Method for preparing a coating substrate, and the coating substrate and its use.

Abstract

The present invention relates to a method for producing a coated substrate, comprising producing a first aqueous suspension and a second aqueous suspension, applying at least one layer of the first aqueous suspension onto the substrate, applying at least one layer of the second aqueous suspension onto the at least one layer of the first aqueous suspension applied onto the substrate, and subjecting the thus coated substrate to a sintering treatment. The first aqueous suspension contains or consists of at least one sintering additive selected from the group consisting of at least one refractory metal carbide, refractory metal silicide, refractory metal nitride, refractory metal boride, silicon, silicon carbide, boron nitride, tungsten carbide, vanadium carbide, molybdenum carbide, boron carbide, and mixtures thereof, and water. The second aqueous suspension similarly contains at least one refractory metal carbide and water. Furthermore, the second aqueous suspension may contain at least one 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 content in weight percent of the at least one sintering additive in the second aqueous suspension based on the total weight of the second aqueous suspension is lower than the content in weight percent of the at least one sintering additive in the first aqueous suspension based on the total weight of the first aqueous suspension. Alternatively, the second aqueous suspension may be additive-free. 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 preparing a coated substrate, wherein a first aqueous suspension and a second aqueous suspension are prepared, at least one layer of the first aqueous suspension is applied to a substrate, at least one layer of the second aqueous suspension is applied to at least one layer of the first aqueous suspension applied to the substrate, and the substrate thus coated is subjected to a sintering process. The first aqueous suspension comprises or comprises at least one sintering additive selected from the group consisting of at least one refractory metal carbide, silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, and water. The second aqueous suspension also comprises at least one refractory metal carbide and water. Furthermore, the second aqueous suspension may contain at least one sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, wherein the weight percentage of at least one sintering additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, is lower than the weight percentage of at least one sintering additive in the first aqueous suspension, based on the total weight of the first aqueous suspension. Alternatively, the second aqueous suspension may not contain any sintering additive. The present invention further relates to coating substrates prepared or that can be prepared using the method according to the present invention and the use of such coating 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. Due to this treatment, the preparation of ceramic layers via hot-pressure is not possible. Coatings are prepared, for example, via CVD treatment, where a dense layer of several micrometers is deposited on a substrate via the gas phase. An example is a single-layer TaC coating. 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 generating 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. Since refractory metal carbides are mainly compounds with strong covalent bonds and very little self-diffusion, the first challenge is to optimize the sintering process to obtain the greatest possible degree of compression. Particularly in the field of no-pressure sintering, a common method for increasing sintering activity is the use of sintering aids that transform into a liquid molten phase during the sintering process, thus resulting in favorable particle rearrangement (liquid-phase sintering). Preferably, it should be ensured that the sintering aid forms a stable molten phase under given sintering conditions (temperature, pressure, etc.). When using selected sintering additives, it may also be advantageous to adapt the sintering conditions for ideal sintering results, for example, by increasing the system pressure in an inert gas atmosphere.

[0004] From already published literature (see, for example, US2013 / 0061800A1), it is known that the degree of compression during pressureless sintering of TaC coatings can be maximized by using certain transition metals such as cobalt as sintering additives. However, cobalt is a highly toxic substance, raising environmental, health, and safety concerns regarding suspension-based coating technologies. Furthermore, the use of certain transition metals as sintering additives can result in highly flammable powder mixtures, which also poses a safety problem. The use of refractory metal carbide protective layers in semiconductor crystal growth also requires that, under no circumstances should hazardous impurities, including transition metals such as cobalt, nickel, and iron (as known from the aforementioned literature), enter the growth atmosphere from the internal structure of the reactor in which the coating will be applied.

[0005] Starting from this, the object of the present invention is to specify a method for preparing a coating substrate that is low in risk from a safety standpoint and is particularly well suited for use in high-temperature applications such as semiconductor crystal growth. Furthermore, the object of the present invention is to provide a coating substrate that can be prepared in a safer manner from a safety standpoint and is particularly well suited for use in high-temperature applications such as semiconductor crystal growth.

[0006] This objective is achieved by the features of claim 1 relating to a method for preparing a coating substrate, and by the features of claim 10 relating to a coating substrate. Claim 15 specifies possible uses of the coating substrate according to the present invention. Dependent claims represent advantageous developments. [Brief explanation of the drawing]

[0007] [Figure 1] Some exemplary variations of the method according to the present invention are shown. [Figure 2] The density distribution within a layer system for an exemplary coating substrate according to the present invention is shown in the graph. [Figure 3] An overview diagram of the method steps performed after the preparation of the aqueous suspension is shown. [Figure 4] This shows a comparison of the degree of compression of the first sintered layer 4 and the second sintered layer 5 (derived from a second aqueous suspension without sintering additives). [Figure 5] This shows a comparison of the degree of compression of the first sintered layer 4 and the second sintered layer 5 (derived from a second aqueous suspension without sintering additives). [Modes for carrying out the invention]

[0008] Therefore, according to the present invention, a) a first aqueous suspension is prepared comprising or comprising: a) at least one sintering additive selected from the group consisting of at least one refractory metal carbide, silicon, hafnium, zirconium, vanadium, tantalum pentoxide (Ta2O5), boron carbide (B4C), silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride (or zirconium diboride, ZrB2), refractory metal silicides, and mixtures thereof; and water. b) Prepare a second aqueous suspension containing at least one refractory metal carbide and water, the second aqueous suspension being - The sintered additive comprises at least one selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide (Ta2O5), boron carbide (B4C), silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride (or zirconium diboride, ZrB2), refractory metal silicides, and mixtures thereof, wherein the weight percentage of the at least one sintered additive in the second aqueous suspension based on the total weight of the second aqueous suspension is less than the weight percentage of the at least one sintered additive in the first aqueous suspension based on the total weight of the first aqueous suspension, or - Contains no sintering additives, c) Apply at least one layer of the first aqueous suspension to the substrate, d) Apply at least one layer of the second aqueous suspension to at least one layer of the first aqueous suspension applied to the substrate. e) After step d), the (coated) substrate is subjected to a sintering process. A method for preparing the coating substrate is specified. In step a) of the method according to the present invention, a first aqueous suspension is prepared, and in step b) of the method according to the present invention, a second aqueous suspension is prepared. Step b) can be performed before step a), after step a), or (at least partially) concurrently with step a). The first aqueous suspension and / or the second aqueous suspension can be prepared (each) by mixing the components that will be contained in each suspension. The first aqueous suspension and the second aqueous suspension each contain at least one refractory metal carbide and water. The at least one refractory metal carbide contained in the first aqueous suspension and the at least one refractory metal carbide contained in the second aqueous suspension may be the same refractory metal carbide or different refractory metal carbides. Furthermore, the first aqueous suspension contains at least one sintered additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof. The second aqueous suspension may also include a sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, wherein the weight percentage of at least one sintering additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, is lower in this case than the weight percentage of at least one sintering additive in the first aqueous suspension, based on the total weight of the first aqueous suspension. Alternatively, the second aqueous suspension may not contain any sintering additive.For example, the second aqueous suspension does not need to contain sintering additives selected from the group consisting of silicon; tantalum pentoxide; silicon carbide; tungsten carbide; vanadium carbide; molybdenum carbide; boron nitride; tantalum nitride; zirconium nitride; niobium nitride; tantalum diboride; tungsten diboride; zirconium boride; refractory metal silicides, e.g., TaSi2, MoSi2, ZrSi2; transition metals, e.g., hafnium, zirconium, vanadium; boron carbide (B4C); silicon nitride (Si3N4); carbon; and mixtures thereof. Preferably, the second aqueous suspension comprises at least one refractory metal carbide, water, and optionally at least one sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof. The at least one sintering additive contained in the first aqueous suspension and the at least one sintering additive contained in the second aqueous suspension may be the same sintering additive or different sintering additives.

[0009] The first aqueous suspension contains at least one sintering additive, preferably selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof.

[0010] If the second aqueous suspension contains at least one sintering additive, the at least one sintering additive contained in the second aqueous suspension is preferably selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof.

