Method for preparing a coated substrate, a coated substrate, and its use

Abstract

The present invention relates to a method for producing a coated substrate, in which a porous substrate is first provided with at least one surface sealing layer in at least one region of the surface. At least one aqueous suspension is then applied to the at least one surface sealing layer, the at least one aqueous suspension comprising at least one refractory metal carbide and water. The substrate is then subjected to a sintering treatment. The present invention further relates to a coated substrate produced or capable of being produced using the method according to the invention, and to the use of such a coated substrate.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing coated substrates. In this method, first, at least one surface sealing layer is provided on at least one area of ​​the surface of a porous substrate. Next, at least one aqueous suspension is applied to at least one surface sealing layer, the at least one aqueous suspension comprising at least one refractory metal carbide and water. Next, the substrate is subjected to a sintering process. The present invention further relates to coated substrates manufactured or that can be manufactured using the method according to the present invention, and to the use of such coated substrates.

[0002] Refractory metal carbides such as tantalum carbide (TaC) are generally characterized by their high mechanical, chemical, and thermal resistance. The use of these materials is primarily focused on high-temperature applications, such as in semiconductor crystal growth, where highly corrosive and aggressive species exist, thus limiting the usability of existing (e.g., graphite) components or significantly reducing their service life. Since it has been demonstrated that producing components of proven volume and complex geometric shapes from refractory metal carbides at low cost using hot-pressure treatments described in the literature is difficult, coatings are preferred. In this treatment, the formation of ceramic layers via hot-pressure is not possible. Coatings are produced, for example, via CVD treatment, which deposits a dense layer of several micrometers onto a substrate via a gas phase. An example of this is a TaC coating with a single-layer structure. However, this cost-intensive method prevents the realization of coating components with arbitrary geometric shapes and sizes, and with arbitrary layer thicknesses. To ensure greater flexibility in these areas, there is the option of applying the coating to the substrate via a wet ceramic treatment (dipping, brushing, or spraying). This can be achieved, for example, via an organic solvent suspension (see, for example, US2013 / 0061800A1). To produce the desired protective coating properties, a sintering process is added downstream of the initial suspension coating process.

[0003] In addition to the creation of a mechanically stable coating (high abrasion and adhesion resistance) through the final sintering process, a high degree of compression is simultaneously required to optimally protect the substrate from corrosive media in high-temperature applications. Beyond the requirement of high compression, it is also necessary to minimize crack formation in the coating after sintering to ultimately ensure the protective coating properties of the refractory metal carbide coating and to maximize protection of the base substrate from corrosive media in high-temperature applications. Cracks can occur during the sintering process, for example, during compression or shrinkage, or during cooling. Shrinkage cracks can be avoided if the applied green sheet exhibits a uniform or homogeneous thickness progression, thus allowing for uniform compression. If there is heterogeneity (such as depressions) in the layer progression, shrinkage cracks can easily occur, which may expand longitudinally or transversely during further stages of the sintering process or later under operating conditions. Crack formation during cooling is due to the release of excessive thermal tensile stress induced by the typically large difference in thermal expansion coefficients between the refractory metal carbide coating and the base substrate.

[0004] However, in suspension-based coating of porous substrates such as CFC substrates with refractory metal carbide coatings, obtaining a homogeneous layer spread is more difficult due to the strong penetration behavior of the porous substrate and the resulting penetration of the suspension into the pores, and therefore, heterogeneous spread (extent) of the refractory metal carbide coating occurs.

[0005] Starting from this, an object of the present invention is to provide a method for manufacturing a coated substrate that can obtain a substrate having a refractory metal carbide coating that extends as uniformly as possible and is as crack-free as possible. In addition, an object of the present invention is to provide a coated substrate having a refractory metal carbide coating that extends as uniformly as possible and is as crack-free as possible.

[0006] This objective is achieved by the features of claim 1 relating to a method for manufacturing a coated substrate, and by the features of claim 11 relating to a coated substrate. The potential uses of the coated substrate according to the present invention are described in claim 15. Dependent claims represent advantageous further developments. [Brief explanation of the drawing]

[0007] [Figure 1] The image shows the cross-sectional polishing of the coated substrate. [Figure 2] The REM record of the cross-sectional polishing is shown. [Figure 3] The image shows the cross-sectional polishing of the coated substrate. [Figure 4] The REM record of the cross-sectional polishing is shown. [Figure 5] The image shows the cross-sectional polishing of the coated substrate. [Modes for carrying out the invention]

[0008] Therefore, according to the present invention, a) Provide at least one surface sealing layer on at least one region of the surface of the porous substrate; b) Applying at least one aqueous suspension to at least one surface sealing layer, wherein at least one aqueous suspension comprises at least one refractory metal carbide and water; and c) After step b), the substrate is subjected to a sintering process. A method for manufacturing a coated substrate is provided. In step a) of the method according to the present invention, first, at least one surface sealing layer is provided on at least one region of the surface of the porous substrate. In this process, at least one surface sealing layer is provided on one region (or one partial region) of the surface of the porous substrate, or on multiple regions (or multiple partial regions) of the surface of the porous substrate, or on the entire surface of the porous substrate. One surface sealing layer or multiple surface sealing layers can be provided on at least one region of the surface of the porous substrate.

[0009] The porous substrate may preferably be a carbon substrate, more preferably a graphite substrate, and most preferably an isotropic graphite substrate. In this context, isotropic graphite is understood to mean graphite produced by isotropic pressure treatment. The porous substrate may, for example, be a crucible, preferably a carbon crucible, particularly preferably a graphite crucible, and very particularly preferably an isotropic graphite crucible.

[0010] The pores in the porous layer preferably have an average pore size (preferably on the surface) in the range of 0.5 μm to 5 μm. The average pore size (preferably on the surface) can be determined, for example, by the mercury intrusion method (DIN 66133:1993-06).

