Diamond substrate, method for producing the same, and sensor

Abstract

To provide 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.SOLUTION: 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 vol.% or more to 7.000 vol.% or less of a hydrocarbon gas, 85.000 vol.% or more and less than 99.995 vol.% of a hydrogen gas, and 5.0×10-5 vol.% or more to 8.000 vol.% or less 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.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a diamond substrate, a manufacturing method thereof, and a sensor. [Background technology]

[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 band gap semiconductors, diamond has a very high breakdown field strength of 10 MV / cm, making it possible to operate at high voltages. It also has the highest thermal conductivity of any known substance, making it excellent at dissipating heat. Furthermore, its extremely high carrier mobility and saturated drift velocity make it suitable for use in 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, even when compared with semiconductors such as silicon carbide and gallium nitride, and is said to be the ultimate semiconductor.

[0005] Furthermore, diamond has the nitrogen-vacancy center (NVC) phenomenon that exists in the crystal, which makes it possible to manipulate and detect a single spin at room temperature, and the state can be imaged by optically detected magnetic resonance. Taking advantage of this feature, it is expected to be applied in a wide range of fields as a highly sensitive sensor for magnetic fields, electric fields, temperature, pressure, etc. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] US2013 / 0143022A1 [Non-patent literature]

[0007] [Non-Patent Document 1] M.Hatano et al., OYOBUTURI 85, 311 (2016) [Non-Patent Document 2] T. Fukui, et al., APEX 7,055201(2014). [Non-Patent Document 3] H.Ozawa,et.al.,NDF Dia.Symp.29,16(2015). Summary of the Invention [Problem to be solved by the invention]

[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 a 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 a chemical vapor deposition method. In particular, in NVC device applications, which are highly important among diamond applications, it is necessary for the nitrogen-vacancy axis (NV axis) to be highly oriented, and therefore it is desirable for the diamond surface to be a (111) crystal plane in which the NV axis is aligned in the

[0111] direction (Non-Patent Document 1). In addition, for example, when considering application to the medical MRI field, if the diamond substrate that becomes the magnetic sensor part has a large diameter (large aperture), a device that can efficiently measure a wider area can be realized. In addition, it 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 axes aligned in the <0111> direction in the diamond crystal, but also must be formed at a high density.

[0010] The previously reported method for producing high density NVC-forming diamond crystals with a

[0111] orientation is as follows. Studies have been conducted on single-crystal diamond synthesized by high-pressure, high-temperature synthesis (HPHT) as a base substrate and growing it by microwave chemical vapor deposition (CVD) using hydrogen-diluted methane with the addition of nitrogen (Non-Patent Documents 2 and 3). However, in the reported literature, only HPHTIb(111), which is difficult to obtain in a large size for practical use, is used as the base substrate, and furthermore, the details of the gas composition in CVD are unclear in Non-Patent Document 2. In addition, it is unclear whether the CVD conditions in Non-Patent Document 3 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 having a high NV axis orientation (e.g., high

[0111] orientation) and a high density of nitrogen-vacancy centers (NVCs) with a single spin by performing CVD on a base substrate under specified conditions. Another aim of the present invention is to provide such a diamond substrate. Another aim of the present invention is to provide a sensor using the diamond substrate containing the NVC. [Means for solving the problem]

[0012] In order to achieve the above object, the present invention provides a method for producing a diamond substrate by forming a diamond crystal on a base substrate by chemical vapor deposition (CVD) using a source gas containing a hydrocarbon gas and a hydrogen gas as a dilution gas, the method comprising the steps of: In order to form a diamond crystal layer having a nitrogen vacancy center in at least a part of the diamond crystal formed on the base substrate, nitrogen gas or a nitride gas is mixed into the raw material gas, and the amount of each gas contained in the raw material gas is 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. The amount of nitrogen gas or nitride gas is 5.0 x 10 -5 Volume percent or more and 8,000 volume percent or less to form a diamond crystal layer having the nitrogen vacancy center; The hydrocarbon gas in the raw material gas is a carbon isotope. 12 The ratio of C in the hydrocarbon gas is higher than that in natural hydrocarbon gas. 12A method for producing a diamond substrate using a C-enriched hydrocarbon gas is provided.

[0013] According to the method for manufacturing a diamond substrate under such CVD conditions, a diamond substrate can be manufactured in which a diamond crystal layer is formed that is highly crystalline, has a high NV axis orientation (especially a high

[0111] orientation), and has a single spin and high density NVC. Such diamond crystals can be suitable for electronic and magnetic devices.

[0014] At this time, the source gas may further contain oxygen gas or an 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 for removing non-diamond components can be adequately obtained, and the orientation of the diamond crystals can be further improved.

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

[0017] Using methane gas in this manner is preferable because it is a highly pure gas that is inexpensive and easy to obtain, 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, 12 C concentrated hydrocarbon gas 12 C-enriched hydrocarbon gas 12 The volume ratio of the hydrocarbon gas composed of C can be 99.950 volume % or more.

[0021] This is highly effective in forming a single-spin, high-density NVC.

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

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

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

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

[0111] orientation) and at a high density. By using such single crystal diamond (especially single crystal diamond (111)) as a base substrate, step-flow growth is facilitated, and a high-quality single crystal diamond with fewer hillocks, abnormally grown grains, dislocation defects, etc. can be formed.

