EP3046895A1 - Substrate with low-permeability coating for the solidification of silicon - Google Patents

Substrate with low-permeability coating for the solidification of silicon

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Publication number
EP3046895A1
EP3046895A1 EP14780618.6A EP14780618A EP3046895A1 EP 3046895 A1 EP3046895 A1 EP 3046895A1 EP 14780618 A EP14780618 A EP 14780618A EP 3046895 A1 EP3046895 A1 EP 3046895A1
Authority
EP
European Patent Office
Prior art keywords
barrier layer
substrate
layer
silica
barrier
Prior art date
Legal status (The legal status 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 status listed.)
Withdrawn
Application number
EP14780618.6A
Other languages
German (de)
French (fr)
Inventor
Jean-Paul Garandet
Denis Camel
Béatrice Drevet
Nicolas Eustathopoulos
Charles Huguet
Johann Testard
Rayisa VOYTOVYCH
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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 Commissariat a lEnergie Atomique et aux Energies Alternatives CEA filed Critical Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Publication of EP3046895A1 publication Critical patent/EP3046895A1/en
Withdrawn legal-status Critical Current

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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
    • 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
    • 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
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/009—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone characterised by the material treated
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/50—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials
    • C04B41/5025—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements with inorganic materials with ceramic materials
    • C04B41/5035—Silica
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/45—Coating or impregnating, e.g. injection in masonry, partial coating of green or fired ceramics, organic coating compositions for adhering together two concrete elements
    • C04B41/52—Multiple coating or impregnating multiple coating or impregnating with the same composition or with compositions only differing in the concentration of the constituents, is classified as single coating or impregnation
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/85—Coating or impregnation with inorganic materials
    • C04B41/87—Ceramics
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B41/00—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone
    • C04B41/80—After-treatment of mortars, concrete, artificial stone or ceramics; Treatment of natural stone of only ceramics
    • C04B41/81—Coating or impregnation
    • C04B41/89—Coating or impregnation for obtaining at least two superposed coatings having different compositions
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D1/00—Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances
    • 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
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/0087—Uses not provided for elsewhere in C04B2111/00 for metallurgical applications
    • C04B2111/00879—Non-ferrous metallurgy

Definitions

  • the present invention relates more particularly to a crucible useful for the solidification of a silicon ingot from silicon in the molten state.
  • It also relates to a process for preparing such a crucible and the use of such a crucible for the solidification of silicon.
  • the crucibles considered for the growth of the ingot are generally silica crucibles, coated with a layer of oxidized silicon nitride to prevent adhesion of the ingot to the crucible after solidification.
  • the anti-adherence behavior is based essentially on the presence of silicon nitride, S13N4, in the form of oxidized powders, on the surface of the inner walls of the crucibles to which the silicon adheres during its cooling.
  • silicon nitride S13N4
  • the silicon ingot is detached from these walls by cohesive rupture within the silicon nitride layer, thus relaxing the mechanical stresses resulting from the difference in coefficients of thermal expansion.
  • this technique does not prevent contamination of silicon by the impurities present in the silicon nitride powder.
  • this coating can not be used on all types of crucibles including ceramic crucibles such as carbide or silicon nitride. Indeed, these ceramics being chemically reducing, they will have the effect of deoxidizing the coating, which may lead to delamination of the latter.
  • a natural solution would be to achieve a silica barrier layer, to prevent the gases produced during the heat treatment from escaping and thus to prevent the delamination of the coating.
  • Unfortunately the phenomenon of differential expansion makes a pure silica layer not resistant to thermal cycling.
  • the present invention aims precisely to provide new substrates, including new crucibles useful for the solidification of a silicon ingot from silicon in the molten state satisfying these needs.
  • the present invention relates to a substrate coated at least partially at the surface with a coating containing at least one so-called "barrier” layer comprising silica and one or more material (s) X chosen from SiC, Si, S13N4. layer in which the mass quantity of X varies from 25% to 50% relative to the total mass of the barrier layer, said barrier layer being formed of grains of one or more materials X at least partially covered by a silica envelope the barrier layer being disposed in direct contact with the substrate.
  • the inventors have, in fact, discovered that the problems developed above can be solved by at least partially covering the surface of a substrate dedicated to containing or supporting molten silicon, a low permeability coating formed of silica and one or more material (X) X selected from SiC, Si, S13N4, in specified proportions.
  • the coating formed in the context of the present invention in which the barrier layer is in direct contact with the substrate, that is to say that there is no intermediate layer between the substrate and the barrier layer, is advantageous in many ways. he simultaneously exhibits good substrate adhesion properties, satisfactory gas barrier properties.
  • said coating is constituted by said barrier layer.
  • the barrier layer constitutes the outer layer of the substrate, in direct contact with the atmosphere or the container of the substrate, that is to say that the barrier layer is not covered with an additional layer .
  • said coating is formed only in part by the barrier layer to which can be superimposed an additional layer, preferably said auxiliary layer is a release layer.
  • Said adherent layer is then advantageously obtained by oxidizing the outer surface of the barrier layer.
  • the coating formed according to the present invention comprises at least one barrier layer formed of grains of one or more materials X at least partially covered by a silica envelope.
  • the cohesion of the grains is generally obtained by sintering the silica.
  • the coating formed according to the present invention comprises at least one barrier layer in the form of a silica matrix in which are incorporated grains of one or more material (X) X.
  • the grains of one or more material (X) X are coated at least in part with a nanometric layer of silica.
  • the thickness of the "barrier" layer is between 10 and 100 ⁇ , between 20 and 50 ⁇ .
  • the silica envelope that is to say the silica layer formed on the surface of the grains of material (x) X, it may have a thickness ranging from 2 to 100 nm, and in particular from 10 to 30 nm.
  • the substrate is a crucible, in particular useful for the solidification of silicon.
  • the presence of the coating according to the invention makes it possible to obtain a crucible which is reusable subject only to depositing the auxiliary layer, that is to say without requiring one or more pre-treatment steps before reuse.
  • the substrate according to the invention is coated at least partially, and preferably entirely, at the surface, with a coating formed by at least one so-called "barrier" layer.
  • the barrier layer according to the invention makes it possible to maintain the integrity of the substrate.
  • the barrier layer comprises, or even consists of, silica and one or more material (s) X selected from SiC, Si, S13N4, and is such that the mass quantity of X in the barrier layer varies from 25% to 50% relative to the total mass of the barrier layer.
  • the mass quantity of silica in the barrier layer advantageously varies from 50% to 75% relative to the total mass of the barrier layer.
  • the barrier layer comprises, or even consists of, a mixture of silica and silicon carbide (SiC).
  • the barrier layer comprises, or even consists of, a mixture of silica and silicon (Si).
  • the barrier layer comprises, or even consists of, a mixture of silica and silicon nitride (Si 3 N 4 ).
  • the barrier layer comprises, or even consists of, a mixture of silica and two materials X selected from SiC, Si, S13N4.
  • the barrier layer comprises, or even consists of, a mixture of silica and the following three materials X SiC, Si, Si 3 N 4 .
  • the particles of inorganic materials X used in the process for preparing the coating according to the invention, as described more particularly later, are preferably in the form of powders, preferably having a size or a mean diameter ranging from 500 nm to 5 microns, preferably from 0.8 microns to 2 microns.
  • powders examples include silicon nitride (S1 3 N 4) in the form of micron-sized grains and sold under the reference S E10 ® by the company UBE,
  • the particles of inorganic materials X may be prepared prior to the formation of the coating according to the invention.
  • the skilled person is able to implement the methods suitable for the preparation of particles suitable for the invention.
  • the permeability of the barrier layer is less than 10 -15 m, preferably less than 10 -8 m 2 .
  • the permeability of this layer reflects its ability to be passed through by a reference fluid under the effect of a pressure gradient.
  • the permeability (intrinsic or specific) of a substrate and more generally of a medium can be obtained from the Darcy equation: where dP / dx is the pressure gradient in the flow direction and ⁇ is the dynamic viscosity of the fluid.
  • the intrinsic or specific permeability K is independent of the nature of the fluid but depends on the geometry of the medium, and it is expressed in m 2 . In the case of a single-phase flow, the intrinsic or specific permeability K is simplified to "permeability".
  • the permeability is measured by means of a permeameter as described in US Pat. No. 5,361,625 or in patent application EP 1 821 093 A2.
