Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D9/00—Crystallisation
• • 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
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
  • C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
  • B01J19/24—Stationary reactors without moving elements inside
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B20/00—Processes specially adapted for the production of quartz or fused silica articles, not otherwise provided for
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
  • C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
  • C03C17/225—Nitrides
• • 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
  • C04B41/52—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
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • C30B11/00—Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method
  • C30B11/002—Crucibles or containers for supporting the melt
• • C—CHEMISTRY; METALLURGY
  • C30—CRYSTAL GROWTH
  • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
  • 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 to a crucible useful for solidifying 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 treatment of silicon in the molten state.
• 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.
• Photo voltaic cells are, for the most part, 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.
• 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.
• this anti-adherent behavior is based essentially on the presence of silicon nitride, S1 3 N 4 , 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 S1 3 N 4
• 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 contamination which may exist in the areas of the silicon ingot formed in direct contact with or near walls of the crucible, makes the ingot partly unsuitable for use in photo voltaic applications.
• the present invention aims precisely to provide new crucibles useful for the solidification of a silicon ingot from molten silicon, satisfying these needs.
• the inventors have, in fact, discovered that these problems can be solved by forming on the surface of the internal walls of a conventional crucible a polysilazane-based coating consisting of a stack of non-joined tiles having a particular shear strength.
• a silicon ingot formed in contact with this stack is essentially detached by cohesive rupture within said stack.
• Polysilazane has already been selected as a material to enhance the oxidation resistance of certain carbon substrates.
• the methods proposed for its implementation consist in the formation, on the surface of the material to be treated, of a monolayer deriving from the thermal decomposition by pyrolysis of the polysilazane previously deposited (EP 0 411 611 and Journal of the European Ceramic Society , 16 (1996), 1115-1120).
• the present invention relates, according to a first aspect, to a crucible useful for solidifying a silicon ingot from molten silicon, characterized in that it is coated at least partially on its inner surface with least one layer formed of a material obtained by thermal decomposition of polysilazane (s), said layer having a shear strength greater than 1 Pa and less than or equal to 500 MPa and being in the form of a stack of contiguous strata of non-joined tiles.
• s polysilazane
• said layer has a laminated structure, each stratum being formed of non-joined and non-superposed tiles.
• the layer derived from the thermal decomposition of polysilazane has a stratified architecture, considering that it is formed of at least two, even of several superimposed layers and disposed parallel to the treated inner surface of said crucible, each stratum being formed of non-joined tiles.
• the layer considered according to the invention has the appearance of a stack of tiles.
• a layer according to the invention may also be designated in the text as being "a stack of layers", each stratum being formed of non-joined tiles, or even more simply “a stack of tiles", or “Stacking”.
• the stack according to the invention may comprise from 2 to 100 layers of tiles, said layers being superposed and contiguous.
• the term "contiguous" means that the strata in question are contiguous and adjacent.
• the presence of more than three contiguous tile layers within the stack according to the invention makes it possible to obtain a crucible that can be reused as it is, that is to say without having to implement treatment steps. prerequisites before reuse.
• Such a laminated structure also makes it possible to distribute the constraint developed in the multiple interfaces more homogeneously, especially during the cooling of the silicon ingot.
• Polysilazanes are organosilicon polymers whose main backbone consists of a sequence of silicon and nitrogen atoms.
• Such compounds are in particular already used for the purpose of surface formation of various substrates such as, for example, graphite or silica, a coating with antioxidant and sealing properties.
• this type of polymer is particularly advantageous for accessing a layer in the form of a stack of non-joined tiles able, on the one hand, to manifest properties anti-adherent with respect to the solid silicon and, secondly, to ensure an increased level of purity to the corresponding silicon ingot.
• the crucibles according to the invention allow an easy detachment of the solidified silicon ingots, and this significantly reduces their pollution by the release coating.
• the anti-adhesive properties of the crucibles according to the invention are in particular obtained via the presence of the oxidized porous layer whose deoxidation kinetics are slow enough to prevent the infiltration of the liquid silicon into the layer until contact with the substrate, and therefore allow its detachment of the substrate.