[0011] The pores of the porous substrate preferably have an average pore inlet diameter in the range of 0.1 μm to 5 μm. The average pore inlet diameter can be determined, for example, by mercury porosimetry (DIN 15901-1:2019-03).

[0012] The porous substrate preferably has an open porosity in the range of 5% to 20%. The open porosity can be determined, for example, by the mercury intrusion method (DIN66133:1993-06).

[0013] In step b) of the method according to the present invention, at least one aqueous suspension is applied to at least one surface sealing layer (as provided in step a). The at least one aqueous substrate can be applied to one or more partial regions of the at least one surface sealing layer, or to the entire at least one surface sealing layer. The at least one aqueous suspension can be applied to the at least one surface sealing layer in the form of layers. The layers (or more layers) of the at least one aqueous suspension thus applied can be called green layers (or more green layers). In step b), at least one layer of the at least one aqueous suspension is preferably applied to at least one surface sealing layer. According to the present invention, the at least one aqueous suspension comprises at least one refractory metal carbide and water. The at least one aqueous suspension may also consist of at least one refractory metal carbide. The at least one refractory metal carbide is preferably tantalum carbide.

[0014] After step b), the substrate is subjected to a sintering treatment in step c) of the method according to the present invention. At least one protective layer can be produced by the sintering treatment, which consists of at least one aqueous suspension (applied in step b) and containing at least one refractory metal carbide. In other words, at least one aqueous suspension (applied in step b) can be converted into a protective layer containing at least one refractory metal carbide by the sintering treatment.

[0015] The method according to the present invention enables the creation of a refractory metal carbide coating on a substrate that can function as a high-temperature resistant and abrasion-resistant coating or coating system.

[0016] The method according to the present invention is a wet ceramic process for the production of a refractory metal carbide-based coating on a substrate. In contrast to coatings prepared via CVD or PVD processes, coatings prepared via a wet ceramic process exhibit an isotropic texture with a random grain orientation, as a result of which the crack susceptibility is reduced and the diffusion paths of species harmful to the substrate are increased. Due to this, the coated substrates produced in accordance with the present invention exhibit improved protection against erosive substances used in high-temperature applications as compared to coated substrates produced via CVD or PVD processes. Furthermore, the wet ceramic process according to the present invention is less expensive than CVD or PVD processes and also offers greater flexibility in terms of the geometric shape and size of the coated components that can be produced, as well as the layer thickness of the applied coating or layer.

[0017] Furthermore, the method for producing a coated substrate according to the present invention is based on the use of an aqueous suspension. The use of an aqueous suspension has various advantages as compared to the use of an organic suspension. Thus, in contrast to an organic suspension, an aqueous suspension is inexpensive, harmless from an environmental and health perspective, and does not involve safety-related issues of flammable spray mists. Furthermore, the use of an aqueous suspension eliminates the need for pyrolysis for removing organic solvents, which can lead to the undesired introduction of foreign matter into the coating. Furthermore, in contrast to the use of known organic suspensions, the use of an aqueous suspension enables the controlled application of the suspension. In particular, in the spray coating of known organic suspensions, controlled application is not possible because the suspension properties can vary due to the evaporation of the solvent during this process, and thus a homogeneous layer cannot be obtained over time.

[0018] Due to the sintering process, the protective coating obtained in the method according to the present invention is a mechanically stable coating with high wear and adhesion resistance. Furthermore, the sintering process achieves a higher degree of compression with respect to the starting density (green density) after coating.

[0019] At least one surface sealing layer represents an intermediate layer between the porous substrate and at least one protective layer that can be obtained in step c). Due to at least one surface sealing layer, pore inlets (of the pores of the porous substrate) located on at least one region of the surface of the porous substrate can be substantially completely or at least almost completely closed. The surface of at least one region is thus sealed (or so to speak, almost sealed). Therefore, at least one surface sealing layer can be at least one (substantially) closed surface sealing layer. Whether the pore inlets are substantially completely closed or at least almost completely closed can be determined by determining the gas permeability of the porous substrate in the region where the surface sealing layer is provided, where the gas permeability can be determined, for example, by pressure-dependent flow rate measurement according to DIN EN993-4:1995-04. If the measured gas permeability (e.g., by pressure-dependent flow rate measurement according to DIN EN993-4:1995-04) is 0 m 2 In this case, the stomatal inlet is substantially completely closed. Here, the term "substantially" means that a minimum permeability of the stomatal inlet may exist, but is not measurable (e.g., by pressure-dependent flow measurement according to DIN EN993-4:1995-04). The measured gas permeability (e.g., by pressure-dependent flow measurement according to DIN EN993-4:1995-04) is approximately 0 m 2 In this case, the pore inlets are almost completely closed. The pore inlets are, for example, when the measured gas permeability of the porous substrate in the region where the surface sealing layer is provided (e.g., by pressure-dependent flow measurement according to DIN EN993-4:1995-04) is up to 1E-16m 2Either the surface sealing layer is present, or the measured gas permeability of the porous substrate in the region where the surface sealing layer is provided (e.g., by pressure-dependent flow rate measurement according to DIN EN993-4:1995-04) is at most 10% of the measured gas permeability of the porous substrate without the surface sealing layer (e.g., by pressure-dependent flow rate measurement according to DIN EN993-4:1995-04), then the pore inlets located on at least one region of the surface of the porous substrate are at least nearly completely sealed if the gas permeability of the porous substrate in the region where the surface sealing layer is provided is at most 1E-16m 2 Alternatively, the porous substrate can be (almost completely) sealed by the surface sealing layer such that the gas permeability of the porous substrate in the region where the surface sealing layer is provided is at most 10% of the gas permeability of the porous substrate without the surface sealing layer. The gas permeability of the porous substrate in the region where the surface sealing layer is provided is very preferably at most 0 m 2 That is the case.