  • These permeameters are devices for measuring gas permeation through a material (M), they comprise a permeation chamber comprising a first and a second chamber separated by a material (M).
  • the material M corresponds to the material whose permeability is to be measured.
  • a gas or mixture of gases is introduced into the first chamber and then collected in the second chamber where they are analyzed by a suitable detector.
  • the process of permeation of a gas through a material is based on the differences of partial pressures of this gas, also called permeant, on both sides of the material M.
  • the partial pressure of each of the gases having passed through the sample increases until stabilizing when the material M is saturated by permeating.
  • the permeability of the material to the gas considered is deduced by considering the thickness of the sample.
  • the barrier layer preferably has the property of being very slightly porous: it has an open porosity ranging from 0 to 5%, preferably ranging from 0 to 2%.
  • This porosity can be measured by the SEM image analysis method.
  • the coating may be termed a substantially closed porosity coating.
  • the specific surface of the barrier layer is between 5 cm 2 / g and 5 m 2 / g, in particular between 100 cm 2 / g and 1 m 2 / g.
  • the coating further comprises, on the surface of the barrier layer, a release layer, generally a conventional anti-adhesive layer.
  • This release layer can be advantageously obtained by oxidizing the outer surface of the barrier layer, especially by annealing in air at a temperature ranging from 600 ° C. to 900 ° C.
  • Said anti-adhesive layer is particularly advantageous when the substrate is intended for the formation of silicon ingots from molten silicon.
  • the release layer is porous.
  • the invention aims at providing a process for preparing a substrate according to the invention coated at least partially at the surface with a coating forming a gas barrier, said method comprising at least the steps of:
  • s selected material
  • the substrate is a crucible coated at least partially on its inner surface.
  • the fluid medium used in step a) comprises one or more material (s) X in an amount ranging from 15 to 35% by weight relative to the total weight of said fluid.
  • the fluid medium used in step a) comprises silica.
  • the amount of silica in the fluid medium may range from 0% to 15% by weight relative to the total weight of said fluid. It preferably has a size or average diameter of less than 2 microns.
  • the permeability of the barrier layer is advantageously less than 10 -15 m 2 , it can be controlled by the morphology of the initial powders and the characteristics of the heat treatments used.
  • the material (s) X present in the fluid medium are generally silicon derivatives in the form of powders.
  • the material (x) X generally has a micron order size.
  • the powders of silicon X derivatives are of size ranging from 500 nm to 5 microns, preferably from 0.8 microns to 2 microns.
  • Such a compound generally serves to facilitate the application of the liquid coating mixture using conventional equipment.
  • organic binder considered in the context of the present invention may be chosen from polyvinyl alcohol, polyethylene glycol or carboxymethylcellulose.
  • the ratio of the mixture "silica and material X" / binder (s) may be at least 3: 1 and more particularly 5: 1.
  • the fluid medium dedicated to form the coating according to the invention combines from 0 to 20% by weight of at least one binder relative to the total weight of the fluid medium, from 10 to 50% by weight of a mixture of silica and inorganic material (s) X by weight relative to the total weight of the liquid medium, the complement to 100% by weight being water.
  • This mixture may of course contain other additives intended either to improve these qualities at the time of spraying and / or application, or to give the corresponding coating additional properties required.
  • they may be dispersing agents.
  • the liquid medium used in step a) is generally a slip consisting of one or more inorganic material (s) X, water and optionally silica and at least one binder.
  • the slip is generally screened beforehand by passing through a mill in order to reduce the agglomerates of powders.
  • the method according to the invention comprises a step b) of applying the fluid medium to the surface to be treated in an amount sufficient to form a deposit.
  • the use of a fluid medium makes it possible to produce a deposit having a very good surface state.
  • such a gun with a 0.4 mm nozzle can be used at a compressed air pressure of 2.5 bar.
  • This application of the liquid coating mixture can also be carried out by other modes of application, such as, for example, the brush or by soaking the parts in a bath.
  • the application of the fluid mixture for forming the coating can be carried out at room temperature or at a higher temperature.
  • the surface to be treated may be heated so as to be conducive to rapid drying of the applied coating layer.
  • At least the surface to be treated, or even the whole of the material can be heated to a temperature ranging from 25 to 80 ° C., in particular from 30 to
  • the liquid mixture dedicated to form the coating is applied to the surface of the surface to be treated with a thickness adapted to prevent cracking during drying, for example between 20 and 100 ⁇ .
  • step (b) If necessary, it is possible to proceed to one or more other (s) deposit (s) of fluid mixture on the first deposit formed at the end of step (b). In this case the (s) other deposits, posterior, will take place after application and drying of the first deposit.
  • step b) is repeated several times before the implementation of step c).
  • the process according to the invention comprises between step b) of formation of a deposit and step c) of treatment under oxidizing atmosphere, at least one drying step at a temperature below 50 ° C and preferably from
  • the method according to the invention further comprises a step c) of heating in an oxidizing atmosphere, at a temperature and within a time sufficient to allow the formation of the expected barrier layer.
  • the heat treatment of step c) is carried out in an oxidizing atmosphere, more particularly in the presence of air.
  • this step is carried out in an oxidizing atmosphere at a temperature ranging from 1100 ° C. to 1300 ° C., and more particularly from 1150 ° to 1200 ° C.
  • this step is carried out for a period ranging from 1 hour to 5 hours, preferably from 2 hours to 3 hours.
  • this heat treatment is in fact carried out at a temperature adjusted to allow sintering and in particular sintering of the silicon oxide to be obtained, which makes it possible to obtain the permeability in the right range.
  • the piece is allowed to cool to room temperature.
  • the expected barrier layer is obtained, which is generally a silica matrix in which the unoxidized part of the grains of X is incorporated.
  • This layer may also be characterized by an oxygen mass fraction, evaluated according to the IGA technique, ranging from 25% to 40%.
  • the process according to the invention may comprise, after the treatment under oxidizing atmosphere carried out in step c), a treatment step in the presence of a neutral gas at a temperature of between 1400 ° C. and 1500 ° C. .
  • Such a step has the effect of further reducing the creep porosity of the silica.
  • the present invention also relates to substrates having a coating obtained by the process as described above.
  • the substrate treated according to the invention is advantageously a crucible or a mold.
  • the coating according to the invention can be used on all types of substrates such as crucibles, molds or platelets, leaflets, of any kind and known to those skilled in the art to be compatible with the silicon fusion without risks of harmful interactions between the substrate and its contents, in particular between the crucible and the liquid silicon.
  • the substrate is formed by a material chosen from SiC silicon carbide, S13N4 silicon nitride, and composites comprising graphite and silicon carbide or comprising graphite and silicon nitride and silicided graphite.
  • the invention also relates to the use of a crucible according to the invention or prepared according to the method of the invention in particular for the solidification of silicon.
  • a slip consisting of 23% of a mixture of S13N4 powder, 4% PVA polyvinyl alcohol and 73% water in percentages by weight, is passed through a planetary mill filled with silicon carbide or agate balls.
  • silicon carbide or agate balls Since the purpose of the silicon carbide or agate balls is only to reduce the powder agglomerates, silicon nitride balls are also conceivable, the risk of nitrogen pollution being very limited.
  • the fluid medium thus formed is then spray-dried (compressed air pressure of 2.5 bar, 0.4 mm nozzle placed at about thirty centimeters from the substrate) over the entire internal surface of a crucible to be coated.
  • the deposit thus obtained is dried in hot air at a temperature below
  • This layer is then subjected to a step of 3 hours at 1100 ° C. in air for debinding and oxidation of the powders.
  • the mass fraction of oxygen in the coating is 29% measured by the IGA (Interstitial Gas Analysis) technique.
  • IGA Interstitial Gas Analysis
  • Figure 1 is presented the coating obtained at the end of Example 1.
  • This coating is in the form of a matrix of SiO 2 in which are incorporated grains of non-oxidized Si 3 N 4 .

Abstract

The invention relates to a substrate characterised in that it is at least partially surface-coated with a coating containing at least one so-called "barrier" layer comprising silica and one or more material(s) X selected from among SiC, Si, Si3N4, in which layer the amount of X varies between 25 -wt.% and 50.-wt.% in relation to the total weight of the barrier layer, said barrier layer being formed by grains of one or more materials X covered at least partially in a silica shell, and said barrier layer being in direct contact with the substrate.