• the lifetime of the crucibles according to the invention will depend in particular on the number of contiguous tile layers present in the stack, and will be even higher than this number will be important.
• the present invention aims at providing a method for preparing a crucible as defined above, comprising at least the formation of said layer via (a) the formation of a first layer of tiles by (i ) contacting the inner surface of said crucible with a solution comprising at least one polysilazane, (ii) condensation-crosslinking said polysilazane, (iii) pyrolysis under controlled atmosphere and temperature and, optionally, (iv) oxidation annealing, followed by (b) forming at least one new tile stratum, contiguous to the stratum formed in step (a), by replicating steps (i) to (iii) and, optionally, (iv), said method being characterized in that the pyrolysis of step (iii) of said process is carried out at a temperature plateau carried out at a temperature of at least 1000 ° C for at least 1 hour.
• the total number of layers in the stack according to the invention will depend on the repetition number of step (b) indicated above. This number of layers can thus be adjusted with respect to the thickness of the desired stack and the desired properties.
• the present invention also relates, in another of its aspects, the use of a crucible as defined above, for the directed solidification of silicon.
• the crucibles according to the invention are coated at least partially on their inner surface with at least one layer formed of a material obtained by thermal decomposition of polysilazane (s), with said layer being in the form of a stack of non-joined tiles, and having a particular shear strength.
• the term "internal surface” means the outer surface of the walls defining the interior volume of the crucible.
• the "internal volume of the crucible” designates, within the meaning of the invention, the volume defined by the bottom surface and the side walls of the crucible base body.
• the material forming the layer according to the invention derives from the thermal decomposition of polysilazane (s).
• the polysilazanes suitable for the invention may be represented by the following formula: ## STR2 ## wherein R ', R ", R'", R *, R ** and R *** represent independently of one another a hydrogen atom or a substituted or unsubstituted alkyl, aryl, vinyl or (trialkoxysilyl) alkyl radical, n and p having values such that the polysilazane has a mean molecular weight ranging from from 150 to 150,000 g / mol.
• the material forming the layer according to the invention may be based on silicon carbide SiC, silicon nitride Si 3 N 4 and / or silicon oxycarbonitride.
• silicon oxycarbonitride is intended to denote compounds of the general formula Si x O y N z C w , such as, for example, those described in US Pat. No. 5,438,025, for example S1NCO2 or Si No, 52 ⁇ , 45 Co, 3 2 .
• the material forming the layer according to the invention derives from a pyrolysis-type heat treatment of a polysilazane.
• the pyrolysis conditions in terms of temperature, speed and temperature maintenance and / or the nature of the atmosphere considered during the pyrolysis, for example argon or nitrogen, it is possible to on the one hand to access materials of particular composition for a given stratum and thus to make a stack of layers of tiles of identical or different chemical nature and, on the other hand, to modulate the structural organization of each of the strata. It is precisely through this modulation in terms of composition and / or structural organization of the material forming each layer of tiles that it is possible to achieve the required properties, in terms of shear strength of the layer according to the invention.
• the tiles of the stack according to the invention may be silicon carbide SiC, silicon nitride S1 3 N 4 , a mixture of SiC and S1 3 N 4 , or silicon oxycarbonitride SiCNO.
• the tiles forming all of the layers constituting said layer may be of the same material.
• the tiles forming all the layers constituting said layer may consist of two different materials.
• the tiles may have different compositions from one stratum to another, with regard, for example, to different conditions used to form each of the corresponding strata.
• the stack of non-joined tile layers may be made from any technique known to those skilled in the art, and in particular by chemical vapor deposition (CVD) or dipping, and more particularly those described in the publication Bill and al. (J. of the European Ceramic Soc., Vol.16, 1996: 1115).
• CVD chemical vapor deposition
• dipping and more particularly those described in the publication Bill and al. (J. of the European Ceramic Soc., Vol.16, 1996: 1115).
