METHOD FOR MANUFACTURING METAL OXIDE CRYSTAL, METHOD FOR MANUFACTURING METAL OXIDE EPITAXIAL CRYSTAL LAMINATED SUBSTRATE, METHOD FOR MANUFACTURING SEMICONDUCTOR DEVICE, METAL OXIDE CRYSTAL, METAL OXIDE EPITAXIAL CRYSTAL LAMINATED SUBSTRATE, SEMICONDUCTOR DEVICE, AND METAL OXIDE CRYS

Abstract

To provide a method for producing metal oxide crystal that can use raw material containing no halogen element and enables high-speed crystal growth.SOLUTION: A method for producing metal oxide crystal includes a metal oxide crystal formation step for reacting metal oxide gas 111a with oxygen element-containing gas to form the metal oxide crystal 204.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a metal oxide crystal, a method for manufacturing a metal oxide epitaxial crystal multilayer substrate, a method for manufacturing a semiconductor device, a metal oxide crystal, a metal oxide epitaxial crystal multilayer substrate, a semiconductor device, and a metal oxide crystal manufacturing apparatus. [Background technology]

[0002] Metal oxide crystals are important materials that are widely used in industry. For example, Patent Document 1 proposes the application of gallium oxide single crystals to various devices such as optical materials, electrodes, conductors, gas sensors, and optical recording materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-335616 Summary of the Invention [Problem to be solved by the invention]

[0004] Among metal oxide crystals, methods for producing gallium oxide crystals include, for example, MBE (molecular beam epitaxy), HVPE (halide vapor phase epitaxy), MOVPE (metal organic vapor phase epitaxy), and mist CVD (chemical vapor deposition). However, because HVPE uses raw materials containing halogen elements, there is a risk of environmental pollution by halogen compounds and corrosion of equipment. On the other hand, methods other than HVPE have the problem of slow crystal growth speed.

[0005] Therefore, an object of the present invention is to provide a method for manufacturing metal oxide crystals that can use raw materials that do not contain halogen elements and that enable high-speed crystal growth, a method for manufacturing a metal oxide epitaxial crystal laminated substrate, a method for manufacturing a semiconductor device, metal oxide crystals, metal oxide epitaxial crystal laminated substrates, semiconductor devices, and a metal oxide crystal manufacturing apparatus. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the method for producing metal oxide crystals of the present invention is a method for producing metal oxide crystals, characterized in that it includes a metal oxide crystal production step in which a metal oxide gas and an oxygen-containing gas are reacted to produce the metal oxide crystals.

[0007] The method for producing a metal oxide epitaxial crystal multilayer substrate of the present invention comprises the steps of: A method for manufacturing a metal oxide epitaxial crystal laminated substrate in which metal oxide epitaxial crystals are laminated on a crystal substrate, comprising: the metal oxide epitaxial crystal is a metal oxide crystal produced by the method for producing a metal oxide crystal of the present invention, The metal oxide epitaxial crystal is epitaxially grown on the crystal substrate by the method for producing a metal oxide crystal of the present invention.

[0008] The method for manufacturing a semiconductor device of the present invention includes the steps of: A method for manufacturing a semiconductor device including a metal oxide crystal or metal oxide epitaxial crystal laminated substrate, comprising: The metal oxide crystal is produced by the method for producing a metal oxide crystal of the present invention, or the metal oxide epitaxial crystal multilayer substrate is produced by the method for producing a metal oxide epitaxial crystal multilayer substrate of the present invention.

[0009] The metal oxide crystal of the present invention is a metal oxide crystal produced by the method for producing a metal oxide crystal of the present invention.

[0010] The metal oxide epitaxial crystal multilayer substrate of the present invention is a metal oxide epitaxial crystal multilayer substrate produced by the above-described method for producing a metal oxide epitaxial crystal multilayer substrate of the present invention.

[0011] The semiconductor device of the present invention is a semiconductor device manufactured by the method for manufacturing a semiconductor device of the present invention.

[0012] The metal oxide crystal manufacturing apparatus of the present invention is a metal oxide crystal manufacturing apparatus used in the metal oxide crystal manufacturing method of the present invention, the metal oxide epitaxial crystal laminated substrate manufacturing method of the present invention, or the semiconductor device manufacturing method of the present invention, a reaction vessel, a metal oxide gas supply mechanism, and an oxygen-containing gas supply mechanism; the metal oxide gas supply mechanism is capable of continuously supplying the metal oxide gas into the reaction vessel; the oxygen-containing gas supply mechanism can continuously supply the oxygen-containing gas into the reaction vessel; The metal oxide crystal generating step is carried out by reacting the metal oxide gas with the oxygen-containing gas in the reaction vessel. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a method for manufacturing metal oxide crystals that can use raw materials that do not contain halogen elements and that enable high-speed crystal growth, a method for manufacturing a metal oxide epitaxial crystal laminated substrate, a method for manufacturing a semiconductor device, metal oxide crystals, metal oxide epitaxial crystal laminated substrates, semiconductor devices, and metal oxide crystal manufacturing devices. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view that schematically shows an example of an apparatus used in the method for producing Group III nitride crystals of the present invention. [Figure 2] FIG. 2 is a cross-sectional view that schematically shows an example of a method for producing a Group III nitride crystal using the apparatus of FIG. [Figure 3] FIG. 3 is a cross-sectional view that schematically shows another example of a method for producing a Group III nitride crystal using the apparatus of FIG. [Figure 4] FIG. 4 is a cross-sectional view that schematically shows another example of an apparatus used in the method for producing Group III nitride crystals of the present invention. [Figure 5]FIG. 5 is a cross-sectional view that schematically shows an example of a method for producing a Group III nitride crystal using the apparatus of FIG. [Figure 6] FIG. 6 is a cross-sectional view that schematically shows yet another example of an apparatus used in the method for producing Group III nitride crystals of the present invention. [Figure 7] FIG. 7 is a cross-sectional view that schematically shows an example of a method for producing a Group III nitride crystal using the apparatus of FIG. [Figure 8] FIG. 8 is a graph showing an example of the results of analysis (theoretical calculation) of the equilibrium constant K in the Ga2O3 crystal formation reaction. [Figure 9] FIG. 9 is a graph showing an example of the results of analysis (theoretical calculation) of the equilibrium constant K in the In2O3 crystal formation reaction. [Figure 10] FIG. 10 is a graph showing an example of the results of an analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) in the Ga2O3 crystal formation reaction and the equilibrium partial pressure of each gas species present on the Ga2O3 crystal. [Figure 11] FIG. 11 is a graph showing an example of the results of an analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 12] FIG. 12 is a graph showing another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 13] FIG. 13 is a graph showing the analysis results of the VI / III ratio dependency of the parameter (ΔPGa2O3) indicating the driving force of Ga2O3 crystal growth at a crystal growth temperature of 1150°C. [Figure 14] FIG. 14 is a graph showing yet another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 15] FIG. 15 is a graph showing the dependence of the parameter (ΔPGa2O3) indicating the driving force for Ga2O3 crystal growth on the Ga2O supply partial pressure (PoGa2O). [Figure 16]FIG. 16 is a graph showing yet another example of the results of analysis (theoretical calculation) of the equilibrium constant K in the Ga2O3 crystal formation reaction. [Figure 17] FIG. 17 is a graph showing another example of the results of analysis (theoretical calculation) of the partial pressure of each gas in the Ga2O3 crystal growth reaction. [Figure 18] FIG. 18 is a graph showing yet another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 19] FIG. 19 is a graph showing the analysis results of the VI / III ratio dependency of the parameter (ΔPGa2O3) indicating the driving force of Ga2O3 crystal growth at a crystal growth temperature of 1150°C. [Figure 20] FIG. 20 is a graph showing yet another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 21] FIG. 21 is a graph showing yet another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 22] FIG. 22 is a graph showing yet another example of the results of analysis (theoretical calculation) of the partial pressure of each gas in the Ga2O3 crystal growth reaction. [Figure 23] FIG. 23 is a graph showing yet another example of the results of analysis (theoretical calculation) of the partial pressure of each gas in the Ga2O3 crystal growth reaction. [Figure 24] FIG. 24 is a graph showing yet another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 25] FIG. 25 is a graph showing yet another example of the results of analysis (theoretical calculation) of the correlation between the crystal growth temperature (° C.) and ΔPGa2O3 in the Ga2O3 crystal growth reaction. [Figure 26] FIG. 26 is a graph showing an example of the correlation between ΔPGa2O3, which is a parameter indicating the driving force of Ga2O3 crystal growth, and the crystal growth temperature and the hydrogen ratio Fo in the carrier gas. [Figure 27] FIG. 27 is a SEM (scanning electron microscope) photograph of the Ga2O3 crystals produced in Example 1. [Figure 28] FIG. 28 is a Nomarski observation image (photograph) of a SEM (scanning electron microscope) of the Ga2O3 crystal produced in Example 1. [Figure 29] FIG. 29 is a photograph of the 2 μm growth area of ​​the Nomarski observation image of FIG. [Figure 30] Figure 30 is a photograph of the area around the holding jig in the Nomarski observation image of Figure 28. [Figure 31] FIG. 31 is an XRD (X-ray diffraction) spectrum of the Ga2O3 crystal produced in Example 1. [Figure 32] FIG. 32 is a graph showing the XRD spectra of the Ga2O3 crystal of Example 1 (produced by heteroepitaxy growth) and the Ga2O3 crystal of Example 2 (produced by homoepitaxy growth). [Figure 33] FIG. 33 shows the XRD spectrum of Ga2O3 crystal. [Figure 34] FIG. 34 is a SEM (scanning electron microscope) photograph of the Ga2O3 crystals produced in Example 2. [Figure 35] FIG. 35 shows an XRD spectrum of the metal oxide epitaxial crystal laminated substrate (a laminate in which Ga2O3 epitaxial crystals are laminated on a Ga2O3 crystal substrate) produced in Example 2. [Figure 36] FIG. 36 is an SEM image (photograph) of the Ga2O3 crystal produced in Example 4. [Figure 37] FIG. 37 shows an XRD spectrum of the metal oxide epitaxial crystal multilayer substrate (a laminate in which Ga 2 O 3 epitaxial crystals are layered on a GaN crystal substrate) produced in Example 4. [Figure 38] FIG. 38 is an SEM photograph of the surface of the sapphire substrate after crystal growth in Example 5. [Figure 39] FIG. 39 is a SEM-EDS mapping image (photograph) of the deposit in FIG. [Figure 40]FIG. 40 is a graph showing the results of the elemental analysis (EDS line analysis) by the above-mentioned SEM-EDS. [Figure 41] FIG. 41 is an SEM-EDS mapping image (photograph) of another region (a region where a thin deposit was observed on the surface) on the sapphire substrate of FIG. 38, different from those in FIGS. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below with reference to examples, but the present invention is not limited to the following description.

[0016] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide crystal generating step, the partial pressure ratio of the metal oxide gas to the oxygen-containing gas may be in the range of 1000:1 to 1:1000. The partial pressure ratio of the metal oxide gas to the oxygen-containing gas may be, for example, 100:1 to 1:100, 1:1 to 1:100, or 1:1 to 1:50.

[0017] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide crystal generating step, the partial pressure of the oxygen-containing gas may be equal to or higher than the dissociation pressure (decomposition pressure) of the metal oxide crystals.

[0018] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide crystal generating step, the partial pressure of the oxygen-containing gas may be a pressure that exceeds the dissociation pressure (decomposition pressure) of the metal oxide crystals.

[0019] In the method for producing metal oxide crystals of the present invention, for example, the metal element in the metal oxide crystal may be at least one selected from the group consisting of Group I elements, Group II elements, Group III elements, Group IV elements, and lanthanides. The Group I element may be at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), copper (Cu), silver (Ag), and gold (Au). The Group II element may be at least one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), zinc (Zn), cadmium (Cd), and mercury (Hg). The Group III element may be at least one selected from the group consisting of gallium (Ga), indium (In), and aluminum (Al). It is particularly preferable that the Group III element is gallium (Ga). The Group IV element may be, for example, at least one selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), germanium (Ge), tin (Sn), and lead (Pb).

[0020] In the method for producing a metal oxide crystal of the present invention, for example, the metal element in the metal oxide crystal may be at least one selected from the group consisting of Li, Na, K, Rb, Cs, Fr, Cu, Ag, Au, Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg, Al, Ga, In, Ti, Zr, Hf, Ge, Sn, Pb, and Ir.