[0011] For example, the second aqueous suspension comprises at least one refractory metal carbide, water, and optionally at least one sintered additive selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof.

[0012] The second aqueous suspension can be free of sintering additives. For example, the second aqueous suspension may not contain a sintering additive selected from the group consisting of silicon; zirconium boride; refractory metal silicides such as TaSi2, MoSi2, ZrSi2; transition metals; boron carbide (B4C); silicon nitride (Si3N4); carbon; and mixtures thereof.

[0013] The sintering additive can be understood as a substance added as an aid to the sintering of ceramic systems, specifically for the preparation of ceramic components, in order to control the microstructural and spatial development (e.g., shrinkage, grain growth, shape change, and / or homogenization).

[0014] In step c) of the method according to the invention, at least one layer of the first aqueous suspension is applied to a substrate. The substrate can preferably be a carbon substrate, particularly preferably a graphite substrate, and very particularly preferably an isotropic graphite substrate. Isotropic graphite is understood to mean graphite prepared by isostatic pressing. For example, the substrate can be a crucible, preferably a carbon crucible, particularly preferably a graphite crucible, and very particularly preferably an isotropic graphite crucible. For example, at least one layer of the first aqueous suspension can be applied to the substrate by dipping, brushing, spray coating, or a combination thereof. For example, at least one layer of the first aqueous suspension having an average layer thickness of at least 20 μm, preferably from 20 μm to 150 μm, particularly preferably from 30 μm to 100 μm can be applied to the substrate.

[0015] In step d) of the method according to the invention, at least one layer of the second aqueous suspension is applied to at least one layer of the first aqueous suspension applied to the substrate in step c). For example, at least one layer of the second aqueous suspension can be applied by dipping, brushing, spray coating, or a combination thereof. For example, at least one layer of the second aqueous suspension having an average layer thickness of at least 20 μm, preferably from 20 μm to 150 μm, particularly preferably from 30 μm to 100 μm, can be applied to at least one layer of the first aqueous suspension applied to the substrate in step c).

[0016] In step e) of the method according to the invention, the substrate is subjected to a sintering treatment. This is carried out after step d), i.e., after the application of at least one layer of the second aqueous suspension to at least one layer of the first aqueous suspension applied to the substrate. Thus, the coated substrate subjected to the sintering treatment in step e) has both at least one layer of the first aqueous suspension applied in step c) and at least one layer of the second aqueous suspension applied in step d). Thus, in step e), both at least one layer of the first aqueous suspension and at least one layer of the second aqueous suspension are simultaneously subjected to a sintering treatment. At least one first sintered layer containing at least one refractory metal carbide from at least one layer of the first aqueous suspension and also at least one second sintered layer containing at least one refractory metal carbide from at least one layer of the second aqueous suspension can be prepared by the sintering treatment.

[0017] The method according to the invention enables the preparation of a refractory metal carbide-based layer on a substrate that can function as a high-temperature and wear protection layer or a wear-protection layer system.

[0018] The method according to the present invention is a wet ceramic method for preparing a refractory metal carbide coating on a substrate. In contrast to layers prepared via CVD or PVD treatment, layers prepared via wet ceramic treatment exhibit an isotropic texture with random grain size orientation, thereby reducing the susceptibility to cracking and increasing the diffusion pathways of harmful species to the substrate. For this reason, coated substrates prepared according to the present invention have improved protection against corrosive materials used in high-temperature applications compared to coated substrates prepared via CVD or PVD methods. Furthermore, the wet ceramic method according to the present invention is more cost-effective than CVD or PVD methods and also offers greater flexibility in terms of the geometric shape and size of the coating components that can be prepared, and the thickness of the applied coating or layer.

[0019] Furthermore, the method according to the present invention for preparing a coating substrate is based on the use of an aqueous suspension. The use of an aqueous suspension has several advantages over the use of an organic suspension. In contrast to organic suspensions, aqueous suspensions are inexpensive, harmless from an environmental and health standpoint, and do not involve the safety-related issues associated with flammable spray mist. Moreover, when using an aqueous suspension, there is no need for thermal decomposition to remove organic solvents, which can lead to the unwanted intrusion of foreign matter into the coating. Furthermore, in contrast to the use of known organic suspensions, controlled application of the suspension is possible when using an aqueous suspension. In particular, with spray application of known organic suspensions, controlled application is not possible because the suspension properties may fluctuate due to the evaporation of the solvent during the process, and therefore, a homogeneous layer cannot be obtained over time.

[0020] In the method according to the present invention, one or more types of sintering additives are used, and the sintering additive is selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, preferably selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof. The above-mentioned sintering additives used in accordance with the present invention 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 the above-mentioned additives, a high degree of compression of the sintered layer prepared on the substrate can be achieved, thereby providing excellent protection of the substrate from corrosive media in high-temperature applications. Compared with conventional sintering additives such as cobalt, the sintering additives used according to the present invention are distinguished, firstly, by being harmless from a safety and health standpoint. Furthermore, the use of sintering additives according to the present invention and thus the avoidance of certain transition metals such as cobalt, nickel, and iron as sintering additives further prevents the residue of these transition metals in the layer as harmful impurities to the growth atmosphere when the coated substrate is used in high-temperature applications for semiconductor crystal growth.

[0021] Since the second aqueous suspension either does not contain sintering additives or contains a lower weight percent of sintering additives than that contained in the first aqueous suspension, a coating prepared on a substrate using the method according to the present invention has a very advantageous layer structure of at least two different sintered layers. The layer structure comprises at least one first sintered layer disposed on the substrate, comprising or containing at least one refractory metal carbide and at least one sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, and at least The present invention provides a second sintered layer comprising at least one second sintered layer disposed on a first sintered layer, the second sintered layer comprising or comprising at least one refractory metal carbide and optionally at least one sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof. The at least one sintering additive may also be present in at least a partially decomposed form and / or in the form of a reaction product of the reaction between the at least one sintering additive and the at least one refractory metal carbide. The presence of sintering additives in the layers obtained during the sintering process, or a higher proportion of sintering additives, results in greater compression of the sintered layers. After sintering, the second sintered layer of the layer structure has a lower relative density or a lower degree of compression than that of the first sintered layer. The resulting layer structure has a density gradient in which the degree of compression or relative density decreases as the distance from the substrate (i.e., from the first sintered layer to the second sintered layer) increases.For example, at least one first sintered layer may have a relative density of at least 70%, and at least one second sintered layer may have a relative density at least 3% lower than that of the first sintered layer.

[0022] Due to the higher proportion of sintering additives in the first aqueous suspension, the first sintered layer of the prepared coating substrate (i.e., the first layer in the layer structure that is in direct contact with the substrate) has a relatively high degree of compression or a relatively high relative density, for this reason the substrate is very well protected from corrosive media in high-temperature applications. Since the second aqueous suspension contains a lower proportion of sintering additives or does not contain any sintering additives, the second sintered layer of the prepared coating substrate (i.e., the second layer in the layer structure) also contains no sintering additives or only small amounts of them, thereby reducing the risk that sintering additives from the coating may penetrate the growth atmosphere and contaminate it when the prepared coating substrate is used in high-temperature applications in semiconductor crystal growth. In this case, at least one second sintered layer can also function as a protective layer, thereby reducing the risk of sintering additives from at least one first sintered layer entering the growth atmosphere. Furthermore, at least one second sintered layer has a lower degree of compression or lower relative density than at least one first sintered layer, due to a lower proportion of sintering additives in the second aqueous suspension or due to the absence of sintering additives. The resulting higher porosity of at least one second sintered layer provides an advantage when using the coating substrate in high-temperature applications in semiconductor crystal growth, as a larger contact surface for the molten material used in crystal growth is obtained through the higher porosity, thereby increasing the evaporation rate and, consequently, the growth rate.

[0023] Therefore, as a result of the layer system described above, obtained using the method according to the present invention, the coated substrate prepared according to the present invention is particularly well suited for use in high-temperature applications such as semiconductor crystal growth.

