A base substrate for diamond film deposition and a method for manufacturing the same, a method for manufacturing a diamond substrate, and a method for manufacturing a single-crystal diamond self-supporting substrate.

Abstract

This invention provides a novel underlay substrate for diamond film deposition that uses a Si substrate made of single-crystal Si, which allows for the relatively inexpensive production of large-area single-crystal diamond films using the CVD method, and does not require heating of the substrate during the manufacturing process. [Solution] A diamond film deposition substrate for forming a single-crystal diamond film by CVD, comprising a Cu film on a Si substrate made of single-crystal Si(100) or single-crystal Si(111), and a metal film layer comprising one or more metal films on the Cu film, wherein the outermost layer of the metal film layer is a platinum group metal film made of one or more platinum group metals selected from Ir, Pt, Pd, and Rh, and the thickness of the Cu film is 1 nm or more and less than 100 nm.

Description

[Technical Field]

[0001] The present invention relates to a base substrate for forming a single-crystal diamond film by chemical vapor deposition (CVD), a base substrate for diamond film formation, a method for manufacturing the same, a method for manufacturing a diamond substrate using the base substrate, and a method for manufacturing a single-crystal diamond self-supporting substrate using the diamond substrate obtained by the said manufacturing method. [Background technology]

[0002] Diamond possesses many desirable properties, including high thermal conductivity, a wide bandgap, a high dielectric breakdown field, a low dielectric constant, excellent radiation resistance, and superior chemical stability. Furthermore, its extremely high carrier mobility and saturation drift velocity make it promising for applications in power devices utilizing high frequencies and high power. Its Johnson index, a measure of performance, surpasses that of conventional semiconductor materials such as Si and SiC, leading to its reputation as the ultimate semiconductor material. In addition, because diamond allows for quantum manipulation using single electron spins through vacancies in its crystal structure, it is also expected to have applications in quantum sensors for detecting magnetic fields, temperature, and pressure.

[0003] As mentioned above, the use of diamond is expected to be put into practical use in fields such as semiconductors and quantum mechanics. In particular, in these fields, there is a desire for the development of diamond substrates with a surface area and quality comparable to existing materials such as Si and SiC.

[0004] Two methods are known for diamond synthesis: one using ultra-high pressure for growth and another using chemical vapor deposition (CVD). Regarding applications in semiconductors, chemical vapor deposition (CVD) is attracting attention because it allows for the acquisition of large diameters. The CVD method involves placing a substrate inside a reaction tube and flowing a raw material gas and a carrier gas under atmospheric or reduced pressure. The raw material gas is then decomposed and activated by thermal decomposition or plasma to grow a diamond film on the substrate.

[0005] Regarding methods for forming diamond films on a substrate using the CVD method, for example, Patent Document 1 discloses a method in which MgO films and Ir films are laminated on a Si substrate, and a diamond film is grown on top of them. In this method, in order to obtain an Ir film with good crystallinity, it is necessary to improve the crystallinity of the MgO film, and for that purpose, the substrate needs to be heated when the MgO film is formed. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2023-071085 [Overview of the project] [Problems that the invention aims to solve]

[0007] For forming large-area single-crystal diamond films applicable to electronic devices, a silicon (Si) substrate is seemingly ideal as a base substrate, given that large-area substrates are relatively inexpensive to obtain and the difference in thermal expansion with diamond is small. However, in order to epitaxially grow single-crystal diamond on a Si substrate, as disclosed in Patent Document 1, it is necessary to form a platinum group metal film made of a platinum group metal such as Ir on the outermost layer. However, because there is a large difference in lattice constants between Si and platinum group metals, it has been difficult to improve the crystallinity of the platinum group metal film. If the crystallinity of the platinum group metal film cannot be improved, the crystallinity of the single-crystal diamond cannot be improved. In Patent Document 1, an Ir film is laminated on a Si substrate via an MgO film. However, in order to obtain an Ir film with good crystallinity, it is necessary to improve the crystallinity of the MgO film. Therefore, it is necessary to heat the substrate when depositing the MgO film, which leads to the problem of high manufacturing costs.

[0008] Therefore, the object of the present invention is to provide a new base substrate for diamond film deposition, which uses a Si substrate made of single-crystal Si and does not require heating of the substrate during the manufacturing process, and a method for manufacturing the same, a method for manufacturing a diamond substrate using the base substrate, and a method for manufacturing a single-crystal diamond self-supporting substrate using the diamond substrate obtained by the said manufacturing method. [Means for solving the problem]

[0009] The present invention proposes the following embodiments [1] to [7] of a new base substrate for diamond film deposition using a Si substrate made of single crystal Si, which does not require heating of the substrate during the manufacturing process, a method for manufacturing the same, a method for manufacturing a diamond substrate using the base substrate, and a method for manufacturing a single crystal diamond self-supporting substrate using the diamond substrate obtained by the said manufacturing method.