[0026] The single-layer substrate of single crystal diamond may 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.

[0027] As the base substrate in the method for producing a diamond substrate of the present invention, a substrate made of such a single crystal diamond layer can be suitably employed.

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

[0029] In this way, the manufacturing costs can be further reduced.

[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 used.

[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] As the CVD method, one or more of a microwave plasma CVD method, a direct current plasma CVD method, a hot filament CVD method, and an arc discharge plasma jet CVD method can be used.

[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 free-standing substrate comprising a diamond crystal layer having a 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 allows us to obtain a single-crystal diamond free-standing substrate that includes a diamond crystal layer with high crystallinity, high NV axis orientation (especially high <0111> orientation), and high density NVC with a single spin, which can be applied to electronic and magnetic devices.

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

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

[0040] The present invention also provides a diamond substrate including a diamond crystal layer having nitrogen vacancy centers, comprising: the diamond crystal layer having a nitrogen vacancy centre is formed on a diamond crystal layer which does not contain a nitrogen vacancy centre or on a single layer substrate of single crystal diamond; In the carbon atom present in the diamond crystal layer having the nitrogen vacancy center, 12 The abundance ratio of C is higher than the abundance ratio of natural carbon atoms, The diamond substrate is characterized in that the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy center is steep in the interface region with the diamond crystal layer not containing the nitrogen vacancy center or with the single layer substrate of single crystal diamond.

[0041] Such diamond substrates have high crystallinity, high NV axis orientation (especially high <0111> orientation), and high density NVC with a single spin, and therefore are applicable to 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 region until the nitrogen concentration [N] reaches 1 / e (Napier's number) times in the interface region of the diamond crystal layer or single crystal diamond with the single layer substrate which does not contain the nitrogen vacancy center is 1.5 μm or less.

[0043] By having such physical properties that a steep drop in nitrogen concentration is observed in the interface region between the layer containing NVC and the layer not containing NVC, it is possible to obtain a diamond substrate having NVC-containing diamond crystals with better properties.

[0044] In addition, 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 methods for growing diamond, 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 3 It can be assumed that:

[0047] A nitrogen concentration within this range can result in a diamond substrate having 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 center is preferably Ra≦260 nm.

[0049] With such surface roughness, the diffuse reflection of light on the surface of the diamond crystal layer with NVC is suppressed, and the amount of NV 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] A sensor using the diamond substrate of the present invention has high sensitivity and is excellent. Effect of the Invention

[0052] According to the method for manufacturing a diamond substrate of the present invention, a diamond substrate can be manufactured in which a diamond crystal layer is formed that is highly crystalline, has a high NV axis orientation (especially a high

[0111] orientation), and has a single spin and high density NVC. Such diamond crystals can be suitable for electronic and magnetic devices. Furthermore, the diamond substrate of the present invention can provide a diamond substrate that is highly crystalline, has a high

[0111] orientation of the NV axis, and has a single spin and high density NVC, and is applicable to electronic and magnetic devices. Furthermore, the sensor of the present invention can be made to be an excellent sensor with high sensitivity. [Brief description of the drawings]

[0053] [Figure 1] 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. [Diagram 2] FIG. 1 is a schematic diagram showing an example of a diamond substrate (base substrate with a laminated structure of NVC-containing layer / NVC-free layer) of the present invention. [Diagram 3] FIG. 1 is a schematic diagram showing an example of a diamond substrate (NVC-containing layer / base substrate) manufactured by the diamond substrate manufacturing method of the present invention. [Figure 4] FIG. 1 is a schematic diagram showing an example of a diamond substrate (base substrate with an NVC-containing layer / laminate structure) manufactured by the method for manufacturing a diamond substrate of the present invention. [Diagram 5] FIG. 1 is a schematic diagram showing an example of a diamond substrate (a base substrate with a laminated structure of NVC-containing layer / NVC-free layer / layered structure) produced by the method for producing a diamond substrate of the present invention. [Figure 6] FIG. 1 is a schematic diagram showing an example of a single-crystal diamond free-standing substrate (NVC-containing layer / NVC-free layer) obtained by the diamond substrate manufacturing method of the present invention. [Figure 7] 1 is a graph showing the results of SIMS measurement in Example 1. BEST MODE FOR CARRYING OUT THEINVENTION

[0054] The present invention will be described in detail below, but the present invention is not limited thereto. As described above, there has been a need to obtain diamond substrates that are suitable for use in electronic and magnetic devices, have a large diameter (large aperture), high crystallinity, a high NV axis orientation (e.g., high <0111> orientation), and a high density NVC with a single spin.

[0055] As a result of intensive research into the above-mentioned problems, the present inventors have discovered that in a method for producing a diamond substrate by forming a diamond crystal on a starting substrate by a CVD method using a source gas containing a hydrocarbon gas and hydrogen gas as a dilution gas, in order 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, nitrogen gas or a nitride gas is mixed into the source gas, and the amounts of the gases contained in the source gas are adjusted so that 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 the hydrocarbon gas in the raw material gas is a carbon isotope 12 The ratio of C in the hydrocarbon gas is higher than that in natural hydrocarbon gas. 12 We have discovered that a manufacturing method for diamond substrates using C-enriched hydrocarbon gas can produce diamond substrates that are highly crystalline, have a high NV axis orientation (highly oriented

[0111] ), and have a high-density NVC with a single spin, and have thus completed the present invention.

