Base substrate for single-crystal diamond laminate substrate, method for producing same, and method for producing single-crystal diamond substrate

Abstract

The present invention is a base substrate for a single-crystal diamond laminate substrate. The base substrate comprises: an initial substrate that has a linear expansion coefficient smaller than that of single-crystal α-Al2O3 and equal to or greater than 0.5 × 10−6 / K, the initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond; a single-crystal α-Al2O3 layer on the initial substrate; and a heteroepitaxial layer composed of any of an iridium film, a rhodium film, and a platinum film on the single-crystal α-Al2O3 layer. The present invention thereby provides a base substrate that has a large area (large diameter) and high crystallinity and is capable of forming a high-quality single-crystal diamond layer having high purity and low stress.

Description

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

[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.

[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 velocity make it suitable for high-speed devices.

[0004] Therefore, diamond exhibits the highest Johnson Figure of Merit, 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.

[0005] International Publication No. 2024 / 048357

[0006] H. Yamada, Appl. Phys. Lett. 104, 102110 (2014).

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

[0008] Currently, most single-crystal diamonds used for diamond semiconductor fabrication are of type Ib, synthesized by the high-temperature, high-pressure (HPHT) method. This type Ib diamond contains many nitrogen impurities and can only be obtained in sizes up to about 8 mm square, making it impractical. A mosaic method has also been proposed (Non-Patent Literature 1) in which many HPHT substrates (diamond substrates synthesized by the HPHT method) are arranged and joined together, but the problem of incomplete seams remains.

[0009] In contrast, while chemical vapor deposition (CVD) can produce high-purity, large-area diamond crystals of about 6 inches (150 mm) in diameter using polycrystalline diamond, single crystallization suitable for typical electronic devices has been difficult. This is because a suitable combination of materials with small differences in lattice constants and coefficients of thermal expansion between the diamond and the substrate has not been realized. For example, the difference in lattice constants between diamond and single-crystal silicon is as large as 34.3%, making it extremely difficult to heteroepitaxially grow diamond on the substrate surface.

[0010] Therefore, Patent Document 1 discloses a technique for growing single-crystal diamond on a base substrate by giving the initial substrate an appropriate off-angle corresponding to its crystal structure, such as cubic or hexagonal. The base substrate consists of an initial substrate, which is the main constituent layer, and an intermediate layer formed on top of it.

[0011] While the invention described in Patent Document 1 shows significant effects in reducing defects and improving the orientation of heteroepitaxial diamond crystals, it has the problem that the large difference in the coefficient of thermal expansion between the diamond and the initial substrate can lead to peeling or damage of the diamond film during or after CVD, and even damage to the underlying substrate.

[0012] For example, diamond and single crystal α-Al ２ O ３ The difference in the coefficient of linear expansion with respect to (direction c) 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 presence of / K, warping becomes a problem. This will become a major issue when realizing large diameters of 6 inches or more in the future.

[0014] Therefore, single-crystal α-Al is particularly useful for obtaining high-quality, highly oriented diamonds. ２ O ３There is a need for a technology that enables stable single-crystal diamond formation without breakage on a layer.

[0015] The present invention has been made to solve the above problems, and is applicable to electronic and magnetic devices, and is a large-area (large-diameter), high-crystallinity, low in hillocks, abnormal growth particles, dislocation defects, etc., high-purity and low-stress high-quality single-crystal diamond layer. An object is to provide a substrate and a method for manufacturing the same. Further, a method for manufacturing a single-crystal diamond substrate having the above characteristics is also provided.

[0016] The present invention has been made to achieve the above object, and is a substrate for a single-crystal diamond laminated substrate, having a linear expansion coefficient smaller than that of single-crystal α-Al ２ O ３ and 0.5 × 10 －６ / K or more, and an initial substrate containing at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, and a single-crystal α-Al ２ O ３ layer, and a heteroepitaxial layer made of any one of an iridium film, a rhodium film, and a platinum film on the single-crystal α-Al ２ O ３ layer. A substrate is provided.

[0017] According to such a substrate for a single-crystal diamond laminated substrate, a high-quality single-crystal diamond layer having a large area (large diameter), high crystallinity, few hillocks, abnormal growth particles, dislocation defects, etc., high purity and low stress can be formed on the substrate.

[0018] At this time, 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 direction of the crystal axis <10-10> or <11-20> with respect to the outermost surface plane orientation of {0001}, and when the plane orientation of the diamond layer of the single-crystal diamond laminated substrate is {001}, the single-crystal α-Al２ O ３ The layer may have 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 {11-20}.

