Base substrate, single crystal diamond multilayer substrate, and method for producing them

Abstract

To provide a method for producing a base substrate that enables the formation of a high-quality single crystal diamond layer which has high purity and low stress, while having a large area (a large diameter), high crystallinity, less hillocks, less abnormally grown particles, less dislocation defects and the like, and which is applicable to an electronic / magnetic device.SOLUTION: The present invention provides a method for producing a base substrate for a single crystal diamond multilayer substrate, the method comprising: a step for preparing an initial substrate; and a step for forming an intermediate layer on the initial substrate, the intermediate layer being formed of a monolayer or a multilayer film that comprises at least a single crystal Ir film or a single crystal MgO film. In the method, the formation of the single crystal Ir film or the single crystal MgO film, constituting the intermediate layer, is performed using the mist CVD technique.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a base substrate, a single-crystal diamond laminate substrate, and methods 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.

[0003] Among semiconductors, diamond has an extremely 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 material, making it excellent for heat dissipation. Furthermore, its extremely high carrier mobility and saturated drift velocity make it suitable for high-speed devices.

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

[0005] [Non-Patent Document 1] H.Yamada,Appl.Phys.Lett.104,102110(2014). Summary of the Invention [Problem to be solved by the invention]

[0006] 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 there is a demand for the supply of large-area, high-quality diamond substrates.

[0007] Currently, most single-crystal diamonds used to produce diamond semiconductors are so-called type Ib diamonds synthesized by high-pressure, high-temperature (HPHT) methods. This type Ib diamond contains a large amount of nitrogen impurities and can only be obtained up to a maximum size of about 8 mm square, making it of low practical use. A method called the mosaic method, in which multiple HPHT substrates (diamond substrates synthesized by the HPHT method) are lined up and joined together, has also been proposed (Non-Patent Document 1), but the problem of imperfections at the joints remains.

[0008] In contrast, chemical vapor deposition (CVD) can produce high-purity polycrystalline diamond with a large area of ​​approximately 6 inches (150 mm) in diameter, but it has been difficult to produce single crystals suitable for use in ordinary electronic devices. This is because it has not been possible to realize a suitable material combination for the base substrate on which diamond is grown, with small differences in lattice constant and linear expansion coefficient between diamond and the base substrate. For example, the difference in lattice constant between diamond and single-crystal silicon is as much as 34.3%, making it extremely difficult to heteroepitaxially grow diamond on the base substrate surface.

[0009] The present invention has been made to solve the above problems, and aims to provide a base substrate applicable to electronic and magnetic devices, which is large-area (large diameter), highly crystalline, has few hillocks, abnormally grown grains, dislocation defects, etc., and on which a high-purity, low-stress, high-quality single-crystal diamond layer can be formed, and a method for manufacturing the same. It is also another aim to provide a single-crystal diamond laminate substrate having such a single-crystal diamond layer, and a method for manufacturing a single-crystal diamond freestanding substrate. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides a method for manufacturing a base substrate for a single crystal diamond laminate substrate, comprising the steps of preparing an initial substrate and forming an intermediate layer on the initial substrate, the intermediate layer being a single layer or laminated film containing at least a single crystal Ir film or a single crystal MgO film, and wherein the single crystal Ir film or single crystal MgO film constituting the intermediate layer is formed using a mist CVD method.

[0011] According to this method for manufacturing a base substrate, the single-crystal Ir film or single-crystal MgO film that constitutes the intermediate layer is formed by mist CVD, making it possible to form a large-diameter single-crystal Ir film or single-crystal MgO film at low cost. Furthermore, the thickness uniformity of the intermediate layer can be improved. This makes it possible to manufacture a base substrate that is suitable for electronic and magnetic devices, and that is large-diameter, highly crystalline, has few hillocks, abnormally grown grains, dislocation defects, etc., and is capable of forming a high-purity, low-stress, high-quality single-crystal diamond layer.

[0012] In this case, the initial substrate is preferably any one of a single crystal Si substrate, a single crystal α-Al2O3 substrate, a single crystal Fe substrate, a single crystal Ni substrate, and a single crystal Cu substrate.

[0013] These initial substrate materials have a small lattice mismatch with the intermediate layer material, making it easy to epitaxially grow the intermediate layer. Furthermore, large diameters exceeding 6 inches (150 mm) can be obtained, and the price is relatively low.

[0014] The intermediate layer may be a laminated film further including at least one of a single crystal yttria-stabilized zirconia film, a single crystal SrTiO3 film, and a single crystal Ru film.

[0015] By forming such a laminated film, the intermediate layer can be appropriately designed to more appropriately fulfill the role of buffering the lattice mismatch between the initial substrate and the diamond layer.

[0016] The initial substrate may be any one of a Si{111} substrate, an α-Al2O3{0001} substrate, an Fe{111} substrate, a Ni{111} substrate, and a Cu{111} substrate, and the intermediate layer may include at least an Ir{111} film or an MgO{111} film.

[0017] The intermediate layer may further include at least one of an yttria-stabilized zirconia {111} film, an SrTiO3 {111} film, and a Ru {0001} film.

[0018] By using such an initial substrate and intermediate layer, it is possible to produce a base substrate on which a single-crystal diamond {111} layer can be formed.

[0019] In this case, the outermost surface of the initial substrate may be off-angled in the <-1-12> crystal axis direction relative to the {111} cubic crystal plane orientation, or in the <10-10> or <11-20> crystal axis direction relative to the {0001} hexagonal crystal plane orientation.

[0020] By providing an off-angle in this manner, it is possible to more effectively manufacture a base substrate that enables the formation of a high-quality single-crystal diamond {111} layer with high crystallinity and few hillocks, abnormal growths, dislocation defects, etc.

[0021] In this case, the off-angle of the outermost surface of the initial substrate can be set in the range of +0.5 to +15.0° or −0.5 to −15.0°.

[0022] By setting the off angle in this range, the effect of improving quality due to the off angle can be maximized.

[0023] In this case, the outermost surface of the intermediate layer may be off-angled in the <-1-12> crystal axis direction relative to the {111} cubic crystal plane orientation, or in the <10-10> or <11-20> crystal axis direction relative to the {0001} hexagonal crystal plane orientation.

