Diamond substrate and method for manufacturing the same

Abstract

To stably provide a diamond crystal which is obtained by performing CVD under prescribed conditions on a highly oriented (111) diamond base substrate obtained by performing CVD under the same prescribed conditions, has an NV axis of [111] orientation and high-density NVC, and is applicable to an electronic / magnetic device, and to stably provide a method for producing the same.SOLUTION: The method for producing a diamond substrate is a method for producing a (111) - oriented diamond crystal on a base substrate by epitaxial growth using hydrogen-diluted methane as a main raw material gas by a microwave plasma CVD method, a DC plasma CVD method, a hot filament CVD method or an arc discharge plasma jet CVD method, wherein the growth rate is less than 3.8 μm / h.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a diamond substrate and a method for manufacturing the same. [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. 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. 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. Furthermore, diamond has nitrogen-vacancy centers (NVCs) present in the crystal, which allow single spin manipulation and detection at room temperature, and their state can be imaged using optically detected magnetic resonance. Utilizing this feature, 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 fields. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US2013 / 0143022A1 [Patent Document 2] Japanese Patent Publication No. 2020-090408 [Non-patent literature]

[0004] [Non-Patent Document 1] M.Hatano et al., OYOBUTURI 85, 311 (2016) Summary of the Invention [Problem to be solved by the invention]

[0005] 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. In particular, for the highly important NVC device application, a high NV axis orientation is required, and therefore, it is desirable for the diamond surface to have a (111) crystal plane in which the NV axis is aligned in the <0111> direction (Non-Patent Document 1).

[0006] Furthermore, when considering applications in the field of medical MRI, for example, if the diamond substrate that forms the magnetic sensor has a large diameter, it will be possible to realize a device that can measure a wider area efficiently, which will also be advantageous in terms of manufacturing costs.

[0007] Patent Document 1 reports a technology for forming diamond (111) crystals by heteroepitaxial growth using chemical vapor deposition (CVD). However, it is unclear whether the size and properties of the finished crystals are sufficient.

[0008] Therefore, we have invented a laminated substrate having a large diameter and high quality single crystal diamond (111) that can be used in electronic and magnetic devices, a large diameter single crystal diamond (111) free-standing substrate, a method for manufacturing the laminated substrate, and a method for manufacturing the free-standing substrate (Patent Document 2).

[0009] However, when single-crystal diamond (111) is grown to a thickness of 80 μm or more, or when crystal growth is repeated, it has become clear that there is a problem with the reproducibility of the crystal orientation.

[0010] For example, even when hetero diamond (111) was used as the base substrate, the orientation sometimes changed to (001) during crystal growth. This problem occurred whether the base diamond layer was undoped diamond or the N-doped diamond was NVC layer.

[0011] The present invention has been made to solve the above problems, and aims to provide a diamond crystal applicable to electronic and magnetic devices, which has a high density NVC and an NV axis of <0111> orientation, obtained by CVD under specified conditions on a highly oriented (111) diamond base substrate obtained by CVD under the same specified conditions, and a stable method for producing the same. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a method for producing a diamond substrate by epitaxial growth of (111) oriented diamond crystals on a base substrate using hydrogen-diluted methane as the main raw material gas by microwave plasma CVD, DC plasma CVD, hot filament CVD, or arc discharge plasma jet CVD, with a growth rate of less than 3.8 μm / h.

[0013] This method for manufacturing diamond substrates can reliably provide diamond crystals that are applicable to electronic and magnetic devices, in which the NV axis is oriented in the

[0111] direction and the crystals have high density NVC, obtained by CVD under specified conditions on a highly oriented (111) diamond base substrate obtained by CVD under the same specified conditions, and a method for manufacturing such diamond crystals.

[0014] In this case, in the method for producing the (111) oriented diamond crystal by epitaxial growth, a (111) oriented nitrogen-doped diamond crystal can be produced on the base substrate using hydrogen-diluted methane as the main raw material gas and adding nitrogen gas as a dopant.

[0015] Such a method for manufacturing a diamond substrate can more reliably provide diamond crystals that have an NV axis oriented in the

[0111] direction and high density NVC, and that are applicable to electronic and magnetic devices, as well as a method for manufacturing such diamond crystals.

[0016] At this time, it is preferable that the temperature of the base substrate during growth by the microwave plasma CVD method, the DC plasma CVD method, the hot filament CVD method, or the arc discharge plasma jet CVD method is in the range of 600°C to 1050°C.

[0017] This temperature range is preferable because it prevents the growth of non-diamond phases such as amorphous carbon and graphite, prevents the growth rate from increasing too much, allows (111) growth to follow, and prevents (001) growth from becoming dominant.

[0018] In this case, the base substrate can be a single-layer substrate of single-crystal diamond (111).

[0019] Such a base substrate is preferable because it allows the production of a diamond substrate of higher quality.

[0020] In this case, it is preferable that the base substrate is the single crystal diamond (111) and that the main surface has an off-angle in the range of -8.0° to -0.5° or +0.5° to +8.0° relative to the crystal plane orientation (111) in the crystal axis [-1-12] direction or in a three-fold symmetric direction thereof.