[0024] By selecting the amounts of sintering additives in the first and second aqueous suspensions, and optionally adjusting the sintering parameters, the relative densities in individual layers of the layer system can be set so that a desired density gradient can be achieved within the layer system. Here, it is particularly advantageous when the layer system has a low density gradient, because in that case the layer system is more thermally stable.

[0025] A coating substrate that can be prepared using 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 to grow gallium nitride semiconductor crystals, and the layer system obtained in the method according to the present invention in this case functions as a coating for the gallium evaporator. In this case, at least one first sintered layer of the layer system (i.e., a sintered layer derived from a first aqueous suspension) can protect the base material of the gallium evaporator particularly well from corrosive molten gallium due to its higher relative density, while at least one second sintered layer of the layer system (i.e., a sintered layer derived from a second aqueous suspension) can increase the gallium evaporation rate and, consequently, the gallium nitride growth rate due to its larger contact area for molten gallium, resulting from its lower relative density and higher porosity.

[0026] Between steps c) and d), at least one coated substrate is preferably not subjected to the sintering process. This means that a substrate coated with at least one layer of the first aqueous suspension is preferably not subjected to the sintering process before at least one layer of the second aqueous suspension is applied to at least one layer of the first aqueous suspension applied to the substrate. Since the coated substrate is subjected to the sintering process only after step d), at least one layer of the first aqueous suspension applied in step c) and at least one layer of the second aqueous suspension applied in step d) can be sintered simultaneously in the sintering process. This avoids the need to sinter each of the two layers separately after each layer has been applied, thereby eliminating the sintering step. As a result, the process is faster and less expensive. Furthermore, if at least one layer of the second aqueous suspension is applied to an already sintered layer of the first aqueous suspension, the bond may be weakened due to lack of penetration, and therefore delamination may occur more easily when subjected to thermal stress. This can be avoided by sintering the two layers applied in steps c) and d) together during the sintering process after step d).

[0027] In step c) of the method according to the present invention, at least one layer of the first aqueous suspension can be applied to the entire surface of the substrate, or to only one or more sections of the surface of the substrate. In step d) of the method according to the present invention, at least one layer of the second aqueous suspension can be applied to the entire at least one layer of the first aqueous suspension applied in step c), or to only one or more sections of the at least one layer of the first aqueous suspension applied in step c). If the substrate is a crucible, for example, in step c), at least one layer of the first aqueous suspension can be applied to the entire surface of the crucible, and in step d), at least one layer of the second aqueous suspension can be applied to only a section of the at least one layer of the first aqueous suspension located inside the crucible.

[0028] A preferred modification of the method according to the present invention is: - The 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, SiC / SiC fiber composite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof, and / or - The refractory metal silicide in (step a) and / or step b) is 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, and / or - At least one refractory metal carbide in (step a) and / or step b) 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:

[0029] According to a particularly preferred modification of the method according to the present invention, the refractory metal silicide in (step a) and / or step b) is selected from the group consisting of zirconium disilidate (ZrSi2), hafnium disilidate (HfSi2), vanadium disilidate (VSi2), niobium disilidate (NbSi2), tantalum disilidate (TaSi2), molybdenum disilidate (MoSi2), tungsten disilidate (WSi2), and mixtures thereof.

[0030] Due to their non-toxic use in relation to the environment, health, and safety, combined with a melting temperature range between 1400°C and 2200°C, refractory metal silicides selected from the group consisting of titanium silicide, zirconium silicide, hafnium silicide, vanadium silicide, niobium silicide, tantalum silicide, chromium silicide, molybdenum silicide, tungsten silicide, and mixtures thereof, are ideal as sintering additives for high-temperature sintering processes. The use of the above metal silicides as sintering additives allows for the formation of a desired molten phase during the heating phase, and enables desirable particle rearrangement that enhances sintering activity before active sintering. Therefore, the melting temperature of the sintering additive can be lower than the sintering temperature. Furthermore, the boiling temperature of the sintering additive under given pressure conditions can be significantly higher than the sintering temperature used, thereby ensuring a constant stability of the liquid phase throughout the sintering process and avoiding the possibility of evaporation. Furthermore, the melting temperature of the sintering additive can be set lower than the application temperature of the refractory metal carbide coating (e.g., TaC coating), thereby preventing the sintering additive from evaporating during use.

[0031] It is particularly advantageous if at least one of the sintering additives is MoSi2, TaSi2, or a mixture thereof. The above sintering additives have a melting point of about 2050°C and therefore possess high-temperature stability, and are thus particularly suitable for use at high temperatures, for example, in the internal structure of a reactor.

[0032] At least one refractory metal carbide is very preferably tantalum carbide. Tantalum carbide provides a particularly good protective effect for the substrate.

[0033] The substrate may preferably include or consist of a material selected from the group consisting of graphite, preferably isotropic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0034] The substrate preferably comprises or may comprise 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.

[0035] 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.

[0036] The base material very preferably contains or consists of graphite, preferably isotropic graphite.

[0037] A more preferred modification of the method according to the present invention is characterized in that at least one refractory metal carbide and at least one sintering additive are present in the form of particles, and the mean particle size of the particles of at least one sintering additive is less than 5 μm and / or smaller than the mean particle size of the particles of at least one refractory metal carbide. Having a particle size of less than 5 μm for the particles of at least one sintering additive makes it possible to avoid larger pores or even structural deficiencies in the coating after sintering. Having a mean particle size of at least one sintering additive particles smaller than the mean particle size of the particles of at least one refractory metal carbide provides the advantage that the sintering additive particles can accumulate better in the voids within the refractory metal carbide layer. The mean particle size of the particles of at least one refractory metal carbide can preferably be in the range of 0.2 to 2 μm.

[0038] The average particle size of at least one refractory metal carbide particle and / or the average particle size of at least one sintering additive particle can be determined, for example, by laser diffraction (DIN13320:2020-01).

[0039] According to a more preferred modification of the method according to the present invention, at least one refractory metal carbide preferably exists as a powder mixture comprising or consisting of powders of the same refractory metal carbide with different average particle sizes. In other words, here, a powder mixture is used as the at least one refractory metal carbide, and the powder mixture preferably contains different refractory metal carbide particles of the same refractory metal carbide, the particles differing from one another in terms of their average particle size. For example, the powder mixture may preferably contain two types of particles of the same refractory metal carbide, where the average particle diameter of the first type of particles is greater than the average particle diameter of the second type of particles. For example, such a powder mixture can be obtained by mixing different powders of the same refractory metal carbide together in a specific ratio of nano- and micron-sized particles. Since at least one refractory metal carbide exists as a powder mixture, open spaces can be filled more effectively, and the arrangement of refractory metal carbide powder particles on the substrate can be designed to be more void-free. In this way, the relative density of the prepared layer can be increased independently of the presence and amount of sintering additives in the layer.

[0040] At least one refractory metal carbide is preferably present in the preparation of the second aqueous suspension in step b) as a powder mixture containing or consisting of powders of the same refractory metal carbide with different average particle sizes, and the second aqueous suspension preferably does not contain sintering additives. In this way, the relative density of the layers resulting from at least one second suspension can be increased (preferably without using sintering additives), resulting in a lower density gradient in the layered structure, thereby increasing the thermal stability of the layered structure and the quasi-diffusion-inhibiting effect (for example, with respect to the diffusion of impurities into the growth atmosphere). The low density difference avoids abrupt changes in layer density and the resulting non-uniformly distributed thermal stress in the layered system, which can lead to cracks, delamination, or, in the worst case, failure of the layered system. Thus, the layered system is more thermally stable. Furthermore, due to the use of refractory metal carbide particles of different particle sizes, the second layer also has relatively low porosity, which allows it to function as a separation layer from the external atmosphere, resulting in a quasi-diffusion inhibitory effect.