[0024] By providing an off-angle in this manner, it is possible to more effectively manufacture a base substrate that enables the formation of a high-quality single-crystal diamond {111} layer with high crystallinity and few hillocks, abnormal growths, dislocation defects, etc.

[0025] In this case, the off angle of the outermost surface of the intermediate layer can be set in the range of +0.5 to +15.0° or −0.5 to −15.0°.

[0026] By setting the off angle in this range, the effect of improving quality due to the off angle can be maximized.

[0027] Furthermore, in the method for producing a base substrate of the present invention, the initial substrate can be any one of a Si{001} substrate, an α-Al2O3{11-20} substrate, an Fe{001} substrate, a Ni{001} substrate, and a Cu{001} substrate, and the intermediate layer can include at least an Ir{001} film or an MgO{001} film.

[0028] The intermediate layer may further include at least one of an yttria-stabilized zirconia {001} film, an SrTiO3 {001} film, and a Ru {11-20} film.

[0029] By using such an initial substrate and intermediate layer, it is possible to produce a base substrate on which a single-crystal diamond {001} layer can be formed.

[0030] In this case, the outermost surface of the initial substrate is oriented along a crystal axis {001} with respect to the cubic crystal plane direction. <110> The crystal axis is set to the direction of the off-axis, or the hexagonal crystal plane direction is set to the direction of the off-axis. <0001> The direction may be offset.

[0031] By providing an off-angle in this manner, it is possible to more effectively manufacture a base substrate that enables the formation of a high-quality single-crystal diamond {001} layer with high crystallinity and few hillocks, abnormal growths, dislocation defects, etc.

[0032] In this case, the off-angle of the outermost surface of the initial substrate can be set in the range of +0.5 to +15.0° or −0.5 to −15.0°.

[0033] By setting the off angle in this range, the effect of improving quality due to the off angle can be maximized.

[0034] In this case, the outermost surface of the intermediate layer is oriented in a direction parallel to the crystal axis {001} with respect to the cubic crystal plane direction. <110> The off-angle is set in the direction, or the hexagonal crystal plane direction is set to <10-10> or <0001> An off angle can be applied to the direction.

[0035] By providing an off-angle in this manner, it is possible to more effectively manufacture a base substrate that enables the formation of a high-quality single-crystal diamond {001} layer with high crystallinity and few hillocks, abnormal growths, dislocation defects, etc.

[0036] In this case, the off angle of the outermost surface of the intermediate layer can be in the range of +0.5 to +15.0° or −0.5 to −15.0°.

[0037] By setting the off angle in this range, the effect of improving quality due to the off angle can be maximized.

[0038] The present invention also provides a method for manufacturing a single-crystal diamond laminate substrate, comprising the steps of: preparing a base substrate manufactured by any of the above-mentioned methods for manufacturing a base substrate; performing a bias treatment on the surface of the intermediate layer of the base substrate to form diamond nuclei; and growing the diamond nuclei formed on the intermediate layer to perform epitaxial growth, thereby forming a single-crystal diamond layer.

[0039] According to this manufacturing method, it is possible to produce a single crystal diamond laminate substrate that is suitable for use in electronic and magnetic devices, and that has a large-diameter, highly crystalline, high-quality single crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc., high purity, and low stress.

[0040] In the method of manufacturing a monocrystalline diamond laminated substrate of the present invention, the monocrystalline diamond layer can be a {111} crystal.

[0041] The single crystal diamond layer may also be a {001} crystal.

[0042] The method of manufacturing a single crystal diamond laminated substrate of the present invention can form a single crystal diamond layer having these plane orientations.

[0043] The present invention also provides a method for producing a single crystal diamond freestanding substrate, characterized in that only the single crystal diamond layer is extracted from a single crystal diamond laminate substrate produced by any of the above-mentioned methods for producing a single crystal diamond laminate substrate, thereby producing a single crystal diamond freestanding substrate.

[0044] In this manner, a single-crystal diamond freestanding substrate consisting of only a single-crystal diamond layer can be produced.

[0045] Furthermore, an additional single-crystal diamond layer can be formed on the single-crystal diamond free-standing substrate obtained by the above-described method for producing a single-crystal diamond free-standing substrate.

[0046] In this way, it is possible to further form a thicker film by depositing an additional film on the substrate having only the diamond layer.

[0047] The present invention also provides a base substrate for a single crystal diamond laminate substrate, comprising an initial substrate and an intermediate layer formed on the initial substrate and consisting of a single layer or laminated film containing at least a single crystal Ir film or a single crystal MgO film, wherein the film thickness uniformity of the intermediate layer is within ±10% over the entire surface.

[0048] In this way, the base substrate of the present invention can achieve an intermediate layer thickness uniformity of within ±10% across the entire surface, making it possible to provide a base substrate suitable for electronic and magnetic devices, on which a high-quality single-crystal diamond layer can be grown that is large-diameter, highly crystalline, has few hillocks, abnormally grown grains, dislocation defects, etc., and is high in purity and low in stress.

[0049] In this case, the initial substrate can be any one of a single crystal Si substrate, a single crystal α-Al 2 O 3 substrate, a single crystal Fe substrate, a single crystal Ni substrate, and a single crystal Cu substrate.

[0050] These initial substrate materials have a small lattice mismatch with the intermediate layer material, making it easy to epitaxially grow the intermediate layer. Furthermore, large diameters exceeding 6 inches (150 mm) can be obtained, and the price is relatively low.

[0051] The intermediate layer may be a laminated film further including at least one of a single crystal yttria-stabilized zirconia film, a single crystal SrTiO3 film, and a single crystal Ru film.

[0052] By forming such a laminated film, the intermediate layer can be appropriately designed to more appropriately fulfill the role of buffering the lattice mismatch between the initial substrate and the diamond layer.

[0053] The present invention also provides a single-crystal diamond laminate substrate, characterized in that it has a single-crystal diamond layer on the intermediate layer of any of the above-mentioned base substrates.