[0010] [1] A first aspect of the present invention is a base substrate for forming a diamond film by CVD, The structure comprises a Cu film on a Si substrate made of single-crystal Si(100) or single-crystal Si(111), and a metal film layer containing one or more metal films on the Cu film. The outermost layer of the metal film layer is a platinum group metal film made of one or more platinum group metals selected from Ir, Pt, Pd, and Rh. The substrate for diamond film deposition is characterized in that the thickness of the Cu film is 1 nm or more and less than 100 nm.

[0011] [2] A second aspect of the present invention is a substrate for diamond film deposition according to the first aspect, wherein the outermost layer of the metal film layer is a platinum group metal film selected from Ir(100) film, Ir(111) film, Pt(100) film, Pt(111) film, Pd(100) film, Pd(111) film, Rh(100) film, and Rh(111) film. [3] A third aspect of the present invention is a substrate for diamond film deposition according to the second aspect, wherein the outermost layer of the metal film layer has a full width at half maximum of 0.6° or less of the diffraction peaks attributed to (100) or (111) in X-ray diffraction analysis using a wavelength CuKα X-ray source. [4] A fourth aspect of the present invention is a diamond film deposition substrate according to any one of the first to third aspects, wherein one or more layers of metal films are provided between the Cu film and the platinum group metal film, the lattice mismatch between the Cu film and the platinum group metal film being 10% or less. [5] A fifth aspect of the present invention is a base substrate for diamond film deposition according to any one of the first to fourth aspects, wherein the off-angle of the surface layer determined by X-ray diffraction analysis using a wavelength CuKα line as the X-ray source is ±15° or less.

[0012] [6] A sixth aspect of the present invention is a method for manufacturing a base substrate for diamond film deposition according to any one of the first to fifth aspects, characterized in that the deposition rate of the Cu film and the platinum group metal film is less than 20 Å / s.

[0013] [7] A seventh aspect of the present invention is a method for manufacturing a diamond substrate, characterized in that a diamond film is formed by heteroepitaxial growth of diamond on a diamond film deposition substrate according to any one of the first to fifth aspects, using a CVD method which is one of microwave plasma CVD, DC plasma CVD, thermal filament CVD, and arc discharge plasma jet CVD, with a raw material gas which is a carbon source gas and a hydrogen gas.

[0014] [8] An eighth aspect of the present invention is a method for manufacturing a single-crystal diamond self-supporting substrate, characterized in that the base substrate is removed from the diamond substrate obtained by the manufacturing method of the seventh aspect to obtain a single-crystal diamond self-supporting substrate. [Effects of the Invention]

[0015] The underlay substrate for diamond film formation proposed by the present invention can be used to manufacture a diamond substrate by heteroepitaxially growing crystalline diamond on the underlay substrate by CVD method to form a diamond film. Then, the underlay substrate can be removed from the diamond substrate to obtain a single-crystal diamond free-standing substrate, and this single-crystal diamond free-standing substrate can be used for electronic devices and the like. In addition, the underlay substrate for diamond film formation proposed by the present invention is a stack of layers on a Si substrate, and since it is not necessary to heat the substrate in the manufacturing process of the underlay substrate and it can be completed only by a low-temperature process, it is expected to realize large-area formation at a relatively low cost. Note that the underlay substrate for diamond film formation proposed by the present invention does not require heating of the substrate in its manufacturing process, but heating is also possible and heated ones are not excluded.

Brief Description of Drawings

[0016] [Figure 1] It is an optical microscope photograph of the surface of the underlay substrate for diamond film formation after CVD treatment in Example 1 and 2 and Comparative Example 1. [Figure 2] It is the Raman spectroscopy spectrum of the diamond films obtained in Example 1 and 2.

Embodiments for Carrying Out the Invention

[0017] Hereinafter, the present invention will be described based on one embodiment. However, the present invention is not limited to this embodiment.

[0018] <The underlay substrate of the present invention> An underlay substrate (referred to as "the underlay substrate of the present invention") according to an example of an embodiment of the present invention is an underlay substrate for diamond film formation for forming a single-crystal diamond film by CVD method, The aforementioned substrate has a configuration in which a Cu film is provided on a Si substrate made of single crystal Si(100) or single crystal Si(111), and a metal film layer containing one or more metal films is provided on the Cu film, wherein the outermost layer of the metal film layer is a platinum group metal film made of one or more platinum group metals selected from Ir, Pt, Pd, and Rh.

[0019] Note that single crystal Si(100) refers to single crystal Si whose main surface is the (100) plane, and single crystal Si(111) refers to single crystal Si whose main surface is the (111) plane.

[0020] The substrate of the present invention is a base material for growing a diamond film, and the diamond film will grow directly on the outermost surface layer of the substrate of the present invention.

