WO2012094169A2 - Fabrication d'un ruban de cristal doté de ficelles à plusieurs composants - Google Patents

Fabrication d'un ruban de cristal doté de ficelles à plusieurs composants Download PDF

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Publication number
WO2012094169A2
WO2012094169A2 PCT/US2011/066842 US2011066842W WO2012094169A2 WO 2012094169 A2 WO2012094169 A2 WO 2012094169A2 US 2011066842 W US2011066842 W US 2011066842W WO 2012094169 A2 WO2012094169 A2 WO 2012094169A2
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Prior art keywords
ribbon
string
core
cte
cover
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PCT/US2011/066842
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English (en)
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WO2012094169A3 (fr
Inventor
Emanuel M. Sachs
James G. Serdy
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1366 Technologies Inc.
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Priority to TW100148841A priority Critical patent/TW201246269A/zh
Publication of WO2012094169A2 publication Critical patent/WO2012094169A2/fr
Publication of WO2012094169A3 publication Critical patent/WO2012094169A3/fr

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B15/00—Single-crystal growth by pulling from a melt, e.g. Czochralski method
    • C30B15/007—Pulling on a substrate
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/06—Silicon

Definitions

  • Ciszek et al. Filament Material For Edge
  • Ciszek notes that silica fibers break out of the ribbon because silica has a much lower coefficient of thermal expansion (CTE) than does silicon of the growing ribbon material. Hence, stresses develop during cooling.
  • CTE coefficient of thermal expansion
  • the CTE of silicon is approximately (3.5-4) x 10 "6 1/°C, while that of silica is approximately .7 x 10 "6 1/°C.
  • a combination of two or more materials can be used to make a string which, in net, (as that term is discussed below) has a CTE that can be matched to that of silicon. At least one material must have a CTE higher than that of silicon and another must have a CTE lower than that of silicon, so that the proper ratio of CTEs may be matched to silicon.
  • An example pair of materials is silicon carbide (SiC) and silica (Si0 2) , where the CTE of silicon carbide, which is approximately (4-4.5) x 10 "6 1/°C, is higher, and that of silica is lower, than the CTE of silicon, set forth above.
  • a string core may have a composition different from that of a cover on the core.
  • the core may itself have regions of differing composition.
  • the different compositions corresponding to different regions will, in general, have different CTEs.
  • the net CTE of a body, such as a string composed of two or more regions depends on at least: the CTEs of the compositions in the regions; the relative cross-sectional areas of the regions; and the elastic modulii of the compositions in the regions.
  • the behavior can be more complex when the string heats or cools through a temperature range where one or more of the material compositions undergoes some plastic flow.
  • compositions of the regions, the true arbiter of the CTE of a body is by experiment. Suitable experiments for evaluating the relative net CTEs of different bodies are discussed below.
  • strings for ribbon production are deleterious to a silicon crystal, and thus it would be desirable to bar or minimize their diffusion into a growing crystal.
  • Some string materials are porous, which porosity has several problems. One is that impurities from the porous region can diffuse to the silicon ribbon at a high rate, due to the high surface area associated with a porous core. Similarly, some
  • particulate materials that have other beneficial properties such as SiC, cannot be made fully dense, which also then permits diffusion of impurities from and through the porous material.
  • Another problem is that surface porosity of a porous string can act as crack initiation sites.
  • the most desirable product is one with no porosity whatsoever.
  • Such a product may have the maximum strength possible for a given material minimizing crack initiation.
  • interconnected porosity is therefore a common definition of acceptably high density. This is also a metric of importance for the coverings discussed herein, because a covering of density high enough to avoid interconnected porosity can constitute an effective barrier against migration of
  • Another problem with some strings relates to their electrical conductivity. If a solar cell is fabricated with a string whose outer surface is electrically conductive, then the junction of the solar cell must be isolated from this edge either by cutting out the edge, or performing a process such as laser junction isolation as is known in the art.
  • the several objects of inventions disclosed herein include to provide a substantially pure silicon ribbon, grown upon strings, which has relatively large grains, and which is stable and robust throughout normal, typical manufacturing processes, resisting rupture, cracking and other degradation. It is further a goal to provide such crystal ribbons without undue expense or complexity. It is a further goal to provide such a string and ribbon system that can withstand typical handling and use.