[0054] Such a single crystal diamond laminate substrate has a single crystal diamond layer formed on an intermediate layer whose thickness uniformity is within ±10% over the entire surface, and therefore can be a single crystal diamond laminate substrate having a high-quality single crystal diamond layer that is large in diameter, highly crystalline, has few hillocks, abnormally grown grains, dislocation defects, etc., and is high in purity and low in stress, making it suitable for use in electronic and magnetic devices. [Effects of the Invention]

[0055] According to the method for manufacturing a base substrate of the present invention, the single-crystal Ir film or single-crystal MgO film constituting the intermediate layer is formed by mist CVD, enabling the formation of a large-diameter, low-cost single-crystal Ir film or single-crystal MgO film. The thickness uniformity of the intermediate layer can be increased, particularly within ±10% across the entire surface. This allows the manufacture of a large-diameter, highly crystalline base substrate suitable for electronic and magnetic devices, capable of forming a high-purity, low-stress, high-quality single-crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc. Furthermore, by forming a single-crystal diamond layer on this base substrate, a single-crystal diamond laminate substrate having the above-mentioned characteristics can be manufactured. Furthermore, according to the present invention, it is also possible to manufacture a single-crystal diamond freestanding substrate by separating only the single-crystal diamond laminate from such a single-crystal diamond laminate substrate, or to further manufacture a single-crystal diamond freestanding substrate by depositing an additional single-crystal diamond layer on the single-crystal diamond freestanding substrate. [Brief explanation of the drawings]

[0056] [Figure 1] 1 is a flow chart showing an example of a method for manufacturing a base substrate according to the present invention. [Figure 2] FIG. 1 is a flow chart showing an example of the steps of a method for manufacturing a single-crystal diamond laminate substrate and a method for manufacturing a single-crystal freestanding substrate according to the present invention. [Figure 3] 1 is a schematic diagram showing an example of a base substrate of the present invention. [Figure 4] 1 is a schematic diagram showing an example of a single-crystal diamond laminate substrate of the present invention. [Figure 5] FIG. 2 is a schematic view showing another example of the base substrate of the present invention. [Figure 6] FIG. 2 is a schematic diagram showing another example of a single-crystal diamond laminate substrate of the present invention. [Figure 7] 1 is a schematic diagram showing an example of a single-crystal diamond freestanding substrate of the present invention. [Figure 8] FIG. 1 is a schematic diagram showing another example of a single-crystal diamond freestanding substrate of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0057] The present invention will be described in detail below, but the present invention is not limited thereto.

[0058] As mentioned above, there has been a demand for large-diameter, low-cost, high-quality single-crystal diamond laminate substrates. Therefore, the present inventors have conducted extensive research to solve this problem. As a result, they have discovered that the mist CVD method is the optimal method for forming intermediate layers in single-crystal diamond laminate substrates and in base substrates for manufacturing single-crystal diamond laminate substrates, and have completed the present invention.

[0059] The present invention is a method for manufacturing a base substrate for a single-crystal diamond laminate substrate, comprising the steps of preparing an initial substrate and forming an intermediate layer on the initial substrate, the intermediate layer being a single layer or laminated film containing at least a single-crystal Ir film or a single-crystal MgO film, wherein the single-crystal Ir film or the single-crystal MgO film constituting the intermediate layer is formed using a mist CVD method.

[0060] The present invention will now be described in more detail with reference to the drawings, in which like components are designated by like reference numerals.

[0061] First, the base substrate and the single-crystal diamond laminate substrate of the present invention will be described with reference to FIGS.

[0062] As shown in Figure 3, the base substrate 20 for the single crystal diamond laminate substrate of the present invention has an initial substrate 11 and an intermediate layer 21 on the initial substrate 11. In the present invention, the intermediate layer 21 is made of a single layer or a laminated film including at least a single crystal Ir film or a single crystal MgO film. Furthermore, in the present invention, the film thickness uniformity of the intermediate layer 21 can be made within ±10% over the entire surface. Such film thickness uniformity of the intermediate layer 21 can be easily achieved by employing the mist CVD method described below.

[0063] As shown in Figure 4, the single crystal diamond laminate substrate 30 of the present invention has a single crystal diamond layer 31 on the intermediate layer 21 of the base substrate 20 shown in Figure 3. The intermediate layer 21 serves to buffer the lattice mismatch between the initial substrate 11 and the single crystal diamond layer 31.

[0064] In the base substrate 20 of the present invention, the intermediate layer 21 may be a single-crystal Ir film alone or a single-crystal MgO film alone, but a laminated film of these is more preferable. In particular, as shown in FIG. 5, the intermediate layer 21 on the initial substrate 11 is preferably a laminated film consisting of a single-crystal MgO film 22 and a single-crystal Ir film 23. The intermediate layer 21 of the base substrate 20 of the present invention can also be a laminated film containing at least one of a single-crystal Ir film and a single-crystal MgO film, as well as at least one of a single-crystal yttria-stabilized zirconia (YSZ) film, a single-crystal SrTiO3 film, and a single-crystal Ru film. Such a laminated film can be designed to more appropriately buffer the lattice mismatch between the initial substrate 11 and the single-crystal diamond layer 31. As shown in Figure 5, when the intermediate layer 21 on the initial substrate 11 is a laminated film made up of a single-crystal MgO film 22 and a single-crystal Ir film 23, naturally, when a single-crystal diamond laminated substrate 30 is manufactured, the intermediate layer 21 becomes a laminated film made up of a single-crystal MgO film 22 and a single-crystal Ir film 23, as shown in Figure 6.

[0065] In the present invention, the initial substrate 11 is preferably any one of a single crystal Si substrate, a single crystal α-Al2O3 substrate, a single crystal Fe substrate, a single crystal Ni substrate, and a single crystal Cu substrate. These initial substrates 11 (bulk substrates) have a small lattice mismatch with the material of the intermediate layer 21, which facilitates epitaxial growth of the intermediate layer 21 when forming the intermediate layer 21. Furthermore, large diameters exceeding 6 inches (150 mm) can be obtained, and the price can be made relatively low.

