Method of coating a component for use in a CVD-reactor and component produced by the method

Abstract

A method for coating a component comprises heating a base body 2 consisting of graphite to a process temperature in a process chamber of a coating apparatus, simultaneously feeding one or more reactiv

Description

Field of Technology

[0001] The invention relates to a method for coating a component that can be used in a CVD-reactor, in particular an MOCVD-reactor. The component has a base body consisting of graphite and is coated in a process chamber of a coating device, which may also be a CVD-reactor. For this purpose, the base body is heated to a process temperature. A first reactive gas containing a metal is injected into the process chamber. This can be done together with the injection of a carrier gas. A second reactive gas containing carbon is injected into the process chamber simultaneously with the first reactive gas. The two reactive gases can pyrolytically decompose in the process chamber, with the reaction products of this decomposition reaction forming at least one carbide. Several reactive gases, each containing a metal, can also be fed simultaneously into the process chamber together with the carbon-containing reactive gas, so that two different metal carbides are formed. Prior Art

[0002] CN112680720 Al discloses a base plate for a MOCVD-device comprising a coating of SiC-TaC, wherein the SiC-TaC-deposition gradient layer is distributed in a gradient which changes from 0 % to 100 % from the interface to the outer surface, wherein the outer surface comprises solely TaC. A process is known from CN 112680720, by which a base plate consisting of silicon carbide or graphite for an MOCVD-reactor is coated with several layers. A SiC layer is deposited on a C-SiC layer. On top of this layer, another layer is deposited, which is a mixture of two carbides, SiC and TaC. The ratio of the two carbides changes in such a way that the molar fraction of SiC at the interface to the base body or the underlying layer is high and the molar fraction of TaC is low there. The ratios are reversed at the surface of the layer. There, the molar fraction of TaC is considerably higher than the molar fraction of SiC.

[0003] The paper "preparation and ablation properties of Hf(Ta)C codeposition coating for carbon / carbon composites." Corrosion Science 66 (2013) 177-182 describes the technical effect of metal carbide coatings on components.

[0004] A CVD-reactor, and in particular an MOCVD-reactor, uses graphite components that are heated to very high temperatures during operation of the CVD-reactor. Reactive gases are fed into the process chamber of the CVD-reactor, where they react with each other in such a way that a layer grows on a substrate in the process chamber. Highly reactive starting materials are used in particular for the deposition of SiC. To protect the surface of the graphite components exposed to high temperatures and the gaseous starting materials, the surfaces of the graphite components are coated with TaC.

[0005] The coefficient of thermal expansion of TaC is greater than the coefficient of thermal expansion of graphite, so that heating of a component coated in this manner can lead to cracks in the coating or delamination of the coating. The above mentioned CN112680720 discloses a first solution of such problem. Summary of the Invention

[0006] The invention is based on the problem of further developing a generic process for coating a component in such a way that the tendency of forming cracks when the component is heated to high temperatures is further reduced.

[0007] The problem is solved by the invention indicated in the claims. The subclaims represent not only advantageous further developments of the subordinate claims but also independent solutions of the problem.