[0041] A more preferred modification of the method according to the present invention is that the first aqueous suspension and / or the second aqueous suspension are - Each aqueous suspension contains 60 to 90% by weight, preferably 70 to 85% by weight, of at least one refractory metal carbide, and / or - Each aqueous suspension contains 0.1 to 20% by weight, preferably 0.5 to 10% by weight, of at least one sintered additive, based on the total weight of each aqueous suspension. It is characterized by the following:

[0042] For example, the first aqueous suspension may contain at least one sintered additive in an amount of 0.2 to 20.0% by weight, preferably 0.6 to 10.0% by weight, based on the total weight of each aqueous suspension, and / or the second aqueous suspension may contain at least one sintered additive in an amount of 0.1 to 19.9% ​​by weight, preferably 0.5 to 9.9% by weight, based on the total weight of each aqueous suspension.

[0043] According to a more preferred modification of the method according to the present invention, the weight percentage of at least one sintering additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, is approximately 0.1% to 20% by weight, preferably approximately 0.5% to 10% by weight, lower than the weight percentage of at least one sintering additive in the first aqueous suspension, based on the total weight of the first aqueous suspension. In this way, a low density gradient can be obtained in the layer structure of the first layer (i.e., the layer derived from the first aqueous suspension) and the second layer (i.e., the layer derived from the second aqueous suspension), thereby enhancing the thermal stability of the layer structure and the quasi-diffusion inhibition effect (for example, with respect to the diffusion of impurities into the growth atmosphere). The low density difference avoids abrupt changes in layer density and the resulting non-uniformly distributed thermal stress in the layer system, which can lead to cracks, delamination, or, in the worst case, failure of the layer system. Thus, the layer system is more thermally stable. Furthermore, due to the use of sintering additives, the second layer also has a relatively low porosity, which allows it to function as a separation layer from the external atmosphere, resulting in a quasi-diffusion inhibitory effect.

[0044] For example, the weight percentage of at least one sintered additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, can be reduced by 0.1% to 19.9% ​​by weight, preferably 0.5% to 9.9% by weight, compared to the weight percentage of at least one sintered additive in the first aqueous suspension, based on the total weight of the first aqueous suspension.

[0045] The at least one first aqueous suspension and / or at least one second aqueous suspension may contain at least one binder selected from the group consisting of polyvinyl alcohol, polyethylene glycol, polyvinyl butyral, polyacrylic acid, polyurethane, chloroprene rubber, phenolic resin, acrylic resin, carboxymethylcellulose, alginic acid, dextrin, sodium biphenyl-2-yl oxide, polyphenyl oxide, and mixtures thereof, preferably selected from the group consisting of polyvinyl alcohol, sodium biphenyl-2-yl oxide, polyphenyl oxide, and mixtures thereof, and the at least one binder may be present in the at least one first aqueous suspension and / or at least one second aqueous suspension in a proportion of 0.05 to 1% by weight or 0.01 to 5% by weight based on the total weight of each aqueous suspension.

[0046] A more preferred variation of the method according to the present invention is characterized in that the preparation of the first aqueous suspension in step a) and / or the preparation of the second aqueous suspension in step b) is carried out by mixing the components of the suspensions to be prepared with the assistance of a dispersion device, the mixing being carried out with the assistance of a dispersion device, preferably using a grinding medium, and / or over a period of at least 12 hours. In this way, optimal mixing of each aqueous suspension can be achieved, thereby avoiding heterogeneity in the distribution of sintering additives and thus in compression. For example, when mixing with a dispersion device, a rotational speed of up to 1 m / s can be used.

[0047] A more preferred modification of the method according to the present invention is that the application of at least one layer of the first aqueous suspension in step c) and / or the application of at least one layer of the second aqueous suspension in step d) - Performed by dipping, brushing, or spray application, and / or - Performed with an average layer thickness of less than 150 μm, preferably 20 μm to 100 μm, and particularly preferably 30 μm to 80 μm. It is characterized by the following:

[0048] Spray coating is a preferred choice for preparing one or more thin, fast-drying refractory metal carbide layers, preferably having a layer thickness in the range of 20 μm to 80 μm. By using a spray jet and rotating the components at high speed, very thin suspension layers can be applied to a surface that can dry rapidly to very rapidly depending on the solid content of the suspension. The solid content of the refractory metal carbide powder is preferably more than or equal to 70% by weight of the total suspension. Each individual layer to be applied should preferably exhibit similar drying behavior. In principle, fast-drying behavior of the applied suspension layers is desirable because if the drying time of the layers is too long, heterogeneity in the particle distribution may occur due to density differences between the refractory metal carbide and sintering additives.

[0049] A more preferred modification of the method according to the present invention is characterized in that at least one third aqueous suspension is added to the preparation, the third aqueous suspension comprising or consisting of at least one refractory metal carbide and water, the at least one third aqueous suspension does not contain sintering additives, and between steps d) and e), at least one layer of the at least one third aqueous suspension is applied to at least one coated layer of the second aqueous suspension. In this case, at least one layer of the first aqueous suspension, at least one layer of the second aqueous suspension, and at least one layer of the third aqueous suspension can be sintered together (simultaneously) in sintering step e). This forms a stable interlayer bond that is stable even under thermal stress. The at least one refractory metal carbide contained in the at least one third aqueous suspension may be the same as the refractory metal carbide contained in the first aqueous suspension and / or the refractory metal carbide contained in the second aqueous suspension. The at least one refractory metal carbide contained in at least one third aqueous suspension is preferably 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.

[0050] Preferably, a third aqueous suspension can be prepared by adding multiple types of third aqueous suspensions, each comprising or consisting of at least one refractory metal carbide and water, and the multiple types of third aqueous suspensions do not contain sintering additives, and between steps d) and e), at least one layer of each of the third aqueous suspensions is applied to overlap each other on at least one coated layer of the second aqueous suspension, thereby resulting in a layer sequence as a result of the layers of the third aqueous suspension. In this way, the coated substrate obtained after sintering may have a layer sequence of multiple third sintered layers, and the relative density of the multiple sintered layers in the layer sequence decreases as the distance from at least one second sintered layer increases. For example, by adjusting the sintering parameters, the relative density in individual layers of the layer sequence can be set so that a (desired) density gradient in the layer sequence can be achieved.

[0051] A more preferred modification of the method according to the present invention is that the sintering process performed in step d) - Performed at a temperature of 2100°C to 2500°C, preferably 2200°C to 2400°C, and / or - Performed with a holding time of 1 to 15 hours, preferably 2 to 10 hours, and / or - Operated 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 - After the first time segment of the sintering process, the pressure is increased, preferably by 3 bar (300 kPa) to 7 bar (700 kPa), and / or - Performed under an argon atmosphere It is characterized by the following:

[0052] These embodiments of the sintering process make it possible to obtain a particularly favorable ratio between the degree of compression of the first layer of the layered structure (i.e., the layer resulting from the first aqueous suspension) and the degree of compression of the second layer of the layered structure (i.e., the layer resulting from the second aqueous suspension). Furthermore, these embodiments of the sintering process enhance the stability of the molten phase throughout the sintering process.

[0053] A preferred modification, in which the pressure is increased by a preferred 3 bar (300 kPa) to 7 bar (700 kPa) after the first time segment of the sintering process in step e), for example, at a sintering temperature of 2300°C, can prevent the sintering additive from evaporating, while simultaneously ensuring that a stable liquid phase is optimally dispersed between the particles.

[0054] According to a more preferred modification of the method according to the present invention, the substrate is a graphite substrate, preferably an isotropic graphite substrate.

[0055] The present invention relates to a substrate, at least one first sintered layer disposed on the substrate, comprising or comprising at least one refractory metal carbide and at least one sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, and at least one second sintered layer disposed on the at least one first layer, comprising at least one refractory metal The present invention further relates to a coating substrate comprising a carbide and, optionally, a second sintered layer comprising or comprising at least one sintered additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, wherein at least one first layer has a relative density of at least 70%, and the relative density of at least one second layer is at least 3% lower than the relative density of at least one first layer.

[0056] The presence of at least one sintering additive in the first sintered layer and / or the second sintered layer can be detected, for example, by elemental analysis or XRD analysis.

[0057] Relative density can be determined, for example, through REM cross-sectional analysis.