[0020] The pore openings (of the pores of the porous substrate) located in at least one region of the surface of the porous substrate are completely or at least almost completely closed by the surface sealing layer, so that the at least one aqueous suspension applied in step b) cannot penetrate into the pores of the porous substrate or can only penetrate very slightly. Since the at least one aqueous suspension is applied directly to the surface sealing layer instead of to the porous substrate, it is therefore possible to prevent, or at least substantially prevent, the at least one aqueous suspension from penetrating into the pores of the porous substrate during application in step b).

[0021] Without a surface sealing layer, when an aqueous suspension is applied to a porous substrate, a considerable amount of the aqueous suspension penetrates into the pores of the porous substrate, causing heterogeneity within the layer. If such heterogeneity (e.g., depressions) is present in the spread of the layer, slight shrinkage cracks may form, which can spread longitudinally and transversely during further processes of sintering or under subsequent use conditions. Crack formation during cooling is due to a decrease in thermal tensile stress, which is induced by a high and typically large difference in the coefficient of thermal expansion between the refractory metal carbide coating and the (e.g., carbon-based) base substrate.

[0022] Due to the at least one surface sealing layer used in the method according to the present invention, the at least one surface sealing layer can prevent, or at least substantially prevent, the penetration of the aqueous suspension into the pores of the porous substrate, so that a very homogeneous (or uniform) coating can be obtained. Shrinkage cracks within the protective layer can be avoided by the very homogeneous (or uniform) spread of the layer. This is also true, as the uniform or homogeneous transition of the layer allows for uniform compression. The fewer the number of shrinkage cracks present in the obtained protective layer, the better the substrate is protected by the protective layer (e.g., from corrosive media in high-temperature applications). Due to the surface sealing layer used in the present invention, a very homogeneous refractory metal carbide protective layer that is only slightly crackable (or even crack-free) can be obtained, which can effectively protect the layer from external influences (e.g., from corrosive media in high-temperature applications).

[0023] The coefficient of thermal expansion (CTE) of at least one surface sealing layer is preferably matched to the coefficient of thermal expansion of the porous substrate and / or the coefficient of thermal expansion of at least one protective layer.

[0024] Such adaptation can be achieved, for example, by selecting a material that can withstand high temperatures while simultaneously having a CTE intermediate between that of the protective layer and the substrate, and by providing an adapted layer through various coating treatments, for example, via the gas phase or spray sintering. Since the coefficient of thermal expansion (CTE) of at least one surface sealing layer is adapted to the coefficient of thermal expansion of the porous substrate and / or the coefficient of thermal expansion of at least one protective layer, the CTE difference between the porous substrate and at least one protective layer can be compensated, and the degree of thermal stress or thermally induced cracking can be further minimized. In particular, if high thermally induced stress after sintering causes the formation of large cracks or even delamination, thereby compromising the protective layer properties, a surface sealing layer can be used to compensate for or minimize a large CTE difference, depending on the CTE difference between the protective layer and the substrate.

[0025] At least one layer of at least one aqueous suspension is preferably applied to at least one surface sealing layer in step b). The at least one layer of aqueous suspension can be called at least one green layer. The green layer or multiple green layers may exhibit a uniform or homogeneous thickness spread.

[0026] The coating substrate produced by the method according to the present invention can be used, for example, as part of a gallium evaporator or gallium evaporator in a VPE GaN reactor that can be used for growing gallium nitride semiconductor crystals, and the layer system obtained by the process according to the present invention in this case functions as a coating for the gallium evaporator.

[0027] A preferred modification of the method according to the present invention is: - The porous substrate comprises or consists of a material selected from the group consisting of graphite, preferably isotropic graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite material, SiC / SiC fiber composite material, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof; and / or - At least one refractory metal carbide is selected from the group consisting of titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, and mixtures thereof. It is characterized by the following:

[0028] Particularly preferred is that at least one refractory metal carbide is tantalum carbide. Tantalum carbide provides a particularly good protective effect for porous substrates.

[0029] The porous substrate may preferably contain or consist of a material selected from the group consisting of graphite, preferably isotropic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0030] The porous substrate may preferably contain or consist of a material selected from the group consisting of graphite, preferably isotropic graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite, SiC / SiC fiber composite, and mixtures thereof.

[0031] Carbon-based and SiC-based substrates exhibit increased penetration behavior when coated with an aqueous suspension. As a result, the method according to the present invention is particularly suitable for such substrates.

[0032] Most preferably, the porous substrate contains or comprises graphite, preferably isotropic graphite.

[0033] According to a more preferred modification of the method according to the present invention, at least one refractory metal carbide is present in the form of particles in at least one aqueous suspension, where the average particle size (d50 value) of the particles of at least one refractory metal carbide is in the range of 0.2 μm to 2 μm, preferably 0.5 μm to 1.5 μm. The average particle size (d50 value) of the particles of at least one refractory metal carbide can be determined, for example, by laser diffraction (DIN13320:2020-01).

[0034] In a further preferred embodiment of the method according to the invention, the pore inlets located on at least one region of the surface of the porous substrate are sealed by a surface sealing layer such that - the gas permeability of the porous substrate in the region where the surface sealing layer is provided is at most 1E-16 m 2 , preferably at most 1E-17 m 2 , particularly preferably at most 5E-17 m 2 , very particularly preferably 0 m 2 ; and / or - the gas permeability of the porous substrate in the region where the surface sealing layer is provided is at most 10%, preferably at most 1%, particularly preferably at most 0.5% of the gas permeability of the porous substrate without the surface sealing layer and is characterized by being tightly closed in this way.