  • a further object of inventions hereof is to provide a string that can be used with a crystal ribbon, which has a CTE matched to that of the crystal ribbon, which does not provide impurities to the crystal ribbon, and which has a fully dense outer layer to bar such impurity transport. Yet another object is to provide such a string that is electrically non-conductive.
  • the core be composed of more than one material .
  • the ribbon material only wets around the string as far as permitted by the relatively large wetting angle a at the interface 106.
  • the wetting angle is a consequence of the surface energies of the material being wetted and the wetting material.
  • the undesirable weakness of the thin region is further exacerbated by etching the ribbon as a first step in cell fabrication, because such etching further thins this already thin region. (Such etching might be employed for cleaning the surface or for creating a light trapping texture on the surface to enhance the performance of a solar cell.)
  • CTE can be matched in net between a string and a ribbon, for instance a silicon ribbon, if the string is composed of a core, having at least one material, and an outer cover layer having at least two materials.
  • the materials of each the core and the cover are chosen by identity and amounts, so that in net the CTEs of the string and ribbon match.
  • requirements of the core for instance, or other requirements of the core or methods of its manufacture
  • the nucleation potential of the outer cover, which the growing crystal ribbon contacts can be kept to an acceptably low degree.
  • the outer cover may be made to be sufficiently highly wettable, so that the crystal ribbon material wets sufficiently around the circumference of the string, so that the ribbon does not thin down adjacent the string, from a larger thickness further along the ribbon, more distant from the string. It is also possible to achieve the above objectives and also have a sufficiently electrically non-conductive outer cover, for instance with an outer cover predominantly of silica, with some SiC.
  • Such properties include the string's wettability, nucleation propensity, impermeability, and surface roughness. Other properties are governed more predominantly by the core, such as strength. Other properties are affected by both the cover and core. Such properties include the net CTE, and strength and flexibility.
  • the entire string and the growing ribbon can have substantially equal net CTEs.
  • the outer surface of the string should inhibit nucleation of grains in the growing crystal. It should also facilitate wetting of the crystal significantly around the perimeter of the string, to a degree sufficient to provide adequate thickness of the ribbon, and thus strength at the interface between the ribbon and the string.
  • Other embodiments are disclosed in which the CTE of the string and the ribbon are intentionally mismatched, as discussed below.
  • inventions hereof include, but are not limited to: strings, so described, ribbons grown upon such strings, string and ribbon assemblies, methods of making ribbons using such strings, methods of making such strings, and products incorporating such grown ribbons.
  • Fig. 1 shows a schematic plan view in cross-section of a string of the prior art with a portion of ribbon grown thereon;
  • Fig. 2 shows a schematic cross-sectional view of a core of a string of an invention hereof having an inner layer and an outer layer of two different materials;
  • FIG. 3 shows a schematic cross-sectional view of a string of an invention hereof having a composition of two different materials interspersed with each other;
  • FIG. 4 shows, a schematic cross-sectional view of a core of a string of an invention hereof, having a single, central region composed of a single material;
  • FIG. 5 shows a schematic cross-sectional view of a core of a string of an invention hereof, having an outer cover having a composition of two different materials interspersed with each other;
  • Fig. 6 shows a schematic cross-sectional view of a string of an invention hereof, with a ribbon grown thereon, with a small degree of wetting of the ribbon material upon the string;
  • Fig. 7 shows a schematic cross-sectional view of a string of an invention hereof, with a ribbon grown thereon, with a moderate degree of wetting of the ribbon material upon the string;
  • Fig. 8 shows a schematic cross-sectional view of a string of an invention hereof, with a ribbon grown thereon, with a large degree of wetting of the ribbon material around approximately one half the perimeter of the string;
  • Fig. 9 shows a schematic cross-sectional view of a string of an invention hereof, with a ribbon grown thereon, with a large degree of wetting of the ribbon material around substantially all of the perimeter of the string;
  • Fig. 10 shows, schematically, a slurry supply, which is agitated, for application to a string core, thereby forming a cover;
  • Fig. 11 shows, schematically, a wafer cut from a length of string ribbon crystal highlighting a region of the wafer adjacent the string;
  • Fig. 12 shows, schematically, the region of a string crystal, such as shown in Fig. 11, in which the string has been cut away from the ribbon, which string has a CTE that is higher than that of Si;
