Substrate for single-crystal diamond laminated substrate and method for manufacturing the same, and method for manufacturing a single-crystal diamond substrate

Abstract

The objective is to provide a substrate capable of forming a high-quality single-crystal diamond layer with a large area (large diameter), high crystallinity, high purity, and low stress. [Solution] A base substrate for a single-crystal diamond multilayer substrate, wherein the coefficient of thermal expansion is smaller than that of single-crystal α-Al2O3, and is 0.5 × 10 -6 A base substrate comprising an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond with a temperature of 1 / K or higher, a single-crystal α-Al2O3 layer on the initial substrate, and a heteroepitaxial layer on the single-crystal α-Al2O3 layer consisting of an iridium film, a rhodium film, and a platinum film.

Description

[Technical Field]

[0001] The present invention relates to a base substrate for a single-crystal diamond laminated substrate, a method for manufacturing the same, and a method for manufacturing a single-crystal diamond substrate. [Background technology]

[0002] Diamond has a wide bandgap of 5.47 eV at room temperature and is known as a wide-bandgap semiconductor.

[0003] Among semiconductors, diamond has an extremely high dielectric breakdown field strength of 10 MV / cm, enabling high-voltage operation. Furthermore, it possesses the highest thermal conductivity of any known material, resulting in excellent heat dissipation. In addition, its very high carrier mobility and saturation drift rate make it suitable for high-speed devices.

[0004] Therefore, diamond exhibits the highest Johnson Figure of Performance (JP), which indicates performance as a high-frequency, high-power device, compared to semiconductors such as silicon carbide and gallium nitride, and is considered the ultimate semiconductor. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2024 / 048357 [Non-patent literature]

[0006] [Non-Patent Document 1] H.Yamada,Appl.Phys.Lett.104,102110(2014). [Overview of the project] [Problems that the invention aims to solve]

[0007] As described above, diamond is expected to be put into practical use as a semiconductor material or a material for electronic and magnetic devices, and the supply of large-area and high-quality diamond substrates is desired.

[0008] Currently, most of the single-crystal diamonds used for manufacturing diamond semiconductors are diamonds called type Ib synthesized by the high-pressure high-temperature method (HPHT). This type Ib diamond contains a large amount of nitrogen impurities and can only be obtained in a size of up to about 8 mm square at most, and its practicality is low. In addition, a method called the mosaic method in which a large number of HPHT substrates (diamond substrates synthesized by the HPHT method) are arranged and joined together has been proposed (Non-Patent Document 1), but the problem of joint incompleteness remains.

[0009] On the other hand, in the case of the vapor-phase synthesis (Chemical Vapor Deposition: CVD) method, although large-area diamonds with a diameter of about 6 inches (150 mm) can be obtained with high purity for polycrystalline diamonds, it has been difficult to achieve single crystallization suitable for ordinary electronic devices. This is because a suitable combination of materials with a small difference in lattice constant and linear expansion coefficient between diamond and the underlying substrate for forming diamond has not been realized. For example, the difference in lattice constant between diamond and single-crystal Si is as large as 34.3%, so it is very difficult to heteroepitaxially grow diamond on the surface of the underlying substrate.

[0010] Therefore, Patent Document 1 discloses a technique that enables the growth of single-crystal diamond on an underlying substrate by providing an appropriate off-angle according to the crystal structure such as cubic or hexagonal in the initial substrate. The underlying substrate is composed of an initial substrate as the main constituent layer and an intermediate layer formed thereon.

[0011] Although the invention of Patent Document 1 has a great effect on reducing defects and improving orientation of heteroepitaxial diamond crystals, due to the large difference in linear expansion coefficient between diamond and the initial substrate, there is a problem that the diamond film peels off or breaks during or after CVD, and furthermore, the underlying substrate also breaks together.

[0012] For example, the difference in the coefficient of linear expansion between diamond and single crystal α-Al2O3 (c direction) is 4.5 × 10⁻⁶. -6 Because the temperature can reach / K, a large stress is generated between the diamond film and the initial substrate, which can cause film delamination or substrate damage.

[0013] Even single-crystal silicon, which has a coefficient of thermal expansion relatively close to that of diamond, has a difference of 1.7 × 10⁻⁶ in its coefficient of thermal expansion compared to diamond. -6 Because of the / K feature, warping becomes a problem. This will become a major issue when attempting to achieve larger diameters of 6 inches or more in the future.

[0014] Therefore, there is a need for technology that enables the stable formation of single-crystal diamonds without breakage, particularly on single-crystal α-Al2O3 layers that yield high-quality, highly oriented diamonds.

[0015] The present invention was made to solve the above problems and aims to provide a substrate and a method for manufacturing the same that can form a high-quality single-crystal diamond layer with a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress, applicable to electronic and magnetic devices. The invention also provides a method for manufacturing a single-crystal diamond substrate having the above characteristics. [Means for solving the problem]

[0016] The present invention was made to achieve the above objective, and is a base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of linear expansion is smaller than that of single-crystal α-Al2O3 and 0.5 × 10 -6 The present invention provides a base substrate comprising an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond with a temperature of 1 / K or higher, a single-crystal α-Al2O3 layer on the initial substrate, and a heteroepitaxial layer on the single-crystal α-Al2O3 layer consisting of an iridium film, a rhodium film, and a platinum film.

[0017] With such a base substrate for a single-crystal diamond laminate, it becomes possible to form a high-quality single-crystal diamond layer on the base substrate that is large in area (large in diameter), highly crystalline, with few hillocks, abnormally grown particles, dislocation defects, etc., and possesses high purity and low stress.

[0018] In this case, if the surface orientation of the diamond layer of the single-crystal diamond laminate is {111}, the single-crystal α-Al2O3 layer has an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <11-20> with respect to the surface orientation of the outermost surface being {0001}, and if the surface orientation of the diamond layer of the single-crystal diamond laminate is {001}, the single-crystal α-Al2O3 layer has an off-angle in the direction of the crystal axis <10-10> or <11-20> with respect to the surface orientation of the outermost surface being {11-20}. <0001> The offset angle in the direction can be in the range of +4.0 to +24.0° or -4.0 to -24.0°.

[0019] Within this range of off-angles, the heteroepitaxial layer on the single-crystal α-Al2O3 layer will be of higher quality, with greater crystallinity and fewer hillocks, anomalous growth particles, and dislocation defects.

[0020] In this case, the initial substrate and the single-crystal α-Al2O3 layer may have a single layer or a multilayer film containing at least one of the following: an amorphous carbon film, a polycrystalline diamond film, a single-crystal diamond film, a SiC film, a Si film, and an SiO2 film.

[0021] This results in the formation of the single-crystal α-Al2O3 layer more efficiently.

[0022] The present invention has also been made to achieve the above objective, and is a method for manufacturing a base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of linear expansion is smaller than that of single-crystal α-Al2O3 and 0.5 × 10 -6The present invention provides a method for manufacturing a substrate substrate, comprising the steps of: preparing an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, having a temperature of 1 / K or higher; bonding a single-crystal α-Al2O3 layer to the initial substrate; and forming a heteroepitaxial layer by heteroepitaxially growing one of iridium film, rhodium film, or platinum film on the surface of the single-crystal α-Al2O3 layer opposite to the surface to which the initial substrate is bonded.

[0023] According to this method of manufacturing the substrate, it is possible to produce a substrate that has a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, and is of high purity and low stress, and is capable of forming a high-quality single-crystal diamond layer.

[0024] In this case, when forming a diamond layer with a plane orientation of {111} in the single-crystal diamond laminated substrate, the single-crystal α-Al2O3 layer is formed with an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <11-20> relative to the plane orientation of the outermost surface of the single-crystal α-Al2O3 layer which is {0001}, and when forming a diamond layer with a plane orientation of {001} in the single-crystal α-Al2O3 layer, the crystal axis <10-10> or <11-20> relative to the plane orientation of the outermost surface of the single-crystal α-Al2O3 layer which is {11-20} <0001> Layers with off-angles in the range of +4.0 to +24.0° or -4.0 to -24.0° can be formed in the direction.

[0025] This makes it possible to form a high-quality heteroepitaxial layer on the single-crystal α-Al2O3 layer that is more crystalline and has fewer hillocks, abnormally grown particles, and dislocation defects.

[0026] In this case, the single-crystal α-Al2O3 layer can be bonded to the initial substrate via a single-layer or multilayer film containing at least one of an amorphous carbon film, a polycrystalline diamond film, a single-crystal diamond film, a SiC film, a Si film, and an SiO2 film.

