used to inject, circulate, and remove liquid coolant within the second enclosed space 106 between the two walls 102 and
  • the first wall 102 also comprises a vacuum port 180 and a pressure-gauging port 190, which can be connected to a pressure sensor 170 to monitor the pressure within the reactor 100. Further, the vacuum port 180 ensures the first reacting container 100 is able to remain gas tight during any reaction. In other embodiments, both the walls 102 and 104 can be made of materials that are suitable to withstand high temperature up to 2000°C.
  • the induction coil 140 comprises a radio frequency
  • RF induction coil The induction coil 140 is in physical contact with the outer reacting container surface 110 in some embodiments, while the induction coil 140 is not in physical contact in other embodiments.
  • RF induction is the use of a radio frequency magnetic field to transfer energy by means of electromagnetic induction in the near field.
  • a radio-frequency alternating current is passed through a coil of wire that acts as the transmitter, and a second coil or conducting object, magnetically coupled to the first coil, acts as the receiver.
  • suitable methods for heat induction and energy transferring can be employed here to heat up the reacting container 100 to a certain temperature.
  • the open cup 130 comprises a plurality of layers.
  • the open cup 130 comprises three layers: an outer graphite felt insulation layer 132, a middle graphite layer 134, and an inside graphite layer 136.
  • the open container 130 can comprise additional 1 or 2 insulation layers made of suitable materials that can withstand high temperature and are able to insulate.
  • the graphite used here possess certain chemical and physical properties that make it suitable for high-temperature applications, such as thermal radiation shielding and exothermic reaction. Similarly, other types of material that possess the same properties can be used to form the plurality of layers of the open container 130.
  • the reacting container 100 further comprises a quartz stand 150 and a thermocouple 160.
  • the quartz stand comprises a first surface 151, which touches the bottom of the open cup 130.
  • the thermocouple 160 extends through an opposing surface 152 of the quartz stand 150 and the first surface 151 of the quartz stand 150. Further, the thermocouple 160 is in physical contact with the open cup 130. Thus, the thermocouple 160 is able to monitor the open cup 130's temperature.
  • the reacting container 101 can have a volume of 10 liters to 1,000 liters. While specific values chosen for this embodiment are recited, it is to be understood that, within the scope of the invention, the values of all of parameters may vary over wide ranges to suit different applications.
  • the reacting container 101 comprises a top lid 210, a bottom pot 220, an elemental Mg injection tube 212, and a gas injection port 214.
  • the top lid 210 is removably attached to the bottom pot 220.
  • the top lid 210 can be secured to the bottom pot 220 and keep the bottom pot 220 gas tight by methods known to person skilled in the art.
  • a rim 216 of the top lid 210 is screwed to a rim 224 of the of the bottom pot 220.
  • materials that seal and keep a container air tight can be disposed between the rim 216 and the rim 224.
  • the U.S. Patent No. 4,781,565 is incorporated by reference in its entirety to describe the elemental Mg injection tube 212 and the gas injection port 214 in certain embodiments.
  • the bottom pot 220 can be a cylindrically shaped with a substantially flat bottom 226.
  • an outer wall 228 of the bottom pot 220 can be pentagonal, hexagonal, heptagonal, octagonal, nonagonal, or decagonal; and the bottom 226 can comprises a curvature.
  • metal fins encircles the bottom pot 220 to strengthen the pot and dissipate heat during reaction process.
  • a cooling coil 230 wraps around the outer wall 228 and is disposed at the top of the bottom pot 220 to keep the rim 216 and rim 224 cool.
  • the cooling coil 230 is in physical contact with the outer wall 228 and comprises a tubular member to circulate a coolant therethrough.
  • the reacting container 101 further comprises handles
  • FIG. IE illustrates the structure of the outer wall 228.
  • the outer wall 228 comprises an external portion 240, which comprises Inconel.
  • the external portion 240 is lined with a Nickel lining-layer 242.
