Method for synthesizing a planar single crystal diamond, diamond substrate, apparatus, and method of use thereof

Abstract

The present invention relates to a method for synthesizing a planar single crystal diamond having a large surface area, as well as a substrate, an apparatus, and methods of using them.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing a planar single crystal diamond having a large surface area, as well as substrates, devices, and methods of using them.

Background Art

[0002] Diamond is a high-tech material having a series of extreme material properties. These properties enable ultimate solutions for various technical applications that are impossible with any other material. Related fields include mechanics (e.g., cutting tools, ophthalmic scalpels), optics (e.g., windows for high-power lasers, ATR prisms), electronics (e.g., heat spreaders for high-power components, active elements for high voltage and high current), and sensor technology (e.g., magnetic field sensors). Many of these applications require diamond in single crystal form to fully utilize the excellent properties of diamond.

[0003] Single crystal diamond can be synthesized using the high pressure high temperature (HPHT) method or, alternatively, by chemical vapor deposition (CVD). The HPHT method is very limited both in terms of the maximum size of the crystal and in terms of the targeted incorporation of foreign atoms (required for the realization of electronic components, for example).

[0004] There are various techniques for activating the gas phase in alternative CVD processes. These are, for example, the hot filament process (HFCVD) or various electrical processes that excite plasma discharge by direct current (DCPCVD), radio frequency (RFPCVD), microwave (MWPCVD), and corresponding gas injection forms. MWPCVD has been established as one of the most efficient and clean processes for producing high-quality single crystals.

[0005] To synthesize single crystals using CVD, there is an obvious approach of using an existing single crystal obtained from HPHT synthesis as a substrate and further growing it (e.g., using MWPCVD). This is called homoepitaxy. However, its size is significantly limited by the size of the available single crystals.

[0006] Alternatively, there is heteroepitaxy. In this method, a single crystal foreign substrate is used, and diamond is grown on it in an oriented manner. The diamond crystal lattice must be aligned with the crystal lattice of the substrate during growth or nucleation. Various crystal materials have shown that in principle, it is possible to grow oriented diamond on them. However, regarding the crystal quality of the diamond crystals grown on them, iridium is far superior to all other materials.

[0007] Single crystals made of iridium are not a technically feasible option due to their exorbitant price. Instead, a thin iridium layer is heteroepitaxially deposited on a single crystal foreign substrate (so-called base substrate). This base substrate is preferably an oxide single crystal (e.g., MgO, SrTiO 3 , sapphire (Al 2 O 3 )). Therefore, synthesizing single crystal diamond includes, for example, generating a diamond / iridium / MgO layer system.

[0008] Silicon may also be used as a base substrate. However, an additional buffer layer is required between the silicon crystal and the iridium layer to prevent the chemical reaction between Ir and Si. Useful buffer layers include, for example, yttrium-stabilized zirconia (YSZ) or strontium titanate (SrTiO 3 ). The crystal lattices of all components of the resulting multilayer system (e.g., diamond / Ir / YSZ / Si or diamond / Ir / SrTiO 3 / Si) have a fixed orientation relative to each other.

[0009] A very critical step in the heteroepitaxy process is the oriented nucleation of diamond on a foreign surface. For iridium, a process of bias-enhanced nucleation (BEN) has been established. By applying a negative DC voltage (e.g., -150 to -400 V) to the substrate or the substrate holding device, positive ions are accelerated from the plasma to the surface, causing the processes necessary for nucleation at the surface. This process occurs, for example, in a gas atmosphere consisting of hydrogen and methane. Ideally, (for example) a microwave plasma is already burning and a DC voltage is also applied. Alternatively, the nucleation step can also occur as a pure DC discharge.

[0010] After diamond nucleation, the actual thickness grows to a typical thickness ranging from several hundred micrometers to several millimeters. BEN and thickness growth can occur either within the same equipment or in different equipment.

[0011] Heteroepitaxy generates layer systems made of various materials with different expansion coefficients. When cooled at the end of the growth process, the substrate and diamond contract in different ways, resulting in the so-called thermal stress. Since diamond has a smaller expansion coefficient, usually, the compressive stress increases within the diamond and the tensile stress increases within the substrate. Since the iridium layer and any buffer layers are thin, they can be ignored in this consideration. Along with these stresses, bending of the layer system also occurs during cooling. As a result, the layer system in the center of the wafer bulges upward. If all the bending due to the difference in expansion during cooling is purely elastic, assuming the substrate wafer was planar until the end of coating under plasma conditions, neither should be bent after separating the diamond from the substrate.

[0012] In Published Document 1 (S. Kim et al., Appl. Phys. Lett., 117, 202102 (2020)), a diamond crystal grown on a sapphire substrate with a bending radius of 0.906 m is described. Published Document 1 also mentions past efforts where a radius of only 20 cm was achieved for the diamond layer on Ir / MgO. This difference in radius is due to the difference in the expansion coefficients of sapphire and MgO. In Published Document 2 (S. Kim et al., Applied Physics Express, 14, 115501 (2021)), radii of 0.996 m and 2.6 m are specified over a short distance. The explanation for this is based only on the expansion coefficient.

[0013] To clarify the cause of the bending and to develop an efficient strategy to prevent or minimize the bending, the heat flow in a typical plasma CVD system is analyzed below.

[0014] In synthesizing the diamond layer in these processes, plasma is used, and from this plasma, the diamond layer is deposited on the surface of the crystal substrate. The substrate surface faces the plasma and is in contact with or close to the plasma. Feasible growth rates can be achieved at high plasma temperatures of around 3000 °C and 4000 °C. However, the optimal growth conditions for the diamond layer on the substrate surface are achieved only when the temperature of the diamond surface is simultaneously around 1000 °C. This gradient in the gas phase leads to a very large heat flow from the center of the plasma discharge towards the surface of the growing diamond layer. To create and maintain these optimal growth conditions, the heat of the plasma must be dissipated through the diamond layer and the substrate. The resulting heat flow inevitably leads to a temperature gradient in the substrate due to the thermal resistance of the substrate. Due to the extremely high thermal conductivity of diamond, the gradient within the diamond can be neglected compared to the gradient within the substrate (1 / 10 to 1 / 100) if the layer thickness is at most 1 - 2 mm.

[0015] Due to this temperature gradient, the substrate (especially the substrate surface) is deformed during the growth of the diamond layer. Specifically, this means that the substrate surface, which is planar at room temperature, bends convexly during the growth of the diamond layer in the above-described process, and in this case, the diamond layer is deposited on the convexly bent layer.

[0016] Typically, the substrate returns to its original planar shape upon cooling (and upon disappearance of the temperature gradient), or in the case of silicon, undergoes some plastic deformation, but the grown diamond layer retains its curvature even after being fully cooled. This is because diamond can only be plastically deformed at temperatures above approximately 1200°C. In this process, the diamond layer can be detached from the substrate when strongly bent and can be used as a free-standing diamond wafer. This detachment usually does not occur in the case of silicon. This is because the curvature and plastic deformation ability of silicon (above approximately 550°C) are relatively small. Since the diamond wafer retains its convex shape, it is impossible to synthesize a large planar diamond with a large surface area in such a process. This is especially true for substrates with high thermal expansion and insufficient thermal conductivity. SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0017] The present invention has been made to solve the problems in the above-described conventional technology. MEANS FOR SOLVING THE PROBLEM

[0018] This problem is solved by the method according to claim 1, and by the substrate according to claim 24, and by the apparatus according to claim 25, and by the method of using the above apparatus and / or the above substrate according to claim 27. The dependent claims show advantageous embodiments of the present invention.