[0027] This allows the initial substrate and the single-crystal α-Al2O3 layer to be bonded together more efficiently.

[0028] In this case, the thickness of the initial substrate can be 0.03 to 5.00 mm, the thickness of the single-crystal α-Al2O3 layer can be 0.1 to 100 μm, and the thickness of the heteroepitaxial layer can be 0.5 nm (5 Å) to 100 μm.

[0029] An initial substrate of this thickness is cost-effective and easier to handle. Furthermore, with a single-crystal α-Al2O3 layer and heteroepitaxial layer of this thickness, the stress generated between the initial substrate and the single-crystal diamond layer is smaller, allowing for more reliable growth of high-quality single-crystal diamond and the manufacture of an inexpensive substrate.

[0030] This step may include a process of performing a bias treatment on the surface of the heteroepitaxial layer for diamond nucleation.

[0031] This allows for the formation of diamond growth nuclei on the surface of the heteroepitaxial layer, making it possible to manufacture a substrate that allows for the growth of single-crystal diamond layers with better crystallinity and at a more efficient growth rate.

[0032] In this case, a method for manufacturing a single-crystal diamond substrate can be provided, comprising the steps of: preparing a base substrate manufactured by the above-described method for manufacturing a base substrate; heteroepitaxially growing a single-crystal diamond layer on the heteroepitaxial layer; and separating the single-crystal diamond layer from the heteroepitaxial layer.

[0033] This makes it possible to manufacture high-quality single-crystal diamond substrates with a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress.

[0034] In this case, the process may include a step of performing a bias treatment on the surface of the heteroepitaxial layer for diamond nucleation before the step of heteroepitaxial growth of the single-crystal diamond layer.

[0035] This allows diamond growth nuclei to form on the surface of the heteroepitaxial layer, enabling the growth of single-crystal diamond layers with better crystallinity and at a more efficient growth rate.

[0036] In this process, the single-crystal diamond layer can be grown using one of the following methods: microwave CVD, DC plasma CVD, or thermal filament CVD.

[0037] Thus, in the method for manufacturing a single-crystal diamond substrate of the present invention, the single-crystal diamond layer can be grown heteroepitaxially by any of the following methods: microwave CVD, DC plasma CVD, or thermal filament CVD. [Effects of the Invention]

[0038] As described above, the base substrate for a single-crystal diamond laminated substrate of the present invention provides a base substrate on which a high-quality single-crystal diamond layer can be formed, which has a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, etc., and is of high purity and low stress. Furthermore, according to the method for manufacturing a base substrate for a single-crystal diamond laminated substrate of the present invention, it is possible to manufacture a base substrate that has a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, etc., and is of high purity and low stress, making it possible to form a high-quality single-crystal diamond layer. The present invention further provides a method for manufacturing a single-crystal diamond substrate having the above-described characteristics. [Brief explanation of the drawing]

[0039] [Figure 1] This is a schematic diagram showing an example of an embodiment of a base substrate for a single-crystal diamond laminated substrate according to the present invention. [Figure 2] This is a schematic diagram showing an example of a single-crystal diamond laminated substrate according to the present invention. [Figure 3] This is a schematic diagram showing an example of a single-crystal diamond substrate according to the present invention. [Figure 4] This flowchart shows an example of an embodiment of the method for manufacturing a base substrate for a single-crystal diamond laminated substrate and a single-crystal diamond substrate according to the present invention. [Modes for carrying out the invention]

[0040] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0041] As described above, there was a need for a substrate and a method for manufacturing it that could form a high-quality single-crystal diamond layer with a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress, which could be applied to electronic and magnetic devices.

[0042] As a result of diligent research into the above-mentioned problems, the inventors have developed a base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of linear expansion is smaller than that of single-crystal α-Al2O3, and 0.5 × 10 -6The present invention was completed by discovering that a high-quality single-crystal diamond layer with a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress can be formed on the substrate by using an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond with a temperature of 1 / K or higher, a single-crystal α-Al2O3 layer on the initial substrate, and a heteroepitaxial layer on the single-crystal α-Al2O3 layer consisting of an iridium film, a rhodium film, and a platinum film.

[0043] The inventors have also conducted extensive research on the above problem and have come up with a method for manufacturing a base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of thermal expansion is smaller than that of single-crystal α-Al2O3 and is 0.5 × 10 -6 The present invention was completed by discovering that a substrate can be manufactured using a method for producing a substrate that has a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress, and is capable of forming a high-quality single-crystal diamond layer. This method comprises the steps of: preparing an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond with a temperature of 1 / K or higher; bonding a single-crystal α-Al2O3 layer to the initial substrate; and forming a heteroepitaxial layer by heteroepitaxially growing one of iridium film, rhodium film, or platinum film on the surface of the single-crystal α-Al2O3 layer opposite to the surface to which the initial substrate is bonded.

[0044] (Underlay substrate for single-crystal diamond multilayer substrates) The present invention will be described in more detail below with reference to the drawings. Similar components will be denoted by the same reference numerals below. First, the base substrate for the single-crystal diamond laminated substrate of the present invention will be described with reference to Figure 1.

[0045] As shown in Figure 1, the base substrate 30 for the single-crystal diamond laminated substrate of the present invention comprises an initial substrate 11, a single-crystal α-Al2O3 layer 21 on the initial substrate 11, and a heteroepitaxial layer 31 on the single-crystal α-Al2O3 layer 21, which consists of a single layer or laminate containing at least one of a heteroepitaxially grown single-crystal iridium film, a single-crystal rhodium film, or a single-crystal platinum film.

[0046] Traditionally, when attempting to obtain heteroepitaxial diamond using the cost-effective CVD method, there was a problem in that it was not possible to obtain highly crystalline, large-area single-crystal diamonds without damage.

[0047] The inventors have found that by selecting amorphous carbon (DLC), glassy carbon, polycrystalline diamond, or single-crystal diamond (hereinafter simply referred to as "carbon-based material") as the constituent material of the initial substrate 11, which mainly generates stress between itself and the single-crystal diamond layer, the stress generated by thermal expansion is smaller compared to when using a conventional MgO initial substrate or an α-Al2O3 initial substrate, and as a result, damage to the entire substrate can be prevented. Refer to Table 1 below for the coefficient of linear expansion.

[0048] [Table 1]

[0049] The initial substrate 11 is made of materials called amorphous carbon (DLC), glassy carbon, polycrystalline diamond, and single-crystal diamond. These carbon-based materials also differ in their crystallinity and integer linear expansion depending on the manufacturing method and conditions.

[0050] Therefore, the material used for the initial substrate 11 has a coefficient of thermal expansion smaller than that of single crystal α-Al2O3, and is 0.5 × 10 -6 It is specified that the material must contain at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, with a temperature of / K or higher.

[0051] If the initial substrate 11 is made of a carbon-based material as described above, since it is a material of the same element as the diamond to be grown, almost no stress due to thermal expansion occurs, and a large-area single-crystal diamond layer can be formed.

[0052] The carbon-based material constituting the initial substrate 11 may be manufactured by a method such as microwave CVD method, DC plasma CVD method, DC arc plasma CVD method, hot filament CVD method, or RF plasma CVD method, and the crystallinity may be amorphous (diamond-like carbon (DLC)), polycrystalline, or single-crystalline.

[0053] For example, other materials such as DLC and glassy carbon can be manufactured by RF plasma CVD method, DC plasma CVD method, DC arc plasma CVD method, or hot filament CVD method using hydrogen-diluted methane gas as a raw material. The concentration of hydrogen-diluted methane gas may be 0.1 to 20 vol.%, and the pressure may be 7.5×10 -3 ~2.3 Pa.

[0054] Glassy carbon may be obtained by firing and heat-treating a resin.

[0055] For polycrystalline diamond and single-crystalline diamond, they can be manufactured by a method such as microwave CVD method, DC plasma CVD method, DC arc plasma CVD method, or hot filament CVD method using hydrogen-diluted methane gas as a raw material. The concentration of hydrogen-diluted methane gas may be 0.1 to 20 vol.%, and the pressure may be 7.5×10 -3 ~2.3 Pa.

[0056] Regarding single-crystalline diamond, it is also possible to use those synthesized by the HPHT method. Furthermore, it may be a single substrate formed by joining multiple single-crystalline diamond substrates synthesized by the HPHT method or CVD method.

[0057] If it is made of such carbon-based materials, it will be a large-area, low-cost initial substrate 11.