  • the external portion 240 comprises high temperature enduring and corrosion resistant alloys, such as, molybdenum, stainless steel, tungsten, tantalum, titanium, or nickel.
  • the outer wall 228 comprises an internal portion 246, which comprises GRAFOIL with the same chemical and physical properties described above.
  • an insulation layer 244 is disposed between the external portion 240 and the internal portion 246.
  • the insulation layer 244 comprises flexible graphite felt in certain embodiments; while the insulation layer 244 comprises a material that is selected from a group consisting of silicon dioxide (SiC ), silicon nitride (S13N4), silicon carbide (SiC), other non-contaminating materials, and any combination thereof.
  • the insulation layer 244 materials can be porous or in the form of sponges, felts, beds of particles, and/or any combination thereof.
  • an internal heating unit is disposed between the external portion 240 and the insulation layer 244. In other embodiments, the internal heating unit is disposed within the insulation layer 244. Further, in some embodiments, the internal heating unit comprises a RF coil, which does not physically contact the external portion 240 or the insulation layer 244.
  • the heating unit employs resistance heating method or any other methods known in the art to heat the reacting container 101.
  • the reacting container 101 can be heated by an external heating unit.
  • the external heating unit comprises heating tapes and/or hot plate.
  • FIG. IF illustrates an embodiment of the reacting container 102 that can be employed in a semi-continuous or a continuous multi-stage system for reaction and melt coalescence and separation.
  • U. S. Patent No. 8,475,540 is incorporated herein by reference in its entirety to describe the multi-stage system for reaction and melt coalescence and separation.
  • the reacting container 102 comprises a first orifice 250 and a second orifice 260 extending through a bottom 270 of the reacting container.
  • the first orifice 250 and the second orifices extend through the outer wall 228. The first and the second orifices 250 and 260 allow removal of liquefied reaction product generated in the reacting container 102.
  • a plurality of orifices can be disposed in the bottom 270 and/or the outer wall 228.
  • the diameters of the orifices 250 and 260 are less than 1 cm; in other embodiments, the diameters of the orifices 250 and 260 are less than 0.5 cm; and in yet other embodiments, the diameters of the orifices 250 and 260 are less than 2 mm. While specific values chosen for the number and the size of the orifices are recited, it is to be understood that, within the scope of the invention, the values of the number and the size of the orifices can vary over wide ranges to suit different applications.
  • FIGS. 5A-5D illustrate Applicants' method for making high purity elemental silicon (Si 0 ) using different embodiments of the reacting container 100, 101, or 102.
  • Si 0 high purity elemental silicon
  • Mg° elemental magnesium
  • 5N Mg° Log5 purity
  • Mg° comprises a
  • Mg° Log4 purity (herein after as 4N Mg°), which is 99.99% by weight pure of Mg° and comprises less than 1.3 ppmw of B.
  • Mg° is divided into cubes, each of which weighs about 2 g to 4 g.
  • Mg° can be injected into the reacting container
  • injection tube 212 in the form of Mg° particles, Mg° bricks, Mg° sponge, and/or liquid
  • liquid Mg° is added at a temperature of the reacting container 101 from about 662°C and about 725°C.
  • Mg° is added at a temperature below the temperature of the liquid Mg°'s reaction or ignition point in S1F4 atmosphere.
  • step 510 before heating in step 525, the reacting container
  • the reacting container 100, 101, or 102 is evacuated through the vacuum port 180 (FIG.1A). Then the reacting container 100, 101, or 102 is back-filled with inert gas in step 515. In certain embodiments, the back-filling of inset gas in step 515 is repeated one more time. In other embodiments, the back-filling of inert gas in step 515 is repeated two more times. The examples of how many times to back fill the reacting container 100, 101, or 102 with inert gas are not limiting, the reacting container 100, 101, or 102 can be back-filled with inert gas followed with evacuation for several times as long as the residual air in reacting container 100, 101, or 102 is sufficiently low.