[0021] Chemical Vapor Deposition (CVD) is a dry plating technique that uses chemical reactions to create a plating film. In this method, raw material gases and carrier gases are flowed through an apparatus, and energy is supplied to the gases through thermal decomposition or plasma, causing a chemical reaction between the gases to form a plating film on the substrate. The aforementioned CVD method can be any CVD method capable of depositing a single-crystal diamond film. Currently, known CVD methods capable of depositing single-crystal diamond films include microwave plasma CVD, DC plasma CVD, thermal filament CVD, and arc discharge plasma jet CVD, so any of these CVD methods can be adopted.

[0022] The diamond film deposited on the substrate can be any film made of single-crystal diamond. Single-crystal diamond is suitable for, for example, forming semiconductor devices.

[0023] (Si substrate) The substrate of the present invention has a Si substrate made of single crystal Si(100) or single crystal Si(111). Si substrates made of single-crystal Si(100) or single-crystal Si(111) are advantageous for fabricating the base substrates of the present invention having a large area of ​​4 inches (100 mm) or more in diameter, because they have a relatively small difference in thermal expansion coefficient compared to diamond, and large-area substrates can be obtained relatively inexpensively.

[0024] From the viewpoint of mechanical strength, the thickness of the Si substrate is preferably 10 μm or more, more preferably 50 μm or more, and more preferably 100 μm or more. On the other hand, from the viewpoint of manufacturing cost, it is preferably 1000 μm or less, more preferably 800 μm or less, and more preferably 600 μm or less.

[0025] The off-angle of the Si substrate surface is preferably ±15° or less, i.e., it is preferable that the off-angle is in the range of -15° to 15°. If the off-angle of the Si substrate surface is ±15° or less, the off-angle of the outermost surface of the substrate of the present invention can be set to ±15° or less, which is preferable. From this viewpoint, the off-angle of the Si substrate surface is preferably in the range of -15° or more and 15° or less, and more preferably -10° or more or 10° or less, and more preferably -7° or more or 7° or less. To adjust the off-angle of the Si substrate surface to a range of -15° to 15°, the Si substrate cut at a specific angle can be polished, etched, or annealed. However, this method is not the only way to achieve this.

[0026] (Cu film) The substrate of the present invention comprises a Cu film on the above-mentioned Si substrate. The Cu film serves as a substrate for growing platinum group metals on a Si substrate. In other words, it is possible to epitaxially grow platinum group metals on a Cu film. To epitaxially grow diamond, it is preferable to form the outermost layer of the substrate with a platinum group metal as described above. However, because there is a large difference in lattice constants between Si and platinum group metals, attempting to form a platinum group metal film on a Si substrate results in poor crystallinity of the platinum group metal, and consequently, poor crystallinity of the diamond film. In contrast, if a Cu film is formed on a Si substrate and the platinum group metal is grown on the Cu film, the difference in lattice constants between Cu and the platinum group metal is relatively small, allowing for the formation of a highly crystallinity platinum group metal film.

[0027] The thickness of the Cu film is preferably 1 nm or more, more preferably 3 nm or more, and more preferably 5 nm or more, from the viewpoint of film uniformity and stress relaxation. On the other hand, from the viewpoint of preventing peeling due to the difference in thermal expansion coefficient with diamond, it is preferably less than 100 nm, more preferably 50 nm or less, and more preferably 30 nm or less.

[0028] (Metal film layer) The substrate of the present invention has a configuration comprising a metal film layer containing one or more metal films on the Cu film, wherein the outermost layer of the metal film layer is a platinum group metal film made of one or more platinum group metals selected from Ir, Pt, Pd, and Rh. If the outermost layer of the substrate of the present invention, i.e., the outermost layer of the metal film layer, is the platinum group metal film, then a diamond film can be formed on the outermost surface of the substrate of the present invention by heteroepitaxial growth of diamond using the CVD method.

[0029] The platinum group metal film is preferably a platinum group metal film selected from Ir(100) film, Ir(111) film, Pt(100) film, Pt(111) film, Pd(100) film, Pd(111) film, Rh(100) film, and Rh(111) film. An Ir(100) film refers to a film made of Ir whose main surface is the (100) plane, and an Ir(111) film refers to a film made of Ir whose main surface is the (111) plane. The same applies to other platinum group metals.