[0058] The single-crystal α-Al2O3 layer 21 can be a single-crystal α-Al2O3{0001} layer or a single-crystal α-Al2O3{11-20} layer. When the surface orientation of the diamond layer of the single-crystal diamond laminated substrate is {111}, the single-crystal α-Al2O3 layer 21 preferably has an off-angle in the direction of the crystal axis <10-10> or <11-20> with respect to the surface orientation of {0001} of the outermost surface, and when the surface orientation of the diamond layer of the single-crystal diamond laminated substrate is {001}, the single-crystal α-Al2O3 layer 21 preferably has an off-angle in the direction of the crystal axis <10-10> or <11-20> with respect to the surface orientation of {11-20} of the outermost surface. <0001> It is preferable that the directional hub has an off-angle.

[0059] The single-crystal α-Al2O3 layer 21 having such an off-angle results in a higher quality heteroepitaxial layer 31 on the single-crystal α-Al2O3 layer 21, with higher crystallinity and fewer hillocks, anomalous growth particles, and dislocation defects.

[0060] The off-angle in this case is preferably in the range of +4.0 to +24.0° or -4.0 to -24.0°. If the off-angle is +4.0° and -4.0° or higher, a more stable effect of setting the off-angle can be obtained, and if it is +24.0° and -24.0° or lower, a more stable effect of improving quality can be obtained.

[0061] Furthermore, it is more preferable that the above-mentioned off-angle be in the range of greater than +15.0° and less than or equal to +24.0°, or greater than -15.0° and less than or equal to -24.0°. Within this range of off-angles, it becomes possible to achieve a more stable off-angle effect and improve quality.

[0062] In this case, the initial substrate 11 and the single-crystal α-Al2O3 layer 21 may have a single layer or multilayer film containing at least one of the following: an amorphous carbon film, a polycrystalline diamond film, a single-crystal diamond film, a SiC film, a Si film, and an SiO2 film. This results in the formation of the single-crystal α-Al2O3 layer 21 more efficiently.

[0063] The initial substrate 11 is preferably 0.03 to 5.00 mm thick. Initial substrates of this thickness are cost-effective and easier to handle. Furthermore, if the thickness is 0.03mm or more, processes such as double-sided polishing can be performed more effectively.

[0064] The single-crystal α-Al2O3 layer 21 is preferably 0.1 to 100 μm thick. Within this thickness range, processing technology allows for greater uniformity of the film thickness, and if the thickness is 100 μm or less, the stress generated between the initial substrate 11 and the single-crystal diamond layer is smaller, allowing for more reliable growth of the single-crystal diamond.

[0065] The heteroepitaxial layer 31 preferably has a thickness of 0.5 nm (5 Å) to 100 μm. Thus, if the thickness of any of the iridium, rhodium, or platinum films is 5 Å or more, the film thickness uniformity and crystallinity will be higher. Furthermore, if the thickness is 100 μm or less, the stress generated between the initial substrate 11 and the single-crystal diamond layer will be smaller, allowing for more effective growth of the single-crystal diamond, and also resulting in a less expensive substrate.

[0066] As described above, the base substrate 30 for single-crystal diamond laminated substrates of the present invention provides a base substrate with an appropriate combination of initial substrate, layers on the initial substrate, and off-angle, resulting in a base substrate suitable for electronic and magnetic devices, with a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress, capable of forming a high-quality single-crystal diamond layer.

[0067] (Single-crystal diamond multilayer substrate) As shown in Figure 2, a single-crystal diamond layer 41 can be provided on the base substrate for the single-crystal diamond laminated substrate of the present invention on the heteroepitaxial layer 31, thereby forming a single-crystal diamond laminated substrate 40.

[0068] In this case, the single-crystal diamond layer 41 formed on the highly crystalline heteroepitaxial layer 31 formed on the highly crystalline single-crystal α-Al2O3 layer 21 is a high-quality single-crystal diamond layer with a large area (large diameter), high crystallinity, few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress.

[0069] (Method for manufacturing a substrate for a single-crystal diamond laminated substrate) Next, the method for manufacturing a base substrate for a single-crystal diamond laminated substrate according to the present invention will be described with reference to Figure 4. Figure 4 is a flowchart showing an example of an embodiment of the method for manufacturing a base substrate for a single-crystal diamond laminated substrate and a single-crystal diamond substrate according to the present invention. Note that the matters described above regarding the base substrate for a single-crystal diamond laminated substrate may be omitted.

[0070] As shown in Figure 4(a), first, the coefficient of linear expansion is smaller than that of single crystal α-Al2O3, and 0.5 × 10 -6 An initial substrate 11 is prepared, which contains at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, with a temperature of 1 / K or higher.

[0071] By constructing the initial substrate 11 from the carbon-based material described above, it is possible to manufacture a base substrate 30 that is made of the same element as the diamond being grown, and where there is almost no stress due to thermal expansion between the initial substrate 11 and the grown diamond, thereby enabling the formation of a large-area single-crystal diamond layer 41.

[0072] The carbon-based material constituting the initial substrate 11 can be formed using methods such as microwave plasma CVD, DC plasma CVD, DC arc plasma CVD, or thermal filament CVD. Alternatively, it may be a structure in which multiple HPHT substrates or CVD substrates are joined together to form a single substrate.

[0073] The thickness of the initial substrate 11 can be 0.03 to 5.00 mm. If the initial substrate thickness is 0.03 mm or more, handling becomes easier. If it is 5.00 mm or less, it is not too thick, is cost-effective, and allows for easier finishing and polishing, resulting in a better surface condition and favorable bonding in subsequent processes.

[0074] On the surface of the initial substrate 11 made of carbon-based material, at least the surface on which the single-crystal α-Al2O3 layer 21 is bonded should be a smooth polished surface. However, if polishing is difficult, it is efficient to form a single-layer or multi-layer film containing at least one of amorphous carbon (DLC) film, polycrystalline diamond film, single-crystal diamond film, SiC film, Si film, and SiO2 film on the surface of the initial substrate 11 and then smooth it.

[0075] This allows the single-crystal α-Al2O3 layer 21 to be bonded to the initial substrate 11 more efficiently via the single layer or multilayer film.

[0076] The above single-layer or multilayer films can be formed by sputtering, electron beam evaporation, microwave plasma CVD, DC plasma CVD, thermal CVD, thermal filament CVD, etc. The thickness of the single-layer or multilayer film is preferably 0.1 to 10.0 μm, depending on the roughness of the diamond surface of the initial substrate 11. If the thickness of the single-layer or multilayer film is 0.1 μm or more, the film thickness uniformity can be improved from a processing perspective, and if the thickness of the single-layer or multilayer film is 10.0 μm or less, the stress generated between the initial substrate 11 and the single-crystal diamond layer 41 is reduced, allowing the single-crystal diamond layer 41 to grow more reliably.

[0077] Next, as shown in Figure 4(b), a single-crystal α-Al2O3 substrate is bonded to the initial substrate 11 to form a single-crystal α-Al2O3 layer 21. At this time, it is preferable to make the bonding surface of the single-crystal α-Al2O3 substrate with the initial substrate 11 smooth. Furthermore, this bonding process is more effective when both bonding surfaces are cleaned and activated by methods such as plasma treatment, ion beam treatment, neutral atomic beam treatment, or wet etching.

[0078] By bonding an initial substrate 11 made of such a carbon-based material with a single-crystal α-Al2O3 layer 21, a highly crystalline single-crystal α-Al2O3 layer 21 can be formed on the initial substrate 11.

[0079] This bonding process is more effective when both bonding surfaces are cleaned and activated by methods such as plasma treatment or wet etching.

[0080] As the single-crystal α-Al2O3 substrate to be bonded, for example, a single-crystal α-Al2O3 substrate with a diameter of 100 mm and a thickness of 1000 μm, which has been polished on both sides, can be used.

[0081] Furthermore, while the thickness of the single-crystal α-Al2O3 substrate to be bonded is usually around 200 μm to 1000 μm, it is preferable to process it to be thinner in order to reduce stress after single-crystal diamond growth. For example, ions such as hydrogen, oxygen, and carbon may be injected into the portion of the α-Al2O3 layer 21 that is to be thinned, and after bonding, they may be separated by heating as needed, and then the thickness may be adjusted and the surface smoothed by polishing. Alternatively, after bonding, the thickness may be adjusted and the surface smoothed by polishing alone.

