Diamond substrate, method for producing same, and sensor

Abstract

The present invention provides a method for producing a diamond substrate by forming a diamond crystal on a base substrate by a CVD method, wherein in order to form an NVC-containing diamond crystal layer on at least a part of the diamond crystal, a starting material gas contains 0.005% to 7.000% by volume inclusive of a hydrocarbon gas, 85.000% by volume or more but less than 99.995% by volume of a hydrogen gas, and 5.0 × 10-5% to 8.000% by volume inclusive of a nitrogen gas or a nitride gas, and a 12C concentrated hydrocarbon gas which has a higher ratio of a 12C constituent hydrocarbon gas than a natural hydrocarbon gas is used as the hydrocarbon gas in the starting material gas. As a result, the present invention provides a method for producing a diamond substrate, with which it is possible to form a diamond crystal that has a high orientation in the NV axis (for example, high [111] orientation) and high-density nitrogen-vacancy centers (NVC) with a single spin by performing CVD on the base substrate under prescribed conditions.

Description

Diamond substrate, manufacturing method thereof, and sensor

[0001] The present invention relates to a diamond substrate, a method for manufacturing the same, and a sensor.

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

[0003] Among wide bandgap semiconductors, diamond has an extremely high breakdown field strength of 10 MV / cm, enabling high-voltage operation. It also has the highest thermal conductivity of any known material, making it excellent for heat dissipation. Furthermore, its extremely high carrier mobility and saturated drift velocity make it suitable for high-speed devices.

[0004] For this reason, diamond has the highest Johnson figure of merit, which indicates the performance of high-frequency, high-power devices, compared to semiconductors such as silicon carbide and gallium nitride, and is said to be the ultimate semiconductor.

[0005] Furthermore, diamond has the unique property of being able to manipulate and detect single spins at room temperature due to the nitrogen-vacancy center (NVC) phenomenon present in the crystal, and this state can be imaged using optically detected magnetic resonance. Utilizing this property, diamond is expected to be applied in a wide range of fields as a highly sensitive sensor for magnetic fields, electric fields, temperature, pressure, and other phenomena.

[0006] US2013 / 0143022A1

[0007] M. Hatano et al. , OYOBUTURI 85, 311 (2016) T. Fukui, et al. , APEX 7, 055201 (2014). H. Ozawa, et. al. , NDF Dia. Symp. 29, 16 (2015).

[0008] As mentioned above, diamond is expected to be put to practical use as a semiconductor material and a material for electronic and magnetic devices, and the supply of large-area, high-quality diamond substrates is desired. For example, Patent Document 1 reports a technology for forming diamond (111) crystals by heteroepitaxial growth using chemical vapor deposition. Furthermore, particularly for NVC device applications, which are highly important among diamond applications, a high orientation of the nitrogen-vacancy axis (NV axis) is required. Therefore, it is desirable for the diamond surface to have a (111) crystal plane in which the NV axis is aligned in the

[111] direction (Non-Patent Document 1). Furthermore, considering applications in the medical MRI field, for example, a large-diameter diamond substrate serving as a magnetic sensor would enable the realization of a device that can efficiently measure a wider area. This is also advantageous in terms of manufacturing costs.

[0009] Furthermore, when the diamond substrate is used in an electronic or magnetic device, the sensor portion must not only have the NV axis aligned in the

[111] direction in the diamond crystal, but also must be formed with high density.

[0010] The preparation of

[111] -oriented high-density NVC-forming diamond crystals has been reported so far as follows. It has been studied by using a single-crystal diamond synthesized by high-pressure high-temperature synthesis (HPHT) as a base substrate and growing it by microwave chemical vapor deposition (CVD) with the addition of nitrogen to hydrogen-diluted methane (Non-Patent Documents 2 and 3). However, in the reported documents, only HPHTIb (111), which is difficult to obtain in large sizes in practice, is used as the base substrate, and furthermore, in Non-Patent Document 2, the details of the gas composition in CVD are unclear. Furthermore, in Non-Patent Document 3, it is unclear whether the CVD conditions in the document are optimized.

[0011] The present invention has been made to solve the above problems, and aims to provide a method for manufacturing a diamond substrate that can form diamond crystals on a base substrate by performing CVD under specified conditions, with the diamond crystals having a high NV axis orientation (e.g., a high

[111] orientation) and a high density of single-spin nitrogen-vacancy centers (NVCs). Another aim of the present invention is to provide such a diamond substrate. A further aim of the present invention is to provide a sensor that uses a diamond substrate containing the NVCs.

[0012] In order to achieve the above object, the present invention provides a method for manufacturing a diamond substrate by forming a diamond crystal on a starting substrate by chemical vapor deposition (CVD) using a source gas containing a hydrocarbon gas and hydrogen gas as a diluent gas, wherein nitrogen gas or a nitride gas is mixed into the source gas to form a diamond crystal layer having a nitrogen vacancy center in at least a part of the diamond crystal formed on the starting substrate, and the amount of each gas contained in the source gas is set as follows: the amount of hydrocarbon gas is 0.005 vol% or more and 7.000 vol% or less, the amount of hydrogen gas is 85.000 vol% or more and less than 99.995 vol%, and the amount of nitrogen gas or nitride gas is 5.0 × 10 －５ % or more and 8,000 vol % or less to form a diamond crystal layer having the nitrogen vacancy center, and １２ The ratio of hydrocarbon gas composed of C is higher than that in natural hydrocarbon gas. １２ A method for producing a diamond substrate is provided, characterized by using a C-enriched hydrocarbon gas.

[0013] According to the manufacturing method of the diamond substrate under such CVD conditions, it is possible to manufacture a diamond substrate having a diamond crystal layer formed thereon, which has high crystallinity, high orientation of the NV axis (particularly high orientation of

[111] ), and high density NVC with single spin. Such diamond crystals can be suitable for electronic and magnetic devices.

[0014] In this case, the source gas may further contain oxygen gas or oxide gas in an amount of 0.010% by volume or more and 2.000% by volume or less.

[0015] In this way, the effect of oxygen etching to remove non-diamond components can be adequately obtained, and the orientation of the diamond crystals can be further improved.

[0016] The hydrocarbon gas in the source gas may be methane gas.

[0017] The use of methane gas is preferable because it is a highly pure gas that is readily available at low cost and is easy to handle.

[0018] The gas pressure during the formation of diamond crystals by the CVD method can be set to 1.3 kPa (10 Torr) or more and 50.0 kPa (376 Torr) or less.

[0019] Under such gas pressure conditions, the growth of non-single-crystal diamond is more effectively suppressed, and a single-crystal diamond having high crystallinity is obtained.

[0020] In addition, the above １２ C-enriched hydrocarbon gas １２ in C-enriched hydrocarbon gas １２ The volume ratio of the hydrocarbon gas composed of C can be 99.950% by volume or more.

[0021] This is highly effective in forming high density NVCs with a single spin.

[0022] In addition, the above １２ C-enriched hydrocarbon gas １２ in C-enriched hydrocarbon gas １３ The volume ratio of the hydrocarbon gas composed of C can be 0.040% by volume or less.

[0023] This is more effective in forming high density NVCs with a single spin.

[0024] The base substrate may be a single-layer substrate of single-crystal diamond.

[0025] By adopting single crystal diamond as starting substrate in this way, it is possible to form the NV axis of NVC-containing diamond crystal more effectively with high orientation (particularly

[111] high orientation) and high density.By using this single crystal diamond (particularly single crystal diamond (111)) as starting substrate, it is easy to carry out step flow growth, and it is possible to form high-quality single crystal diamond with less hillocks, abnormally grown grains, dislocation defects, etc.

[0026] The single-layer substrate of single-crystal diamond may be any of a high-temperature, high-pressure synthetic single-crystal diamond layer, a heteroepitaxial single-crystal diamond layer, and a CVD synthetic homoepitaxial diamond layer.

[0027] Substrates made of these single crystal diamond layers can be suitably employed as the base substrate in the method for manufacturing a diamond substrate of the present invention.

[0028] Furthermore, in forming diamond crystals by the CVD method, when a diamond crystal layer that does not contain nitrogen vacancy centers is formed, natural hydrocarbon gas can be used.

[0029] This makes it possible to further reduce manufacturing costs.