[0056] Also, 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 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 the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy centres is steep in the interface region with the diamond crystal layer not containing the nitrogen vacancy centres or with the single layer substrate of single crystal diamond, and have completed the present invention.

[0057] For simplicity, in this specification, a diamond crystal layer having a nitrogen vacancy center (NVC) is sometimes referred to as an NVC-containing layer, a diamond crystal layer that does not contain NVC is sometimes referred to as an NVC-free layer, and a single-layer substrate of single crystal diamond that does not contain NVC is sometimes referred to as an NVC-free single-layer substrate. Furthermore, in the following, the above-mentioned layers and substrates will be described using as examples a diamond crystal layer and a single-layer substrate having a (111) main surface (also referred to as a single-crystal diamond (111) layer and a 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 aspect) 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 atom present in the NVC-containing layer 12 is an isotope of carbon.12 The abundance ratio of C is higher than that of natural carbon atoms. The natural abundance ratio of carbon atoms is as is generally known: 12 C is 98.89%, 13 The abundance ratio of C is 1.11%. On the other hand, the NVC-free single-layer substrate of the base substrate 11 12 The abundance ratio of C is not particularly limited, but in particular can be approximately the same as the abundance ratio of the above-mentioned natural carbon atoms.

[0060] Furthermore, the nitrogen concentration profile in the NVC-containing layer 12 is steep in the interface region with the underlying substrate 11, and changes sharply downward from the NVC-containing layer 12 side toward the underlying substrate 11 side. As a specific degree of this steepness, for example, the profile of the nitrogen concentration in the NVC-containing layer 12 is measured by a secondary ion mass spectrometry (SIMS) device using a primary ion species Cs + When measured with a primary acceleration voltage of 16.0 kV and a detection area diameter of 30 μm, the thickness of the descending region in the above-mentioned interface region until the nitrogen concentration [N] reaches 1 / e (Napier's number) times is 1.5 μm or less. An example of the secondary ion mass spectrometer is CAMECA IMS-7f (manufactured by AMETECH Co., Ltd.).

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

[0111] , and a high density NVC 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 device 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 3As described below, in the case of a layer formed by a CVD method, the layer has a relatively high hydrogen concentration as described above. The upper limit of the hydrogen concentration is not particularly limited, but is, 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 characteristics.

[0064] In addition, if the average surface roughness Ra of the NVC-containing layer is 260 nm or less, diffuse reflection of light is suppressed and the amount of NV that can be extracted is reduced. - This is preferable because it is possible to increase the center light. In addition, the smaller the average surface roughness Ra, the better in terms of the diffuse reflection of light described above, and therefore, although there are no limitations, it can be set to, for example, 200 nm. Incidentally, examples of methods for measuring the average surface roughness Ra include the following methods. (Measurement method) Using an atomic force microscopy (AFM) device, for example, NanoScope V / Dimension Icon manufactured by Bruker AXS, measurements are performed in a tapping mode over an area of ​​80 μm×80 μm.

[0065] (Second aspect) Next, the latter example will be described with reference to Figure 2. As shown in Figure 2, in a 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 a non-NVC-containing single-layer substrate like the diamond substrate 100 in FIG. 1, but 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 multi-layer laminate. The outermost surface of the intermediate layer 25 can be a metal layer selected from Ir, Rh, Pd, and Pt. In addition, for the NVC-free layer 23, 12 The abundance ratio of C is not particularly limited, but can be, for example, approximately the same as the abundance ratio of natural carbon atoms.

[0066] The steepness and its degree of the nitrogen concentration profile in the NVC-containing layer 22 at the interface region with the NVC-free layer 23 can be similar to the steepness and its degree of the NVC-containing layer 12 at the interface region with the base substrate 11 in FIG. 1 described above. 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 thereof can be similar to those parameters of the NVC-containing layer 12 in FIG.

[0067] Such a diamond substrate 200 also has high crystallinity, a high

[0111] orientation of the NV axis, and a high density NVC with a single spin, making it suitable for electronic and magnetic devices.

[0068] 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 of manufacturing diamond substrate according to the present invention) Next, the method for producing a diamond substrate according to the present invention will be described. A diamond substrate is manufactured by forming diamond crystals on a base substrate using a raw material gas containing a hydrocarbon gas and hydrogen gas as a dilution gas by the CVD method. The CVD (chemical vapor deposition) method includes microwave plasma CVD method, direct current plasma CVD method, hot filament CVD method, and arc discharge plasma jet CVD method. Among them, the diamond obtained by the microwave plasma CVD method and the direct current plasma CVD method 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 a plurality of the above CVD methods. For example, by combining the direct current plasma CVD method and the microwave plasma CVD method, it is possible to simultaneously perform diamond nucleation and film growth. By combining the direct current plasma CVD method and the hot filament CVD method, it is possible to simultaneously perform diamond nucleation and large-area film growth. In addition, at this time, in order to form an NVC-containing layer on at least a part 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 above-mentioned hydrocarbon gas in the raw material gas contains carbon isotopes 12 The ratio of C in the hydrocarbon gas is higher than that in natural hydrocarbon gas. 12 C Use concentrated hydrocarbon gas.