[0082] Furthermore, the thickness of the single-crystal α-Al2O3 layer 21 after bonding can be set to 0.1 to 100 μm. Thus, if the thickness of the single-crystal α-Al2O3 layer 21 is 0.1 μm or more, thinning can be performed with higher film thickness uniformity. If the thickness is 100 μm or less, the stress generated between the initial substrate 11 and the single-crystal diamond layer 41 is smaller, so the single-crystal diamond can be grown more reliably, and furthermore, it is more cost-effective and can be done at a lower cost.

[0083] The single-crystal α-Al2O3 layer 21 can be a single-crystal α-Al2O3{0001} layer or a single-crystal α-Al2O3{11-20} layer. When forming a diamond layer with a plane orientation of {111} as the diamond layer of a single-crystal diamond laminated substrate, the single-crystal α-Al2O3 layer 21 is formed with an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <11-20> relative to the plane orientation of {0001} of the outermost surface of the single-crystal α-Al2O3 layer 21. When forming a diamond layer with a plane orientation of {001} as the diamond layer of a single-crystal diamond laminated substrate, the single-crystal α-Al2O3 layer 21 is formed with an off-angle in the direction of the crystal axis <10-10> or <11-20> relative to the plane orientation of {11-20> of the outermost surface of the single-crystal α-Al2O3 layer 21. <0001> It is preferable to form a layer having an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction.

[0084] The single-crystal α-Al2O3 layer 21 having such an off-angle results in a higher quality heteroepitaxial layer 31 on the single-crystal α-Al2O3 layer 21, with higher crystallinity and fewer hillocks, anomalous growth particles, and dislocation defects.

[0085] Next, as shown in Figure 4(c), a heteroepitaxial layer 31 is formed by heteroepitaxial growth of an iridium film, a rhodium film, or a platinum film on the surface of the single-crystal α-Al2O3 layer 21 opposite to the surface to which the initial substrate 11 is bonded.

[0086] The heteroepitaxial layer 31 can be grown by, for example, sputtering. The growth conditions are not particularly limited, but for example, it can be grown at a sufficient rate using RF magnetron sputtering.

[0087] The thickness of the heteroepitaxial layer 31 can be set from 0.5 nm (5 Å) to 100 μm. If the thickness is 5 Å or greater, the film thickness uniformity and crystallinity are higher, and if it is 100 μm or less, the stress generated between the initial substrate and the single-crystal diamond is smaller, allowing for more reliable growth of the single-crystal diamond and further reducing costs.

[0088] In this case, it is preferable to perform a bias treatment on the surface of the heteroepitaxial layer 31 for diamond nucleation. Thus, if bias treatment is applied, diamond growth nuclei can be formed on the surface, making it a substrate that allows for the growth of single-crystal diamonds with better crystallinity and at a more efficient growth rate.

[0089] As described above, the base substrate 30 for single-crystal diamond growth of the present invention can be manufactured. Thus, in the present invention, the initial substrate 11, which can be made the thickest in the base substrate 30 and is prone to stress generation due to thermal expansion, has a linear expansion coefficient smaller than that of single-crystal α-Al2O3 and is 0.5 × 10 -6Because amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond with a temperature of 1 / K or higher are used, the stress caused by thermal expansion during the growth of the single-crystal diamond layer 41 can be reduced, and damage to the single-crystal diamond layer 41 and the underlying substrate 30 is almost nonexistent.

[0090] Furthermore, by having a single-crystal α-Al2O3 layer 21 and a heteroepitaxial layer 31 made of iridium, rhodium, or platinum on such an initial substrate 11, these layers function as good buffer layers during the growth of the single-crystal diamond layer 41.

[0091] Furthermore, the single-crystal α-Al2O3 layer 21 is formed by bonding a bulk single-crystal α-Al2O3 substrate to the initial substrate 11. This allows for the formation of a highly crystalline single-crystal α-Al2O3 layer more easily than an α-Al2O3 layer obtained by heteroepitaxial growth, and enables high productivity.

[0092] On such a highly crystalline single-crystal α-Al2O3 layer 21, iridium films, rhodium films, and platinum films (heteroepitaxial layers 31) can be grown with good crystallinity, and a base substrate 30 can be manufactured.

[0093] By growing single-crystal diamond heteroepitaxially on the obtained substrate 30 using the CVD method, a large-area, highly crystalline single-crystal diamond layer 41 can be manufactured at low cost.

[0094] (Method for manufacturing single-crystal diamond substrates) Next, the method for manufacturing a single-crystal diamond substrate according to the present invention will be described with reference to Figures 3 and 4. The present invention provides a method for manufacturing a single-crystal diamond substrate, comprising the steps of: preparing a base substrate 30 manufactured by the above-described method for manufacturing a base substrate (Figure 4(c)); heteroepitaxially growing a single-crystal diamond layer 41 on a heteroepitaxial layer 31 of the base substrate 30 (Figure 4(d)); and separating the single-crystal diamond layer 41 from the heteroepitaxial layer 31 (Figure 4(e)).

[0095] It is preferable to perform a bias treatment on the surface of the heteroepitaxial layer 31 for diamond nucleation before the process of heteroepitaxial growth of the single-crystal diamond layer 41. In this way, by applying a bias treatment beforehand, diamond growth nuclei are formed on the surface, allowing single-crystal diamonds to be grown with better crystallinity and at a more efficient growth rate.

[0096] The method for growing the single-crystal diamond layer 41 is not particularly limited, but it can be grown heteroepitaxially by methods such as microwave CVD, DC plasma CVD, or thermal filament CVD.

[0097] Next, as shown in Figure 4(e), the single-crystal diamond layer 41 is separated to produce a self-supporting single-crystal diamond substrate 41 (Figure 3). Furthermore, a self-supporting single-crystal diamond substrate can also be produced by depositing an additional single-crystal diamond layer on the single-crystal diamond substrate 41.

[0098] The separation method is not particularly limited. For example, the single-crystal diamond substrate 41 can be obtained by immersing the substrate in a wet etching solution such as a hot phosphoric acid solution or a hot mixed acid to separate it into a single-crystal diamond layer 41 / heteroepitaxial layer 31 and a single-crystal α-Al2O3 layer 21 / initial substrate 11, and then removing the remaining heteroepitaxial layer 31 by mechanical polishing. Alternatively, the separation can be performed using a laser processing method.

[0099] By using the method for manufacturing single-crystal diamond substrates according to the present invention, large-area, highly crystalline single-crystal diamond substrates can be manufactured at low cost. [Examples]

[0100] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0101] (Example 1) With a diameter of 50.0 mm and a thickness of 1000 μm, the coefficient of linear expansion is 1 × 10⁻⁶. -6 A single-sided polished polycrystalline diamond substrate with a K-grade finish was prepared as the initial substrate 11. Then, a single-crystal α-Al2O3 substrate with a diameter of 50.0 mm, a thickness of 300 μm, a crystal plane orientation of {0001}, and an off-angle of 16° in the <11-20> direction, which had been polished on both sides, was prepared to be bonded to the side of this initial substrate where single-crystal diamond growth would take place.

[0102] The initial polycrystalline diamond substrate 11 was cleaned with a mixed acid solution and RCA (radio-compression angiography) cleaning. The single-crystal α-Al2O3 substrate was also cleaned with RCA. Furthermore, both bonding surfaces were cleaned and activated with an argon neutral atomic beam before being bonded together by direct bonding.

[0103] Subsequently, the single-crystal α-Al2O3 portion was thinned using a mechanical polishing method to create a 2 μm thick single-crystal α-Al2O3 layer 21.

[0104] Next, an iridium (Ir) film was heteroepitaxially grown on the surface of the single-crystal α-Al2O3 layer 21 to form a single-crystal Ir heteroepitaxial layer 31.

[0105] For single-crystal Ir film deposition, an RF (13.56 MHz) magnetron sputtering method was used, targeting an Ir disk with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate was heated to 850°C, evacuated with a vacuum pump, and the base pressure was approximately 8.0 × 10⁻⁶. -5 After confirming that the pressure was below Pa, Ar gas was introduced.

[0106] The valve opening leading to the exhaust system was adjusted to 14 Pa, and then RF 1500W was applied for 60 minutes to deposit the film. The thickness of the resulting single-crystal Ir film was approximately 2 μm.

[0107] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an X-ray diffraction (XRD) instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector.

[0108] As a result, the pole method detected an Ir(111) plane diffraction peak when the Ir(111) plane was oriented in the direction normal to the main surface of the substrate, while the Ir(111) plane diffraction peak was not detected when the Ir(001) plane was oriented in the direction normal to the main surface of the substrate.