[0019] Within this range of off-angles, single crystal α-Al ２ O ３ The heteroepitaxial layer on the layer will be of higher quality, with greater crystallinity and fewer hillocks, abnormally grown particles, and dislocation defects.

[0020] At this time, 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 It may have a single layer or a multilayer film containing at least one of the films.

[0021] As a result, the single crystal α-Al ２ O ３ The layers are formed 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 thermal expansion is that of single-crystal α-Al ２ O ３ Smaller than 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, and a step of preparing the initial substrate containing single-crystal α-Al ２ O ３ The process of bonding the layers, and the single crystal α-Al ２ O ３ The present invention provides a method for manufacturing a base substrate, 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.

[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 surface 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 When a 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>, with respect to the surface orientation of the outermost surface of the layer being {0001}, and a layer with a surface orientation of {001} is formed as the diamond layer of 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 can be 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 <0001>, relative to the surface orientation of the outermost surface of the layer {11-20}.

[0025] As a result, the single crystal α-Al ２ O ３ A high-quality heteroepitaxial layer with higher crystallinity and fewer hillocks, abnormally grown particles, and dislocation defects can be formed on top of the existing layer.

[0026] At this time, the 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 The initial substrate can be bonded to it via a single-layer or multilayer film containing at least one of the films.

[0027] As a result, the initial substrate and the single crystal α-Al ２ O ３ It allows for more efficient bonding of layers.

[0028] At this time, the thickness of the initial substrate is 0.03 to 5.00 mm, and the single crystal α-Al ２ O ３ The thickness of the 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. ２ O ３ With layers and heteroepitaxial layers, 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 diamonds and enabling the manufacture of inexpensive substrates.

[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.

[0038] As described above, the base substrate for a single-crystal diamond laminated substrate of the present invention makes it 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 possessing high purity and low stress. Furthermore, the manufacturing method for the base substrate for a single-crystal diamond laminated substrate of the present invention makes it possible to manufacture a base substrate that is large in area (large in diameter), highly crystalline, with few hillocks, abnormally grown particles, dislocation defects, etc., and possessing high purity and low stress. The present invention further provides a manufacturing method for a single-crystal diamond substrate having the above-described characteristics.

[0039] 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. This is a schematic diagram showing an example of a single-crystal diamond laminated substrate according to the present invention. This is a schematic diagram showing an example of a single-crystal diamond substrate according to the present invention. This is a flowchart showing an example of an embodiment of a method for manufacturing a base substrate for a single-crystal diamond laminated substrate and a method for manufacturing a single-crystal diamond substrate according to the present 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 problem, the inventors have found a base substrate for a single-crystal diamond laminated substrate, wherein the coefficient of linear thermal expansion is that of single-crystal α-Al ２ O ３ Smaller than 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, and a single-crystal α-Al on the initial substrate. ２ O ３ The layer and the single crystal α-Al ２ O ３ We have discovered that by using a substrate having a heteroepitaxial layer consisting of one of iridium, rhodium, or platinum films on top of it, it is possible to form a high-quality single-crystal diamond layer on the substrate that is large in area (large in diameter), highly crystalline, with few hillocks, abnormally grown particles, dislocation defects, high purity, and low stress, thereby completing the present invention.

[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 linear expansion is that of single-crystal α-Al ２ O ３ Smaller than 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, and a step of preparing the initial substrate containing single-crystal α-Al ２ O ３ The process of bonding the layers, and the single crystal α-Al ２ O ３The present invention was completed by discovering that a substrate can be manufactured using a method for manufacturing a substrate, which includes the step of forming a heteroepitaxial layer by heteroepitaxially growing one of the iridium film, rhodium film, or platinum film on the surface of the layer opposite to the surface to which the initial substrate is bonded, thereby forming 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.

[0044] (Underlayment for Single-Crystal Diamond Multilayer Substrate) 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 underlayment for the single-crystal diamond multilayer 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 and a single crystal α-Al on the initial substrate 11. ２ O ３ Layer 21 and single crystal α-Al ２ O ３ The layer 21 has a heteroepitaxial layer 31 which is made up of a single layer or multilayer film 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 selected 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 that mainly generates stress between itself and the single-crystal diamond layer, and compared it to the conventional MgO initial substrate or α-Al ２ O ３ We found that, compared to cases using initial substrates, the stress caused by thermal expansion is smaller, and as a result, damage to the entire substrate can be prevented. Refer to Table 1 below for the coefficient of linear expansion.

[0048]

[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 coefficient of thermal expansion depending on the manufacturing method and conditions.