[0070] Further details are provided below. (First manufacturing method) In order to form the NV axis with a high

[0111] orientation and high density, it is preferable to use a single-layer substrate of single crystal diamond as the base substrate, and in particular, it is preferable to use epitaxial growth using single crystal diamond (111) as the base substrate. 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] The single-layer substrate of single crystal diamond used as the base substrate 31 may 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 adopted as the base substrate 31.

[0072] In the source gas for forming the NVC-containing layer 32, methane gas, acetylene, ethylene, ethane, propane, etc. can be used as a hydrocarbon gas. However, methane gas is preferable because it is easy to obtain high purity gas at low cost and is easy to handle.

[0073] If the amount of hydrocarbon gas such as methane gas is less than 0.005% by volume, the etching effect by hydrogen becomes so strong that diamond does not grow, so the amount of hydrocarbon gas should be in the range of 0.005% by volume or more, more preferably 0.01% or more, and most preferably 0.05% by volume or more. On the other hand, if the amount of hydrocarbon gas exceeds 7,000% by volume, the diamond will become polycrystallized if grown for a long period of time, making it impossible to obtain a high-quality single crystal; therefore, the amount should be in the range of 7,000% by volume or less, preferably 6.5% by volume or less, and more preferably 6.0% by volume or less.

[0074] In addition, in this raw material gas, the amount of nitrogen gas or nitride gas is 5.0 × 10 -5 Below vol.%, the amount of nitrogen doped into the diamond crystal is too small, resulting in a low NVC density. Therefore, the range of the amount of nitrogen gas or nitride gas is 5.0×10-5 % by volume or more, preferably 5.0×10 -4 % by volume or more, more preferably 1.0×10 -3 Volume percent or more is better. On the other hand, if the amount of nitrogen gas or nitride gas exceeds 8.000% by volume, the diamond will become polycrystallized after long-term growth, and good quality single crystals cannot be obtained. Therefore, the amount of nitrogen gas or nitride gas is set to 8.000% by volume or less, and more preferably 0.500% by volume or less. As the nitride gas, ammonia, nitrogen oxide, nitrogen dioxide, etc. can be used, but nitrogen gas is preferable because it is easy to obtain high purity gas at low cost and is easy to handle.

[0075] In addition, adding oxygen gas or oxide gas is preferable because it removes non-diamond components and improves the orientation of diamond crystal. When adding oxygen gas or oxide gas, it is preferable to make it 0.010 volume % or more to obtain a moderate oxygen etching effect. On the other hand, it is preferable to make it 2.000 volume % or less to effectively prevent diamond growth from being hindered by the excessive etching effect of oxygen.

[0076] The hydrogen gas used as the dilution gas should be at least 85.000% by volume but less than 99.995% by volume.

[0077] In this case, if the gas pressure in forming diamond crystals by each CVD method is set to 1.3 kPa (10 Torr) or more and 50.0 kPa (376 Torr) or less, polycrystallization of diamond can be effectively prevented, and high-quality single crystals can be obtained. In order to effectively prevent situations where a gas pressure is too low, making it difficult for discharge to occur and where the plasma density is too low to obtain high-quality single crystal diamond, the gas pressure is set to the lower limit as described above, and a more preferable range is 12.0 kPa (90 Torr) or higher. On the other hand, in order to effectively prevent problems such as difficulty in generating discharge, deterioration of crystallinity due to high temperatures, and further reduction in the area in which diamond is formed due to excessively high gas pressure, the upper limit is set as above, and it is preferable that the pressure is 33.3 kPa (250 Torr) or less.

[0078] In addition, the hydrocarbon gas in the source gas for the CVD method contains carbon isotope carbon-12( 12 C) The ratio of isotopes in the hydrocarbon gas is higher than that in natural hydrocarbon gas. 12 The use of C-enriched hydrocarbon gas enables the formation of high-density NVCs, which can be used to realize 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, by volume). And the ratio as above 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 natural abundance of carbon atoms.

[0079] The above 12 In C-enriched hydrocarbon gas, 12 Using a gas containing 99.950 vol% or more (100 vol% or less) of a hydrocarbon gas composed of C is effective for forming a single spin and high density NVC. In addition, among the carbon isotopes, 12 The second most common after C 13 Reducing the amount of hydrocarbon gas composed of C is also effective in forming a denser NVC. 12 C-enriched hydrocarbon gas, especially 13 Setting the amount of hydrocarbon gas composed of C to 0.040 vol. % or less (0 vol. % or more) is also effective enough to form high-density NVC with a single spin. 12 C-enriched hydrocarbon gas 12Hydrocarbon gas composed of C 13 The volume percentage of the hydrocarbon gas composed of C can be adjusted, for example, by using each commercially available gas having a high purity.

[0080] When diamond substrate 300 in FIG. 3 is manufactured using a non-NVC-containing single-layer substrate as base substrate 31, a substrate similar to diamond substrate 100 shown in FIG. 1 can be manufactured.

[0081] In this manner, it is possible to manufacture a diamond substrate having a diamond crystal layer with high crystallinity, high NV axis orientation in the

[0111] direction, and high density NVC with a single spin, which is suitable for use as a substrate for various devices (substrate for sensors).

[0082] (Second manufacturing method) In addition, 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. Fig. 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 Fig. 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 as the base substrate 41.

[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 preferable because it makes it easier to form a single crystal diamond layer thereon by increasing the density of diamond nuclei during nucleation treatment (bias treatment).