[0109] Furthermore, using the out-of-plane method, only the main diffraction intensity peak and its multiple reflection peaks at 2θ=40.7°, which are attributed to Ir(111), were observed, confirming that the heteroepitaxial layer 31 is an epitaxially grown single-crystal Ir(111) crystal.

[0110] As described above, the base substrate 30 of the present invention was manufactured (see Figure 1).

[0111] Next, the substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the substrate 30 on which the heteroepitaxial layer 31 was formed was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶. -4 After confirming that the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=5.0 vol.%) was introduced into the treatment chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.3 × 10⁻⁶. 4 After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and the plasma was exposed for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0112] Next, a single-crystal diamond layer 41 was heteroepitaxially grown using microwave CVD. Here, the bias-treated substrate 30 was set in the chamber of the microwave CVD apparatus, and the base pressure was increased to approximately 1.3 × 10⁻⁶ using a vacuum pump. -4 After exhausting the gas until the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=4.0 vol.%), the raw material gas, was introduced into the treatment chamber at a flow rate of 1000 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.5 × 10⁻⁶. 4 After setting the temperature to Pa, a microwave of 3500W was applied, and film deposition was carried out for 150 hours. The substrate temperature during film deposition was measured with a pyrometer and was found to be 960°C.

[0113] The obtained single-crystal diamond layer 41 was a perfectly continuous film with no delamination across its entire 50 mm diameter surface. A schematic cross-sectional view of the single-crystal diamond laminated substrate 40 manufactured in this manner is shown in Figure 2.

[0114] Next, the single-crystal α-Al2O3 portion of the single-crystal α-Al2O3 layer 21 was etched with hot phosphoric acid. Furthermore, the Ir portion of the heteroepitaxial layer 31 was removed by dry etching. This resulted in the acquisition of a single-crystal diamond (self-supporting) substrate 41 (see Figure 3).

[0115] Finally, a single-crystal diamond layer (additional single-crystal diamond layer) was homoepitaxially grown again using microwave CVD. This additional single-crystal diamond layer was formed under the same conditions as when the single-crystal diamond layer 41 was formed.

[0116] The resulting single-crystal diamond layer was also a perfectly continuous film with no damage across its entire 50mm diameter.

[0117] A 2mm square section was cut from this single-crystal diamond self-supporting substrate to be used as an evaluation sample, and its film thickness and crystallinity were evaluated.

[0118] Regarding the film thickness, the total thickness of the diamond layer was found to be approximately 400 μm when the sample thickness was measured using a Mitutoyo ID-SX2 digital indicator.

[0119] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector. As a result, only a diffraction intensity peak attributed to diamond(111) was observed at 2θ=43.9°, confirming that the diamond layer is an epitaxially grown single-crystal diamond{111} crystal.

[0120] Applying these single-crystal diamond {111} multilayer substrates and self-supporting substrates to electronic and magnetic devices allows for the creation of high-performance devices. For example, high-performance power devices can be obtained. Moreover, since they can be produced on large-diameter substrates, manufacturing costs can be kept low.

[0121] (Example 2) With a diameter of 50.0 mm and a thickness of 1000 μm, the coefficient of linear expansion is 1 × 10⁻⁶. -6 A single-sided polished polycrystalline diamond substrate of type / K was prepared as the initial substrate 11.

[0122] Since the surface roughness of the polycrystalline diamond was high (Ra = 10 nm), a 10 μm thick polycrystalline diamond film with fine grain size was formed using the thermal filament CVD method.

[0123] Subsequently, the polycrystalline diamond film was polished using the chemical mechanical polishing (CMP) method until the Ra value was 0.3 nm or less. The thickness of the fine-grained polycrystalline diamond film after polishing was 0.5 μm.

[0124] Then, a single-crystal α-Al2O3 substrate was prepared, with a diameter of 50.0 mm, a thickness of 300 μm, a crystal plane orientation of {0001}, and an off-angle of 16° in the <11-20> direction, which had been polished on both sides, to be bonded to the side of the initial substrate 11 on which single-crystal diamond growth would be performed.

[0125] The initial polycrystalline diamond substrate 11 was cleaned with a mixed acid solution and RCA cleaning. The single-crystal α-Al2O3 substrate was also RCA cleaned. Furthermore, both bonding surfaces were cleaned and activated with an argon ion beam before being bonded together by direct bonding.

[0126] Subsequently, the single-crystal α-Al2O3 portion was thinned using a mechanical polishing method to create a 2 μm thick single-crystal α-Al2O3 layer 21.

[0127] Next, an iridium (Ir) film was heteroepitaxially grown on the surface of the single-crystal α-Al2O3 layer 21 to form a single-crystal Ir heteroepitaxial layer 31.

[0128] For single-crystal Ir film deposition, an RF (13.56 MHz) magnetron sputtering method was used, targeting an Ir disk with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate was heated to 850°C, evacuated with a vacuum pump, and the base pressure was approximately 8.0 × 10⁻⁶. -5 After confirming that the pressure was below Pa, Ar gas was introduced.

[0129] The valve opening leading to the exhaust system was adjusted to 14 Pa, and then RF 1500W was applied for 60 minutes to deposit the film. The thickness of the resulting single-crystal Ir film was approximately 2 μm.

[0130] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an X-ray diffraction (XRD) instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector.

[0131] As a result, the pole method detected an Ir(111) plane diffraction peak when the Ir(111) plane was oriented in the direction normal to the main surface of the substrate, while the Ir(111) plane diffraction peak was not detected when the Ir(001) plane was oriented in the direction normal to the main surface of the substrate.

[0132] Furthermore, using the out-of-plane method, only the main diffraction intensity peak and its multiple reflection peaks at 2θ=40.7°, which are attributed to Ir(111), were observed, confirming that the heteroepitaxial layer 31 is an epitaxially grown single-crystal Ir(111) crystal.

[0133] As described above, the base substrate 30 of the present invention was manufactured (see Figure 1). Next, the substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the substrate 30 on which the heteroepitaxial layer 31 was formed was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶. -4 After confirming that the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=5.0 vol.%) was introduced into the treatment chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.3 × 10⁻⁶. 4 After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and the plasma was exposed for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0134] Next, a single-crystal diamond layer 41 was heteroepitaxially grown using microwave CVD. Here, the bias-treated substrate 30 was set in the chamber of the microwave CVD apparatus, and the base pressure was increased to approximately 1.3 × 10⁻⁶ using a vacuum pump. -4 After exhausting the gas until the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=4.0 vol.%), the raw material gas, was introduced into the treatment chamber at a flow rate of 1000 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.5 × 10⁻⁶. 4 After setting the temperature to Pa, a microwave of 3500W was applied, and film deposition was carried out for 150 hours. The substrate temperature during film deposition was measured with a pyrometer and was found to be 960°C.

[0135] The obtained single-crystal diamond layer 41 was a perfectly continuous film with no delamination across its entire 50 mm diameter surface. A schematic cross-sectional view of the single-crystal diamond laminated substrate 40 manufactured in this manner is shown in Figure 2.

[0136] Next, the single-crystal α-Al2O3 portion of the single-crystal α-Al2O3 layer 21 was etched with hot phosphoric acid. Furthermore, the Ir portion, which is the heteroepitaxial layer 31, was removed by dry etching. As a result, a single-crystal diamond self-supporting substrate 41 was obtained (see Figure 3).

[0137] Finally, a single-crystal diamond layer (additional single-crystal diamond layer) was homoepitaxially grown again using microwave CVD. This additional single-crystal diamond layer was formed under the same conditions as when the diamond film was formed as described above.

[0138] The resulting single-crystal diamond layer was also a perfectly continuous film with no damage across its entire 50mm diameter.

[0139] A 2mm square was cut from this single-crystal diamond self-supporting substrate 41 to be used as an evaluation sample, and its film thickness and crystallinity were evaluated. Regarding the film thickness, the thickness of the sample was measured using a Mitutoyo ID-SX2 digital indicator, and the total thickness of the diamond layer was found to be approximately 400 μm.

[0140] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA, and semiconductor detector.

[0141] As a result, only a diffraction intensity peak attributed to diamond(111) was observed at 2θ=43.9°, confirming that the diamond layer is an epitaxially grown single-crystal diamond{111} crystal.

[0142] Applying these single-crystal diamond {111} multilayer substrates and self-supporting substrates to electronic and magnetic devices allows for the creation of high-performance devices. For example, high-performance power devices can be obtained. Moreover, since they can be produced on large-diameter substrates, manufacturing costs can be kept low.