  • the inert gas is argon. In other embodiments, the inert gas is from the Periodic Table Group 0 gases, such as helium, argon and the like.
  • step 520 silicon tetrafluoride (S1F4) gas is added through a gas injection port
  • the pressure within the reacting container 100, 101, or 102 is constantly monitored by the pressure sensor 170. Once the interior pressure of the reacting container 100, 101, or 102 reaches about a range of about 0.1 standard atmospheric pressure (atm) to 10 atm. One standard atmospheric pressure is about 101325 Pascal (Pa). Once a desired interior pressure of the S1F4 gas, the gas injection port 214 is shut off to prevent over-filling of more S1F4 gas.
  • the reacting container 100, 101, or 102 is filled with S1F4, in step 525, the reacting container 100, 101, or 102 is heated to a certain temperature by supplying power to the induction coil 140. In certain embodiments, the temperature of the reacting container 100, 101, or 102 is heated to a certain temperature by supplying power to the induction coil 140. In certain embodiments, the temperature of the reacting container 100,
  • the temperature of the reacting container 100, 101, or 102 is monitored via the thermocouple 160.
  • the temperature of the reacting container 100, 101, or 102 is monitored by an optical pyrometer focused on the reacting container 100, 101, or 102.
  • the reacting container 100, 101, or 102 is heated to between about 800°C and about 2000°C.
  • the reacting container 100, 101, or 102 is heated to between about 1200°C and about 1600°C.
  • the reacting container 100, 101, or 102 is heated to between about 1250°C and about 1450°C. Heating temperatures may vary throughout the heating step, and particularly throughout the S1F4 and Mg exothermic reaction process.
  • the actual temperature may fluctuate and may not be held constant at said temperature.
  • a reaction zone 280 (FIG. ID) reaches the predetermined temperature
  • the Mg° in any selected form is dropped into first reacting container 100, 101 , or 102 at a controlled rate via the material injection tube 212 in step 530.
  • the controlled rate of injecting Mg° is determined by a desired rate of reaction. If a faster rate of reaction is desired, a faster controlled rate of Mg° injection is used. If a slower rate of reaction is desired, a slower controlled rate of Mg° injection is used.
  • the controlled rate of injecting Mg° is also determined by a height of a pool of molten Mg° in the reaction zone 280 (FIG. ID).
  • the Mg° is injected at a rate such that when melted a pool of molten elemental magnesium comprises a height less than about 10 cm; the Mg° is injected at another rate such that when melted a pool of molten elemental magnesium comprises a height less than about 5 cm; and the Mg° is injected at yet another rate such that when melted a pool of molten elemental magnesium comprises a height less than about 3 cm.
  • Mg° piece is fed in the first reacting container 100 when reaction turbulence subsides.
  • step 535 the temperature of the reaction zone 280 and the S1F4 pressure inside the reacting container 100, 101, or 102 are monitored continuously.
  • the S1F4 gas should always be in excess of Mg° to ensure complete reaction of Mg°, therefore, the pressure of S1F4 gas in the reaction zone 280 is maintained at about 0.1 to 10 atm in certain embodiments. In other embodiments, the pressure of S1F4 gas in the reaction zone 280 is maintained at about 0.5 atm to 1.5 atm. In yet other embodiments, the pressure of the S1F4 gas in the reaction zone 280 is maintained at about 0.8 atm to 1.2 atm.
  • the pressure of the S1F4 gas in the reaction zone 280 is maintained at about 1 atm.
  • the pressure of the S1F4 gas may vary throughout step 520, and particularly throughout the S1F4 and Mg exothermic reaction process. Thus, where it is said that the first reacting container 100 is pressurized to a nominal pressure, the actual pressure of the S1F4 gas may fluctuate and may not be held constant at the pressure.