[0019] In the method according to the present invention, plasma can be generated and maintained in a reactor for plasma chemical vapor deposition. In a first step, epitaxial diamond nuclei may be generated (e.g., using BEN). This step may be carried out in a separate apparatus (e.g., as a pure DC discharge beforehand). Next, this plasma is used to grow at least one diamond layer on the substrate surface. Advantageously, several diamond layers grow due to slightly different process parameters, so that ultimately, diamond with a thickness of several millimeters is produced. The diamond layer can be a single or multiple atomic layers, as well as a diamond layer with a thickness of several micrometers to several millimeters.

[0020] The substrate surface is the surface of the substrate arranged in the reactor that faces the plasma. The substrate may have a single material or multiple materials, or may consist of a single material or multiple materials. For example, the substrate may have multiple layers arranged overlapping each other, with the top layer having the substrate surface.

[0021] Preferably, the substrate has a base substrate on which a single-crystal epitaxial layer is deposited, thereby enabling high-crystallinity diamond nucleation. This top layer (i.e., the surface facing the plasma) for diamond nucleation is preferably iridium. Advantageously, a buffer layer may be arranged between the base substrate and the top layer. When referring to the substrate surface and its reshaping below, this may mean reshaping the surface of the base substrate that faces the plasma. Alternatively, this may also include the top layer for diamond nucleation if the reshaping process is carried out after the diamond nucleation layer and any buffer layer are applied.

[0022] According to the present invention, the substrate surface is reshaped into a concave shape before the diamond layer grows. The substrate surface reshaped into a concave shape has the property that the distance extending between any two points on the substrate surface is located outside the substrate. This may mean that the curvature of the substrate surface is not zero, or that the radius of curvature of the substrate surface is not infinite (specifically, shorter than 50 m). A deviation from a spherical shape (specifically, being a parabolic shape or an elliptical shape) is also assumed. An aspherical aberration-correcting shape is also assumed. This is a shape in which the curvature along the first spatial direction is deviated from the curvature along the second spatial direction. In this case, the substrate surface has two or more radii of curvature. The aspherical aberration-correcting shape can be advantageously used in the case of a single-crystalline base substrate whose linear expansion coefficient is direction-dependent. Hereinafter, the concave reshaping performed before the diamond layer grows is also referred to as pre-curvature.

[0023] The expression "before the growth of the diamond layer" means here and hereinafter that the reshaping is performed before the above-described process of growing the diamond layer on the substrate surface. For example, it is quite conceivable that the substrate already has a diamond layer by a previous coating process. Before the diamond layer grows, this may specifically mean that the substrate surface and the substrate are outside the reactor. Advantageously, the substrate surface is formed when there is no temperature gradient in the substrate and / or when the substrate is at room temperature. During plastic reshaping, the substrate will advantageously be at a higher temperature than at the brittle-ductile transition.

[0024] Advantageously, the reshaping of the substrate surface is performed by milling and / or turning and / or laser ablation and / or grinding and / or polishing and / or by plastic deformation of the substrate before the diamond layer grows. As an advantage brought about by the reshaping by plastic deformation, in the case of a crystalline substrate surface, each point of the crystal lattice has the same orientation with respect to the local substrate surface. In particular, the reshaping may be performed before the diamond nucleation layer (preferably made of iridium) and any buffer layer are applied.

[0025] The present invention is based on the idea of pre-bending the substrate surface such that only the deformation occurring during the growth of the diamond layer results in a substantially planar substrate surface having a radius of curvature (or, in the case of anastigmatic pre-curvature, a plurality of radii of curvature) exceeding 5 m. Advantageously, the radius of curvature during the growth of the diamond layer exceeds 10 m, preferably exceeds 20 m, and particularly preferably exceeds 100 m. In this way, a diamond coating can grow on a planar substrate surface. This makes it possible to produce planar single-crystal diamond over a large area.

[0026] As initially stated, the substrate surface typically deforms under the general physical conditions during the growth of the diamond layer. The general conditions during the growth of the diamond layer will be referred to later as the planned growth conditions. This means the physical conditions under which the diamond layer grows efficiently on the substrate surface by chemical vapor deposition. The corresponding parameter ranges will be described later in this specification.

[0027] Optional processes leading to the growth of a curved diamond layer will be described in detail below. Those processes are based substantially on the fact that heat is transferred through the substrate under the process conditions. During the growth of the diamond layer, the temperature in the central part of the plasma becomes considerably higher than the temperature of the substrate surface. The heat in the central part of the plasma is first dissipated in the gas phase to the substrate surface or, after diamond nucleation, to the surface of the growing diamond layer, from where it is dissipated through the diamond layer and the substrate. Since the material of the substrate generally has a non-zero coefficient of thermal conductivity, a corresponding temperature gradient is generated along the direction of heat transfer due to heat transfer. Specifically, this means that the temperature of the substrate surface facing the plasma is higher than the temperature of the lower surface of the substrate that does not face the plasma. The surface of the substrate that does not face the plasma will be referred to below as the substrate lower surface.

[0028] The material of the substrate also typically has a non-zero or greater than zero coefficient of thermal expansion. The temperature gradient along the direction of heat transfer consequently causes various linear expansions of the substrate along the direction of heat transfer. The various linear expansions perpendicular to the direction of heat transfer cause deformation of the entire substrate and thus also deformation of the substrate surface. The substrate expands more at the substrate surface than at the substrate bottom surface. This is because the temperature of the substrate surface is higher. In a substrate that is initially planar, when the substrate bottom surface and the substrate surface are planar and parallel to each other at thermal equilibrium and / or at room temperature, the substrate surface is typically bent convexly under the planned growth conditions. This means that the distance extending between any two points on the substrate surface is located within the substrate.

[0029] According to the present invention, the substrate surface is then pre-bent before the diamond layer grows, which is done such that the substrate surface becomes substantially planar as a result of the deformation of the substrate under the planned growth conditions in the reactor. For this purpose, the substrate surface is re-formed concave before the diamond layer is applied. The re-forming must be done such that the radius of curvature of the substrate surface, which is generated by the deformation of the substrate surface during the growth of the diamond layer, becomes 5 m or more. This means that the substrate is substantially planar during the growth of the diamond layer. Whether the substrate surface is convex with a radius of curvature greater than 5 m or concave with a radius of curvature greater than 5 m during growth is irrelevant.