[0021] An off-angle within this range is preferred because it facilitates step flow growth and results in a high-quality single-crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc.

[0022] In this case, the base substrate made of the single crystal diamond (111) can be a high-temperature, high-pressure synthetic single crystal diamond, a heteroepitaxial single crystal diamond, a CVD synthetic homoepitaxial diamond, or a single crystal diamond that is a combination of these.

[0023] Such a base substrate is preferable because it allows the production of a diamond substrate of even higher quality.

[0024] In the present invention, the base substrate may have a laminated structure consisting of a lower layer substrate and an intermediate layer on the lower layer substrate.

[0025] Such a base substrate is preferable because it allows the production of a diamond substrate of even higher quality.

[0026] In this case, the outermost surface of the intermediate layer can be a metal layer selected from Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn and Ti.

[0027] The use of such a metal layer is preferable because it makes it easier for the diamond nuclei to have a high density when subjected to nucleation treatment (bias treatment), and makes it easier for a single crystal diamond layer to be formed thereon.

[0028] In this case, the lower substrate can be a single substrate made of Si, MgO, Al2O3, SiO2, Si3N4, SiC, Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn, or Ti, or a laminate selected from Si, MgO, Al2O3, SiO2, Si3N4, SiC, Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn, and Ti.

[0029] These materials are preferred because they allow easy setting of the crystal plane orientation (including the off-angle) of the main surface of the base substrate, are relatively inexpensive, and are readily available.

[0030] In this case, the lower substrate may have a main surface oriented in the (111) plane, or may further include a layer between the lower substrate and the intermediate layer, the main surface of which has a (111) plane orientation.

[0031] Such a method for manufacturing a diamond substrate is preferable because it enables more efficient epitaxial growth.

[0032] In this case, the main surface of the lower substrate having the (111) plane orientation can have an off angle in the range of -8.0° to -0.5° or +0.5° to +8.0° relative to the (111) crystal plane orientation in the crystal axis [-1-12] direction or its three-fold symmetric direction.

[0033] An off-angle within this range is preferred because it facilitates step flow growth and results in a high-quality single-crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc.

[0034] Furthermore, in the present invention, in the method for manufacturing a diamond substrate, the total thickness of the diamond formed on the base substrate can be set to 80 to 2000 μm.

[0035] Such a total thickness is preferable because it is easy to obtain highly (111) oriented crystals.

[0036] In the present invention, in the method for producing a diamond substrate, it is preferable that no Si-containing member is used in the chamber in which CVD is performed.

[0037] Such a method for manufacturing a diamond substrate is preferable because it prevents Si from being mixed into the diamond crystal.

[0038] In this case, it is preferable to use sapphire for the observation window of the chamber in which the CVD is performed.

[0039] Even such a method for manufacturing a diamond substrate is preferable because it does not cause Si to become mixed into the diamond crystal.

[0040] Furthermore, in the present invention, a (111) oriented diamond substrate can be obtained by removing the base substrate from the layered substrate containing the (111) oriented diamond crystal obtained by the above method for manufacturing a diamond substrate.

[0041] Such a method for manufacturing a diamond substrate is preferable because it allows a free-standing diamond substrate to be obtained, thereby reducing the causes of noise in practical use.

[0042] In addition, in the present invention, a (111) oriented diamond substrate can be obtained by removing the base substrate, the lower substrate, or both the intermediate layer and the lower substrate from a layered substrate containing the (111) oriented diamond crystal obtained by the above-mentioned method for manufacturing a diamond substrate.

[0043] Even such a method for manufacturing a diamond substrate is preferable because it is possible to obtain a diamond substrate with a free-standing structure and reduce the causes of noise in practical use.

[0044] In the present invention, it is also preferable to smooth the surface of the (111) oriented diamond crystal obtained by the above method for producing a diamond substrate.

[0045] Such a method for manufacturing a diamond substrate is preferable because it results in a diamond substrate that is more suitable as a substrate for electronic and magnetic devices.

[0046] The present invention also provides a diamond substrate, which, when measured by an X-ray diffraction apparatus using the pole method with a Cu anticathode as the X-ray generating unit, under conditions of an output of 45 kV and 200 mA, an evaluation diffraction plane of (111), a diffraction angle 2θ = 43.9°, and a step width of 1°, detects a (111) plane diffraction peak when the (111) plane is oriented in the normal direction to the main surface of the substrate, but does not detect a (111) plane diffraction peak when the (001) plane is oriented in the normal direction to the main surface of the substrate.

[0047] Such a diamond substrate can be obtained by CVD under specified conditions on a highly oriented (111) diamond base substrate, and by CVD under the same specified conditions, the NV axis will be oriented in the

[0111] direction and have high density NVC, making it a substrate made of diamond crystals suitable for electronic and magnetic devices.

[0048] In this case, it is preferable that the diamond substrate has a rocking curve half-width of 0.90° or less when measured by an X-ray diffractometer using an out-of-plane method, a Cu anticathode as the X-ray generating unit, an output of 45 kV, 200 mA, an evaluation diffraction surface (111), a diffraction angle 2θ = 43.9°, and a step width of 0.001°.