[0058] At least one sintering additive may also be present in the first sintering layer and / or the second sintering layer in at least a partially decomposed form and / or in the form of a reaction product of the reaction between at least one sintering additive and at least one refractory metal carbide.

[0059] The at least one refractory metal carbide contained in the first sintered layer and the at least one refractory metal carbide contained in the second sintered layer may be the same refractory metal carbide or different refractory metal carbides. The second sintered layer may contain a sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, wherein the weight percentage of the at least one sintering additive in the second sintered layer based on the total weight of the second sintered layer is, in this case, preferably less than the weight percentage of the at least one sintering additive in the first sintered layer based on the total weight of the first sintered layer. The at least one sintering additive contained in the first sintered layer and the at least one sintering additive contained in the second sintered layer may be the same sintering additive or different sintering additives. Alternatively, the second sintered layer may not contain any sintering additives.

[0060] The first sintered layer contains at least one sintering additive, preferably selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof.

[0061] If the second sintered layer contains at least one sintering additive, the at least one sintering additive contained in the second sintered layer is preferably selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof.

[0062] The coated substrate according to the present invention has a highly advantageous layer structure composed of at least two different sintered layers. Due to the relative density of at least one first sintered layer being at least 70%, the substrate is very well protected from erosive or corrosive substances in high-temperature applications, such as molten material during semiconductor crystal growth. At least one second sintered layer has a relative density or a degree of compression at least 3% lower than that of at least one first sintered layer. The layer structure thus obtained has a density gradient in which the degree of compression or relative density decreases as the distance from the substrate, i.e., from at least one first sintered layer to at least one second sintered layer, increases.

[0063] The resulting higher porosity of at least one second sintered layer compared to at least one first sintered layer provides an advantage when using a coating substrate in high-temperature applications in semiconductor crystal growth, as a larger contact surface for the molten material used in crystal growth is obtained through the higher porosity, thereby increasing the evaporation rate and, consequently, the growth rate.

[0064] Therefore, as a result of the advantageous layering system described above, the coated substrate according to the present invention is particularly well suited for use in high-temperature applications such as semiconductor crystal growth.

[0065] A preferred embodiment of the coating substrate according to the present invention is: - The 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, SiC / SiC fiber composite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof, and / or - The refractory metal silicide (in the first sintered layer and / or the second sintered layer) is 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, and / or - At least one refractory metal carbide (in the first and / or second sintered layer) 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:

[0066] According to a particularly preferred embodiment of the coating substrate according to the present invention, the refractory metal silicide (in the first sintered layer and / or the second sintered layer) is selected from the group consisting of zirconium disilicate (ZrSi2), hafnium disilicate (HfSi2), vanadium disilicate (VSi2), niobium disilicate (NbSi2), tantalum disilicate (TaSi2), molybdenum disilicate (MoSi2), tungsten disilicate (WSi2), and mixtures thereof.

[0067] At least one refractory metal carbide is very preferably tantalum carbide.

[0068] The substrate may preferably include or consist of a material selected from the group consisting of graphite, preferably isotropic graphite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof.

[0069] The substrate preferably comprises or may comprise 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.

[0070] The base material very preferably contains or consists of graphite, preferably isotropic graphite.

[0071] The substrate can preferably be a carbon substrate, particularly preferably a graphite substrate, and very preferably an isotropic graphite substrate. Isotropic graphite is understood to mean graphite prepared by isotropic pressure treatment. For example, the substrate can be a crucible, preferably a carbon crucible, particularly preferably a graphite crucible, and very preferably an isotropic graphite crucible.

[0072] Furthermore, it is preferable that at least one first sintered layer and at least one second sintered layer are essentially free of cobalt, nickel, and iron. "Essentially free of cobalt, nickel, and iron" is understood here to mean that at least one first sintered layer and at least one second sintered layer may contain minimal amounts of cobalt, nickel, and / or iron that do not interfere with the use of the coating substrate, for example, in semiconductor crystal growth. A formulation design in which at least one first sintered layer and at least one second sintered layer are essentially free of cobalt, nickel, and iron is preferably understood to mean that at least one first sintered layer and at least one second sintered layer contain, based on the total weight of at least one first sintered layer and at least one second sintered layer, not exceeding 1% by weight of cobalt, more preferably not exceeding 0.1% by weight, not exceeding 1% by weight of nickel, and not exceeding 1% by weight of iron, particularly preferably not exceeding 0.1% by weight. Furthermore, at least one first sintered layer and at least one second sintered layer are particularly preferably free of cobalt, nickel, and iron.

[0073] By using one or more sintering additives selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, the use of cobalt, nickel, and iron as sintering additives can be omitted. As a result, at least one first sintered layer and at least one second sintered layer preferably do not contain (essentially) cobalt, nickel, and iron. Consequently, in one application, for example in high-temperature applications in semiconductor crystal growth, there is no possibility that cobalt, nickel, and iron will leak out from the coating substrate as impurities and adversely affect the application.

[0074] Furthermore, starting from the particle size of the initial spray layer or sprayed particles, it is preferable that the particles grow by at least 1.5 times, preferably in the range of 1.5 to 10 times, and particularly preferably in the range of 1.5 to 5 times.

[0075] A more preferred embodiment of the coating substrate according to the present invention is that at least one first sintered layer is - Having a relative density higher than 75%, preferably higher than 80%, particularly preferably higher than 90%, very particularly preferably higher than 95%, and / or - 1e -11 m 2 Lower than, preferably 1e -13 m 2 Having a lower transmittance than, and / or - Having an adhesive strength of at least 2 MPa, preferably at least 4 MPa, and / or - Having an average layer thickness of at least 20 μm, preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm. It is characterized by the following:

[0076] Furthermore, at least one second sintered layer, - Having a relative density at least 5%, preferably at least 10%, particularly preferably 10% to 30%, very particularly preferably 15% to 25%, particularly 18% to 22%, lower than the relative density of at least one first sintered layer, and / or - 1e -11 m 2 Lower than, preferably 1e -12 m 2 Having a lower transmittance than, and / or - Having an adhesive strength of at least 2 MPa, preferably at least 4 MPa, and / or - Having an average layer thickness of at least 20 μm, preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm. It is preferable.

[0077] Relative density can be determined, for example, by REM cross-sectional analysis. Average layer thickness can be determined, for example, by cross-sectional analysis. Transmittance can be determined, for example, by measuring the gas volume flow rate through the sample as a function of the pressure difference through the sample and converting it to Darcy's transmittance constant. Adhesion strength can be determined, for example, by tensile testing.

[0078] At least one first sintered layer preferably has a lower transmittance than at least one second sintered layer.

[0079] At least one first sintered layer preferably has higher adhesive strength than at least one second sintered layer.

[0080] At least one first sintered layer preferably has a thickness less than at least one second sintered layer.

[0081] The at least one first sintered layer is particularly preferably having lower transmittance, higher adhesive strength, and less thickness than the at least one second sintered layer.

[0082] According to a more preferred embodiment of the coating substrate according to the present invention, the coating substrate comprises at least one third sintered layer disposed on at least one second sintered layer, the third sintered layer comprising or consisting of at least one refractory metal carbide, the at least one third sintered layer not comprising sintering additives, and the relative density of the at least one third sintered layer being at least 5%, preferably at least 10%, particularly preferably 10% to 30%, very particularly preferably 15% to 25%, and especially particularly 18% to 22% lower than the relative density of the at least one second sintered layer. The at least one refractory metal carbide contained in the at least one third sintered layer may be the same as the refractory metal carbide contained in the at least one first sintered layer and / or the refractory metal carbide contained in the at least one second sintered layer. The at least one refractory metal carbide contained in at least one third sintered layer is preferably 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.

[0083] Furthermore, it is preferable that at least one third sintered layer comprises a layer array of multiple sintered layers, and the relative density of the multiple sintered layers within the layer array decreases as the distance from at least one second sintered layer increases. The relative density can be determined, for example, by REM cross-sectional analysis.

[0084] Furthermore, the coating substrate according to the present invention can or preferably be prepared using the method according to the present invention for preparing the coating substrate. The present invention also relates to the use of the coating substrate according to the present invention in semiconductor crystal growth, wherein the coating substrate is preferably a coating crucible.