Description

Substrat à revêtement peu perméable pour solidification de silicium  Substrate with low permeability coating for silicon solidification
La présente invention se rapporte à un substrat possédant un revêtement particulier, destiné à être mis en contact avec un silicium fondu.  The present invention relates to a substrate having a particular coating, intended to be brought into contact with a molten silicon.
La présente invention se rapporte plus particulièrement à un creuset utile pour la solidification d'un lingot de silicium à partir de silicium à l'état fondu.  The present invention relates more particularly to a crucible useful for the solidification of a silicon ingot from silicon in the molten state.
Elle concerne également un procédé de préparation d'un tel creuset ainsi que l'utilisation d'un tel creuset pour la solidification de silicium.  It also relates to a process for preparing such a crucible and the use of such a crucible for the solidification of silicon.
Les creusets selon l'invention sont notamment utilisables dans des procédés de fusion et de solidification de silicium, à des fins par exemple d'obtention de silicium de haute pureté pour des applications dans la génération d'énergie photovoltaïque. Ainsi, les cellules photovoltaïques sont, pour l'essentiel, fabriquées à partir de silicium mono- ou poly-cristallin, obtenu à partir de la solidification de silicium liquide dans des creusets. Ce sont les plaquettes découpées dans le lingot formé au sein du creuset qui servent de base à la fabrication des cellules.  The crucibles according to the invention are particularly useful in silicon melting and solidification processes, for example for obtaining high purity silicon for applications in the generation of photovoltaic energy. Thus, the photovoltaic cells are essentially made from mono- or poly-crystalline silicon, obtained from the solidification of liquid silicon in crucibles. It is the platelets cut in the ingot formed in the crucible which serve as a basis for the manufacture of the cells.
Les creusets considérés pour la croissance du lingot sont généralement des creusets en silice, revêtus d'une couche de nitrure de silicium oxydé pour éviter l'adhérence du lingot au creuset après solidification.  The crucibles considered for the growth of the ingot are generally silica crucibles, coated with a layer of oxidized silicon nitride to prevent adhesion of the ingot to the crucible after solidification.
Plus précisément, le comportement anti-adhérent repose pour l'essentiel sur la présence de nitrure de silicium, S13N4, à l'état de poudres oxydées, en surface des parois internes des creusets auxquelles adhère le silicium au cours de son refroidissement. En refroidissant, le lingot de silicium se détache de ces parois par rupture cohésive au sein de la couche de nitrure de silicium, relaxant ainsi les contraintes mécaniques issues de la différence de coefficients d'expansion thermique.  More specifically, the anti-adherence behavior is based essentially on the presence of silicon nitride, S13N4, in the form of oxidized powders, on the surface of the inner walls of the crucibles to which the silicon adheres during its cooling. By cooling, the silicon ingot is detached from these walls by cohesive rupture within the silicon nitride layer, thus relaxing the mechanical stresses resulting from the difference in coefficients of thermal expansion.
Toutefois, cette technique ne permet pas de prévenir une contamination du silicium par les impuretés présentes dans la poudre de nitrure de silicium.  However, this technique does not prevent contamination of silicon by the impurities present in the silicon nitride powder.
En outre, ce revêtement ne peut pas être utilisé sur tous types de creusets notamment sur les creusets en céramique tels que le carbure ou le nitrure de silicium. En effet, ces céramiques étant chimiquement réductrices, elles vont avoir pour effet de désoxyder le revêtement, ce qui peut conduire à une délamination de ce dernier.  In addition, this coating can not be used on all types of crucibles including ceramic crucibles such as carbide or silicon nitride. Indeed, these ceramics being chemically reducing, they will have the effect of deoxidizing the coating, which may lead to delamination of the latter.
Une solution naturelle serait de réaliser une couche barrière de silice, afin d'empêcher que les gaz produits lors du traitement thermique s'échappent et ainsi d'empêcher la délamination du revêtement. Malheureusement le phénomène de dilatation différentielle fait qu'une couche de silice pure ne résiste pas au cyclage thermique. A natural solution would be to achieve a silica barrier layer, to prevent the gases produced during the heat treatment from escaping and thus to prevent the delamination of the coating. Unfortunately the phenomenon of differential expansion makes a pure silica layer not resistant to thermal cycling.
Par ailleurs, du fait de transformations de forme et de structure au cours du cycle de fusion-solidification du silicium, les creusets utilisés dans l'industrie ne sont pas toujours réutilisables.  Moreover, due to transformations of shape and structure during the melting-solidification cycle of silicon, crucibles used in industry are not always reusable.
Il demeure par conséquent à ce jour un besoin de substrats notamment de creusets possédant un revêtement assurant une barrière étanche aux gaz, ces substrats étant susceptibles de subir plusieurs cycles thermiques consécutifs et à ce titre réutilisables.  Therefore, there remains to date a need for substrates including crucibles having a coating providing a gas-tight barrier, these substrates being capable of undergoing several consecutive thermal cycles and as such reusable.
Il demeure également un besoin de substrats notamment de creusets permettant un détachement aisé du lingot de silicium après son refroidissement, tout en limitant la contamination de ce lingot par le revêtement anti-adhérent.  There is also a need for substrates including crucibles allowing easy detachment of the silicon ingot after cooling, while limiting the contamination of the ingot by the non-stick coating.
Enfin, dans la perspective d'une production à l'échelle industrielle, il est souhaitable de disposer d'un procédé de fabrication de creusets par des techniques à bas coût et ne nécessitant que peu d'étapes de mise en œuvre.  Finally, in the perspective of production on an industrial scale, it is desirable to have a crucible manufacturing process by low cost techniques and requiring only few implementation steps.
La présente invention vise précisément à proposer de nouveaux substrats, notamment de nouveaux creusets utiles pour la solidification d'un lingot de silicium à partir de silicium à l'état fondu satisfaisant ces besoins.  The present invention aims precisely to provide new substrates, including new crucibles useful for the solidification of a silicon ingot from silicon in the molten state satisfying these needs.
Ainsi la présente invention concerne un substrat revêtu au moins partiellement en surface, d'un revêtement contenant au moins une couche dite « barrière » comprenant de la silice et un ou plusieurs matériau(x) X choisi(s) parmi SiC, Si, S13N4, couche dans laquelle la quantité massique de X varie de 25% à 50% par rapport à la masse totale de la couche barrière, ladite couche barrière étant formée de grains d'un ou plusieurs matériaux X recouverts au moins partiellement par une enveloppe de silice, la couche barrière étant disposée en contact direct avec le substrat.  Thus, the present invention relates to a substrate coated at least partially at the surface with a coating containing at least one so-called "barrier" layer comprising silica and one or more material (s) X chosen from SiC, Si, S13N4. layer in which the mass quantity of X varies from 25% to 50% relative to the total mass of the barrier layer, said barrier layer being formed of grains of one or more materials X at least partially covered by a silica envelope the barrier layer being disposed in direct contact with the substrate.
De manière surprenante et avantageuse, les inventeurs ont, en effet, découvert que les problèmes développés ci-dessus peuvent être résolus en recouvrant au moins partiellement la surface d'un substrat dédié à contenir ou supporter du silicium fondu, d'un revêtement faiblement perméable formé de silice et d'un ou plusieurs matériau(x) X choisi(s) parmi SiC, Si, S13N4, dans des proportions déterminées.  Surprisingly and advantageously, the inventors have, in fact, discovered that the problems developed above can be solved by at least partially covering the surface of a substrate dedicated to containing or supporting molten silicon, a low permeability coating formed of silica and one or more material (X) X selected from SiC, Si, S13N4, in specified proportions.
Le revêtement formé dans le cadre de la présente invention dans lequel la couche barrière est en contact direct avec le substrat, c'est-à-dire qu'il n'y a pas de couche intermédiaire entre le substrat et la couche barrière, est avantageux à plusieurs titres. Il manifeste simultanément des bonnes propriétés d'adhésion au substrat, des propriétés « barrière » aux gaz satisfaisantes. The coating formed in the context of the present invention in which the barrier layer is in direct contact with the substrate, that is to say that there is no intermediate layer between the substrate and the barrier layer, is advantageous in many ways. he simultaneously exhibits good substrate adhesion properties, satisfactory gas barrier properties.