[0021] The method for producing a metal oxide crystal of the present invention may be carried out, for example, by using a method in which the metal oxide crystal is selected from the group consisting of α-Ga2O3, α-In2O3, α-Ir2O3, β-Ga2O3, β-In2O3, β-Ir2O3, β-Al2O3, ε-Ga2O3, ε-In2O3, ε-Ir2O3, ε-Al2O3, c-Ga2O3, c-In2O3, c-Ir2O3, c-Al2O3, and LiCsBO 10, LiB3O5, SrB4O7, or two or more thereof. In the present invention, the "metal oxide crystal" may contain, for example, only metal and oxygen as elements, or may further contain elements other than metal and oxygen. Examples of elements other than metal and oxygen include, but are not limited to, boron (B). In the present invention, the "metal oxide crystal" may be, for example, a binary crystal containing only one metal and oxygen as elements, or may be a ternary, quaternary, or other crystal containing one or more other elements. Examples of ternary, quaternary, or other crystals include the aforementioned Li-Cs-BO and Li-BO. In the present invention, examples of the metal oxide crystal formed from two or more crystals include a laminate of two or more different crystal layers, and a mixed crystal of two or more crystals. The mixed crystal is not particularly limited, but may be, for example, a mixed crystal containing a lanthanoid element and an aluminum element.

[0022] In the method for producing a metal oxide crystal of the present invention, for example, the metal oxide crystal may be a laminate of two or more crystal layers having different metal element compositions or electrical conductivities.

[0023] In the metal oxide crystal production method of the present invention, for example, in the metal oxide crystal generation step, the metal oxide gas may be at least one selected from the group consisting of GaO, indium oxide, aluminum oxide, iridium oxide, Group I element oxide, Group II element oxide, Group III element oxide, Group IV element oxide, and lanthanoid oxide. The indium oxide may be, for example, InO (indium(I) oxide). The aluminum oxide may be, for example, AlO (aluminum(I) oxide). The iridium oxide may be, for example, IrO (iridium(I) oxide). Furthermore, in the Group I element oxide, Group II element oxide, Group III element oxide, Group IV element oxide, and lanthanoid oxide, the Group I element, Group II element, Group III element, Group IV element, and lanthanoid are not particularly limited, and may be, for example, the elements described above.

[0024] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide crystal generating step, the oxygen-containing gas may contain at least one of elemental oxygen and an oxygen compound. In the present invention, the elemental oxygen is not particularly limited, but examples thereof include O2 (oxygen), O3 (ozone), O 2- (oxide ions), O2 2- (peroxide ion), with O being particularly preferred. In the present invention, the oxygen compound is not particularly limited, but examples thereof include HO (water), CO (carbon dioxide), CO (carbon monoxide), NO (nitrogen dioxide), NO (nitric oxide), NO (dinitrogen oxide), alcohol, etc. The alcohol is also not particularly limited, but examples thereof include methanol (methyl alcohol), ethanol (ethyl alcohol), 1-propanol (n-propyl alcohol), 2-propanol (isopropyl alcohol), etc.

[0025] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide crystal generation step, the oxygen-containing gas may be at least one selected from the group consisting of O2, H2O, CO2, CO, NO2, NO, N2O, and alcohol.

[0026] In the method for producing metal oxide crystals of the present invention, for example, the reaction between the metal oxide gas and the oxygen-containing gas may be carried out at 650°C or higher in the metal oxide crystal generation step. For example, when producing gallium (III) oxide, i.e., Ga2O3, by crystal growth, α-type (α-Ga2O3) tends to grow at low temperatures, while β-type (β-Ga2O3) tends to grow at high temperatures. Since the threshold between the α-type and β-type is approximately 650°C, when producing β-Ga2O3, it is preferable to carry out the reaction between the metal oxide gas and the oxygen-containing gas at 650°C or higher.

[0027] In the method for producing metal oxide crystals of the present invention, for example, the reaction between the metal oxide gas and the oxygen-containing gas may be carried out at a temperature lower than 650°C in the metal oxide crystal generating step. As described above, when producing Ga2O3 by crystal growth, α-type (α-Ga2O3) tends to grow at low temperatures, while β-type (β-Ga2O3) tends to grow at high temperatures, with the threshold between the α-type and β-type being approximately 650°C. Therefore, when producing α-Ga2O3, it is preferable to react the metal oxide gas with the oxygen-containing gas at a temperature lower than 650°C.

[0028] In the method for producing metal oxide crystals of the present invention, the reaction temperature in the metal oxide crystal production step is not particularly limited. For example, when the metal oxide crystals to be produced are IrO2, the reaction temperature in the metal oxide crystal production step may be set to 900°C or less or less to suppress or prevent IrO2 from becoming IrO3 and volatilizing.

[0029] The method for producing metal oxide crystals of the present invention may further include, for example, a metal oxide gas generation step of generating the metal oxide gas, in which the metal oxide gas may be generated by reacting a metal with an oxidizing agent in a heated state, or by reacting a solid metal oxide raw material with a reducing gas in a heated state to generate the metal oxide gas.

[0030] In the metal oxide gas generation step of the metal oxide crystal manufacturing method of the present invention, the metal is not particularly limited, and may be, for example, one or more of the metals exemplified as metal elements of the metal oxide crystal. That is, the metal may be, for example, at least one selected from the group consisting of Group I elements, Group II elements, Group III elements, Group IV elements, and lanthanides. The Group I element may be, for example, at least one selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), copper (Cu), silver (Ag), and gold (Au). The Group II element may be, for example, at least one selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), zinc (Zn), cadmium (Cd), and mercury (Hg). The Group III element may be, for example, at least one selected from the group consisting of gallium (Ga), indium (In), and aluminum (Al). Gallium (Ga) is particularly preferred as the Group III element. The Group IV element may be, for example, at least one selected from the group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf), germanium (Ge), tin (Sn), and lead (Pb). The metal may be, for example, at least one selected from the group consisting of Li, Na, K, Rb, Cs, Fr, Cu, Ag, Au, Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg, Al, Ga, In, In, Ti, Zr, Hf, Ge, Sn, Pb, and Ir. The metal may be, for example, a metal consisting of the same element as the metal element contained in the metal oxide crystal to be produced, as described above.

[0031] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide gas generation step, the oxidizing agent may be at least one selected from the group consisting of O2, H2O, CO2, CO, NO2, NO, N2O, and alcohol.

[0032] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide gas generation step, the metal oxide solid raw material may be at least one selected from the group consisting of Ga2O3, Ir2O3, In2O3, and Al2O3.

[0033] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide gas generation step, the reducing gas may be at least one selected from the group consisting of H2, HO, alcohol, carbon monoxide (CO), and hydrocarbons. The hydrocarbons are not particularly limited, but examples include methane, ethane, propane, n-butane, isobutane (2-methyl-2-propane), ethylene, and acetylene, and one or more of these may be used alone or in combination.

[0034] In the method for producing metal oxide crystals of the present invention, for example, in the metal oxide gas generation step, the reaction between the metal and the oxidizing agent or the reaction between the metal oxide solid raw material and the reducing gas may be carried out at 650°C or higher.

[0035] In the method for producing metal oxide crystals of the present invention, for example, at least one gas selected from the group consisting of H2, N2, air, and a rare gas may be present in the reaction system. The reaction system is not particularly limited and may be, for example, the reaction system of the metal oxide crystal production step or the reaction system of the metal oxide gas production step. H2, N2, air, and a rare gas can be used as an airflow control gas, taking advantage of their low reactivity with, for example, the raw materials for metal oxide crystals (the metal oxide gas, the oxygen-containing gas, the metal, the oxidizing agent, the metal oxide solid raw material, the reducing gas, etc.). Note that, hereinafter, the airflow control gas may be referred to as a "carrier gas." The rare gas is not particularly limited, but examples include helium (He), neon (Ne), and argon (Ar), and may be used alone or in combination of two or more.

[0036] In the method for producing metal oxide crystals of the present invention, for example, a dopant may be further present in the reaction system. The reaction system is not particularly limited and may be, for example, the reaction system of the metal oxide crystal production step or the reaction system of the metal oxide gas production step. The dopant can be used, for example, to control the conductivity of the produced metal oxide crystals. The metal oxide crystals produced by the method for producing metal oxide crystals of the present invention can be used for applications such as semiconductors by controlling the conductivity. However, the purpose of adding the dopant is not limited to these and may be used for any other purpose.

[0037] In the method for producing metal oxide crystals of the present invention, the dopant is not particularly limited, and may be, for example, at least one selected from the group consisting of a simple substance of an element other than the metal oxide crystal, an oxide of the element, a hydride of the element, and an organic compound. Examples of the other element include, but are not particularly limited to, silicon (Si). The simple substance of the other element is also not particularly limited, and may be, for example, silicon (silicon simple substance). For example, silicon may be mixed as a dopant into a simple metal (e.g., metallic gallium) that is the raw material for the metal oxide crystal of the present invention. The oxide of the other element is not particularly limited, and may be used alone or in combination of two or more. The hydride of the other element is not particularly limited, and may be used alone or in combination of two or more. The organic compound is not particularly limited, and may be used alone or in combination of two or more.

[0038] In the method for producing a metal oxide crystal of the present invention, for example, the metal oxide crystal may be a semiconductor.

[0039] In the method for producing a metal oxide crystal of the present invention, for example, the metal oxide crystal may be at least one of an n-type semiconductor and a p-type semiconductor. For example, the metal oxide crystal may be a laminate of two or more layers of metal oxide crystal, and may be a laminate including an n-type semiconductor layer and a p-type semiconductor layer.

[0040] The method for producing a metal oxide crystal of the present invention may be, for example, a method for epitaxially growing the metal oxide crystal on a crystal substrate by the method for producing a metal oxide crystal of the present invention, and then separating the metal oxide crystal from the crystal substrate to form a free-standing crystal.

[0041] In the method for producing a metal oxide epitaxial crystal multi-layer substrate of the present invention, the crystal substrate may be, for example, a crystal substrate formed from the same material as the metal oxide epitaxial crystal (hereinafter, sometimes simply referred to as a "homogeneous substrate"). In the method for producing a metal oxide epitaxial crystal multi-layer substrate of the present invention, the crystal substrate may be, for example, a crystal substrate formed from a material different from that of the metal oxide epitaxial crystal (hereinafter, sometimes simply referred to as a "heterogeneous substrate"). Here, "a material different from the metal oxide epitaxial crystal" includes not only a material having a different composition from that of the metal oxide epitaxial crystal, but also a material having the same composition as that of the metal oxide epitaxial crystal but a different crystal form. For example, the crystal substrate may be a β-gallium oxide single crystal, and the metal oxide epitaxial crystal may be an α-gallium oxide single crystal. Furthermore, for example, sapphire (aluminum oxide crystal), SiC (silicon carbide) crystal, or the like may be used as the crystal substrate, which is a heterogeneous substrate, and the metal oxide epitaxial crystal (for example, gallium oxide crystal, such as β-gallium oxide single crystal or α-gallium oxide single crystal) may be laminated thereon.

[0042] In the method for producing a metal oxide epitaxial crystal multilayer substrate of the present invention, for example, the crystal substrate may be a β-gallium oxide single crystal. When the crystal substrate is a β-gallium oxide single crystal, the crystal plane orientation of the crystal substrate is not particularly limited, but is preferably a plane orientation that eliminates crystal defects in the crystal substrate through crystal growth (that is, that eliminates crystal defects originating from the crystal substrate from the metal oxide epitaxial crystal), specifically, for example, (-201), (010), (001), (100), etc.

[0043] In the method for producing a metal oxide epitaxial crystal multilayer substrate of the present invention, the metal oxide epitaxial crystal may be, for example, a β-gallium oxide single crystal or an α-gallium oxide single crystal. These β-gallium oxide single crystals and α-gallium oxide single crystals may be single-layered or multi-layered, and may be doped or undoped. In these cases, the crystal substrate may be a homogeneous substrate or a heterogeneous substrate.

[0044] Next, specific embodiments of the present invention will be described in more detail by way of examples.

[0045] 1. Method for producing metal oxide crystals of the present invention As described above, the method for producing metal oxide crystals of the present invention is characterized by including a metal oxide crystal production step of reacting a metal oxide gas with an oxygen-containing gas to produce the metal oxide crystals.

[0046] The method for producing metal oxide crystals of the present invention does not require the use of halides (e.g., GaCl) as raw materials, and therefore can prevent the production of by-products containing halogens. Therefore, the production method of the present invention can suppress the adverse effects of the by-products on crystal production. As a result, for example, it is possible to produce metal oxide crystals over a long period of time, and large, thick metal oxide crystals can be obtained. Furthermore, the production method of the present invention can produce metal oxide crystals by epitaxial growth on a substrate, as described below, and can also suppress coloration of the resulting metal oxide crystals.