[0085] The coating substrate 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 to grow gallium nitride semiconductor crystals, and the layer system contained in the coating substrate according to the present invention functions as a coating for the gallium evaporator in this case. In this case, the base material of the gallium evaporator can be protected particularly well from corrosive molten gallium by at least one first sintered layer due to its higher relative density, while the gallium evaporation rate and consequently the gallium nitride growth rate can also be increased by the lower relative density and higher porosity of at least one second sintered layer of the layer system, due to the larger contact surface for molten gallium.

[0086] The present invention also relates to the following embodiments.

[0087] Appearance 1 a) Prepare a first aqueous suspension comprising or consisting of at least one sintered additive selected from the group consisting of at least one refractory metal carbide, silicon, zirconium boride, refractory metal silicides, and mixtures thereof, and water. b) Prepare a second aqueous suspension containing at least one refractory metal carbide and water, the second aqueous suspension being - The sintered additive comprises at least one selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof, wherein the weight percentage of the at least one sintered additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, is less than the weight percentage of the at least one sintered additive in the first aqueous suspension, based on the total weight of the first aqueous suspension, or - Does not contain sintering additives, c) Apply at least one layer (2) of the first aqueous suspension to the substrate (1), d) Apply at least one layer (3) of the second aqueous suspension to at least one layer (2) of the first aqueous suspension applied to the substrate (1), e) After step d), the substrate (1) is subjected to a sintering process. A method for preparing a coating substrate.

[0088] Appearance 2 - The 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, SiC / SiC fiber composite, carbide ceramics, nitride ceramics, oxide ceramics, and mixtures thereof, and / or - The refractory metal silicide is selected from the group consisting of titanium silicide, zirconium silicide, hafnium silicide, vanadium silicide, niobium silicide, tantalum silicide, chromium silicide, molybdenum silicide, tungsten silicide, 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. A method according to a prior embodiment, characterized by the features described above.

[0089] Appearance 3 - At least one refractory metal carbide and at least one sintered additive are present in the form of particles, where the average particle size of the particles of at least one sintered additive is less than 5 μm and / or smaller than the average particle size of the particles of at least one refractory metal carbide and / or - At least one refractory metal carbide preferably exists as a powder mixture comprising or consisting of powders of the same refractory metal carbide that differ in terms of the average particle size of the particles. A method according to any one of the preceding embodiments, characterized by the above.

[0090] Pattern 4 The first aqueous suspension and / or the second aqueous suspension are - Each aqueous suspension contains 60 to 90% by weight, preferably 70 to 85% by weight, of at least one refractory metal carbide, and / or - Each aqueous suspension contains 0.1 to 20% by weight, preferably 0.5 to 10% by weight, of at least one sintered additive, based on the total weight of each aqueous suspension. A method according to any one of the preceding embodiments, characterized by the above.

[0091] Appearance 5 A method according to any one of the preceding embodiments, characterized in that the weight percentage of at least one sintered additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, is 0.1% to 20% by weight, preferably 0.5% to 10% by weight, lower than the weight percentage of at least one sintered additive in the first aqueous suspension, based on the total weight of the first aqueous suspension.

[0092] Appearance 6 The preparation of the first aqueous suspension in step a) and / or the preparation of the second aqueous suspension in step b) is carried out by mixing the components of the suspension to be prepared with the assistance of a dispersion device, wherein the mixing is carried out with the assistance of a dispersion device, preferably using a grinding medium and / or over a period of at least 12 hours, according to any one of the preceding embodiments.

[0093] Appearance 7 The application of at least one layer (2) of the first aqueous suspension in step c) and / or the application of at least one layer (3) of the second aqueous suspension in step d) - Performed by dipping, brushing, or spray application, and / or - Performed with an average layer thickness of less than 150 μm, preferably 20 μm to 100 μm, and particularly preferably 30 μm to 80 μm. A method according to any one of the preceding embodiments, characterized by the above.

[0094] Appearance 8 Further, prepare at least one third aqueous suspension, the third aqueous suspension comprising or consisting of at least one refractory metal carbide and water, wherein the at least one third aqueous suspension does not contain sintering additives. Between steps d) and e), at least one layer of at least one third aqueous suspension is applied to at least one coated layer (3) of the second aqueous suspension. A method according to any one of the preceding embodiments, characterized by the above.

[0095] Appearance 9 The sintering process in step e) is - Performed at a temperature of 2100°C to 2500°C, preferably 2200°C to 2400°C, and / or - Performed with a holding time of 1 to 15 hours, preferably 2 to 10 hours, and / or - Operated 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 - After the first time segment of the sintering process, the pressure is increased, preferably by 3 bar (300 kPa) to 7 bar (700 kPa), and / or - Performed under an argon atmosphere A method according to any one of the preceding embodiments, characterized by the above.

[0096] Appearance 10 A coated substrate comprising a substrate (1), at least one first sintered layer (4) disposed on the substrate (1) and containing or consisting of at least one refractory metal carbide and at least one sintering additive selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof, and at least one second sintered layer (5) disposed on at least one first sintered layer (4), the second sintered layer containing or consisting of at least one refractory metal carbide and optionally at least one sintering additive selected from the group consisting of silicon, zirconium boride, refractory metal silicides, and mixtures thereof, wherein at least one first sintered layer (4) has a relative density of at least 70% and the relative density of at least one second sintered layer (5) is at least 3% lower than the relative density of at least one first sintered layer (4).

[0097] Aspect 11 At least one first sintered layer (4) has - a relative density higher than 75%, preferably higher than 80%, particularly preferably higher than 90%, and very particularly preferably higher than 95%, and / or - 1e -11 m 2 lower, preferably lower than 1e -13 m 2 and having a lower transmittance, and / or - an adhesive strength of at least 2 MPa, preferably at least 4 MPa, and / or - an average layer thickness of at least 20 μm, preferably from 20 μm to 150 μm, particularly preferably from 30 μm to 100 μm The coated substrate according to Aspect 10, characterized by the above.

[0098] Aspect 12 At least one second sintered layer (5) has - a relative density at least 5%, preferably at least 10%, particularly preferably from 10% to 30%, very particularly preferably from 15% to 25%, especially from 18% to 22% lower than the relative density of at least one first sintered layer, and / or - 1e -11 m 2 Lower than, preferably 1e -12 m 2 Having a lower transmittance than, and / or - Having an adhesive strength of at least 2 MPa, preferably at least 4 MPa, and / or - Having an average layer thickness of at least 20 μm, preferably 20 μm to 150 μm, and particularly preferably 30 μm to 100 μm. A coated substrate according to embodiment 10 or 11, characterized by the above.

[0099] Appearance 13 The coating substrate comprises at least one third sintered layer disposed on at least one second sintered layer (5) and comprising or consisting of at least one refractory metal carbide, wherein the at least one third sintered layer does not contain sintering additives, and the relative density of the at least one third sintered layer is at least 5% lower than the relative density of the at least one second sintered layer (5). Here, at least one third sintered layer preferably comprises a layer array of multiple sintered layers, where the relative density of the multiple sintered layers in the layer array decreases as the distance from at least one second sintered layer (5) increases. A coating substrate according to any one of embodiments 10 to 12, characterized in that

[0100] Appearance 14 A coated substrate according to any one of embodiments 10 to 13, characterized in that the coated substrate can be prepared or is prepared using a method according to any one of embodiments 1 to 9.

[0101] Appearance 15 Use of a coating substrate according to any one of embodiments 10 to 14 in semiconductor crystal growth, wherein the coating substrate is preferably a coating crucible.

[0102] The present invention will be described in more detail based on the following drawings and examples, without limiting it to the parameters specifically shown.