[0049] Such a diamond substrate can be made of diamond crystals of higher quality. [Effects of the Invention]

[0050] As described above, the method for manufacturing a diamond substrate of the present invention makes it possible to provide a diamond substrate that is applicable to electronic and magnetic devices, which has high crystallinity, a high NV axis orientation in the

[0111] direction, and high density NVC, on a base substrate of HPHT, hetero-, or homo-epitaxial diamond. Furthermore, the diamond substrate of the present invention has high crystallinity, a high <0111> orientation of the NV axis, and high density NVC, making it applicable to electronic and magnetic devices. [Brief explanation of the drawings]

[0051] [Figure 1] 1 is a diagram showing an example of forming a (111) oriented nitrogen-doped diamond crystal on a base substrate of a single-layer substrate according to the present invention. [Figure 2] 1 is a diagram showing an example of forming a (111) oriented nitrogen-doped diamond crystal on a base substrate having a layered structure according to the present invention. [Figure 3] 1 is a diagram showing an example in which a (111) oriented diamond crystal and a (111) oriented nitrogen-doped diamond crystal are formed on a base substrate having a layered structure according to the present invention. [Figure 4] 1 is a diagram showing an example of a (111) oriented nitrogen-doped diamond crystal / diamond substrate on which a (111) oriented diamond crystal remains according to the present invention. [Figure 5] 1 is a diagram illustrating a plane orientation. [Figure 6] 1 is a diagram showing the results of XRD pole point measurement of the polished nitrogen-undoped single crystal (111) oriented diamond substrate of Example 1. [Figure 7] 1 is a diagram showing the results of a three-dimensional display of the measurement results of the XRD pole point method of the polished nitrogen-undoped single crystal (111) oriented diamond substrate of Example 1. [Figure 8] 1 is a diagram showing the fluorescence spectrum of the (111) oriented nitrogen-doped diamond crystal of Example 1 at an excitation light wavelength of 532 nm. [Figure 9] 1 is a diagram showing the analysis results obtained by the EBSD method. DETAILED DESCRIPTION OF THE INVENTION

[0052] As mentioned above, for electronic and magnetic devices, it was necessary to stably obtain diamond substrates with a high (111) orientation of the diamond crystal, a high <0111> orientation of the NV axis when nitrogen-doped, and high density NVC.

[0053] As a result of extensive research into the above-mentioned problems, the inventors have found that the method for manufacturing a diamond substrate of the present invention can stably provide diamond crystals applicable to electronic and magnetic devices, which have an NV axis oriented in

[0111] and high density NVC, obtained by CVD under specified conditions on a highly oriented (111) diamond base substrate obtained by CVD under the same specified conditions, and a manufacturing method thereof, and have thus completed the present invention.

[0054] That is, the present invention is a method for producing a (111) oriented diamond crystal by epitaxial growth on a base substrate using hydrogen-diluted methane as the main raw material gas by microwave plasma CVD, DC plasma CVD, hot filament CVD, or arc discharge plasma jet CVD, and is a method for producing a diamond substrate with a growth rate of less than 3.8 μm / h.

[0055] The present invention will be described in detail below, but the present invention is not limited thereto.

[0056] The following description will be made with reference to the drawings.

[0057] First, the terms used in this specification will be defined. In this specification, a crystal layer or crystal film whose main surface is a (111) plane will be simply referred to as a "(111) layer" or "(111) film." For example, a single-crystal diamond layer whose main surface is a (111) plane will be referred to as a "single-crystal diamond (111) layer."

[0058] The relationship between the off-angle and the [-1-12] direction is shown in Figure 5. Figure 5 shows a conceptual diagram of the off-angle and the [-12-1] and [2-1-1] directions, which are three-fold symmetric directions of the [-1-12] direction, of a substrate whose main surface is a (111) plane. TIFF2026034565000002.tif1080

[0059] (diamond substrate) The present invention provides a diamond substrate, which, when measured by an X-ray diffraction apparatus using the pole method with a Cu anticathode as the X-ray generating unit, under conditions of an output of 45 kV and 200 mA, an evaluation diffraction plane of (111), a diffraction angle 2θ = 43.9°, and a step width of 1°, detects a (111) plane diffraction peak when the (111) plane is oriented in the normal direction to the main surface of the substrate, but does not detect a (111) plane diffraction peak when the (001) plane is oriented in the normal direction to the main surface of the substrate.

[0060] In this case, it is preferable that the diamond substrate has a rocking curve half-width of 0.90° or less when measured by an X-ray diffractometer using an out-of-plane method, a Cu anticathode as the X-ray generating unit, an output of 45 kV, 200 mA, an evaluation diffraction surface (111), a diffraction angle 2θ = 43.9°, and a step width of 0.001°.

[0061] Such high-quality diamond substrates with a highly oriented NV axis and high density NVC are applicable to electronic and magnetic devices and can be manufactured by the following method.