[0030] In an advantageous embodiment of the method, the radius of curvature of the substrate surface can be determined while the plasma is being generated and maintained, and in particular, during the growth of the diamond layer. The radius of curvature can be determined non - contact, for example, by means of fringe projection or other laser scanning methods, or by reflecting two parallel light beams on the substrate surface or the diamond layer. The process parameters of the plasma used in the chemical vapor deposition method can be finely adjusted so that the radius of curvature of the substrate surface exceeds 5 m during the growth of the diamond layer. Even when the process parameters are changed, it is advantageous if the temperature of the substrate surface remains within a range suitable for diamond growth. This can be achieved, for example, by appropriately readjusting the cooling of the lower surface of the substrate on - site.

[0031] There may potentially be a situation where the measurement of the radius of curvature is hindered by the growing diamond layer. This can be avoided by appropriate analysis or appropriate measurement methods. Alternatively or additionally, it may be possible to directly measure the radius of curvature of the diamond layer during its growth instead of the substrate surface after the diamond layer growth has progressed.

[0032] In some embodiments of the present invention, when the substrate surface is concave during the growth of the diamond layer, it is possible to control (e.g., increase) the power density coupled to the plasma, and / or the temperature of the plasma, and / or the pressure of the process gas. Advantageously, when the substrate surface is convex during the growth of the diamond layer, it is possible to control (e.g., decrease) the power density coupled to the plasma, and / or the temperature of the plasma, and / or the pressure of the process gas. It is particularly advantageous if the substrate surface is measured while the diamond layer is growing.

[0033] It may also be possible to later identify the radius of curvature and / or surface characteristics (e.g., concave or convex) of the substrate surface that exist or existed during growth. This can be done, for example, by measuring the radius of curvature of the lower surface of the diamond layer that has grown and has already been cooled and removed from the substrate. Such measurements can also be carried out, in particular, outside the reactor. In this case, the above method may be carried out multiple times either with different process parameters and a substrate having the same pre-curvature of the substrate surface, or with the same process parameters and a substrate surface having a different pre-curvature. During cooling, the substrate attempts to return to its original shape under pure elastic tension, but this return is prevented by the adhering diamond layer. As the temperature decreases, the stress in the diamond layer and the substrate increases, and eventually, they usually separate from each other. Due to the small difference in the expansion coefficients between Si and diamond and the good thermal conductivity of Si, delamination usually does not occur on this base substrate, and the substrate detaches chemically and / or mechanically. After the diamond and the substrate are separated, the lower surface of the diamond layer has the radius of curvature of each substrate surface during the growth of the diamond layer. The radius of curvature of each substrate surface during the growth of the diamond layer can thus be identified later by measuring the diamond layer. By adjusting the process parameters or the pre-curvature radius accordingly, it is possible to approach the optimal parameters.

[0034] In one embodiment of the method, the temperature of the substrate surface can advantageously be higher than 900 °C, preferably 950 °C, particularly preferably 1000 °C, and / or can advantageously be lower than 1250 °C, preferably 1200 °C, particularly preferably 1150 °C. Irrespective of this, it is particularly advantageous if the temperature of the surface on which the diamond growth process occurs is higher than 900 °C, preferably 950 °C, particularly preferably 1000 °C, and / or is advantageously lower than 1250 °C, preferably 1200 °C, particularly preferably 1150 °C.

[0035] As diamond layer growth progresses, diamond growth no longer occurs directly on the substrate surface but on top of the already grown diamond layer. This further diamond layer may, for example, interfere with optical temperature measurement of the substrate surface. Diamond is typically transparent to the measurement wavelengths used, but may also emit infrared radiation, whereby, for example, in high-temperature measurements, the combination of the diamond and the substrate surface is measured. Irrespective of this, a temperature gradient may occur between the substrate surface and the surface of the growing diamond layer. Since diamond has a high thermal conductivity (about 400 W / (mK) at 1000 °C), this temperature difference is typically small (a few °C) under the planned process conditions and the expected diamond layer thickness and plays only a secondary role when setting process parameters. However, if the thickness of the diamond layer is known, it is also conceivable to calculate this temperature gradient and accordingly correct the measured values. Alternatively or additionally, it is conceivable to directly measure the temperature of the diamond layer.

[0036] Advantageously, the volume density of the power absorbed by the plasma is greater than 10 W / cm 3 and preferably greater than 20 W / cm 3 and particularly preferably greater than 50 W / cm 3 and / or, advantageously, less than 500 W / cm3, preferably less than 250 W / cm3, particularly preferably less than 100 W / cm3.

[0037] In an advantageous embodiment of the invention, the pressure of the process gas used in the chemical vapor deposition method in the reactor is greater than 20 mbar, preferably greater than 50 mbar, particularly preferably greater than 100 mbar, and / or less than 500 mbar, preferably less than 400 mbar, particularly preferably less than 300 mbar. Advantageously, as the process gas, a gas mixture of methane and hydrogen with a methane concentration of 2 to 20% is used. To accelerate growth, a low concentration of nitrogen (10 to 500 ppm) may be added.

[0038] Also, the areal power density absorbed in the gas phase above the substrate surface and / or above the surface of the growing diamond layer is 50 W / cm 2 , preferably greater than 100 W / cm 2 , and / or less than 1000 W / cm 2 , preferably less than 750 W / cm 2 would be advantageous. The areal power density of the general plasma at the substrate surface determines the power to be dissipated through the substrate. Therefore, the areal power density absorbed in the gas phase above the substrate surface and / or above the surface of the growing diamond layer affects the heat flow and thus also affects the degree of deformation of the substrate. The areal power density may be defined as the total coupled power generated when a visible plasma ball is vertically emitted onto a horizontal plane divided by the area.

[0039] The substrate surface is 1 cm 2 or more, preferably 10 cm 2 or more, more preferably 50 cm 2 or more, particularly preferably 200 cm 2 or more, or most preferably 300 cm 2 or more, according to the method according to any one of the preceding claims.

[0040] Advantageously, the thickness of the substrate is 0.5 mm or more, preferably 1 mm or more, particularly preferably 2 mm or more, and / or 20 mm or less, particularly preferably 10 mm or less. In an advantageous embodiment, the thickness of the substrate is 3 mm.

[0041] Advantageously, the generation and maintenance of the plasma can be carried out by irradiating with electromagnetic waves, specifically by irradiating with radio waves or by irradiating with microwaves. Advantageously, the frequency of the microwaves is higher than 0.5 GHz, preferably higher than 0.75 GHz, particularly preferably higher than 0.9 GHz, and / or lower than 20 GHz, preferably lower than 10 GHz, particularly preferably lower than 5 GHz.

[0042] Plasma generation can also be carried out using a DC voltage or an AC voltage, or within a plasma jet.

[0043] As an example, two procedures for determining the pre-curvature are described.

[0044] In the first procedure for determining the pre-curvature, a theoretical pre-curvature of the substrate surface may be assumed. Next, the degree to which such a theoretically pre-bent substrate surface deforms under the planned growth conditions may be calculated. Next, the theoretically assumed pre-curvature in the calculation may be adjusted, for example, in iterative steps until the substrate becomes planar according to the calculation under the planned growth conditions. Next, the substrate may be pre-bent with this theoretically determined pre-curvature.