[0047] Furthermore, as described above, the method for producing metal oxide crystals of the present invention may further include a metal oxide gas generation step of generating the metal oxide gas, in which the metal oxide gas is generated by reacting a metal with an oxidizing agent under heating, or by reacting a metal oxide solid raw material with a reducing gas under heating. In this way, for example, it is possible to obtain metal oxide crystals without generating solid by-products in the metal oxide crystal generation step. If solid by-products are not generated in the metal oxide crystal generation step, for example, there is no need to introduce a filter or the like to remove the by-products, which is advantageous in terms of cost. Furthermore, in the metal oxide gas generation step, for example, the generation of by-products (e.g., solid by-products) can be further suppressed by reacting in the presence of a reducing gas.

[0048] In the following, among the methods for producing metal oxide crystals of the present invention, a method in which a metal and an oxidizing agent are reacted in a heated state to produce the metal oxide gas in the metal oxide gas production step may be referred to as "method for producing metal oxide crystals (A)." Furthermore, in the following, among the methods for producing metal oxide crystals of the present invention, a method in which a solid metal oxide raw material is reacted with a reducing gas in a heated state to produce the metal oxide gas in the metal oxide gas production step may be referred to as "method for producing metal oxide crystals (B)."

[0049] Furthermore, as described above, the method for producing metal oxide crystals of the present invention allows for high-speed crystal growth. However, in the method for producing metal oxide crystals of the present invention, the crystal growth rate is not particularly limited and can be any rate, and crystals can also be grown at a low rate. In the method for producing metal oxide crystals of the present invention, the growth rate of metal oxide crystals may be, for example, 0.001 μm / hour or more, 0.01 μm / hour or more, 0.1 μm / hour or more, 0.5 μm / hour or more, or 1 μm / hour or more, and may be, for example, 10,000 μm / hour or less, 1,000 μm / hour or less, 500 μm / hour or less, 100 μm / hour or less, or 50 μm / hour or less, and may be, for example, 0.001 to 10,000 μm / hour, 0.01 to 1,000 μm / hour, 0.1 to 500 μm / hour, 1 to 500 μm / hour, or 1 to 100 μm / hour.

[0050] [1-1. Examples of methods for producing metal oxide crystals and crystal growth rates, etc.] Below, various examples of the method for producing metal oxide crystals of the present invention are shown, along with theoretical calculation results of the growth rate of metal oxide crystals. Note that the theoretical calculation results shown in this specification are theoretical calculation results under specific conditions. The results of actually practicing the present invention may not necessarily match the theoretical calculation results due to variations in various conditions.

[0051] The graph in Figure 8 shows the results of analysis (theoretical calculation) of the equilibrium constant K in the Ga2O3 crystal growth reaction according to the following chemical reaction formulas (1) to (4). The reactions of the following chemical reaction formulas (1) and (3) correspond to the metal oxide crystal growth step in the metal oxide crystal production method of the present invention, in which a metal oxide gas is reacted with an oxygen-containing gas to produce the metal oxide crystal. The reactions of the following chemical reaction formulas (2) and (4) are examples of reactions in the HVPE method. In the following chemical reaction formulas (1) to (4), (g) represents a gas, and (s) represents a solid. This is the same for all the following reaction formulas. In the graph in Figure 8, the vertical axis represents the common logarithm of the equilibrium constant K. The horizontal axis represents the crystal growth temperature [°C] or 1000 / T [K -1] (where T represents the crystal growth temperature [K]). In the graph of Figure 8, the analysis (theoretical calculation) of the equilibrium constant K was derived using experimentally obtained data published in thermodynamic databases such as the following references [1] to [3]. The same applies to the following figures. (1) Ga2O(g) + O2(g) = Ga2O3(s) (2)2GaCl(g)+(3 / 2)O2(g)=Ga2O3(s)+Cl2(g) (3)Ga2O(g)+2H2O(g)=Ga2O3(s)+2H2(g) (4)2GaCl(g)+3H2O(g)=Ga2O3(s)+2HCl(g)+2H2(g) [1] MW Chase Jr. (Ed.), NIST-JANAF Thermochemical Tables, fourth ed. The American Chemical Society and the American Institute of Physics for the National Institute of Standards and Technology, Gaithersburg, 1998. [2] LV Gurvich, IV Veyts, CB Alcock (Eds.), Thermodynamic Properties of Individual Substances, vol. 3, USSR Academy of Sciences, Institute for High Temperatures and State Institute of Applied Chemistry in cooperation with the National Standard Reference Data Service of the USSR, Moscow, 1994. [3] I. Barin (Ed.), Thermochemical Data of Pure Substances, Wiley, New York, 1989.

[0052] As can be seen from the graph in Figure 8, when O2(g) is used as the oxygen-containing gas, it was confirmed that, in theory, the metal oxide crystal manufacturing method (1) of the present invention has a larger equilibrium constant K than the HVPE method (2), i.e., a faster reaction rate (crystal growth rate). Furthermore, when HO(g) is used as the oxygen-containing gas, it was confirmed that the metal oxide crystal manufacturing method (3) of the present invention has a larger equilibrium constant K than the HVPE method (4), i.e., a faster reaction rate (crystal growth rate). In other words, from the analysis results in Figure 8, it was confirmed that, in theory, the metal oxide crystal manufacturing method of the present invention has a faster crystal growth rate than the HVPE method.

[0053] The graph in FIG. 9 shows the results of analysis (theoretical calculation) of the equilibrium constant K in the In2O3 crystal growth reaction according to the following chemical reaction formulas (1a) to (4a). The reactions of the following chemical reaction formulas (1a) and (3a) correspond to the metal oxide crystal growth step in the metal oxide crystal production method of the present invention, in which a metal oxide gas is reacted with an oxygen-containing gas to produce the metal oxide crystal. The reactions of the following chemical reaction formulas (2a) and (4a) are examples of reactions in the HVPE method. In the following chemical reaction formulas (1a) to (4a), (g) represents a gas, and (s) represents a solid. This is the same for all the following reaction formulas. In the graph in FIG. 9, the vertical axis represents the common logarithm of the reaction rate K. The horizontal axis represents the crystal growth temperature [°C] or 1000 / T [K -1 ] (where T is the crystal growth temperature [K]). (1a) In2O(g) + O2(g) = In2O3(s) (2a)2InCl(g)+(3 / 2)O2(g)=In2O3(s)+Cl2(g) (3a)In2O(g)+2H2O(g)=In2O3(s)+2H2(g) (4a)2InCl(g)+3H2O(g)=In2O3(s)+2HCl(g)+2H2(g)

[0054] As can be seen from the graph in Figure 9, when O2(g) is used as the oxygen-containing gas, it was confirmed that the equilibrium constant K of the metal oxide crystal manufacturing method (1a) of the present invention is greater than that of the HVPE method (2a), i.e., the reaction rate (crystal growth rate) is faster. Furthermore, when H2O(g) is used as the oxygen-containing gas, it was confirmed that the equilibrium constant K of the metal oxide crystal manufacturing method (3a) of the present invention is greater than that of the HVPE method (4a), i.e., the reaction rate (crystal growth rate) is faster. In other words, the analysis results in Figure 9 confirm that, in theory, when producing In2O3 crystals, as with the production of Ga2O3, the crystal growth rate of the metal oxide crystal manufacturing method of the present invention is faster than that of the HVPE method.

[0055] Next, in the reaction of chemical reaction formula (3) in FIG. 8, in addition to the chemical reaction formula (3) (shown again below), for example, the following reactions (a) to (g) are thought to occur. (3)Ga2O(g)+2H2O(g)=Ga2O3(s)+2H2(g) (a) GaO(g) = GaO(g) + Ga(g) (b) Ga2O(g) = 2Ga(g) + (1 / 2)O2(g) (c)Ga2O(g)+H2O(g)=2GaH(g)+O2(g) (d)Ga2O(g)+2H2O(g)=2GaH2(g)+(3 / 2)O2(g) (e)Ga2O(g)+3H2O(g)=2GaH3(g)+2O2(g) (f) Ga2O(g) + H2O(g) = 2GaOH(g) (g)H2(g) + (1 / 2)O2(g) = H2O(g)

[0056] The gas species involved in the reactions of the chemical reaction formula (3) and the chemical reaction formulas (a) to (g) are 11 types: Ga2O, GaO, Ga, O2, H2, H2O, GaH, GaH2, GaH3, GaOH, and inert gas (IG). Assume that these 11 gas species are simultaneously present on the Ga2O3 substrate. These gas species are related by the eight independent chemical reaction formulas of the chemical reaction formula (3) and the chemical reaction formulas (a) to (g). The growth conditions are the temperature of the growth section, the total pressure, the Ga2O supply partial pressure (P o Ga2O ), H2O supply partial pressure (P o H2O ), hydrogen ratio in carrier gas F o In addition to the equilibrium equations for the eight chemical reactions mentioned above (for example, the equilibrium equation (3A) below is obtained from the chemical reaction equation (3)), we consider a total of 11 equations as constraints: an equation for constant total pressure, an equation giving the stoichiometric ratio for Ga2O3 production (Ga and oxygen atomic ratio of 2:3), and an equation giving the constant number of hydrogen and IG atoms in the gas phase. By solving these simultaneous equations, we can obtain the equilibrium partial pressures of the 11 gas species. Figure 10 shows the equilibrium partial pressures of each gas species present on the Ga2O3 crystal as a function of temperature.

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[0057] In the graph of Figure 10, the horizontal axis represents the temperature of the growth region, i.e., the temperature of each gas, which was assumed to be equal to the crystal growth temperature. The vertical axis represents the equilibrium partial pressure [atm] of each substance (gas). Note that 1.0 atm is 1.01325 x 10 5 The theoretical calculations for the graph in Figure 10 were performed assuming the following reaction conditions: Growth temperature = Crystal growth temperature (variable) ·Total pressure P tot =1.0atm GaO supply partial pressure P o Ga2O =1.0×10 -4 ATM H2O supply partial pressure P oH2O =1.0×10 -3 ATM ·Supply VI / III ratio ((P o Ga2O +P o H2O ) / 2P o Ga2O )=5.5 Hydrogen ratio in carrier gas F o =P o H2 / (P o H2 +P o IG )=1.0×10 -4

[0058] As shown in the graph in Figure 10, if the crystal growth temperature is too high, the equilibrium partial pressure of Ga2O(g) increases due to the Ga2O3 decomposition reaction as the crystal growth temperature increases. Specifically, the parameter (ΔP Ga2O3 ) decreases at growth temperatures above 1100°C, and at temperatures above 1320°C, it has been confirmed that it acts in the direction of negative growth (etching) of Ga2O3 crystal growth. However, the results in Figure 10 are theoretical calculation results under the conditions mentioned above. Actual experimental results may not necessarily match the results in Figure 10 due to variations in various conditions. Also, ΔP Ga2O3 can be calculated from the partial pressure of each gas using the following formula: ΔP Ga2O3 =(1 / 2)[2P o Ga2O -(P Ga +P GaO +2P Ga2O +P GaH +P GaH2 +P GaH3 +P GaOH )]

[0059] The graph in Figure 11 shows the hydrogen ratio in the carrier gas F under the conditions in Figure 10. o to 1.0 x 10 -4 The crystal growth temperature (℃) and ΔP were varied in the range of ∼1. Ga2O3In FIG. 11, the horizontal axis represents the crystal growth temperature (°C) and the vertical axis represents ΔP Ga2O3 As shown in the figure, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 is the crystal growth temperature and F o This means that theoretically, F o It was confirmed that the smaller the Ga2O3 crystal growth rate, the faster the Ga2O3 crystal growth rate.

[0060] The graph in Figure 12 shows the supply VI / III ratio ((P o Ga2O +P o H2O ) / 2P o Ga2O ) in the range of 0.5 to 250.5, and the crystal growth temperature (℃) and ΔP Ga2O3 In FIG. 12, the horizontal axis represents the crystal growth temperature (°C) and the vertical axis represents ΔP Ga2O3 As shown in the figure, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 increased with increasing supply VI / III ratio. This confirmed that, theoretically, the Ga2O3 crystal growth rate tends to increase as the supply VI / III ratio increases.