  • the separation of Si 0 from the reaction product between S1F4 and Mg exothermic reaction process can be performed in a batch mode, a semi-continuous mode, or a continuous mode. If the separation of Si 0 is performed in a batch mode, the step 536 transitions to step 540 in FIG.5B. In step 540, when there are more Mg°, the steps 530 and 535 will be repeated until there is no more Mg° in the material injection tube 214. When there is no more Mg°, step 545 will be performed.
  • step 545 after the reaction for the last piece/amount of Mg° added subsides, the reacting container 100, 101, or 102 is allowed to cool by filling in and circulating one or more Periodic Table Group 0 gas in the reacting container 100, 101, or 102.
  • Periodic Table Group 0 gas In certain embodiments, argon gas is used to cool the reacting container 100, 101, or 102.
  • the cooling coil 230 is used to cool the reacting container 100, 101, or 102.
  • the reaction product is collected and analyzed in step 550. For example, the morphology of the reaction product is studied by optical microscopy and the constituent phases are analyzed using X-ray powder diffraction (XRD).
  • XRD X-ray powder diffraction
  • FIG.2C illustrates that the reaction product was brownish, and XRD detected crystalline phases consisting mainly of MgF2, Mg2Si, and small amounts of Si and unreacted Mg.
  • Thermochemical analysis using the HSC program and data indicates that in this temperature range— Mg2Si is more stable than Mg or Si at this temperature, and its stability decreases with increasing temperature.
  • FIG.2B illustrates the XRD spectrum and the peaks and amount of Si 0 increased and that of Mg2Si formed decrease significantly to trace levels. Further, both brown lava-like globular formations and metallic powders can be seen in the reaction product, as shown in FIG. 3B.
  • FIG.2A illustrates the XRD spectrum and shows that the main reaction product are silicon crystallites dispersed in a matrix of MgF2, with only a trace amount of Mg2Si left. The Mg is completely reacted based on the weight balance analysis.
  • a phase diagram of Mg-Si shows that Mg2Si might be present with Si and Mg at temperatures below about 1081.4°C. Therefore, the reacting container temperature needs to be above about 1081°C (not necessarily initially during the beginning of the reaction between S1F4 and Mg) in order to completely eliminate Mg2Si. For example, when the reaction product is heated in S1F4 at temperatures above 1200°C, a complete reaction could be achieved and no Mg2Si peaks are detected.
  • the reaction product generated in step 535 will go through steps 560-585 to separate Si from the reaction product.
  • the reaction product generated from step 535 is loaded in a second container 200.
  • the second container 200 can be heated to any temperature sufficient to melt silicon.
  • the second container 200 is heated inside a RF field to about 1420°C in step 565.
  • the second container 200 can be heated to a temperature of about 1400°C to about 1700°C or from about 1500°C to about 1600°C.
  • the actual temperature can fluctuate and may not be held constant at the temperature.
  • most of the silicon powders coalesced and sunk to the bottom as large Si balls (> 1 mm in diameter) in step 570 i.e., the melt coalescence and separation step, as shown in FIG.7A.
  • molten Si has a density of 2.47 g/cm 3 and MgF2 has a density of 2.34 g/cm 3 at around 1420°C; Si has a higher surface tension.
  • FIG.6B shows the spherical frozen shape of Si (bright circles) surrounded by the darker MgF2.
  • FIG. 7A shows a product of Si in a fluoride after melt coalescence and separation step and the product is collected in step 575.
  • FIG.7B illustrates a purified Si ingot after cleaning the fluoride by known methods in the art.
  • step 580 the second container 200 is allowed to cool by filling in and circulating one or more Periodic Table Group 0 gas in the reacting container 100, 101, or 102.
  • argon gas is used to cool down the second container 200.
  • the reaction product is analyzed in step 580.
  • the purity of the final silicon product is critical to produce solar-grade silicon.