• the morphological characteristics of the tiles obtained according to the invention will of course also depend on the conditions of their formation, and in particular on the nature of the deposition solution as well as on the parameters chosen for the heat treatment and in particular on the temperature.
• each of the strata of tiles forming the stack according to the invention may be between 0.2 and 50 ⁇ , in particular between 1 and 50 ⁇ , for example between 0.5 and 20 ⁇ . for example between 1 and 5 ⁇ .
• the thickness of the stack according to the invention may be between 10 and 500 ⁇ , in particular between 20 and 500 ⁇ , for example between 30 and 400 ⁇ , preferably between 50 and 200 ⁇ .
• the lateral spacing between two tiles can be between 0.1 ⁇ and 20 ⁇ , in particular be less than 5 ⁇ , and preferably less than 1 ⁇ .
• the lateral dimension of the tiles can be between 4 ⁇ and 150 ⁇ , for example between 10 ⁇ and 30 ⁇ .
• the thickness and lateral dimension of the tiles as well as the lateral spacing between two tiles can be determined conventionally by scanning electron microscopy (SEM).
• a tile is characterized by a dimension of thickness less than its lateral dimension (length, width, diameter).
• the lateral dimension / thickness ratio of the tiles may be between 1.2 and 200.
• the layer in the form of a stack of non-joined tiles according to the invention is also characterized by its shear strength, which must be greater than 1 Pa and less than or equal to 500 MPa.
• the "shear strength" of a layer means the mechanical resistance to stress developed in the plane of the layer.
• This shear strength parameter can be determined by any conventional technique known to those skilled in the art, and in particular by the measurement defined in ASTM D1002, for example by the eXpert 2611 machine manufacturer ADMET.
• the layer according to the invention should not be subject to a phenomenon of disintegration or crumbling during simple manipulation of the crucible. Similarly, it must not be altered by the stresses induced during the melting of the silicon charge, in particular those induced by natural convection.
• the layer according to the invention has a shear strength greater than 1 Pa, for example greater than 10 kPa, especially greater than 50kPa.
• the layer according to the invention must also have a shear strength lower than the stress induced by the difference in thermal expansion between the solidifying silicon and the crucible substrate.
• the layer according to the invention has a shear strength lower than the critical stress in shear silicon, that is to say less than the minimum stress which promotes the appearance of dislocations of silicon when it is in his field of plasticity.
• the layer according to the invention may have a shear strength of less than or equal to 300 MPa, for example less than or equal to 200 MPa, for example less than or equal to 100 MPa, for example less than or equal to 5 MPa.
• the invention may be advantageously carried out on any type of conventional crucible, and for example on crucibles consisting of a dense ceramic substrate, for example silicon carbide SiC, silicon nitride S1 3 N 4 or silica Si0 2 , or a porous substrate, for example graphite.
• a dense ceramic substrate for example silicon carbide SiC, silicon nitride S1 3 N 4 or silica Si0 2
• a porous substrate for example graphite.
• a graphite substrate will be selected, and in particular isostatic, pyrolytic, glassy, fibrous, carbon-carbon composite or flexible graphite which advantageously have good temperature resistance.
• the crucible may further comprise at least partially on its inner surface an intermediate insulating layer.
• This intermediate insulating layer is then located between the inner surface of the crucible and the coating layer according to the invention, that is to say formed of a material obtained by thermal decomposition of polysilazane (s).
• Such an intermediate insulating layer is intended to isolate said substrate from the layer of the coating.
• this layer is generally formed, at least partially, on the inner surface of said crucible prior to the formation of the layer formed of a material obtained by thermal decomposition of polysilazane (s) according to the invention.
• This intermediate insulating layer affixed to the surface of the material forming said crucible may in particular be a dense and continuous layer of ceramic capable of ensuring a barrier or even antioxidant behavior.
• this intermediate insulating layer may be formed of at least two different materials, alternately constituting this insulating layer.