  • Fig. 13 shows, schematically, the region of a string crystal, such as shown in Fig. 11, in which the string has been cut away from the ribbon, which string has a CTE that is lower than that of Si.
  • the materials of the cover can be silica and silicon carbide. Material systems other than with silicon are also possible.
  • the term core means the portion of the string that is subsequently covered with the cover (also called a coating) layer or layers.
  • the core itself can consist of a single homogeneous material or a mixture of more than one material, or, it can be constructed of layers.
  • a core can have, within it, yet another core, which inner core, is covered.
  • a core is meant to be a string-like body made by any method, but which has one or more undesirable aspects that can be ameliorated with a cover.
  • the cover is not necessary to the fabrication of a string ribbon per se, using such a core.
  • a small diameter inner-most core can be coated with refractory material by chemical vapor deposition as is currently
  • the inner most core can be carbon and the refractory material deposited by CVD can be silicon carbide.
  • This two component, carbon and SiC string could be used to grow string ribbon silicon, but it has the undesirable properties of nucleating many grains and also of being electrically
  • the inventors hereof have discovered that it would benefit from a cover provided in a subsequent step as taught in this specification.
  • the two component carbon and SiC body can be considered itself to be a core, which is then covered by something else to deal with the nucleation and conductivity .
  • the resulting body is generally porous.
  • powder precursors are not always available in acceptable levels of purity, powder based methods, especially when there is porosity present, may create unacceptable levels of chemical contamination.
  • a covering can solve this problem.
  • any of these bodies can be considered and used as a core, to which a cover is applied, as taught herein.
  • An invention hereof has a string with a core and a cover, also referred to herein in some places, as an outer cover or a coating.
  • the composition of a cover may be
  • a core 220 may have a central region 222 of one material, for instance carbon or tungsten, and an outer region 224 of another material, for instance SiC.
  • a body 220 as shown, composed of carbon and SiC, can be designed to have a CTE that is in net, close to that of silicon. SiC is not suitable as an outer surface for making string ribbon, because it nucleates very readily, and it is electrically conductive.
  • FIG. 3 at 320 Another form of core, as shown in Fig. 3 at 320, can have a body 322 that can be formed from a mixture of two different particles, for instance SiC, 323 and silica, 325.
  • This mixture can be heat-treated to increase its density, and can be provided with a CTE that is sufficiently equal to that of silicon. But such a mixture with a matched CTE would need to be about 55% by volume SiC, and thus, will not be fully dense. Thus, it would not be suitable alone, as a string, for at least the reason that impurities could diffuse from it to the silicon ribbon.
  • a basic core configuration can be a single material, in a homogeneous region 420.
  • a core can be of carbon, or other suitable material.
  • Fig. 5 shows a structure of a string of an invention hereof that can have all of the desired properties: net matched CTE, diffusion barrier, a nucleation inhibiting surface, electrical insulation and wettability.
  • a core 520 which may be of either a dual layer construction, such as 220 shown in Fig. 2, an interspersed construction, such as 320 shown in Fig. 3, or a single material such as shown at 420 in Fig. 4, is surrounded by an outer cover 524.
  • the outer cover is a dual component body, which can be a composition formed from a particle mixture, with
  • SiC 523 and silica 525 The more SiC that is present in the mixture, the greater will be the degree that silicon will wet around the string.
  • the net CTE of the core 520 and the cover 524 can be adjusted to be substantially equal to that of silicon, because the relative amounts necessary for other considerations permit that.
  • the silica provides a very low nucleation propensity. The amount of SiC that is needed to provide an adequate amount of wettability does not destroy this low nucleation propensity. Further, such a combination can be processed to full density, and it is also non-conductive.
  • the outer layer 524 may be formed by traversing a core 1020, as described above, through a slurry 1021 composed of a mixture of silica and silicon carbide powders and then firing this composite string 1003.
  • the slurry is contained in a vessel, which has a hole in its base.
  • the slurry is retained by capillary attachment to orifice 1042 where it forms a liquid cap in the shape of a portion of a spherical surface.
  • the height H of the slurry above the retention plane must be kept low, so as to guarantee that the slurry does not leak out.