[0008] First of all and essentially, it is proposed that the mass flows of the reactive gases are changed in time in such a way that a layer grows on the surface which has carbon atoms not chemically bonded to the metal atoms as a further constituent. The layer consists of a mixture of one or more metal carbides and carbon. The mole fraction of the metal carbides in the layer can have a lower value at the interface to the surface of the base body than at the surface of the layer. Thus, according to the invention, the layer consists of an alloy of at least one metal carbide and carbon, wherein the carbon may be present in the mixture in the form of graphite or carbon clusters. The molar ratio of the at least one carbide to the carbon changes over the thickness of the layer from 0,5 to 1. That means different to the state of the art the growth of the layer starts with a deposition of tantalum carbides on the graphite surface. This leads to a further improvement of the layer against cracking. The component produced by the process consists of a graphite base body and a layer deposited thereon, in which the molar ratio of the metal carbides in the region of the interface to the surface is smaller than at the surface of the layer. The process according to the invention is preferably carried out in such a way that a mixture of one or more metal carbides and carbon is formed at the interface to the base body. The molar ratio between the total amount of metal carbides and the carbon not bonded to the metals changes with increasing distance from the interface to the surface of the base body in such a way that the molar fraction of the metal carbides in the layer composition increases steadily. At the surface of the layer, the molar fraction of the metal carbides in the layer is preferably 100%. At the interface, the total molar content of the metal carbides may be approximately 50%. However, it is also possible that initially only carbon is deposited at the interface and the molar fraction of the one or more metal carbides increases steadily over the entire layer thickness to 100%. According to such a variant of the invention, two reactive gases are each fed into the process chamber with a carrier gas. One reactive gas may consist of molecules containing the element Ta and another reactive gas may consist of molecules containing the element Hf. These two reactive gases are fed into the process chamber together with a reactive gas whose molecules contain carbon, for example methane or another hydrocarbon, and optionally a carrier gas. During the deposition process, the mass flow ratio of the two reactive gases, each containing a metal, to the reactive gas containing the carbon is continuously changed in such a way that the proportion of the mass flow of the gas containing the one or more metals increases continuously. A layer is formed which consists of at least two phases. A first phase is formed by a metal carbide. A further phase is formed by carbon. A further phase may be provided, which is also formed by a metal carbide. According to a further preferred embodiment of the process according to the invention, the molar ratio of the reactive gases containing the metals remains constant throughout the deposition process. In the layer, HfC and TaC are preferably deposited in a substantially constant molar ratio. The molar ratio of HfC to the total molar ratio of the metal carbides can be between 2% and 15% or between 5% and 10% over the entire layer. The component can be a ceiling of a process chamber of a CVD-reactor or a susceptor of a CVD-reactor or an MOCVD-reactor. The layer consisting of the one or both metal carbides and carbon is deposited at a process temperature ranging from 1200°C to 1800°C. The duration of deposition of the layer may be from one to two hours. According to a preferred embodiment of the invention, the reactive gases each containing a metal compound are formed in a sublimation source. The Hf-containing reactive gas may be HfCh, which is fed into a process chamber together with H2 or a noble gas, for example argon. The Ta containing reactive gas can be TaCh, which is also fed into the CVD-reactor together with H2 or a noble gas, for example argon. Preferably, a first process gas is formed which consists of TaCh and H2 and which is provided by a Ta source. Preferably, a second process gas is formed which consists of HfCh and H2 and which is provided by an Hf source. The mass flow ratio between the first process gas flow and the second process gas flow may be 3 / 5. The mass flow of the carrier gas is preferably controlled by mass flow controllers and measured by mass flow meters. The component thus produced may have one or more further layers, preferably consisting only of metal carbides or at least one metal carbide. Brief Description of the Drawings

[0009] In the following, the invention is explained in more detail with reference to embodiment examples. It shows: Fig. 1 Schematically a section through a base body 1 with a layer 4 deposited thereon, Fig. 2 schematically showing the molar fraction X of Ta(Hf)C in layer 4, Fig. 3 schematic of the molar fraction Y of carbon Y not bonded in the carbide in layer 4, and Fig. 4 schematic of the structure of an apparatus for producing the coating shown in Figs. 1 to 3. Description of Embodiments

[0010] In a known process, a coating of TaC is deposited on a base body 2 consisting of graphite in an apparatus as shown in Fig. 4. This is done by simultaneously feeding a gaseous starting material containing Ta together with a gaseous starting material containing carbon into a process chamber 11 of a coating device 10. By simultaneously feeding a gaseous starting material containing Hf into the process chamber 11, a solid solution Ta(Hf)C in a polycrystalline form can be deposited as a layer 4 on the substrate 1. Since the thermal expansion coefficients of such a coating 4 and the base body 2 are different from each other, cracking may occur in the coating 4 when the component 1 is used, for example, in an MOCVD-reactor. Concomitantly, the coating 4 may delaminate from the base body 2.

[0011] In order to counteract this disadvantage, a mixture of several constituents is deposited on the surface 3 of the base body 2 according to the invention. The mixture contains, on the one hand, a carbide, which in the embodiment example can be TaC, and, on the other hand, carbon, for example in the form of graphite. The coating process is carried out in such a way that a layer 4 grows on the surface 3 of the base body 2, which is a mixture of the metal carbide on the one hand and carbon, in particular graphite, on the other. The mole fraction of the metal carbide has a lower value at the surface 3 than at the surface 5 of the layer 4. The mole fraction of the carbon, in particular of the graphite, has a higher value at the surface 3 of the base body 2 than at the surface 5 of the layer 4. There, the mole fraction of the carbon can be zero or 50 %.