[0035] The gas permeability can be determined, for example, by pressure-dependent flow measurement according to DIN EN993-4:1995-04.

[0036] According to a further preferred variant of the method according to the invention, at least one surface sealing layer is selected from the group consisting of a pyrolytic carbon layer, a silicon carbide layer, a silicon layer, a zirconium diboride layer, a tantalum nitride layer, a silicon nitride layer, a tungsten carbide layer, and combinations thereof.

[0037] A further preferred variant of the method according to the invention is that in step a), at least one surface sealing layer is provided on the porous substrate, where - at least one part of the surface of the porous substrate is impregnated with at least one polymerizable resin and subsequently the resin is carbonized; and / or - at least one part of the surface of the porous substrate is impregnated with at least one polysilane and subsequently the polysilane is pyrolyzed; and / or - silicon is infiltrated into the pores of the porous substrate and the silicon is optionally at least partially converted to silicon carbide; and / or - Depositing at least one layer selected from the group consisting of a pyrolysis carbon layer, a silicon carbide layer, a silicon nitride layer, a tungsten carbide layer, and combinations thereof onto a porous substrate by CVD; and / or - A suspension containing tungsten carbide is applied to at least a portion of the surface of a porous substrate, and then subjected to a sintering process; and / or - At least one layer selected from the group consisting of a silicon layer, a zirconium boride layer, a tantalum nitride layer, and combinations thereof is deposited on a porous substrate by spray treatment. It is characterized by the following:

[0038] There are various preferable possibilities for providing at least one surface sealing layer on the porous substrate in step a).

[0039] In step a), for example, at least one surface sealing layer can be provided on the porous substrate, in which at least one polymerizable resin is impregnated into at least a portion of the surface of the porous substrate, and then the resin is carbonized. In this respect, ● Impregnation with at least one polymerizable resin, wherein a solution containing at least one polymerizable resin is applied to at least one portion of the surface once or multiple times; and / or ● Select at least one polymerizable resin from the group consisting of polyimides, polybenzimidazoles, bismaleimides, polyaryl ketones, polyphenylene sulfides (in solution), and mixtures thereof; and / or ● Carbonization is performed by heat treatment at temperatures between 20°C and 400°C; and / or ● The thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of at least one protective layer, where the difference between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of at least one protective layer is preferably 1e -6 Smaller than / K It would be even more preferable.

[0040] In a more preferred modified form, step a) can provide at least one surface sealing layer to the porous substrate, where at least a portion of the surface of the porous substrate is impregnated with at least one type of polysilane, and then the polysilane is thermally decomposed. In this view, ● Impregnation with at least one type of polysilane, wherein a solution containing at least one type of polysilane is applied to at least one portion of the surface once or multiple times; and / or ● Select at least one polysilane from the group consisting of polycarbosilane, polysiloxane, polysilazane, and mixtures thereof; and / or ● Thermal decomposition is performed by heat treatment at temperatures between 20°C and 1800°C; and / or ● The thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of at least one protective layer, where the difference between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of at least one protective layer is preferably 1e -6 Smaller than / K It would be even more preferable.

[0041] In a more preferred modification, step a) can provide at least one surface sealing layer on the porous substrate, where silicon is permeated into the pores on the surface of the porous substrate and converted to silicon carbide at least partially. In this view, ● Silicon infiltration and at least partial conversion of silicon to silicon carbide are performed, wherein the silicon-containing suspension is applied to a porous substrate, and the applied suspension is subjected to a sintering treatment at a temperature higher than 1420°C, wherein the infiltration treatment (i.e., silicon infiltration) is preferably integrated into the sintering treatment (i.e., sintering treatment at a temperature higher than 1420°C); and / or ● The obtained surface sealing layer has a thickness in the range of 5 μm to 300 μm, preferably 5 μm to 100 μm; and / or ● After the partial conversion of silicon to silicon carbide, the unconverted silicon is preferably removed by grinding and / or milling; and / or ● The thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of at least one protective layer, where the difference between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of at least one protective layer is preferably 2e -6 Greater than / K It would be even more preferable.

[0042] In a more preferred modification, in step a), at least one surface sealing layer can be provided on the porous substrate, where at least one layer selected from the group consisting of pyrolysis carbon, silicon carbide layer, silicon nitride layer, tungsten carbide layer, and combinations thereof is deposited on the porous substrate by CVD. In this view, deposition is performed on the porous substrate by CVD, where a reactive gas species (e.g., CH3SiCl3, H2, etc. for the production of CVD-SiC) moves onto the surface of the porous substrate, and preferably, a chemically bonded surface sealing layer is formed (on the porous substrate) at a temperature in the range of 800°C to 1400°C.

[0043] In a more preferred modification, at least one surface sealing layer can be provided on the porous substrate in step a), where a suspension containing tungsten carbide is applied to at least a portion of the porous substrate, and then subjected to a sintering process. From this perspective, ● Sintering is performed at a temperature higher than 2000℃; and / or ● The thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of at least one protective layer, where the difference between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of at least one protective layer is preferably 2e -6 Smaller than / K It would be even more preferable.

[0044] A more preferred modification of the method according to the present invention is characterized in that, prior to step a), the difference between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of at least one refractory metal carbide layer is determined, and a preferred method for providing at least one surface sealing layer on the porous substrate in step a) is selected by reference to this difference.

[0045] The selection of the surface sealing layer follows the coefficient of thermal expansion (CTE) of the substrate to be coated or the difference in CTE between the substrate and the protective layer. This is because the thermal stress on the coating during the thermal sintering cycle is determined by the CTE difference (Therm.Stress ~ ΔCTE * ΔT). Cracks may occur during this process. This means that if the CTE difference is <0.8E-6 / K, the layer will remain crack-free, and if the CTE difference is <2.5E-6 / K, the layer will have only slight cracks.