[0143] (Example 3) With a diameter of 50.0 mm and a thickness of 1000 μm, the coefficient of linear expansion is 1 × 10⁻⁶. -6 A single-sided polished polycrystalline diamond substrate of type / K was prepared as the initial substrate 11.

[0144] Since the surface roughness of the polycrystalline diamond was high (Ra = 10 nm), a 10 μm thick polycrystalline diamond film with fine grain size was formed using the thermal filament CVD method. Subsequently, this polycrystalline diamond surface film was polished using the chemical mechanical polishing (CMP) method until the Ra value was 0.3 nm or less. The thickness of the fine-grained polycrystalline diamond film after polishing was 0.5 μm.

[0145] Then, to be bonded to the side of this initial substrate 11 on which single-crystal diamond growth will be performed, a substrate with a diameter of 50.0 mm, a thickness of 300 μm, and a crystal plane orientation of {11-20} is used. <0001> A single-crystal α-Al2O3 substrate was prepared, which had been polished on both sides with an off-angle of 10° in the direction.

[0146] The initial polycrystalline diamond substrate 11 was cleaned with a mixed acid solution and RCA cleaning. The single-crystal α-Al2O3 substrate was also RCA cleaned. Furthermore, both bonding surfaces were cleaned and activated with an argon ion beam before being bonded together by direct bonding.

[0147] Subsequently, the single-crystal α-Al2O3 portion was thinned using a mechanical polishing method to create a 2 μm thick single-crystal α-Al2O3 layer 21.

[0148] Next, an iridium (Ir) film was heteroepitaxially grown on the surface of the single-crystal α-Al2O3 layer 21 to form a single-crystal Ir heteroepitaxial layer 31.

[0149] For single-crystal Ir film deposition, an RF (13.56 MHz) magnetron sputtering method was used, targeting an Ir disk with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate was heated to 850°C, evacuated with a vacuum pump, and the base pressure was approximately 8.0 × 10⁻⁶. -5After confirming that the pressure was below Pa, Ar gas was introduced. The opening of the valve leading to the exhaust system was adjusted to 7 Pa, and then RF 1500W was applied to deposit the film for 50 minutes. The thickness of the obtained single-crystal Ir film was approximately 2 μm.

[0150] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an X-ray diffraction (XRD) instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector.

[0151] As a result, the pole method detected an Ir(111) plane diffraction peak when the Ir(100) plane was oriented in the direction normal to the main surface of the substrate, while the Ir(111) plane diffraction peak was not detected when the Ir(111) plane was oriented in the direction normal to the main surface of the substrate.

[0152] Furthermore, using the out-of-plane method, only the main diffraction intensity peak assigned to Ir(200) at 2θ=47.2° and Ir(400) at 2θ=106.3° were observed, confirming that the heteroepitaxial layer 31 is an epitaxially grown single-crystal Ir(100) crystal.

[0153] As described above, the base substrate 30 of the present invention was manufactured (see Figure 1). Next, the substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the substrate 30 on which the heteroepitaxial layer 31 was formed was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶. -4 After confirming that the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=5.0 vol.%) was introduced into the treatment chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.3 × 10⁻⁶. 4 After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and the plasma was exposed for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0154] Next, a single-crystal diamond layer 41 was heteroepitaxially grown using microwave CVD. Here, the bias-treated substrate 30 was set in the chamber of the microwave CVD apparatus, and the base pressure was increased to approximately 1.3 × 10⁻⁶ using a vacuum pump. -4 After exhausting the gas until the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=4.0 vol.%), the raw material gas, was introduced into the treatment chamber at a flow rate of 1000 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.5 × 10⁻⁶. 4 After setting the temperature to Pa, a microwave of 3500W was applied, and film deposition was carried out for 150 hours. The substrate temperature during film deposition was measured with a pyrometer and was found to be 960°C.

[0155] The obtained single-crystal diamond layer 41 was a perfectly continuous film with no delamination across its entire 50 mm diameter surface. A schematic cross-sectional view of the single-crystal diamond laminated substrate 40 manufactured in this manner is shown in Figure 2.

[0156] Next, the single-crystal α-Al2O3 portion of the single-crystal α-Al2O3 layer 21 was etched with hot phosphoric acid. Furthermore, the Ir portion of the heteroepitaxial layer 31 was removed by dry etching. This resulted in the acquisition of a single-crystal diamond self-supporting substrate 41 (see Figure 3).

[0157] Finally, a single-crystal diamond layer (additional single-crystal diamond layer) was homoepitaxially grown again using microwave CVD. This additional single-crystal diamond layer was formed under the same conditions as when the diamond film was formed as described above. The resulting single-crystal diamond layer was also a perfectly continuous film with no damage across its entire 50mm diameter.

[0158] A 2mm square was cut from this single-crystal diamond self-supporting substrate 41 to be used as an evaluation sample, and its film thickness and crystallinity were evaluated. Regarding the film thickness, the thickness of the sample was measured using a Mitutoyo ID-SX2 digital indicator, and the total thickness of the diamond layer was found to be approximately 480 μm.

[0159] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA, and semiconductor detector.

[0160] As a result, only a diffraction intensity peak attributed to diamond (400) was observed at 2θ = 119.5°, confirming that the diamond layer is an epitaxially grown single-crystal diamond {001} crystal.

[0161] Applying the single-crystal diamond {001} laminated substrate and self-supporting substrate to electronic and magnetic devices allows for the creation of high-performance devices. For example, high-performance power devices can be obtained. Moreover, since these can be produced on large-diameter substrates, manufacturing costs can be kept low.

[0162] (Example 4) With a diameter of 50.0 mm and a thickness of 1000 μm, the coefficient of linear expansion is 2 × 10⁻⁶. -6 A glassy carbon substrate with one side polished to a single-kylion state was prepared as the initial substrate 11. Then, a single-crystal α-Al2O3 substrate with a diameter of 50.0 mm, a thickness of 300 μm, a crystal plane orientation of {0001}, and an off-angle of 16° in the <11-20> direction, which had been polished on both sides, was prepared to be bonded to the side of this initial substrate where single-crystal diamond growth would take place.

[0163] The initial glassy carbon substrate 11 was cleaned with a mixed acid solution and RCA. The single-crystal α-Al2O3 substrate was also cleaned with RCA. Furthermore, both bonding surfaces were cleaned and activated with an argon neutral atomic beam before being bonded together by direct bonding.

[0164] Subsequently, the single-crystal α-Al2O3 portion was thinned using a mechanical polishing method to create a 2 μm thick single-crystal α-Al2O3 layer 21.

[0165] Next, an iridium (Ir) film was heteroepitaxially grown on the surface of the single-crystal α-Al2O3 layer 21 to form a single-crystal Ir heteroepitaxial layer 31.

[0166] For single-crystal Ir film deposition, an RF (13.56 MHz) magnetron sputtering method was used, targeting an Ir disk with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate was heated to 850°C, evacuated with a vacuum pump, and the base pressure was approximately 8.0 × 10⁻⁶. -5 After confirming that the pressure was below Pa, Ar gas was introduced. The opening of the valve leading to the exhaust system was adjusted to 14 Pa, and then RF 1500W was applied for 60 minutes to deposit the film. The thickness of the obtained single-crystal Ir film was approximately 2 μm.

[0167] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an X-ray diffraction (XRD) instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector.

[0168] As a result, the pole method detected an Ir(111) plane diffraction peak when the Ir(111) plane was oriented in the direction normal to the main surface of the substrate, while the Ir(111) plane diffraction peak was not detected when the Ir(001) plane was oriented in the direction normal to the main surface of the substrate.

[0169] Furthermore, using the out-of-plane method, only the main diffraction intensity peak and its multiple reflection peaks at 2θ=40.7°, which are attributed to Ir(111), were observed, confirming that the heteroepitaxial layer 31 is an epitaxially grown single-crystal Ir(111) crystal.

[0170] As described above, the base substrate 30 of the present invention was manufactured (see Figure 1). Next, the substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the substrate 30 on which the heteroepitaxial layer 31 was formed was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶. -4After confirming that the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=5.0 vol.%) was introduced into the treatment chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.3 × 10⁻⁶. 4 After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and the plasma was exposed for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0171] Next, a single-crystal diamond layer 41 was heteroepitaxially grown using microwave CVD. Here, the bias-treated substrate 30 was set in the chamber of the microwave CVD apparatus, and the base pressure was increased to approximately 1.3 × 10⁻⁶ using a vacuum pump. -4 After exhausting the gas until the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=4.0 vol.%), the raw material gas, was introduced into the treatment chamber at a flow rate of 1000 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.5 × 10⁻⁶. 4 After setting the temperature to Pa, a microwave of 3500W was applied, and film deposition was carried out for 150 hours. The substrate temperature during film deposition was measured with a pyrometer and was found to be 960°C.