[0050] Therefore, the material used for the initial substrate 11 is single crystal α-Al, which has a coefficient of thermal expansion. ２ O ３ Smaller than 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, then since it is made of the same element as the diamond being grown, there will be almost no stress due to thermal expansion, 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 methods such as microwave CVD, DC plasma CVD, DC arc plasma CVD, thermal filament CVD, or R.F. plasma CVD, and may be amorphous (diamond-like carbon (DLC)), polycrystalline, or single-crystal.

[0053] Other materials, such as DLC and glassy carbon, can be manufactured using hydrogen-diluted methane gas as a raw material, employing R.F. plasma CVD, DC plasma CVD, DC arc plasma CVD, or thermal filament CVD. The concentration of the hydrogen-diluted methane gas is 0.1 to 20 vol. %, and the pressure is 7.5 × 10⁻⁶. －３ ~2.3 Pa is sufficient.

[0054] Glassy carbon can also be made by firing and heat-treating resin.

[0055] Polycrystalline and single-crystal diamonds can be produced using hydrogen-diluted methane gas as a raw material by microwave CVD, DC plasma CVD, DC arc plasma CVD, or thermal filament CVD. The concentration of the hydrogen-diluted methane gas is 0.1 to 20 vol. %, and the pressure is 7.5 × 10⁻⁶. －３ ~2.3 Pa is sufficient.

[0056] The single-crystal diamond can be synthesized using the HPHT method, or it can be made by joining together multiple single-crystal diamond substrates synthesized using either the HPHT or CVD method to form a single substrate.

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

[0058] Single crystal α-Al ２ O ３ Layer 21 is single crystal α-Al ２ O ３ {0001} layer or single crystal α-Al ２ O ３ It can be made into a {11-20} layer. When the crystal orientation of the diamond layer of the single-crystal diamond laminated substrate is {111}, single-crystal α-Al ２ O ３ The 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}, and when the surface orientation of the diamond layer of the single-crystal diamond laminated substrate is {001}, single-crystal α-Al ２ O ３ The layer 21 preferably has an off-angle in the direction of the crystal axis <10-10> or <0001> with respect to the surface orientation of {11-20}.

[0059] Single crystal α-Al ２ O ３ Because layer 21 has such an off-angle, single crystal α-Al ２ O ３ The heteroepitaxial layer 31 on layer 21 becomes a high-quality layer with higher crystallinity and fewer hillocks, abnormally grown particles, and dislocation defects.

[0060] At this time, the off-angle 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 more, the effect of setting the off-angle more stably can be obtained. If it is +24.0 and -24.0° or less, the effect of more stable high-quality can be obtained.

[0061] Further, the off-angle is more preferably 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°. In such a range of off-angle, the effect of setting the off-angle more stably can be obtained, and the effect of high-quality can be obtained.

[0062] At this time, between the initial substrate 11 and the single-crystal α-Al ２ O ３ layer 21, it can have a single-layer or laminated film including at least one of an amorphous carbon film, a polycrystalline diamond film, a single-crystal diamond film, a SiC film, a Si film, and a SiO ２ film. Thereby, the single-crystal α-Al ２ O ３ layer 21 is formed more efficiently.

[0063] The initial substrate 11 is preferably 0.03 to 5.00 mm thick. With an initial substrate of such a thickness, it is cost-effective and easier to handle. Also, if the thickness is 0.03 mm or more, double-sided polishing and the like can be performed better.

[0064] The single-crystal α-Al ２ O ３ layer 21 is preferably 0.1 to 100 μm thick. In such a thickness range, the film thickness uniformity is higher in terms of processing technology. If the thickness is 100 μm or less, the stress generated between the initial substrate 11 and the single-crystal diamond layer is smaller, so that the single-crystal diamond can be grown more reliably.

[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 film, rhodium film, and platinum film is 5 Å or more, the film thickness uniformity and crystallinity will be higher. Also, 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, so that the single crystal diamond can be grown more effectively, and furthermore, it can be an inexpensive base substrate.

[0066] As described above, according to the base substrate 30 for a single crystal diamond laminated substrate of the present invention, it becomes a base substrate with an appropriate combination of an initial substrate, a layer on the initial substrate, and an off-angle, and is suitable for electronic and magnetic devices, with a large area (large diameter), high crystallinity, few hillocks, abnormal growth particles, dislocation defects, etc., and high purity and low stress, and can form a high-quality single crystal diamond layer.

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

[0068] At this time, the single crystal diamond layer 41 formed on the highly crystalline heteroepitaxial layer 31 formed on the highly crystalline single crystal α -Al ２ O ３ layer 21 has a large area (large diameter), high crystallinity, few hillocks, abnormal growth particles, dislocation defects, etc., and is a high-quality single crystal diamond layer with high purity and low stress.