[0045] Another method for determining the pre-curvature is to calculate the curvature of the substrate surface of a planar (i.e., not pre-bent) substrate under the planned growth conditions. Under these conditions, the non-pre-bent substrate surface is convex and has a specific radius of curvature. This radius of curvature is computable and may be used as the radius of curvature of the concave pre-curvature.

[0046] In an advantageous embodiment of the method according to the invention, the substrate surface is reshaped so as to be concave and to have a radius of curvature R before the diamond layer grows. The value of R is determined using the material parameters of the substrate and the heat flux density J flowing from the top to the bottom of the substrate during the growth of the diamond layer. Advantageously, the material parameters of the base substrate may be used. The value of R decreases as the value of the heat flux density J increases. The thermal conductivity λ of the substrate can act as a material parameter. The value of R increases as the value of λ increases. The coefficient of thermal expansion α can also act as a further material parameter. The value of R decreases as the value of α increases. This means that the greater the heat flux density and / or the greater the coefficient of thermal expansion of the substrate material, the more the substrate surface must be pre-bent. Further, the greater the thermal conductivity of the substrate material, the less the substrate surface must be pre-bent.

[0047] In a particularly advantageous embodiment of the method, the radius of curvature R (i.e., the pre-curvature 1 / R) when pre-bending the substrate surface is calculated. To calculate the pre-curvature 1 / R, the formula 1 / R = αJ / λ may be used. Here, α is the thermal expansion coefficient of the substrate material, λ is the thermal conductivity of the substrate material, and J is the heat flux density flowing from the substrate surface to the substrate bottom surface. The heat flux density is defined as the heat output per unit cross-sectional area of the substrate. The heat flux density is preferably greater than 0.2×10 6 W / m 2 and more preferably greater than 0.5×10 6 W / m 2 and / or preferably less than 5×10 6 W / m 2 and more preferably less than 3×10 6 W / m 2 and particularly preferably less than 2×10 6 W / m 2 .

[0048] However, the material parameters themselves may be temperature-dependent and may be taken into account when calculating the pre-curvature. Furthermore, the material parameters in a multilayer system may vary from layer to layer. To determine the pre-curvature so that the substrate surface is planar during the growth of the diamond layer, it is fully conceivable to use calculation methods other than the above-described method (specifically, numerical methods such as the finite element method). Irrespective of this, it is also conceivable to include in the calculation the heat transfer between the substrate and the substrate holding device and / or the heat transfer through the substrate holding device.

[0049] Also, it may be advantageous if the substrate bottom surface is convex before the diamond layer grows. Thereby, the substrate can be deformed into a flat substrate under optimal growth conditions. The advantage of a flat substrate is that a uniform thermal contact between the substrate bottom surface and the substrate holding device can be more easily generated. Before the diamond layer grows, the radius of the convex substrate bottom surface can be greater than or equal to the radius of the concave substrate surface.

[0050] It is particularly advantageous if the substrate surface contains iridium and / or contains at least to some extent silicon, silicon dioxide, magnesium oxide, strontium titanate, yttrium-stabilized zirconium dioxide, and / or sapphire. It is particularly advantageous if the substrate surface and / or the substrate containing the substrate surface is a crystal, preferably a single crystal. It is particularly preferred if the local mosaic width is less than 0.5°. The local mosaic width means the mosaic width within a volume of 2 mm in diameter. The mosaic width means the polarity and azimuthal orientation distribution of the crystal lattice forming the substrate surface, which can be measured by X-ray diffraction.

[0051] It is even more advantageous if the substrate surface and / or the substrate containing the substrate surface is a cubic crystal and the crystal orientation of the surface is on average (001) or (111), or a trigonal crystal and the crystal orientation of the surface is on average (0001) or (11-20) or (1-102) or (10-10). It is particularly advantageous if the deviation of the average surface orientation of the substrate surface and / or the substrate containing the substrate surface from the aforementioned orientation is at most 10°. The expressions in parentheses represent the Miller indices of the crystal planes. These are specified in a coordinate system extended by the local crystal lattice.

[0052] In an advantageous embodiment of the process, the substrate surface is coated with one or more epitaxial layers before and / or after reshaping and before the diamond layer grows. The epitaxial layer can contain or consist of Ir, yttrium-stabilized zirconium dioxide, or Ir / SrTiO 3 and can contain or consist of.

[0053] The substrate contains or consists of silicon and is advantageously pre-bent so that the curvature before the diamond layer grows is greater than 0.04 1 / m, preferably greater than 0.1 1 / m, and / or less than 0.7 1 / m, preferably less than 0.5 1 / m. - Comprising or consisting of sapphire, it is advantageous if the curvature before the growth of the diamond layer is greater than 0.26 1 / m, preferably greater than 0.5 1 / m, and / or less than 5.2 1 / m, preferably less than 2 1 / m. - Comprising or consisting of magnesium, it is advantageous if the curvature before the growth of the diamond layer is greater than 0.46 1 / m, preferably greater than 1 1 / m, and / or less than 8 1 / m, preferably less than 4 1 / m.

[0054] The present invention also relates to a substrate for synthesizing a planar single-crystal diamond layer. The substrate according to the present invention has a substrate surface. The substrate surface is bent concave before the growth of the diamond layer. During the growth of the diamond layer, the substrate surface is substantially planar under general conditions (i.e., the radius of curvature is 5 m or more).

[0055] The substrate - Comprising or consisting of silicon, it is advantageous if the curvature before the growth of the diamond layer is greater than 0.04 1 / m, preferably greater than 0.1 1 / m, and / or less than 0.7 1 / m, preferably less than 0.5 1 / m. - Comprising or consisting of sapphire, it is advantageous if the curvature before the growth of the diamond layer is greater than 0.26 1 / m, preferably greater than 0.5 1 / m, and / or less than 5.2 1 / m, preferably less than 2 1 / m. - Comprising or consisting of magnesium, it is advantageous if the curvature before the growth of the diamond layer is greater than 0.46 1 / m, preferably greater than 1 1 / m, and / or less than 8 1 / m, preferably less than 4 1 / m.

[0056] After the preferred plastic deformation of the base substrate, the crystallographic surface of the substrate can have substantially the same orientation as the local substrate surface at every point on the deformed concave substrate surface.

[0057] This can mean that the angle between the tangent plane at a point on the substrate surface and a given indexed lattice plane of the crystalline material forming the surface at this point is the same at all points on the substrate surface or differs from each other by less than 1°, preferably less than 0.5°, particularly preferably less than 0.2°.

[0058] Preferably, the angle between the equally indexed lattice planes of the crystalline material at any two points P1 and P2 on the substrate surface is at most 1°, preferably at most 0.5° greater than the angle between the tangent planes at these two points P1 and P2.

[0059] Preferably, the plastic deformation is carried out such that the crystal structure becomes substantially single crystal during growth and the deviation (mosaic width) is 1° or less, preferably 0.5° or less, particularly preferably 0.2° or less.

[0060] Preferably, the crystal lattice in the plastically deformed state is not twisted by the surface normal vector at various points on the surface. Directions within the crystal lattice that are perpendicular to the plane in which the shortest connecting line between the two points runs within the surface can preferably be parallel or substantially parallel to each other at both points. Directions within the crystal lattice that are perpendicular to the plane spanned by the surface normal vectors at the two points can preferably be parallel or substantially parallel to each other at both points.