  • This method allows the passage of the core through the slurry without requiring that the core bend, and so eliminates a possible source of breakage during the covering process. It is useful to keep the slurry circulating using methods known in the art, to prevent settling of the particles in the slurry. It has been found that only a small amount of silicon carbide powder need be included with the silica to result in silicon wetting fully around the perimeter of the string, with the resulting larger cross sectional thickness of the silicon crystal, and a stronger silicon ribbon adjacent the string. Various example formulations are discussed below.
  • the propensity of a surface to nucleate grains may be assessed in several ways.
  • the most direct way is to fabricate string with the material in question as a covering and to count the number of grains that are nucleated per unit length of ribbon edge.
  • One suitable method is to measure the amount of undercooling possible with a candidate material. A small disk of the candidate material may be placed in a
  • the undercooling is the amount by which the temperature of of an interface may drop below the melting point of the silicon prior to the inititiation of solidification of the silicon. The inventors have found that the allowable undercooling at an interface of silica and silicon is over 100°C.
  • the core may be formed from one, or more materials.
  • ingredients, and their relative amounts can be adjusted to achieve a good compromise in matching the net CTE of the entire string to that of the growing ribbon crystal, as well as achieving sufficient wettability to provide a relatively thick crystal ribbon adjacent the string, and also
  • Mixtures of two or more materials may be created by mixing powders of the materials and applying the powder to the surface of a core.
  • One effective method of application as shown with reference to Fig. 10, is to create a slurry 1021 of the powders and to pass the core 1020 through the slurry 1021 so that a uniform, thin coating 1024 is applied as discussed above.
  • a water-based slurry of fine powders can be created using dispersion methods known in the art
  • the slurry is kept in a pot 1040, which is agitated, as indicated by the circulation arrows.
  • the coated slurry is then dried and fired at high temperature .
  • the cover layer be fully dense before it enters the silicon melt for string ribbon growth, or at least that it have a very small amount of open porosity.
  • Such high-density coatings can be made when using powder mixtures that have a high silica content. Silica contents of greater than about 50% by volume will work. At the temperatures at which the coating is fired, the silica becomes very soft and this allows the mixture of silica and silicon carbide to densify by viscous phase sintering. Viscous phase sintering is dramatically faster than solid state sintering and thus, a fully dense cover layer can be created quickly, at relatively low temperature? and at low cost.
  • this firing may be conducted in air, thereby reducing the cost of the process as compared to one having the need to fire in an inert atmosphere.
  • silica and SiC are well suited to firing in air.
  • firing in air is advantageous because the surface of the SiC
  • the outer cover layer can thus be sintered to full density, forming a layer substantially impervious to the penetration of molten silicon. This layer also acts as a barrier to diffusion of impurities from within the string, outward into the silicon.
  • the methods of creating a cover layer with powders can be applied to a core that is fully dense, or to a core that has open porosity. It can be applied to cores that are made by a wide range of methods, including, but not limited to: chemical vapor deposition, extrusion, pulling, pultrusion and others including the methods disclosed in U.S. Patent No. 7,824,602, Ceramic Processing and Shaped Ceramic Bodies, in the names of Sachs, Naiman and Serdy, the full disclosure of which is fully incorporated herein by reference.
  • Creating the cover with mixtures of powders also provides a path toward matching the CTE of the string to the silicon.
  • the covering can also be matched by varying the ratio of silica to silicon carbide appropriately. More typically, if the core has a CTE higher than that of silicon, then the covering can make the overall string matched in net CTE by providing a CTE lower than that of silicon, by using more silica and less silicon carbide in the coating, assuming that the other desired properties can be achieved with this other mixture.
  • Creating the cover of mixtures of two or more materials, including as mixtures of powders, also allows for the change in CTE between core and cover to be less abrupt than it otherwise might be — as discussed above in the case of a pure silica cover on a SiC core.
  • the core and cover can have the same CTE, as mentioned above. Minimizing the CTE mismatch between core and cover will help prevent the cover from detaching from the core and will reduce the rate of dissolution of the cover as it traverses through the molten silicon, because the state of stress will be lower. Similarly, the ability to handle the string before passing through the silicon melt may be enhanced.
  • the CTE of the core should be increased, so that the CTE of the cover may be decreased by using a lesser fraction of silicon carbide in the cover, thereby allowing for viscous phase sintering of the cover.