[0069] (Manufacturing method of base substrate for single crystal diamond laminated substrate) Next, the manufacturing method of the base substrate for a single crystal diamond laminated substrate of the present invention will be described with reference to FIG. 4. FIG. 4 is a flowchart showing an example of an embodiment of the manufacturing method of the base substrate for a single crystal diamond laminated substrate and the manufacturing method of a single crystal diamond substrate of 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 that of single crystal α-Al ２ O ３ Smaller than 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 initial substrate thickness 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 easy finishing and polishing, resulting in a better surface condition and more favorable bonding in subsequent processes.

[0074] Of the surface of the initial substrate 11 made of carbon-based material, at least single crystal α-Al ２ O ３ The surface on which layer 21 is bonded should ideally be a smooth polished surface, but if polishing is difficult, an amorphous carbon (DLC) film, polycrystalline diamond film, single-crystal diamond film, SiC film, Si film, and SiO film may be applied to the surface of the initial substrate 11. ２ It is efficient to form a single-layer or multilayer film containing at least one of the films before smoothing it.

[0075] As a result, single crystal α-Al ２ O ３The layer 21 can be bonded to the initial substrate 11 more efficiently via the single layer or multilayer film.

[0076] The above single-layer or multilayer film can be formed by sputtering, electron beam deposition, 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, so the single-crystal diamond layer 41 can be grown more reliably.

[0077] Next, as shown in Figure 4(b), single crystal α-Al is placed on the initial substrate 11. ２ O ３ The substrates are bonded together, single crystal α-Al ２ O ３ Layer 21 is formed. At this time, single crystal α-Al ２ O ３ It is also advisable to smooth the bonding surface of the substrate to the initial substrate 11. Furthermore, this bonding is more effective when both bonding surfaces are cleaned and activated by plasma treatment, ion beam treatment, neutral atomic beam treatment, wet etching, etc.

[0078] An initial substrate 11 made of such a carbon-based material and a single crystal α-Al ２ O ３ By bonding layer 21 to the initial substrate 11, a highly crystalline single crystal α-Al ２ O ３ Layer 21 can be formed.

[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] Bonding single crystals α-Al ２ O ３ As a substrate, for example, a single crystal α-Al with a diameter of 100 mm and a thickness of 1000 μm, polished on both sides. ２ O３ A circuit board can be used.

[0081] Also, the single crystal α-Al to be bonded. ２ O ３ The substrate thickness is usually around 200 μm to 1000 μm, but it is preferable to process it to be thinner in order to reduce stress after single-crystal diamond growth. For example, α-Al ２ O ３ Ions such as hydrogen, oxygen, and carbon may be injected into the portion of layer 21 that needs 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] And then, the single crystal α-Al after bonding. ２ O ３ The thickness of layer 21 can be set to 0.1 to 100 μm. In this way, single crystal α-Al ２ O ３ If the thickness of 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] Single crystal α-Al ２ O ３ Layer 21 is single crystal α-Al ２ O ３ {0001} layer or single crystal α-Al ２ O ３ It can be a {11-20} layer. When forming a diamond layer with a {111} plane orientation in a single-crystal diamond laminated substrate, single-crystal α-Al ２ O ３ Layer 21 is made of single crystal α-Al ２ O ３When forming a layer 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 surface orientation of the outermost surface of layer 21 which is {0001}, and when forming a diamond layer with a surface orientation of {001} as the diamond layer of a single-crystal diamond laminated substrate, single-crystal α-Al ２ O ３ Layer 21 is made of single crystal α-Al ２ O ３ 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 of the crystal axis <10-10> or <0001> with respect to the surface orientation of the outermost surface of layer 21, which is {11-20}.

[0084] Single crystal α-Al ２ O ３ Because layer 21 has such an off-angle, single crystal α-Al ２ O ３ The heteroepitaxial layer 31 on layer 21 becomes a high-quality layer with higher crystallinity and fewer hillocks, abnormally grown particles, and dislocation defects.

[0085] Next, as shown in Figure 4(c), single crystal α-Al ２ O ３ A heteroepitaxial layer 31 is formed by heteroepitaxial growth of an iridium film, a rhodium film, or a platinum film on the surface of 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 the R.F. magnetron sputtering method.

[0087] The thickness of the heteroepitaxial layer 31 can be set to 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. With this bias treatment, diamond growth nuclei can be formed on the surface, making it a substrate that can grow single-crystal diamond 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, is made of single-crystal α-Al with a coefficient of linear expansion. ２ O ３ Smaller than 0.5 × 10 －６ Because 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, single crystal α-Al can be placed on such an initial substrate 11. ２ O ３ The presence of layer 21, and furthermore, a heteroepitaxial layer 31 made of either an iridium film, a rhodium film, or a platinum film, allows these to function as good buffer layers during the growth of the single-crystal diamond layer 41.