[0046] Therefore, the composition of the sealing layer is selected such that the CTE of the substrate being sealed matches the CTE of the layer as closely as possible. This is illustrated by the following example. ● If CTE (substrate) > 5.8E-6 / K: Encapsulators containing PyC, ZrB2, or TaB2 and mixtures thereof. ● If CTE (substrate) > 4E-6 / K: Sealants consisting of a SiC layer, ZrB2, TaB2, and mixtures thereof. ● When CTE (substrate) > 1.5E-5 / K: According to a more preferred modified form of the method of the present invention, the thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of at least one protective layer, where the difference between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of at least one protective layer is 2e -6 / K is greater than or equal to 1e -6 Smaller than / K

[0047] A more preferred modification of the method according to the present invention is that at least one aqueous suspension is - Containing 60 to 90 wt%, preferably 70 to 85 wt%, of at least one refractory metal carbide based on the total weight of the aqueous suspension; and / or - The aqueous suspension contains 0.01 to 0.5 wt% of a dispersant based on the total weight, where the dispersant is preferably selected from the group consisting of polyvinyl alcohol; polyacrylic acid; polyvinylpyrrolidone; polyalkylene glycol ether; and bases, preferably tetrabutylammonium hydroxide, tetramethylammonium hydroxide, polyethyleneimine, inorganic bases, especially NaOH, ammonium hydroxide; and mixtures thereof, more preferably selected from the group consisting of ammonium hydroxide, polyalkylene glycol ether, and mixtures thereof; and / or - The aqueous suspension contains 0.01 to 5 wt% of a binder based on the total weight, wherein the binder is preferably selected from the group consisting of polyethylene glycol, polyvinyl butyral, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, carboxymethylcellulose, alginic acid, dextrin, sodium biphenyl-2-yl oxide, polyphenyl oxide, and mixtures thereof; more preferably selected from the group consisting of sodium biphenyl-2-yl oxide, polyphenyl oxide, and mixtures thereof; and / or - Manufactured by mixing its components with the assistance of a dispersion device, where the mixing is preferably carried out with the assistance of a dispersion device while using a grinding element and / or over a period of time of at least 12 hours. It is characterized by the following:

[0048] Preferably, optimal mixing of the aqueous suspension can be achieved by mixing the components with the aid of a dispersion device while using a grinding element and / or over a period of at least 12 hours, thereby further avoiding heterogeneity in dispersion and thus in compression. In mixing with a dispersion device, for example, a rotational speed of up to 1 m / s can be used.

[0049] At least one aqueous suspension may contain at least one binder selected from the group consisting of polyethylene glycol, polyvinyl butyral, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, carboxymethylcellulose, alginic acid, dextrin, sodium biphenyl-2-yl oxide, polyphenyl oxide, and mixtures thereof, more preferably selected from the group consisting of sodium biphenyl-2-yl oxide, polyphenyl oxide, and mixtures thereof, wherein the at least one binder may be contained in the at least one aqueous suspension in a proportion of 0.05 to 1 wt% or 0.01 to 5 wt% based on the total weight of the aqueous suspension.

[0050] According to a modified version of a preferred embodiment, at least one aqueous suspension may preferably contain a sintering additive selected from the group consisting of refractory metal silicides, refractory metal nitrides, refractory metal borides, silicon, silicon carbide, boron nitride, tungsten carbide, vanadium carbide, molybdenum carbide, boron carbide, and mixtures thereof, wherein the sintering additive is particularly preferably selected from the group consisting of silicon, zirconium boride, refractory metal carbides, and mixtures thereof.

[0051] The refractory metal silicide is preferably selected from the group consisting of titanium silicide, zirconium silicide, e.g., zirconium disilicate (ZrSi2), hafnium silicide, e.g., hafnium disilicate (HfSi2), vanadium silicide, e.g., vanadium disilicate (VSi2), niobium silicide, e.g., niobium disilicate (NbSi2), tantalum silicide, e.g., tantalum disilicate (TaSi2), chromium silicide, molybdenum silicide, e.g., molybdenum disilicate (MoSi2), tungsten silicide, e.g., tungsten disilicate (WSi2), and mixtures thereof.

[0052] The refractory metal nitride is preferably selected from the group consisting of titanium nitride, zirconium nitride, hafnium nitride, vanadium nitride, niobium nitride, tantalum nitride, chromium nitride, molybdenum nitride, tungsten nitride, and mixtures thereof.

[0053] The refractory metal boride is preferably selected from the group consisting of titanium boride, zirconium boride, hafnium boride, vanadium boride, niobium boride, tantalum boride, chromium boride, molybdenum boride, tungsten boride, and mixtures thereof.

[0054] These sintering additives have been shown to have at least the same or even better effect in terms of the degree of compression compared to transition metals (e.g., cobalt, nickel, iron, etc.) used as sintering additives in the prior art, due to their properties (e.g., melting point, boiling point, etc.). Therefore, by using them, a high degree of compression of the sintered layer can be achieved, thereby providing very good protection of the substrate from corrosive media in high-temperature applications. Compared with sintering additives used in the prior art, such as cobalt, the sintering additives mentioned are, first and foremost, harmless from a safety and health standpoint. Their use as sintering additives and thus the avoidance of certain transition metals such as cobalt, nickel, and iron further prevents these transition metals from being retained in the layer as harmful contaminants to the growth atmosphere when used as coating substrates in high-temperature applications in semiconductor crystal growth.