[0030] In the present invention, the outermost surface layer of the substrate, in other words, the outermost surface layer of the metal film layer, in other words, the platinum group metal film constituting the outermost surface layer, preferably has a full width at half maximum of 0.6° or less of the diffraction peaks attributed to (100) or (111) in X-ray diffraction analysis using a wavelength CuKα X-ray source. If the crystallinity of the platinum group metal film is this high, the crystallinity of the diamond film formed by heteroepitaxial growth on it can also be increased, which is preferable. From this viewpoint, platinum group metal films are preferably such that, in X-ray diffraction analysis using a CuKα wavelength X-ray source, the full width at half maximum of the diffraction peaks attributed to (100) or (111) is 0.6° or less, and more preferably 0.55° or less, and even more preferably 0.5° or less. To increase the crystallinity of the platinum group metal film, it is preferable to interpose an "other metal film" between the Cu film and the platinum group metal film, the film being made of a metal with a lattice constant between the lattice constant of Cu and the lattice constant of the platinum group metal constituting the platinum group metal film.

[0031] The thickness of the platinum group metal film is preferably 1 nm or more, more preferably 3 nm or more, and more preferably 5 nm or more, from the viewpoint of not influencing the other contacting material with the lattice constant of one contacting material and from the viewpoint of film uniformity. On the other hand, from the viewpoint of manufacturing cost, it is preferably 10 μm or less, more preferably 5 μm or less, and more preferably 1 μm or less.

[0032] The metal film layer in the substrate of the present invention may consist of the platinum group metal film, or it may include "other metal films" other than the platinum group metal film. When the "other metal film" is provided, it is preferable that the "other metal film" is interposed between the Cu film and the platinum group metal film, and in order to reduce the degree of lattice constant difference between the two and improve the crystallinity of the platinum group metal film, it is preferable that the metal of the "other metal film" is a metal having a lattice constant between the lattice constant of Cu and the lattice constant of the platinum group metal constituting the platinum group metal film. For example, since there is a large difference in lattice constants between Cu (lattice constant 3.61 Å) and Pt (lattice constant 3.92 Å), the crystallinity of a platinum group metal film made of Pt can be improved by interposing a metal film layer made of Pd (lattice constant 3.89 Å), which has a lattice constant intermediate between the two, as a buffer layer. Furthermore, metals with a face-centered cubic crystal structure are preferred.

[0033] From this viewpoint, it is preferable that the "other metal film" has a lattice mismatch of 10% or less with both the Cu film and the platinum group metal film. That is, it is preferable that the lattice mismatch with the Cu film is 10% or less, of which 8% or less, and of which 7% or less, and the lattice mismatch with the platinum group metal film is 10% or less, of which 8% or less, and of which 7.5% or less.

[0034] A lattice mismatch occurs, for example, when the lattice constant of the metal constituting the "other metal film" is a1, and the lattice constant of the Cu constituting the Cu film is a2. Grid mismatch (%) = (|a1-a2| / a2) × 100 This is the value obtained by [the formula / method].

[0035] The "other metal film" interposed between the Cu film and the platinum group metal film may consist of one layer or two or more layers. If there are two or more layers, it is preferable that the lattice mismatch between the lattice constant of Cu and the lattice constant of the platinum group metal constituting the platinum group metal film is 10% or less for each layer.

[0036] Examples of metals that constitute the aforementioned "other metal film" include platinum group metals, γ-Fe, Os, Co, and Hf. However, the material is not limited to these.

[0037] Examples of combinations of the platinum group metal of the platinum group metal film and the metal of the "other metal film" include Pt / Pd, Pt / Ir, Pt / Rh, Pt / γ-Fe, Pt / Os, Pt / Co, Pt / Hf, Ir / Rh, Ir / γ-Fe, Ir / Os, Ir / Co, Ir / Hf, Pd / Ir, Pd / Rh, Pd / γ-Fe, Pd / Os, Pd / Co, Pd / Hf, Rh / γ-Fe, Rh / Os, Rh / Co, Rh / Hf, etc. Of these, Pt / Pd, Pt / Ir, Pt / Rh, Pt / γ-Fe, Pt / Hf, Ir / γ-Fe, Ir / Hf, and more preferably Pt / Pd, Pt / γ-Fe, Pt / Hf, Ir / γ-Fe, Ir / Hf. From the perspective of heteroepitaxial growth, the order of layering should be such that the lattice constants of the layers approach that of diamond, in the order of copper, "other metal film," and then the platinum group metal film which forms the outermost layer for diamond growth. On the other hand, depending on the manufacturing conditions, the layering order may be arbitrary, without being bound by the above-mentioned order of lattice constants, in order to minimize crystal defects.

[0038] When the metal film layer consists of the platinum group metal film, the thickness of the metal film layer is the same as the thickness of the platinum group metal film. If the metal film layer includes "other metal films" other than the platinum group metal film, the thickness of the "other metal films" is preferably 1 nm or more from the viewpoint of film uniformity, more preferably 3 nm or more, and more preferably 5 nm or more. On the other hand, from the viewpoint of manufacturing cost, it is preferably 10 μm or less, more preferably 5 μm or less, and more preferably 1 μm or less. If there are two or more "other metal films," the thickness of each layer is the same as the thickness of the other metal films.