Les expressions « compris entre... et ... », « allant de... à... » sont équivalentes et, sauf mention contraire, doivent s'entendre bornes incluses. Selon une variante, ledit revêtement est constitué par ladite couche barrière.  The expressions "between ... and ...", "from ... to ..." are equivalent and, unless otherwise stated, must be understood to include limits. According to a variant, said coating is constituted by said barrier layer.
Selon cette mise en œuvre, la couche barrière constitue la couche externe du substrat, en contact direct avec l'atmosphère ou le contenant du substrat, c'est-à-dire que la couche barrière n'est pas recouverte d'une couche additionnelle.  According to this implementation, the barrier layer constitutes the outer layer of the substrate, in direct contact with the atmosphere or the container of the substrate, that is to say that the barrier layer is not covered with an additional layer .
Selon une autre variante, ledit revêtement n'est formé qu'en partie par la couche barrière à laquelle peut être superposée une couche annexe, de préférence ladite couche annexe est une couche anti-adhérente.  According to another variant, said coating is formed only in part by the barrier layer to which can be superimposed an additional layer, preferably said auxiliary layer is a release layer.
Ladite couche adhérente est alors avantageusement obtenue en oxydant la surface externe de la couche barrière.  Said adherent layer is then advantageously obtained by oxidizing the outer surface of the barrier layer.
Selon une première variante, le revêtement formé selon la présente invention comprend au moins une couche barrière formée de grains d'un ou plusieurs matériaux X recouverts au moins partiellement par une enveloppe de silice.  According to a first variant, the coating formed according to the present invention comprises at least one barrier layer formed of grains of one or more materials X at least partially covered by a silica envelope.
Dans ce cas la cohésion des grains est généralement obtenue par frittage de la silice.  In this case, the cohesion of the grains is generally obtained by sintering the silica.
Selon une autre variante, le revêtement formé selon la présente invention comprend au moins une couche barrière se présentant sous la forme d'une matrice de silice dans laquelle sont incorporés des grains d'un ou plusieurs matériau(x) X.  According to another variant, the coating formed according to the present invention comprises at least one barrier layer in the form of a silica matrix in which are incorporated grains of one or more material (X) X.
Plus particulièrement les grains d'un ou plusieurs matériau(x) X sont revêtus au moins en partie d'une couche nanométrique de silice.  More particularly, the grains of one or more material (X) X are coated at least in part with a nanometric layer of silica.
Avantageusement, l'épaisseur de la couche « barrière» est comprise entre 10 et 100 μπι, entre 20 et 50 μιη.  Advantageously, the thickness of the "barrier" layer is between 10 and 100 μπι, between 20 and 50 μιη.
Pour ce qui est de l'enveloppe de silice c'est-à-dire la couche de silice formée en surface des grains de matériau(x) X, elle peut posséder une épaisseur variant de 2 à 100 nm, et notamment de 10 à 30 nm. Avantageusement, le substrat est un creuset, en particulier utile pour la solidification de silicium.  With regard to the silica envelope, that is to say the silica layer formed on the surface of the grains of material (x) X, it may have a thickness ranging from 2 to 100 nm, and in particular from 10 to 30 nm. Advantageously, the substrate is a crucible, in particular useful for the solidification of silicon.
Il peut également s'agir d'une partie d'un creuset qui par assemblage avec une ou plusieurs autres pièces, permet précisément de former ledit creuset. La présence du revêtement selon l'invention permet d'obtenir un creuset qui est réutilisable sous réserve uniquement de déposer la couche annexe, c'est-à-dire sans requérir une ou plusieurs étapes de traitement préalables avant réutilisation. It may also be a part of a crucible which by assembly with one or more other parts, precisely allows to form said crucible. The presence of the coating according to the invention makes it possible to obtain a crucible which is reusable subject only to depositing the auxiliary layer, that is to say without requiring one or more pre-treatment steps before reuse.
D'autres caractéristiques et avantages de l'invention ressortiront mieux de la description qui suit. Cette description correspond à un mode de mise en œuvre particulier de l'invention et est donnée à titre purement illustratif et non limitatif.  Other features and advantages of the invention will become more apparent from the following description. This description corresponds to a particular mode of implementation of the invention and is given purely by way of illustration and not limitation.
Comme indiqué précédemment, le substrat selon l'invention est revêtu au moins partiellement, et de préférence entièrement, en surface, d'un revêtement formé d'au moins une couche dite « barrière ».  As indicated above, the substrate according to the invention is coated at least partially, and preferably entirely, at the surface, with a coating formed by at least one so-called "barrier" layer.
Au regard de sa composition et de sa perméabilité, la couche barrière selon l'invention permet de conserver l'intégrité du substrat.  With regard to its composition and its permeability, the barrier layer according to the invention makes it possible to maintain the integrity of the substrate.
Sans vouloir être lié à une quelconque théorie, il semble que les produits gazeux susceptibles d'être générés à l'interface substrat/couche barrière, lors des traitements thermiques (SiO, CO) ne vont pas pouvoir s'évacuer à travers le revêtement. On s'affranchit ainsi des problèmes liés à la délamination du revêtement et à son infiltration par le silicium liquide au cours de différents cycles.  Without wishing to be bound to any theory, it seems that the gaseous products that can be generated at the substrate / barrier layer interface during thermal treatments (SiO, CO) will not be able to escape through the coating. This eliminates the problems associated with the delamination of the coating and its infiltration by liquid silicon during different cycles.
Ainsi, la couche barrière comprend, voire est constituée de, silice et d'un ou plusieurs matériau(x) X choisi(s) parmi SiC, Si, S13N4, et est telle que la quantité massique de X dans la couche barrière varie de 25% à 50% par rapport à la masse totale de la couche barrière.  Thus, the barrier layer comprises, or even consists of, silica and one or more material (s) X selected from SiC, Si, S13N4, and is such that the mass quantity of X in the barrier layer varies from 25% to 50% relative to the total mass of the barrier layer.
En conséquence, la quantité massique de silice dans la couche barrière varie avantageusement de 50% à 75% par rapport à la masse totale de la couche barrière.  As a result, the mass quantity of silica in the barrier layer advantageously varies from 50% to 75% relative to the total mass of the barrier layer.
Selon une première variante de l'invention, la couche barrière comprend, voire est constituée de, un mélange de silice et de carbure de silicium (SiC).  According to a first variant of the invention, the barrier layer comprises, or even consists of, a mixture of silica and silicon carbide (SiC).
Selon une deuxième variante de l'invention, la couche barrière comprend, voire est constituée de, un mélange de silice et de silicium (Si).  According to a second variant of the invention, the barrier layer comprises, or even consists of, a mixture of silica and silicon (Si).
Selon une troisième variante préférée de l'invention, la couche barrière comprend, voire est constituée de, un mélange de silice et de nitrure de silicium (Si3N4). According to a third preferred variant of the invention, the barrier layer comprises, or even consists of, a mixture of silica and silicon nitride (Si 3 N 4 ).
Selon une quatrième variante de l'invention, la couche barrière comprend, voire est constituée de, un mélange de silice et de deux matériaux X choisis parmi SiC, Si, S13N4. Selon une cinquième variante de l'invention, la couche barrière comprend, voire est constituée de, un mélange de silice et des trois matériaux X suivants SiC, Si, Si3N4. According to a fourth variant of the invention, the barrier layer comprises, or even consists of, a mixture of silica and two materials X selected from SiC, Si, S13N4. According to a fifth variant of the invention, the barrier layer comprises, or even consists of, a mixture of silica and the following three materials X SiC, Si, Si 3 N 4 .
Les particules de matériaux inorganiques X mises en œuvre dans le procédé de préparation du revêtement selon l'invention, comme décrit plus particulièrement par la suite, se présentent de préférence sous la forme de poudres, ayant de préférence une taille ou un diamètre moyen allant de 500 nm à 5 microns, de préférence de 0,8 microns à 2 microns.  The particles of inorganic materials X used in the process for preparing the coating according to the invention, as described more particularly later, are preferably in the form of powders, preferably having a size or a mean diameter ranging from 500 nm to 5 microns, preferably from 0.8 microns to 2 microns.