  • the other considerations include to minimize nucleation of grains to an acceptable degree, and also to achieve a string that is wetted to a degree sufficient to avoid unacceptable fragility of the ribbon at its edges, and which is electrically insulating.
  • nucleating grains The continued growth of a grain requires that a critical radius of solid form. If the SiC particles are smaller than this critical size, the likelihood of grain nucleation is very small, or the nucleation of grains may even become impossible, resulting in the low nucleation behavior of silica (but, without using silica, or using only a relatively small amount) with increased wetting and
  • the string may have a CTE that is
  • An iterative, practical way to evaluate the CTE match or mismatch condition of a string, as compared to its associated ribbon, is to use a laser to cut a thin sliver of ribbon from the edge.
  • a laser can be used to cut 1 to 2 mm inward from the edge of a piece of grown string ribbon, typically for a length of at least 200 mm and preferably more. If there is no stress caused by the string, this piece will remain straight after separating from the larger portion of the string ribbon. If it curves so that it is concave toward the body of the ribbon from which it was separated, that means that the CTE of the string is lower than that of the silicon ribbon. If it curves so that the sliver is convex toward the body of the ribbon from which it was separated, that means that the CTE of the string is higher than that of the silicon ribbon, which would likely be too high for successful, typical use.
  • a deliberately lower CTE of a string, as compared to the ribbon, will beneficially result in the silicon ribbon in the very corners of a cut wafer to be in compression and therefore more resistant to failure than in a condition of zero stress.
  • Fig. 11 shows, schematically, a length of silicon ribbon 1104 grown between two strings 1102, pointing out the regions BC of the ribbon under discussion.
  • Brittle materials such as silicon, are stronger in compression than in tension. It is perhaps easiest to understand the potentially
  • Fig. 12 shows, schematically, this situation.
  • a sliver 1234 is cut out of the edge BC of the ribbon 1204 in a case where the string 1202 has a CTE higher than that of silicon.
  • the sliver 1234 will be convex with respect to the body of ribbon from which it was removed.
  • the silicon ribbon 1204 adjacent to the ends of the sliver 1234 must have been in tension before the sliver was cut out, as shown by the arrows T, which represent the forces applied to the ribbon 1204.
  • the ribbon is in tension, with forces pulling outward at both edges 1204. This is detrimental, since brittle materials are weak in tension .
  • Fig. 13 shows, schematically, the situation where the CTE of the string 1302 is lower than that of silicon ribbon 1304. Such a situation creates the opposite effect, where the silicon ribbon at the very edges is in compression, as indicated by the inward pointing arrows C. As the very corner of a cut wafer is the most common origin of cracks in a wafer, this is potentially very beneficial to mechanical yields during processing.
  • SiC is somewhat electrically conductive. If a solar cell is fabricated with a string whose outer surface is SiC, then the junction of the solar cell must be isolated from this edge either by cutting out the edge, or performing a process such as laser junction isolation as is known in the art. Either method results in the loss of energy generating area. The same is true of any string with a conductive surface, whether it be made of SiC, carbon, alloys of SiC and carbon, or other conductive materials. However, when the covering is made of a mixture of SiC and silica with a significant silica content, the coating material will be non- conductive, because individual SiC particles, or small aggregates of SiC particles, will be surrounded by silica.
  • the individual SiC particles are themselves coated with silica by oxidation, further guaranteeing a non- conductive string, even at higher SiC content.
  • a non- conductive string eliminates the problem of shorting of the p-n junction of the solar cell, thereby eliminating the need for edge removal or junction isolation.
  • Silica and SiC are not the only non-conductive combinations that can be used. Any combination that is non-conductive will have this
  • the core is made from powders, it can be made with controlled roughness based on the particle size of powders used and also based on the degree of
  • the cover made from powders will adhere to the core better than it might to a smooth core, due both to more surface area of contact and to mechanical interlocking.
  • Fig. 6 shows a core 620 and a cover 624 composed of approximately 90% silica and approximately 10% SiC. The silicon can be seen to have wetted the
  • Fig. 7 shows a similar core 720 and a cover 724 composed of approximately 80% silica and approximately 20% SiC.
  • the silicon has wetted the composite string to a greater degree, over a region of circumference subtended by angle S g , that is approximately 90 degrees, thus resulting in a ribbon 704 with a larger thickness t near to the string 702.
  • this ribbon will be less fragile than the one shown at Fig. 6.
  • Fig8. H shows a similar core a cover 824 composed of approximately 70% silica and approximately 30% SiC.