[0039] The thickness of each layer in the substrate of the present invention can be measured by cross-sectional scanning electron microscope (SEM), TEM, stylus step meter, spectroscopic ellipsometry, X-ray reflectivity measurement, quartz crystal oscillator, etc. However, the method is not limited to these.

[0040] (Off-angle of the outermost surface) The outermost surface of the substrate of the present invention preferably has an off-angle of ±15° or less, that is, an off-angle in the range of -15° to 15°. For example, if the outermost platinum group metal film is an Ir(111) film, it is preferable that the outermost main surface of the substrate has an off-angle of -15° to 15° in the direction of the crystal axis [-1-1 2] or in the direction of its threefold symmetry, with respect to the crystal plane orientation (111). If the outermost surface of the substrate of the present invention has the above-mentioned off-angle, step flow growth is easily achieved, and high-quality single-crystal diamond crystals with fewer hillocks, abnormally grown particles, and dislocation defects can be formed. Furthermore, since growth in the step direction is easily achieved, it can be said that good crystals are more likely to be obtained. From this viewpoint, the outermost surface of the substrate of the present invention is preferably in the range of -15° to 15°, and more preferably in the range of -10° or more or 10° or less, and more preferably in the range of -7° or more or 7° or less.

[0041] To adjust the off-angle of the outermost surface of the substrate of the present invention to a range of -15° to 15°, a Si substrate cut at a specific angle can be polished, etched, or annealed. However, the method is not limited to this.

[0042] (Shape and size) The shape of the substrate used in this invention is not particularly limited. Examples include a disc-shaped wafer, a rod-shaped rod, and a thinly sliced ​​plate. The size of the substrate used in this invention is not particularly limited. The diameter (also called the aperture) should be greater than or equal to the diameter of the diamond film to be grown.

[0043] From the viewpoint of mechanical strength, the thickness of the substrate of the present invention is preferably 10 μm or more, more preferably 50 μm or more, and more preferably 100 μm or more. On the other hand, from the viewpoint of manufacturing cost, it is preferably 1000 μm or less, more preferably 800 μm or less, and more preferably 600 μm or less.

[0044] <Method for manufacturing a substrate according to the present invention> The substrate of the present invention can be manufactured by forming a Cu film on a Si substrate made of single-crystal Si(100) or single-crystal Si(111), and then forming a metal film layer containing one or more metal films on the Cu film.

[0045] Si substrates made of single-crystal Si(100) or single-crystal Si(111) can be purchased and prepared.

[0046] To form a Cu film on a Si substrate, for example, the Cu film can be formed on the Si substrate by chemical vapor deposition or physical vapor deposition. However, the method is not limited to this.

[0047] When forming a metal film layer containing one or more metal films on a Cu film, if the metal film layer consists of a platinum group metal film, the platinum group metal film can be formed, for example, by chemical vapor deposition or physical vapor deposition. However, the method is not limited to this. Furthermore, if "other metal films" other than the platinum group metal film are to be provided, these "other metal films" may be formed on the Cu film by, for example, chemical vapor deposition or physical vapor deposition. However, the method is not limited to this.

[0048] Examples of the above-mentioned chemical vapor deposition include thermal CVD, catalytic chemical vapor deposition (Cat-CVD), photo-CVD, plasma CVD, epitaxial CVD, atomic layer deposition (ALD), metal-organic vapor deposition (MOCVD), and liquid-phase CVD. On the other hand, examples of the above physical deposition methods include resistance heating deposition, electron beam deposition, molecular beam epitaxy, ion plating, ion beam deposition, sputtering, pulsed laser deposition, and arc deposition.

[0049] It is preferable that the deposition rate of the Cu film and the platinum group metal film be less than 20 Å / s. When the material to be deposited, namely Cu or platinum group metals, slowly flies and deposits onto a Si substrate, Cu film, or "other metal film," it can move into a stable state during the deposition process, resulting in a smoother surface, fewer defects, and even higher crystallinity. From this viewpoint, it is preferable that the deposition rate of the Cu film and the platinum group metal film be less than 20 Å / s, and more preferably 15 Å / s or less, more preferably 13 Å / s or less, and more preferably 10 Å / s or less. However, from the viewpoint of manufacturing cost, it is preferable that the deposition rate of the Cu film and the platinum group metal film be 1 Å / s or more, and more preferably 3 Å / s or more, and more preferably 5 Å / s or more.

[0050] <Manufacturing method for diamond substrates> On the substrate of the present invention, a diamond film can be formed by heteroepitaxial growth of diamond using the CVD method, thereby manufacturing a diamond substrate (also referred to as "the diamond substrate of the present invention") consisting of a diamond film and the substrate of the present invention. Furthermore, when growing diamonds heteroepitaxially, if necessary, diamond nuclei may be formed on the surface film of the underlying substrate by bias treatment.