Selon une variante de réalisation, il peut s'agir de poudres disponibles commercialement. A titre d'exemple de telles poudres, on peut citer le nitrure de silicium (S13N4) sous forme de grains de taille micronique et commercialisé sous la référence S E10® par la société UBE, According to an alternative embodiment, it may be commercially available powders. Examples of such powders include silicon nitride (S1 3 N 4) in the form of micron-sized grains and sold under the reference S E10 ® by the company UBE,
Selon une autre variante de réalisation, les particules de matériaux inorganiques X peuvent être préparées préalablement à la formation du revêtement selon l'invention. L'homme du métier est à même de mettre en œuvre les méthodes adaptées à la préparation des particules convenant à l'invention.  According to another variant embodiment, the particles of inorganic materials X may be prepared prior to the formation of the coating according to the invention. The skilled person is able to implement the methods suitable for the preparation of particles suitable for the invention.
Avantageusement, la perméabilité de la couche barrière est inférieure à 10"15 m , de préférence inférieure à 10 8 m2. Advantageously, the permeability of the barrier layer is less than 10 -15 m, preferably less than 10 -8 m 2 .
La perméabilité de cette couche traduit son aptitude à se laisser traverser par un fluide de référence sous l'effet d'un gradient de pression.  The permeability of this layer reflects its ability to be passed through by a reference fluid under the effect of a pressure gradient.
La perméabilité (intrinsèque ou spécifique) d'un substrat et plus généralement d'un milieu peut être obtenue à partir de l'équation de Darcy : dans laquelle dP/dx est le gradient de pression dans la direction du flux et μ est la viscosité dynamique du fluide. The permeability (intrinsic or specific) of a substrate and more generally of a medium can be obtained from the Darcy equation: where dP / dx is the pressure gradient in the flow direction and μ is the dynamic viscosity of the fluid.
Ainsi la perméabilité intrinsèque ou spécifique K est indépendante de la nature du fluide mais dépend de la géométrie du milieu, et elle s'exprime en m2. Dans le cas d'un flux en phase simple (single-phase flow), la perméabilité intrinsèque ou spécifique K est simplifiée en « perméabilité ». Thus the intrinsic or specific permeability K is independent of the nature of the fluid but depends on the geometry of the medium, and it is expressed in m 2 . In the case of a single-phase flow, the intrinsic or specific permeability K is simplified to "permeability".
La perméabilité est mesurée au moyen d'un perméamètre tel que décrit dans le brevet US 5 361 625 ou dans la demande de brevet EP 1 821 093 A2. Ces perméamètres sont des dispositifs de mesure de perméation de gaz à travers un matériau (M), ils comprennent une enceinte de perméation comprenant une première et une deuxième chambre séparée par un matériau (M). Le matériau M correspond au matériau dont on cherche à mesurer la perméabilité. The permeability is measured by means of a permeameter as described in US Pat. No. 5,361,625 or in patent application EP 1 821 093 A2. These permeameters are devices for measuring gas permeation through a material (M), they comprise a permeation chamber comprising a first and a second chamber separated by a material (M). The material M corresponds to the material whose permeability is to be measured.
Généralement, un gaz ou mélange de gaz est introduit dans la première chambre puis collecté dans la deuxième chambre où ils sont analysés par un détecteur approprié. Le processus de perméation d'un gaz à travers un matériau repose sur les différences de pressions partielles de ce gaz, appelé aussi perméant, de part et d'autre du matériau M. La pression partielle de chacun des gaz ayant traversé l'échantillon augmente jusqu'à se stabiliser quand le matériau M est saturé en perméant.  Generally, a gas or mixture of gases is introduced into the first chamber and then collected in the second chamber where they are analyzed by a suitable detector. The process of permeation of a gas through a material is based on the differences of partial pressures of this gas, also called permeant, on both sides of the material M. The partial pressure of each of the gases having passed through the sample increases until stabilizing when the material M is saturated by permeating.
A partir du flux de perméation ainsi calculé, on déduit la perméabilité du matériau au gaz considéré en considérant l'épaisseur de l'échantillon.  From the permeation flux thus calculated, the permeability of the material to the gas considered is deduced by considering the thickness of the sample.
La couche barrière présente préférentiellement la propriété d'être très peu poreuse : elle présente une porosité ouverte allant de 0 à 5%, de préférence allant de 0 à 2%.  The barrier layer preferably has the property of being very slightly porous: it has an open porosity ranging from 0 to 5%, preferably ranging from 0 to 2%.
Cette porosité peut être mesurée par la méthode d'analyse d'image par MEB. This porosity can be measured by the SEM image analysis method.
Dans le cas d'une porosité inférieure à 2%, le revêtement peut être qualifié de revêtement à porosité sensiblement fermée. In the case of a porosity of less than 2%, the coating may be termed a substantially closed porosity coating.
En outre, avantageusement, la surface spécifique de la couche barrière est comprise entre 5 cm2/g et 5 m2/g, en particulier entre 100 cm2/g et 1 m2/g. In addition, advantageously, the specific surface of the barrier layer is between 5 cm 2 / g and 5 m 2 / g, in particular between 100 cm 2 / g and 1 m 2 / g.
Selon un mode préféré de l'invention, le revêtement comprend, en outre, en surface de la couche barrière, une couche anti-adhérente, généralement une couche antiadhérente classique.  According to a preferred embodiment of the invention, the coating further comprises, on the surface of the barrier layer, a release layer, generally a conventional anti-adhesive layer.
Cette couche anti-adhérente peut être avantageusement obtenue en oxydant la surface externe de la couche barrière notamment par un recuit sous air à une température allant de 600°C à 900°C.  This release layer can be advantageously obtained by oxidizing the outer surface of the barrier layer, especially by annealing in air at a temperature ranging from 600 ° C. to 900 ° C.
Ladite couche anti-adhérente est particulièrement avantageuse lorsque le substrat est destiné à la formation de lingots de silicium à partir de silicium fondu.  Said anti-adhesive layer is particularly advantageous when the substrate is intended for the formation of silicon ingots from molten silicon.
Contrairement à la couche barrière, la couche anti-adhérente est poreuse.  Unlike the barrier layer, the release layer is porous.
II relève des compétences de l'homme du métier d'ajuster la durée et la température de l'étape de recuit oxydant permettant d'obtenir une surface anti-adhérente appropriée. Procédé It is within the skill of those skilled in the art to adjust the duration and the temperature of the oxidizing annealing step to obtain a suitable non-stick surface. Process
Selon un autre de ses aspects, l'invention vise à proposer un procédé de préparation d'un substrat selon l'invention revêtu au moins partiellement en surface par un revêtement formant barrière aux gaz, ledit procédé comprenant au moins les étapes consistant à :  According to another of its aspects, the invention aims at providing a process for preparing a substrate according to the invention coated at least partially at the surface with a coating forming a gas barrier, said method comprising at least the steps of:
a) disposer d'un milieu fluide comprenant un ou plusieurs matériau(x) X choisi parmi SiC, Si, Si3N4 ; a) having a fluid medium comprising one or more material (x) X selected from SiC, Si, Si 3 N 4 ;
b) appliquer ledit milieu fluide sur la surface du substrat en une quantité suffisante pour y former un dépôt, b) applying said fluid medium to the surface of the substrate in an amount sufficient to form a deposit,
c) traiter ledit dépôt sous atmosphère oxydante, à une température comprise entre 1000 °C et 1300 °C et dans des conditions suffisantes pour former une couche dite « barrière » comprenant de la silice et un ou plusieurs matériau(x) X choisi(s) parmi SiC, Si, Si3N4, couche dans laquelle la quantité massique de X varie de 25% à 50% par rapport à la masse total de la couche barrière, ladite couche barrière étant formée de grains d'un ou plusieurs matériaux X recouverts au moins partiellement par une enveloppe de silice, la couche barrière étant disposée en contact direct avec le substrat. c) treating said deposition under an oxidizing atmosphere, at a temperature of between 1000 ° C. and 1300 ° C. and under conditions sufficient to form a so-called "barrier" layer comprising silica and one or more selected material (s) X (s) ) among SiC, Si, Si 3 N 4 , in which the mass quantity of X varies from 25% to 50% relative to the total mass of the barrier layer, said barrier layer being formed from grains of one or more materials X covered at least partially by a silica shell, the barrier layer being disposed in direct contact with the substrate.
Plus particulièrement le substrat est un creuset revêtu au moins partiellement sur sa surface interne.  More particularly, the substrate is a crucible coated at least partially on its inner surface.