[0084] (Third manufacturing method) Furthermore, as shown in FIG. 5, a diamond substrate 500 can be produced in which a nitrogen-undoped diamond layer (non-NVC-containing 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 base substrate 51 (lower substrate 54, intermediate layer 55) having a laminated structure. When forming the NVC-free layer 53, it is preferable to form it using a natural hydrocarbon gas, since this can further reduce the manufacturing cost. In particular, the diamond 500 of FIG. 5 can be manufactured similar to the diamond substrate 200 shown in FIG.

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

[0086] 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. For example, if the average surface roughness Ra of the surface of the NVC-containing layer is set to 260 nm or less (0 nm or more), diffuse reflection of light is suppressed, and the extracted NV - The center light can be increased.

[0087] In addition, in the present invention, the starting substrate can be removed from the diamond substrate including the NVC-containing layer on the starting substrate obtained by the above-mentioned diamond substrate manufacturing method. This makes it possible to obtain a single crystal diamond free-standing substrate including the NVC-containing layer. 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 starting substrate is a single layer as in the first manufacturing embodiment, the whole starting substrate can be removed. In addition, when the starting substrate is composed of a lower layer substrate and an intermediate layer as in the second manufacturing embodiment or the third manufacturing embodiment, only the lower layer substrate can be removed, or both the lower layer substrate and the intermediate layer can be removed. In addition, a part of the starting substrate 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, FIG. 6 shows a case in which the base substrate 51 portion (lower substrate 54 and intermediate layer 55) is removed from the diamond substrate 500 in FIG. 5 to produce a diamond substrate 600 (freestanding structure substrate of diamond substrate) consisting of an NVC-containing layer 52 / nitrogen-undoped diamond layer (non-NVC-containing 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, a wet or dry etching treatment, or the like, which may be appropriately selected according to the materials of the base substrate, the lower substrate, and the intermediate layer. The above treatments may also be combined. EXAMPLES

[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 As the lower substrate in the base substrate, a single-side polished single-crystal MgO substrate (hereinafter referred to as "single-crystal MgO (111) substrate") was prepared, which had a diameter of 10.0 mm, a thickness of 1.0 mm, a main surface that was a (111) plane, and an off-angle of 4° in the crystal axis [-1-1 2] direction.

[0091] Next, a single-crystal Ir film intermediate layer was formed on the surface of the prepared single-crystal MgO(111) substrate by RF magnetron sputtering. To form the single-crystal Ir film, radio frequency (RF) magnetron sputtering (13.56 MHz) was used with 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 lower substrate, a single-crystal MgO(111) substrate, was heated to 840°C, and the base pressure was 6×10 -7 Torr (approx. 8.0×10 -5 After confirming that the pressure had dropped to below 3×10 Pa, Ar gas was introduced at 50 sccm. Next, the opening of the valve leading to the exhaust system was adjusted to reduce the pressure to 3×10 -1 Torr (approximately 39.9 Pa), and then RF power of 1000 W was input and film formation was carried out for 15 minutes, resulting in a single crystal Ir film with a thickness of 1.0 μm.

[0092] The single crystal Ir film was grown heteroepitaxially on the single crystal MgO (111) substrate obtained as described above, following the off-angle of the single crystal MgO substrate. The 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, incident optical system 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. The surface was (111) with an off-angle of 4° in the crystal axis [-1-1 2] direction. In addition, 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 is hereinafter referred to as “Ir(111) film”.

[0093] Next, a nucleation treatment (bias treatment) was performed as a pretreatment for diamond nucleation. The substrate was placed on a flat 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 (approx. 1.3×10 -4 After confirming that the pressure had dropped to below 100 Torr (approximately 1.3×10 Pa), hydrogen-diluted methane gas (CH4 / (CH4+H2)=5.0% by volume) was introduced into the processing chamber at a flow rate of 500 sccm. The opening of the valve leading to the exhaust system was adjusted to reduce the pressure to 100 Torr (approximately 1.3×10 4 After the substrate was heated to a voltage of 1 Pa, a negative voltage was applied to the electrode on the substrate side, and the substrate (Ir(111) film) surface was exposed to plasma for 90 seconds, thereby subjecting the surface to a 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 at 1×10 -6 Torr (approx. 1.3×10 -4 After confirming that the pressure in the tank had dropped below 99.9999 Pa, the raw material, a mixture of natural methane gas (purity ≧ 99.9999% by volume) and hydrogen gas (purity ≧ 99.99999% by volume), was added. Methane gas 4.000% by volume Hydrogen gas 96.000% by volume The pressure in the chamber was adjusted to 120 Torr (approximately 1.6 × 10 4 After adjusting the pressure to 3 Pa, a microwave of 3000 W was input and deposition was performed for 71 hours until the thickness reached approximately 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 volume12 A mixed gas of C-enriched methane gas, hydrogen gas (purity ≧ 99.99999% by volume), and nitrogen gas (purity ≧ 99.99999% by volume) was added. Methane gas 0.100% by volume Hydrogen gas 99.850% by volume Nitrogen gas 0.050% by volume The volume ratio was changed to 100 and the gas was introduced into the chamber at a flow rate of 500 sccm. The pressure and microwave power were kept the same. Under these conditions, deposition was carried out for 5 hours, and the nitrogen-doped diamond layer was deposited to a thickness of approximately 6 μm. In this manner, 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 produce 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 of about 6 μm and an undoped single crystal diamond (111) substrate of about 250 μm in thickness. The front surface of the diamond substrate having the laminated structure was polished to finish it.