  • the silicon can has wetted the composite string 802 to a greater degree, almost half-way around the perimeter, over a region of circumference subtended by angle S h , that is approximately 175 degrees, thus resulting in a ribbon 804 with a larger thickness t near to the string.
  • this ribbon will be less fragile than the two shown at Figs . 6 and 7.
  • Fig. 9 shows a similar core and a cover 924 composed of silica and more than 30% SiC. As can be seen, the silicon has wetted the composite string 902 fully around its perimeter, resulting in a ribbon 904 having a thickness t that is as thick, or slightly thicker than the diameter of the string 902.
  • the composite string has a core, predominantly for strength and to provide a major portion of CTE matching.
  • the string has a multi-component cover, one component having nucleation inhibiting properties, and another component having wetting enhancing properties. (Both components may also have other properties.)
  • the outer cover may for instance be between approximately 70% and approximately 90% Silica, and
  • the wettability of the outer cover is such as provides wetting of the ribbon around a portion of the circumference that is subtended by an angle of at least about 50-60 degrees, and which may be as large as the entire circumference .
  • a core may be made by extrusion of a slurry that is a mixture of silica and silicon carbide powders according to the methods of US Patent 7,824,602, Sachs, Naiman and Serdy.
  • a relatively low viscosity slurry is extruded at relatively low pressures directly into a bath containing a boron containing agent that rapidly cross links a polymer contained in the slurry and then dries to form a green fiber.
  • the green fiber is 150-500 microns in diameter, with a preferred range of 200-350 microns.
  • the mixture is approximately 55-65% by volume SiC and 45-35% by volume silica.
  • This mixture is chosen so that the CTE of the of the mixture is approximately equal to that of silicon, but generally slightly higher than that of silicon for reasons explained below. If the core is fired at this stage, it will have a diameter of between about 100 and about 400 microns preferably between about 150 and about 250 microns.
  • This core is then covered with a mixture of silica and silicon carbide powders.
  • the covering is accomplished according to the method shown in Figure 10.
  • the slurry for the covering will be a mixture of 95-55% by volume silica and 5-45% by volume SiC.
  • a preferred range is 85-70% by volume silica and 15-30% by volume SiC.
  • both silica and SiC particles are .1-5 microns in size, with 1-3 microns being a preferred size range.
  • a preferred range is 85-70% by volume silica and SiC particles.
  • the covering is added to the core while the core is still green.
  • the covering is dried, for example by the passage of warm air, and the core and covering are then fired together, typically at temperatures of approximately 1500°C for 1-10 minutes in an air environment.
  • the firing may be performed in air as the presence of oxygen only helps to oxidize the surface of the SiC powder and promote bonding to the silica.
  • the dried covering is typically 4-30 microns thick with a range of 6-20 microns being preferred. After firing, the covering is typically 2-20 microns thick with a range of 3-15 microns being preferred.
  • the mixture used in the core has more SiC than silica, it is very difficult to cause it to fully densify in a practical and economical firing cycle and therefore retains significant porosity in the final, fired product.
  • the covering being high in silica
  • the core is made by CVD of stoichimetric or non- stoichiometric SiC.
  • cores are known in the art and are made by depositing onto a very small diameter fiber made of carbon, tungsten, or other refractory material.
  • the starting fiber is approximately 35 microns in diameter and the SiC is deposited up to a diameter of approximately 140 microns.
  • This core may be covered in much the same manner as described above in the context of Example 1. Again, the bond between cover and core will be strong because there is not a drastic difference in CTE between core and cover and because firing in air will cause the outside of the core to oxidize and bond well to the silica.
  • the outer layer of the CVD core be stoichiometric SiC to allow for oxidation during firing and good bonding to the silica component of the covering.
  • SiC can be of several grain structures, including Alpha and Beta.
  • the silica is typically amorphous silicon dioxide, however it can also be composed of some fractions of crystalline silicon dioxide, such as the
  • Other materials systems can include silicon oxide (SiO) for the relatively less wetting material as well as some forms of silicon oxy-carbide, silicon oxy-nitride, silicon nitride and boron nitride.
  • the more wetted material can include some forms of silicon nitride, and silicon carbo- nitride .
  • Such a system may be of a core and a cover, either of which may be one or two or more components . What is required is that the properties of CTE net match, nucleation inhibition and wettability are such that undue stresses and strains do not arise in the fabrication process, and that the ribbon may be grown to an acceptable thickness near to the string.