[0091] Furthermore, single crystal α-Al ２ O ３ Layer 21 is made of bulk single crystal α-Al ２ O ３ It is formed by bonding a substrate and an initial substrate 11, and is obtained by heteroepitaxial growth of α-Al ２ O ３ Highly crystalline single crystal α-Al is easier to form than layers. ２ O ３ It can form layers and can be formed with high productivity.

[0092] Such a highly crystalline single crystal α-Al ２ O ３An iridium film, a rhodium film, and a platinum film (heteroepitaxial layer 31) can be grown on layer 21 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 a Single Crystal Diamond Substrate) Next, the method for manufacturing a single crystal diamond substrate of the present invention will be described with reference to Figures 3 and 4. The method for manufacturing a single crystal diamond substrate of the present invention is 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. By performing this bias treatment in advance, diamond growth nuclei are formed on the surface, allowing single-crystal diamond 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 for example, it can be grown heteroepitaxially by microwave CVD, DC plasma CVD, thermal filament CVD, etc.

[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 method of separation is not particularly limited; for example, by immersing in a wet etching solution such as a hot phosphoric acid solution or a hot mixed acid, the single-crystal diamond layer 41 / heteroepitaxial layer 31 and the single-crystal α-Al ２ O ３ After separating the layer 21 from the initial substrate 11, the remaining heteroepitaxial layer 31 can be removed by mechanical polishing to obtain a single-crystal diamond substrate 41. 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.

[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) Diameter 50.0 mm, thickness 1000 μm, linear thermal expansion coefficient 1 × 10⁻⁶ －６ A single-sided polished polycrystalline diamond substrate of type K was prepared as the initial substrate 11. Then, a single-crystal α-Al single crystal, polished on both sides 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, was prepared to be bonded to the side of this initial substrate where single-crystal diamond growth would take place. ２ O ３ I prepared the circuit board.

[0102] The initial polycrystalline diamond substrate 11 was cleaned with a mixed acid and RCA. Additionally, single-crystal α-Al ２ O ３ The substrates were cleaned using RCA. Furthermore, both bonding surfaces were cleaned and activated with an argon neutral atomic beam before being bonded together by direct bonding.

[0103] Subsequently, single crystal α-Al was produced by mechanical polishing. ２ O ３ The portion is thinned to create a 2 μm thick single crystal α-Al ２ O ３ Layer 21 was completed.

[0104] Next, single crystal α-Al ２ O ３An iridium (Ir) film was heteroepitaxially grown on the surface of layer 21 to form a heteroepitaxial layer 31 of single-crystal Ir.

[0105] For the deposition of single-crystal Ir films, an R.F. (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 a R.F. of 1500 W 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 the out-of-plane method with an X-ray diffraction (XRD) apparatus (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA 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, the Out-of-Plane method revealed only the main diffraction intensity peak and its multiple reflection peaks at 2θ = 40.7°, which are attributed to Ir(111), 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 is below Pa, dilute the hydrogen with methane (CH4).４ / (CH ４ +H ２ A solution of 5.0 vol. %) was introduced into the treatment chamber at a flow rate of 500 sccm. The pressure was adjusted to 1.3 × 10 by adjusting the opening of the valve leading to the exhaust system. ４ After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and exposed to the plasma for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0112] Next, a single-crystal diamond layer 41 was heteroepitaxially grown by 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 by a vacuum pump. －４ After exhausting until the pressure drops below Pa, the raw material gas is hydrogen-diluted methane (CH4). ４ / (CH ４ +H ２ A solution of 4.0 vol. %) 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, single crystal α-Al ２ O ３ Single crystal α-Al of layer 21 ２ O ３ The portion was etched with thermal phosphoric acid. Furthermore, the Ir portion of 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).

[0115] Finally, a single-crystal diamond layer (additional single-crystal diamond layer) was homoepitaxially grown again by 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 complete, continuous film with no damage across its entire 50 mm diameter.

[0117] A 2 mm 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 sample thickness was measured using a Mitutoyo ID-SX2 digital indicator, and the total thickness of the diamond layer was found to be approximately 400 μm.

[0119] Crystallinity was measured from the outermost surface of the film using the pole method and the out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, output 45kV, 200mA, 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 the single-crystal diamond {111} 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.

[0121] (Example 2) Diameter 50.0 mm, thickness 1000 μm, linear expansion coefficient 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 polished 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-Al with a diameter of 50.0 mm, a thickness of 300 μm, a crystal plane orientation {0001}, and an off-angle of 16° in the <11-20> direction, which has been polished on both sides, is bonded to the surface of the initial substrate 11 on which single crystal diamond growth will be performed. ２ O ３ I prepared the circuit board.