[0061] Figure 13 shows the parameter (ΔP Ga2O3 ) at a crystal growth temperature of 1150°C. In Fig. 13(a), the vertical axis represents the equilibrium partial pressure [atm] of each substance (gas), and the horizontal axis represents the VI / III ratio. The definition of the VI / III ratio is as explained in Fig. 10 and Fig. 12. Fig. 13(a) shows that when the VI / III ratio is about 1 or more, P H2O >P Ga2OIt was confirmed that under these crystal growth conditions, Ga2O3 crystal growth proceeds through the reaction Ga2O(g) + 2H2O(g) = Ga2O3(s) + 2H2(g), and that when the VI / III ratio is less than approximately 1, the H2O supply partial pressure is insufficient, which acts in the direction of negative growth (etching) of Ga2O3 crystal growth. On the other hand, in Figure 13(b), the vertical axis is ΔP, a parameter that indicates the driving force of Ga2O3 crystal growth. Ga2O3 The horizontal axis represents the VI / III ratio. As shown in Figure 13(b), under these crystal growth conditions, it was confirmed that the gradient of the driving force for growth changes when the VI / III ratio is approximately 10 or more.

[0062] The graph in Figure 14 shows the Ga2O supply partial pressure P o Ga2O to 1.0×10 -4 atm~1.0×10 -3 The crystal growth temperature (℃) and ΔP were varied in the range of Ga2O3 The figure shows the results of calculating the correlation between the H2O supply partial pressure P o H2O is always the VI / III ratio ((P o Ga2O +P o H2O ) / 2P o Ga2O ) is 5.5, 1.0×10 -3 atm~1.0×10 -2 In Fig. 14, the horizontal axis represents the crystal growth temperature (°C) and the vertical axis represents ΔP Ga2O3 As shown in the figure, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 is the GaO supply partial pressure P o Ga2O This indicates that the GaO supply partial pressure P o Ga2O It was confirmed that the larger the value, the faster the Ga2O3 crystal growth rate.

[0063] The graph in Figure 15 shows the parameter (ΔP Ga2O3) of GaO supply partial pressure (P o Ga2O ) dependency. In Fig. 15, the horizontal axis is P o Ga2O and the vertical axis is ΔP Ga2O3 As shown in Figure 15, the driving force for Ga2O3 growth (ΔP Ga2O3 ) was confirmed to increase in proportion to the increase in GaO supply partial pressure.

[0064] The graph in Figure 16 shows the results of analysis (theoretical calculation) of the equilibrium constant K in the Ga2O3 crystal growth reaction according to the following chemical reaction formulas (1) to (7). The following chemical reaction formulas (1) to (4) are the same as the chemical reaction formulas (1) to (4) in Figure 1, respectively. The following chemical reaction formulas (5) to (7) correspond to the metal oxide crystal growth step in the metal oxide crystal production method of the present invention, in which a metal oxide gas is reacted with an oxygen-containing gas to produce the metal oxide crystal. The following chemical reaction formula (5) is an example in which the oxygen-containing gas is nitrous oxide (NO). The following chemical reaction formula (6) is an example in which the oxygen-containing gas is carbon dioxide (CO2). The following chemical reaction formula (7) is an example in which the oxygen-containing gas is nitric oxide (NO). In the graph in Figure 16, the vertical axis represents the common logarithm of the equilibrium constant K. The horizontal axis represents the crystal growth temperature [°C] or 1000 / T [K -1 ] (where T represents the crystal growth temperature [K]). In the graph of FIG. 16, the analysis (theoretical calculation) of the equilibrium constant K was derived using the same data as in FIG. (1) Ga2O(g) + O2(g) = Ga2O3(s) (2)2GaCl(g)+(3 / 2)O2(g)=Ga2O3(s)+Cl2(g) (3)Ga2O(g)+2H2O(g)=Ga2O3(s)+2H2(g) (4)2GaCl(g)+3H2O(g)=Ga2O3(s)+2HCl(g)+2H2(g) (5)Ga2O(g)+2N2O(g)=Ga2O3(s)+2N2(g) (6)Ga2O(g)+2CO2(g)=Ga2O3(s)+2CO(g) (7)Ga2O(g)+2NO(g)=Ga2O3(s)+N2(g)

[0065] As can be seen from the graph in Figure 16, it was confirmed that the metal oxide crystal manufacturing methods (5) and (7) of the present invention have a larger equilibrium constant K than all other reactions, i.e., a faster reaction rate (crystal growth rate). It was also confirmed that the metal oxide crystal manufacturing method (6) of the present invention has a larger equilibrium constant K than the HVPE method (4), i.e., a faster reaction rate (crystal growth rate). Thus, it was confirmed that the metal oxide crystal manufacturing method of the present invention enables crystal growth at a high speed comparable to the HVPE method.

[0066] In the reaction of chemical reaction formula (6) in Figure 16, in addition to chemical reaction formula (6) (shown again below), the following reactions (h) to (q) are thought to occur. The graph in Figure 17 shows the theoretical calculation results of the partial pressures of each substance in these reactions. (6)Ga2O(g)+2CO2(g)=Ga2O3(s)+2CO(g) (h) GaO(g) = GaO(g) + Ga(g) (i) Ga2O(g) = 2Ga(g) + (1 / 2)O2(g) (j)Ga2O(g)+2H2(g)=2GaH(g)+H2O(g) (k)Ga2O(g)+3H2(g)=2GaH2(g)+H2O(g) (l)Ga2O(g)+4H2(g)=2GaH3(g)+H2O(g) (m)Ga2O(g)+H2(g)+CO2(g)=2GaOH(g)+CO(g) (n)CO2(g) = CO(g) + (1 / 2)O2(g) (o) CO2(g) = C(g) + O2(g) (p)CO2(g)+4H2(g)=CH4(g)+2H2O(g) (q)H2(g) + (1 / 2)O2(g) = H2O(g) The gas species involved in the reactions of the chemical reaction formula (6) and the chemical reaction formulas (h) to (q) are 15 types: Ga2O, GaO, Ga, GaH, GaH2, GaH3, GaOH, CO2, CO, C, CH4, O2, H2O, H2, and IG. Assume that these 15 gas species are simultaneously present on the Ga2O3 substrate. These gas species are related by the 11 independent chemical reaction formulas of the chemical reaction formula (6) and the chemical reaction formulas (h) to (q). The growth conditions are the temperature of the growth section, the total pressure, the Ga2O supply partial pressure (P o Ga2O ), CO2 supply partial pressure (P o CO2 ), hydrogen ratio in carrier gas F o In addition to the equilibrium equations for the 11 chemical reactions mentioned above (for example, the equilibrium equation (6A) below is obtained from the chemical reaction equation (6)), we consider a total of 15 equations as constraints: an equation for constant total pressure, an equation giving the stoichiometric ratio for Ga2O3 production (Ga and oxygen atomic ratio of 2:3), and two equations giving the constant number of carbon, hydrogen, and Ig atoms in the gas phase. By solving these simultaneous equations, we can obtain the equilibrium partial pressures of 15 gas species. Figure 17 shows the equilibrium partial pressures of each gas species present on the Ga2O3 crystal as a function of temperature.

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[0067] In the graph of Figure 17, the horizontal axis represents the temperature of the growth region, i.e., the temperature of each gas, which was assumed to be equal to the crystal growth temperature. The vertical axis represents the partial pressure [atm] of each substance (gas). Note that 1.0 atm is 1.01325 x 10 5 The theoretical calculations for the graph in Figure 17 were performed under the following reaction conditions: Growth temperature = Crystal growth temperature (variable) ·Total pressure P tot =1.0atm GaO supply partial pressure P o Ga2O =1.0×10 -4 ATM CO2 supply partial pressure P oCO2 =5.0×10 -4 ATM ·Supply VI / III ratio ((P o Ga2O+2P o CO2) / 2P o GaO) = 5.5 F o =0 (completely non-hydrogen system)

[0068] As shown in the graph in Figure 17, it was confirmed that when the crystal growth temperature is too high, the equilibrium partial pressure of Ga2O(g) increases due to the Ga2O3 decomposition reaction as the crystal growth temperature increases. Specifically, the parameter (ΔP Ga2O3 ) decreases at growth temperatures above 1100°C, and at temperatures above 1550°C, it has been confirmed that it acts in the direction of negative growth (etching) of Ga2O3 crystal growth. However, the results in Figure 17 are theoretical calculation results under the conditions mentioned above. Actual experimental results may not necessarily match the results in Figure 17 due to variations in various conditions. Also, ΔP Ga2O3 can be calculated from the partial pressure of each gas using the following formula: ΔP Ga2O3 =(1 / 2)[2P o Ga2O -(P Ga +P GaO +2P Ga2O )]

[0069] The graph in Figure 18 shows the supply VI / III ratio ((P o Ga2O +2P o CO2 ) / 2P o Ga2O ) in the range of 0.55 to 500.5, and the crystal growth temperature (℃) and ΔP Ga2O3 The figure shows the results of calculating the correlation between the CO2 supply partial pressure P o CO2 is 5.0×10 to vary the supply VI / III ratio. -6 atm~5.0×10 -2The partial pressure of the other gases was fixed and not changed, and the CO2 supply partial pressure P o CO2 By varying only the supply VI / III ratio ((P o Ga2O +2P o CO2 ) / 2P o Ga2O The hydrogen ratio in the carrier gas, F o is 1.0 x 10 -4 In FIG. 18, the horizontal axis represents the crystal growth temperature (°C), and the vertical axis represents ΔP Ga2O3 As shown in the figure, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 increased with increasing supply VI / III ratio. This confirmed that, theoretically, the Ga2O3 crystal growth rate tends to increase as the supply VI / III ratio increases.

[0070] Figure 19 shows the parameter (ΔP Ga2O3 The analysis results of the dependence of the VI / III ratio on the crystal growth temperature of 1150°C are shown below. o is 1.0 x 10 -4 In the figure, the vertical axis represents the equilibrium partial pressure [atm] of each substance (gas), and the horizontal axis represents the VI / III ratio. The definition of the VI / III ratio is as explained in Figures 17 and 18. As shown in the figure, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 It was confirmed that increases with increasing supply VI / III ratio, and that the gradient of the driving force for growth changes and becomes almost constant when the VI / III ratio is about 20 or more.

[0071] The graph in Figure 20 shows the Ga2O supply partial pressure Po Ga2O to 1.0×10 -4 atm~1.0×10 -3 The crystal growth temperature (℃) and ΔP were varied in the range of Ga2O3 The figure shows the results of calculating the correlation between the CO2 supply partial pressure P o CO2 is 5.0 x 10 -4atm~5.0×10 -3 The supply VI / III ratio ((P o Ga2O +2P o CO2 ) / 2P o Ga2O ) was fixed at 5.5. The hydrogen ratio in the carrier gas, F o is 1.0 x 10 -4 As shown in the figure, when the supply VI / III ratio is fixed at 5.5, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 is the GaO supply partial pressure Po Ga2O It was confirmed that the Ga2O3 crystal growth temperature is approximately 1700°C or less by selecting the conditions, and that the Ga2O3 crystal growth temperature is approximately 1700°C or less without negative growth (etching).

[0072] The theoretical calculations for the graph in FIG. 21 were performed assuming the following reaction conditions: Growth temperature = Crystal growth temperature (variable) ·Total pressure P tot =1.0atm GaO supply partial pressure P o Ga2O =1.0×10 -4 ATM CO2 supply partial pressure P o CO2 =5.0×10 -4 ATM ·Supply VI / III ratio ((P o Ga2O +2P o CO2 ) / 2P o Ga2O )=5.5 Hydrogen ratio in carrier gas F o =P o H2 / (P o H2 +P o IG )=0~1.0

[0073] In addition, under the conditions of Figure 21, ΔP, which is a parameter indicating the driving force for Ga2O3 crystal growth,Ga2O3 can be expressed by the following formula: ΔP Ga2O3 =(1 / 2)[2P o Ga2O -(P Ga +P GaO +2P Ga2O +P GaH +P GaH2 +P GaH3 +P GaOH )]

[0074] As shown in Figure 21, under these conditions, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 is the crystal growth temperature and the hydrogen ratio in the carrier gas F o This indicates that the hydrogen gas H2 does not exist in the non-hydrogen system (F o It was confirmed that the highest temperature and high speed growth was possible at 1000°C or higher. o =1×10 ―3 It was confirmed that the following was necessary:

[0075] The graph in Figure 22 shows the results of the non-hydrogen system (F o =0) or a completely hydrogen system (F o The theoretical calculation results of the partial pressure of each substance when the reaction is carried out at a temperature of 1.0 atm (=1) are shown below. In both the left and right graphs in Figure 22, the horizontal axis is the temperature of the growth section, i.e., the temperature of each gas, which is assumed to be equal to the crystal growth temperature. In addition, the vertical axis of both graphs is the partial pressure [atm] of each substance (gas). Note that 1.0 atm is 1.01325 x 10 5 As shown in Figure 22, Ga2O3 crystal growth is possible at a high temperature of 1100°C in the non-hydrogen system, whereas the maximum temperature at which Ga2O3 crystal growth is possible in the hydrogen system is 700°C. This is because increasing the hydrogen supply partial pressure causes significant decomposition of Ga2O3 by hydrogen, reducing the driving force for growth.