  • the level of impurities that have relatively low separation coefficients, such as boron and phosphorus, are great concerns to the purity of the final silicon product because other metallic impurities that have large segregation coefficient between solid and liquid Si phases during crystal pulling are expected to accumulate in the liquid phase, thus are removed from solid crystal Si phase. Therefore, the levels of impurities having low segregate coefficient in the as-produced Si product are critical and need to be at or below 1 part per million (ppm) level.
  • the phosphorus level of the Si product obtained using 5N Mg is only at about 0.1 ppmw and the boron level is only at about 0.77 ppmw.
  • This Si product yields a P-type silicon after crystal growth.
  • the phosphorus level of the Si product obtained using 4N Mg is only at about 2.6 ppmw and the boron level is only at about 1.3 ppmw.
  • step 537 transitions to step 605 in FIG. 5C.
  • step 535 runs continuously, part of the molten MgF2 is discharged continuously into a second container 200 via the orifice 260 (FIG.
  • the receiving second container 200 is disposed below the reacting container 100, 101, or 102 and the molten MgF2 flows into the receiving second container 200 via the orifice 260.
  • the diameter of the orifice 260 is less than 1 cm. In other embodiments, the diameter of the orifice 260 is less than 0.5 cm. In yet other embodiments, the diameter of the orifice 260 is less than 2 mm.
  • step 615 if the reacting container 100, 101, or 102 has more capacity to generate more reaction product in step 535, the reaction in step 535 will continue and the discharging of molten MgF2 in step 610 will continue as well.
  • the reacting container 100 if the reacting container 100, 101, or 102 has more capacity to generate more reaction product in step 535, the reaction in step 535 will continue and the discharging of molten MgF2 in step 610 will continue as well.
  • the reaction in step 535 will stop.
  • the temperature of the reacting container 100, 101, or 102 is increased to above the melting point of Si so that both remaining
  • MgF2 and the generated Si can be discharged into a second receiving container 200 in step 620.
  • the second receiving container 200 can be cooled to let molten Si to slowly solidify to obtain a further purified obtain poly crystalline or single crystal Si ingot in fluoride (FIG. 7A).
  • generated molten Si can be directly cooled in the reacting container 100, 101, or 102 to slowly solidify to obtain a further purified obtain poly crystalline or single crystal Si ingot in fluoride (FIG. 7A). Further purification methods known in the art can be used in step 630 to remove fluoride (FIG. 7B).
  • step 538 transitions to step 705 in FIG.5D.
  • the reacting container 100, 101, or 102 does not need to stop the reaction process in step 535 since byproduct MgF2 and Si are both discharged into the second receiving container 200 and a third receiving container 300 respectively from steps 710, 715, and 720.
  • the third receiving container 300 When the third receiving container 300 is filled with Si, the third receiving container 300 will be cooled to collect polycrystalline or single crystal Si ingot in step 725.
  • further purification methods known in the art can be used in step 730 to obtain polycrystalline or single crystal Si ingot (FIG. 7B).
  • an empty receiving container 300 will be used to collect Si from the first reacting container 100 continuously.
  • the continuous mode is largely useful in solar cell industry because the production capacity of Si with high purity is increased compared to semi-continuous mode or batch mode.
  • the first receiving container 200, or the third receiving container 300 can be melted and separated by using a centrally located heat source such as those provided by a plasma torch, arc, or electrode.
  • a centrally located heat source such as those provided by a plasma torch, arc, or electrode.
  • 650°C which is the melting point of Mg.
  • inventors performed experiments in which the graphite crucible was preheated to 650°C, above 800°C, and above 1000°C, respectively, in 1 atm pressure of S1F4 before inventors drop-fed pieces of Mg metal into the hot crucibles.
  • Run 1 In the first run, the graphite crucible was pre-heated to 650°C (just above the melting point of Mg), and the pressure of S1F4 was slightly higher than 1 atm. When the Mg was dropped into the hot crucible, it did not ignite after 5 minutes. Inventors think the delay was probably due to heat transfer from the hot crucible to the cold Mg piece. After heating power was increased, the Mg "ignited” and gave off a bright flame, the temperature of the reactor increased to above 700°C, and simultaneously the pressure of S1F4 dropped. The peak reaction rate was relatively slow, the flame took ⁇ 1 minute to diminish, and no spark and a minimum amount of dust flew out of the crucible.