[0125] The initial polycrystalline diamond substrate 11 was cleaned with a mixed acid and RCA. Additionally, single-crystal α-Al ２ O ３ The substrates were cleaned using RCA. Furthermore, both bonding surfaces were purified and activated with an argon ion beam before direct bonding was performed.

[0126] Subsequently, single crystal α-Al was produced by mechanical polishing. ２ O ３ The portion is thinned to create a 2 μm thick single crystal α-Al ２ O ３ Layer 21 was completed.

[0127] Next, single crystal α-Al ２ O ３ An iridium (Ir) film was heteroepitaxially grown on the surface of layer 21 to form a heteroepitaxial layer 31 of single-crystal Ir.

[0128] For the deposition of single-crystal Ir films, an R.F. (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 a R.F. of 1500 W 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 the out-of-plane method with an X-ray diffraction (XRD) apparatus (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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, the Out-of-Plane method revealed only the main diffraction intensity peak and its multiple reflection peaks at 2θ = 40.7°, which are attributed to Ir(111), 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 base substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the base 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 is below Pa, dilute the hydrogen with methane (CH4). ４ / (CH ４ +H ２ A solution of 5.0 vol. %) was introduced into the treatment chamber at a flow rate of 500 sccm. The pressure was adjusted to 1.3 × 10 by adjusting the opening of the valve leading to the exhaust system. ４ After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and exposed to the plasma for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0134] Next, a single-crystal diamond layer 41 was heteroepitaxially grown by 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 by a vacuum pump. －４ After exhausting until the pressure drops below Pa, the raw material gas is hydrogen-diluted methane (CH4). ４ / (CH ４ +H ２ A solution of 4.0 vol. %) 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. ４After 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, single crystal α-Al ２ O ３ Single crystal α-Al of layer 21 ２ O ３ The portion was etched with thermal 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 complete, continuous film with no damage across its entire 50 mm diameter.

[0139] A 2 mm 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 the out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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 the single-crystal diamond {111} 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.

[0143] (Example 3) Diameter 50.0 mm, thickness 1000 μm, linear expansion coefficient 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, the polycrystalline diamond surface film was polished using the chemical mechanical polishing (CMP) method until the Ra was 0.3 nm or less. The thickness of the fine-grained polycrystalline diamond film after polishing was 0.5 μm.

[0145] Then, a single crystal α-Al with a diameter of 50.0 mm, a thickness of 300 μm, a crystal plane orientation {11-20}, and an off-angle of 10° in the <0001> direction, which has been polished on both sides, is bonded to the surface of the initial substrate 11 on which single crystal diamond growth will be performed. ２ O ３ I prepared the circuit board.

[0146] The initial polycrystalline diamond substrate 11 was cleaned with a mixed acid and RCA. Additionally, single-crystal α-Al ２ O ３ The substrates were cleaned using RCA. Furthermore, both bonding surfaces were purified and activated with an argon ion beam before direct bonding was performed.

[0147] Subsequently, single crystal α-Al was produced by mechanical polishing. ２ O ３ The portion is thinned to create a 2 μm thick single crystal α-Al ２ O ３ Layer 21 was completed.

[0148] Next, single crystal α-Al ２ O ３An iridium (Ir) film was heteroepitaxially grown on the surface of layer 21 to form a heteroepitaxial layer 31 of single-crystal Ir.

[0149] For the deposition of single-crystal Ir films, an R.F. (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 7 Pa, and then R.F. 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 the out-of-plane method with an X-ray diffraction (XRD) apparatus (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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, the Out-of-Plane method revealed only the main diffraction intensity peak assigned to Ir(200) at 2θ = 47.2° and Ir(400) at 2θ = 106.3°, 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 base substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the base 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 is below Pa, dilute the hydrogen with methane (CH4). ４ / (CH ４ +H ２A solution of 5.0 vol. %) was introduced into the treatment chamber at a flow rate of 500 sccm. The pressure was adjusted to 1.3 × 10 by adjusting the opening of the valve leading to the exhaust system. ４ After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and exposed to the plasma for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0154] Next, a single-crystal diamond layer 41 was heteroepitaxially grown by 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 by a vacuum pump. －４ After exhausting until the pressure drops below Pa, the raw material gas is hydrogen-diluted methane (CH4). ４ / (CH ４ +H ２ A solution of 4.0 vol. %) 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, single crystal α-Al ２ O ３ Single crystal α-Al of layer 21 ２ O ３ The portion was etched with thermal phosphoric acid. Furthermore, the Ir portion of 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).