[0062] (Method of manufacturing diamond substrate) The present invention is a method for producing a (111) oriented diamond crystal by epitaxial growth on a base substrate using hydrogen-diluted methane as the main raw material gas by microwave plasma CVD, DC plasma CVD, hot filament CVD, or arc discharge plasma jet CVD, and is a method for producing a diamond substrate with a growth rate of less than 3.8 μm / h.

[0063] If the growth rate is 3.8 μm / h or higher, the crystal growth mode changes from (111) oriented growth to (001) oriented growth, and the desired (111) highly oriented crystals cannot be obtained. Conversely, if the growth rate is kept below 3.8 μm / h, growth continues while maintaining the (111) orientation, and the desired (111) highly oriented crystals can be obtained. However, a rate of 3.3 μm / h or less is preferable because it provides more stable crystal growth.

[0064] In this case, in the method for producing the (111) oriented diamond crystal by epitaxial growth, a (111) oriented nitrogen-doped diamond crystal can be produced on the base substrate using hydrogen-diluted methane as the main raw material gas and adding nitrogen gas as a dopant.

[0065] At this time, it is preferable that the temperature of the base substrate during growth by the microwave plasma CVD method, the DC plasma CVD method, the hot filament CVD method, or the arc discharge plasma jet CVD method is in the range of 600°C to 1050°C.

[0066] If the temperature is above 600°C, non-diamond phases such as amorphous carbon and graphite do not grow, while if the temperature is below 1050°C, the growth rate does not increase too much, allowing (111) growth to follow and preventing (001) growth from becoming dominant.

[0067] In this case, the base substrate can be a single-layer substrate of single-crystal diamond (111).

[0068] FIG. 1 shows a substrate in which a (111) oriented nitrogen-doped diamond crystal (NVC-containing diamond layer) 2 is formed on a base substrate 1 .

[0069] In this case, it is preferable that the base substrate is the single crystal diamond (111) and that the main surface has an off-angle in the range of -8.0° to -0.5° or +0.5° to +8.0° relative to the crystal plane orientation (111) in the crystal axis [-1-12] direction or in a three-fold symmetric direction thereof.

[0070] If the off-angle is within this range, step flow growth is facilitated, resulting in a high-quality single-crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc.

[0071] In this case, the base substrate made of the single crystal diamond (111) can be a high-temperature, high-pressure synthetic single crystal diamond, a heteroepitaxial single crystal diamond, a CVD synthetic homoepitaxial diamond, or a single crystal diamond that is a combination of these.

[0072] In the present invention, the base substrate may have a laminated structure consisting of a lower layer substrate and an intermediate layer on the lower layer substrate.

[0073] FIG. 2 shows a substrate in which a (111) oriented nitrogen-doped diamond crystal 5 is formed on a layered structure base substrate (base substrate 3, intermediate layer 4).

[0074] The intermediate layer may be a single layer or a laminate of multiple layers. The outermost surface of the intermediate layer is preferably a metal layer selected from Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn and Ti. The use of such a metal layer is preferred because it makes it easier for the diamond nuclei to have a high density during nucleation treatment (bias treatment), and makes it easier for a single-crystal diamond layer to be formed thereon.

[0075] In this case, the lower substrate can be a single substrate made of Si, MgO, Al2O3, SiO2, Si3N4, SiC, Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn, or Ti, or a laminate selected from Si, MgO, Al2O3, SiO2, Si3N4, SiC, Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn, and Ti.

[0076] These materials allow easy setting of the crystal plane orientation (including the off-angle) of the main surface of the base substrate, and are also relatively inexpensive and readily available.

[0077] Naturally, the base substrate may be one in which the lower substrate and intermediate layer are made of the same material. Note that a substrate made of a single material selected from Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn, and Ti may also be used as the base substrate.

[0078] In this case, the lower substrate may have a main surface oriented in the (111) plane, or may further include a layer between the lower substrate and the intermediate layer, the main surface of which has a (111) plane orientation.

[0079] This allows for more efficient epitaxial growth.

[0080] In this case, the main surface of the lower substrate having the (111) plane orientation can have an off angle in the range of -8.0° to -0.5° or +0.5° to +8.0° relative to the (111) crystal plane orientation in the crystal axis [-1-12] direction or its three-fold symmetric direction.

[0081] If the off-angle is within this range, step flow growth is facilitated, and a high-quality single-crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc. can be obtained.

[0082] When the off-angle is greater than -0.5° and less than +0.5°, growth in the step direction is difficult, making it difficult to obtain good crystals. When the off-angle is less than -8.0° or greater than +8.0°, long-term growth leads to polycrystallization, making it impossible to obtain good-quality single crystals.

[0083] Furthermore, in the present invention, in the method for manufacturing a diamond substrate, the total thickness of the diamond formed on the base substrate can be set to 80 to 2000 μm.

[0084] With such a total thickness, it is easy to obtain highly (111) oriented crystals.

[0085] A thickness of 80 μm or more results in fewer dislocation defects and higher orientation, while a thickness of 2000 μm or less results in the same growth position relative to the plasma as in the initial growth stage, preventing increases in substrate temperature and growth rate, and preventing excessive abnormal growth.