  • the reaction product was brownish, and XRD detected crystalline phases consisting mainly of MgF2, Mg2Si, and small amounts of Si and unreacted Mg, as shown in FIG. 2A.
  • the crucible was lined with GRAFOIL, and some of the reaction product stuck to it, so peaks of carbon were also observed in the XRD spectrum as well.
  • Thermochemical analysis using the HSC program and data indicates that in this temperature range— Mg2Si is more stable than Mg or Si at this temperature, and its stability decreases with increasing temperature.
  • Run 2 The crucible was preheated to a temperature of 820°C, and the Mg ignited
  • FIG. 3A shows a photo of the reaction product retrieved after Run 2.
  • Run 3 The starting temperature of the crucible was further increased to 1020°C to minimize the formation of Mg2Si and to facilitate the consolidation of the Si product.
  • the reaction took off 30 seconds after Mg chunks were dropped into crucible, and more violent bursts of dark powder and fire balls were observed. This lasted about 35 seconds.
  • a flat, dense reaction product was also obtained at the bottom of the crucible, indicating that the temperature at the reaction zone clearly reached over 1260°C, the melting point of MgF2.
  • the Mg was completely reacted based on the weight balance analysis.
  • XRD analysis (FIG. 2C) showed the main reaction products were MgF2 and Si, with only a trace amount of Mg2Si left (note that XRD can detect phases as low as 1% by weight).
  • Mg solubility in MgF2 increases with temperature and therefore, the permeability of Mg through the product film increases with temperature. This is a likely cause of the bursts of reaction and formation of powders from the homogeneous gas-gas phase reaction. As the temperature increased further, the MgF2 melted. Mg has a solubility of about 0.3 to 0.6 mole% in molten MgF2, so Mg can diffuse through the liquid product layer to reach and react with the S1F4 generating flames. Eventually the pool of Mg (1) was depleted and left a hole inside the reaction product, which was visible in the reaction products, as shown in FIG. 3B. Eventually, the reaction decayed, the temporary high temperatures reached locally (close to but below the adiabatic temperature) dropped, and the pressure of S1F4 remained constant indicating the reaction had finished.
  • FIG. 6A shows a cross section of the reaction product in a graphite crucible.
  • the starting temperature for this run was 1020°C.
  • Several mm-sized Si beads (metallic and shinning) were clearly observable to be embedded in the MgF2 media (darker area in photo). This clearly demonstrates that the temperature at the reaction zone reached the melting point of Si (1412°C) so that Si micro-droplets could migrate through liquid MgF2 and coalesce into larger droplets, a consequence of its high surface tension.
  • Mg can break through or diffuse out and react with Si to form stable Mg2Si, which has a relatively low melting point, thus explaining why metallic Mg2Si beads were seen in Run 1.
  • Mg2Si was no longer the most stable phase, so Mg further diffused out to react with S1F4 to form more Si and MgF2.
  • FIG. 6B shows the cross section of the product in the crucible after the melt- separation process.
  • Most of the silicon powders coalesced and sunk to the bottom as large Si balls (> 1 mm in diameter). This was expected since molten Si has a density of 2.47 g/cm3 and MgF2 has a density of 2.34 g/cm3 at around 1420°C; Si has a higher surface tension.
  • the crucible was heated inside a RF field and, therefore, the smaller silicon particles could have been maintained and dispersed in the melt by electromagnetically induced force.
  • those particles that were smaller than 10 microns were observed by high-magnification microscopy and identified by the grey color of the salt surrounding them.
  • Inventors estimate that the total weight of the small-yet-uncoalesced particles was less than 1%.