[0097] Finally, the finished laminated diamond substrate was analyzed by SIMS, XRD, NVC density, and surface roughness. SIMS measurement device: CAMECA IMS-7f, primary ion species 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 about 5 μm from the outermost surface of the film was [N] = 4.5 × 10 17 atoms / cm 3 It was. In general, the depth where the nitrogen concentration [N] in a 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 changes 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. 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 device: Rigaku Smart Lab. The crystallinity was analyzed from the outermost surface of the film under the following conditions: 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°, receiving side 2.5°, slit entrance 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. As a result, only a diffraction intensity peak at 2θ=43.9° attributed to diamond (111) was observed, confirming that the nitrogen-doped single crystal diamond film had grown epitaxially on the undoped single crystal diamond (111) layer.

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

[0101] In addition, when the surface of the diamond substrate was measured over an area of ​​80 μm × 80 μm using an atomic force microscope (Bruker AXS NanoScope V), the average surface roughness Ra was 187 nm.

[0102] The isotope abundance ratio of the 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 O2 + The carbon concentration in the diamond crystal was measured 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. the result, 12 The abundance of C is 99.995%, which is the proportion of carbon in natural carbon atoms. 12 It was higher than the abundance of C (98.89%). 13 The abundance ratio of C was 0.005%.

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

[0104] Example 2 As a base substrate, a single-side polished single crystal diamond substrate was prepared, which was 2 mm square, 200 μm thick, had a (111) main surface, and had an off-angle of 4.0° in the crystal axis [-1-1 2] direction. The manufacturing method of this single crystal diamond substrate is as follows. First, the nitrogen-undoped single crystal diamond layer was formed in the same manner as in Example 1, and a nitrogen-undoped single crystal diamond layer / Ir(111) film / single crystal MgO(111) substrate was obtained. Next, the Ir(111) film / single crystal MgO(111) substrate was removed to obtain 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. Then, the substrate was cut out with a laser to obtain a nitrogen-undoped single crystal diamond(111) free-standing single layer substrate having a size of 2 mm square and a thickness of about 250 μm. The front surface of the substrate was polished to obtain a single crystal diamond substrate having a size of 2 mm square, a thickness of about 200 μm, a main surface of (111), and an off angle of 4° in the crystal axis [-1-1 2] direction, which was polished on one side, and which was to become a base substrate.

[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 (approx. 1.3×10 -4 After confirming that the temperature is below 1 Pa, 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. Methane gas 0.100% by volume Hydrogen gas 99.850% by volume Nitrogen gas 0.050% by volume The pressure in the chamber was adjusted to 120 Torr (approximately 1.6 × 10 4 After setting the pressure at 1000 MPa, a microwave power of 3500 W was input and deposition was carried out for 96 hours, thereby depositing a nitrogen-doped single crystal diamond layer until it reached a thickness of approximately 218 μm. In this manner, 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 subjected to SIMS and XRD analyses. 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 , hydrogen concentration is [H] = 1.5 × 10 17 atoms / cm 3 It was. The steepness (thickness of the 1 / e-fold drop region) of the nitrogen concentration profile in the interface region in the nitrogen-doped layer was about 1.0 μm.

[0107] X-ray diffraction measurement device: Rigaku Smart Lab. The crystallinity was analyzed from the outermost surface of the film under the following conditions: 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°, receiving side 2.5°, slit entrance 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. As a result, only a diffraction intensity peak at 2θ=43.9° attributed to diamond (111) was observed, confirming that the nitrogen-doped single crystal diamond film had grown epitaxially on the undoped single crystal diamond (111) layer.

[0108] Furthermore, we performed NVC evaluations using a confocal microscope (incident wavelength 532 nm), including photoluminescence measurement, confocal microscope image observation, optically detected magnetic resonance (ODMR) measurement, and Rabi oscillations. As a result, NVC light with a wavelength of 637 nm was detected, and the NVC density calculated from the electron spin relaxation time T = 19.9 μs was 1.4 × 10 17 / cm 3 It was. Therefore, 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. the result, 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 the like in the nitrogen-doped layer in Example 2 were as follows. Nitrogen concentration: 1.4×10 18 atoms / cm 3 Hydrogen concentration: 1.5×10 17 atoms / cm 3 NVC density: 1.4×10 17 / cm 3 12 C and 13 C abundance ratio: 12 C is 99.995%, 13 C is 0.005% Steepness at interface region: approx. 1.0 μm

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

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

[0114] Example 3 When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used is as follows: Methane gas 0.005% by volume ( 12 C composition methane gas / 13 C Composition methane gas = 99.500% by volume / 0.500% by volume Hydrogen gas 99.945% 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 nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate.

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

[0116] Example 4 When epitaxially growing nitrogen-doped single crystal diamond, the raw material is 12 C composition methane gas / 13 C composition methane gas = 99.995% by volume / 0.005% by volume 12 A mixture of C-enriched methane gas, hydrogen gas (purity > 99.99999% by volume), and nitrogen gas (purity > 99.99995% by volume) is added in the following volume ratios: 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 nitrogen-doped single crystal diamond layer / undoped single crystal diamond (111) substrate.