[0066] The following describes the manufacturing methods for the base substrate and single crystal diamond laminate substrate shown in Figures 3 to 6. The manufacturing method for the base substrate of the present invention will be described with reference to Figure 1, and the manufacturing method for the single crystal diamond laminate substrate of the present invention will be described with reference to Figure 2. Furthermore, the present invention can manufacture a single crystal diamond freestanding substrate 35 consisting of a single crystal diamond layer 31 shown in Figure 7, and a single crystal diamond freestanding substrate 40 consisting of a single crystal diamond layer 31 and an additional single crystal diamond layer 41 shown in Figure 8, and the manufacturing method for these will also be described with reference to Figure 2.

[0067] (Preparation step: step S11 in Figure 1) First, an initial substrate 11 is prepared (step S11). The initial substrate 11 is preferably any one of a single crystal Si substrate, a single crystal α-Al2O3 substrate, a single crystal Fe substrate, a single crystal Ni substrate, and a single crystal Cu substrate (bulk substrate). These listed materials for the initial substrate 11 have a small lattice mismatch with the material of the intermediate layer 21, making it easy to epitaxially grow the intermediate layer 21. In addition, large diameters exceeding 6 inches (150 mm) can be obtained, and the price is relatively low.

[0068] When the initial substrate 11 is one of the above substrates, the substrate can be any of a Si{111} substrate, an α-Al2O3{0001} substrate, an Fe{111} substrate, a Ni{111} substrate, and a Cu{111} substrate, depending on the plane orientation. The initial substrate 11 can also be any of a Si{001} substrate, an α-Al2O3{11-20} substrate, an Fe{001} substrate, a Ni{001} substrate, and a Cu{001} substrate.

[0069] The surface of the initial substrate 11 on which the intermediate layer 21 is to be formed is preferably polished to Ra≦0.5 nm, thereby enabling the formation of a smooth intermediate layer 21 with few defects.

[0070] When a {111} crystal plane orientation is desired for the single-crystal diamond layer 31, the outermost surface of the initial substrate 11 can be made to have an off-angle in the crystal axis <-1-12> direction relative to the cubic crystal plane orientation {111}, or an off-angle in the crystal axis <10-10> or <11-20> direction relative to the hexagonal crystal plane orientation {0001}. By making the outermost surface of the initial substrate 11 off-angle in this way, it becomes possible to more effectively obtain a high-quality intermediate layer 21 that is highly crystalline and has fewer hillocks, abnormal growths, dislocation defects, etc., as the intermediate layer 21 to be formed on that surface.

[0071] In this case, the off-angle of the outermost surface of the initial substrate 11 is preferably in the range of +0.5 to +15.0° or -0.5 to -15.0°. If this off-angle is +0.5 or -0.5° or more, the effect of imparting an off-angle is sufficiently obtained, and if it is +15.0 or -15.0° or less, the effect of improving quality is sufficiently obtained. Furthermore, within these ranges, the deviation from the {111} crystal plane of the outermost surface is not too large, making it easy to use according to the purpose.

[0072] On the other hand, if it is desired to obtain a single crystal diamond layer with a {001} crystal plane orientation, the outermost surface of the initial substrate 11 should be aligned along the crystal axis {001} with respect to the cubic crystal plane orientation {001}. <110> The off-angle is set in the direction, or the hexagonal crystal plane direction is set to <10-10> or <0001> By providing an off-angle to the outermost surface of the initial substrate 11 in this manner, it becomes possible to more effectively obtain a high-quality intermediate layer 21 that is highly crystalline and has fewer hillocks, abnormal growths, dislocation defects, etc., as the intermediate layer 21 to be formed on the surface.

[0073] In this case, the off-angle of the outermost surface of the initial substrate 11 is preferably in the range of +0.5 to +15.0° or -0.5 to -15.0°. If this off-angle is +0.5 or -0.5° or more, the effect of imparting an off-angle is sufficiently obtained, and if it is +15.0 or -15.0° or less, the effect of improving quality is sufficiently obtained. Furthermore, within these ranges, the deviation from the {111} crystal plane of the outermost surface is not too large, making it easy to use according to the purpose.

[0074] (Intermediate layer formation step: step S12 in FIG. 1) After the initial substrate 11 is prepared in step S11, an intermediate layer 21 made of a single layer or a multilayer film including at least a single crystal Ir film or a single crystal MgO film is formed on the initial substrate 11 (step S12). Here, a feature of the present invention is that the single crystal Ir film or the single crystal MgO film constituting the intermediate layer 21 is formed by a mist CVD method.

[0075] Furthermore, the intermediate layer 21 may be a laminated film further including at least one of a single crystal yttria stabilized zirconia (YSZ) film, a single crystal SrTiO3 film, and a single crystal Ru film.

[0076] If a {111} crystal orientation is desired for the single-crystal diamond layer 31, at least the outermost surface of the intermediate layer 21 should also have a {111} crystal orientation in the case of a cubic crystal, or a {0001} orientation in the case of a hexagonal crystal. In this case, the intermediate layer 21 may include at least an Ir{111} film or an MgO{111} film. The intermediate layer 21 may further include at least one of an yttria-stabilized zirconia {111} film, an SrTiO3 {111} film, and a Ru{0001} film.

[0077] On the other hand, if a {001} crystal orientation is desired for the single-crystal diamond layer 31, at least the outermost surface of the intermediate layer 21 should also have a {001} crystal orientation in the case of a cubic crystal, or a {11-20} crystal orientation in the case of a hexagonal crystal. In this case, the intermediate layer may include at least an Ir{001} film or an MgO{001} film. Furthermore, the intermediate layer 21 may further include at least one of an yttria-stabilized zirconia {001} film, an SrTiO3 {001} film, and a Ru{11-20} film.

[0078] In the present invention, the single-crystal Ir film or single-crystal MgO film that constitutes intermediate layer 21 is formed using the mist CVD method, as described above. The effects of the present invention can be obtained by using the mist CVD method for at least one layer that constitutes intermediate layer 21. The other layers that constitute intermediate layer 21 can also be formed by sputtering, electron beam evaporation, atomic layer deposition, molecular beam epitaxy, pulsed laser deposition, or other methods in addition to the mist CVD method. For metal and metal oxide films that can constitute the above-listed intermediate films, such as a single-crystal Ir film, single-crystal MgO film, single-crystal yttria-stabilized zirconia (YSZ) film, single-crystal SrTiO3 film, and single-crystal Ru film, the mist CVD method is preferably used, as it allows for large-diameter, low-cost formation.