[0061] Preferably, the crystal structure follows the curvature of the surface without wrapping around the surface normal vector.

[0062] In an advantageous embodiment of the substrate, the substrate surface has one or more epitaxial layers. The epitaxial layer can comprise or consist of Ir, yttrium-stabilized zirconium dioxide, or Ir / SrTiO 3 and can contain or consist of.

[0063] The present invention also relates to an apparatus for holding a substrate that can be used to synthesize a diamond layer according to the method already described above. For this purpose, the apparatus has at least two concentrically arranged cylinders. These cylinders are arranged one inside the other along a common cylinder axis and are formed so as to be offset relative to each other. This can mean that at least one first cylinder is a hollow cylinder, for example, a hollow cylinder whose inner radius is larger than the outer radius of the second cylinder. These cylinders are arranged such that all the inner edges and / or all the outer edges of the upper end faces of these cylinders are located on a common spherical surface. Thereby, the substrate can be arranged such that its lower surface of the substrate rests on the apparatus according to the present invention and can come into contact with the edges of the upper end face. Since the cylinders can be offset relative to each other, the apparatus can adapt to the deformation of the lower surface of the substrate. This means that a stable and / or uniform thermal contact between the substrate and the apparatus according to the present invention can be ensured even if the substrate is deformed.

[0064] Each cylinder of the apparatus is advantageously cooled so that sufficient heat dissipation occurs on the lower surface of the substrate. It is also conceivable that the individual segments can be shifted to change the thermal contact between the substrate and the holding device. Thereby, it is possible to adjust the temperature of the substrate in a controlled manner as required.

[0065] Advantageously, one of the cylinders of the apparatus is configured as a solid cylinder. The solid cylinder is the innermost cylinder of the apparatus. The solid cylinder is arranged such that the intersection of the cylinder axis and the upper end face of the solid cylinder and / or the outer edge of the upper end face of the solid cylinder is located on a common spherical surface.

[0066] Hereinafter, the present invention will be described with calculation examples and six drawings.

[0067] The drawings are as follows.

Brief Description of the Drawings

[0068]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0069] FIG. 1 shows the growth of a diamond layer in a prior art process. FIG. 1(a) shows a single crystal base substrate 1a having a plurality of mutually parallel planes with a crystallographically determined orientation. Examples of this include Si (silicon), Al 2 O 3 (sapphire), MgO (magnesium oxide), or SrTiO 3(Strontium titanate) exists. Figure 1(b) shows a heteroepitaxial coating of metal 1b on the base substrate, on which diamond layer nucleation and growth will occur later. The last layer of the heteroepitaxial layer is advantageously iridium. In the case of a substrate with an oxide, Ir can usually grow directly on a single crystal. For example, in the case of Si, a YSZ buffer layer is also required. The base substrate 1a forms the substrate 1 together with the epitaxial metal layer and possibly a further buffer layer 1b. The surface 1c is the substrate surface.

[0070] In Figure 1(c), the substrate 1 is placed in a reactor for chemical vapor deposition (CVD) and deposited on the cooled substrate carrier 2. Figure 1(d) shows the state where the microwave 3 is irradiated into the reactor, the plasma 4 is ignited and maintained. The plasma 4 can also be generated using a DC voltage or an AC voltage (for example, a high-frequency or radio-frequency AC voltage) instead of the microwave. The power of the plasma 4 is mainly dissipated as heat, which is indicated by the arrow marked "heat". A part of this heat is dissipated through the substrate 1. This is to keep the substrate surface at a temperature suitable for diamond growth.

[0071] The heat flow through the substrate 1 causes a temperature gradient, which results in the bending of the substrate (Figure 1(e)). The substrate surface is convex in this case. Therefore, the central part of the substrate bends upward.

[0072] Figure 1(f) shows the state where the diamond layer 5 has grown on the substrate surface. After epitaxial nucleation on iridium, the diamond 5 grows conformally on the bent substrate surface and exhibits the same shape as the outer shape of the bent substrate surface at the interface. Regarding the crystal lattice, the diamond follows the orientation of iridium when it exists under the process conditions.

[0073] The temperature gradient within the substrate disappears during cooling. As shown in Fig. 1(g), the substrate attempts to bend in the opposite direction. An elastic tension is generated between the diamond and the substrate. On the oxide, which is the base substrate, the stress is too high, and usually, the diamond layer cracks. Ideally, this occurs throughout, and as a result, no cracks occur in the diamond wafer. When Si is used, the entire diamond / Ir / YSZ / Si system usually remains intact, and the substrate detaches chemically and / or mechanically from the diamond layer. In both cases, the diamond disk retains the curvature generated during growth.

[0074] Fig. 2 shows a method of pre-bending the surface of the base substrate 1a into a concave shape by single-crystal mechanical processing / machining / chemical processing. Optionally, uneven shaping with two curved and parallel surfaces is also possible. As a result of pre-bending the substrate surface according to the present invention, after the diamond layer has grown, a diamond disk 6 that appears flat on the outside is obtained. In that case, the crystallographic plane has a continuously changing orientation (gradient) across the wafer diameter.

[0075] Fig. 3 shows a method similar to the method shown in Fig. 2, the difference being that the surface of the base substrate 1a is pre-bent into a concave shape by plastic deformation. In this example, the lower surface of the substrate is convex. Optionally, in this example, the lower surface may be flat. By pre-bending the substrate surface by plastic deformation according to the present invention, a diamond disk 6 is obtained in which not only the outer surface is flat but also the crystal lattice orientation is the same throughout the crystal. Due to the initially convex lower surface of the substrate, the substrate can lie completely flat on a flat substrate holding device during the growth of the diamond layer (Fig. 3(f)).

[0076] Figure 4 is a flow diagram of an exemplary embodiment of the present method having method steps X1 to X8. Method steps X6 and X7a, b may be considered optional. In a first step, the surface of the base substrate is deformed (X1). X1 indicates deforming the base substrate such that the substrate surface becomes concave. Optionally, the lower surface of the substrate may also be deformed. Advantageously, a convex shape is provided thereto. In method step X2, an epitaxial iridium layer is grown on this deformed surface (e.g., by electron beam evaporation or sputtering). An additional epitaxial buffer layer is required on silicon, which is inserted between the base substrate and iridium. Next, the substrate or substrate wafer is placed on a substrate holding device in a plasma reactor (step X3). The substrate is arranged such that the lower surface of the substrate rests on the substrate holding device and the substrate surface faces the space where plasma can be generated. In a further method step (X4), process gas is introduced, the pressure is set, and power is applied to initiate a plasma discharge. With the assistance of an additional negative DC voltage, epitaxial diamond nuclei are generated on the substrate surface (BEN). This step may be carried out without an initial plasma discharge. That is, only a DC voltage discharge is used for nucleation. In step X5, a process gas mixture and process conditions (gas mixture, pressure, temperature, applied power) for thickness growth are selected. In an optional method step X6, the curvature of the substrate and / or the surface of the diamond layer where the growth process occurs may be measured in situ (i.e., while it is in the reactor, especially during the growth of the diamond layer). In method steps X7a and X7b, process parameters such as pressure, temperature, and / or power may be controlled based on the measurement results in method step X6 such that the radius of curvature of the substrate surface exceeds 5 m. Specifically, when measuring the concave curvature of the substrate surface, the pressure and / or plasma temperature and / or coupled power are further increased until the radius of curvature exceeds 5 m. Conversely, when measuring the convex curvature, the pressure and / or plasma temperature and / or coupled power are decreased until the radius of curvature exceeds 5 m. In the final method step X8, diamond growth is continued with the set process parameters.In a further method step (not shown), the substrate having the diamond layer may be removed from the reactor after completion of the coating, and the resulting diamond wafer may be removed from the substrate.