Plus particulièrement, le milieu fluide utilisé à l'étape a) comprend un ou plusieurs matériau(x) X en une quantité allant de 15 à 35 % en poids par rapport au poids total dudit fluide.  More particularly, the fluid medium used in step a) comprises one or more material (s) X in an amount ranging from 15 to 35% by weight relative to the total weight of said fluid.
Avantageusement, le milieu fluide utilisé à l'étape a) comprend de la silice. Ainsi, la quantité de silice dans le milieu fluide peut aller de 0% à 15% en poids par rapport au poids total dudit fluide. Elle a de préférence une taille ou diamètre moyen inférieur à 2 microns.  Advantageously, the fluid medium used in step a) comprises silica. Thus, the amount of silica in the fluid medium may range from 0% to 15% by weight relative to the total weight of said fluid. It preferably has a size or average diameter of less than 2 microns.
La perméabilité de la couche barrière est avantageusement inférieure à 10"15 m2, elle peut être contrôlée par la morphologie des poudres initiales et les caractéristiques des traitements thermiques utilisés The permeability of the barrier layer is advantageously less than 10 -15 m 2 , it can be controlled by the morphology of the initial powders and the characteristics of the heat treatments used.
Le ou les matériau(x) X présents dans le milieu fluide sont généralement des dérivés du silicium sous la forme de poudres. Les matériau(x) X possèdent généralement une taille d'ordre micronique. Généralement, les poudres de dérivés du silicium X sont de taille allant de 500 nm à 5 microns, de préférence de 0,8 microns à 2 microns. The material (s) X present in the fluid medium are generally silicon derivatives in the form of powders. The material (x) X generally has a micron order size. Generally, the powders of silicon X derivatives are of size ranging from 500 nm to 5 microns, preferably from 0.8 microns to 2 microns.
Le milieu liquide utilisé à l'étape a), outre le ou les matériaux inorganiques X et éventuellement la silice, contient avantageusement une quantité efficace d'au moins un liant organique.  The liquid medium used in step a), in addition to the inorganic material or materials X and optionally silica, advantageously contains an effective amount of at least one organic binder.
Un tel composé a généralement pour fonction de faciliter l'application du mélange liquide de revêtement en utilisant des équipements traditionnels.  Such a compound generally serves to facilitate the application of the liquid coating mixture using conventional equipment.
Ainsi le liant organique considéré dans la cadre de la présente invention peut être choisi parmi l'alcool polyvinylique, le polyéthylèneglycol ou encore la carboxyméthylcellulose.  Thus, the organic binder considered in the context of the present invention may be chosen from polyvinyl alcohol, polyethylene glycol or carboxymethylcellulose.
Par exemple le rapport du mélange « silice et matériau X » / liant(s) peut être d'au moins 3 : 1 et plus particulièrement 5: 1.  For example, the ratio of the mixture "silica and material X" / binder (s) may be at least 3: 1 and more particularly 5: 1.
Le milieu fluide comprend en outre généralement de l'eau.  The fluid medium furthermore generally comprises water.
D'une manière générale, le milieu fluide dédié à former le revêtement conforme à l'invention associe de 0 à 20 % en poids d'au moins un liant par rapport au poids total du milieu fluide, de 10 à 50 % en poids d'un mélange de silice et de matériau(x) inorganique(s) X en poids par rapport au poids total du milieu liquide, le complément à 100 % en poids étant de l'eau.  In general, the fluid medium dedicated to form the coating according to the invention combines from 0 to 20% by weight of at least one binder relative to the total weight of the fluid medium, from 10 to 50% by weight of a mixture of silica and inorganic material (s) X by weight relative to the total weight of the liquid medium, the complement to 100% by weight being water.
Ce mélange peut bien entendu contenir d'autres additifs destinés soit à améliorer ces qualités au moment de la pulvérisation et/ou l'application, soit pour conférer au revêtement correspondant des propriétés annexes requises.  This mixture may of course contain other additives intended either to improve these qualities at the time of spraying and / or application, or to give the corresponding coating additional properties required.
Il peut par exemple s'agir d'agents dispersants.  For example, they may be dispersing agents.
Le milieu liquide utilisé à l'étape a) est généralement une barbotine constituée d'un ou plusieurs matériau(x) inorganique(s) X, d'eau et éventuellement de silice et d'au moins un liant.  The liquid medium used in step a) is generally a slip consisting of one or more inorganic material (s) X, water and optionally silica and at least one binder.
La barbotine est généralement préalablement tamisée par passage dans un broyeur afin de réduire les agglomérats de poudres. Le procédé selon l'invention comprend une étape b) d'application du milieu fluide sur la surface à traiter en une quantité suffisante pour former un dépôt. L'utilisation d'un milieu fluide permet de réaliser un dépôt présentant un très bon état de surface. The slip is generally screened beforehand by passing through a mill in order to reduce the agglomerates of powders. The method according to the invention comprises a step b) of applying the fluid medium to the surface to be treated in an amount sufficient to form a deposit. The use of a fluid medium makes it possible to produce a deposit having a very good surface state.
Par exemple, un tel pistolet, muni d'une buse de 0,4 mm, peut être utilisé à une pression d'air comprimé de 2,5 bars.  For example, such a gun with a 0.4 mm nozzle can be used at a compressed air pressure of 2.5 bar.
Cette application du mélange liquide de revêtement peut être également effectuée par d'autres modes d'application, tels que par exemple le pinceau, ou encore par trempage des pièces dans un bain.  This application of the liquid coating mixture can also be carried out by other modes of application, such as, for example, the brush or by soaking the parts in a bath.
Ces techniques d'application relèvent clairement des compétences de l'homme de l'art et ne sont pas décrites ici de manière détaillée.  These application techniques are clearly within the skill of those skilled in the art and are not described here in detail.
L'application du mélange fluide destiné à former le revêtement peut être réalisé à température ambiante ou à une température supérieure. La surface à traiter peut être chauffée de manière à être propice à un séchage rapide de la couche de revêtement appliquée.  The application of the fluid mixture for forming the coating can be carried out at room temperature or at a higher temperature. The surface to be treated may be heated so as to be conducive to rapid drying of the applied coating layer.
Dans ce mode de réalisation, au moins la surface à traiter, voire l'ensemble du matériau, peut être chauffée à une température variant de 25 à 80°C, notamment de 30 à In this embodiment, at least the surface to be treated, or even the whole of the material, can be heated to a temperature ranging from 25 to 80 ° C., in particular from 30 to
50 °C, conduisant ainsi à l'évaporation du solvant. 50 ° C, thus leading to the evaporation of the solvent.
Le mélange liquide dédié à former le revêtement est appliqué en surface de la surface à traiter avec une épaisseur adaptée pour empêcher tout craquage durant le séchage, par exemple comprise entre 20 et 100 μιη.  The liquid mixture dedicated to form the coating is applied to the surface of the surface to be treated with a thickness adapted to prevent cracking during drying, for example between 20 and 100 μιη.
Si nécessaire, il est possible de procéder à un ou plusieurs autre(s) dépôt(s) de mélange fluide sur le premier dépôt formé à l'issue de l'étape (b). Dans ce cas le(s) autres dépôts, postérieurs, auront lieu après application et séchage du premier dépôt.  If necessary, it is possible to proceed to one or more other (s) deposit (s) of fluid mixture on the first deposit formed at the end of step (b). In this case the (s) other deposits, posterior, will take place after application and drying of the first deposit.
Ainsi selon un mode particulier du procédé selon l'invention, l'étape b) est renouvelée plusieurs fois avant la mise en œuvre de l'étape c).  Thus according to a particular embodiment of the method according to the invention, step b) is repeated several times before the implementation of step c).
Selon un autre mode particulier, le procédé selon l'invention comprend entre l'étape b) de formation d'un dépôt et l'étape c) de traitement sous atmosphère oxydante, au moins une étape de séchage à une température inférieure à 50°C et de préférence allant de According to another particular embodiment, the process according to the invention comprises between step b) of formation of a deposit and step c) of treatment under oxidizing atmosphere, at least one drying step at a temperature below 50 ° C and preferably from
20°C et 50°C. 20 ° C and 50 ° C.
Le procédé selon l'invention comprend en outre une étape c) de chauffage en atmosphère oxydante, à une température et dans un délai suffisants pour permettre la formation de la couche barrière attendue. Le traitement thermique de l'étape c) est réalisé en atmosphère oxydante, plus particulièrement en présence l'air. The method according to the invention further comprises a step c) of heating in an oxidizing atmosphere, at a temperature and within a time sufficient to allow the formation of the expected barrier layer. The heat treatment of step c) is carried out in an oxidizing atmosphere, more particularly in the presence of air.