[0079] A film-forming device using the mist CVD method consists of a mist-forming unit that uses ultrasonic vibrations to turn a raw material solution containing atoms of the material to be formed into mist, a carrier gas supply unit that supplies a carrier gas to transport the mist, a chamber in which a substrate is set and film-forming takes place, and an exhaust system that discharges unnecessary raw materials.

[0080] Inside the chamber, the substrate is heated on a heater stage and rotated as necessary to ensure highly crystalline and uniform film formation. The flow of the source gas is also controlled to ensure highly crystalline and uniform film formation.

[0081] Alternatively, a substrate can be placed on a heater stage installed in an open system, and mist can be supplied to the surface of the substrate from a mist discharge nozzle to form a film by a thermal reaction.

[0082] The raw material solution is not particularly limited as long as it contains at least the metal atoms to be deposited and can be turned into mist, and may be either an inorganic material or an organic material.

[0083] The raw material solution is not particularly limited as long as it can turn the metal atoms into mist, but a solution in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt can be suitably used as the raw material solution. Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salt forms include metal chloride salts, metal bromide salts, and metal iodide salts. In addition, solutions in which the metals are dissolved in hydrobromic acid, hydrochloric acid, hydrogen iodide, etc. can also be used as aqueous salt solutions.

[0084] The raw material solution may also contain additives such as hydrohalic acid and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, with hydrobromic acid and hydroiodic acid being preferred. Examples of oxidizing agents include peroxides such as hydrogen peroxide, sodium peroxide, barium peroxide, and benzoyl peroxide, as well as hypochlorous acid, perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0085] A magnesium chloride aqueous solution can also be used as the raw material solution for forming MgO.

[0086] To obtain an oxide composed of multiple metal elements, a plurality of raw material solutions may be mixed and turned into mist, or separate raw material solutions may be prepared for each element and each may be turned into mist.

[0087] It is preferable to heat the substrate to a temperature in the range of 200 to 850°C during film formation.

[0088] As described above, the intermediate layer 21 can be formed not only as a single layer of the above-mentioned materials, but also as a laminated structure, achieving good quality. For example, starting from the surface side, the layers can be Ir film / MgO film followed by the initial substrate 11. Similarly, a laminated structure such as Ir film / YSZ film or Ir film / SrTiO3 film can be used to more effectively buffer lattice mismatch. Figure 5 shows an example in which a single-crystal MgO film 22 and a single-crystal Ir film 23 are laminated on the initial substrate 11, as described above. In this example, the layers are Ir film / MgO film followed by the initial substrate 11, starting from the surface side.

[0089] The thickness of the intermediate layer 21 is preferably 5 nm or more and 50 μm or less. If the thickness of the intermediate layer 21 is 5 nm or more, it will not be removed in the subsequent diamond formation process. Furthermore, if the thickness of the intermediate layer 21 is 50 μm or less, this is sufficient as the thickness of the intermediate layer 21. Furthermore, if the thickness is 50 μm or less, the film formation time will not be long and the surface roughness can be kept low. Therefore, polishing is not necessarily required, and the film can be formed at low cost.

[0090] The outermost surface of intermediate layer 21 may be off-angled in the crystal axis <-1-12> direction relative to the cubic crystal plane orientation {111}, or in the crystal axis <10-10> or <11-20> direction relative to the hexagonal crystal plane orientation {0001}. This makes it possible to more effectively obtain, as single crystal diamond layer 31 formed on the surface, a high-quality single crystal diamond {111} layer with high crystallinity and few hillocks, abnormal growths, dislocation defects, etc.

[0091] In this case, the off-angle of the outermost surface of the intermediate layer 21 is preferably in the range of +0.5 to +15.0° or -0.5 to -15.0°. If this off-angle is +0.5 or -0.5° or more, the effect of providing an off-angle is sufficiently obtained, and if it is +15.0 or -15.0° or less, the effect of improving quality is sufficiently obtained. Furthermore, within these ranges, the deviation from the {111} crystal plane of the outermost surface is not too large, making it easy to use according to the purpose.

[0092] The crystal plane orientation is {001}, whereas in cubic crystals, the crystal axis <110> The off-angle is given to the direction, and the hexagonal crystal plane orientation {11-20} is <10-10> or <0001> By providing an off-angle in the direction, it is possible to obtain a high-quality single-crystal diamond {001} layer with high crystallinity and few hillocks, abnormal growths, dislocation defects, etc. as the diamond formed on the surface.

[0093] In this case, the off-angle of the outermost surface of the intermediate layer 21 is preferably in the range of +0.5 to +15.0° or -0.5 to -15.0°. If this off-angle is +0.5 or -0.5° or more, the effect of providing an off-angle is sufficiently obtained, and if it is +15.0 or -15.0° or less, the effect of improving quality is sufficiently obtained. Furthermore, within these ranges, the deviation from the {001} crystal plane of the outermost surface is not too large, making it easy to use according to the purpose.

[0094] By carrying out steps S11 and S12 in FIG. 1 as described above, the base substrate 20 of the present invention (see FIGS. 3 and 5) can be manufactured.

[0095] The present invention further provides a method for manufacturing a single crystal diamond laminate substrate 30, comprising the steps of preparing a base substrate 20 manufactured by the method for manufacturing a base substrate 20 as described above, performing bias treatment to form diamond nuclei on the surface of the intermediate layer 21 of the base substrate 20, and growing the diamond nuclei formed on the intermediate layer 21 to perform epitaxial growth, thereby forming a single crystal diamond layer 31. This will be explained in more detail below.

[0096] Steps S11 and S12 in Fig. 2 are the same as steps S11 and S12 in Fig. 1. Steps S11 and S12 produce a base substrate 20. Further, subsequent steps S13 and S14 shown in Fig. 2 are carried out to produce a single-crystal diamond laminate substrate 30.