[0012] A suitable device for this purpose is shown in Figure 4. A CVD-reactor 10 can have a housing made of stainless steel. In the housing 10 there is a process chamber 11. The process chamber 11 has walls which can be heated to a process temperature by heating devices 19, 20. The process temperatures are preferably in a range between 1200°C and 1800°C. A supply line 12 for feeding reactive process gases into the process chamber 11 opens into a gas inlet member, with which the process gas is fed into the process chamber 11. The process gas flows through the process chamber 11. In a pyrolytic reaction, the components of the process gas decompose within the process chamber 11. A 20 to 50 gm thick coating grows on the surface 3 of the base body 2. The reaction prod ucts formed during the reaction in the process chamber 11 and a carrier gas used for transporting the reactive gases can be sucked out of the process chamber 11 by a discharge line 18 connected to a gas outlet member of the coating device 10 and a pump 21 connected thereto. By means of the pump 21, a total pressure can be set in the process chamber 11 in a range between 2 and lOOmbar.

[0013] A preferred device shown in Figure 4 has a gas supply system comprising a Ta source 7, a Hf source 9 and a C source 13. In the Ta source 7, a tanta-lum-containing starting material 6, which is TaCF, is stored. A starting material containing Hf, which is HfCh, is stored in the Hf source 9.

[0014] An H2 source 17 is provided, which is connected to gas lines and mass flow controllers 15,16 of the Ta source 7 and the Hf source 9 arranged in the gas lines. The mass flow controllers 15,16 are each used to preset a hydrogen flow that flows through a container formed by the Ta source 7 and the Hf source 9, respectively. The two sources 7, 9 are sublimation sources. The Ta source material 6 and the Hf source material 8, in particular in powder form, stored in the containers evaporates at a preset temperature at which the respective container is maintained. The vapor of the Ta starting material 6 or the Hf stating material 8 is fed from the carrier gas through the feed line into the process chamber 11.

[0015] The C source 13 may include methane. A methane flow rate is adjusted by a mass flow controller 14. The mass flow of the reactive gas containing the carbon thus adjusted also enters the process chamber 11 through the feed line 12.

[0016] In variants of the device, several feed lines can open into the process chamber 11 separately from one another. Through the feed lines opening sepa rately from each other into the process chamber 11, the reactive gases that are different from each other, for example TaCh transported with H2 or HfCh transported with H2 or methane, can be fed into the process chamber 11.

[0017] To carry out the process, a base body 2 consisting of graphite is first inserted into the process chamber 11. This can be done in such a way that the broad side surfaces facing away from each other and all narrow side surfaces of a flat base body 2 are exposed on all sides. The base body 2 can be supported by needle-shaped supports.

[0018] After a loading opening of the coating device 10, which is not shown, is closed, the process chamber 11 can be evacuated. After heating the process chamber 11, which is preferably a hotwall reactor, the reactive gases are fed into the process chamber such that an alloy-type mixture is deposited on the surface 3 of the base body 2, the mixture comprising crystalline material of TaC and HfC and substantially amorphous material of carbon. The mixing ratio of the reactive gases is adjusted so that the following mixture is obtained (Ta(Hf)C)xCy is deposited. The mole fraction y of the carbon component of the mixture can be at least 0.5. The mole fraction of the metal carbide component x can be at most 0.5.

[0019] During the deposition process, which can be 60 minutes to 120 minutes, the mass flow of the carrier gas is continuously increased by the mass flow controllers 15,16 or the temperature 7, 9 is continuously increased so that the mass flow of the reactive gases containing the metals Ta and Hf continuously increases. The mass flow of methane flowing through mass flow controller 14, on the other hand, is steadily decreased. The mass flow controllers 14,15 and 16 are controlled by a control device 22 in such a way that, at the beginning of the deposition of the layer 4, substantially more carbon is fed into the process chamber 11 than would be required for the deposition of a pure metal carbide, so that, on the one hand, the carbon formed by the decomposition reaction in the process chamber 11 reacts with the metals Hf and Ta formed there by further decomposition reactions to form a metal solid solution and, on the other hand, is deposited as, for example, amorphous carbon on the surface 3. With increasing layer thickness and time, the mass fluxes of the reactive gases TaCh and HfCh are increased and / or the mass flux of CH4 is decreased, so that the ratio x / y increases. At the end of the layer growth, the amount of carbon fed into the process chamber 11 is just sufficient to deposit only metal carbides.

[0020] The ratio of the carrier gases flowing through the mass flow controllers 14,15 is preferably kept constant during the deposition process or varied in such a way that the mass ratio of Hf to Ta does not change. Preferably, in addition to the amorphous carbon, a crystalline, in particular polycrystalline material is formed in the form of TaC doped with Hf, where the hafnium content is in the range between 5% and 10%. A further layer consisting only of one or more metal carbides can be deposited on this layer. The layer according to the invention forms a transition layer between the base body and such a further layer.