Avantageusement, cette étape est réalisée en atmosphère oxydante à une température allant de 1100 °C à 1300 °C, et plus particulièrement de 1150 à 1200 °C.  Advantageously, this step is carried out in an oxidizing atmosphere at a temperature ranging from 1100 ° C. to 1300 ° C., and more particularly from 1150 ° to 1200 ° C.
Plus particulièrement cette étape est effectuée pendant une durée allant de 1 heure à 5 heures, de préférence allant de 2 heures à 3 heures.  More particularly, this step is carried out for a period ranging from 1 hour to 5 hours, preferably from 2 hours to 3 hours.
Dans le cadre de la présente invention, ce traitement thermique est en effet réalisé à une température ajustée pour permettre l'obtention d'un frittage et notamment d'un frittage de l'oxyde de silicium, ce qui permet d'obtenir la perméabilité dans la gamme adéquate. A l'issue de ce traitement thermique, la pièce est laissée refroidir à température ambiante.  In the context of the present invention, this heat treatment is in fact carried out at a temperature adjusted to allow sintering and in particular sintering of the silicon oxide to be obtained, which makes it possible to obtain the permeability in the right range. At the end of this heat treatment, the piece is allowed to cool to room temperature.
A l'issue de ce traitement, on obtient la couche barrière attendue qui se présente généralement comme une matrice de silice dans laquelle est incorporée la partie non oxydée des grains de X. Cette couche peut également être caractérisée par une fraction massique en oxygène, évaluée selon la technique IGA, allant de 25% à 40%.  At the end of this treatment, the expected barrier layer is obtained, which is generally a silica matrix in which the unoxidized part of the grains of X is incorporated. This layer may also be characterized by an oxygen mass fraction, evaluated according to the IGA technique, ranging from 25% to 40%.
Selon une autre variante, le procédé selon l'invention peut comprendre après le traitement sous atmosphère oxydante réalisé à l'étape c), une étape de traitement en présence d'un gaz neutre à une température comprise entre 1400°C et 1500°C.  According to another variant, the process according to the invention may comprise, after the treatment under oxidizing atmosphere carried out in step c), a treatment step in the presence of a neutral gas at a temperature of between 1400 ° C. and 1500 ° C. .
Une telle étape a pour effet de réduire encore la porosité par fluage de la silice. Such a step has the effect of further reducing the creep porosity of the silica.
La présente invention a également pour objet les substrats possédant un revêtement obtenu par le procédé tel que décrit précédemment. The present invention also relates to substrates having a coating obtained by the process as described above.
Dans le cas de creusets dédié à la fabrication de lingots, il est particulièrement avantageux de superposer une couche anti-adhérente sur la couche barrière.  In the case of crucibles dedicated to the manufacture of ingots, it is particularly advantageous to superpose a release layer on the barrier layer.
Le substrat traité selon l'invention est avantageusement un creuset ou un moule.  The substrate treated according to the invention is advantageously a crucible or a mold.
Un des avantages de la présente invention est que le revêtement selon l'invention peut être utilisé sur tous types de substrats tels que creusets, moules ou encore plaquettes, feuillets, de toute nature et connus de l'homme du métier pour être compatible avec la fusion du silicium sans risques de d'interactions préjudiciables entre le substrat et son contenu notamment entre le creuset et le silicium liquide.  One of the advantages of the present invention is that the coating according to the invention can be used on all types of substrates such as crucibles, molds or platelets, leaflets, of any kind and known to those skilled in the art to be compatible with the silicon fusion without risks of harmful interactions between the substrate and its contents, in particular between the crucible and the liquid silicon.
De manière préférée, le substrat est formé par un matériau choisi parmi le carbure de silicium SiC, le nitrure de silicium S13N4, les composites comprenant du graphite et du carbure de silicium ou comprenant du graphite et du nitrure de silicium et le graphite siliciuré. Preferably, the substrate is formed by a material chosen from SiC silicon carbide, S13N4 silicon nitride, and composites comprising graphite and silicon carbide or comprising graphite and silicon nitride and silicided graphite.
Selon un autre de ses aspects, l'invention concerne aussi l'utilisation d'un creuset selon l'invention ou préparé selon le procédé de l'invention notamment pour la solidification de silicium.  According to another of its aspects, the invention also relates to the use of a crucible according to the invention or prepared according to the method of the invention in particular for the solidification of silicon.
L'invention va maintenant être décrite au moyen de l'exemple suivant donné bien entendu à titre illustratif et non limitatif de l'invention. The invention will now be described by means of the following example given of course by way of illustration and not limitation of the invention.
Exemple Example
Une barbotine, constituée à 23 % d'un mélange de poudre de S13N4, 4 % d'alcool polyvinylique PVA et 73 % d'eau en pourcentages massiques, est passée dans un broyeur planétaire rempli de billes en carbure de silicium ou en agate.  A slip, consisting of 23% of a mixture of S13N4 powder, 4% PVA polyvinyl alcohol and 73% water in percentages by weight, is passed through a planetary mill filled with silicon carbide or agate balls.
L'objectif des billes en carbure de silicium ou en agate n'étant que de réduire les agglomérats de poudre, des billes en nitrure de silicium sont également envisageables, le risque de pollution à l'azote étant très limité.  Since the purpose of the silicon carbide or agate balls is only to reduce the powder agglomerates, silicon nitride balls are also conceivable, the risk of nitrogen pollution being very limited.
Le milieu fluide ainsi formé est ensuite pistoletté (pression d'air comprimé de 2,5 bars, buse de 0,4 mm placée à une trentaine de centimètres du substrat) sur la totalité de la surface interne d'un creuset à revêtir.  The fluid medium thus formed is then spray-dried (compressed air pressure of 2.5 bar, 0.4 mm nozzle placed at about thirty centimeters from the substrate) over the entire internal surface of a crucible to be coated.
Le dépôt ainsi obtenu est séché à l'air chaud à une température inférieure à The deposit thus obtained is dried in hot air at a temperature below
50 °C. 50 ° C.
On obtient ainsi une sous-couche d'une épaisseur de l'ordre de 50 μπι constituée de poudres liées par le PVA.  An underlayer of a thickness of about 50 μπι consisting of powders bound by PVA is thus obtained.
Cette couche est ensuite soumise à un palier de 3h à 1100 °C sous air pour déliantage et oxydation des poudres.  This layer is then subjected to a step of 3 hours at 1100 ° C. in air for debinding and oxidation of the powders.
Une fois ce traitement d'oxydation réalisé, la fraction massique d'oxygène dans le revêtement est de 29% mesurée par la technique IGA (Interstitial Gas Analysis). Cette technique, bien connue de l'homme de l'art, permet d'établir que la fraction volumique de silice correspondante est de 64%, ce qui correspond à une teneur en silice de 56% en poids par rapport au poids total du revêtement. La quantité massique de Si3N4 par rapport à la masse totale du mélange de silice et Si3N4, est donc de 44%. Once this oxidation treatment has been carried out, the mass fraction of oxygen in the coating is 29% measured by the IGA (Interstitial Gas Analysis) technique. This technique, well known to those skilled in the art, makes it possible to establish that the corresponding volume fraction of silica is 64%, which corresponds to a silica content of 56% by weight relative to the total weight of the coating. . The quantity by weight of Si 3 N 4 relative to the total mass of the silica mixture and Si 3 N 4 is therefore 44%.
En figure 1 est présenté le revêtement obtenu à l'issue de l'exemple 1. Ce revêtement se présente comme une matrice de S1O2 dans laquelle sont incorporés des grains de Si3N4 non oxydés. In Figure 1 is presented the coating obtained at the end of Example 1. This coating is in the form of a matrix of SiO 2 in which are incorporated grains of non-oxidized Si 3 N 4 .