  • FIG. 6B shows the spherical frozen shape of Si (bright circles) surrounded by the darker MgF2. It was estimated that the surface tension of Si in molten MgF2 was approximately 0.31 J/cm 2 , significantly smaller than that in inert air. Also, the meniscus of the molten MgF2 at the graphite crucible wall indicated that MgF2 wet the crucible walls. Since molten MgF2 does not wet pure graphite, inventors suspected (and later confirmed experimentally) that this wetting behavior change indicated the graphite wall changed in chemistry.
  • Si + C SiC (3) Inventors think that a thin film of carbide was mainly responsible for the change in wetting behavior.
  • the purity of the final silicon product was the main focus of this work since the goal was to produce solar-grade silicon.
  • inventors were interested in the levels of residual Mg and those of dopant elements B and P.
  • Table 2 shows the impurity distribution and levels in the Si product after melt separation, with 4N and 5N Mg as the starting reducing agent, respectively.
  • the amount of Mg detected is probably due to the dissolution of Mg into molten silicon.
  • the value of 2300 ppm is close enough to what FIG. 8 shows for the solubility of Mg in Si, which goes through a maximum (typical in Si) as the temperature drops from its melting point to about 1250°C where it reaches levels around 1000 of ppmw (0.1%).
  • B and P have relatively low separation coefficients, and cannot be removed easily by solidification processes. Therefore, their levels in the as-produced Si product are critical and need to be at or below 1-ppm level.
  • the Si product obtained using 5N Mg has very encouraging B and P levels, both are sub-ppm. Since P is much lower and only at 0.1 ppmw, this product should yield a P-type silicon after crystal growth.
  • Si obtained using 4N Mg has borderline levels of B and P. This product will still be P type after crystal growth, but the cell efficiency obtained from this silicon may be lower than that with good solar-grade silicon.

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Abstract

L'invention concerne un procédé de fabrication de silicium élémentaire de haute pureté pour des panneaux solaires. Le procédé consiste à faire réagir du tétrafluorure de silicium avec du magnésium élémentaire pour générer un produit de réaction, et à séparer le silicium élémentaire du fluorure de magnésium.
PCT/US2016/058952 2015-10-26 2016-10-26 Procédé et appareil pour la production de silicium de qualité solaire WO2017075108A1 (fr)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111194246A (zh) * 2017-10-05 2020-05-22 朗姆研究公司 包括用于生产硅管的炉和模具的电磁铸造系统

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Publication number Priority date Publication date Assignee Title
WO1983002443A1 (fr) * 1982-01-05 1983-07-21 Stanford Res Inst Int Procede et appareil de production de silicium a partir d'acide fluosilicique
US20030057615A1 (en) * 2001-09-07 2003-03-27 Eckert C. Edward Dispensing system for molten aluminum
RU2358906C2 (ru) * 2007-06-19 2009-06-20 Закрытое Акционерное Общество "Солар Си" Способ восстановления кремния
US20100221171A1 (en) * 2007-06-19 2010-09-02 Andrey Pavlovich Chukanov Method for producing polycrystalline silicon

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1983002443A1 (fr) * 1982-01-05 1983-07-21 Stanford Res Inst Int Procede et appareil de production de silicium a partir d'acide fluosilicique
US20030057615A1 (en) * 2001-09-07 2003-03-27 Eckert C. Edward Dispensing system for molten aluminum
RU2358906C2 (ru) * 2007-06-19 2009-06-20 Закрытое Акционерное Общество "Солар Си" Способ восстановления кремния
US20100221171A1 (en) * 2007-06-19 2010-09-02 Andrey Pavlovich Chukanov Method for producing polycrystalline silicon

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111194246A (zh) * 2017-10-05 2020-05-22 朗姆研究公司 包括用于生产硅管的炉和模具的电磁铸造系统
CN111194246B (zh) * 2017-10-05 2022-04-26 朗姆研究公司 包括用于生产硅管的炉和模具的电磁铸造系统

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