[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 complete, continuous film with no damage across its entire 50 mm diameter.

[0158] A 2 mm 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 the out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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] By applying the single-crystal diamond {001} laminated substrate and self-supporting substrate to electronic and magnetic devices, high-performance devices can be obtained. For example, high-performance power devices can be obtained. Moreover, since they can be obtained as large-diameter substrates, manufacturing costs can be kept low.

[0162] (Example 4) Diameter 50.0 mm, thickness 1000 μm, linear expansion coefficient 2 × 10⁻⁶ －６ A glassy carbon substrate with one side polished to a single-crystal diamond of type K was prepared as the initial substrate 11. Then, a single crystal α-Al 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. ２ O ３ I prepared the circuit board.

[0163] The initial glassy carbon substrate 11 was cleaned with a mixed acid and RCA. Additionally, single crystal α-Al ２ O ３ The substrates were cleaned using RCA. Furthermore, both bonding surfaces were cleaned and activated with an argon neutral atomic beam before being bonded together by direct bonding.

[0164] Subsequently, single crystal α-Al was produced by mechanical polishing.２ O ３ The portion is thinned to create a 2 μm thick single crystal α-Al ２ O ３ Layer 21 was completed.

[0165] Next, single crystal α-Al ２ O ３ An iridium (Ir) film was heteroepitaxially grown on the surface of layer 21 to form a heteroepitaxial layer 31 of single-crystal Ir.

[0166] For the deposition of single-crystal Ir films, an R.F. (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 R.F. 1500W was applied to deposit the film for 60 minutes. 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 the out-of-plane method with an X-ray diffraction (XRD) apparatus (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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, the Out-of-Plane method revealed only the main diffraction intensity peak and its multiple reflection peaks at 2θ = 40.7°, which are attributed to Ir(111), 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 base substrate 30 was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the base 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 is below Pa, dilute the hydrogen with methane (CH4). ４ / (CH ４ +H ２ A solution of 5.0 vol. %) was introduced into the treatment chamber at a flow rate of 500 sccm. The pressure was adjusted to 1.3 × 10 by adjusting the opening of the valve leading to the exhaust system. ４ After setting the temperature to Pa, a negative voltage was applied to the substrate-side electrode and exposed to the plasma for 90 seconds to bias-treat the surface of the heteroepitaxial layer 31.

[0171] Next, a single-crystal diamond layer 41 was heteroepitaxially grown by 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 by a vacuum pump. －４ After exhausting until the pressure drops below Pa, the raw material gas is hydrogen-diluted methane (CH4). ４ / (CH ４ +H ２ A solution of 4.0 vol. %) 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, single crystal α-Al ２ O ３ Single crystal α-Al of layer 21 ２ O ３The portion was etched with thermal phosphoric acid. Furthermore, the Ir portion of 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).

[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 complete, continuous film with no damage across its entire 50 mm diameter.

[0175] A 2 mm 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 the out-of-plane method with an XRD instrument (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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 the single-crystal diamond {111} 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.

[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 was polished on both sides and 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 R.F. (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 R.F. 1500W was applied to deposit the film for 60 minutes. 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 the out-of-plane method with an X-ray diffraction (XRD) apparatus (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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, the Out-of-Plane method revealed only the main diffraction intensity peak and its multiple reflection peaks at 2θ = 40.7°, which are attributed to Ir(111). This confirmed that the single-crystal Ir layer is an epitaxially grown single-crystal Ir(111) crystal.

[0185] The base substrate was manufactured as described above. Next, the base substrate was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the base 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 is below Pa, dilute the hydrogen with methane (CH4). ４ / (CH ４ +H ２A solution of 5.0 vol. %) was introduced into the treatment chamber at a flow rate of 500 sccm. The pressure was adjusted to 1.3 × 10 by adjusting the opening of the valve leading to the exhaust system. ４ After setting to Pa, a negative voltage was applied to the substrate-side electrode and 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 until the pressure drops below Pa, the raw material gas is hydrogen-diluted methane (CH4). ４ / (CH ４ +H ２ A solution of 4.0 vol. %) 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) Single crystal α-Al with a diameter of 50.0 mm, a thickness of 1000 μm, a crystal plane orientation of {0001}, and a double-sided polished off-angle of 10° in the <11-20> direction. ２ O ３ A circuit board was prepared as the initial circuit board.