[0055] According to a more preferred modification of the method according to the present invention, in step b), the application of at least one aqueous suspension is carried out by dipping, brushing, and / or spray application. In step b), the application of at least one aqueous suspension is particularly preferably carried out by spray application. Spray application is a preferred choice for producing one or more thin, fast-drying refractory metal carbide coatings having a layer thickness preferably in the range of 20 μm to 80 μm. In this process, a very thin suspension layer can be applied to a surface by passing the components through a spray jet and rotating them at high speed. Depending on the solids content of the suspension, this layer can dry rapidly to very rapidly. The preferred solids content of the refractory metal carbide powder is higher than or equal to 70% by weight of the total suspension. Each individual layer to be applied should preferably exhibit similar drying behavior. Fast-drying behavior of the applied suspension layers is generally preferred because if the drying time of the layers is too long, heterogeneity in particle dispersion may occur due to density differences between the refractory metal carbide and sintering additives.

[0056] Preferably, in step b), at least one layer of aqueous suspension having an average layer thickness of 20 μm, preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm, can be applied to at least one surface sealing layer.

[0057] A more preferred modification of the method according to the present invention is that the sintering process in step c) - At a temperature of 2100°C to 2500°C, preferably 2200°C to 2400°C; and / or - Holding time of 1 to 15 hours, preferably 2 to 10 hours, and / or - At a pressure of 0.1 bar (10 kPa) to 10 bar (1000 kPa), preferably 0.7 bar (70 kPa) to 5 bar (500 kPa), and / or - Under an argon atmosphere It is characterized by being checked.

[0058] On the other hand, these designs of the sintering process ensure that the resulting protective coating has particularly high mechanical stability, with especially high abrasion and adhesion resistance. These designs of the sintering process further enhance the stability of the molten phase throughout the entire sintering process.

[0059] The present invention further relates to a coated substrate comprising a porous substrate, at least one surface sealing layer disposed on at least one region of the surface of the porous substrate, and at least one protective layer disposed on the at least one surface sealing layer, the protective layer comprising at least one refractory metal carbide.

[0060] Due to at least one surface sealing layer, at least one protective layer can be obtained with very high homogeneity, with only slight cracking (or even no cracking at all), thereby allowing at least one protective layer to better protect the porous substrate from external influences (such as corrosive media in high-temperature applications).

[0061] Due to at least one surface sealing layer, pore openings (of the pores of the porous substrate) located on at least one region of the surface of the porous substrate can be completely or at least almost completely closed.

[0062] The protective layer, which is placed on at least one surface sealing layer, may not contain hafnium carbide and / or zirconium carbide.

[0063] For example, at least one surface sealing layer contains tantalum carbide and does not contain any other refractory metal carbides. At least one surface sealing layer may contain tantalum carbide.

[0064] Preferably, the protective layer disposed on at least one surface sealing layer does not contain refractory metal borides.

[0065] A preferred embodiment of the coating substrate according to the present invention is characterized in that at least one protective layer disposed on at least one surface sealing layer has an average layer thickness of at least 20 μm, preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm.

[0066] According to a more preferred embodiment of the coating substrate according to the present invention, the standard deviation of at least one protective layer is less than 6%, preferably in the range of 0.5% to 6%, and particularly preferably in the range of 1% to 6%.

[0067] The standard deviation of the average layer thickness is a measure of the homogeneity (or uniformity) of the layer thickness. The smaller the standard deviation of the average layer thickness of at least one protective layer, the more homogeneous (or uniform) the layer thickness of at least one protective layer will be.

[0068] The optical extent of at least one protective layer can be presented and evaluated using a classical method with cross-sectional polishing. Optical observation of the cross-sectional polishing and qualitative classification into homogeneous or heterogeneous layer systems can be performed here.

[0069] The average thickness of at least one protective layer can be determined similarly using cross-sectional polishing of the coated substrate. Once the average thickness is determined, and multiple point measurements are performed in the cross-sectional polishing of the layer, the standard deviation can then be calculated, which further provides a quantitative estimate of the homogeneity of the layer's spread.

[0070] For example, homogeneity can be quantified using the standard deviation of layer thickness as follows: - Preparation of the cross-section of the coating substrate (i.e., layer + substrate) - Measurement of the distance (layer thickness) between interfaces and layer surfaces based on recorded cross-sectional images. - For example, layer thickness analysis in a region with a maximum extent of 4 cm. - The number of individual layer thickness measurements is at least 25 per 1 cm measurement area. - The intervals between individual layer thickness measurements are regular. - Determination of the standard deviation across all individual layer thickness measurements For example, with a standard deviation of 6% or less, the stratum in question can be assumed to be homogeneous.

[0071] By referring to plan views without performing complex cross-sectional polishing preparations, a quick qualitative description of the layer's homogeneity can already be created.

[0072] It is even more preferable that at least one surface sealing layer is selected from the group consisting of a pyrolysis carbon layer, a silicon carbide layer, a silicon nitride layer, a tungsten carbide layer, and combinations thereof.

[0073] - The porous substrate comprises or consists of a material selected from the group consisting of graphite, preferably isotropic graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite material, SiC / SiC fiber composite material, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof; and / or - At least one refractory metal carbide is selected from the group consisting of titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, and mixtures thereof. It would be even more preferable.

[0074] Particularly preferred is that at least one refractory metal carbide is tantalum carbide.

[0075] The porous substrate may preferably contain or consist of a material selected from the group consisting of graphite, preferably isotropic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0076] The porous substrate may preferably contain or consist of a material selected from the group consisting of graphite, preferably isotropic graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite, SiC / SiC fiber composite, and mixtures thereof.

[0077] Most preferably, the porous substrate contains or comprises graphite, preferably isotropic graphite.

[0078] The porous substrate may preferably be a carbon substrate, more preferably a graphite substrate, and most preferably an isotropic graphite substrate. In this context, isotropic graphite is understood to mean graphite produced by isotropic pressure treatment. The porous substrate may, for example, be a crucible, preferably a carbon crucible, particularly preferably a graphite crucible, and very particularly preferably an isotropic graphite crucible.