[0076] In the reaction of chemical reaction formula (5) in Figure 16, in addition to the chemical reaction formula (5) (shown again below), it is thought that the following reactions (y1) to (y10) also occur. The graph in Figure 23 shows the theoretical calculation results of the partial pressures of each substance in these reactions. (5)Ga2O(g)+2N2O(g)=Ga2O3(s)+2N2(g) (y1)Ga2O(g) = GaO(g) + Ga(g) (y2)Ga2O(g) = 2Ga(g) + (1 / 2)O2(g) (y3)Ga2O(g)+2H2(g)=2GaH(g)+H2O(g) (y4)Ga2O(g)+3H2(g)=2GaH2(g)+H2O(g) (y5)Ga2O(g)+4H2(g)=2GaH3(g)+H2O(g) (y6)Ga2O(g)+H2(g)+N2O(g)=2GaOH(g)+N2(g) (y7)N2O(g) = NO(g) + (1 / 2)N2(g) (y8)N2O(g) = N2(g) + (1 / 2)O2(g) (y9)N2O(g)+4H2(g)=2NH3(g)+H2O(g) (y10)H2(g)+(1 / 2)O2(g)=H2O(g) The gas species involved in the reactions of the chemical reaction formula (5) and the chemical reaction formulas (y1) to (y10) are 15 types: Ga2O, GaO, Ga, GaH, GaH2, GaH3, GaOH, N2O, NO, N2, NH3, O2, H2O, H2, and IG. Assume that these 15 gas species are simultaneously present on the Ga2O3 substrate. These gas species are related by the 11 independent chemical reaction formulas of the chemical reaction formula (5) and the chemical reaction formulas (y1) to (y10). The growth conditions are the temperature of the growth section, the total pressure, the Ga2O supply partial pressure (P o Ga2O ), NO supply partial pressure (P o N2O ), hydrogen ratio in carrier gas F oIn addition to the equilibrium equations for the 11 chemical reactions mentioned above (for example, the equilibrium equation (5A) below is obtained from the chemical reaction equation (5)), we consider a total of 15 equations as constraints: an equation for constant total pressure, an equation giving the stoichiometric ratio for Ga2O3 production (Ga and oxygen atomic ratio of 2:3), and two equations giving the constant number of nitrogen, hydrogen, and IG atoms in the gas phase. By solving these simultaneous equations, we can obtain the equilibrium partial pressures of 15 gas species. Figure 23 shows the equilibrium partial pressures of each gas species present on the Ga2O3 crystal as a function of temperature.

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[0077] In the graph of Figure 23, the horizontal axis represents the temperature of the growth region, i.e., the temperature of each gas, which was assumed to be equal to the crystal growth temperature. The vertical axis represents the partial pressure [atm] of each substance (gas). Note that 1.0 atm is 1.01325 x 10 5 The theoretical calculations for the graph in Figure 23 were performed assuming the following reaction conditions: Growth temperature = Crystal growth temperature (variable) ·Total pressure P tot =1.0atm GaO supply partial pressure P o Ga2O =1.0×10 -4 ATM N2O supply partial pressure P o N2O =1.0×10 -3 ATM ·Supply VI / III ratio ((P o Ga2O +P o N2O ) / 2P o Ga2O )=5.5 F o =0 (completely non-hydrogen system)

[0078] As shown in Figure 23, it was confirmed that Ga2O3(s) crystals can be produced at high temperatures (1500°C) through the reaction of chemical reaction formula (5), i.e., Ga2O(g) + 2N2O(g) = Ga2O3(s) + 2N2(g).

[0079] The graph in Figure 24 shows the supply VI / III ratio ((P o Ga2O +P o N2O ) / 2P o Ga2O ) in the range of 0.55 to 500.5, and the crystal growth temperature (℃) and the parameter indicating the driving force of Ga2O3 crystal growth (ΔP Ga2O3 ) and the results of calculating the correlation between the VI / III ratio and ΔP Ga2O3 The partial pressure (atm) of each gas is also shown. o N2O is 1.0×10 to vary the supply VI / III ratio. -5 atm~1.0×10 -1 The partial pressure of the other gases was fixed and not changed, and the NO supply partial pressure P o N2O By varying only the supply VI / III ratio ((P o Ga2O +P o N2O ) / 2P o Ga2O The hydrogen ratio in the carrier gas, F o is 1.0 x 10 -4 In addition, ΔP Ga2O3 can be calculated from the partial pressure of each gas using the following formula: ΔP Ga2O3 =(1 / 2)[2P o Ga2O -(P Ga +P GaO +2P Ga2O +P GaH +P GaH2 +P GaH3 +P GaOH )]

[0080] As shown in the graph in Figure 24, the parameter (ΔP Ga2O3 ) was confirmed to increase with an increase in the supply VI / III ratio. o N2O =2×10 -4 atm) or more, ΔP Ga2O3 was confirmed to be almost maximum.

[0081] The graph in Figure 25 shows the GaO supply partial pressure P o Ga2O to 1.0×10 -4 atm~1.0×10 -3 The crystal growth temperature (℃) and ΔP were varied in the range of Ga2O3 The figure shows the results of calculating the correlation between the NO supply partial pressure P o N2O is 1.0 x 10 -3 atm~1.0×10 -2 The supply VI / III ratio ((P o Ga2O +P o N2O ) / 2P o Ga2O ) was fixed at 5.5. The hydrogen ratio in the carrier gas, F o is 1.0 x 10 -4 As shown in the figure, when the supply VI / III ratio is fixed at 5.5, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 is the GaO supply partial pressure P o Ga2O It was confirmed that the Ga2O3 crystal growth without negative growth (etching) was possible at crystal growth temperatures of approximately 1800°C or less by selecting the conditions.

[0082] The theoretical calculations for the graph in FIG. 26 were performed assuming the following reaction conditions: Growth temperature = Crystal growth temperature (variable) ·Total pressure P tot =1.0atm GaO supply partial pressure P o Ga2O =1.0×10 -4 ATM N2O supply partial pressure P o N2O =1.0×10 -3 ATM ·Supply VI / III ratio ((P o Ga2O +P o N2O ) / 2P o Ga2O )=5.5 Hydrogen ratio in carrier gas F o =P o H2 / (P o H2 +P o IG )=0~1.0

[0083] In addition, under the conditions of Figure 26, ΔP, which is a parameter indicating the driving force for Ga2O3 crystal growth, Ga2O3 can be expressed by the following formula: ΔP Ga2O3 =(1 / 2)[2P o Ga2O -(P Ga +P GaO +2P Ga2O +P GaH +P GaH2 +P GaH3 +P GaOH )]

[0084] As shown in Figure 26, under these conditions, ΔP, a parameter that indicates the driving force for Ga2O3 crystal growth, Ga2O3 is the crystal growth temperature and the hydrogen ratio in the carrier gas F o This indicates that the hydrogen gas H2 does not exist in the non-hydrogen system (F o It was confirmed that the highest temperature and high speed growth was possible at 1000°C or higher. o =1×10 ―3 It was confirmed that the following was necessary:

[0085] Specifically, the method for producing metal oxide crystals of the present invention can be carried out, for example, as follows.

[0086] [1-2. Metal oxide crystal manufacturing equipment] FIG. 1 shows an example of the configuration of a manufacturing apparatus used in the metal oxide crystal manufacturing method of the present invention. For clarity, the size and ratio of each component in the figure are different from the actual size and ratio. The manufacturing apparatus 100 in FIG. 1 corresponds to the metal oxide crystal manufacturing apparatus of the present invention and can be used in the metal oxide crystal manufacturing method of the present invention. As shown in the figure, the manufacturing apparatus 100 of this example has a first container 101, a second container 102, and a substrate support unit 103 disposed therein. The second container 102 is fixed to the left side of the first container 101 in the figure. The substrate support unit 103 is fixed to the bottom surface of the first container 101. The second container 102 has a metal mounting unit 14 on its bottom surface. The second container 102 is equipped with an oxidizing gas inlet pipe 105 on its left side and a metal oxide gas outlet pipe 106 on its right side in the figure. The oxidizing gas inlet pipe 105 allows for continuous introduction (supply) of an oxidizing gas into the second container 102. The oxidizing gas introduced from the oxidizing gas introduction pipe 105 corresponds to the oxidizing agent that reacts with the metal in the metal oxide gas generation step of the metal oxide crystal manufacturing method of the present invention. In the figure, the first container 101 is equipped with gas introduction pipes 107a and 107b on the left side and an exhaust pipe 108 on the right side. An oxygen-containing gas can be continuously introduced (supplied) into the first container 101 from at least one of the gas introduction pipes 107a and 107b. Furthermore, first heating mechanisms 109a and 109b and second heating mechanisms 200a and 200b are disposed outside the first container 101. However, the manufacturing apparatus used in the manufacturing method of the present invention is not limited to this example. For example, in this example, only one second container 102 is disposed inside the first container 101, but multiple second containers 102 may be disposed inside the first container 101. Furthermore, in this example, there is one oxidizing gas introduction pipe 105, but there may be a plurality of oxidizing gas introduction pipes 105. Note that although the manufacturing apparatus 100 in Fig. 1 is described as an apparatus used in the manufacturing method (A) of metal oxide crystals, it can also be used in the manufacturing method (B) of metal oxide crystals, as will be described later.

[0087] In the manufacturing apparatus 100 of Fig. 1, the first vessel 101 corresponds to the "reaction vessel" in the metal oxide crystal manufacturing apparatus of the present invention. The second vessel 102 and the metal oxide gas outlet pipe 106 correspond to the "metal oxide gas supply mechanism" in the metal oxide crystal manufacturing apparatus of the present invention. As will be described later, a metal oxide gas can be generated in the second vessel 102, and the metal oxide gas can be continuously supplied into the first vessel 101 via the metal oxide gas outlet pipe 106.

[0088] The shape of the first container is not particularly limited. Examples of the shape of the first container include a cylindrical shape, a square prism shape, a triangular prism shape, and a combination thereof. Examples of materials for forming the first container include quartz, alumina, aluminum titanate, mullite, tungsten, and molybdenum. The first container may be homemade or purchased commercially. An example of a commercially available first container is the "Quartz Reaction Tube" manufactured by Phoenix Techno Co., Ltd.

[0089] The shape of the second container is not particularly limited. The shape of the second container can be, for example, the same as the shape of the first container. Examples of materials for forming the second container include quartz, tungsten, stainless steel, molybdenum, aluminum titanate, mullite, and alumina. The second container may be homemade or purchased as a commercially available product. An example of a commercially available second container is "SUS316BA Tube" manufactured by MEC Technica Co., Ltd.

[0090] The first heating mechanism and the second heating mechanism can be conventionally known heating mechanisms. Examples of the heating mechanism include a ceramic heater, a high-frequency heating device, a resistance heater, and a light-collecting heater. One type of heating mechanism may be used alone, or two or more types may be used in combination. It is preferable that the first heating mechanism and the second heating mechanism are controlled independently.

[0091] FIG. 4 shows another example of the configuration of a manufacturing apparatus used in the metal oxide crystal manufacturing method (A). As shown in the figure, this manufacturing apparatus 300 is the same as the manufacturing apparatus 100 of FIG. 1 except that it has a second container 301 instead of the second container 102 and further has a metal introduction pipe 302. As shown in the figure, the second container 301 is equipped with an oxidizing gas introduction pipe 105 at the upper part of the left side surface, a metal introduction pipe 302 at the lower part of the left side surface, and a metal oxide gas outlet pipe 106 at the right side surface. The oxidizing gas introduction pipe 105 allows for continuous introduction (supply) of an oxidizing gas into the second container 301. The metal introduction pipe 302 allows for continuous introduction (supply) of a metal into the second container 301. Furthermore, the second container 301 does not have a metal mounting portion 104, but instead has a large depth (vertical width) of the second container 301 itself, allowing metal to accumulate in the lower part of the second container 301. In the production apparatus of FIG. 4 , first vessel 101 corresponds to the "reaction vessel" in the metal oxide crystal production apparatus of the present invention. Metal introduction pipe 302 can be referred to as the "metal supply mechanism." Oxidizing gas introduction pipe 105 can be referred to as the "oxidizing agent supply mechanism." Gas introduction pipes 107a and 107b can be referred to as the "oxygen-containing gas supply mechanism." In the present invention, the metal oxide crystal production apparatus may be, for example, a metal supply mechanism capable of continuously supplying the metal into the reaction vessel, an oxidizing agent supply mechanism capable of continuously supplying the oxidizing agent into the reaction vessel, and an oxygen-containing gas supply mechanism capable of continuously supplying the oxygen-containing gas into the reaction vessel, as in the apparatus of FIG. 4 , and the metal, the oxidizing agent, and the oxygen-containing gas are reacted in the reaction vessel to produce the metal oxide crystal.