[0172] The obtained single-crystal diamond layer 41 was a perfectly continuous film with no delamination across its entire 50 mm diameter surface. A schematic cross-sectional view of the single-crystal diamond laminated substrate 40 manufactured in this manner is shown in Figure 2.

[0173] Next, the single-crystal α-Al2O3 portion of the single-crystal α-Al2O3 layer 21 was etched with hot phosphoric acid. Furthermore, the Ir portion of the heteroepitaxial layer 31 was removed by dry etching. This resulted in the acquisition of a single-crystal diamond self-supporting substrate 41 (see Figure 3).

[0174] Finally, a single-crystal diamond layer (additional single-crystal diamond layer) was homoepitaxially grown again using microwave CVD. This additional single-crystal diamond layer was formed under the same conditions as when the diamond film was formed as described above. The resulting single-crystal diamond layer was also a perfectly continuous film with no damage across its entire 50mm diameter.

[0175] A 2mm square was cut from this single-crystal diamond self-supporting substrate 41 to be used as an evaluation sample, and its film thickness and crystallinity were evaluated. Regarding the film thickness, the thickness of the sample was measured using a Mitutoyo ID-SX2 digital indicator, and the total thickness of the diamond layer was found to be approximately 400 μm.

[0176] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA, and semiconductor detector.

[0177] As a result, only a diffraction intensity peak attributed to diamond(111) was observed at 2θ=43.9°, confirming that the diamond layer is an epitaxially grown single-crystal diamond{111} crystal.

[0178] Applying these single-crystal diamond {111} multilayer substrates and self-supporting substrates to electronic and magnetic devices allows for the creation of high-performance devices. For example, high-performance power devices can be obtained. Moreover, since they can be produced on large-diameter substrates, manufacturing costs can be kept low.

[0179] (Comparative Example 1) A single-crystal MgO substrate with a diameter of 50.0 mm, a thickness of 1000 μm, a crystal plane orientation of {111}, and an off-angle of 4° in the <-1-12> direction, which had been polished on both sides, was prepared as the initial substrate.

[0180] Next, an iridium (Ir) film was heteroepitaxially grown on the surface of the initial substrate to form a single-crystal Ir intermediate layer.

[0181] For the deposition of the Ir intermediate layer, an RF (13.56 MHz) magnetron sputtering method was used, targeting an Ir disk with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate was heated to 850°C, evacuated with a vacuum pump, and the base pressure was approximately 8.0 × 10⁻⁶. -5 After confirming that the pressure was below Pa, Ar gas was introduced. The opening of the valve leading to the exhaust system was adjusted to 14 Pa, and then RF 1500W was applied for 60 minutes to deposit the film. The thickness of the obtained single-crystal Ir film was approximately 2 μm.

[0182] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an X-ray diffraction (XRD) instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector.

[0183] As a result, the pole method detected an Ir(111) plane diffraction peak when the Ir(111) plane was oriented in the direction normal to the main surface of the substrate, while the Ir(111) plane diffraction peak was not detected when the Ir(001) plane was oriented in the direction normal to the main surface of the substrate.

[0184] Furthermore, using the out-of-plane method, only the main diffraction intensity peak and its multiple reflection peaks at 2θ=40.7°, which are attributed to Ir(111), were observed, confirming that the single-crystal Ir layer is an epitaxially grown single-crystal Ir(111) crystal.

[0185] The base substrate was manufactured in the manner described above. Next, the substrate underwent a pretreatment (bias treatment) for diamond nucleation. Here, the substrate on which the single-crystal Ir layer was formed was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶. -4 After confirming that the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=5.0 vol.%) was introduced into the treatment chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.3 × 10⁻⁶. 4After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and the substrate was exposed to the plasma for 90 seconds to bias-treat the surface of the intermediate layer.

[0186] Next, a single-crystal diamond layer was heteroepitaxially grown using microwave CVD. Here, the bias-treated substrate was placed in the chamber of the microwave CVD apparatus, and the base pressure was increased to approximately 1.3 × 10⁻⁶ using a vacuum pump. -4 After exhausting the gas until the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=4.0 vol.%), the raw material gas, was introduced into the treatment chamber at a flow rate of 1000 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.5 × 10⁻⁶. 4 After setting the temperature to Pa, a microwave of 3500W was applied, and film deposition was carried out for 150 hours. The substrate temperature during film deposition was measured with a pyrometer and was found to be 960°C.

[0187] After the film deposition process was complete and the substrate was removed, cracks were found in the diamond film, and parts of the original substrate were damaged.

[0188] (Comparative Example 2) A single-crystal α-Al2O3 substrate with a diameter of 50.0 mm, a thickness of 1000 μm, a crystal plane orientation of {0001}, and a double-sided polished finish with an off-angle of 10° in the <11-20> direction was prepared as the initial substrate.

[0189] Next, an iridium (Ir) film was heteroepitaxially grown on the surface of the initial substrate to form a single-crystal Ir intermediate layer.

[0190] For the deposition of the Ir intermediate layer, an RF (13.56 MHz) magnetron sputtering method was used, targeting an Ir disk with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate was heated to 850°C, evacuated with a vacuum pump, and the base pressure was approximately 8.0 × 10⁻⁶. -5 After confirming that the pressure was below Pa, Ar gas was introduced. The opening of the valve leading to the exhaust system was adjusted to 14 Pa, and then RF 1500W was applied for 60 minutes to deposit the film. The thickness of the obtained single-crystal Ir film was approximately 2 μm.

[0191] Crystallinity was measured from the outermost surface of the film using the pole method and out-of-plane method with an X-ray diffraction (XRD) instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45kV output, 200mA output, and semiconductor detector.

[0192] As a result, the pole method detected an Ir(111) plane diffraction peak when the Ir(111) plane was oriented in the direction normal to the main surface of the substrate, while the Ir(111) plane diffraction peak was not detected when the Ir(001) plane was oriented in the direction normal to the main surface of the substrate.

[0193] Furthermore, using the out-of-plane method, only the main diffraction intensity peak and its multiple reflection peaks at 2θ=40.7°, attributed to Ir(111), were observed, confirming that the intermediate layer is an epitaxially grown single-crystal Ir(111) crystal.

[0194] The base substrate was manufactured in the manner described above. Next, the substrate underwent a pretreatment (bias treatment) for diamond nucleation. Here, the substrate with a single-crystal Ir intermediate layer was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶. -4 After confirming that the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=5.0 vol.%) was introduced into the treatment chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.3 × 10⁻⁶. 4 After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and the substrate was exposed to the plasma for 90 seconds to bias-treat the surface of the intermediate layer.

[0195] Next, a single-crystal diamond layer was heteroepitaxially grown using microwave CVD. Here, the bias-treated substrate was placed in the chamber of the microwave CVD apparatus, and the base pressure was increased to approximately 1.3 × 10⁻⁶ using a vacuum pump. -4After exhausting the gas until the pressure was below Pa, hydrogen-diluted methane (CH4 / (CH4+H2)=4.0 vol.%), the raw material gas, was introduced into the treatment chamber at a flow rate of 1000 sccm. The opening of the valve leading to the exhaust system was adjusted to set the pressure to 1.5 × 10⁻⁶. 4 After setting the temperature to Pa, a 3500W microwave was applied to perform film deposition. The temperature reached 980°C after 1 hour from the start of deposition, 1000°C after 6 hours, and then failed after 23 hours. The large stress generated by the difference in thermal expansion between the initial substrate and the diamond layer made it difficult to achieve stable film deposition over a long period of time.

[0196] As described above, according to the embodiments of the present invention, it is possible to manufacture a substrate capable of forming a high-quality single-crystal diamond layer with a large area (large diameter), high crystallinity, no peeling or damage, high purity, and low stress, and it is possible to manufacture such a high-quality single-crystal diamond substrate using this substrate.