[0051] The aforementioned CVD method may be any of the following: microwave plasma CVD, DC plasma CVD, thermal filament CVD, and arc discharge plasma jet CVD. Among these, the diamond obtained by microwave plasma CVD or DC plasma CVD is preferred because it can form a high-quality single-crystal diamond film with high crystallinity, few hillocks, abnormally grown particles, and dislocation defects, and good impurity control.

[0052] The raw material gas used in the CVD method can be any raw material gas capable of forming a single-crystal diamond film. Currently, raw material gases known to be capable of forming single-crystal diamond films include carbon source gases, such as hydrocarbons, alcohols, ketones, and oxygen-containing compounds such as carbon dioxide, to which hydrogen gas is added. The carbon source gas can be one or more selected from the group consisting of hydrocarbons, alcohols, ketones, and oxygen-containing compounds such as carbon dioxide. Examples of hydrocarbons include methane gas, acetylene, ethylene, ethane, and propane. Examples of alcohols include methanol and ethanol. Examples of ketones include acetone. In this process, intentionally adding nitrogen or oxygen gas to the source gas can improve the rate of diamond film deposition. Furthermore, intentionally adding elemental sources such as B or N to the source gas can dope the synthesized diamond film with these elements. N-doped diamond, in particular, possesses unique luminescence centers and therefore has potential applications in quantum mechanics.

[0053] Examples of carrier gases used in the CVD method, that is, carrier gases mixed with the raw material gas to ensure uniform diffusion of the raw material gas, include hydrogen, oxygen, and nitrogen.

[0054] The apparatus and conditions for performing the CVD method can be those of known apparatus and methods. For example, when employing the microwave plasma CVD method, increasing the microwave output increases the plasma density, which in turn raises the temperature of the substrate exposed to the plasma. A higher temperature of the substrate promotes diamond film growth. On the other hand, if the temperature of the substrate becomes too high, graphite-like carbon components will form, reducing the crystallinity of the diamond film. Therefore, it is preferable to adjust the output of the microwave and other devices for each apparatus. Furthermore, the diamond film deposition substrate proposed in this invention is constructed by laminating each layer on a Si substrate, and since it does not require heating the substrate during the manufacturing process of the substrate and can be completed solely by a low-temperature process, it is expected that large-area deposition can be achieved at a relatively low cost. In this context, "heating the substrate" refers to intentionally heating the substrate itself, and does not include the substrate's temperature rising due to deposited materials or other factors. Furthermore, while heating the substrate is not always necessary, this does not preclude the possibility of doing so.

[0055] In Raman spectroscopy measurements, the diamond film exhibits diffraction peaks attributable to single-crystal diamond, such as 1330 cm⁻¹. -1 ±10cm -1 The half-width of the peak is 50cm -1 Preferably the following, especially 45 cm -1 Among them, 35cm -1 The following is even more preferable:

[0056] The lower limit of the diamond film thickness is preferably a thickness that does not disappear during etching or polishing when forming the device, and the upper limit of the thickness is preferably a thickness that does not result in any wasted material that is not used when forming the device. From this viewpoint, the thickness of the diamond film is preferably 1 μm or more, more preferably 5 μm or more, more preferably 10 μm or more, more preferably 50 μm or more, and more preferably 100 μm or more. On the other hand, it is preferably 800 μm or less, more preferably 700 μm or less, and more preferably 500 μm or less.

[0057] The diamond substrate of the present invention obtained as described above can also be used as a base substrate for forming a diamond film with a greater thickness. That is, a diamond substrate with an even thicker diamond film can be manufactured by further heteroepitaxially growing diamond on the diamond film of the diamond substrate of the present invention using the CVD method.

[0058] Furthermore, by removing the underlying substrate of the present invention from the diamond substrate of the present invention, a single-crystal diamond self-supporting substrate can be obtained. The single-crystal diamond self-supporting substrate obtained in this way reduces the sources of noise in actual use, thus enabling the realization of highly sensitive electronic and magnetic devices. The method for removing the substrate according to the present invention is not particularly limited. For example, mechanical treatment such as polishing, or wet or dry etching treatment may be selected as appropriate.

[0059] <Explanation of terms and phrases> In this invention, when "α~β" (where α and β are arbitrary numbers) is written, unless otherwise specified, it means "α or greater and β or less," and also includes the meaning of "preferably greater than α" or "preferably less than β." Furthermore, when written as "α or greater" or "α ≤" (where α is any number), unless otherwise specified, it includes the meaning of "preferably greater than α," and when written as "β or less" or "≤β" (where β is any number), unless otherwise specified, it also includes the meaning of "preferably less than β." [Examples]

[0060] The following describes an example of an embodiment of the present invention. However, the present invention is not limited to the embodiment described below.