[0030] The base substrate may have a laminated structure consisting of a lower layer substrate and an intermediate layer on the lower layer substrate.

[0031] In the present invention, a substrate having such a laminated structure can also be employed.

[0032] In this case, the outermost surface of the intermediate layer may be a metal layer selected from Ir, Rh, Pd and Pt.

[0033] By forming the outermost surface of the intermediate layer with such a type of metal layer, the diamond nuclei tend to have a high density when subjected to nucleation treatment (bias treatment), making it easier for a single crystal diamond layer to form thereon.

[0034] The CVD method may be one or more of microwave plasma CVD, direct current plasma CVD, hot filament CVD, and arc discharge plasma jet CVD.

[0035] One of these CVD methods can be suitably used, or a combination of two or more of them can be used.

[0036] Furthermore, the present invention can also obtain a single-crystal diamond freestanding substrate comprising a diamond crystal layer having the nitrogen vacancy center by removing the base substrate from the diamond substrate comprising the diamond crystal layer having the nitrogen vacancy center obtained by the above-mentioned method for manufacturing a diamond substrate.

[0037] This makes it possible to obtain a single-crystal diamond freestanding substrate including a diamond crystal layer having high crystallinity, a high orientation of the NV axis (particularly a high

[111] orientation), and a high density of NVC with a single spin, which is applicable to electronic and magnetic devices.

[0038] Furthermore, the surface of the diamond crystal layer having the nitrogen vacancy center of the diamond substrate obtained by the above-described method for manufacturing a diamond substrate and including the diamond crystal layer having the nitrogen vacancy center can be smoothed.

[0039] This suppresses diffuse reflection of light on the surface of the diamond crystal layer having NVC, and the NVC that can be extracted is － The center light can be increased.

[0040] The present invention also provides a diamond substrate including a diamond crystal layer having a nitrogen vacancy center, wherein the diamond crystal layer having the nitrogen vacancy center is formed on a diamond crystal layer not including a nitrogen vacancy center or a single-layer substrate of a single crystal diamond, and wherein the carbon atoms present in the diamond crystal layer having the nitrogen vacancy center are each an isotope of carbon. １２The present invention provides a diamond substrate characterized in that the abundance ratio of C is higher than the abundance ratio of natural carbon atoms, and the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy centers is steep in the interface region with the diamond crystal layer not containing the nitrogen vacancy centers or with the single-layer substrate of single-crystal diamond.

[0041] Such diamond substrates have high crystallinity, high NV axis orientation (especially

[111] highly oriented), and high density of single-spin NVCs, making them suitable for use in electronic and magnetic devices.

[0042] In particular, the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy center is measured by a secondary ion mass spectrometer using the primary ion species Cs + When measured at a primary acceleration voltage of 16.0 kV and a detection area diameter of 30 μm, it is preferable that the thickness of the descending area, at the interface area of ​​the diamond crystal layer or single crystal diamond not containing the nitrogen vacancy center with the single layer substrate, until the nitrogen concentration [N] reaches 1 / e (Napier's number) times, is 1.5 μm or less.

[0043] By having such a physical property that the nitrogen concentration drops sharply in the interface region between the layer with NVC and the layer without NVC, it is possible to obtain a diamond substrate having NVC-containing diamond crystals with better properties.

[0044] Furthermore, the hydrogen concentration [H] in the diamond crystal layer having the nitrogen vacancy center is 1×10 １６ atoms / cm ３ The above may be the case.

[0045] Among the diamond growth methods, when the CVD method is used, the hydrogen concentration in the diamond crystal layer is relatively high, unlike high-temperature, high-pressure synthetic diamond.

[0046] The nitrogen concentration [N] in the diamond crystal layer having the nitrogen vacancy center is 1×10 １７ atoms / cm ３ ≦[N]≦9×10 １９ atoms / cm ３It can be assumed that:

[0047] A diamond substrate having a nitrogen concentration in this range can have NVC-containing diamond crystals with better properties.

[0048] The average surface roughness Ra of the surface of the diamond crystal layer having the nitrogen vacancy centers is preferably Ra≦260 nm.

[0049] With such surface roughness, diffuse reflection of light on the surface of the diamond crystal layer having NVC is suppressed, and the NVC that can be extracted is reduced. － The center light can be increased.

[0050] The present invention also provides a sensor using the diamond substrate described above.

[0051] The sensor using the diamond substrate of the present invention is highly sensitive and excellent.

[0052] According to the manufacturing method of the diamond substrate of the present invention, it is possible to manufacture a diamond substrate having a diamond crystal layer formed thereon, which has high crystallinity, a high NV axis orientation (particularly a high

[111] orientation), and a single spin and high density NVC. Such diamond crystals can be suitable for electronic and magnetic devices. Furthermore, according to the diamond substrate of the present invention, it is possible to provide a diamond substrate that is highly crystallinity, a high

[111] orientation of the NV axis, and a single spin and high density NVC, which can be applied to electronic and magnetic devices. Furthermore, according to the sensor of the present invention, it is possible to make a highly sensitive and excellent sensor.

[0053] FIG. 1 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / NVC-free single layer substrate) of the present invention. FIG. 2 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / NVC-free layer / underlying substrate with a laminated structure) of the present invention. FIG. 3 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / underlying substrate) manufactured by the method for manufacturing a diamond substrate of the present invention. FIG. 4 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / underlying substrate with a laminated structure) manufactured by the method for manufacturing a diamond substrate of the present invention. FIG. 5 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / NVC-free layer / underlying substrate with a laminated structure) manufactured by the method for manufacturing a diamond substrate of the present invention. FIG. 6 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / NVC-free layer / underlying substrate with a laminated structure) manufactured by the method for manufacturing a diamond substrate of the present invention. FIG. 7 is a schematic diagram showing an example of a single-crystal diamond freestanding substrate (NVC-containing layer / NVC-free layer) obtained by the method for manufacturing a diamond substrate of the present invention. FIG. 8 is a graph showing the results of SIMS measurement in Example 1.

[0054] The present invention will be described in detail below, but is not limited thereto. As described above, there has been a need to obtain a diamond substrate suitable for electronic and magnetic devices, which has a large diameter (large aperture), high crystallinity, a high orientation of the NV axis (for example, a high

[111] orientation), and a high density of NVC with a single spin.

[0055] As a result of intensive research into the above-mentioned problems, the present inventors have discovered a method for producing a diamond substrate by CVD, in which a source gas containing a hydrocarbon gas and hydrogen gas as a diluent gas is used to form a diamond crystal layer having a nitrogen vacancy center on at least a part of the diamond crystal formed on the source substrate, by mixing nitrogen gas or a nitride gas into the source gas, and adjusting the amounts of the gases contained in the source gas to 0.005% by volume or more and 7.000% by volume or less for the hydrocarbon gas, 85.000% by volume or more and less than 99.995% by volume or more for the hydrogen gas, and 5.0×10 －５ % or more and 8,000% or less by volume to form a diamond crystal layer having the nitrogen vacancy center, and １２ The ratio of hydrocarbon gas composed of C is higher than that in natural hydrocarbon gas.１２ We have found that a diamond substrate manufacturing method using a C-enriched hydrocarbon gas can produce a diamond substrate with high crystallinity, a high NV axis orientation (high

[111] orientation), and a high density NVC with a single spin, and have completed the present invention.

[0056] Also, a diamond substrate including a diamond crystal layer having a nitrogen vacancy center, wherein the diamond crystal layer having the nitrogen vacancy center is formed on a diamond crystal layer not including a nitrogen vacancy center or a single-layer substrate of a single crystal diamond, and a carbon isotope, １２ The inventors have found that the above-mentioned problems can be similarly solved by a diamond substrate in which the abundance ratio of C is higher than the abundance ratio of natural carbon atoms, and in which the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy centers is steep in the interface region with the diamond crystal layer not containing the nitrogen vacancy centers or with the single-layer substrate of single-crystal diamond, and have completed the present invention.