Claims

REVENDICATIONS
1. Substrat caractérisé en ce qu'il est revêtu au moins partiellement en surface, d'un revêtement contenant au moins une couche dite « barrière » comprenant de la silice et un ou plusieurs matériau(x) X choisi(s) parmi SiC, Si, S13N4, couche dans laquelle la quantité massique de X varie de 25% à 50% par rapport à la masse totale de la couche barrière, ladite couche barrière étant formée de grains d'un ou plusieurs matériaux X recouverts au moins partiellement par une enveloppe de silice, la couche barrière étant disposée en contact direct avec le substrat. A substrate characterized in that it is coated at least partially at the surface with a coating containing at least one so-called "barrier" layer comprising silica and one or more material (s) X chosen from SiC, If, S13N4, a layer in which the mass quantity of X varies from 25% to 50% relative to the total mass of the barrier layer, said barrier layer being formed of grains of one or more materials X at least partially covered by a silica shell, the barrier layer being disposed in direct contact with the substrate.
2. Substrat selon la revendication 1, caractérisé en ce que la couche barrière présente une porosité ouverte allant de 0 à 5%.  2. Substrate according to claim 1, characterized in that the barrier layer has an open porosity ranging from 0 to 5%.
3. Substrat selon l'une des revendications précédentes caractérisé en ce que la couche barrière présente une perméabilité inférieure à 10"15 m2. 3. Substrate according to one of the preceding claims characterized in that the barrier layer has a permeability less than 10 "15 m 2 .
4. Substrat selon l'une des revendications précédentes caractérisé en ce que la couche barrière se présente sous la forme d'une matrice de silice dans laquelle sont incorporés des grains d'un ou plusieurs matériau(x) X.  4. Substrate according to one of the preceding claims characterized in that the barrier layer is in the form of a silica matrix in which are incorporated grains of one or more material (x) X.
5. Substrat selon l'une des revendications précédentes caractérisé en ce que la couche barrière comprend entre 50% et 75% de silice en poids par rapport à son poids total.  5. Substrate according to one of the preceding claims characterized in that the barrier layer comprises between 50% and 75% silica by weight relative to its total weight.
6. Substrat selon l'une des revendications précédentes, caractérisée en ce que l'épaisseur de la couche « barrière» est comprise entre 10 μιη et 100 μιη et préférentiellement entre 20 μιη et 50 μιη.  6. Substrate according to one of the preceding claims, characterized in that the thickness of the "barrier" layer is between 10 μιη and 100 μιη and preferably between 20 μιη and 50 μιη.
7. Substrat selon l'une des revendications précédentes, caractérisé en ce que la surface spécifique de la couche barrière est comprise entre 5 cm2/g et 5 m2/g, en particulier entre 100 cm2/g et 1 m2/g. 7. Substrate according to one of the preceding claims, characterized in that the specific surface of the barrier layer is between 5 cm 2 / g and 5 m 2 / g, in particular between 100 cm 2 / g and 1 m 2 / boy Wut.
8. Substrat selon l'une des revendications précédentes, caractérisé en ce que le revêtement comprend, en outre, en surface de la couche barrière, une couche antiadhérente.  8. Substrate according to one of the preceding claims, characterized in that the coating further comprises, on the surface of the barrier layer, an anti-adhesive layer.
9. Substrat selon l'une des revendications précédentes, caractérisée en ce qu'il est formé par un matériau choisi parmi le carbure de silicium SiC, le nitrure de silicium S13N4, les composites comprenant du graphite et du carbure de silicium ou comprenant du graphite et du nitrure de silicium et le graphite siliciuré. 9. Substrate according to one of the preceding claims, characterized in that it is formed by a material selected from silicon carbide SiC, silicon nitride S13N4, the composites comprising graphite and silicon carbide or comprising graphite and silicon nitride and silicided graphite.
10. Substrat selon l'une des revendications précédentes caractérisé en ce qu'il s'agit d'un creuset pour la solidification de silicium. 10. Substrate according to one of the preceding claims characterized in that it is a crucible for the solidification of silicon.
11. Procédé de préparation d'un substrat selon l'une des revendications précédentes, ledit substrat étant revêtu au moins partiellement en surface par un revêtement formant barrière aux gaz, caractérisé en ce que ledit procédé comprend au moins les étapes consistant à :  11. A method of preparing a substrate according to one of the preceding claims, said substrate being coated at least partially at the surface with a coating forming a gas barrier, characterized in that said method comprises at least the steps of:
a) disposer d'un milieu fluide comprenant au moins un ou plusieurs matériau(x) X choisi parmi SiC, Si, Si3N4, a) having a fluid medium comprising at least one or more materials (x) X selected from SiC, Si, Si 3 N 4 ,
b) appliquer ledit milieu fluide sur la surface du substrat, en une quantité suffisante pour y former un dépôt, b) applying said fluid medium to the surface of the substrate, in an amount sufficient to form a deposit,
c) traiter ledit dépôt sous atmosphère oxydante, à une température comprise entre 1000 °C et 1300 °C et dans des conditions suffisantes pour former une couche dite « barrière » comprenant de la silice et un ou plusieurs matériau(x) X choisi(s) parmi SiC, Si, Si3N4, couche dans laquelle la quantité massique de X varie de 25% à 50% par rapport à la masse totale de la couche barrière, ladite couche barrière étant formée de grains d'un ou plusieurs matériaux X recouverts au moins partiellement par une enveloppe de silice, la couche barrière étant disposée en contact direct avec le substrat. c) treating said deposition under an oxidizing atmosphere, at a temperature of between 1000 ° C. and 1300 ° C. and under conditions sufficient to form a so-called "barrier" layer comprising silica and one or more selected material (s) X (s) ) among SiC, Si, Si 3 N 4 , in which the mass quantity of X varies from 25% to 50% relative to the total mass of the barrier layer, said barrier layer being formed of grains of one or more materials X covered at least partially by a silica shell, the barrier layer being disposed in direct contact with the substrate.
12. Procédé selon la revendication 1 1 dans lequel le milieu fluide comprend en outre de la silice.  12. The method of claim 11 wherein the fluid medium further comprises silica.
13. Procédé selon la revendication 11 ou 12, caractérisé en ce qu'il comprend, entre l'étape b) de formation d'un dépôt et l'étape c) de traitement sous atmosphère oxydante, au moins une étape de séchage à une température inférieure à 50°C et de préférence allant de 20°C et 50°C.  13. The method of claim 11 or 12, characterized in that it comprises, between the step b) of forming a deposit and the step c) of treatment in an oxidizing atmosphere, at least one drying step at a temperature below 50 ° C and preferably from 20 ° C to 50 ° C.
14. Procédé selon l'une des revendications 11 à 13, dans lequel l'étape de traitement sous atmosphère oxydante est effectuée à une température allant de 1100°C à 14. The method according to one of claims 11 to 13, wherein the treatment step in an oxidizing atmosphere is carried out at a temperature ranging from 1100 ° C to
1300°C et de préférence entre 1150°C et 1200°C. 1300 ° C and preferably between 1150 ° C and 1200 ° C.
15. Procédé selon l'une des revendications 11 à 14, dans lequel l'étape c) de traitement sous atmosphère oxydante est effectuée pendant une durée allant de 1 heure à 5 heures, de préférence allant de 2 heures à 3 heures.  15. Method according to one of claims 11 to 14, wherein the step c) treatment under an oxidizing atmosphere is carried out for a period ranging from 1 hour to 5 hours, preferably from 2 hours to 3 hours.
16. Procédé selon l'une des revendications 11 à 15 comprenant, après le traitement sous atmosphère oxydante, une étape de traitement en présence d'un gaz neutre à une température comprise entre 1400°C et 1500°C. 16. Method according to one of claims 11 to 15 comprising, after the treatment in an oxidizing atmosphere, a treatment step in the presence of a neutral gas at a temperature between 1400 ° C and 1500 ° C.
17. Procédé selon la revendication 11 dans lequel l'étape b) est renouvelée plusieurs fois avant la mise en œuvre de l'étape c). 17. The method of claim 11 wherein step b) is repeated several times before the implementation of step c).
18. Procédé selon l'une des revendications 1 1 à 17 dans lequel le milieu fluide utilisé à l'étape a) comprend un ou plusieurs matériau(x) X en une quantité allant de 15 à 35 % en poids par rapport au poids total dudit fluide.  18. Method according to one of claims 1 1 to 17 wherein the fluid medium used in step a) comprises one or more material (x) X in an amount ranging from 15 to 35% by weight relative to the total weight. said fluid.
EP14780618.6A 2013-09-16 2014-09-12 Substrate with low-permeability coating for the solidification of silicon Withdrawn EP3046895A1 (en)

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