[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 R.F. (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 14 Pa, and then R.F. 1500W was applied to deposit the film for 60 minutes. 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 the out-of-plane method with an X-ray diffraction (XRD) system (RIGAKU SmartLab). The measurement conditions were: Cu cathode, 45 kV output, 200 mA output, and a 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, the Out-of-Plane method revealed only the main diffraction intensity peak and its multiple reflection peaks at 2θ = 40.7°, which are attributed to Ir(111), confirming that the intermediate layer is an epitaxially grown single-crystal Ir(111) crystal.

[0194] The base substrate was manufactured as described above. Next, the base substrate was subjected to a pretreatment (bias treatment) for diamond nucleation. Here, the base substrate with the single-crystal Ir intermediate layer formed on it was set on a flat electrode, and the base pressure was approximately 1.3 × 10⁻⁶ －４ After confirming that the pressure is below Pa, dilute the hydrogen with methane (CH4). ４ / (CH ４ +H ２ A solution of 5.0 vol. %) was introduced into the treatment chamber at a flow rate of 500 sccm. The pressure was adjusted to 1.3 × 10 by adjusting the opening of the valve leading to the exhaust system. ４ After setting to Pa, a negative voltage was applied to the substrate-side electrode and 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 until the pressure drops below Pa, the raw material gas is hydrogen-diluted methane (CH4). ４ / (CH ４ +H ２ A solution of 4.0 vol. %) 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 substrate to Pa, a 3500W microwave was applied to perform film deposition. The temperature reached 980°C 1 hour after the start of deposition, 1000°C at 6 hours, and then failed at 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 that of single-crystal α-Al ２ O ３ Smaller than 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, and a single-crystal α-Al on the initial substrate. ２ O ３ Layer and single crystal α-Al ２ O ３ A base substrate having a heteroepitaxial layer on top of it, which is made of an iridium film, a rhodium film, or a platinum film. [2]: When the surface orientation of the diamond layer of the single crystal diamond laminate substrate is {111}, the single crystal α-Al ２ O ３The 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 {0001}, and 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 base substrate of [1], wherein 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 base substrate of [1] or [2] above, comprising having a single layer or multilayer film containing at least one of the films. [4]: ​​A method for manufacturing a base substrate for a single crystal diamond multilayer substrate, wherein the coefficient of thermal expansion is that of single crystal α-Al ２ O ３ Smaller than 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, and a step of preparing the initial substrate containing single-crystal α-Al ２ O ３ The process of bonding the layers, and the single crystal α-Al ２ O ３ A method for manufacturing a base substrate, comprising the step of forming a heteroepitaxial layer by heteroepitaxial growth of 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 surface orientation of {111} as the diamond layer of the single crystal diamond laminated substrate, the single crystal α-Al ２ O ３ As a layer, the single crystal α-Al ２ O ３When a 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>, with respect to the surface orientation of the outermost surface of the layer being {0001}, and a layer with a surface orientation of {001} is formed as the diamond layer of 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 method for manufacturing the substrate substrate according to [4], comprising forming a layer 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 being {11-20}. [6]: The 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 the base substrate according to [4] or [5] above, comprising bonding the initial substrate to the base substrate via a single layer or multilayer film containing at least one of the films. [7]: The initial substrate has a thickness of 0.03 to 5.00 mm, and the single crystal α-Al ２ O ３A method for manufacturing a substrate according to [4], [5], or [6], comprising setting the thickness of the 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 a 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 substrate manufactured by the method for manufacturing a substrate according to [4], [5], [6], [7], or [8]; 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], further 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] , further 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.

Claims

1. A base substrate for a single-crystal diamond laminated substrate, wherein 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 comprising at least one of amorphous carbon, glassy carbon, polycrystalline diamond, and single-crystal diamond, having a temperature of 1 / K or higher, and single-crystal α-Al on the initial substrate ２ O ３ The layer and 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 plane orientation of {0001} on the outermost surface. When the plane orientation of the diamond layer of the single-crystal diamond laminated substrate is {001}, 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 <0001> direction of the crystal axis with respect to the plane orientation of {11-20} on the outermost surface. The base substrate according to claim 1, characterized in that it is such.

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, wherein 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, and a step of preparing an initial substrate containing single-crystal α-Al ２ O ３ The process of bonding the layers, and the 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 When a 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>, with respect to the surface orientation of the outermost surface of the layer being {0001}, and when a diamond layer with a surface orientation of {001} is formed as the diamond layer of 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 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 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 it 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 by 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 substrate manufactured by the method for manufacturing a substrate described in claim 4; heteroepitaxially growing a single-crystal diamond layer on the heteroepitaxial layer; and 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 heteroepitaxial growth of the single-crystal diamond layer, the single-crystal diamond layer is grown by any of the following methods: microwave CVD, DC plasma CVD, and thermal filament CVD.

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