[0057] In this specification, for the sake of simplicity, the diamond crystal layer that has nitrogen vacancy center (NVC) can be referred to as NVC-containing layer, the diamond crystal layer that does not contain NVC can be referred to as NVC-free layer, and the single-layer substrate of single-crystal diamond that does not contain NVC can be referred to as NVC-free single-layer substrate.In addition, with regard to these above-mentioned layer and substrate, the following will be explained by taking as an example the diamond crystal layer and single-layer substrate that main surface is (111) (also referred to as single-crystal diamond (111) layer and single-crystal diamond (111) substrate, respectively), but the present invention is not limited thereto.

[0058] (Diamond substrate and sensor of the present invention) The diamond substrate of the present invention will be described. The diamond substrate of the present invention is a diamond substrate including an NVC-containing layer, and the NVC-containing layer is formed on an NVC-free single-layer substrate or an NVC-free layer.

[0059] (First embodiment) First, the former example will be described with reference to Fig. 1. As shown in Fig. 1, in the diamond substrate 100 of the present invention, an NVC-containing layer 12 is formed on a base substrate 11, which is an NVC-free single-layer substrate (single-crystal diamond (111) substrate). In the NVC-containing layer 12, the carbon atoms present in the NVC-containing layer 12 contain an NVC-containing isotope, １２ The abundance ratio of carbon is higher than that of natural carbon atoms. １２ C is 98.89%, １３ On the other hand, the NVC-free single layer substrate of the base substrate 11 has a C content of 1.11%. １２ The abundance ratio of C is not particularly limited, but it can be set to the same extent as the abundance ratio of the above-mentioned natural carbon atoms.

[0060] The nitrogen concentration profile in the NVC-containing layer 12 is steep in the interface region with the base substrate 11, and changes sharply downward from the NVC-containing layer 12 side toward the base substrate 11 side. The specific degree of this steepness can be determined, for example, by measuring the nitrogen concentration profile in the NVC-containing layer 12 using a secondary ion mass spectrometry (SIMS) device and determining the concentration of primary ions Cs + When measured at a primary acceleration voltage of 16.0 kV and a detection area diameter of 30 μm, the thickness of the descending region in the interface region until the nitrogen concentration [N] reaches 1 / e (Napier's number) times is 1.5 μm or less. The smaller the thickness of this descending region exhibiting steepness, the better, and the lower limit is not particularly limited, but can be, for example, 1.0 μm, and more preferably 0.5 μm. An example of a secondary ion mass spectrometer is the CAMECA IMS-7f (manufactured by Ametec Co., Ltd.).

[0061] The diamond substrate 100 of the present invention has high crystallinity, a high

[111] orientation of the NV axis, and high density NVCs with a single spin, and is therefore applicable to electronic and magnetic devices.

[0062] Here, the NVC-containing layer 12 was analyzed by the SIMS apparatus CAMECA IMS-7f using the primary ion species Cs ＋ When measured at a primary acceleration voltage of 16.0 kV and a detection area diameter of 30 μm, the hydrogen concentration [H] was 1×10 １６ atoms / cm ３ As will be described later, in the case of a layer formed by a CVD method, the layer will have a relatively high hydrogen concentration. The upper limit of the hydrogen concentration is not particularly limited, but may be, for example, 1×10 １８ atoms / cm ３ It can be said that:

[0063] In addition, the nitrogen concentration [N] in the NVC-containing layer 12 is 1×10 １７ atoms / cm ３ ≦[N]≦9×10 １９ atoms / cm ３ By having such a nitrogen concentration, it is possible to obtain a diamond substrate having an NVC-containing layer with better properties.

[0064] In addition, when the average surface roughness Ra of the surface of the NVC-containing layer is 260 nm or less, diffuse reflection of light is suppressed, and the NV that can be extracted is － This is preferable because it can increase the center light. The smaller the average surface roughness Ra, the better, due to the diffuse reflection of light mentioned above. Therefore, it cannot be limited, but it can be set to, for example, 200 nm. The average surface roughness Ra can be measured, for example, by the following method. (Measurement Method) An atomic force microscope (AFM) analyzer, such as a NanoScope V / Dimension Icon manufactured by Bruker AXS, is used to measure an area of ​​80 μm × 80 μm in tapping mode.

[0065] (Second embodiment) Next, the latter example will be explained with reference to FIG. 2. As shown in FIG. 2, in the diamond substrate 200 of the present invention, an NVC-free layer 23 is formed on a base substrate 21, and an NVC-containing layer 22 is formed on the NVC-free layer 23. The base substrate 21 is not particularly limited, and can be an NVC-free single-layer substrate like the diamond substrate 100 in FIG. 1, but it can also be a laminated structure consisting of a lower substrate 24 and an intermediate layer 25 thereon, as shown in FIG. 2. For example, the lower substrate 24 can be a single-crystal MgO substrate. The intermediate layer 25 can be a single layer or a laminate of multiple layers. The outermost surface of the intermediate layer 25 can be a metal layer selected from Ir, Rh, Pd, and Pt. As for the NVC-free layer 23, １２ The abundance ratio of C is not particularly limited, but may be, for example, approximately the same as the abundance ratio of natural carbon atoms.

[0066] The steepness and degree of the nitrogen concentration profile in the NVC-containing layer 22 at the interface region with the non-NVC-containing layer 23 can be similar to the steepness and degree of the NVC-containing layer 12 at the interface region with the base substrate 11 in the above-mentioned Fig. 1. In addition, the ranges of the hydrogen concentration and nitrogen concentration in the NVC-containing layer 22 and the range of the average surface roughness Ra of the surface can also be similar to those parameters in the NVC-containing layer 12 in Fig. 1.

[0067] Such a diamond substrate 200 also has high crystallinity, the NV axis is highly oriented in the

[111] direction, and has a high density of NVC with a single spin, making it suitable for electronic and magnetic devices.

[0068] The various sensors of the present invention using the diamond substrates 100 and 200 of the present invention include, for example, current, temperature and biomagnetic sensors, each of which is highly sensitive and excellent.

[0069] (Method for manufacturing a diamond substrate according to the present invention) Next, the method for manufacturing a diamond substrate according to the present invention will be described. An outline will be first explained. A diamond substrate is manufactured by forming diamond crystals on a base substrate using a source gas containing a hydrocarbon gas and hydrogen gas as a dilution gas by a CVD method. Examples of this CVD (chemical vapor deposition) method include microwave plasma CVD, direct current plasma CVD, hot filament CVD, and arc discharge plasma jet CVD. Among these, the diamond obtained by microwave plasma CVD and direct current plasma CVD is a high-quality single-crystal diamond with high crystallinity, few hillocks, abnormally grown grains, and dislocation defects, and good impurity controllability. Furthermore, CVD may be performed by combining multiple of the above CVD methods. For example, by combining a direct current plasma CVD method with a microwave plasma CVD method, it is possible to simultaneously perform diamond nucleation and film growth. By combining a direct current plasma CVD method with a hot filament CVD method, it is possible to simultaneously perform diamond nucleation and large-area film growth. In this case, in order to form an NVC-containing layer on at least a portion of the diamond crystal, at least nitrogen gas or nitride gas is mixed into the raw material gas (oxygen gas or oxide gas may be further mixed if necessary), and the amount of each gas (hydrocarbon gas, hydrogen gas, nitrogen gas or nitride gas (and also oxygen gas or oxide gas)) contained in the raw material gas is limited to a predetermined range as described below. Furthermore, the hydrocarbon gas in the raw material gas may contain carbon isotopes, １２ The ratio of hydrocarbon gas composed of C is higher than that in natural hydrocarbon gas. １２ C-enriched hydrocarbon gas is used.

[0070] This will be described in further detail below. (First manufacturing mode) In order to form the NV axis with a high

[111] orientation and high density, it is preferable to use a single-layer substrate of single-crystal diamond as the base substrate, and in particular, epitaxial growth using single-crystal diamond (111) as the base substrate is preferable. Figure 3 shows a diamond substrate 300 in which an NVC-containing layer 32 is formed on a base substrate 31. Referring to Figure 3, it is preferable to use a single-layer substrate of single-crystal diamond, in particular single-crystal diamond (111), as the base substrate 31.

[0071] Furthermore, the single-layer substrate of single-crystal diamond used as the starting substrate 31 can be any one of a high-temperature, high-pressure synthetic single-crystal diamond layer, a heteroepitaxial single-crystal diamond layer, and a CVD synthetic homoepitaxial diamond layer. In the manufacturing method of the present invention, these single-crystal diamonds can be suitably used as the starting substrate 31.