[0097] (Bias treatment process: S13 in Figure 2) A bias treatment is performed on the surface of the intermediate layer 21 of the base substrate 20 to form diamond nuclei (step S13). The base substrate 20 with the intermediate layer 21 formed thereon is placed in a reduced pressure chamber, and after reducing the pressure with a vacuum pump, a direct current discharge is used to form diamond nuclei with the same crystal orientation as the outermost surface of the intermediate layer 21. The discharge gas is preferably hydrogen-diluted methane.

[0098] (Single crystal diamond layer process: S14 in Figure 2) Next, the diamond nuclei formed on the intermediate layer 21 are grown epitaxially to form a single-crystal diamond layer 31 (step S14). That is, a single-crystal layer is formed on the bias-treated base substrate 20. This step can be performed by a vapor phase synthesis (CVD) method such as microwave plasma CVD, DC plasma CVD, hot filament CVD, or arc discharge CVD.

[0099] The single crystal diamond layer 31 may consist of a single layer of undoped or doped diamond, or a stacked structure of undoped and doped diamond.

[0100] By carrying out steps S13 and S14 after steps S11 and S12, the single crystal diamond laminated substrate 30 of the present invention (see FIGS. 4 and 6) can be manufactured.

[0101] Furthermore, in the above-mentioned method for manufacturing a single crystal diamond laminate substrate, a single crystal diamond {111} can be obtained by orienting either or both of the initial substrate 11 and the intermediate layer 21 in the {111} crystal orientation in the case of a cubic crystal or in the {0001} crystal orientation in the case of a hexagonal crystal.

[0102] On the other hand, in the above-mentioned method for manufacturing a single crystal diamond laminate substrate, a single crystal diamond {001} can be obtained by orienting either the initial substrate 11 or the intermediate layer 21, or both, in the {001} crystal orientation in the case of a cubic crystal or in the {11-20} crystal orientation in the case of a hexagonal crystal.

[0103] The present invention also provides a method for producing a single crystal diamond freestanding substrate, in which only the single crystal diamond layer 31 is extracted from the single crystal diamond laminated substrate 30 produced by the above-mentioned method through steps S11 to S14, and a single crystal diamond freestanding substrate 35 (see FIG. 7) is produced. This will be explained in more detail below.

[0104] (Single crystal diamond extraction process: S15 in Figure 2) In this step, after the single crystal diamond layer 31 formation step (step S14), only the single crystal diamond layer 31 is made into a single crystal diamond freestanding substrate 35 (step S15). Such a freestanding substrate can be formed using chemical etching, laser irradiation, polishing, or the like.

[0105] The advantage of being self-sustaining is that it makes it easier to process additional films and device fabrication.

[0106] Furthermore, when diamond is used in electronic and magnetic devices, a single-crystal diamond freestanding substrate made up of only a single-crystal diamond layer may be more advantageous because it is not affected by intermediate layers and below.

[0107] (Additional single crystal diamond deposition process: S16 in Figure 2) Furthermore, in the present invention, a single crystal diamond freestanding substrate 40 (see FIG. 8) can be manufactured by forming an additional single crystal diamond layer 41 (step S16) on the single crystal diamond freestanding substrate 35 obtained up to step S15. In other words, an additional film can be formed on the single crystal diamond freestanding substrate 35 shown in FIG. 7, which consists only of the single crystal diamond layer 31. Because the film is formed on a single material, there is no damage and it is effective in reducing stress. This step is also advantageous for thickening the diamond film.

[0108] The additional single crystal diamond layer 41 formed in this step may be undoped or doped, or a combination thereof.

[0109] Before the additional single crystal diamond layer 41 is formed, the surface of the underlying single crystal diamond freestanding substrate 35 is polished to obtain a smooth crystal with few defects.

[0110] The methods for manufacturing the base substrate, single crystal diamond laminate substrate, and single crystal diamond freestanding substrate of the present invention as explained above make it possible to provide a method for manufacturing at low cost laminate substrates suitable for use in electronic and magnetic devices, which have a large diameter, highly crystalline, high quality single crystal diamond layer with few hillocks, abnormally grown grains, dislocation defects, etc., high purity, and low stress. [Example]

[0111] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0112] Example 1 A single-crystal Si wafer having a diameter of 150 mm, a thickness of 1000 μm, a crystal plane orientation of (111), and a double-side polished wafer with an off-angle of −3° in the [−1-12] direction was prepared as an initial substrate 11 (step S11 in FIGS. 1 and 2).

[0113] Next, an MgO film was heteroepitaxially grown on the surface of the initial substrate by mist CVD to form the first layer of the intermediate layer 21 (single-crystal MgO film 22 in FIG. 5) under the following conditions (step S12 in FIGS. 1 and 2).

[0114] A magnesium oxide aqueous solution was used as the raw material solution in the mist CVD method. The raw material solution was placed in a mist generator. Next, the flow control valve was opened to supply carrier gas from the carrier gas source into the chamber. After the atmosphere in the chamber was thoroughly replaced with carrier gas, the flow rate of the carrier gas was adjusted to 10,000 sccm and the flow rate of the dilution carrier gas to 30,000 sccm. Oxygen was used as the carrier gas.

[0115] Next, the ultrasonic vibrator was vibrated at 2.4 MHz, and the vibrations were propagated through the water to atomize the raw material solution, generating mist. The mist was introduced into the chamber via a supply pipe using a carrier gas. The mist was thermally reacted with the initial substrate, which was placed on a hot plate in the chamber under atmospheric pressure and heated to 750°C, to heteroepitaxially grow an MgO (111) film on the surface of the initial substrate 11 to a thickness of 1 μm.

[0116] Next, an Ir film (single-crystal Ir film 23 in FIG. 5) was heteroepitaxially grown on the single-crystal MgO (111) film 22 to form an intermediate layer 21 of a laminated structure of Ir film / MgO.