[0092] 6 shows yet another example of the configuration of a manufacturing apparatus used in the metal oxide crystal manufacturing method (A). As shown in the figure, this manufacturing apparatus 500 has a carrier gas introduction pipe 107c and an oxygen-containing gas introduction pipe 107d instead of the gas introduction pipes 107a and 107b. The right side of the second container 102 does not have the metal oxide gas outlet pipe 106, but instead is entirely open, allowing the metal oxide gas to be discharged. The carrier gas introduction pipe 107c surrounds the outer periphery of the second container 102 from its left end to its right end, and the oxygen-containing gas introduction pipe 107d surrounds the outer periphery of the carrier gas introduction pipe 107c from its left end to its right end. A carrier gas can be introduced through the carrier gas introduction pipe 107c, and an oxygen-containing gas can be introduced through the oxygen-containing gas introduction pipe 107d. The substrate support part 103 is attached near the outlet of the exhaust pipe 108, and is disposed so that the surface of the substrate 202 attached to the substrate support part 103 is located in front of the right side surface of the second container 102. Other than these, the manufacturing apparatus 500 in FIG. 6 is similar to the manufacturing apparatus 100 in FIG. 1.

[0093] Furthermore, the manufacturing apparatus used in the manufacturing method of the metal oxide crystal is not limited to the configurations shown in Figures 1, 4, and 6. For example, heating mechanisms 109a, 109b, 200a, and 200b, and substrate support unit 103 may be omitted, but from the standpoint of reactivity and operability, it is preferable to include these components. Furthermore, the manufacturing apparatus used in the manufacturing method of the present invention may include other components in addition to the above-mentioned components. Examples of other components include a mechanism for controlling the temperature of the first heating mechanism and the second heating mechanism, and a mechanism for adjusting the pressure and introduction amount of the gas used in each step.

[0094] The production apparatus used in the method (A) for producing metal oxide crystals can be produced, for example, by assembling the above-mentioned components and, if necessary, other components, by a conventionally known method.

[0095] [1-3. Manufacturing steps and reaction conditions in the manufacturing method (A) of metal oxide crystals] Next, each step, reaction conditions, raw materials used, etc. in the manufacturing method (A) of metal oxide crystals will be described. However, the present invention is not limited thereto. Below, an embodiment of carrying out the manufacturing method (A) of metal oxide crystals using the manufacturing apparatus of FIG. 1, or alternatively, using the manufacturing apparatus of FIG. 4 or 6, will be described. The manufacturing apparatus of FIG. 1, 4, or 6 can itself be said to be a "metal oxide crystal generation mechanism" for generating the metal oxide crystals of the present invention. Furthermore, as will be described later, since the metal oxide crystals are generated on the substrate 202 placed on the substrate support 103, the substrate support 103 can also be said to be a "metal oxide crystal generation mechanism."

[0096] First, as shown in FIG. 2 (or FIG. 5 or 7), the substrate 202 is placed on the substrate support 103 in advance. The substrate 202 is not particularly limited, but may be, for example, as described above, a sapphire substrate, a seed crystal formed from a metal oxide (e.g., a β-gallium oxide single crystal), or a base layer (substrate body) formed from sapphire or the like on which a metal oxide seed crystal is formed. The substrate 202 can be appropriately selected depending on the form of the metal oxide crystal to be grown thereon. As described above, the material of the substrate 202 body or the seed crystal formed thereon may be the same as or different from the metal oxide crystal to be grown thereon, but it is preferable that they are the same.

[0097] Next, as shown in FIG. 2 (or FIG. 7), the metal 110 is placed on the metal placement portion 104. Or, when using the manufacturing apparatus of FIG. 4, as shown in FIG. 5, the metal 402 is introduced from the metal introduction pipe 302 into the interior of the second container 301, and stored at the lower part inside the second container 301 as the metal 110. From the metal introduction pipe 302, the metal 402 can be continuously introduced into the interior of the second container 301. For example, the amount by which the metal 402 is consumed and decreased due to the reaction can be introduced from the metal introduction pipe 302 for replenishment. The metal is not particularly limited, and examples include aluminum (Al), gallium (Ga), indium (In), thallium (Tl), etc., and it may be used alone or in combination of two or more types. For example, as the metal, at least one selected from the group consisting of aluminum (Al), gallium (Ga), and indium (In) may be used. In this case, the composition of the produced metal oxide crystal is, for example, Al s Ga t In {1-(s+t)} O 1.5 (where 0 ≦ s ≦ 1, 0 ≦ t ≦ 1, s + t ≦ 1). Also, for the metal 110, for example, a dopant material or the like may coexist and react. The dopant is not particularly limited, and examples include silicon.

[0098] Also, as ternary or higher metal oxide crystals produced using two or more types of group III element metals, for example, Ga x In 1-x O 1.5 (0 < x < 1) crystals can be mentioned. Note that in order to produce ternary or higher nitride crystals, it is preferable to generate reduction product gases of at least two different group III element oxides. In this case, it is preferable to use a manufacturing apparatus provided with two or more of the second containers.

[0099] When a Group III element metal is used as the metal, the Group III element metal has a relatively low melting point and therefore easily becomes liquid when heated. Once liquid, it can be easily supplied continuously to the inside of the reaction vessel (inside the second vessel 301 in FIG. 5). Among the Group III element metals, gallium (Ga) is particularly preferable. Gallium nitride (GaN) produced from gallium is extremely useful as a material for semiconductor devices, and gallium has a low melting point of approximately 30°C and becomes liquid even at room temperature, making it particularly easy to supply continuously to the reaction vessel. Note that when only gallium is used as the Group III element metal, the metal oxide crystal produced is gallium oxide (III) (Ga2O3).

[0100] Next, metal 110 is heated using first heating mechanisms 109a and 109b, and substrate 202 is heated using first heating mechanisms 200a and 200b. In this state, oxidizing gas 201a (or 401a) is introduced through oxidizing gas introduction pipe 105, and gases 203a and 203b are introduced through gas introduction pipes 107a and 107b. Gases 203a and 203b contain an oxygen-containing gas. Gases 203a and 203b may further contain a carrier gas. For example, both gases 203a and 203b may each be a mixed gas of an oxygen-containing gas and a carrier gas, or one of gases 203a and 203b may be an oxygen-containing gas and the other a carrier gas. When using the apparatus of FIG. 6 (FIG. 7), oxygen-containing gas 203f is introduced from oxygen-containing gas introduction pipe 107d instead of gas introduction pipes 107a and 107b, and carrier gas 203e is introduced from carrier gas introduction pipe 107c, and carrier gas 203g is similarly introduced from outside oxygen-containing gas introduction pipe 107d. Carrier gases 203e and 203g are, for example, nitrogen gas (N), as will be described in detail later. Oxidizing gas 201a (or 401a) corresponds to the "oxidizing agent" in the method for producing metal oxide crystals of the present invention and is not particularly limited, but is preferably at least one selected from the group consisting of HO gas, O gas, CO gas, and CO gas, as described above, and is particularly preferably HO gas. The oxidizing gas 201a (or 401a) introduced (supplied) into the second container 102 (or 301) comes into contact with the surface of the metal 110 (oxidizing gas 201b or 401b). This causes the metal 110 to react with the oxidizing gas 201b (or 401b) to generate a metal oxide gas 111a (metal oxide gas generation step). The flow rate of the oxidizing gas is, for example, 0.0001 to 50 Pa m 3 / s, preferably 0.001 to 10 Pa m 3 / s, and more preferably 0.005 to 1 Pa m 3 / s range.

[0101] In the metal oxide gas generating step of the present invention, the metal is preferably reacted with the oxidizing gas in a heated state, from the viewpoint of promoting the generation of the metal oxide gas. In this case, the temperature of the metal is not particularly limited, but is preferably in the range of 650 to 1500°C, more preferably in the range of 900 to 1300°C, and even more preferably in the range of 1000 to 1200°C.

[0102] In the metal oxide gas generating step, it is particularly preferable that the metal is gallium, the oxidizing gas is HO gas, and the metal oxide gas is Ga O. In this case, the reaction formula can be expressed by, for example, the following formula (I), but is not limited thereto. 2Ga+H2O → Ga2O+H2(I)

[0103] In the method for producing metal oxide crystals of the present invention, the metal oxide gas generation step may be carried out in a mixed gas atmosphere of the oxidizing gas and an inert gas in order to control the partial pressure of the oxidizing gas. The proportions of the oxidizing gas and the inert gas relative to the total amount of the mixed gas are not particularly limited. However, it is preferable that the proportion of the oxidizing gas is 0.001% by volume or more but less than 100% by volume, and the proportion of the inert gas is greater than 0% by volume but less than 99.999% by volume, more preferably, the proportion of the oxidizing gas is 0.01% by volume or more but less than 80% by volume, and the proportion of the inert gas is 20% by volume or more but less than 99.99% by volume, and even more preferably, the proportion of the oxidizing gas is 0.1% by volume or more but less than 60% by volume, and the proportion of the inert gas is 40% by volume or more but less than 99.9% by volume. In the production method of the present invention, examples of the inert gas include nitrogen gas, helium gas, argon gas, and krypton gas. Among these, nitrogen gas is particularly preferred. Examples of methods for creating the mixed gas atmosphere include a method in which an inert gas introduction pipe (not shown) is provided in the second container in addition to the oxidizing gas introduction pipe, and an inert gas is introduced therethrough; or a method in which a gas is prepared in advance by mixing the hydrogen gas and the inert gas at a predetermined ratio, and the gas is introduced through the oxidizing gas introduction pipe. When the inert gas introduction pipe is provided and the inert gas is introduced, the flow rate of the inert gas can be appropriately set depending on the flow rate of the oxidizing gas, etc. The flow rate of the inert gas is, for example, 0.1 to 150 Pa m 3 / s, preferably 0.2 to 30 Pa m 3 / s, and more preferably 0.3 to 10 Pa m 3 / s range.

[0104] The generated metal oxide gas 111a is discharged (metal oxide gas 111b) to the outside of the second container 102 (or 301) through the metal oxide gas discharge pipe 106. Note that although the metal oxide gas 111b is illustrated as GaO in FIG. 5, this is not limiting. A first carrier gas may be introduced to discharge the metal oxide gas 111b to the outside of the second container 102 (or 301) through the metal oxide gas discharge pipe 106. For example, the same carrier gas as the inert gas may be used as the first carrier gas. The flow rate (partial pressure) of the first carrier gas may be the same as the flow rate (partial pressure) of the inert gas. Furthermore, when the inert gas is introduced, the inert gas may be used as the first carrier gas.

[0105] The generation of the metal oxide gas 111a (111b) may be carried out, for example, under pressurized conditions, or under reduced pressure conditions, or under conditions where neither pressurization nor depressurization is performed. The pressure under the pressurized conditions is not particularly limited, but is preferably 1.0×10 5 ~1.50×10 7 Pa, and more preferably 1.05 × 10 5 ~5.00×10 6 Pa, and more preferably 1.10 × 10 5 ~9.90×10 5 The pressure is in the range of 1×10 Pa. Examples of the pressurizing method include a method of pressurizing with the oxidizing gas, the first carrier gas, etc. The pressure reduction conditions are not particularly limited, but are preferably 1×10 1 ~1×10 5 It is preferably in the range of 1×10 Pa, and more preferably 1×10 2 ~9×10 4 Pa, and more preferably 5 × 10 3 ~7×10 4 The range is Pa.

[0106] Metal oxide gas (e.g., GaO gas) 111b delivered to the outside of second container 102 (or 301) through metal oxide gas delivery pipe 106 reacts with oxygen-containing gas 203c introduced into first container 101, producing metal oxide (e.g., GaO) crystals 204 on substrate 202 (metal oxide crystal production step). In this case, when the metal oxide gas is GaO gas and the oxygen-containing gas is water vapor (HO), the reaction formula can be expressed by, for example, formula (II) below, but is not limited thereto. Note that excess gas after the reaction can be discharged as exhaust gas 203d from exhaust pipe 108. Ga2O+2H2O→Ga2O3+2H2(II)

[0107] In the production method of the present invention, the oxygen-containing gas is not particularly limited, but is, for example, as described above.