[0072] As the source gas for forming the NVC-containing layer 32, hydrocarbon gases such as methane gas, acetylene, ethylene, ethane, and propane can be used, but methane gas is preferred because it is a highly pure gas that is readily available at low cost and is easy to handle.

[0073] If the amount of hydrocarbon gas such as methane gas is less than 0.005 vol%, the etching effect of hydrogen is high, and diamond cannot grow, so the range of hydrocarbon gas amount should be 0.005 vol% or more, more preferably 0.01% or more, and most preferably 0.05 vol% or more.On the other hand, if the amount of hydrocarbon gas is more than 7.000 vol%, diamond will become polycrystallized when growing for a long time, and therefore good single crystal cannot be obtained, so the range should be 7.000 vol% or less, preferably 6.5 vol% or less, and more preferably 6.0 vol% or less.

[0074] In addition, in this raw material gas, the amount of nitrogen gas or nitride gas is 5.0 × 10 －５ If the nitrogen doping amount is less than 5.0×10 vol%, the diamond crystal will be doped with too little nitrogen, resulting in a low NVC density. －５% by volume or more, preferably 5.0 × 10 －４ % by volume or more, more preferably 1.0 × 10 －３ % or more by volume. On the other hand, if the amount of nitrogen gas or nitride gas exceeds 8.000% by volume, diamond will become polycrystalline if grown for a long time, and therefore good quality single crystal cannot be obtained. Therefore, the amount of nitrogen gas or nitride gas should be 8.000% by volume or less, and more preferably 0.500% by volume or less. As nitride gas, ammonia, nitric oxide, nitrogen dioxide, etc. can be used, but nitrogen gas is preferred because high purity gas is cheap and easy to obtain and easy to handle.

[0075] In addition, adding oxygen gas or oxide gas is preferable because it can remove non-diamond components and further improve the orientation of diamond crystal.When adding oxygen gas or oxide gas, by making it 0.010 volume % or more, it can obtain a moderate oxygen etching effect.On the other hand, by making it 2.000 volume % or less, it can effectively prevent the etching effect of oxygen from being too large and diamond growth from being stopped.

[0076] The hydrogen gas used as the dilution gas is preferably 85.000% by volume or more and less than 99.995% by volume.

[0077] At this time, when the gas pressure in forming diamond crystal by each CVD method is set to be 1.3kPa (10Torr) or more and 50.0kPa (376Torr) or less, it can effectively prevent diamond from polycrystallizing, so can obtain good quality single crystal.In order to effectively prevent that the gas pressure is too low, it is difficult to generate discharge, and plasma density is too low, so that it is impossible to obtain good quality single crystal diamond, the gas pressure is set to the lower limit as above, and more preferably the range is 12.0kPa (90Torr) or more.On the other hand, in order to effectively prevent that the gas pressure is too high, it is difficult to generate discharge, and the crystallinity is reduced due to high temperature, and the range of diamond formation is reduced, so it is set to the upper limit as above, and more preferably the range is 33.3kPa (250Torr) or less.

[0078] In addition, the hydrocarbon gas in the source gas in the CVD method is a carbon isotope, carbon-12 ( １２ C) The ratio of hydrocarbon gases composed of isotopes is higher than that in natural hydrocarbon gases. １２ The use of C-enriched hydrocarbon gas allows for the formation of high-density NVCs, which allows for the realization of highly sensitive sensors (such as magnetic sensors). Here, the ratio in natural hydrocarbon gas is: １２ The ratio of hydrocarbon gas composed of C is 98.89%, １３ The ratio of the hydrocarbon gas composed of C is 1.11% (for example, volume ratio). １２ By using C-enriched hydrocarbon gas, １２ It is also possible to form diamond crystals in which the abundance of C is higher than the abundance of natural carbon atoms.

[0079] The aforementioned １２ In C-enriched hydrocarbon gas, １２ Using a hydrocarbon gas consisting of C with a volume ratio of 99.950% or more (100% or less) is more effective in forming a single-spin, high-density NVC. １２ The second most common after C １３ Reducing the amount of hydrocarbon gas composed of C is also effective in forming higher density NVCs. １２ Among C-enriched hydrocarbon gases, especially １３ Setting the hydrocarbon gas composed of C to 0.040% by volume or less (0% by volume or more) is also effective enough to form high density NVCs with a single spin. １２ in C-enriched hydrocarbon gas １２ Hydrocarbon gas composed of C １３ The volume percentage of the hydrocarbon gas composed of C can be adjusted by using, for example, each commercially available gas with high purity.

[0080] When the diamond substrate 300 shown in FIG. 3 is manufactured using an NVC-free single-layer substrate as the base substrate 31, it is possible to manufacture a substrate similar to the diamond substrate 100 shown in FIG.

[0081] In this way, it is possible to manufacture a diamond substrate having a diamond crystal layer with high crystallinity, a high

[111] orientation of the NV axis, and a single spin and high density NVC, which is suitable as a substrate for various devices (sensor substrates).

[0082] (Second manufacturing mode) Furthermore, in the manufacturing method of the diamond substrate of the present invention, the base substrate may be a laminated structure consisting of a base substrate and an intermediate layer on the base substrate. Figure 4 shows a diamond substrate 400 in which an NVC-containing layer is formed on a laminated structure base substrate. That is, the diamond substrate 400 in Figure 4 is a diamond substrate 400 in which an NVC-containing layer 42 is formed on the base substrate 41 using a laminated structure consisting of a base substrate 44 and an intermediate layer 45.

[0083] The lower substrate 44 is not particularly limited, and for example, a single-crystal MgO substrate or the like can be used. The intermediate layer 45 may be a single layer or a laminate of multiple layers. The outermost surface of the intermediate layer 45 is preferably a metal layer selected from Ir, Rh, Pd, and Pt. The use of such a metal layer is preferred because it makes it easier to increase the density of diamond nuclei during nucleation treatment (bias treatment), making it easier to form a single-crystal diamond layer thereon.

[0084] (Third Manufacturing Mode) Furthermore, as shown in Fig. 5, a diamond substrate 500 can be manufactured in which a nitrogen-undoped diamond layer (NVC-free layer) 53 (made of a single crystal) and an NVC-containing layer 52 (made of a single crystal) are formed in this order on a laminated structure base substrate 51 (lower layer substrate 54, intermediate layer 55). When forming the NVC-free layer 53, it is preferable to form it using a natural hydrocarbon gas. This is because manufacturing costs can be further reduced. In particular, the diamond 500 of Fig. 5 can be manufactured to be similar to the diamond substrate 200 shown in Fig. 2.

[0085] In the second and third manufacturing modes, the conditions for the amount of each gas (hydrocarbon gas, hydrogen gas, nitrogen gas, or nitride gas) when forming the NVC-containing layer, １２ C-enriched hydrocarbon gas１２ The condition "the ratio of hydrocarbon gas composed of C > the ratio in natural hydrocarbon gas" is the same as that in the first production mode. In addition, the other conditions mentioned above, such as the use of oxygen gas or oxide gas, gas pressure, etc., can also be the same as those in the first production mode.

[0086] Furthermore, in any of the first to third manufacturing modes, a step of smoothing the surface of the NVC-containing layer may be included. Smoothing can be performed by mechanical polishing, chemical-mechanical polishing, plasma treatment, sputtering, chemical etching, or the like. If the average surface roughness Ra of the surface of the NVC-containing layer is, for example, 260 nm or less (0 nm or more), diffuse reflection of light is suppressed, and the extracted NV is reduced. － The center light can be increased.

[0087] Furthermore, in the present invention, the undersubstrate can be removed from the diamond substrate containing an NVC-containing layer on the undersubstrate obtained by the above-mentioned diamond substrate manufacturing method. This allows for a single-crystal diamond freestanding substrate containing an NVC-containing layer to be obtained. In this way, a diamond substrate with a high proportion of NVC-containing portions can reduce the cause of noise in practical use, making it possible to realize highly sensitive electronic and magnetic devices. In addition, when the undersubstrate is a single layer as in the first manufacturing embodiment, the entire undersubstrate can be removed. In addition, when the undersubstrate consists of a undersubstrate and an intermediate layer as in the second manufacturing embodiment and the third manufacturing embodiment, only the undersubstrate can be removed, or both the undersubstrate and the intermediate layer can be removed. In addition, a portion of the undersubstrate can be removed. Furthermore, the nitrogen-undoped diamond layer can also be removed, leaving only the NVC-containing layer.