[0086] The chamber inner walls of the typical CVD equipment used to manufacture the diamond substrates are made of stainless steel, the stages are made of stainless steel and molybdenum, the insulators are Si3N4, SiC, Al2O3, BN, etc., and the observation window is made of SiO2. When diamond is manufactured using such a typical CVD equipment, Si becomes mixed into the diamond crystal, forming silicon-vacancy centers (SiVCs), which become a noise source when the diamond substrate is used in an electronic or magnetic sensor.

[0087] Therefore, in the present invention, in the method for producing a diamond substrate, it is preferable not to use any Si-containing member in the chamber where CVD is performed.

[0088] In particular, the observation window of the chamber where CVD is performed is thought to be a source of Si contamination, and therefore, it is preferable to use sapphire for the observation window of the chamber where CVD is performed.

[0089] Furthermore, in the present invention, a (111) oriented diamond substrate can be obtained by removing the base substrate from the layered substrate containing the (111) oriented diamond crystal obtained by the above method for manufacturing a diamond substrate.

[0090] In addition, in the present invention, a (111) oriented diamond substrate can be obtained by removing the base substrate, the lower substrate, or both the intermediate layer and the lower substrate from a layered substrate containing the (111) oriented diamond crystal obtained by the above-mentioned method for manufacturing a diamond substrate.

[0091] By increasing the proportion of NVC-containing parts, the causes of noise during actual use can be reduced, making it possible to realize highly sensitive electronic and magnetic devices.

[0092] Figure 3 shows a diamond substrate in which a (111) oriented diamond crystal 6 and a (111) oriented nitrogen-doped diamond crystal 5 are formed in this order on a layered base substrate (lower layer substrate 3, intermediate layer 4).

[0093] FIG. 4 shows a case where the base substrate portion has been removed to provide a free-standing substrate of (111) oriented nitrogen-doped diamond crystal 5 / (111) oriented diamond crystal 6 .

[0094] In the present invention, it is also preferable to smooth the surface of the (111) oriented diamond crystal obtained by the above method for producing a diamond substrate.

[0095] For smoothing, mechanical polishing, chemical-mechanical polishing, plasma treatment, sputtering treatment, chemical etching, etc. may be used. [Example]

[0096] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0097] Example 1 As a base substrate, a single-side polished single-crystal MgO substrate (hereinafter referred to as "single-crystal MgO (111) substrate") was prepared. The substrate had a diameter of 20.0 mm, a thickness of 1.0 mm, a (111) plane as its main surface, and an off-angle of +4° in the crystal axis [-1-12] direction relative to the (111) crystal plane orientation.

[0098] 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 6 inches (150 mm) in diameter, 5.0 mm thick, and 99.9% or higher purity.

[0099] The single-crystal MgO(111) substrate, which is the lower substrate, is heated to 800°C, and the base pressure is 6×10 -7 Torr (approx. 8.0 × 10 -5 After confirming that the pressure had dropped 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 After adjusting the pressure to Torr (approximately 39.9 Pa), 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.

[0100] The single-crystal Ir film deposited on the single-crystal MgO(111) substrate (Ir(111) film / single-crystal MgO(111) substrate) obtained as described above grew heteroepitaxially, following the misorientation of the single-crystal MgO(111) substrate. Analysis of this single-crystal Ir film using out-of-plane X-ray diffraction at a wavelength of λ = 1.54 Å revealed that the surface was a (111) plane with a +4° misorientation along the [-1-12] axis relative to the (111) crystal plane orientation. Furthermore, the full width at half maximum (FWHM) of the diffraction peak at 2θ = 40.7° attributed to Ir(111) was 0.142°. Hereafter, this single-crystal Ir film will be referred to as the "Ir(111) film."

[0101] Next, a nucleation treatment (bias treatment) was performed as a pretreatment for diamond nucleation. The Ir(111) film / single-crystal MgO(111) substrate was placed on a 25 mm diameter flat electrode 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 100 Torr (approximately 1.3 × 10 Pa), hydrogen-diluted methane gas (CH4 / (CH4+H2) = 5.0 vol.%) 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 Ir(111) film / single-crystal MgO(111) substrate was exposed to plasma for 90 seconds by applying a negative voltage to the electrode on the Ir(111) film / single-crystal MgO(111) substrate side, the Ir(111) film surface of the Ir(111) film / single-crystal MgO(111) substrate was bias-treated.

[0102] On the Ir(111) film / single-crystal MgO(111) substrate prepared as described above, (111)-oriented diamond crystals were heteroepitaxially grown by microwave plasma CVD. The bias-treated Ir(111) film / single-crystal MgO(111) substrate was placed in the chamber of a microwave plasma CVD apparatus, and the base pressure was set to 1×10 -6 Torr (approx. 1.3 × 10 -4After confirming that the pressure has dropped below 1 Pa, the substrate temperature is set to 860 to 970°C and a mixture of methane gas and hydrogen gas is introduced. Methane gas 3.0000vol.%, Hydrogen gas 97.0000vol.%, The pressure in the chamber was adjusted to 110 Torr (approximately 1.5 × 10 4 After the pressure was increased to 1 Pa, microwaves of 3500 W were applied to perform film growth for 99 hours until the film reached a thickness of approximately 140 μm (growth rate: 1.4 μm / h).