• the first type of one of the materials can be formed mainly, or even solely, of SiO 2 silica, and the other material can be formed mainly, or even only, of silicon carbide SiC.
• the crucibles according to the invention may in particular be obtained by means of a preparation process comprising at least the formation of said layer via (a) the formation of a first layer of tiles by (i) setting contacting the inner surface of said crucible with a solution comprising at least one polysilazane, (ii) condensation-crosslinking said polysilazane, (iii) pyrolysis under controlled atmosphere and temperature, and optionally (iv) oxidation annealing, followed by b) forming at least one new tile stratum contiguous to the stratum formed in step (a), by reproducing steps (i) to (iii) and, optionally, (iv), said method being characterized in that the pyrolysis of step (iii) of said process is carried out at a temperature plateau carried out at a temperature of at least 1000 ° C for at least 1 hour.
• a method according to the invention may comprise a preliminary step of forming an intermediate insulating layer on the inner surface of said crucible.
• the number of layers of tiles in the layer according to the invention will depend on the number of repetitions of steps (a) and (b).
• the stack according to the invention may comprise from 2 to 100 layers formed of tiles, these layers being superposed and contiguous.
• one of the steps (a) or (b) is carried out under a reactive atmosphere with respect to the material derived from the polysilazane, for example under nitrogen or under air, and the other step under an inert atmosphere, for example under argon.
• the polysilazane solution can be deposited by any conventional technique known to those skilled in the art, and for example be deposited by dipping, by turning, by pistoltician or with the aid of a brush.
• the solution comprising at least one polysilazane may also comprise a solvent, for example an aprotic anhydrous solvent, and a polymerization initiator, for example of the organic peroxide type.
• a solvent for example an aprotic anhydrous solvent
• a polymerization initiator for example of the organic peroxide type.
• aprotic anhydrous solvent there may be mentioned toluene, dimethylformamide, dimethylsulfoxide and dibutyl ether.
• polymerization initiator As a polymerization initiator, particular mention may be made of dicumyl peroxide, diperoxyester and peroxycarbonate.
• the morphological characteristics of the tiles obtained according to the invention depend in particular on the viscosity of the polysilazane solution deposited, and therefore in particular on the volume concentration of polysilazane in this solution.
• the polysilazane solution used according to the invention comprises from 5 to 90% by volume, in particular from 10 to 70% by volume, for example from 10 to 50% by volume, for example from 20 to 50% by volume of polysilazane (s).
• This solution may also further comprise silicon carbide powders and / or silicon nitride powders and / or silicon powders.
• the addition of such powders advantageously makes it possible to adjust the viscosity of the polysilazane solution, and thus to better control the morphology of the tile layers of the stack according to the invention.
• the pyrolysis step is carried out under a controlled atmosphere, for example in an atmosphere consisting of argon, nitrogen or air, preferably argon.
• An additional step of oxidation annealing in air can also be performed.
• This annealing step is of particular interest when the pyrolysis step is carried out under an atmosphere consisting of argon, nitrogen or ammonia.
• the material obtained is in effect then either SiC or S1 3 N 4 , or a material of intermediate composition and it may be advantageous to oxidize it to increase its shear strength.
• This annealing step is also advantageous for reinforcing the shear strength of a stack of tile layers obtained by pyrolysis carried out under an atmosphere consisting of argon and / or nitrogen.
• the shear strength of such a stack of tile layers is already greater than 1 Pa and less than or equal to 500 MPa.
• the annealing step has a lower interest since the material obtained is already oxidized at the end of the pyrolysis.
• the method according to the invention makes it possible to limit, or even avoid, the contamination of the silicon ingot, and thus to obtain silicon ingots of greater purity compared to those obtained to date, and this while implementing conventional and inexpensive deposition techniques.
• the average purity of the coatings obtained from polysilazane solutions is greater than 99.5% by weight, or even 99.996% by weight, which is much greater than that of coatings obtained from powders, for example S1 powders. 3 N 4 which have purities of the order of 98%, or even 99.96% or even less than 98%, or even 99.96%.