[0088] As an example of the production of this single crystal diamond freestanding substrate, Figure 6 shows a case in which the base substrate 51 portion (lower layer substrate 54 and intermediate layer 55) is removed from the diamond substrate 500 of Figure 5 to produce a diamond substrate 600 (freestanding diamond substrate) consisting of an NVC-containing layer 52 / nitrogen-undoped diamond layer (NVC-free layer) 53.

[0089] The method for removing the base substrate is not particularly limited. It may be a mechanical treatment such as polishing, an optical treatment such as laser, or a wet or dry etching treatment, and may be appropriately selected depending on the materials of the base substrate, the lower substrate, and the intermediate layer. Furthermore, the above treatments may be combined.

[0090] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. (Example 1) A single-side polished single-crystal MgO substrate (hereinafter referred to as a "single-crystal MgO (111) substrate") having a diameter of 10.0 mm, a thickness of 1.0 mm, a main surface of the (111) plane, and an off-angle of 4° in the crystal axis [-1-12] direction was prepared as a lower-layer substrate in a base substrate.

[0091] Next, an intermediate layer of single-crystal Ir film was formed on the surface of the prepared single-crystal MgO (111) substrate by RF magnetron sputtering. To form the single-crystal Ir film, a radio-frequency (RF) magnetron sputtering method (13.56 MHz) was used, using an Ir target with a diameter of 6 inches (150 mm), a thickness of 5.0 mm, and a purity of 99.9% or higher. The single-crystal MgO (111) substrate, which was the lower substrate, was heated to 840°C, and a base pressure of 6 × 10 was applied. －７ Torr (approx. 8.0 x 10 －５ After confirming that the pressure had dropped to 3×10 Pa or less, Ar gas was introduced at 50 sccm. Next, the opening of the valve connected to the exhaust system was adjusted to reduce the pressure to 3×10 －１ Torr (approximately 39.9 Pa), RF power of 1000 W was input and film formation was carried out for 15 minutes, thereby obtaining a single-crystal Ir film having a thickness of 1.0 μm.

[0092] A single-crystal Ir film was deposited on the single-crystal MgO (111) substrate obtained as described above, and heteroepitaxial growth was performed following the misorientation of the single-crystal MgO substrate. This single-crystal Ir film was analyzed by X-ray diffraction. Measurement equipment: Rigaku Smart Lab, wavelength λ = 1.54 Å, output 45 kV, 200 mA, semiconductor detector, Ge (220) channel-cut monochromator, solar slit input side 2.5°, receiving side 2.5°, slit input side IS = 1 mm, length limit 0.5 mm, receiving side RS1 = 1.0 mm, RS2 = 1.1 mm, step width 0.004°, scanning speed 3° / min. Analysis conditions revealed a (111) surface with a 4° misorientation along the crystal axis [-1-1 2]. The full width at half maximum (FWHM) of the diffraction peak at 2θ=40.7° attributable to Ir (111) was 0.125°. This single crystal Ir film will be referred to as an "Ir (111) film" hereinafter.

[0093] Next, a nucleation treatment (bias treatment) was carried out as a pretreatment for diamond nucleation. The substrate was placed on a flat plate electrode with a diameter of 25 mm in the treatment chamber, with the Ir (111) film side facing up. The base pressure was 1 × 10 －６ Torr (approximately 1.3 x 10 －４ After confirming that the pressure had dropped below 1 Pa, hydrogen diluted methane gas (CH ４ / (CH ４ +H ２ ) = 5.0% by volume was introduced into the processing chamber at a flow rate of 500 sccm. The opening of the valve connected to the exhaust system was adjusted to reduce the pressure to 100 Torr (approximately 1.3 × 10 ４ Pa), a negative voltage was applied to the electrode on the substrate side, and the surface of the substrate (Ir(111) film) was exposed to plasma for 90 seconds, thereby subjecting the surface to bias treatment.

[0094] Diamond was heteroepitaxially grown on the Ir(111) film / single-crystal MgO(111) substrate prepared as described above by microwave plasma CVD. The bias-treated Ir(111) film / single-crystal MgO(111) substrate was set in the chamber of a microwave plasma CVD apparatus, and the base pressure was set to 1×10 －６ Torr (approximately 1.3 x 10－４ After confirming that the pressure in the chamber had dropped to 120 Torr (approximately 1.6×10 Pa), a mixture of the raw materials, natural methane gas (purity ≧ 99.9999% by volume) and hydrogen gas (purity ≧ 99.99999% by volume), was introduced into the chamber at a flow rate of 500 sccm in a volume ratio of methane gas 4.000% by volume and hydrogen gas 96.000% by volume. The opening of the valve connected to the exhaust system was adjusted to reduce the pressure in the chamber to 120 Torr (approximately 1.6×10 ４ After the pressure was adjusted to 1 Pa, a microwave of 3000 W was input and film formation was carried out for 71 hours until the film reached a thickness of about 250 μm (nitrogen-undoped diamond layer).

[0095] Continuing, the raw material, １２ C-composition methane gas / １３ C Composition methane gas = 99.995% by volume / 0.005% by volume １２ A mixed gas containing C-enriched methane gas, hydrogen gas (purity ≥ 99.99999 vol%), and nitrogen gas (purity ≥ 99.99999 vol%) was introduced into the chamber at a flow rate of 500 sccm, with the volume ratio of methane gas 0.100 vol%, hydrogen gas 99.850 vol%, and nitrogen gas 0.050 vol%. The pressure and microwave power remained the same. Under these conditions, film formation was carried out for 5 hours, and a nitrogen-doped diamond layer was formed to a thickness of approximately 6 μm. In this way, a diamond layer was heteroepitaxially grown on the Ir(111) film / single-crystal MgO(111) substrate to obtain a laminated substrate.

[0096] After this, the Ir (111) film / single-crystal MgO (111) substrate was removed to form a free-standing substrate. First, the single-crystal MgO (111) substrate was removed by wet etching, and then the Ir (111) film was removed by polishing. As a result, a single-crystal diamond (111) laminated substrate was obtained, with a diameter of 10 mm, consisting of a nitrogen-doped single-crystal diamond film approximately 6 μm thick and an undoped single-crystal diamond (111) substrate approximately 250 μm thick. The surface side of the diamond substrate with this laminated structure was polished to a finish.

[0097] Finally, the finished diamond substrate with the laminated structure was analyzed by SIMS, XRD, NVC density, and surface roughness. SIMS measurement equipment: CAMECA IMS-7f was used, and the primary ion species was Cs ＋ The nitrogen concentration [N] in the diamond crystal was measured under the conditions of a primary acceleration voltage of 16.0 kV and a detection area diameter of 30 μm. The SIMS measurement results, including the hydrogen concentration [H] described later, are shown in Figure 7. As a result, the nitrogen concentration at a depth of approximately 5 μm from the outermost surface of the film was [N] = 4.5 × 10 １７ atoms / cm ３ Generally, the depth at which the nitrogen concentration [N] in the nitrogen-doped diamond film becomes 1 / e is considered to be the interface between the nitrogen-doped layer and the undoped layer. In this case, the profile in the interface region changed abruptly at a thickness of about 1.0 μm.

[0098] Next, the hydrogen concentration [H] in the diamond crystal was measured under the same SIMS conditions. As a result, the hydrogen concentration at a depth of about 5 μm from the top surface was [H]=1.5×10 １７ atoms / cm ３ It was.

[0099] X-ray diffraction measurement equipment: Rigaku Corporation Smart Lab, wavelength λ = 1.54 Å, output 45 kV, 200 mA, semiconductor detector, incident optical system Ge (220) channel cut monochromator, solar slit input side 2.5 °, light receiving side 2.5 °, slit incident side IS = 1 mm, length limit 0.5 mm, light receiving side RS1 = 1.0 mm, RS2 = 1.1 mm, step width 0.004 °, scanning speed 3 ° / min, crystallinity was analyzed from the film's outermost surface under the following conditions. As a result, only the diffraction intensity peak at 2θ = 43.9 ° attributed to diamond (111) was observed, and it was confirmed that the nitrogen-doped single crystal diamond film was epitaxially grown on the undoped single crystal diamond (111) layer.