[0117] The single-crystal Ir film 23 was formed by RF (13.56 MHz) magnetron sputtering using an Ir target with a diameter of 8 inches (200 mm), a thickness of 5 mm, and a purity of 99.9% or higher. The substrate on which the single-crystal MgO film 22 had already been formed was heated to 800°C and evacuated with a vacuum pump until the base pressure reached approximately 8.0 × 10 -5 After confirming that the pressure was below 1 Pa, Ar gas was introduced. The opening of the valve connected to the exhaust system was adjusted to 13 Pa, and then RF 1500 W was input and film deposition was carried out for 30 minutes. The obtained film thickness was approximately 1 μm.

[0118] In this manner, the base substrate 20 shown in FIG. 5 was produced.

[0119] Next, the starting substrate 20 was subjected to a pretreatment (bias treatment) for diamond nucleation (step S13 in FIG. 2). Here, the starting substrate 20 on which the intermediate layer 21 was formed was set on a flat electrode, and a base pressure of about 1.3×10 -4 After confirming that the pressure was below 1.3 × 10 Pa, hydrogen-diluted methane (CH4 / (CH4+H2) = 5.0 vol.%) was introduced into the processing chamber at a flow rate of 500 sccm. The opening of the valve connected to the exhaust system was adjusted to reduce the pressure to 1.3 × 10 4 After setting the potential at Pa, a negative voltage was applied to the substrate-side electrode, and the surface of the intermediate layer 21 (ie, the surface of the single-crystal Ir(111) film 23) was exposed to plasma for 90 seconds, thereby subjecting the surface to bias treatment.

[0120] Subsequently, a single-crystal diamond layer 31 (undoped diamond film) was heteroepitaxially grown by microwave CVD (step S14 in FIG. 2). Here, the bias-treated base substrate 20 was set in the chamber of a microwave CVD apparatus, and a base pressure of approximately 1.3×10 was applied by a vacuum pump. -4 After exhausting the chamber to a pressure of 1.5 × 10 Pa or less, the source gas, hydrogen-diluted methane (CH4 / (CH4+H2) = 5.0 vol.%), was introduced into the chamber at a flow rate of 1000 sccm. The opening of the valve connected to the exhaust system was adjusted to reduce the pressure to 1.5 × 10 4 After the pressure was adjusted to Pa, direct current was applied to carry out film formation for 100 hours. The substrate temperature during film formation was measured with a pyrometer and found to be 980°C.

[0121] The obtained single crystal diamond layer 31 was a completely continuous film without peeling over the entire 150 mm diameter surface. A cross-sectional schematic diagram of the multilayer substrate (single crystal diamond laminate substrate 30) is shown in FIG.

[0122] Next, the Si wafer serving as the initial substrate 11 was etched with a mixed acid solution of hydrofluoric acid and nitric acid. Furthermore, the stacked film of the single-crystal MgO film 22 and the single-crystal Ir film 22 serving as the intermediate layer 21 was removed by dry etching. This resulted in a single-crystal diamond (111) freestanding substrate 35 (step S15 in FIG. 2).

[0123] Finally, a single-crystal diamond layer (additional single-crystal diamond layer 41) was heteroepitaxially grown again by microwave CVD (step S16 in FIG. 2). The formation of this additional single-crystal diamond layer 41 was carried out under the same conditions as those used to form the undoped diamond film described above.

[0124] The obtained single crystal diamond layer 41 was also a completely continuous film without any peeling over the entire 150 mm diameter area. A cross-sectional schematic diagram of a single crystal diamond freestanding substrate 40 consisting of the single crystal diamond layer 31 and the additional single crystal diamond layer 41 is shown in Figure 8.

[0125] A 2 mm square was cut out from this single crystal diamond freestanding substrate 40 to serve as an evaluation sample, and the film thickness and crystallinity were evaluated.

[0126] The film thickness was determined by observing the cross section of the sample with a scanning secondary electron microscope (SEM), and the total thickness of the diamond layer was found to be approximately 400 μm.

[0127] The crystallinity of the film was measured from the top surface using an X-ray diffraction (XRD) device (RIGAKU SmartLab). As a result, only a diffraction intensity peak at 2θ = 43.9° attributed to diamond (111) was observed, confirming that the diamond layer was an epitaxially grown single-crystal diamond (111).

[0128] If the single crystal diamond (111) laminated substrate and freestanding substrate are applied to electronic and magnetic devices, high performance devices can be obtained, for example, high performance power devices.

[0129] Moreover, since it can be obtained on a large diameter substrate, it is possible to keep the manufacturing cost low.

[0130] Example 2 In Example 1, the single crystal Ir film 23 of the intermediate layer 21 was also formed by the mist CVD method, and the same production process was carried out. As a result, a single crystal diamond (111) laminated substrate 30 and a single crystal diamond (111) free-standing substrate 40, each having a diameter of 150 mm, were obtained.

[0131] Example 3 In Example 1, the same procedure was followed except that the material of the initial substrate 11 was changed to α-Al2O3 (0001), and a single crystal diamond (111) laminated substrate 30 and a single crystal diamond (111) free-standing substrate 40, each having a diameter of 150 mm, were obtained.

[0132] Example 4 In Example 1, the initial substrate 11 was made of single crystal Si (001) with an off angle of 6° in the

[0110] direction, and the same procedure was repeated to produce a single crystal diamond (001) laminated substrate 30 and a single crystal diamond (001) free-standing substrate 40, each having a diameter of 150 mm.

[0133] Example 5 In Example 1, the fabrication was carried out in the same manner as in Example 1, except that the structure of the initial substrate 11 was changed to α-Al2O3(11-20). As a result, a single crystal diamond (001) laminated substrate 30 and a single crystal diamond (001) free-standing substrate 40, each having a diameter of 150 mm, were obtained.

[0134] 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]

[0135] 11...initial board, 20...Base substrate 21...middle class, 22...Single crystal MgO film, 23...single crystal Ir film, 30...single crystal diamond laminate substrate, 31...single crystal diamond layer, 35...Single-crystal diamond freestanding substrate, 40...Single-crystal diamond freestanding substrate, 41...Additional single crystal diamond layer.