• FIG. 1 schematically shows a side view of a crucible according to the invention
• FIG. 2 schematically shows a top view of a crucible according to the invention.
• the crucible (1) is coated on its inner surface (2) with a layer (3) formed of a material obtained by thermal decomposition of polysilazane (s).
• This layer (3) is in the form of a stack of non-joined tiles (4), which gives it a cracked appearance on its upper surface shown in Figure 2.
• this stack comprises several contiguous tile layers (4a) and (4b), each stratum being formed of non-contiguous and non-overlapping tiles.
• the crucible to be treated is immersed in the various solutions described below using a nacelle and tongs.
• the crucible used is a graphite crucible 2020PT TM of the company CARBONE LORRAINE having an outer diameter of 50 mm, an inner diameter of 30 mm and a height of 50 mm, which is previously cleaned with acetone before being put into operation. during the melting of the silicon, it is covered by a silica cover.
• the surface of the crucible to be treated according to the invention is, in addition, previously coated with an insulating thick continuous SiC layer about 6 ⁇ thick, according to the protocol described in the publication Bill et al. (J. of the European Ceramic Soc., Vol.16, 1996: 1115) cited above.
• the graphite of the crucible is thus infiltrated to a depth of approximately 50 ⁇ .
• a multi-layer layer according to the invention or a stack of non-joined tiles according to the invention was formed on this crucible, according to the following protocol.
• Each tile stratum is formed by dipping from a solution containing 30% by volume of polysilazane (Ceraset PSZ20 TM from CLARIANT) in toluene, this solution further comprising 0.1% by weight of dicumyl peroxide ( Luperox DC) as a polymerization initiator.
• the crucible is immersed in this solution by following three cycles of soaking for 5 minutes, each soaking cycle being followed by a polymerization annealing at 200 ° C for 2 hours, followed by pyrolysis for two hours at 1400 hours. ° C, all under nitrogen, then an oxidation annealing under air for two hours at 1000 ° C.
• a stack of non-contiguous tiles with a thickness of between 180 and 200 ⁇ is thus obtained, which consists of layers of tiles of variable thickness ranging between 13 and 28 ⁇ .
• the crucible according to the invention thus formed is tested as follows:
• 70 g of solid silicon are then placed manually and very gently in the resulting crucible, then melted according to the following cycle: rise in temperature at a rate of 200 ° C. per hour up to 1000 ° C. under a primary vacuum, followed by 1-hour stage with introduction of a static argon atmosphere, then temperature rise at a rate of 150 ° C per hour up to 1500 ° C and maintained at this temperature for 4 hours, and finally descent at a rate of 50 ° C per hour up to 1200 ° C, and then maintain at this temperature for 1 hour.
• the cooling is then carried out freely until room temperature.
• the silicon ingot thus formed is detached from the crucible according to the invention by cohesive rupture inside the coating.
• the purity of the coating used in the crucible will be found in the silicon ingot. Pure silicon is obtained at more than 99.6% or even more than 99.996%.
• the crucible used is identical to the crucible described in Example 1.
• the surface of the crucible to be treated according to the invention is first coated with an insulating dense continuous layer of SiC about 45 ⁇ thick, coated with an insulating layer of Si0 2 of about 4 ⁇ , obtained by reactive infiltration according to the protocol described in the publication Israel et al. (J. of the European Ceramic Soc., Vol 31, (201 1), 2167-2174).
• a stack of non-joined tiles according to the invention was formed on the surface of the SiO 2 intermediate layer according to the protocol described in Example 1.
• the crucible according to the invention thus formed, and tested according to the protocol described in Example 1, proves to be capable of forming silicon ingots of purity greater than 99.996%.
• the crucible used is a vitreous silica crucible manufactured by MondiaQuartz having an outer diameter of 50 mm, an internal diameter of 30 mm and a height of 50 mm, it is previously cleaned with acetone before being used. .
• a stack of non-joined tiles according to the invention was formed according to the protocol described in Example 1.