[0077] Figure 5 shows two graphs. Figure 5a shows a graph of the calculated curvature of the (initially planar) substrate surface of various base substrate materials as a function of the heat flux density. Since the iridium layer and any additional buffer layer are typically much thinner than the base substrate (thinner than 1 / 1000 of the base substrate), their influence may be ignored. 10 6 W / m 2 The unit of heat flux density is plotted on the X-axis, and the calculated curvature is shown on the Y-axis in units of 1 / m as the reciprocal of the calculated radius of curvature. These data points are shown as filled squares for the case of silicon, filled circles for the case of sapphire (Al 2 O 3 ), and filled triangles for the case of magnesium oxide (MgO). It can be clearly recognized that the relationship between the heat flux density and the curvature is linear. The gradient depends on the material under consideration, being smallest for silicon and largest for magnesium oxide.

[0078] The gradient for the case of sapphire is located between the gradient for the case of silicon and the gradient for the case of MgO. Since the substrate is initially planar, there is no curvature without heat flow, and all straight lines intersect at the origin of the coordinates.

[0079] Figure 5a also shows that the single-crystal sapphire substrate is anisotropic. The reason is that if the crystal axes are different, the coefficient of thermal expansion is different. In the case of sapphire, this difference can be up to 8.5%. If the crystal for the synthesis of (111)-oriented diamond is c-axis oriented, the bending will be isotropic and will be represented by the curve 1 / R(Al2O3_a-axis). For the preferred synthesis of (001)-oriented diamond, an alternative A-plane cut (11-20) is used. Iridium grows with a uniform orientation on the resulting rectangular surface cell (along with its cubic cell). The curvature becomes anisotropic in the plasma. The curvature in one direction as a function of the heat flux density is shown by the dashed curve (1 / R(Al2O3_a-axis)), and the curvature in the perpendicular direction is shown by the solid curve (1 / R(Al2O3_c-axis)). To compensate for such anisotropic curvature, the substrate may be pre-bent in an aspherical aberration correction manner.

[0080] Figure 5b shows a graph indicating the calculated curvature of the central part of the (initially planar) substrate surface at various heat flux densities for various substrate materials. This calculation is for a circular wafer with a diameter of 10 cm. 6 W / m 2 The heat flux density in units of W / m is plotted on the X-axis, and the calculated curvature in units of mm is shown on the Y-axis. These data points are shown as filled squares for the case of silicon, as filled circles for the case of sapphire (Al 2 O 3 ) and as filled triangles for the case of magnesium oxide (MgO).

[0081] It will also be recognized that in the parameter range of interest, the relationship between the heat flux density and the curvature is approximately linear. The curvature increases in the order of silicon, sapphire, and magnesium oxide for the same heat flux density.

[0082] In the following examples, the radius of curvature and curvature generated when a diamond layer grows on the substrate surface of each substrate of silicon, sapphire, and MgO, which is initially planar, are calculated. In the following calculations, it is assumed that the heat flux density is 10 6 W / m 2 .

[0083] It is assumed that the temperature of the substrate surface is 1000 °C. Also, it is assumed that the power coupled to the plasma is 30 kW. In the case of lateral calculation, the plasma ball must be the same size as the substrate. One-third of 30 kW, that is, 10 kW, will be dissipated through the substrate. In this example, it is assumed that the size of the substrate surface is 100 cm 2 . (This corresponds to a round disk with a diameter of 11.3 cm.) This area also corresponds to the cross-sectional area of the substrate through which heat transfer occurs. Also, it is assumed that the heat flow from the plasma through the substrate to the substrate surface is the same at any point on the substrate surface. That is, it is assumed that there is a completely uniform plasma across the entire substrate. Therefore, the heat flux density J in this example is J = 10 kW / 100 cm 2 = 100 W / cm 2 = 10 6 W / m 2 .

[0084] Furthermore, regarding the thermal conductivity of the substrate, the values of each base substrate at 1000 °C are assumed. In the literature, as the material parameter of λ, in the case of silicon, it is 25 W / (mK), in the case of sapphire, it is 7.5 W / (mK) (5 - 10 W / (mK)), and in the case of MgO, it is 8 W / (mK).

[0085] Therefore, the temperature difference between the upper and lower surfaces of a wafer with a thickness d = 0.1 cm is, in the case of silicon, (J × d) / λ = 10 6 W / m 2 × 10 -3 m / (25 W / (mK)) = 40 K, in the case of sapphire, (J × d) / λ = 10 6 W / m2 ×10 -3 m / (7.5 W / (mK)) = 133 K、 For MgO, (J×d) / λ = 10 6 W / m 2 ×10 -3 m / (8 W / (mK)) = 125 K.

[0086] The bend is the result of the difference in linear expansion between the substrate surface and the substrate bottom surface caused by the temperature difference. The temperature difference is For silicon, the difference between 960 °C and 1000 °C, For sapphire, the difference between 867 °C and 1000 °C, For MgO, the difference between 875 °C and 1000 °C.

[0087] The coefficient of expansion at approximately 1000 °C is For silicon, 4.5×10 -6 K -1 、 For polycrystalline sapphire, 9.75×10 -6 K -1 、 For MgO, 16×10 -6 K -1 is.

[0088] As a result of this, the expansion difference between the bottom surface and the top surface (at d = 0.1 cm) is For silicon, 4.5×10 -6 K -1 ×40 K = 1.8×10 -4 、 For sapphire, 9.75×10 -6 K -1 ×133 K = 1.3×10 -3 、 For MgO, 16×10 -6 K -1 ×125 K = 2.0×10 -3 is.

[0089] The radius of curvature R is For silicon, R = 10 -3 m / 1.8×10-4 = 5.56 m, In the case of sapphire, R = 10 -3 m / 1.3×10 -3 = 0.77 m, In the case of MgO, R = 10 -3 m / 2×10 -3 = 0.5 m.

[0090] In the case of a round wafer with a diameter D = 10 cm, the curvature h applied to the central part thereby is In the case of silicon, h = 0.2 mm, In the case of sapphire, h = 1.6 mm, In the case of MgO, h = 2.5 mm.

[0091] The curvature of the diamond disk grown on sapphire or MgO is so large that it can no longer be flattened perceptibly by subsequent machining (e.g., polishing). Another disadvantage is that the orientation of the crystal lattice changes continuously across the diameter of the diamond wafer.