Claims

1. A method for manufacturing a base substrate for a single-crystal diamond laminate substrate, comprising: providing an initial substrate; forming an intermediate layer made of a single layer or a laminated film including at least a single-crystal MgO film on the initial substrate; and A method for manufacturing a base substrate, characterized in that the single-crystal MgO film constituting the intermediate layer is formed by mist CVD.

2. The initial substrate is a single crystal Si substrate, a single crystal α-Al ２ O ３ 2. The method for manufacturing a base substrate according to claim 1, wherein the base substrate is any one of a single crystal Fe substrate, a single crystal Ni substrate, and a single crystal Cu substrate.

3. The intermediate layer may further include a single crystal yttria-stabilized zirconia film, a single crystal SrTiO ３ 3. The method for manufacturing a base substrate according to claim 1, wherein the base substrate is a laminated film containing at least one of a Ru film and a single-crystal Ru film.

4. The initial substrate is a Si{111} substrate, an α-Al ２ O ３ The substrate is one of a {0001} substrate, an Fe{111} substrate, a Ni{111} substrate, and a Cu{111} substrate; 4. The method for manufacturing a base substrate according to claim 1, wherein the intermediate layer includes at least an MgO {111} film.

5. The intermediate layer may further include a yttria-stabilized zirconia {111} film, a SrTiO ３ 5. The method for producing a base substrate according to claim 4, wherein the base substrate contains at least one of a {111} film and a Ru{0001} film.

6. 6. The method for producing a base substrate according to claim 4 or 5, wherein the outermost surface of the initial substrate is off-angled in the crystal axis <-1-12> direction with respect to the cubic crystal plane orientation {111}, or is off-angled in the crystal axis <10-10> or <11-20> direction with respect to the hexagonal crystal plane orientation {0001}.

7. 7. The method for producing a base substrate according to claim 6, wherein the off-angle of the outermost surface of the initial substrate is set in the range of +0.5 to +15.0° or −0.5 to −15.0°.

8. 8. The method for producing a base substrate according to any one of claims 4 to 7, wherein the outermost surface of the intermediate layer is off-angled in the crystal axis <-1-12> direction with respect to the cubic crystal plane orientation {111}, or is off-angled in the crystal axis <10-10> or <11-20> direction with respect to the hexagonal crystal plane orientation {0001}.

9. 9. The method for producing a base substrate according to claim 8, wherein the off-angle of the outermost surface of the intermediate layer is set in the range of +0.5 to +15.0° or −0.5 to −15.0°.

10. The initial substrate is a Si{001} substrate, an α-Al ２ O ３ The substrate is one of a {11-20} substrate, an Fe{001} substrate, a Ni{001} substrate, and a Cu{001} substrate; 4. The method for manufacturing a base substrate according to claim 1, wherein the intermediate layer includes at least an MgO{001} film.

11. The intermediate layer may further include a yttria-stabilized zirconia {001} film, a SrTiO ３ 11. The method for producing a base substrate according to claim 10, wherein the base substrate contains at least one of a {001} film and a Ru{11-20} film.

12. 12. The method for producing a base substrate according to claim 10 or 11, wherein the outermost surface of the initial substrate is off-angled in the crystal axis <110> direction with respect to the cubic crystal plane orientation {001}, or is off-angled in the crystal axis <10-10> or <0001> direction with respect to the hexagonal crystal plane orientation {11-20}.

13. 13. The method for producing a base substrate according to claim 12, wherein the off-angle of the outermost surface of the initial substrate is set in the range of +0.5 to +15.0° or −0.5 to −15.0°.

14. The method for producing a base substrate according to any one of claims 10 to 13, characterized in that the outermost surface of the intermediate layer is off-angled in the crystal axis <110> direction with respect to the cubic crystal plane orientation {001}, or is off-angled in the <10-10> or <0001> direction with respect to the hexagonal crystal plane orientation {11-20}.

15. 15. The method for producing a base substrate according to claim 14, wherein the off-angle of the outermost surface of the intermediate layer is in the range of +0.5 to +15.0° or −0.5 to −15.0°.

16. A method for manufacturing a single crystal diamond laminate substrate, comprising the steps of: a step of preparing a base substrate manufactured by the method for manufacturing a base substrate according to any one of claims 1 to 15; applying a bias treatment to the surface of the intermediate layer of the base substrate for diamond nucleation; growing the diamond nuclei formed on the intermediate layer to perform epitaxial growth to form a single crystal diamond layer; 1. A method for producing a single-crystal diamond laminate substrate, comprising:

17. 17. The method for producing a monocrystalline diamond laminated substrate according to claim 16, wherein the monocrystalline diamond layer is a {111} crystal.

18. 17. The method for producing a monocrystalline diamond laminated substrate according to claim 16, wherein the monocrystalline diamond layer is a {001} crystal.

19. A method for producing a single crystal diamond freestanding substrate, characterized in that only the single crystal diamond layer is extracted from a single crystal diamond laminated substrate produced by the method for producing a single crystal diamond laminated substrate as defined in any one of claims 16 to 18, thereby producing a single crystal diamond freestanding substrate.

20. 20. A method for producing a single-crystal diamond freestanding substrate, comprising forming an additional single-crystal diamond layer on the single-crystal diamond freestanding substrate obtained by the method for producing a single-crystal diamond freestanding substrate according to claim 19.

21. In a base substrate for a single crystal diamond laminate substrate, An initial substrate; an intermediate layer made of a single layer or a laminated film including at least a single-crystal MgO film on the initial substrate; and A base substrate characterized in that the thickness uniformity of the intermediate layer is within ±10% over the entire surface.

22. The initial substrate is a single crystal Si substrate, a single crystal α-Al ２ O ３ 22. The base substrate according to claim 21, which is any one of a substrate, a single crystal Fe substrate, a single crystal Ni substrate, and a single crystal Cu substrate.

23. The intermediate layer may further comprise a single crystal yttria-stabilized zirconia film, a single crystal SrTiO ３ 23. The base substrate according to claim 21, which is a laminated film including at least one of a Ru film and a single-crystal Ru film.

24. 24. A single-crystal diamond laminate substrate, comprising a single-crystal diamond layer on the intermediate layer of a base substrate according to any one of claims 21 to 23.

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