[0079] The coefficient of thermal expansion (CTE) of at least one surface sealing layer is preferably matched to the coefficient of thermal expansion of the porous substrate and / or the coefficient of thermal expansion of at least one protective layer. In this way, the CTE difference between the porous substrate and at least one protective layer can be compensated for, and the size of thermal stress or thermally induced cracks can be further minimized as a result. In particular, if high thermally induced stress after sintering causes the formation of large cracks or even delamination, thereby compromising the protective layer properties, the surface sealing layer can be used to compensate for or minimize large CTE differences between the protective layer and the substrate, depending on the CTE difference.

[0080] The thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of at least one protective layer, where the difference between the thermal expansion coefficient of the substrate and the thermal expansion coefficient of at least one protective layer is 2e -6 / K is greater than or equal to 1e -6 It is also preferable that it be smaller than / K.

[0081] A more preferred embodiment of the coated substrate according to the present invention is characterized in that the coated substrate can be manufactured or is manufactured using the method according to the present invention.

[0082] Furthermore, the present invention also relates to the use of a coating substrate according to the present invention in semiconductor crystal growth, wherein the coating substrate is preferably a coating crucible.

[0083] Without limiting the present invention to the parameters specifically shown, the present invention will be described in more detail with reference to the following drawings and examples.

[0084] Embodiment 1 Porous graphite substrate (average pore size: 1.8 μm, particle size: 10 μm, R a A surface sealing layer was prepared on a 1.5 μm thick surface, where silicon was infiltrated into the pores of the porous substrate, converting the silicon to silicon carbide, at least partially. For this purpose, a fine amount of silicon was applied to the surface of the porous graphite substrate and subsequently subjected to heat treatment at a temperature of 1500°C for a duration of 5 hours in a vacuum atmosphere. The resulting surface sealing layer is a silicon carbide layer.

[0085] Next, an aqueous suspension was applied in layer form to the acquired surface sealing layer, where the aqueous suspension consisted of 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water. The substrate with the aqueous suspension was then subjected to a sintering process at a temperature of 2300°C with a residence time of 10 hours and a pressure of 1 bar (100 kPa).

[0086] In this way, a coated graphite substrate was obtained comprising a porous graphite substrate, a silicon carbide surface sealing layer disposed on the porous graphite substrate, and a TaC protective layer disposed on the silicon carbide surface sealing layer.

[0087] To analyze the coated substrate, a cross-sectional polish was generated. An image of this cross-sectional polish is shown in Figure 1. Figure 2 further shows the REM record of the cross-sectional polish.

[0088] The average thickness and standard deviation of the TaC layer were determined by referring to cross-sectional polishing. For this purpose, individual layer thickness measurements were taken at at least 25 measurement points per 1 cm measurement range. Here, the distance (layer thickness) between the interface and the layer surface was measured by referring to the recorded cross-sectional polishing image, and the spacing between individual measurement points was regular. In this way, a value of 64.8 μm was determined for the average layer thickness of the TaC layer. Furthermore, it was determined that the standard deviation across all individual layer thickness measurements was 3.3 μm (5.1%).

[0089] Since the standard deviation does not exceed 6%, this TaC layer is therefore a homogeneous layer.

[0090] Embodiment 2 Porous graphite substrate (average pore size: 1.8 μm, particle size: 10 μm, R a A surface sealing layer was prepared on a 1.5 μm thick surface, where silicon was infiltrated into the pores of the porous substrate, converting the silicon to silicon carbide, at least partially. For this purpose, coarse silicon powder was applied to the surface of a porous graphite substrate and subsequently subjected to heat treatment at a temperature of 1500°C for a duration of 5 hours in a vacuum atmosphere. The resulting surface sealing layer is a silicon carbide layer.

[0091] Next, an aqueous suspension was applied in layer form to the acquired surface sealing layer, where the aqueous suspension consisted of 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water. The substrate with the aqueous suspension was then subjected to a sintering process at a temperature of 2300°C with a residence time of 10 hours and a pressure of 1 bar (100 kPa).

[0092] In this way, a coated graphite substrate was obtained comprising a porous graphite substrate, a silicon carbide surface sealing layer disposed on the porous graphite substrate, and a TaC protective layer disposed on the silicon carbide surface sealing layer.

[0093] To analyze the coated substrate, a cross-sectional polish was produced. An image of this cross-sectional polish is shown in Figure 3. Figure 4 further shows the REM record of the cross-sectional polish.

[0094] The average thickness and standard deviation of the TaC layer were determined by referring to cross-sectional polishing. For this purpose, individual layer thickness measurements were taken at at least 25 measurement points per 1 cm measurement range, and the distance (layer thickness) between the interface and the layer surface was measured by referring to the recorded cross-sectional polishing image, where the spacing between individual measurement points was regular. In this way, a value of 75.3 μm was determined for the average layer thickness of the TaC layer. Furthermore, it was determined that the standard deviation across all individual layer thickness measurements was 3.5 μm (4.7%).

[0095] Since the standard deviation does not exceed 6%, this TaC layer is therefore a homogeneous layer.

[0096] Comparative Example Porous graphite substrate without any surface sealing layer (average pore size: 1.8 μm, particle size: 10 μm, R a An aqueous suspension was applied in layers to a substrate (1.5 μm thick), where the aqueous suspension consisted of 80 wt% TaC powder, 0.1 wt% tetrabutylammonium hydroxide, 1 wt% polyvinyl alcohol, and 18.9 wt% water. The substrate with the aqueous suspension was then subjected to a sintering process at 2300°C with a residence time of 10 hours and a pressure of 1 bar (100 kPa).

[0097] In this way, a coated graphite substrate was obtained that includes a porous graphite substrate and a TaC protective layer disposed on the porous graphite substrate, but does not include a surface sealing layer disposed between the substrate and the protective layer.