[0103] In this way, a (111) oriented diamond crystal was heteroepitaxially grown on the Ir(111) film / single crystal MgO(111) substrate to obtain a laminated substrate.

[0104] After this, the Ir(111) film / single-crystal MgO(111) substrate was removed to obtain a free-standing substrate. First, the single-crystal MgO(111) substrate was removed by etching, and then the Ir(111) film was removed by polishing. As a result, a free-standing substrate ((111)-oriented diamond substrate) with a diameter of 20 mm and a (111)-oriented diamond crystal size of 140 μm was obtained.

[0105] The surface of the (111)-oriented diamond crystal of the (111)-oriented diamond substrate was smoothed and mirror-finished by skiff polishing. The surface of the (111)-oriented diamond crystal was measured over a 290 μm × 218 μm area using an optical surface roughness meter (ZYGO New View 5032), and the average surface roughness was found to be Ra = 0.4 (nm) (polished nitrogen-undoped single-crystal (111)-oriented diamond substrate).

[0106] Next, the polished nitrogen-undoped single-crystal (111) oriented diamond substrate was subjected to X-ray diffraction analysis. For the analysis, the crystallinity was measured from the outermost surface of the crystal using an X-ray diffraction (XRD) device (RIGAKU SmartLab, X-ray wavelength λ=1.54 Å).

[0107] First, the crystal orientation was examined using the pole point method. The sample was placed on a stage with the surface facing upward, and a Cu anticathode was used as the X-ray generator. The output was 45 kV, 200 mA, and the sample was moved in the diameter direction (α) and circumferential direction (β) while measurements were taken at an evaluation diffraction plane (111) and a diffraction angle 2θ = 43.9° with a step width of 1°.

[0108] As a result, a (111) diffraction peak was detected when the (111) plane was facing the normal direction of the main surface of the substrate, but no (111) diffraction peak was detected when the (001) plane was facing the normal direction of the main surface of the substrate. The results are shown in Figure 6.

[0109] As shown in Figure 6, when the (111) plane faces the normal direction of the main surface of the substrate, the (111) plane diffraction peak was observed near α = 0°, β = 0°. Furthermore, when the (111) plane faces the side direction of the main surface of the substrate, the (111) plane diffraction peak was observed near α = 70.6° and β = 120° intervals. Figure 7 shows a 3D display of the results in Figure 6. It was clearly a (111) oriented crystal.

[0110] On the other hand, when the (001) plane is oriented normal to the main surface of the substrate, the (111) plane diffraction peaks are detected at α=54.7° and β at 90° intervals, but they were not detected in the polished nitrogen-undoped single crystal (111)-oriented diamond substrate of the present invention.

[0111] Next, using the same XRD equipment as above, we examined the crystal orientation using the out-of-plane method. Using a Cu anticathode as the X-ray generator, we obtained a rocking curve under the following conditions: output 45 kV 200 mA, evaluation diffraction plane (111), diffraction angle 2θ = 43.9°, incident angle ω = 23-29°, step width 0.001°, and scan rate 1° / min. The results showed an off-angle of +5° and a rocking curve half-width of 0.665°.

[0112] Therefore, the polished nitrogen-undoped single-crystal (111)-oriented diamond substrate was a highly (111)-oriented crystal. If such a substrate is applied to electronic and magnetic devices, high-performance devices can be obtained.

[0113] Furthermore, a mixed gas containing methane gas, hydrogen gas, and nitrogen gas was applied to the polished nitrogen-undoped single-crystal (111) oriented diamond substrate by the microwave plasma CVD method described above. Methane gas 0.4000vol.%, Hydrogen gas 99.5995vol.% Nitrogen gas 0.0005vol.%, The volume ratio of the gas was 1.5×10 and the gas was introduced into the chamber at a flow rate of 500 sccm. The microwave power was 3500 W and the pressure was 110 Torr (approximately 1.5×10 4 The pressure and microwave power were kept the same at 1000 kJ / cm² (Pa) for 8 hours. After raising the substrate temperature to 680°C, film formation was carried out under these conditions for 5 hours, growing a nitrogen-doped layer ((111)-oriented nitrogen-doped diamond crystal) to a thickness of approximately 8 μm (growth rate 1.6 μm / h). In this way, a (111)-oriented nitrogen-doped diamond crystal / polished nitrogen-undoped single-crystal (111)-oriented diamond laminate substrate was obtained.

[0114] Finally, SIMS and PL analyses were performed on the finished (111) oriented nitrogen-doped diamond crystal / polished nitrogen-undoped single crystal (111) oriented diamond laminate substrate.