• Example 4 The crucible according to the invention thus formed, and tested according to the protocol described in Example 1, also proves to be conducive to forming very pure silicon ingots.
• Example 4
• the crucible used is a 2020PT TM graphite crucible from the company
• CARBONE LORRAINE having an external diameter of 50 mm, an internal diameter of 30 mm and a height of 50 mm, it is first cleaned with acetone and then degassed under a primary vacuum at 50 ° C. for 30 minutes, before being put into artwork.
• SiC approximately 14 ⁇ thick SiC approximately 14 ⁇ thick, according to the protocol described in the publication Bill et al.
• a stack of thin layers according to the invention was formed on this crucible, according to the following protocol.
• the layer according to the invention is made from a solution containing 30% by volume of polysilazane (Ceraset PSZ20 TM from Clariant) in toluene, this solution also comprising 0.1% by weight of dicumyl peroxide ( Luperox DC) as a polymerization initiator.
• the crucible is immersed using a nacelle and tongs in this solution and then it leaves the bath slowly, and the excess liquid is evacuated by gravity.
• the soaking is followed by a polymerization step under argon for one hour at 150 ° C. and then pyrolysis under argon for two hours at 1000 ° C.
• a layer of thickness between 60 and 95 ⁇ is thus obtained, which consists of a stack of layers, each layer being formed of tiles of variable thickness, between 3 and 12 ⁇ .
• the crucible according to the invention thus formed is tested as follows:
• 70 g of electronic grade silicon are then manually deposited very gently in the resulting crucible.
• the silicon is then melted by following the following cycle: temperature rise at a rate of 200 ° C. per hour to 1000 ° C. under primary vacuum, followed by a one-hour stage with introduction of a static argon atmosphere, then temperature rise at a rate of 150 ° C per hour up to 1500 ° C and maintained at this temperature for 4 hours, and finally descent at a speed of 50 ° C per hour to 1200 ° C.
• the cooling is then carried out freely until room temperature.
• the silicon ingot thus formed is detached from the crucible according to the invention after a few shocks on its periphery mainly by cohesive rupture inside the coating.
• the crucible used is a vitreous silica crucible manufactured by MondiaQuartz having an outer diameter of 50 mm, an inside diameter of 45 mm and a height of 50 mm, it is previously cleaned with acetone before being used. .
• a stack of thin layers according to the invention was formed on this crucible, from a solution containing 50% by volume of polysilazane (Ceraset PSZ20 TM from Clariant) in anhydrous dibutyl ether (Sigma Aldrich).
• the crucible is immersed using a nacelle and tongs in this solution and then it leaves the bath slowly, and the excess liquid is evacuated by gravity.
• the soaking is followed by a polymerization step under argon for two hours at 200 ° C. and then pyrolysis under argon for two hours at 1000 ° C.
• a layer of thickness between 65 and 110 ⁇ is thus obtained, which consists of a stack of layers, each layer being formed of tiles of variable thickness, between 1 and 10 ⁇ .
• the crucible according to the invention thus formed is tested as follows:
• the cooling is then carried out freely until room temperature.
• the silicon ingot thus formed is detached from the crucible according to the invention after a few shocks on its periphery mainly by cohesive rupture inside the coating.
• the crucible used is a graphite crucible R6510 TM manufactured by the company SGL-Carbon having an outer diameter of 50 mm, an internal diameter of 40 mm and a height of 50 mm.
• SiC layer is coated with an insulating dense continuous SiC layer about 70 ⁇ thick, obtained by chemical vapor phase reaction (CVD).
• the SiC layer is oxidized beforehand by annealing at 1200 ° C. in air for 5 hours.
• a stack of thin layers according to the invention was formed on this crucible, from a solution containing 50% by volume of polysilazane (Ceraset PSZ20 TM from Clariant) in anhydrous dibutyl ether (Sigma Aldrich). More precisely, the crucible is immersed with a nacelle and tongs in this solution, then it leaves the bath slowly, and the excess liquid is evacuated by gravity. The soaking is followed by a polymerization step under air for two hours at 200 ° C. and then pyrolysis under air for two hours at 1000 ° C.