[0117] The various measurement results were as follows: Nitrogen concentration: 1.0×10 18 atoms / cm 3 Hydrogen concentration: 1.5×10 17 atoms / cm 3 NVC density: 9.5×10 16 / cm 3 12 C and 13 C abundance ratio: 12 C is 99.995%, 13 C is 0.005% Steepness at interface region: approx. 1.2 μm

[0118] Comparative Example 2 When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used is as follows: Methane gas 0.001% by volume Hydrogen gas 99.949% by volume Nitrogen gas 0.050% by volume The rest of the process was similar to that of 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, the volume ratio of methane gas was too low, which made it difficult for the nitrogen-doped single crystal diamond to grow, and so the deposition was discontinued midway.

[0119] Comparative Example 3 When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used is as follows: Methane gas 14.000% by volume Hydrogen gas 85.950% by volume Nitrogen gas 0.050% by volume The rest of the process was similar to that of 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 in the nitrogen-doped layer became polycrystalline.

[0120] Comparative Example 4 When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used is as follows: Methane gas 0.100% by volume Hydrogen gas approx. 99.850% by volume Nitrogen gas 0.00001% 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 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 those of each of the Examples and Comparative Example 1.

[0121] Comparative Example 5 When epitaxially growing nitrogen-doped single crystal diamond, the mixed gas used is as follows: Methane gas 0.100% by volume Hydrogen gas 85.900% by volume Nitrogen gas 14.000% by volume The rest of the process was similar to that of 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 in the nitrogen-doped layer became polycrystalline.

[0122] Thus, in the case of the present invention in Examples 1-4, it was possible to produce a high density NVC. This allows a highly sensitive sensor to be produced. On the other hand, when the conditions of the present invention are not satisfied as in Comparative Example 1, the NVC density is inferior to that of the present invention even if the nitrogen concentration is the same as that of the present invention. In Comparative Examples 2, 3, and 5, the growth of the nitrogen-doped single crystal diamond layer was not good to begin with. In Comparative Example 4, the NVC density was significantly reduced.

[0123] Example 5 In the case of Example 1 and Example 2, the undoped and nitrogen-doped single crystal diamonds were formed using the CVD methods of direct current plasma CVD, hot filament CVD, and arc discharge plasma jet CVD, respectively, or a combination of multiple CVD methods, and the resulting nitrogen-doped layers had an NVC density of 4.4 × 10 16 -1.4×10 17 / cm 3 The diamond crystals were single crystals with a (111) orientation. Also, 12 C and 13 Various measurement results 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] (Example 6 and Example 7) When epitaxially growing nitrogen-doped single crystal diamond, the nitrogen gas in the mixed gas used is increased by 5.0×10 compared to Example 2. -5 % by volume (Example 6) or 8,000% by volume (Example 7), and the volume percentage of hydrogen gas was adjusted accordingly. The rest of the process was carried out 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. In each case, the nitrogen-doped single crystal diamond did not become polycrystallized, and various measurement results were comparable to those of the other examples, with the NVC density being better than that of each comparative example.

[0125] The present specification includes the following aspects. [1]: A method for manufacturing a diamond substrate by forming diamond crystals on a base substrate using a source gas containing a hydrocarbon gas and a dilution gas, such as hydrogen gas, by any one of the chemical vapor deposition (CVD) methods, In order to form a diamond crystal layer having a nitrogen vacancy center in at least a part of the diamond crystal formed on the base substrate, nitrogen gas or a nitride gas is mixed into the raw material gas, and the amount of each gas contained in the raw material gas is 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. The amount of nitrogen gas or nitride gas is 5.0 x 10 -5 Volume percent or more and 8,000 volume percent or less to form a diamond crystal layer having the nitrogen vacancy center; The hydrocarbon gas in the raw material gas is a carbon isotope. 12 The ratio of C in the hydrocarbon gas is higher than that in natural hydrocarbon gas. 12 A method for manufacturing diamond substrates using C-enriched hydrocarbon gas. [2]: The method for producing 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]: The method for producing 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 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 above 12 C concentrated hydrocarbon gas 12 C-enriched hydrocarbon gas 12 The method for manufacturing a diamond substrate according to any one of the above [1] to [4], wherein the volume ratio of the hydrocarbon gas composed of C is 99.950 volume % or more. [6]: The above 12 C concentrated hydrocarbon gas 12 C-enriched hydrocarbon gas 13 The method for manufacturing a diamond substrate according to any one of the above [1] to [5], 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 any one of [1] to [6] above, wherein the base substrate is a single-layer substrate of single crystal diamond. [8]: The method for producing 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 synthetic homoepitaxial diamond layer. [9]: A method for manufacturing a diamond substrate according to any one of [1] to [8] above, wherein in forming a diamond crystal by the CVD method, a diamond crystal layer not containing a nitrogen vacancy center is formed using a natural hydrocarbon gas.

[10] : The method for producing a diamond substrate according to any one of [1] to [9] above, wherein the base substrate has a laminated structure comprising a lower-layer substrate and an intermediate layer on the lower-layer substrate.

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

[10] above, 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 producing a diamond substrate according to any one of [1] to

[11] above, wherein the CVD method is one or more of a microwave plasma CVD method, a direct current plasma CVD method, a hot filament CVD method, and an arc discharge plasma jet CVD method.