[0061] [Example 1] As a base substrate, a substrate made of single-crystal Si (hereinafter referred to as "single-crystal Si(100) substrate") was prepared, measuring 10.0 mm square, with a thickness of 0.5 mm, and polished on one side with an off-angle of ±1° or less, and whose main surface is a (100) plane. The aforementioned off-angle is the off-angle of the surface of a single-crystal Si(100) substrate measured in X-ray diffraction analysis using a CuKα wavelength X-ray source.

[0062] On this single-crystal Si(100) substrate, Cu was deposited using electron beam evaporation at a deposition rate of 10 Å / s to form a Cu film with a thickness of 20 nm. Specifically, the single-crystal Si(100) substrate was set in a chamber, and a dry pump and a turbomolecular pump were used to deposit 1.0 × 10⁻¹⁶ -5The system was evacuated until the pressure dropped below Pa. Then, the distance between the deposition source and the substrate was maintained at 700 mm, and the Cu deposition source was irradiated with an electron beam without heating the substrate. In this process, the deposition rate of the Cu film was measured in real time using a film thickness gauge utilizing a quartz crystal oscillator, and the thickness of the Cu film was determined based on that value.

[0063] As described above, a single-crystal Si(100) substrate with a Cu film deposited on its surface was used to deposit a 20 nm thick Pd film by electron beam evaporation at a deposition rate of 10 Å / s without exposure to air. Subsequently, a 100 nm thick Pt film was formed by depositing Pt at a deposition rate of 5 Å / s. Thus, a diamond deposition substrate (sample) was prepared, consisting of a Cu film and two metal film layers (Pd film and Pt film) laminated on the single-crystal Si(100) substrate. In this case, the thickness of the Pd and Pt films was determined using the same method as for the Cu film.

[0064] X-ray diffraction analysis of the Pt film, which is the outermost layer of the aforementioned diamond deposition substrate (sample), using CuKα wavelength as the X-ray source revealed that the surface had a (100) plane. In addition, a 200 diffraction peak attributed to Pt(100) appeared at 2θ = 46.4°, with a full width at half maximum of 0.44°. Furthermore, the off-angle of the outermost surface layer of the diamond film deposition substrate (sample) is estimated to be ±1° or less, given that the off-angle of a single-crystal Si(100) substrate is ±1° or less.

[0065] Next, diamond was grown on a base substrate (sample) for diamond deposition using microwave plasma CVD. Specifically, a diamond film deposition substrate (sample) is placed inside the chamber, and a rotary pump is used to... -2Vacuum evacuation was carried out until the pressure reached below Pa, and hydrogen gas and methane gas were introduced into the chamber at a flow rate of 10:1 vol% and a total of 110 sccm. After the gas introduction, the output of the microwave was set to 1.0 kW to confirm the generation of plasma, and then the opening degree of the valve leading to the rotary pump was adjusted to set the pressure to 200 Pa. Thereafter, film deposition was carried out for 30 minutes with the microwave output set to 1.5 kW, and nucleation was confirmed using an optical microscope (see Figure 1). After confirming nucleation, film deposition was further carried out for 1.5 hours with the microwave output set to 1.5 kW to form a diamond film with a thickness of 5 μm on the underlying substrate (sample). At this time, the thickness of the diamond film was determined based on the film deposition rate per hour. Specifically, the underlying substrate on which the diamond film was deposited was divided, and the cross-section was observed with a scanning electron microscope to measure the film thickness of the diamond film and determine the film deposition rate.

[0066] Regarding the obtained diamond film, Raman spectroscopic measurement was carried out using a laser beam with an excitation length of 512 nm. As a result, a Raman peak was confirmed at 1330 cm -1 attributed to diamond, and its full width at half maximum was 7.79 cm -1 (see Figure 2).

[0067] [Example 2] Plasma was generated on the underlying substrate (sample) for diamond film deposition obtained in Example 1 under the same conditions as in Example 1, and the pressure was set to 200 Pa. Thereafter, film deposition was carried out for 30 minutes with the microwave output set to 1.75 kW, and nucleation was confirmed using an optical microscope (see Figure 1). After confirming nucleation, film deposition was further carried out for 1.5 hours with the microwave output set to 1.75 kW to obtain a diamond film with a thickness of 10 μm on the underlying substrate. At this time, the thickness of the diamond film was determined in the same manner as in Example 1.

[0068] Regarding the obtained diamond film, Raman spectroscopic measurement was carried out. As a result, a Raman peak was confirmed at 1331 cm -1 attributed to diamond, and its full width at half maximum was 8.11 cm -1 (see Figure 2).