[0021] Figure 2 shows the proportion x of Ta(Hf) in the total amount of material in the coating 4, which increases continuously with the thickness of the layer 4 from 0.5 to 1. Figure 3 shows the proportion y of carbon in the coating 4, which decreases continuously with the thickness of the layer 4. The sum of x and y may be 1.

[0022] In one embodiment of the process, TaCh is maintained at temperatures of 190°C to 210°C in Ta source 7. A mass flow of about 5L / min of hydrogen flows through the mass flow controller 16. The HF source 9 can be maintained at a temperature between 250°C and 350°C. A mass flow of about 3L / min of hydrogen flows through mass flow controller 15. A total mass flow of 10L / min flows into the process chamber.

[0023] In an embodiment not shown, only one sublimation source can be used, in which a mixture of a Ta starting material and a Hf starting material is included.

[0024] The growth process is preferably carried out in such a way that a Ta(Hf)C layer with an additional carbon content is initially deposited at the interface 3 of the layer 4 to the base body 2, with this carbon content decreasing steadily during the layer growth, i.e. with increasing layer thickness of the layer 4, until stoichiometric Ta(Hf)C is deposited at the surface 5 or in a region below the surface 5. With this method, a layer 4 with sufficient resistance and chemical inertness is deposited on the base body, which does not detach when the component 1 is used in an MOCVD-reactor. A further layer can be deposited on the first layer 4. This layer then has no carbon phase, but only one metal carbide phase or several metal carbide phases.

[0025] The component 1 can be a susceptor, a ceiling plate, a gas inlet organ or a gas outlet organ of an MOCVD-reactor, which is used to deposit SiC layers on substrates. Such a device is described, for example, in DE 10 2018 128 558 Al.

[0026] The foregoing serves to explain the inventions covered by the application as a whole, which also independently advance the prior art at least by the following combinations of features in each case, wherein two, more or all of these combinations of features may also be combined, namely:

[0027] A process characterized in that the mass flows of the reactive gases are changed in time in such a way that the layer 4 contains carbon as a further constituent, wherein a molar fraction of the carbon at the interface to the surface 3 of the base body 2 has a higher value than at the surface 5 of the layer 4.

[0028] A component produced by a method according to the above-mentioned feature, characterized in that the layer 4 contains carbon as a further constituent, a molar fraction of the carbon having a higher value at the interface to the surface 3 of the base body 2 than at the surface 5 of the layer.

[0029] A method or a component, which is characterized in that the total molar fraction of the metal carbides at the interface to the surface 3 is max. 50% and / or that the total molar fraction of the metal carbides at the surface 5 of the layer 4 is 100%.

[0030] A process characterized in that the metal of another reactive gas is hafnium and / or that a tantalum-containing reactive gas and a hafnium-containing reactive gas are simultaneously fed into the process chamber 11 such that the molar ratio of hafnium to tantalum over the entire thickness of the layer 4 is in the range between 2% and 15% and / or between 5% and 10%.

[0031] A component characterized in that the metal carbides are HfC and TaC, and a molar ratio of the HfC to the molar ratio of all carbides over the entire layer 4 is in a range between 2% and 15% or between 5% and 10%.

[0032] A component characterized in that the component 1 is a part and / or a susceptor or a top plate of a process chamber of a CVD-reactor or an MOCVD-reactor.

[0033] A method characterized in that the process temperature T is in the range between 1200°C and 1800°C and / or that the duration of deposition of the layer is one to two hours.

[0034] A process characterized in that the hafnium-containing reactive gas is HfCU, which is fed together with H2 or a noble gas into the process chamber 4 and / or that the tantalum-containing reactive gas is TaCh, which is fed together with H2 or a noble gas into the process chamber and / or that the carbon-containing reactive gas is methane or another hydrocarbon and / or that the hafnium source and / or the tantalum source is a sublimation source.

[0035] A process characterized in that the total pressure in the process chamber is in the range between 2 to 100 mbar.

[0036] All of the disclosed features are essential to the invention (individually, but also in combination with each other). In the disclosure of the application, the disclosure content of the associated / attached priority documents (copy of the prior application) is hereby also fully included, also for the purpose of including features of these documents in claims of the present application. The sub-claims characterize, even without the features of a claim referred to, with their features independent inventive further developments of the prior art, in particular in order to make divisional applications on the basis of these claims. The invention indicated in each claim may additionally have one or more of the features indicated in the above description, in particular with reference numerals and / or in the list of reference numerals. The invention also relates to forms of design in which individual features mentioned in the above description are not realized, in particular to the extent that they are recognizably dispensable for the respective intended use or can be replaced by other means having the same technical effect. List of Reference signs 1 Component 2 Basic Body 3 Surface 4 Layer 5 Surface 6 Ta source material (TaCh) 7 Ta source 8 Hf source material (HfCL) 9 Hf source 10 Coating device 11 Process chamber 12 Feed line 13 C source (CH4) 14 Mass flow controller 15 Mass flow controller 16 Mass flow controller 17 H2 source 18 Discharge 19 Heating device 20 Heating device 21 Pump 22 Control device