• a layer of thickness between 60 and 90 ⁇ is thus obtained, which consists of a stack of layers, each layer being formed of tiles of variable thickness, between 1 and 10 ⁇ .
• the crucible according to the invention thus formed is tested as follows:
• the cooling is then carried out freely until room temperature.
• the silicon ingot thus formed is detached from the crucible according to the invention after a few shocks on its periphery mainly by cohesive rupture inside the coating.
• the crucible used is a vitreous silica crucible manufactured by the company
• MondiaQuartz has an outer diameter of 50 mm, an inner diameter of 45 mm and a height of 50 mm, it is previously cleaned with acetone before being implemented.
• a stack of thin layers according to the invention was formed on this crucible, from a solution containing 80% by volume of polysilazane (Ceraset PSZ20 TM from Clariant) in anhydrous dibutyl ether (Sigma Aldrich).
• the polysilazane solutions are applied to the crucible by spray gassing.
• the pistoltician is followed by polymerization step under air for thirty minutes at 500 ° C on a hot plate.
• This pistoltician / polymerization sequence at 500 ° C. is repeated six times, and then the crucible thus coated undergoes a pyrolysis step at 1000 ° C. for one hour under nitrogen.
• the crucible according to the invention thus formed is tested as follows:
• the cooling is then carried out freely until room temperature.
• the silicon ingot thus formed is detached from the crucible according to the invention after a few shocks on its periphery, mainly by cohesive rupture inside the coating.
• the crucibles used are vitreous silica crucibles manufactured by MondiaQuartz having an external diameter of 145 mm, an internal diameter of 140 mm and a height of 150 mm, they are first cleaned with acetone and ethanol before to be implemented.
• control crucible The inner surface of the control crucible is coated in its entirety with a standard non-stick coating made of silicon nitride powder (SNE10, UBE) suspended in a mixture of water and PVA. This suspension is sprayed into 4 successive layers on the inner surface of the crucible, with air drying for 5 minutes between each layer, then it is oxidized at 900 ° C for 2 hours in air in position on its substrate. This succession of steps, 4-layer spraying / drying / oxidation, is repeated twice.
• SNE10 silicon nitride powder
• the vertical walls of the crucible according to the invention are coated on its inner surface with the same coating as above.
• the internal surface forming the bottom of the crucible according to the invention is coated with a stack of thin layers according to the invention, formed from a solution containing 50% by volume of polysilazane (Ceraset PSZ20 TM). CLARIANT company) in anhydrous dibutyl ether (Sigma Aldrich).
• This sequence of deposition / rotation / polymerization / pyrolysis steps is repeated thirty times, and then the bottom of the crucible thus coated is subjected to an oxidation annealing by exposing the crucible in air for two hours at 1000 ° C.
• a layer of thickness between 50 and 120 ⁇ is obtained, which consists of a stack of layers, each layer being formed of tiles of variable thickness, between 1 and 10 ⁇ .
• the crucibles thus formed are tested as follows:
• the silicon ingot formed in the control crucible is detached from the crucible spontaneously.
• the ingot formed in the crucible according to the invention that is to say, whose bottom is in accordance with the invention, comes off after a few shocks on its periphery mainly by cohesive rupture inside the coating.
• the ingots thus obtained are cut into vertical slices 20 mm thick, and life analyzes of the minority carriers in these slices are performed.
• the principle of this measurement is as follows: a pulsed laser excitation of the surface (up to 1 mm deep) makes it possible to generate electron-hole pairs in the semiconductor material which will recombine after a characteristic time (duration of life) which is strongly dependent on the amount of impurities present, from the materials of the crucible.
• the mapping of the lifetimes in the slices of the ingots is carried out by measuring the photoconductivity decay induced by the generation of these charge carriers, and is carried out on a WT200 device from Semilab.

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• 2010
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