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  • Laminated Bodies (AREA)

Abstract

L'invention concerne une ficelle de cristallogenèse en ruban comportant une âme et une couverture externe, la couverture étant composée d'au moins deux matériaux différents, choisis avec le matériau de l'âme en une quantité et en un type tels que le coefficient de dilatation thermique de l'âme couverte correspond en net, à celui du ruban de silicium. Le matériau de couverture est également choisi de sorte que le silicium mouille aisément de manière significative autour de la ficelle, sous-tendant un angle d'au moins environ 55 degrés, jusqu'à une ficelle complètement mouillée, donnant un ruban résistant relativement épais adjacent à la ficelle, plus proche en épaisseur du diamètre de la ficelle. Ceci évite un ruban mince, fragile, près de la ficelle. Pour un ruban de silicium, une couverture peut être une composition mélangée qui est principalement en silice, avec un peu de SiC. L'âme peut également être composée de silice et de SiC, en différentes proportions, et de géométrie différente. Ou, l'âme peut être un matériau unique, tel que du carbone. Le SiC présent dans la couverture en une quantité aussi faible que 10 % en volume permet un mouillage périphérique d'au moins environ 55 degrés de la circonférence de la ficelle et ne forme pas excessivement de germes cristallins. Des quantités plus élevées de SiC sont également avantageuses. En utilisant ces mêmes matériaux, ou des matériaux similaires, la couverture externe peut être rendue complètement dense et exempte d'impuretés potentiellement nuisibles pour le silicium. La couverture peut être électriquement non conductrice. Plutôt que du carbure de silicium, on peut utiliser du nitrure de silicium, et d'autres matériaux. Il est également possible de ne pas faire correspondre volontairement le coefficient de dilatation thermique de la ficelle et du ruban, de telle sorte que le ruban est en compression aux extrémités des ficelles, ce qui aide à prévenir une rupture du ruban.
PCT/US2011/066842 2011-01-06 2011-12-22 Fabrication d'un ruban de cristal doté de ficelles à plusieurs composants WO2012094169A2 (fr)