[0197] This specification includes the following embodiments: [1]: A base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of linear expansion is smaller than that of single-crystal α-Al2O3 and 0.5 × 10 -6 An initial substrate comprising an amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond having a temperature of 1 / K or higher; a single-crystal α-Al2O3 layer on the initial substrate; and a heteroepitaxial layer on the single-crystal α-Al2O3 layer consisting of an iridium film, a rhodium film, and a platinum film. [2]: When the plane orientation of the diamond layer of the single-crystal diamond laminate is {111}, the single-crystal α-Al2O3 layer has an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <11-20> with respect to the plane orientation of the outermost surface being {0001}, and when the plane orientation of the diamond layer of the single-crystal diamond laminate is {001}, the single-crystal α-Al2O3 layer has an off-angle in the direction of the crystal axis <10-10> or <11-20> with respect to the plane orientation of the outermost surface being {11-20} <0001> The substrate substrate described above [1], wherein the substrate has an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction. [3]: The substrate according to [1] or [2] above, wherein the initial substrate and the single-crystal α-Al2O3 layer have a single layer or multilayer film comprising at least one of an amorphous carbon film, a polycrystalline diamond film, a single-crystal diamond film, a SiC film, a Si film, and an SiO2 film. [4]: A method for manufacturing a base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of thermal expansion is smaller than that of single-crystal α-Al2O3 and 0.5 × 10 -6 A method for manufacturing a substrate, comprising the steps of: preparing an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond having a temperature of 1 / K or higher; bonding a single-crystal α-Al2O3 layer to the initial substrate; and forming a heteroepitaxial layer by heteroepitaxially growing one of iridium film, rhodium film, and platinum film on the surface of the single-crystal α-Al2O3 layer opposite to the surface to which the initial substrate is bonded. [5]: When forming a diamond layer with a plane orientation of {111} in the single-crystal diamond laminated substrate, the single-crystal α-Al2O3 layer is formed such that the plane orientation of the outermost surface of the single-crystal α-Al2O3 layer is {0001} and the off-angle is in the direction of the crystal axis <10-10> or <11-20>, in the range of +4.0 to +24.0° or -4.0 to -24.0°. When forming a diamond layer with a plane orientation of {001} in the single-crystal α-Al2O3 layer, the off-angle is in the direction of the crystal axis <10-10> or <11-20> with respect to the plane orientation of the outermost surface of the single-crystal α-Al2O3 layer is {11-20} <0001> A method for manufacturing the substrate substrate described above [4], comprising forming a layer having an off-angle in the direction of +4.0 to +24.0° or -4.0 to -24.0°. [6]: A method for manufacturing the base substrate according to [4] or [5], comprising bonding the single-crystal α-Al2O3 layer to the initial substrate via a single layer or multilayer film comprising at least one of an amorphous carbon film, a polycrystalline diamond film, a single-crystal diamond film, a SiC film, a Si film, and an SiO2 film. [7]: A method for manufacturing the substrate substrate according to [4], [5], or [6], comprising setting the thickness of the initial substrate to 0.03 to 5.00 mm, the thickness of the single crystal α-Al2O3 layer to 0.1 to 100 μm, and the thickness of the heteroepitaxial layer to 0.5 nm (5 Å) to 100 μm. [8]: A method for manufacturing the substrate substrate according to [4], [5], [6], or [7], comprising the step of performing a bias treatment on the surface of the heteroepitaxial layer for diamond nucleation. [9]: A method for manufacturing a single-crystal diamond substrate, comprising the steps of: preparing a base substrate manufactured by the method for manufacturing a base substrate described in [4], [5], [6], [7] or [8] above; heteroepitaxially growing a single-crystal diamond layer on the heteroepitaxial layer; and separating the single-crystal diamond layer from the heteroepitaxial layer.

[10] : A method for manufacturing a single-crystal diamond substrate according to [9], comprising the step of performing a bias treatment on the surface of the heteroepitaxial layer for diamond nucleation before the step of heteroepitaxial growth of the single-crystal diamond layer.

[11] : A method for manufacturing a single-crystal diamond substrate according to [9] or

[10] , comprising growing the single-crystal diamond layer by any of the following methods in the step of heteroepitaxial growth of the single-crystal diamond layer: microwave CVD, DC plasma CVD, and thermal filament CVD.

[0198] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0199] 11...Initial substrate, 21...Single crystal α-Al2O3 layer, 30...Underlay substrate, 31... Heteroepitaxial layer, 40... Single-crystal diamond multilayer substrate, 41…Single-crystal diamond layer (single-crystal diamond substrate).

Claims

1. A base substrate for a single-crystal diamond laminated substrate, The coefficient of linear thermal expansion is that of single crystal α-Al ２ O ３ Smaller than, and 0.5 × 10 －６ An initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, which has a temperature of 1 / K or higher, The initial substrate contains a single crystal α-Al ２ O ３ Layers, The single crystal α-Al ２ O ３ A substrate characterized by having a heteroepitaxial layer on top of it, which is made of one of iridium film, rhodium film, or platinum film.

2. When the plane orientation of the diamond layer of the single-crystal diamond laminated substrate is {111}, the single-crystal α-Al ２ O ３ layer has an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the <10-10> or <11-20> direction of the crystal axis with respect to the outermost surface plane orientation of {0001}, When the surface orientation of the diamond layer of the single-crystal diamond laminated substrate is {001}, the single-crystal α-Al ２ O ３ The substrate substrate according to claim 1, characterized in that the layer has an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <0001> with respect to the surface orientation of the outermost surface {11-20}.

3. The initial substrate and the single crystal α-Al ２ O ３ Between the layers are amorphous carbon film, polycrystalline diamond film, single-crystal diamond film, SiC film, Si film and SiO ２ The substrate according to claim 1 or 2, characterized in that it has a single layer or a multilayer film comprising at least one of the films.

4. A method for manufacturing a base substrate for a single-crystal diamond laminated substrate, The coefficient of linear thermal expansion is that of single crystal α-Al ２ O ３ Smaller than, and 0.5 × 10 －６ A step of preparing an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, which has a temperature of 1 / K or higher, The initial substrate is made of single crystal α-Al ２ O ３ The process of bonding the layers together, The aforementioned single crystal α-Al ２ O ３ A method for manufacturing a substrate substrate, characterized by comprising the step of forming a heteroepitaxial layer by heteroepitaxially growing an iridium film, a rhodium film, or a platinum film on the surface of the layer opposite to the surface to which the initial substrate is bonded.

5. When forming a diamond layer with a plane orientation of {111} in the single-crystal diamond laminated substrate, the single-crystal α-Al ２ O ３ As a layer, the single crystal α-Al ２ O ３ A layer is formed in which the surface orientation of the outermost surface of the layer has an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <11-20> with respect to {0001}. When forming a diamond layer with a surface orientation of {001} in the aforementioned single-crystal diamond laminated substrate, the single-crystal α-Al ２ O ３ As a layer, the single crystal α-Al ２ O ３ The method for manufacturing a substrate according to claim 4, characterized in that a layer is formed having an off-angle in the range of +4.0 to +24.0° or -4.0 to -24.0° in the direction of the crystal axis <10-10> or <0001> with respect to the surface orientation of the outermost surface of the layer which is {11-20}.

6. The aforementioned single crystal α-Al ２ O ３ The layers are amorphous carbon film, polycrystalline diamond film, single-crystal diamond film, SiC film, Si film and SiO ２ A method for manufacturing a base substrate according to claim 4, characterized in that the base substrate is bonded to the initial substrate via a single layer or multilayer film containing at least one of the films.

7. The initial substrate thickness is 0.03 to 5.00 mm, and the single crystal α-Al ２ O ３ The method for manufacturing a substrate according to claim 4, characterized in that the thickness of the layer is 0.1 to 100 μm, and the thickness of the heteroepitaxial layer is 0.5 nm (5 Å) to 100 μm.

8. A method for manufacturing a substrate according to any one of claims 4 to 7, characterized in that it includes a step of performing a bias treatment on the surface of the heteroepitaxial layer for diamond nucleation.

9. A method for manufacturing a single-crystal diamond substrate, A step of preparing a substrate manufactured by the substrate manufacturing method described in claim 4, The process involves heteroepitaxially growing a single-crystal diamond layer on the aforementioned heteroepitaxial layer, A method for manufacturing a single-crystal diamond substrate, characterized by comprising the step of separating the single-crystal diamond layer from the heteroepitaxial layer.

10. The method for manufacturing a single-crystal diamond substrate according to claim 9, characterized in that it includes a step of performing a bias treatment on the surface of the heteroepitaxial layer for diamond nucleation before the step of heteroepitaxial growth of the single-crystal diamond layer.

11. The method for manufacturing a single-crystal diamond substrate according to claim 9 or 10, characterized in that, in the step of heteroepitaxially growing the single-crystal diamond layer, the single-crystal diamond layer is grown by one of the following methods: microwave CVD, DC plasma CVD, or thermal filament CVD.

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