[0103] Figure 1 shows some exemplary variations of the method according to the present invention. In this example, a (closed) crucible, preferably a graphite crucible, such as an isotropic graphite crucible, is used as the substrate 1, and the crucible is used in semiconductor crystal growth. In this application, a growth atmosphere is present inside the crucible. Figure 1 schematically depicts, here, step A, the coating of a first layer 2 onto the entire surface of the substrate 1, and step B, the coating of a second layer 3 onto a portion of the first layer 2 coated on the inside of the substrate 1. Thus, a specific layer configuration or specific layer structure consisting of two layers is obtained. The first layer 2 is obtained by coating a layer of a first aqueous suspension consisting of tantalum carbide, water, and a sintering additive selected from the group consisting of silicon, hafnium, zirconium, vanadium, tantalum pentoxide, boron carbide, silicon carbide, tungsten carbide, vanadium carbide, molybdenum carbide, boron nitride, tantalum nitride, zirconium nitride, niobium nitride, tantalum diboride, tungsten diboride, zirconium boride, refractory metal silicides, and mixtures thereof, preferably silicon, zirconium boride, refractory metal silicides, and mixtures thereof. The second layer 3 is obtained by coating a layer of a second aqueous suspension consisting of tantalum carbide and water, and therefore free of sintering additives. The coating of the first layer 2 in step A and the coating of the second layer 3 in step B can be performed by spray coating, respectively. Only after applying the second layer 3 is the (coating) substrate sintered in step C, thereby sintering the first layer 2 and the second layer 3 together, forming the first sintered layer 4 from the first layer 2 and the second sintered layer 5 from the second layer 3. During sintering, the layer configuration or layer structure is compressed as intended.

[0104] The resulting coated substrate has a highly advantageous layer structure consisting of two different sintered layers 5 and 6. Due to the use of sintering additives in the first layer 2, the sintered layer 4 has a high relative density, and as a result, the substrate is very well protected from corrosive melts used in semiconductor crystal growth. The second sintered layer 5 has a lower relative density than the first sintered layer 4 due to the absence of sintering additives in the second layer 3. The resulting layer structure has a density gradient in which the degree of compression or relative density decreases as the distance from the substrate (i.e., from the first sintered layer 4 to the second sintered layer 5) increases. The resulting higher porosity of the second sintered layer 5 compared to the first sintered layer 4 provides an advantage when using the coated substrate in semiconductor crystal growth, as the higher porosity provides a larger contact surface for the melt used in crystal growth, thereby increasing the evaporation rate and, consequently, the growth rate.

[0105] Figure 2 graphically shows the density distribution within a layer system for an exemplary coated substrate according to the present invention, where the graph shows the relative sintered density as a function of layer thickness (or distance from the substrate surface). The exemplary coated substrate described herein has a layer structure with three sintered layers of different relative densities. Point 0 on the x-axis represents the substrate surface, where t represents the layer thickness of the entire coating comprising the first, second, and third sintered layers. The value of Δx represents the distance between two layers of different densities, so Δx1 corresponds to the thickness of the first sintered layer, Δx2 corresponds to the thickness of the second sintered layer, and Δx3 corresponds to the thickness of the third sintered layer. The difference in density between adjacent sintered layers is quantified by Δρ. The first sintered layer, i.e., the sintered layer in direct contact with the substrate, has a relative density of at least 70%. In the graph shown in Figure 2, it can be seen that as the distance from the substrate increases, the relative density in the sintered layers of the layer system decreases; that is, the second sintered layer has a relative density (at least 5%) lower than the first sintered layer, and the third sintered layer has a relative density (at least 5%) lower than the second sintered layer. As a result, a density gradient is created within the layer system. To determine the values ​​shown in the graph, SEM images of the polished cross section can be used to distinguish over which Δx uniform density exists. In this case, the sintered density can be calculated based on the determined Δx and the mass of this region determined during coating. The density difference between adjacent layers with an extent of Δx is quantified by Δρ.

[0106] Embodiment Example 1 First, a first aqueous suspension was prepared consisting of 80% by weight tantalum carbide, 1% by weight silicon as a sintering additive, and 19% by weight water, and a second aqueous suspension consisting of 80% by weight tantalum carbide and 20% by weight water. Therefore, the second aqueous suspension does not contain the sintering additive. The average powder particle size of the TaC particles is preferably in the range of 0.2 to 2 μm. To prepare the aqueous suspensions, the mixtures of each component were mixed with the assistance of a dispersion device (with a maximum rotational speed of 1 m / s) and, if necessary, with a grinding medium. The mixing process may take at least 12 hours.

[0107] Next, layer 2 of the first aqueous suspension was applied to the substrate 1, preferably a graphite substrate, such as an isotropic graphite substrate. The application was carried out by spray coating, and layer 2 of the first aqueous suspension was applied with an average layer thickness ranging from 20 to 80 μm. Alternatively, the application can also be carried out by, for example, dipping or brushing.

[0108] Next, layer 3 of the second aqueous suspension is applied to the section of layer 2 of the first aqueous suspension that has been applied to the substrate. Here again, the application is carried out by spray coating, and layer 3 of the second aqueous suspension is applied with an average layer thickness ranging from 20 to 80 μm. Alternatively, here too, the application can be carried out by, for example, dipping or brushing.

[0109] After the two layers 2 and 3 were applied, the coated substrate was subjected to sintering under an argon atmosphere at a temperature of 2300°C, a holding time of 3 hours, and a pressure of 5 bar (500 kPa). Since the sintering of all applied layers is carried out in a single sintering pass, all individually applied layers are sintered together, resulting in a layer system with stable bonding even under high thermal stress. The first sintered layer 4, derived from layer 2 of the first aqueous suspension, has a high relative density exceeding 70% due to the use of sintering additives. Since no sintering additives are present in the second aqueous suspension, the second sintered layer 5, derived from layer 3 of the second aqueous suspension, has a lower relative density and, consequently, a higher porosity compared to the first sintered layer 4.

[0110] Figure 3 shows an overview of the method steps performed after the preparation of the aqueous suspension.

[0111] In the prepared sintered substrate, the first sintered layer 4 is determined, for example, by an apparatus that measures the gas volume flow rate through the sample as a function of the pressure difference through the sample and by conversion to Darcy's permeability constant, 1e -13 m 2It has a lower transmittance than [another material]. The adhesive strength of the first sintered layer 4, as determined by tensile testing, is greater than 4 MPa. Furthermore, the first sintered layer 4 has an average layer thickness of 25 μm to 30 μm, as determined by cross-sectional analysis.

[0112] In addition, based on the determination of the geometric density via the mass and volume of the compressed layers, the degree of compression of the first sintered layer 4 (derived from a first aqueous suspension containing 1 wt% silicon as a sintering additive) and the second sintered layer 5 (derived from a second aqueous suspension without a sintering additive) can be compared. The increase in the degree of compression can be quantified by the relative density (14.5 g / cm³). 3 This relates to the ratio between the geometric density and theoretical density of TaC having a value of . The comparison results are shown in Figure 4, where the relative density of the first sintered layer 4 is represented by a triangle and the relative density of the second sintered layer 5 is represented by a circle. Figure 4 shows that the first sintered layer 4 has a relative density of over 70% and is significantly higher than the second sintered layer 5. This demonstrates that the use of silicon as a sintering additive achieves a higher degree of compression in the sintered layer.

[0113] Embodiment Example 2 First, a first aqueous suspension was prepared consisting of 80% by weight tantalum carbide, 1% by weight molybdenum silicide (MoSi2) as a sintering additive, and 19% by weight water. A second aqueous suspension was prepared consisting of 80% by weight tantalum carbide and 20% by weight water. Therefore, the second aqueous suspension does not contain the sintering additive. The average powder particle size of the TaC particles is preferably in the range of 0.2 to 2 μm. To prepare the aqueous suspensions, the mixtures of each component were mixed with the assistance of a dispersion device (with a maximum rotational speed of 1 m / s) and, if necessary, with a grinding medium. The mixing process may take at least 12 hours.

[0114] Next, layer 2 of the first aqueous suspension was applied to the substrate 1, preferably a graphite substrate, such as an isotropic graphite substrate. The application was carried out by spray coating, and layer 2 of the first aqueous suspension was applied with an average layer thickness ranging from 20 to 80 μm. Alternatively, the application can also be carried out by, for example, dipping or brushing.