[0092] The angular changes in the polar orientation of the crystal lattice from -5 cm to +5 cm at radii of 5.6 m, 0.77 m, and 0.5 m are calculated as follows. That is, In the case of silicon, 2×arcsin(50 / 5600) = 1.02° (±0.51°), In the case of sapphire, 2×arcsin(50 / 770) = 7.44° (±3.72°), In the case of MgO, 2×arcsin(50 / 500) = 11.48° (±5.74°).

[0093] In the following examples, the value range of the suitable pre-curvature radius (or pre-curvature) that enables the growth of a planar diamond layer is calculated. Unless otherwise specified, the same assumptions as in the above examples are made. The power coupled to the plasma is estimated to be 5 kW to 100 kW. Here, it is assumed that 40% of this power is dissipated in the form of heat through the substrate. If the area is 100 cm 2 then, the heat flux density due to this is 0.2 - 4×106 W / m 2 As a result, the range of the curvature 1 / R and the radius R to be applied to the wafer before coating is 1 / R(Si): 0.036 - 0.72 m -1 , R(Si): 1.4 - 27.8 m, 1 / R(Al2O3_poly): 0.26 - 5.2 m -1 , R(Al2O3_poly): 0.19 - 3.8 m, 1 / R(MgO): 0.4 - 8 m -1 , R(MgO): 0.125 - 2.5 m.

[0094] Figure 6 shows two cross-sectional views of an apparatus according to the present invention for holding a substrate for the synthesis of a large surface area planar single crystal diamond. Figure 6a shows the substrate 1 before the diamond layer grows thereon, and the substrate surface is already pre-bent in a concave shape. An epitaxial metal layer 2 is applied to the substrate surface. The lower surface of the substrate is convex. The illustrated substrate 1 and apparatus are those at the time when there is no heat flow through the substrate (for example, in method step c of Figure 3), or those after the time of method step X3 of Figure 4, for example. The substrate 1 is placed such that its lower surface is in contact with an apparatus 6 for holding the substrate. The apparatus 6 consists of four cylinders 7a, 7b, 7c, 7d. The three outer cylinders 7a, 7b, 7c are formed as hollow cylinders, and the central cylinder 7d is formed as a solid cylinder. The four cylinders 7a, 7b, 7c, 7d are arranged on a common cylinder axis 8 and are formed such that they can be displaced relative to each other in an arrangement where one is inside the other. This means that the outer radius of a certain cylinder is smaller than the inner radius of the cylinder one size larger than it. These four cylinders are displaced relative to each other such that the three outer cylinders 7a, 7b, 7c each contact the lower surface of the substrate at their respective inner edges. The central solid cylinder 7d contacts the lower surface of the substrate at the intersection of its upper end face and the common cylinder axis.

[0095] Figure 6b shows the substrate 1 on the device 6 that holds the substrate during the growth of the diamond layer 5. Due to the heat flow passing through the substrate 1, the substrate 1 deforms with respect to the substrate as shown in Figure 6a. According to the present invention, the radius of curvature of the substrate surface becomes greater than 5 m during the growth of the diamond layer. The substrate surface in Figure 6b is planar, and a planar (single crystal) diamond layer 5 can grow. The cylinders 7a, 7b, 7c, 7d are shifted such that their respective upper end faces contact the planar lower surface of the substrate (now, still).

[0096] In an exemplary embodiment of the mounting device shown in Figure 6, the wall thicknesses of the hollow cylinders 7a, 7b, 7c are substantially the same. It is also fully conceivable to use one or more cylinders with different wall thicknesses. The shape of the end faces of the cylinders of the device according to the present invention is also not limited to the illustrated end face shapes. There can also be advantageous embodiments where the end face is not planar and / or the inner edge or outer edge has an inclined or rounded edge.

[0097] The heat transfer between the lower surface of the substrate and the mounting 6 occurs partly by heat conduction (i.e., through the contact surface between the cylinder and the lower surface of the substrate) and partly by convection. The heat transfer by convection occurs through the process gas. Controlling the heat transfer between the lower surface of the substrate and the device 6 can be done, for example, by moving the individual cylinders of the holding device to affect the temperature of the substrate surface. For example, there can be an embodiment where the heat transfer can be reduced by the substrate 1 not contacting all of the cylinders 7a, 7b, 7c, 7d. As a result of the reduced heat transfer, the temperature of the entire substrate rises, and thus the temperature of the substrate surface also rises. Utilizing the fact that the heat transfer through the substrate can be controlled in this way, it is possible to keep the temperature of the substrate surface within a range suitable for diamond growth, which is also possible when the process parameters of the plasma change.

Claims

1. A method for synthesizing at least one diamond layer, comprising: generating a plasma (4) in a plasma chemical vapor deposition reactor; growing the at least one diamond layer (5) on a substrate surface (1c) of a substrate (1) by the generated plasma; reshaping the substrate surface (1c) into a concave shape so that a radius of curvature of the substrate surface (1c) becomes 5 m or more during growth of the diamond layer before growing the diamond layer; a method.

2. The method according to claim 1, wherein a radius of curvature of the substrate surface (1c) during growth of the diamond layer (5) is preferably 10 m or more, particularly preferably 20 m or more, and very particularly preferably 100 m or more.

3. The method according to any one of claims 1 to 2, wherein the radius of curvature of the substrate surface (1c) is measured during generation and holding of the plasma (4), and process parameters of the plasma chemical vapor deposition are set so that the radius of curvature of the substrate surface (1c) becomes 5 m or more during growth of the diamond layer (5).

4. The method according to any one of claims 1 to 3, wherein when the substrate surface (1c) becomes concave during growth of the diamond layer (5), a coupling power and / or temperature of the plasma (4) and / or a total pressure of the process gas are increased, and / or when the substrate surface (1c) becomes convex during growth of the diamond layer (5), the coupling power and / or the temperature of the plasma (4) and / or the total pressure of the process gas are decreased.

5. The method according to any one of claims 1 to 4, wherein a temperature of the substrate surface (1c) during growth of the at least one diamond layer is 900 °C or more, preferably 950 °C or more, particularly preferably 1000 °C or more, and / or 1250 °C or less, preferably 1200 °C or less, particularly preferably 1150 °C or less.

6. The volume density of the power absorbed in the plasma (4) is 10 W / cm ３ or more, preferably 20 W / cm ３ or more, particularly preferably 50 W / cm ３ or more, and / or 500 W / cm ３ or less, preferably 250 W / cm ３ or less, particularly preferably 100 W / cm ３ or less, The method according to any one of claims 1 to 5.

7. The method according to any one of claims 1 to 6, wherein a pressure of the process gas is 20 mbar or more, preferably 50 mbar or more, particularly preferably 100 mbar or more, and / or 500 mbar or less, preferably 400 mbar or less, particularly preferably 300 mbar or less.

8. The areal density of the power absorbed by the plasma (4) over the surface of the substrate (1c) is 50 W / cm ２ or more, preferably 100 W / cm ２ or more, and / or 1000 W / cm ２ or less, preferably 750 W / cm ２ or less. The method according to any one of claims 1 to 7.