[0115] The nitrogen concentration [N] in the (111)-oriented nitrogen-doped diamond crystal / polished nitrogen-undoped single-crystal (111)-oriented diamond laminate substrate was measured using a secondary ion mass spectrometry (SIMS) device (CAMECA IMS-7f). As a result, the nitrogen concentration [N] at a depth of approximately 8 μm from the outermost surface of the (111)-oriented nitrogen-doped diamond crystal / polished nitrogen-undoped single-crystal (111)-oriented diamond laminate substrate was [N] = 6 × 10 17 atoms / cm 3 It was.

[0116] Next, measurements were taken using a photoluminescence (PL) spectrometer (JASCO NRS-4500) under the following conditions: excitation light wavelength 532 nm, excitation light intensity 0.02 mW, integration time 1 second, integration number 3, objective lens 100x, and room temperature (approximately 298 K). As a result, a sharp peak of NV-center (NVC) light (wavelength 637 nm) was observed. On the other hand, silicon vacancy center light (wavelength 738 nm) was not detected. The results are shown in Figure 8.

[0117] Therefore, the obtained (111)-oriented nitrogen-doped diamond crystal was a (111)-oriented nitrogen-doped diamond crystal with an NV axis oriented in

[0111] and with NVC formed at a high density. If this (111)-oriented nitrogen-doped diamond crystal is applied to electronic and magnetic devices, it will become a high-performance device. For example, a highly sensitive magnetic sensor can be obtained.

[0118] Example 2 A polished nitrogen-undoped single-crystal (111) oriented diamond substrate was prepared in the same manner as in Example 1, except that the substrate temperature was 800 to 850°C, the film formation time was 45 hours, and the growth rate was 0.7 µm / h.

[0119] Example 3 The substrate temperature is set to 860 to 1020°C, and a mixture of methane and hydrogen gas is used as the raw material. Methane gas 4.0000vol.%, Hydrogen gas 96.0000vol.%, A polished nitrogen-undoped single-crystal (111) oriented diamond substrate was prepared in the same manner as in Example 1, except that the volume ratio was changed to 100 hours and the growth rate was changed to 2.4 μm / h.

[0120] (Comparative Example 1) Diamond crystals were heteroepitaxially grown by microwave plasma CVD on an Ir(111) film / single-crystal MgO(111) substrate prepared in the same manner as in Example 1. 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 -6Torr (approx. 1.3 × 10 -4 After confirming that the pressure has dropped below 100 Pa, the substrate temperature is set to 830 to 1090°C and a mixture of methane gas and hydrogen gas is introduced. Methane gas 3.0000vol.%, Hydrogen gas 97.0000vol.%, The pressure in the chamber was adjusted to 110 Torr (approximately 1.5 × 10 4 After the pressure was increased to 1 Pa, microwaves of 3500 W were applied to perform film formation for 96 hours, and the film was grown until the thickness reached approximately 500 μm (growth rate 5.2 μm / h).

[0121] In this way, diamond crystals were heteroepitaxially grown on the Ir(111) film / single-crystal MgO(111) substrate to obtain a laminated substrate.

[0122] After this, the Ir(111) film / single-crystal MgO(111) substrate was removed to obtain a free-standing substrate. First, the single-crystal MgO(111) substrate was etched away, and then the Ir(111) film was removed by polishing. As a result, a free-standing substrate (diamond substrate) of undoped single-crystal diamond film with a diameter of 20 mm was obtained. The surface of the diamond substrate was then skiff-polished to a mirror finish, yielding a polished nitrogen-undoped single-crystal diamond substrate.

[0123] Next, the polished nitrogen-undoped single crystal diamond substrate was subjected to X-ray diffraction analysis to examine the crystal orientation in the same manner as in Example 1. Furthermore, the cross section of the sample was also analyzed by electron backscatter diffraction (EBSD), a type of electron beam diffraction method. The analysis results by EBSD are shown in Figure 9.

[0124] (Comparative Example 2) The substrate temperature is set to 860 to 1060°C, and a mixture of methane and hydrogen gas is used as the raw material. Methane gas 6.0000vol.%, Hydrogen gas 94.0000vol.%, A polished nitrogen-undoped single crystal diamond substrate was produced in the same manner as in Comparative Example 1, except that the volume ratio of the nitrogen-doped single crystal diamond substrate was 100 ppm and the nitrogen-doped single crystal diamond substrate was 100 ppm, the film formation time was 20 hours, and the growth rate was 3.9 μm / h.

[0125] The film formation conditions are shown in Table 1. [Table 1]

[0126] As can be seen from FIG. 9, when the growth rate was less than 3.8 μm / h, the crystals were oriented in the (111) direction, but not in the (001) direction.

[0127] 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. [Explanation of symbols]

[0128] 1...Base substrate, 2...(111) oriented nitrogen-doped diamond crystal, 3...Underlayer substrate, 4...intermediate layer, 5...(111) oriented nitrogen-doped diamond crystal, 6...(111) oriented diamond crystal.

Claims

1. A method for producing a diamond substrate by epitaxial growth of a (111) oriented diamond single crystal on a base substrate using hydrogen diluted methane as the main raw material gas by microwave plasma CVD, DC plasma CVD, hot filament CVD, or arc discharge plasma jet CVD, characterized in that the growth rate is less than 3.8 μm / h.