Priority Applications (1)

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TW100148841A TW201246269A (en) 2011-01-06 2011-12-27 Crystal ribbon fabrication with multi-component strings

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US201161430429P 2011-01-06 2011-01-06
US61/430,429 2011-01-06

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WO2012094169A3 WO2012094169A3 (fr) 2012-08-23

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050239382A1 (en) * 2003-10-09 2005-10-27 Micron Technology, Inc. Planarizing solutions including abrasive elements, and methods for manufacturing and using such planarizing solutions
US20070100039A1 (en) * 2005-10-27 2007-05-03 Hancock Robert R Jr Non-reactive additives for fiber coatings
US20080213725A1 (en) * 2003-09-24 2008-09-04 Nobel Biocare Ab (Publ) Method and Arrangement for a Dental Installation
US20080290067A1 (en) * 2006-05-23 2008-11-27 Hiroshi Yoshida Microstructure, pattern medium and process for producing same
US20090061224A1 (en) * 2007-08-31 2009-03-05 Evergreen Solar, Inc. Ribbon Crystal String with Extruded Refractory Material
US20090149016A1 (en) * 2007-12-06 2009-06-11 Samsung Electronics Co., Ltd. Semiconductor device and method of fabricating the same
US20090301386A1 (en) * 2007-06-14 2009-12-10 Evergreen Solar, Inc. Controlling Transport of Gas Borne Contaminants Across a Ribbon Surface
US20100055412A1 (en) * 2008-09-03 2010-03-04 Evergreen Solar, Inc. String With Refractory Metal Core For String Ribbon Crystal Growth

Patent Citations (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20080213725A1 (en) * 2003-09-24 2008-09-04 Nobel Biocare Ab (Publ) Method and Arrangement for a Dental Installation
US20050239382A1 (en) * 2003-10-09 2005-10-27 Micron Technology, Inc. Planarizing solutions including abrasive elements, and methods for manufacturing and using such planarizing solutions
US20070100039A1 (en) * 2005-10-27 2007-05-03 Hancock Robert R Jr Non-reactive additives for fiber coatings
US20080290067A1 (en) * 2006-05-23 2008-11-27 Hiroshi Yoshida Microstructure, pattern medium and process for producing same
US20090301386A1 (en) * 2007-06-14 2009-12-10 Evergreen Solar, Inc. Controlling Transport of Gas Borne Contaminants Across a Ribbon Surface
US20090061224A1 (en) * 2007-08-31 2009-03-05 Evergreen Solar, Inc. Ribbon Crystal String with Extruded Refractory Material
US20090061163A1 (en) * 2007-08-31 2009-03-05 Evergreen Solar, Inc. Ribbon Crystal String for Increasing Wafer Yield
US7651768B2 (en) * 2007-08-31 2010-01-26 Evergreen Solar, Inc. Reduced wetting string for ribbon crystal
US20090149016A1 (en) * 2007-12-06 2009-06-11 Samsung Electronics Co., Ltd. Semiconductor device and method of fabricating the same
US20100055412A1 (en) * 2008-09-03 2010-03-04 Evergreen Solar, Inc. String With Refractory Metal Core For String Ribbon Crystal Growth

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WO2012094169A3 (fr) 2012-08-23

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