[0098] To analyze the coated substrate, a cross-sectional polishing sample was prepared. An image of this cross-sectional polishing sample is shown in Figure 5.

[0099] The average thickness and standard deviation of the TaC layer were determined by referring to cross-sectional polishing. For this purpose, individual layer thickness measurements were taken at at least 25 measurement points per 1 cm measurement range, and the distance (layer thickness) between the interface and the layer surface was measured by referring to the recorded cross-sectional polishing image, where the spacing between individual measurement points was regular. In this way, a value of 44.7 μm was determined for the average layer thickness of the TaC layer. Furthermore, it was determined that the standard deviation across all individual layer thickness measurements was 5.3 μm (11.8%).

[0100] Since the standard deviation is greater than 6%, this TaC layer is therefore a heterogeneous layer.

Claims

1. a) Provide at least one surface sealing layer on at least one region of the surface of the porous substrate; b) Applying at least one aqueous suspension to the at least one surface sealing layer, wherein the at least one aqueous suspension comprises at least one refractory metal carbide and water; and c) After step b), the porous substrate is subjected to a sintering process. The at least one surface sealing layer is selected from the group consisting of a pyrolysis carbon layer, a zirconium boride layer, a silicon carbide layer, a silicon nitride layer, and combinations thereof. The porous substrate is made of a material selected from the group consisting of graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite material, SiC / SiC fiber composite material, and mixtures thereof. The thermal expansion coefficient of the porous substrate is smaller than that of the thermal expansion coefficient of the at least one refractory metal carbide. The thermal expansion coefficient of the at least one surface sealing layer is between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of the at least one refractory metal carbide. The aqueous suspension is applied to the at least one surface sealing layer in step b) such that it has an average layer thickness of 20 μm to 150 μm. A method for producing a coated substrate.

2. - The at least one refractory metal carbide is selected from the group consisting of titanium carbide, zirconium carbide, hafnium carbide, vanadium carbide, niobium carbide, tantalum carbide, chromium carbide, molybdenum carbide, tungsten carbide, and mixtures thereof. The method according to claim 1.

3. The method according to claim 1, wherein the at least one refractory metal carbide is present in the form of particles in the at least one aqueous suspension, and the average particle size (d50 value) of the particles of the at least one refractory metal carbide is in the range of 0.2 μm to 2 μm.

4. The pore openings located on at least one region of the surface of the porous substrate are sealed by the surface sealing layer. - The gas permeability of the porous substrate in the region where the surface sealing layer is provided is a maximum of 1E-16m ２ Here, the gas permeability is determined by pressure-dependent flow rate measurement in accordance with DIN EN993-4:1995-04; and / or - The gas permeability of the porous substrate in the region where the surface sealing layer is provided is at most 10% of the gas permeability of the porous substrate without the surface sealing layer, where the gas permeability is determined by pressure-dependent flow rate measurement in accordance with DIN EN993-4:1995-04. It is so tightly closed off, The method according to claim 1.

5. In step a), - Impregnating at least a portion of the surface of the porous substrate with at least one polymerizable resin, and subsequently carbonizing the resin; and / or - Impregnating at least a portion of the surface of the porous substrate with at least one type of polysilane, and subsequently thermally decomposing the polysilane; and / or - To impregnate silicon into the pores of the porous substrate, and to convert the silicon to silicon carbide, at least partially. By providing at least one surface sealing layer on the porous substrate; and / or - Depositing at least one layer selected from the group consisting of a layer of pyrolysis carbon, a silicon carbide layer, a silicon nitride layer, and combinations thereof onto the porous substrate by CVD; and / or - At least one layer selected from the group consisting of a silicon layer, a zirconium boride layer, a tantalum nitride layer, and combinations thereof is deposited on the porous substrate by spray treatment. The method according to claim 1.

6. The at least one aqueous suspension is - comprising 60 to 90 wt% of the at least one refractory metal carbide based on the total weight of the aqueous suspension; and / or - Containing 0.01 to 0.5 wt% of a dispersant relative to the total weight of the aqueous suspension; and / or - Containing 0.01 to 5 wt% of a binder based on the total weight of the aqueous suspension; and / or - Manufactured by mixing its components with the assistance of a dispersion device, The method according to claim 1.

7. The method according to claim 1, wherein in step b), the application of the at least one aqueous suspension is carried out by dipping, brushing, and / or spray application.

8. The sintering process in step c) is performed as follows: - At temperatures of 2100°C to 2500°C, and / or - With a holding time of 1 to 15 hours, and / or - At a pressure of 0.1 bar (10 kPa) to 10 bar (1000 kPa), and / or - Under an argon atmosphere The method according to claim 1, which is carried out.

9. A porous substrate, at least one surface sealing layer disposed on at least one region of the surface of the porous substrate, and at least one protective layer disposed on the at least one surface sealing layer, comprising at least one refractory metal carbide, The at least one surface sealing layer is selected from the group consisting of a pyrolysis carbon layer, a zirconium boride layer, a silicon carbide layer, a silicon nitride layer, and combinations thereof. The porous substrate is made of a material selected from the group consisting of graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite material, SiC / SiC fiber composite material, and mixtures thereof. The thermal expansion coefficient of the porous substrate is smaller than the thermal expansion coefficient of the at least one protective layer. The thermal expansion coefficient of the at least one surface sealing layer is between the thermal expansion coefficient of the porous substrate and the thermal expansion coefficient of the at least one protective layer. The at least one protective layer is a coating substrate having an average layer thickness of 20 μm to 150 μm.

10. The coated substrate according to claim 9, wherein the relative standard deviation of the thickness of the at least one protective layer is 6% or less.

11. Use of a coating substrate according to any one of claims 9 to 10 in semiconductor crystal growth.

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