2. 2. The method for producing a diamond substrate according to claim 1, characterized in that in the method for producing the (111) oriented diamond single crystal by epitaxial growth, a (111) oriented nitrogen-doped diamond single crystal is produced on the base substrate using hydrogen diluted methane as the main raw material gas and adding nitrogen gas as a dopant.

3. 3. A method for manufacturing a diamond substrate according to claim 1, wherein the temperature of the base substrate during growth by the microwave plasma CVD method, the direct current plasma CVD method, the hot filament CVD method, or the arc discharge plasma jet CVD method is set in the range of 600°C to 1050°C.

4. 4. The method for manufacturing a diamond substrate according to claim 1, wherein the base substrate is a single-layer substrate of single-crystal diamond (111).

5. 5. The method for manufacturing a diamond substrate according to claim 4, wherein the base substrate is the single crystal diamond (111), and the main surface has an off-angle in the range of -8.0° to -0.5° or +0.5° to +8.0° relative to the crystal plane orientation (111) in the crystal axis [-1-12] direction or in a three-fold symmetric direction thereof.

6. 6. A method for manufacturing a diamond substrate according to claim 4 or claim 5, characterized in that the base substrate made of single crystal diamond (111) is a high-temperature, high-pressure synthetic single crystal diamond, a heteroepitaxial single crystal diamond, a CVD synthetic homoepitaxial diamond, or a single crystal diamond made by combining these.

7. 4. The method for manufacturing a diamond substrate according to claim 1, wherein the starting substrate has a laminated structure consisting of a lower layer substrate and an intermediate layer on the lower layer substrate.

8. 8. The method for producing a diamond substrate according to claim 7, wherein the outermost surface of the intermediate layer is a metal layer selected from Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn and Ti.

9. The lower substrate is a single layer of Si, MgO, and Al ２ O ３ , SiO ２ , Si ３ N ４ , a substrate made of SiC, Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn, or Ti, or a substrate made of Si, MgO, or Al ２ O ３ , SiO ２ , Si ３ N ４ 9. The method for manufacturing a diamond substrate according to claim 7 or 8, characterized in that the diamond substrate is a laminate selected from the group consisting of SiC, Ir, Rh, Pd, Pt, Cu, Ni, Fe, Cr, Mn and Ti.

10. 10. A method for manufacturing a diamond substrate according to any one of claims 7 to 9, characterized in that the lower substrate has a main surface with a (111) surface orientation, or further includes a layer between the lower substrate and the intermediate layer, the layer having a main surface with a (111) surface orientation.

11. 11. The method for manufacturing a diamond substrate according to claim 10, wherein the main surface of the lower substrate having the (111) plane orientation has an off-angle in the range of -8.0° to -0.5° or +0.5° to +8.0° relative to the crystal plane orientation (111) in the crystal axis [-1-12] direction or in a direction three times symmetrical thereto.

12. 12. The method for manufacturing a diamond substrate according to claim 1, wherein the total thickness of the diamond formed on the base substrate is 80 to 2000 μm.

13. 13. The method for manufacturing a diamond substrate according to claim 1, wherein no Si-containing member is used in a chamber for carrying out CVD.

14. 14. The method for producing a diamond substrate according to claim 13, wherein sapphire is used for an observation window of a chamber in which the CVD is performed.

15. 7. A method for producing a diamond substrate, comprising removing the base substrate from a layered substrate containing the (111) oriented diamond single crystal obtained by the method for producing a diamond substrate according to any one of claims 1 to 6, to obtain a (111) oriented diamond single crystal substrate.

16. A method for producing a diamond substrate, characterized in that the base substrate, the lower substrate, or both the intermediate layer and the lower substrate are removed from a layered substrate containing the (111) oriented diamond single crystal obtained by the method for producing a diamond substrate according to any one of claims 7 to 11, to obtain a (111) oriented diamond single crystal substrate.

17. A method for producing a diamond substrate, characterized by smoothing the surface of the (111) oriented diamond single crystal obtained by the method for producing a diamond substrate according to any one of claims 1 to 16.

18. A diamond single crystal substrate, characterized in that, when measured by an X-ray diffraction apparatus using the pole method with a Cu anticathode as the X-ray generating unit, under the conditions of an output of 45 kV 200 mA, an evaluation diffraction plane (111), a diffraction angle 2θ = 43.9°, and a step width of 1°, a (111) plane diffraction peak is detected when the (111) plane is facing the normal direction of the main surface of the substrate, while no (111) plane diffraction peak is detected when the (001) plane is facing the normal direction of the main surface of the substrate.

19. The diamond substrate according to claim 18, characterized in that the diamond single crystal substrate has a rocking curve half-width of 0.90° or less when measured by an X-ray diffractometer using an out-of-plane method with a Cu anticathode as the X-ray generating unit under the conditions of an output of 45 kV, 200 mA, an evaluation diffraction plane (111), a diffraction angle 2θ = 43.9°, and a step width of 0.001°.

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