[0100] Furthermore, NVC evaluations such as photoluminescence measurement, confocal microscope image observation, optically detected magnetic resonance (ODMR) measurement, and Rabi oscillation were performed using a confocal microscope (incident wavelength 532 nm). As a result, NVC light with a wavelength of 637 nm was detected, and the relaxation time T of the electron spin was measured.２ = 58.2 μs, the NVC density calculated is 4.4 × 10 １６ / cm ３ Therefore, the obtained nitrogen-doped film was a single-crystal diamond (111) crystal with a high density of NVC.

[0101] Furthermore, when an 80 μm×80 μm area of ​​the surface of the diamond substrate was measured using an atomic force microscope (NanoScope V, manufactured by Bruker AXS), the average surface roughness Ra was found to be 187 nm.

[0102] The isotope abundance ratio of carbon atoms in the nitrogen-doped layer of the NVC-containing diamond (111) substrate was measured. Measurement conditions: SIMS measurement device: CAMECA IMS-7f, primary ion species: O ２ ＋ , the carbon concentration in the diamond crystal under the conditions of a primary acceleration voltage of 11.0 kV and a detection area diameter of 30 μm [ １２ C] and [ １３ C] was measured. １２ The abundance of C is 99.995%, which is the highest in natural carbon atoms. １２ It was higher than the abundance ratio of C (98.89%). １３ The abundance ratio of C was 0.005%.

[0103] The NVC density and other properties of the nitrogen-doped layer in Example 1 were as follows: Nitrogen concentration: 4.5×10 １７ atoms / cm ３ Hydrogen concentration: 1.5 x 10 １７ atoms / cm ３ NVC density: 4.4×10 １６ / cm ３ １２ C and １３ Abundance ratio of C: １２ C is 99.995%, １３ C 0.005% Steepness in interface region: approx. 1.0 μm

[0104] ​Example 2 A single-side polished single-crystal diamond substrate was prepared as a base substrate. The substrate had dimensions of 2 mm square, 200 μm thickness, a (111) main surface, and an off-angle of 4.0° in the crystal axis [−1-12] direction. The method for manufacturing this single-crystal diamond substrate is as follows. First, the same procedure as in Example 1 was followed to form a nitrogen-undoped single-crystal diamond layer, resulting in a nitrogen-undoped single-crystal diamond layer / Ir(111) film / single-crystal MgO(111) substrate. Next, the Ir(111) film / single-crystal MgO(111) substrate was removed to form a free-standing substrate. Specifically, the single-crystal MgO(111) substrate was removed by wet etching, and then the Ir(111) film was removed by polishing. The substrate was then cut using a laser to obtain a 2 mm square, approximately 250 μm thick free-standing nitrogen-undoped single-crystal diamond (111) single-layer substrate. The front surface of the substrate was polished to obtain a single-side polished single crystal diamond substrate that served as a base substrate, having a size of 2 mm square, a thickness of approximately 200 μm, a main surface with a (111) orientation, and an off-angle of 4° in the crystal axis [−1-12] direction.

[0105] Nitrogen-doped single-crystal diamond was epitaxially grown on the base substrate prepared as described above by microwave plasma CVD. The base substrate was set in the chamber of a microwave plasma CVD apparatus, and the base pressure was set to 1×10 －６ Torr (approximately 1.3 x 10 －４ After confirming that the temperature has dropped to or below Pa, the raw material １２ C-composition methane gas / １３ C Composition methane gas = 99.995% by volume / 0.005% by volume １２ A mixed gas of C-enriched methane gas, hydrogen gas (purity >99.99999% by volume), and nitrogen gas (purity >99.99995% by volume) was introduced into the chamber at a flow rate of 500 sccm in a volume ratio of methane gas 0.100% by volume, hydrogen gas 99.850% by volume, and nitrogen gas 0.050% by volume. The opening of the valve connected to the exhaust system was adjusted to reduce the pressure inside the chamber to 120 Torr (approximately 1.6 x 10 ４After the pressure was adjusted to 1 Pa, a microwave power of 3500 W was input and film formation was carried out for 96 hours, thereby growing a nitrogen-doped single crystal diamond layer until the thickness reached about 218 μm. In this way, a laminated diamond substrate of nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate was obtained.

[0106] Finally, the finished laminated substrate was analyzed by SIMS and XRD. Next, the nitrogen concentration [N] and hydrogen concentration [H] in the diamond crystal were measured under the same SIMS conditions as in Example 1. As a result, the nitrogen concentration at a depth of about 5 μm from the top surface was [N]=1.4×10 １８ atoms / cm ３ , the hydrogen concentration is [H] = 1.5 × 10 １７ atoms / cm ３ The steepness of the nitrogen concentration profile in the interface region of the nitrogen-doped layer (thickness of the descending region multiplied by 1 / e) was about 1.0 μm.

[0107] X-ray diffraction measurement equipment: Rigaku Corporation Smart Lab, wavelength λ = 1.54 Å, output 45 kV, 200 mA, semiconductor detector, incident optical system Ge (220) channel cut monochromator, solar slit input side 2.5 °, light receiving side 2.5 °, slit incident side IS = 1 mm, length limit 0.5 mm, light receiving side RS1 = 1.0 mm, RS2 = 1.1 mm, step width 0.004 °, scanning speed 3 ° / min, crystallinity was analyzed from the film's outermost surface under the following conditions. As a result, only the diffraction intensity peak at 2θ = 43.9 ° attributed to diamond (111) was observed, and it was confirmed that the nitrogen-doped single crystal diamond film was epitaxially grown on the undoped single crystal diamond (111) layer.

[0108] Furthermore, NVC evaluations such as photoluminescence measurement, confocal microscope image observation, optically detected magnetic resonance (ODMR) measurement, and Rabi oscillation were performed using a confocal microscope (incident wavelength 532 nm). As a result, NVC light with a wavelength of 637 nm was detected, and the relaxation time T of the electron spin was measured. ２ = 19.9 μs, the NVC density calculated is 1.4 × 10 １７ / cm ３Therefore, the obtained nitrogen-doped film was a single-crystal diamond (111) crystal with a high density of NVC.

[0109] The isotope abundance ratio of carbon atoms in the nitrogen-doped layer of the NVC-containing diamond (111) substrate was measured under the same conditions as in Example 1. １２ The abundance ratio of C is 99.995%. １３ The abundance ratio of C was 0.005%.

[0110] If the NVC-containing diamond (111) substrate is applied to electronic and magnetic devices, high-performance devices can be obtained, such as highly sensitive magnetic sensors.

[0111] The NVC density and other properties of the nitrogen-doped layer in Example 2 were as follows: Nitrogen concentration: 1.4×10 １８ atoms / cm ３ Hydrogen concentration: 1.5 x 10 １７ atoms / cm ３ NVC density: 1.4×10 １７ / cm ３ １２ C and １３ Abundance ratio of C: １２ C is 99.995%, １３ C 0.005% Steepness in interface region: approx. 1.0 μm

[0112] (Comparative Example 1) When epitaxially growing nitrogen-doped single crystal diamond, natural methane gas (purity ≧ 99.9999% by volume) that had not been carbon isotope enriched was used as the methane gas in the raw material, and the rest was produced in the same manner as in Example 2 to obtain a laminated diamond substrate of a nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate.

[0113] The crystallinity determined by XRD, the nitrogen concentration [N] determined by SIMS, and the hydrogen concentration [H] determined were the same as those in Example 2. The other results were summarized as follows: Nitrogen concentration: 1.4×10 １８ atoms / cm ３ ​Hydrogen concentration: 1.5 x 10 １７ atoms / cm ３ NVC density: 1.2×10 １６ / cm ３ １２ C and １３ Abundance ratio of C: １２ C is 98.892%, １３ C: 1.108% (almost the same as the natural abundance ratio) Steepness in the interface region: about 2.5 μm (much gentler than in Examples 1 and 2)

[0114] Example 3 When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used was as follows: methane gas 0.005 vol % ( １２ C-composition methane gas / １３ C Composition Methane gas = 99.500 vol% / 0.500 vol%) Hydrogen gas 99.945 vol% Nitrogen gas 0.050 vol% Other than that, the same preparation as in Example 2 was carried out to obtain a laminated diamond substrate of a nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate.