Claims

1. Method for coating a component (1), wherein a base body (2) of the component (1) consisting of graphite is heated to a process temperature (T) in a process chamber (11) of a coating device (10), wherein a reactive gas containing tantalum and a further reactive gas containing hafnium and a carbon-containing reactive gas are simultaneously fed into the process chamber (11), wherein the reactive gases react to form metal carbides, and a layer (4) comprising the metal carbides grows on the surface (3), wherein a molar fraction of the metal carbides in the layer (4) at the interface with the surface (3) of the base body (2) has a lower value than at the surface (5) of the layer, wherein the mass flows of the reactive gases are changed over time in such a way that the layer (4) contains carbon as a further constituent, a molar fraction of the carbon having a higher value at the interface to the surface (3) of the base body (2) than at the surface (5) of the layer (4), characterized in that the total molar fraction of the metal carbides at the interface to the surface (3) is no more than 50%.

2. Method according to claim 1, wherein the total molar fraction of the metal carbides at the surface (5) of the layer (4) is 100%.

3. Method according to one of claim 1 or 2, characterized in that the molar ratio of hafnium to tantalum over the entire thickness of the layer (4) is in the range between 2% and 15%.

4. Method for coating a component (1), wherein a base body (2) of the component (1) consisting of graphite is heated to a process temperature (T) in a process chamber (11) of a coating device (10), wherein a reactive gas containing tantalum and a carbon-containing reactive gas are simultaneously fed into the process chamber (11), wherein the reactive gases react to formtantalum carbides, and a layer (4) comprising the tantalum carbides grows on the surface (3), wherein a molar fraction of the tantalum carbides in the layer (4) at the interface with the surface (3) of the base body (2) has a lower value than at the surface (5) of the layer, wherein the mass flows of the reactive gases are changed over time in such a way that the layer (4) contains carbon as a further constituent, a molar fraction of the carbon having a higher value at the interface to the surface (3) of the base body (2) than at the surface (5) of the layer (4), characterized in that a further reactive gas containing hafnium is fed simultaneously with the tantalum-containing reactive gas into the process chamber (11), so that the molar ratio of hafnium to tantalum over the entire thickness of the layer (4) is in the range between 2% and 15%.

5. Method according to one of the preceding claims, characterized in that the process temperature (T) is in the range of 1200°C to 1800°C.

6. Method according to one of the preceding claims, characterized in that the duration of the deposition of the layer is one to two hours.

7. Method according to one of the preceding claims, characterized in that the hafnium-containing reactive gas is HfCU, which is fed together with H2 or a noble gas into the process chamber (4).

8. Method according to one of the preceding claims, characterized in that the tantalum-containing reactive gas is TaCls, which is fed together with H2 or a noble gas into the process chamber.

9. Method according to one of the preceding claims, characterized in that the carbon-containing reactive gas is methane or another hydrocarbon.

10. Method according to one of the preceding claims, characterized in that the hafnium source and / or the tantalum source is a sublimation source.

11. Method according to one of the preceding claims, characterized in that the total pressure in the process chamber is in the range between 2 to 100 mbar.

12. Component produced by a method according to claim 1, consisting of a base body (2) made of graphite and a layer (4) deposited thereon, which has metal carbides, wherein the metal carbides are HfC and TaC, wherein a molar fraction of the metal carbides in the layer (4) has a lower value at the interface to the surface (3) of the base body (2) than at the surface (5) of the layer (4), wherein the layer (4) contains carbon as a further constituent, a molar fraction of the carbon having a higher value at the interface to the surface (3) of the base body (2) than at the surface (5) of the layer, characterized in that the total molar fraction of the metal carbides at the interface to the surface (3) is no more than 50% and a molar ratio of HfC to the molar ratio of all carbides over the entire layer (4) is in the range between 2 % and 15 %.

13. Component according to claim 12, wherein the total molar fraction of the metal carbides at the surface (5) of the layer (4) is 100%.

14. Component according to claim 12 or claim 13, characterized in that the component (1) is a part of a process chamber of a CVD-reactor or an MOCVD-reactor.

15. Component according to claim 14, wherein the part is a susceptor or a ceiling.

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