[0108] In the metal oxide crystal growth step, the temperature of the substrate (i.e., the crystal growth temperature) is not particularly limited, but from the viewpoint of ensuring a high crystal growth rate and improving crystallinity, it is preferably in the range of 700 to 1500°C, more preferably 1000 to 1400°C, and even more preferably 1100 to 1350°C. Furthermore, as described above, the method for producing metal oxide crystals includes an initial crystal growth step and a later crystal growth step, and the crystal growth temperature in the later crystal growth step is preferably higher than the crystal growth temperature in the initial crystal growth step. In this case, the crystal growth temperature in the initial crystal growth step is, for example, 700 to 1400°C, more preferably 900 to 1300°C, and even more preferably 1000 to 1200°C. Furthermore, the crystal growth temperature in the later crystal growth step is, for example, 1000 to 1500°C, more preferably 1100 to 1400°C, and even more preferably 1200 to 1350°C. It is more preferable that the crystal growth temperature in the initial crystal growth step is equal to or higher than the crystal growth temperature in the substrate manufacturing step.

[0109] The metal oxide crystallization step may be carried out under pressurized conditions, reduced pressure conditions, or under conditions where neither pressurization nor reduced pressure is applied. 5 ~1.50×10 7 Pa, and more preferably 1.05 × 10 5 ~5.00×10 6 Pa, and more preferably 1.10 × 10 5 ~9.90×10 5 The pressure reduction conditions are not particularly limited, but are in the range of 1×10 1 ~1×10 5 It is preferably in the range of 1×10 Pa, and more preferably 1×10 2 ~9×10 4 Pa, and more preferably 5 × 10 3 ~7×10 4 The range is Pa.

[0110] In the metal oxide crystallization step, the supply amount of the metal oxide gas (for example, GaO gas, reference numeral 111b in FIGS. 24 and 7) is, for example, 5×10 -5 ~5×10 1 mol / hr, preferably in the range of 1×10 -4 The range is preferably 2×10 to 5 mol / hour. -4 ~5×10 -1 The supply amount of the metal oxide gas can be adjusted by, for example, adjusting the flow rate of the first carrier gas in generating the metal oxide gas.

[0111] The flow rate of the oxygen-containing gas can be appropriately set depending on conditions such as the temperature of the substrate, etc. The flow rate of the oxygen-containing gas is, for example, 0.1 to 150 Pa·m 3 / s, preferably 0.3 to 60 Pa m 3 / s, and more preferably 0.5 to 30 Pa m 3 / s range.

[0112] A second carrier gas may be introduced to transport the introduced oxygen-element-containing gas to a crystal growth region (near the substrate support 103 inside the first vessel 101 in FIGS. 1 to 7). The second carrier gas may be introduced through a carrier gas introduction pipe (107c in FIGS. 6 and 7) provided separately from the oxygen-element-containing gas introduction pipe, as shown in FIGS. 6 and 7, or may be mixed with the oxygen-element-containing gas and introduced through the oxygen-element-containing gas introduction pipe. The second carrier gas (carrier gases 203e and 203g in FIG. 7) may be the same as the first carrier gas. The position of the carrier gas introduction pipe is not particularly limited. For example, the second carrier gas may be introduced from the periphery of the outlet (outlet for the Group III element-containing gas) of the second vessel 102, as shown in the carrier gas introduction pipe 107c in FIGS. 6 and 7. By doing so, for example, it is possible to suppress or prevent the generated group III element nitride (e.g., GaN) from precipitating at the outlet (outlet for discharging the group III element-containing gas) of the second container 102, causing the outlet of the second container 102 to become clogged.

[0113] When the carrier gas introduction pipe is provided to introduce the second carrier gas, the flow rate of the second carrier gas can be appropriately set depending on the flow rate of the oxygen-containing gas, etc. The flow rate of the second carrier gas is, for example, 0.1 to 150 Pa m 3 / s, preferably 0.8 to 60 Pa m 3 / s, and more preferably 1.5 to 30 Pa m 3 / s range.

[0114] The mixing ratio A:B (volume ratio) of the oxygen-containing gas (A) to the second carrier gas (B) is not particularly limited, but is preferably in the range of 2 to 80:98 to 20, more preferably in the range of 5 to 60:95 to 40, and even more preferably in the range of 10 to 40:90 to 60. The mixing ratio A:B (volume ratio) can be set, for example, by a method of preparing a predetermined mixing ratio in advance, or by a method of adjusting the flow rate (partial pressure) of the oxygen-containing gas and the flow rate (partial pressure) of the second carrier gas.

[0115] The metal oxide crystal (e.g., GaO crystal) generating step is preferably carried out under pressurized conditions. The pressurizing conditions are as described above. Examples of pressurizing methods include pressurizing with the nitrogen-containing gas, the second carrier gas, etc.

[0116] The metal oxide crystal growth process may be performed in an atmosphere of a gas containing a dopant. In this way, dopant-containing GaN crystals can be generated. Examples of the dopant include Si, S, Se, Te, Ge, Fe, Mg, and Zn. One type of dopant may be used alone, or two or more types may be used in combination. Examples of the dopant-containing gas include monosilane (SiH), disilane (SiH), triethylsilane (SiH(CH)), tetraethylsilane (Si(CH)), HS, HSe, HTe, GeH, GeO, SiO, MgO, and ZnO. One type of dopant-containing gas may be used alone, or two or more types may be used in combination.

[0117] The dopant-containing gas may be introduced, for example, through a dopant-containing gas introduction pipe (not shown) provided separately from the oxygen-element-containing gas introduction pipe, or may be mixed with the oxygen-element-containing gas and introduced through the oxygen-element-containing gas introduction pipe. When the second carrier gas is introduced, the dopant-containing gas may be introduced after being mixed with the second carrier gas.

[0118] The concentration of the dopant in the gas containing the dopant is not particularly limited, but is, for example, in the range of 0.001 to 100,000 ppm, preferably in the range of 0.01 to 1,000 ppm, and more preferably in the range of 0.1 to 10 ppm.

[0119] The rate of production of the metal oxide crystals (e.g., Ga2O3 crystals) is not particularly limited. As described above, the rate may be, for example, 0.001 μm / hour or more, 0.01 μm / hour or more, 0.1 μm / hour or more, 0.5 μm / hour or more, or 1 μm / hour or more, or may be, for example, 10,000 μm / hour or less, 1,000 μm / hour or less, 500 μm / hour or less, 100 μm / hour or less, or 50 μm / hour or less, or may be, for example, 0.001 to 10,000 μm / hour, 0.01 to 1,000 μm / hour, 0.1 to 500 μm / hour, 1 to 500 μm / hour, or 1 to 100 μm / hour.

[0120] Although the method for producing metal oxide crystals (A) can be performed as described above, the method for producing metal oxide crystals (A) is not limited thereto. For example, as described above, it is preferable to carry out the reaction in the method for producing metal oxide crystals (A) by further adding a reducing gas to the reaction system. Also, as described above, it is more preferable to carry out the reaction by mixing the reducing gas with at least one of the oxidizing gas and the oxygen-containing gas. That is, in FIG. 24 or 7, the reducing gas may be mixed with at least one of the oxygen-containing gas 203a, 203b (or 203f) and the oxidizing gas 201a (or 401a). In the production method of the present invention, it is more preferable to mix the reducing gas with the oxidizing gas. This, for example, can suppress the generation of by-products in the reaction between the metal and the oxidizing gas in the metal oxide gas generation step, thereby further improving the reaction efficiency (the efficiency of generating the metal oxide gas). As a specific example, in the reaction between gallium (the metal) and H2O gas (the oxidizing gas), by mixing H2 gas (the reducing gas) with H2O gas, it is possible to suppress the generation of Ga2O3, which is a by-product, and further increase the generation efficiency of Ga2O gas (the metal oxide gas).

[0121] Furthermore, in the method (A) for producing metal oxide crystals, by allowing the reducing gas to coexist in the reaction system, it is possible to produce, for example, larger-sized metal oxide crystals. For example, metal oxide crystals are grown on a seed crystal and then sliced ​​to produce plate-shaped semiconductor wafers formed from the metal oxide crystals. However, as metal oxide crystals grow, they tend to become tapered into a pyramidal shape, and only small semiconductor wafers are obtained at the tips of the pyramidal crystals. However, in the production method of the present invention, when the reducing gas is coexisted in the reaction system, for unknown reasons, it is sometimes easier to obtain columnar (i.e., non-tapered) crystals rather than pyramidal crystals. Unlike pyramidal crystals, such columnar metal oxide crystals can be sliced ​​to produce semiconductor wafers (metal oxide crystals) with large diameters in most parts.

[0122] In the method (A) for producing metal oxide crystals, the reducing gas may be, for example, hydrogen gas; carbon monoxide gas; hydrocarbon gases such as methane gas and ethane gas; hydrogen sulfide gas; sulfur dioxide gas; or the like, and may be used alone or in combination. Among these, hydrogen gas is particularly preferred. The hydrogen gas is preferably highly pure. The purity of the hydrogen gas is particularly preferably 99.9999% or more.

[0123] When the metal oxide gas generating step is carried out in the coexistence of the reducing gas, the reaction temperature is not particularly limited, but from the viewpoint of suppressing the generation of by-products, it is preferably 900° C. or higher, more preferably 1000° C. or higher, and even more preferably 1100° C. or higher. The upper limit of the reaction temperature is not particularly limited, but is, for example, 1500° C. or lower.

[0124] When the reducing gas is used in the method (A) for producing metal oxide crystals, the amount of the reducing gas used is not particularly limited, but is, for example, 1 to 99% by volume, preferably 3 to 80% by volume, and more preferably 5 to 70% by volume, based on the total volume of the oxidizing gas and the reducing gas. The flow rate of the reducing gas can be appropriately set depending on the flow rate of the oxidizing gas, etc. The flow rate of the reducing gas is, for example, 0.01 to 100 Pa m 3 / s, preferably 0.05 to 50 Pa m 3 / s, and more preferably 0.1 to 10 Pa m 3 / s. As described above, the generation of the metal oxide gas 111a (111b) is preferably carried out under pressurized conditions, and the pressure is, for example, as described above. As a pressurizing method, for example, pressurization may be performed using the oxidizing gas and the reducing gas.

[0125] The method (A) for producing metal oxide crystals of the present invention is a vapor phase growth method, but it can also be carried out without using a halide as a raw material. Unlike conventional methods (such as the halogenated vapor phase growth method described in JP-A-52-23600), not using a halide allows metal oxide crystals to be produced without producing halogen-containing by-products. This makes it possible to prevent, for example, environmental pollution and equipment corrosion caused by halogen-containing by-products.

[0126] [1-4. Manufacturing process and reaction conditions in the manufacturing method (B) of metal oxide crystals] Next, the manufacturing steps and reaction conditions in the manufacturing method (B) of metal oxide crystals will be explained using examples.

[0127] The metal oxide crystal manufacturing method (B) can be carried out using, for example, the manufacturing apparatus 100 shown in Figure 1 or 6. Specifically, the metal mounting section 104 is used as the metal oxide solid raw material mounting section 104. The oxidizing gas introduction pipe 105 is used as the reducing gas introduction pipe 105.

[0128] Hereinafter, the method (B) for producing metal oxide crystals will be described in detail with reference to FIG. 2, using an example in which the production apparatus shown in FIG. 1 or 6 is used, the metal oxide solid raw material is Ga2O3, the reductant gas is Ga2O gas, the reducing gas is hydrogen gas, the oxygen-containing gas is HO gas, and the metal oxide crystals produced are Ga2O3 crystals. However, the method (B) for producing metal oxide crystals is not limited to the following example. As described above, the method (B) for producing metal oxide crystals has a metal oxide gas production step and a metal oxide crystal production step.

[0129] First, GaO is placed on the metal oxide solid source mounting portion 104, and a substrate 202 is placed on the substrate support portion 103. Next, the GaO is heated using the first heating mechanisms 109a and 109b, and the substrate 202 is heated using the first heating mechanisms 200a and 200b. In this state, hydrogen gas 201a is introduced through the reducing gas inlet pipe 105, and H2O gases 203a and 203b are introduced through the gas inlet pipes 107a and 107b. The introduced hydrogen gas 201b reacts with the GaO to generate GaO gas (see formula (III) below). The generated GaO gas 111a passes through the reduced product gas outlet pipe 106 and is discharged to the outside of the second container 102 as GaO gas 111b. The extracted Ga2O gas 111b reacts with the introduced H2O gas 203c, and Ga2O3 crystals 204 are produced on the substrate 202 (represented by the following formula (IV)). Ga2O3+2H2→Ga2O+2H2O(III) Ga2O+2H2O→Ga2O3+2H2(IV)

[0130] As can be seen from the formulas (III) and (IV), the only by-products produced in the metal oxide crystal manufacturing method (B) are water and hydrogen. In other words, no solid by-products are generated. The water and hydrogen can be discharged in gaseous or liquid form, for example, from the exhaust pipe 108. As a result, for example, Ga2O3 crystals can be produced over a long period of time, and large, thick Ga2O3 crystals can be obtained. Furthermore, for example, there is no need to introduce a filter or the like to remove by-products, which is advantageous in terms of cost. However, the metal oxide crystal manufacturing method (B) is not limited to the above description.