[0115] The results of various measurements were as follows: Nitrogen concentration: 1.5 x 10 １８ atoms / cm ３ Hydrogen concentration: 1.5 x 10 １７ atoms / cm ３ NVC density: 1.2×10 １７ / cm ３ １２ C and １３ Abundance ratio of C: １２ C is 99.500%, １３ C 0.500% Steepness in interface region: approx. 1.0 μm

[0116] Example 4 When epitaxially growing nitrogen-doped single crystal diamond, the raw material １２ C-composition methane gas / １３ C Composition methane gas = 99.995% by volume / 0.005% by volume １２ ​​A mixed gas of C-enriched methane gas, hydrogen gas (purity >99.99999% by volume), and nitrogen gas (purity >99.99995% by volume) was added in the following volume ratio: methane gas 7.000% by volume, hydrogen gas 92.950% by volume, nitrogen gas 0.050% by volume. The rest of the process was carried out in the same manner as in Example 2, to obtain a laminated diamond substrate of a nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate.

[0117] The results of various measurements were as follows: Nitrogen concentration: 1.0 x 10 １８ atoms / cm ３ Hydrogen concentration: 1.5 x 10 １７ atoms / cm ３ NVC density: 9.5×10 １６ / cm ３ １２ C and １３ Abundance ratio of C: １２ C is 99.995%, １３ C 0.005% Abruptness in the interface region: approx. 1.2 μm

[0118] (Comparative Example 2) When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used was as follows: methane gas 0.001 vol %, hydrogen gas 99.949 vol %, nitrogen gas 0.050 vol %. The rest was produced in the same manner as in Example 2, and an attempt was made to manufacture a laminated diamond substrate of nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate. However, perhaps because the volume ratio of methane gas was too low, the nitrogen-doped single crystal diamond was difficult to grow, and so film formation was stopped midway.

[0119] ​(Comparative Example 3) When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used was as follows: methane gas 14.000 volume %, hydrogen gas 85.950 volume %, nitrogen gas 0.050 volume %. The rest was produced in the same manner as in Example 2, and an attempt was made to manufacture a laminated diamond substrate of nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate. However, perhaps because the volume ratio of methane gas was too high, the diamond of the nitrogen-doped layer became polycrystalline.

[0120] (Comparative Example 4) When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used was as follows: methane gas 0.100 vol %, hydrogen gas approximately 99.850 vol %, nitrogen gas 0.00001 vol %. The rest was produced in the same manner as in Example 2 to obtain a laminated diamond substrate of nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate. However, perhaps because the volume ratio of nitrogen gas was too low, the NVC density was significantly lower than in each of the Examples and Comparative Example 1.

[0121] (Comparative Example 5) When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used was as follows: methane gas 0.100 volume %, hydrogen gas 85.900 volume %, nitrogen gas 14.000 volume %. The rest was produced in the same manner as in Example 2, and an attempt was made to manufacture a laminated diamond substrate of nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate. However, perhaps because the volume ratio of nitrogen gas was too high, the diamond of the nitrogen-doped layer became polycrystalline.

[0122] Thus, in the case of the products of the present invention in Examples 1-4, it was possible to produce high-density NVC. This makes it possible to produce highly sensitive sensors. On the other hand, when the conditions of the present invention were not met, as in Comparative Example 1, the NVC density was inferior to that of the products of the present invention, even if the nitrogen concentration, etc. were comparable to those of the products of the present invention. Furthermore, in Comparative Examples 2, 3, and 5, the growth of the nitrogen-doped single crystal diamond layer was poor to begin with. Furthermore, in Comparative Example 4, the NVC density was significantly reduced.

[0123] Example 5 Whether the undoped and nitrogen-doped single crystal diamonds in Examples 1 and 2 were formed using the CVD methods of DC plasma CVD, hot filament CVD, and arc discharge plasma jet CVD, respectively, or a combination of multiple CVD methods, the resulting nitrogen-doped layers had NVC densities of 4.4×10 １６ -1.4 x 10 １７ / cm ３ The diamond was a single crystal (111) formed to a degree. １２ C and １３ The results of various measurements such as the abundance ratio of C and the steepness in the interface region were similar to those of the other examples, and were good values.

[0124] (Examples 6 and 7) When epitaxially growing nitrogen-doped single crystal diamond, the nitrogen gas in the mixed gas used was increased by 5.0 × 10 compared to Example 2. －５ The nitrogen-doped single crystal diamond layer was obtained by changing the volume percentage of the nitrogen-doped single crystal diamond layer to 8.000 volume percent (Example 6) or 8.000 volume percent (Example 7), and the volume percentage of the hydrogen gas was adjusted accordingly. The rest of the process was carried out in the same manner as in Example 2, and a laminated diamond substrate of a nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate was obtained. The nitrogen-doped single crystal diamond did not polycrystallize, and various measurement results were comparable to those of the other Examples, and the NVC density was also better than that of each Comparative Example.

[0125] This specification includes the following aspects. [1]: A method for manufacturing a diamond substrate by forming a diamond crystal on a starting substrate using a source gas containing a hydrocarbon gas and hydrogen gas as a diluent gas by any one of chemical vapor deposition (CVD) methods, wherein nitrogen gas or nitride gas is mixed into the source gas to form a diamond crystal layer having a nitrogen vacancy center in at least a part of the diamond crystal formed on the starting substrate, and the amount of each gas contained in the source gas is set as follows: the amount of hydrocarbon gas is 0.005% by volume or more and 7.000% by volume or less, the amount of hydrogen gas is 85.000% by volume or more and less than 99.995% by volume, and the amount of nitrogen gas or nitride gas is 5.0 x 10－５ % or more and 8,000 vol % or less to form a diamond crystal layer having the nitrogen vacancy center, and １２ The ratio of hydrocarbon gas composed of C is higher than that in natural hydrocarbon gas. １２ A method for manufacturing a diamond substrate using a C-enriched hydrocarbon gas. [2]: A method for manufacturing a diamond substrate according to [1] above, wherein the source gas further contains oxygen gas or an oxide gas in an amount of 0.010 volume % or more and 2.000 volume % or less. [3]: A method for manufacturing a diamond substrate according to [1] or [2] above, wherein the hydrocarbon gas in the source gas is methane gas. [4]: ​​A method for manufacturing a diamond substrate according to any one of [1] to [3] above, wherein the gas pressure in forming diamond crystals by the CVD method is 1.3 kPa (10 Torr) or more and 50.0 kPa (376 Torr) or less. [5]: The １２ C-enriched hydrocarbon gas １２ in C-enriched hydrocarbon gas １２ The method for manufacturing a diamond substrate according to any one of [1] to [4] above, wherein the volume ratio of the hydrocarbon gas composed of C is 99.950 volume % or more. [6]: １２ C-enriched hydrocarbon gas １２ in C-enriched hydrocarbon gas １３The method for manufacturing a diamond substrate according to any one of [1] to [5] above, wherein the volume ratio of the hydrocarbon gas composed of C is 0.040 volume % or less. [7]: The method for manufacturing a diamond substrate according to any one of [1] to [6] above, wherein the starting substrate is a single-layer substrate of single-crystal diamond. [8]: The method for manufacturing a diamond substrate according to [7] above, wherein the single-layer substrate of single-crystal diamond is any one of a high-temperature, high-pressure synthetic single-crystal diamond layer, a heteroepitaxial single-crystal diamond layer, and a CVD-synthesized homoepitaxial diamond layer. [9]: The method for manufacturing a diamond substrate according to any one of [1] to [8] above, wherein a natural hydrocarbon gas is used when forming a diamond crystal layer that does not contain nitrogen vacancy centers in the formation of the diamond crystal by the CVD method.

[10] : The method for manufacturing a diamond substrate according to any one of [1] to [9] above, wherein the starting substrate has a layered structure consisting of a lower-layer substrate and an intermediate layer on the lower-layer substrate.

[11] : The method for manufacturing a diamond substrate according to

[10] above, wherein the outermost surface of the intermediate layer is a metal layer selected from Ir, Rh, Pd, and Pt.