[13] : A method for producing a diamond substrate, comprising removing the undersubstrate from a diamond substrate obtained by any one of the methods for producing a diamond substrate according to any one of [1] to

[12] above, the diamond substrate comprising a diamond crystal layer having a nitrogen vacancy center, to obtain a single-crystal diamond free-standing substrate comprising a diamond crystal layer having a nitrogen vacancy center.

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

[13] above.

[15] : A diamond substrate comprising a diamond crystalline layer having nitrogen vacancy centers, the diamond crystal layer having a nitrogen vacancy centre is formed on a diamond crystal layer which does not contain a nitrogen vacancy centre or on a single layer substrate of single crystal diamond; In the carbon atom present in the diamond crystal layer having the nitrogen vacancy center, 12 The abundance ratio of C is higher than the abundance ratio of natural carbon atoms, A diamond substrate, wherein the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy centres is steep in an interface region with the diamond crystal layer not containing the nitrogen vacancy centres or with the single layer substrate of single crystal diamond.

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

[15] above, 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 region until the nitrogen concentration [N] reaches 1 / e (Napier's number) times at the interface region with the diamond crystal layer or single crystal diamond substrate not containing the nitrogen vacancy center is 1.5 μm or less.

[17] : The hydrogen concentration [H] in the diamond crystal layer having the nitrogen vacancy center is 1×10 16 atoms / cm 3 The above is the diamond substrate

[16] .

[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 The diamond substrate according to any one of

[15] to

[17] above.

[19] : The diamond substrate according to 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 center is Ra≦260 nm.

[20] : A sensor using a diamond substrate, any of the above

[15] to

[19] .

[0126] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0127] 11, 21, 31, 41, 51...Base substrate, 12, 22, 32, 42, 52... NVC-containing layer, 23, 53...NVC-free layer, 24, 44, 54…Lower layer board, 25, 45, 55...middle class, 100, 200, 300, 400, 500…Diamond substrate, 600...Freestanding single crystal diamond substrate.

Claims

1. A method for manufacturing a diamond substrate by forming a diamond crystal on a base substrate by chemical vapor deposition (CVD) using a source gas including a hydrocarbon gas and a dilution gas including hydrogen gas, comprising: In order to form a diamond crystal layer having a nitrogen vacancy center in at least a part of the diamond crystal formed on the base substrate, nitrogen gas or a nitride gas is mixed into the raw material gas, and the amount of each gas contained in the raw material gas is The amount of the hydrocarbon gas is 0.005% by volume or more and 7.000% by volume or less, The amount of hydrogen gas is 85.000 vol.% or more and less than 99.995 vol.%; The amount of nitrogen gas or nitride gas is 5.0 x 10 －５ % by volume or more and 8.000% by volume or less to form a diamond crystal layer having the nitrogen vacancy center; The hydrocarbon gas in the raw material gas is a carbon isotope. 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. 2. The method for producing a diamond substrate according to claim 1, 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. 3. The method for manufacturing a diamond substrate according to claim 1, wherein the hydrocarbon gas in the source gas is methane gas.

4. 3. The method for producing a diamond substrate according to claim 1, wherein a gas pressure in forming the diamond crystal by the CVD method is set to 1.3 kPa (10 Torr) or more and 50.0 kPa (376 Torr) or less.

5. The above 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 above 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. 3. The method for producing a diamond substrate according to claim 1, wherein the base substrate is a single-layer substrate of single crystal diamond.

8. 8. The method for producing a diamond substrate according to claim 7, 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 synthetic homoepitaxial diamond layer.

9. 3. The method for producing a diamond substrate according to claim 1, wherein in forming the diamond crystal by the CVD method, when a diamond crystal layer not containing a nitrogen vacancy center is formed, a natural hydrocarbon gas is used.

10. 3. The method for producing a diamond substrate according to claim 1, wherein the base substrate has a laminated structure comprising a lower layer substrate and an intermediate layer on the lower layer substrate.

11. 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. 3. The method for manufacturing a diamond substrate according to claim 1, wherein the CVD method is at least one of a microwave plasma CVD method, a direct current plasma CVD method, a hot filament CVD method, and an arc discharge plasma jet CVD method.

13. 3. 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 according to 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 a surface of a diamond crystal layer having a nitrogen vacancy center of a diamond substrate obtained by the method for manufacturing a diamond substrate according to claim 1 or 2, the diamond crystal layer having a nitrogen vacancy center being formed.

15. 1. A diamond substrate comprising a diamond crystal layer having nitrogen vacancy centers, the diamond crystal layer having a nitrogen vacancy centre is formed on a diamond crystal layer which does not contain a nitrogen vacancy centre or on a single layer substrate of single crystal diamond; In the carbon atom present in the diamond crystal layer having the nitrogen vacancy center, １２ The abundance of C is higher than the abundance of natural carbon atoms, A diamond substrate characterized in that the nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy center is steep in the interface region with the diamond crystal layer not containing the nitrogen vacancy center or with the single layer substrate of single crystal diamond.

16. The nitrogen concentration profile in the diamond crystal layer having the nitrogen vacancy center was 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. 18. The diamond substrate according to claim 15, wherein the average surface roughness Ra of the surface of the diamond crystal layer having the nitrogen vacancy center is Ra≦260 nm.

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

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