[0069] [Comparative Example 1] In Example 1, a base substrate (sample) for diamond film deposition was prepared in the same manner as in Example 1, except that the film deposition time of the electron beam evaporation method was extended to set the thickness of the Cu film to 100 nm. The off-angle of the outermost surface layer of the diamond film deposition substrate (sample) is estimated to be ±1° or less, based on the fact that the off-angle of a single-crystal Si(100) substrate is ±1° or less.

[0070] On the diamond film deposition substrate (sample) prepared as described above, we attempted to fabricate a diamond film in the same manner as in Example 1. However, during diamond film fabrication, the metal film layer and Cu film peeled off from the single-crystal Si(100) substrate, and a diamond film could not be obtained (see Figure 1).

[0071] <Result> In Examples 1 and 2, optical microscopy and Raman spectroscopy measurements confirmed the formation of a diamond film on the diamond deposition substrate. On the other hand, no diamond film was observed on the thick Cu film substrate of Comparative Example 1.

[0072] <Consideration> Comparing Examples 1 and 2 with Comparative Example 1, it was found that a thinner Cu film deposited on the Si substrate prevented peeling during CVD processing, allowing the diamond film to grow more effectively. Therefore, it was determined that the Cu film thickness must be at least less than 100 nm. This is presumed to be because the difference in thermal expansion coefficients between Si and Cu is large, and if the Cu film is too thick, extremely large stresses will be generated between the two materials as the temperature rises during CVD processing.

[0073] Comparing Examples 1 and 2 (Figure 2), the full width at half maximum of the peak attributed to diamond obtained from Raman spectroscopy measurements was smaller for the diamond film obtained in Example 1 than for the diamond film obtained in Example 2. This indicates that the crystallinity of the resulting diamond film can be improved by controlling the amount of power applied, i.e., the plasma density and substrate temperature.

[0074] From the above examples, it was confirmed that a diamond film can be directly deposited on a substrate by using a substrate with a structure in which metal film layers containing a Cu film and a metal film are sequentially stacked on a Si substrate. Since large Si substrates can be selected and used, it is possible to grow diamond films over large areas, making it applicable to semiconductor fields and other areas where large-area production is required. Furthermore, the diamond film deposition substrate fabricated in the example does not require heating of the substrate, unlike conventional substrates in which a platinum group metal film is laminated on a Si substrate via an oxide layer. This allows for lower temperatures in the fabrication process and eliminates the need for equipment required for depositing the oxide layer. Furthermore, it is presumed that if elemental sources such as B and N are intentionally added to the raw material gas, these elements will be doped into the synthesized diamond film. In particular, N-doped diamond has a unique luminescence center and can therefore be applied to quantum fields.

Claims

1. A base substrate for forming a diamond film by CVD, The structure comprises a Cu film on a Si substrate made of single-crystal Si (100) or single-crystal Si (111), and a metal film layer containing one or more metal films on the Cu film. The outermost layer of the metal film layer is a platinum group metal film made of one or more platinum group metals selected from Ir, Pt, Pd, and Rh. A base substrate for diamond film deposition, characterized in that the thickness of the Cu film is 1 nm or more and less than 100 nm.

2. The diamond film deposition substrate according to claim 1, wherein the outermost layer of the metal film layer is a platinum group metal film selected from Ir(100) film, Ir(111) film, Pt(100) film, Pt(111) film, Pd(100) film, Pd(111) film, Rh(100) film, and Rh(111) film.

3. The outermost layer of the metal film layer has a full width at half maximum of 0.6° or less in X-ray diffraction analysis using wavelength CuKα as the X-ray source, wherein the diffraction peaks attributed to (100) or (111) are 0.6° or less, as described in claim 2.

4. The diamond film deposition substrate according to claim 1, comprising one or more layers of a metal film between the Cu film and the platinum group metal film, wherein the lattice mismatch between the Cu film and the platinum group metal film is 10% or less.

5. The base substrate for diamond film deposition according to claim 1, wherein the off-angle of the surface layer determined by X-ray diffraction analysis using wavelength CuKα as the X-ray source is ±15° or less.

6. A method for manufacturing a base substrate for diamond film deposition according to any one of claims 1 to 5, A method for manufacturing a substrate for diamond film deposition, characterized in that the deposition rate of the Cu film and the platinum group metal film is less than 20 Å / s.

7. A method for manufacturing a diamond substrate, characterized by forming a diamond film on a diamond film deposition substrate according to any one of claims 1 to 5 by heteroepitaxial growth of diamond using a raw material gas containing a carbon source gas and hydrogen gas, using one of the following CVD methods: microwave plasma CVD, DC plasma CVD, thermal filament CVD, and arc discharge plasma jet CVD.

8. A method for manufacturing a single-crystal diamond self-supporting substrate, characterized by removing the underlayment substrate from a diamond substrate obtained by the manufacturing method described in claim 7 to obtain a single-crystal diamond self-supporting substrate.

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