[12] : A method for manufacturing a diamond substrate according to any one of [1] to

[11] above, using one or more of microwave plasma CVD, DC plasma CVD, hot filament CVD, and arc discharge plasma jet CVD as the CVD method.

[13] : A method for manufacturing a diamond substrate, comprising removing the base substrate from a diamond substrate comprising a diamond crystal layer having nitrogen vacancy centers, obtained by the method for manufacturing a diamond substrate according to any one of [1] to

[12] above, to obtain a single-crystal diamond freestanding substrate comprising a diamond crystal layer having nitrogen vacancy centers.

[14] : A method for manufacturing a diamond substrate, comprising smoothing the surface of the diamond crystal layer having nitrogen vacancy centers of a diamond substrate comprising a diamond crystal layer having nitrogen vacancy centers, obtained by the method for manufacturing a diamond substrate according to any one of [1] to

[13] above.

[15] : A diamond substrate including a diamond crystal layer having a nitrogen vacancy center, wherein the diamond crystal layer having the nitrogen vacancy center is formed on a diamond crystal layer not including a nitrogen vacancy center or on a single-layer substrate of a single crystal diamond, and the carbon atom present in the diamond crystal layer having the nitrogen vacancy center is an isotope of carbon. １２ A diamond substrate in which the abundance ratio of C is higher than the abundance ratio of natural carbon atoms, and the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy centers is steep in the interface region with the diamond crystal layer not containing the nitrogen vacancy centers or with the single-layer substrate of single-crystal diamond.

[16] : The nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy centers is measured by a secondary ion mass spectrometer using a primary ion species Cs + The diamond substrate of the above

[15] , wherein, when measured at a primary acceleration voltage of 16.0 kV and a detection area diameter of 30 μm, the thickness of the descending area until the nitrogen concentration [N] reaches 1 / e (Napier's number) times in the diamond crystal layer not containing the nitrogen vacancy center or in the interface area with the single-layer substrate of the single-crystal diamond is 1.5 μm or less.

[17] : The diamond substrate of the above

[15] , wherein the hydrogen concentration [H] in the diamond crystal layer having the nitrogen vacancy center is 1×10 １６ atoms / cm ３

[18] : The diamond substrate according to

[16] above, wherein the nitrogen concentration [N] in the diamond crystal layer having the nitrogen vacancy center is 1×10 or more. １７ atoms / cm ３ ≦[N]≦9×10 １９ atoms / cm ３ The diamond substrate of any one of

[15] to

[17] above, wherein

[19] : The diamond substrate of any one of

[15] to

[18] above, wherein the average surface roughness Ra of the surface of the diamond crystal layer having the nitrogen vacancy centers is Ra≦260 nm.

[20] : A sensor using the diamond substrate of any one of

[15] to

[19] above.

[0126] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A method for manufacturing a diamond substrate by forming a diamond crystal on a starting substrate by chemical vapor deposition (CVD) using a raw material gas containing a hydrocarbon gas and hydrogen gas as a diluent gas, wherein nitrogen gas or a nitride gas is mixed into the raw material gas to form a diamond crystal layer having a nitrogen vacancy center in at least a part of the diamond crystal formed on the starting substrate, and the amount of each gas contained in the raw material gas is set as follows: the amount of hydrocarbon gas is 0.005 vol% or more and 7.000 vol% or less, the amount of hydrogen gas is 85.000 vol% or more and less than 99.995 vol%, and the amount of nitrogen gas or nitride gas is 5.0 x 10 －５ % or more and 8,000 vol % or less to form a diamond crystal layer having the nitrogen vacancy center, and １２ The ratio of C in the hydrocarbon gas is higher than that in natural hydrocarbon gas. １２ A method for manufacturing a diamond substrate, comprising using a C-enriched hydrocarbon gas.

2. The method for producing a diamond substrate according to claim 1, characterized in that the source gas further contains oxygen gas or an oxide gas in an amount of 0.010 volume % or more and 2.000 volume % or less.

3. The method for manufacturing a diamond substrate according to claim 1 or 2, characterized in that the hydrocarbon gas in the source gas is methane gas.

4. A method for manufacturing a diamond substrate according to claim 1 or 2, characterized in that the gas pressure in forming the diamond crystal by the CVD method is 1.3 kPa (10 Torr) or more and 50.0 kPa (376 Torr) or less.

5. The foregoing １２ C enriched hydrocarbon gas, １２ In C-enriched hydrocarbon gas １２ 3. The method for manufacturing a diamond substrate according to claim 1, wherein the volume ratio of the hydrocarbon gas composed of C is 99.950 volume % or more.

6. The foregoing １２ C enriched hydrocarbon gas, １２ In C-enriched hydrocarbon gas １３ 3. The method for manufacturing a diamond substrate according to claim 1, wherein the volume ratio of the hydrocarbon gas composed of C is 0.040 volume % or less.

7. The method for producing a diamond substrate according to claim 1 or 2, characterized in that the base substrate is a single-layer substrate of single crystal diamond.

8. The method for producing a diamond substrate as set forth in claim 7, characterized in that the single-layer substrate of single crystal diamond is any one of a high-temperature, high-pressure synthetic single crystal diamond layer, a heteroepitaxial single crystal diamond layer, and a CVD synthetic homoepitaxial diamond layer.

9. A method for manufacturing a diamond substrate as described in claim 1 or 2, characterized in that in forming the diamond crystal by the CVD method, when forming a diamond crystal layer that does not contain a nitrogen vacancy center, a natural hydrocarbon gas is used.

10. A method for producing a diamond substrate according to claim 1 or 2, wherein the base substrate has a laminated structure consisting of a lower layer substrate and an intermediate layer on the lower layer substrate.

11. The method for producing a diamond substrate according to claim 10, wherein the outermost surface of the intermediate layer is a metal layer selected from the group consisting of Ir, Rh, Pd and Pt.

12. A method for manufacturing a diamond substrate as described in claim 1 or 2, characterized in that the CVD method is one or more of microwave plasma CVD method, direct current plasma CVD method, hot filament CVD method and arc discharge plasma jet CVD method.

13. A method for producing a diamond substrate, comprising removing the base substrate from a diamond substrate including a diamond crystal layer having a nitrogen vacancy center, the diamond substrate being obtained by the method for producing a diamond substrate as defined in claim 1 or 2, to obtain a single-crystal diamond free-standing substrate including a diamond crystal layer having a nitrogen vacancy center.

14. A method for manufacturing a diamond substrate, comprising smoothing the surface of a diamond crystal layer having nitrogen vacancy centers of a diamond substrate obtained by the method for manufacturing a diamond substrate according to claim 1 or 2, the diamond crystal layer having nitrogen vacancy centers.

15. A diamond substrate including a diamond crystal layer having a nitrogen vacancy center, the diamond crystal layer having the nitrogen vacancy center being formed on a diamond crystal layer not including a nitrogen vacancy center or a single-layer substrate of a single crystal diamond, and a carbon isotope that is ... １２ 1. A diamond substrate comprising: a diamond crystal layer having a nitrogen vacancy center and a diamond crystal layer that does not contain a nitrogen vacancy center; and a diamond crystal layer that does not contain a nitrogen vacancy center ...

16. The nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy center is measured by a secondary ion mass spectrometer using the primary ion species Cs + 16.0 kV, and a detection area diameter of 30 μm, the diamond crystal layer not including the nitrogen vacancy center or the interface region of the single crystal diamond with the single layer substrate has a thickness of 1.5 μm or less until the nitrogen concentration [N] reaches 1 / e (Napier's number).

17. The hydrogen concentration [H] in the diamond crystal layer having the nitrogen vacancy center is 1×10 １６ atoms / cm ３ 17. The diamond substrate according to claim 16, characterized in that:

18. The nitrogen concentration [N] in the diamond crystal layer having the nitrogen vacancy center is 1×10 １７ atoms / cm ３ ≦[N]≦9×10 １９ atoms / cm ３ 18. The diamond substrate according to claim 15, wherein 19. A diamond substrate according to any one of claims 15 to 17, characterized in that the average surface roughness Ra of the surface of the diamond crystal layer having the nitrogen vacancy centers is Ra≦260 nm.

20. A sensor using a diamond substrate according to any one of claims 15 to 17.

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