[0115] Next, layer 3 of the second aqueous suspension is applied to the section of layer 2 of the first aqueous suspension that has been applied to the substrate. Here again, the application is carried out by spray coating, and layer 3 of the second aqueous suspension is applied with an average layer thickness ranging from 20 to 80 μm. Alternatively, here too, the application can be carried out by, for example, dipping or brushing.

[0116] After the two layers 2 and 3 were applied, the coated substrate was subjected to sintering under an argon atmosphere at a temperature of 2300°C, a holding time of 3 hours, and a pressure of 5 bar (500 kPa). Since the sintering of all applied layers is carried out in a single sintering pass, all individually applied layers are sintered together, resulting in a layer system with stable bonding even under high thermal stress. The first sintered layer 4, derived from layer 2 of the first aqueous suspension, has a high relative density of at least 70% due to the use of sintering additives. Since no sintering additives are present in the second aqueous suspension, the second sintered layer 5, derived from layer 3 of the second aqueous suspension, has a lower relative density and, consequently, a higher porosity compared to the first sintered layer 4.

[0117] Figure 3 shows an overview of the method steps performed after the preparation of the aqueous suspension.

[0118] In the prepared coating substrate, the first sintered layer 4 is determined, for example, by an apparatus that measures the gas volume flow rate through the sample as a function of the pressure difference through the sample and by conversion to Darcy's permeability constant, 1e -13 m 2It has a lower transmittance than [another material]. The adhesive strength of the first sintered layer 4, as determined by tensile testing, is greater than 4 MPa. Furthermore, the first sintered layer 4 has an average layer thickness of 45 μm to 50 μm, as determined by cross-sectional analysis.

[0119] Based on the determination of the geometric density via the mass and volume of the compressed layers, a comparison of the degree of compression of the first sintered layer 4 (derived from a first aqueous suspension containing 1 wt% of the sintering additive MoSi2) and the second sintered layer 5 (derived from a second aqueous suspension without the sintering additive) can be made. The quantification of the increase in the degree of compression is based on the relative density (14.5 g / cm³). 3 This relates to the ratio between the geometric density and theoretical density of TaC having a value of . The comparison results are shown in Figure 5, where the relative density of the first sintered layer 4 is represented by a cross and the relative density of the second sintered layer 5 is represented by a circle. From Figure 5, it is clear that the relative density of the first sintered layer 4 is higher than 70%. Furthermore, the first sintered layer has a significantly higher relative density than the second sintered layer 5. This demonstrates that a higher degree of compression in the sintered layer can be achieved by using MoSi2 as a sintering additive.

Claims

1. a) Prepare a first aqueous suspension comprising at least one sintered additive selected from the group consisting of at least one refractory metal carbide, titanium silicide, zirconium silicide, hafnium silicide, vanadium silicide, niobium silicide, tantalum silicide, chromium silicide, molybdenum silicide, tungsten silicide, and mixtures thereof, and water. b) Prepare a second aqueous suspension, the second aqueous suspension being: - Complies with at least one refractory metal carbide, water, and at least one sintered additive selected from the group consisting of titanium silicide, zirconium silicide, hafnium silicide, vanadium silicide, niobium silicide, tantalum silicide, chromium silicide, molybdenum silicide, tungsten silicide, and mixtures thereof, wherein the weight percentage of the at least one sintered additive in the second aqueous suspension based on the total weight of the second aqueous suspension is lower than the weight percentage of the at least one sintered additive in the first aqueous suspension based on the total weight of the first aqueous suspension, or - Consists of at least one refractory metal carbide and water, c) Apply at least one layer of the first aqueous suspension to the substrate, d) Apply at least one layer of the second aqueous suspension to the at least one layer of the first aqueous suspension applied to the substrate. e) After step d), the substrate is subjected to a sintering process. The substrate is made of a material selected from the group consisting of graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite, SiC / SiC fiber composite, carbide ceramics, nitride ceramics, and mixtures thereof. A method for preparing a coating 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 at least one refractory metal carbide and the at least one sintered additive each exist in the form of particles, and the average particle size of the particles of the at least one sintered additive is less than 5 μm and / or smaller than the average particle size of the particles of the at least one refractory metal carbide and / or - The at least one refractory metal carbide exists as a powder mixture containing or consisting of powders that differ in terms of the average particle size of the particles. The method according to claim 1.

4. The first aqueous suspension and / or the second aqueous suspension are - Each of the aqueous suspensions contains 60 to 90% by weight of at least one refractory metal carbide, and / or - Based on the total weight of each of the aqueous suspensions, the mixture contains 0.1 to 20% by weight of at least one of the sintered additives, The method according to claim 1.

5. The method according to claim 1, wherein the weight percentage of the at least one sintered additive in the second aqueous suspension, based on the total weight of the second aqueous suspension, is 0.1% to 20% by weight lower than the weight percentage of the at least one sintered additive in the first aqueous suspension, based on the total weight of the first aqueous suspension.

6. The method according to claim 1, wherein the preparation of the first aqueous suspension in step a) and / or the preparation of the second aqueous suspension in step b) are carried out by mixing the components of the first aqueous suspension and / or the second aqueous suspension to be prepared, with the assistance of a dispersion device.

7. The coating of the at least one layer of the first aqueous suspension in step c) and / or the coating of the at least one layer of the second aqueous suspension in step d) - Performed by dipping, brushing, or spray application, and / or - Performed with an average layer thickness of less than 150 μm. The method according to claim 1.

8. Further prepare at least one third aqueous suspension, the third aqueous suspension comprising at least one refractory metal carbide and water. Between steps d) and e), at least one layer of the at least one third aqueous suspension is applied to the at least one coated layer of the second aqueous suspension. The method according to claim 1.

9. The sintering process in step e) is - Performed at temperatures of 2100°C to 2500°C, and / or - Performed with a retention time of 1 to 15 hours, and / or - Performed at pressures ranging from 0.1 bar (10 kPa) to 10 bar (1000 kPa), and / or - After the first time segment of the sintering process, the pressure is increased, and / or - Performed under an argon atmosphere, The method according to claim 1.

10. The material comprises a substrate, at least one refractory metal carbide disposed on the substrate, and at least one sintering additive selected from the group consisting of titanium silicide, zirconium silicide, hafnium silicide, vanadium silicide, niobium silicide, tantalum silicide, chromium silicide, molybdenum silicide, tungsten silicide, and mixtures thereof, and at least one second sintering layer disposed on the at least one first sintering layer, the at least one refractory metal carbide, and optionally at least one sintering additive selected from the group consisting of titanium silicide, zirconium silicide, hafnium silicide, vanadium silicide, niobium silicide, tantalum silicide, chromium silicide, molybdenum silicide, tungsten silicide, and mixtures thereof, wherein the at least one first sintering layer has a relative density of at least 70%, and the relative density of the at least one second sintering layer is at least 3% lower than the relative density of the at least one first sintering layer. The substrate is a coating substrate made of a material selected from the group consisting of graphite, carbon fiber reinforced carbon (CFC), C / SiC fiber composite, SiC / SiC fiber composite, carbide ceramics, nitride ceramics, and mixtures thereof.

11. The at least one first sintered layer is - Having a relative density higher than 75%, and / or - 1e －１１ I understand ２ Having a lower transmittance than, and / or - Having an adhesive strength of at least 2 MPa, and / or - Having an average layer thickness of at least 20 μm, The coating substrate according to claim 10.

12. The at least one second sintered layer is - Having a relative density at least 5% lower than the relative density of the at least one first sintered layer, and / or - 1e －１１ I understand ２ Having a lower transmittance than, and / or - Having an adhesive strength of at least 2 MPa, and / or - Having an average layer thickness of at least 20 μm, The coating substrate according to claim 10.

13. The coating substrate comprises at least one third sintered layer made of at least one refractory metal carbide, disposed on the at least one second sintered layer, wherein the relative density of the at least one third sintered layer is at least 5% lower than the relative density of the at least one second sintered layer. The coating substrate according to claim 10.

14. Use of a coating substrate according to any one of claims 10 to 13 in semiconductor crystal growth.

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