9. The generation of the plasma (4) is carried out by irradiation with microwaves, radio waves, or by a direct current voltage, or by an alternating current voltage, or within a plasma jet, according to the method of any one of claims 1 to 8.

10. Before growing the diamond layer (5), the substrate surface (1c) is reshaped into a concave shape with a radius of curvature R, R increases with λ, R decreases with an increase in the values of J and α, λ is the thermal conductivity of the substrate having the substrate surface, α is the coefficient of thermal expansion of the substrate, and J is the heat flux density flowing from the upper surface of the substrate to the lower surface of the substrate during the growth of the diamond layer (5). The method according to any one of claims 1 to 9.

11. Before the growth, the substrate surface (1c) is bent into a concave shape, the curvature 1 / R is calculated according to 1 / R = aJ / l, and J used as the heat flux density in the calculation is preferably 0.2×10 ６ W / m ２ or more, particularly preferably 0.5×10 ６ W / m ２ or more, and / or 5×10 ６ W / m ２ or less, preferably 3×10 ６ W / m ２ or less, particularly preferably 2×10 ６ W / m ２ or less. The method according to any one of claims 1 to 10.

12. The lower surface of the substrate before growth has a convex shape with a radius equal to or greater than the radius of the upper surface of the substrate, according to the method of any one of claims 1 to 11.

13. The surface of the substrate (1c) is 1 cm ２ or more, preferably 10 cm ２ or more, more preferably 50 cm ２ or more, particularly preferably 200 cm ２ or more, or most preferably 300 cm ２ or more. The method according to any one of claims 1 to 12

14. The thickness of the substrate is 0.5 mm or more, preferably 1 mm or more, particularly preferably 2 mm or more, and / or 20 mm or less, preferably 15 mm or less, particularly preferably 10 mm or less, according to the method of any one of claims 1 to 13.

15. The reshaping of the substrate surface (1c) is carried out by milling and / or turning and / or laser ablation and / or grinding and / or polishing of the substrate (1), according to the method of any one of claims 1 to 14.

16. The reshaping of the substrate surface is carried out by plastic deformation of the substrate, and the angle between the tangent plane at a point on the substrate surface and a given indexed lattice plane of the crystalline material forming the surface at this point is the same at all points on the substrate surface or differs from each other by less than 1°, preferably less than 0.5°, particularly preferably less than 0.2°. And / or, the angle between the equally indexed lattice planes of the crystalline material at any two points P1 and P2 on the substrate surface is at most 1°, preferably at most 0.5° greater than the angle between the tangent planes at these two points P1 and P2. The method according to any one of claims 1 to 15.

17. The method according to any one of claims 1 to 16, wherein the substrate surface (1c) and / or the substrate (1) including the substrate surface (1c) contains at least to some extent iridium, silicon, silicon dioxide, magnesium oxide, strontium titanate, yttrium-stabilized zirconium dioxide, and / or sapphire.

18. The method according to any one of claims 1 to 17, wherein the substrate surface (1c) and / or the substrate (1) including the substrate surface (1c) is crystalline, preferably a single crystal with a local mosaic width of less than 0.5°.

19. The method according to any one of claims 1 to 18, wherein when the substrate surface (1c) and / or the substrate (1) including the substrate surface (1c) is a cubic crystal, the crystal orientation of the surface is on average (001) or (111), and when it is a trigonal crystal, the crystal orientation of the surface is on average (0001) or (11-20) or (1-102) or (10-10).

20. The method according to any one of claims 1 to 19, wherein the deviation of the average surface orientation of the substrate surface (1c) and / or the substrate (1) including the substrate surface (1c) from each of the crystal orientations is at most 10°.

21. Before and / or after said reshaping and before said growth of said diamond layer, an epitaxial layer (1b) comprising or consisting of iridium or Ir / YSZ or Ir / SrTiO ３ is applied to said surface of said base substrate (1a), the method according to any one of claims 1 to 20.

22. Before the growth of the diamond layer (5), the substrate surface (1c) is reshaped into a concave shape with a first radius of curvature along a first spatial direction and into a concave shape with a second radius of curvature along a second spatial direction, and the first radius of curvature is not the same as the second radius of curvature, so that during the growth of the diamond layer, the radius of curvature along the first spatial direction and the radius of curvature along the second spatial direction are 5 m or more. The method according to any one of claims 1 to 21.

23. The substrate surface is bent into a concave shape before the growth, and its curvature 1 / R is -In the case of a substrate containing Si, preferably 0.04 1 / m or more, particularly preferably 0.1 1 / m or more, and / or 0.7 1 / m or less, particularly preferably 0.5 1 / m, -In the case of a substrate containing sapphire, preferably 0.26 1 / m or more, particularly preferably 0.5 1 / m or more, and / or preferably 5.2 1 / m or less, particularly preferably 2 1 / m. - In the case of a substrate containing magnesium oxide, it is preferably 0.4 1 / m or more, particularly preferably 1 1 / m or more, and / or preferably 8 1 / m or less, particularly preferably 4 1 / m. The method according to any one of claims 1 to 22.

24. A substrate (1) for the synthesis of a diamond layer (5) including a substrate surface (1c), wherein the substrate surface (1c) has a radius of curvature of 5 m or more, preferably 10 m or more, particularly preferably 20 m or more, and particularly very preferably 100 m or more during the growth of the diamond layer (5) in the method according to any one of claims 1 to 23, and is bent in a concave shape with such a curvature.

25. An apparatus (6) for supporting a substrate (1) for synthesizing a diamond layer (5) according to any one of claims 1 to 24, wherein the apparatus includes at least two concentrically arranged cylinders (7) and the cylinders are arranged one inside the other along a common cylinder axis (8) so as to be displaceable relative to each other, and all the inner edges and / or all the outer edges of the upper end faces of the cylinders (7) are arranged to be located on a common spherical surface. Apparatus (6).

26. The apparatus (6) according to claim 25, wherein one of the cylinders (7) is configured as a solid cylinder (7d), and the intersection of the common cylinder axis (8) and the upper end face of the solid cylinder (7d) is located on the common spherical surface, and / or the outer edge of the upper end face of the solid cylinder (7d) is located on the common spherical surface.

27. A method of using the apparatus (6) according to claim 25 or 26 in the method according to any one of claims 1 to 23, wherein the apparatus (6) is in the reactor, while the diamond layer (5) is growing on the substrate surface (1c) according to the method, the lower surface of the substrate on the opposite side of the substrate surface (1c) is arranged to be in contact with all the inner edges and / or all the outer edges of the upper end faces of the cylinders (7a, 7b, 7c, 7d). Method of use.

28. The radius of curvature of the lower surface of the substrate is changed during the implementation of the method, and the cylinders (7a, 7b, 7c, 7d) of the apparatus are during the implementation of the method, During the growth of the diamond layer (5), shift relative to each other such that the lower surface of the substrate contacts all inner edges and / or all outer edges of the upper end surfaces of the cylinders (7a, 7b, 7c, 7d). The method of use according to claim 27.

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