[0131] The GaO used as the metal oxide solid raw material is preferably in a powder or granular form, since the GaO can have a large surface area and thus can promote the generation of GaO gas.

[0132] To produce ternary or higher-component metal oxide crystals, it is preferable to generate at least two different metal oxide gases. In this case, it is preferable to use a production apparatus equipped with two or more second vessels.

[0133] The hydrogen gas preferably has a high purity. The purity of the hydrogen gas is preferably 99.9999% or more. The flow rate (partial pressure) of the hydrogen gas can be appropriately set depending on conditions such as the temperature of the Ga2O3. The partial pressure of the hydrogen gas is, for example, in the range of 0.2 to 2000 kPa, preferably in the range of 0.5 to 1000 kPa, and more preferably in the range of 1.5 to 500 kPa.

[0134] As described above, from the viewpoint of controlling the partial pressure of hydrogen gas, it is preferable to generate the GaO gas in a mixed gas atmosphere of hydrogen gas and an inert gas. Examples of methods for creating the mixed gas atmosphere include providing an inert gas inlet pipe (not shown) in addition to the reducing gas inlet pipe in the second container and introducing the inert gas therethrough, or preparing a gas mixture of the hydrogen gas and the inert gas at a predetermined ratio and introducing the gas through the reducing gas inlet pipe. When providing the inert gas inlet pipe and introducing the inert gas, the flow rate (partial pressure) of the inert gas can be appropriately set depending on the flow rate of the hydrogen gas, etc. The partial pressure of the inert gas is, for example, in the range of 0.2 to 2000 kPa, preferably in the range of 2.0 to 1000 kPa, and more preferably in the range of 5.0 to 500 kPa.

[0135] The ratio of the hydrogen gas and the ratio of the inert gas to the mixed gas are as described above. The ratio of the hydrogen gas and the ratio of the inert gas to the mixed gas can be set, for example, by preparing the mixed gas in advance at a predetermined ratio or by adjusting the flow rate (partial pressure) of the hydrogen gas and the flow rate (partial pressure) of the inert gas.

[0136] A first carrier gas may be introduced to discharge the GaO gas to the outside of the second container through the reduced product gas discharge pipe. The first carrier gas may be, for example, the same as the inert gas. The flow rate (partial pressure) of the first carrier gas may be the same as the flow rate (partial pressure) of the inert gas. When the inert gas is introduced, the inert gas may be used as the first carrier gas.

[0137] The GaO gas is preferably generated under pressurized conditions. The pressurized conditions are not particularly limited, but are preferably 1.01×10 5 ~1.50×10 7 Pa, and more preferably 1.05 × 10 5 ~5.00×10 6in the range of Pa, and more preferably, 1.10×10 5 ~9.90×10 5 Pa. Examples of the pressurization method include pressurization with the hydrogen gas, the first carrier gas, etc.

[0138] As described above, when reducing gases of at least two different group III element oxides are generated, ternary or higher nitrides crystals, for example, are formed on the substrate. Examples of the ternary or higher nitrides crystals include Ga x In 1-x O 1.5 (0 < x < 1) crystals.

[0139] The supply amount of the Ga2O gas is, for example, in the range of 5×10 -5 ~1×10 -1 mol / hour, preferably in the range of 1×10 -4 ~1×10 -2 mol / hour, and more preferably in the range of 2×10 -4 ~5×10 -4 mol / hour. The supply amount of the Ga2O gas can be adjusted, for example, by adjusting the flow rate (partial pressure) of the first carrier gas in the production of the Ga2O gas.

[0140] The flow rate (partial pressure) of the H2O gas can be appropriately set according to conditions such as the temperature of the substrate. The partial pressure of the H2O gas is, for example, in the range of 0.2~3000 kPa, preferably in the range of 0.5~2000 kPa, and more preferably in the range of 1.5~1000 kPa.

[0141] In order to transfer the introduced H2O gas to the crystal growth region, a second carrier gas may be introduced. The second carrier gas may be introduced, for example, by providing a carrier gas introduction pipe (not shown) separately from the nitrogen-containing gas introduction pipe, or may be introduced from the nitrogen-containing gas introduction pipe after being mixed with the H2O gas. As the second carrier gas, for example, the same gas as the first carrier gas can be used.

[0142] When the carrier gas introduction pipe is provided to introduce the second carrier gas, the flow rate (partial pressure) of the second carrier gas can be appropriately set depending on the flow rate (partial pressure) of the nitrogen-containing gas, etc. The partial pressure of the second carrier gas is, for example, in the range of 0.2 to 3000 kPa, preferably in the range of 0.5 to 2000 kPa, and more preferably in the range of 1.5 to 1000 kPa.

[0143] The mixing ratio A:B (volume ratio) of the HO gas (A) and the second carrier gas (B) is not particularly limited, but is preferably in the range of 3 to 80:97 to 20, more preferably in the range of 8 to 60:92 to 40, and even more preferably in the range of 10 to 40:90 to 60. The mixing ratio A:B (volume ratio) can be set, for example, by a method of preparing a predetermined mixing ratio in advance, or by a method of adjusting the flow rate (partial pressure) of the HO gas and the flow rate (partial pressure) of the second carrier gas.

[0144] The GaO crystals are preferably produced under pressurized conditions. The pressurization conditions are as described above. Examples of pressurization methods include pressurization using the HO gas, the second carrier gas, or the like.

[0145] The Ga2O3 crystal may be produced in an atmosphere of a gas containing a dopant. In this way, a Ga2O3 crystal containing a dopant can be produced. Examples of the dopant include Si, S, Se, Te, Ge, Fe, Mg, and Zn. One type of dopant may be used alone, or two or more types may be used in combination. Examples of the gas containing the dopant include monosilane (SiH4), disilane (Si2H6), triethylsilane (SiH(C2H5)3), tetraethylsilane (Si(C2H5)4), H2S, H2Se, H2Te, GeH4, Ge2O, SiO, MgO, and ZnO. One type of dopant-containing gas may be used alone, or two or more types may be used in combination.

[0146] The dopant-containing gas may be introduced, for example, through a dopant-containing gas introduction pipe (not shown) provided separately from the nitrogen-containing gas introduction pipe, or may be mixed with the HO gas and introduced through the nitrogen-containing gas introduction pipe. When the second carrier gas is introduced, the dopant-containing gas may be introduced after being mixed with the second carrier gas.

[0147] The concentration of the dopant in the gas containing the dopant is not particularly limited, but is, for example, in the range of 0.001 to 100,000 ppm, preferably in the range of 0.01 to 1,000 ppm, and more preferably in the range of 0.1 to 10 ppm.

[0148] The growth rate of the GaO crystals is not particularly limited. As described above, the growth rate may be, for example, 0.001 μm / hour or more, 0.01 μm / hour or more, 0.1 μm / hour or more, 0.5 μm / hour or more, or 1 μm / hour or more, and may be, for example, 10,000 μm / hour or less, 1,000 μm / hour or less, 500 μm / hour or less, 100 μm / hour or less, or 50 μm / hour or less, and may be, for example, 0.001 to 10,000 μm / hour, 0.01 to 1,000 μm / hour, 0.1 to 500 μm / hour, 1 to 500 μm / hour, or 1 to 100 μm / hour.

[0149] The manufacturing method of the present invention can also produce metal oxide crystals when a metal oxide other than Ga2O3 is used, in the same manner as when Ga2O3 crystals are produced using Ga2O3.

[0150] Examples of the metal oxides other than Ga2O3 include oxides of Group III elements, such as In2O3 when the Group III element is In, Al2O3 when the Group III element is Al, B2O3 when the Group III element is B, and Tl2O3 when the Group III element is Tl. The metal oxides other than Ga2O3 may be used singly or in combination of two or more.

[0151] [1-5. Metal oxide crystals, etc. produced by the metal oxide crystal production method (A) or (B)] The size of the metal oxide crystals produced by the method for producing metal oxide crystals is not particularly limited, but for example, the major axis is preferably 15 cm (about 6 inches) or more, more preferably 20 cm (about 8 inches) or more, and particularly preferably 25 cm (about 10 inches) or more. The height of the metal oxide crystals is also not particularly limited, but may be, for example, 1 cm or more, preferably 5 cm or more, and more preferably 10 cm or more. However, the production method of the present invention is not limited to the production of such large-sized metal oxide crystals, and can also be used, for example, to produce metal oxide crystals of the same size as conventional crystals with higher quality. Furthermore, for example, the height (thickness) of the metal oxide crystals is not particularly limited, as described above.

[0152] In the metal oxide crystal, the dislocation density is not particularly limited, but is preferably 1.0×10 7 cm -2 or less, more preferably 1.0 × 10 4 cm -2 or less, more preferably 1.0 × 10 3 cm -2 or less, more preferably 1.0 × 10 2 cm -2 or less. The dislocation density is ideally 0, but is usually not 0, and therefore, for example, it is particularly preferably a value exceeding 0 and not exceeding the measurement limit of the measuring instrument. The dislocation density value may be, for example, an average value for the entire crystal, but it is more preferable if the maximum value in the crystal is not greater than the above value. Furthermore, in the metal oxide crystal of the present invention, the half widths of the symmetric reflection component (002) and the asymmetric reflection component (102) in the XRC half width are each, for example, 300 seconds or less, preferably 100 seconds or less, more preferably 30 seconds or less, and ideally 0.

[0153] The method for producing a metal oxide crystal of the present invention may further include, for example, a crystal regrowth step in which the produced metal oxide crystal is further grown. Specifically, the crystal regrowth step may involve, for example, cutting the produced metal oxide crystal to expose an arbitrary face (e.g., a c-face, an m-face, an a-face, or other non-polar face), and using that face as a crystal growth face to further grow the metal oxide crystal. This makes it possible to produce a metal oxide crystal that has a large area of ​​the arbitrary face and is thick.

[0154] [2. Metal Oxide Crystals and Semiconductor Devices] The metal oxide crystal of the present invention is a metal oxide crystal produced by the production method of the present invention, or a metal oxide crystal produced by further growing the metal oxide crystal. The metal oxide crystal of the present invention is, for example, large in size and has few defects and high quality. The quality is not particularly limited, but for example, the dislocation density is preferably in the above-mentioned numerical range. The size is also not particularly limited, but for example, is as described above. The use of the metal oxide crystal of the present invention is also not particularly limited, but for example, it can be used in semiconductor devices because it has semiconducting properties. In the present invention, the metal oxide crystal is not particularly limited, but Al x Ga y In 1-x-y O 1.5 (0≦x≦1, 0≦y≦1, x+y≦1), with Ga2O3 being particularly preferred. The metal is, for example, at least one selected from the group consisting of gallium (Ga), indium (In), and aluminum (Al), with Ga being particularly preferred.

[0155] According to the present invention, it is possible to provide metal oxide (e.g., Ga2O3) crystals with a diameter of 6 inches or more, which was not possible with conventional technology. As a result, by using metal oxide instead of Si in semiconductor devices such as power devices and high-frequency devices, where the large diameter of Si (silicon) is the standard, it is possible to further improve performance. As a result, the impact of the present invention on the semiconductor industry is extremely large. The metal oxide crystals of the present invention are not limited to these, and can be used in any semiconductor device such as a solar cell, or for any application other than semiconductor devices.

[0156] The semiconductor device of the present invention is not particularly limited and may be any item that operates using a semiconductor. Examples of items that operate using a semiconductor include semiconductor elements and electrical equipment using the semiconductor elements. Examples of the semiconductor elements include high-frequency devices and power devices such as diodes and transistors, and light-emitting devices such as light-emitting diodes (LEDs) and laser diodes (LDs). Examples of electrical equipment using the semiconductor elements include mobile phone base stations equipped with the high-frequency devices, solar cell control devices and power control devices for electrically driven vehicles equipped with the power devices, and displays, lighting equipment, and optical disk drives equipped with the light-emitting devices. For example, blue-emitting laser diodes (LDs) are used in high-density optical disks and displays, while blue-emitting light-emitting diodes (LEDs) are used in displays and lighting. Ultraviolet LDs are expected to be applied in biotechnology, and ultraviolet LEDs are expected to serve as an alternative ultraviolet source to mercury lamps. Inverters using the III-V group compound of the present invention as a power semiconductor for the inverter can also be used for power generation using solar cells, for example. Furthermore, as mentioned above, the metal oxide crystal of the present invention is not limited to these, and can be applied to any other semiconductor device or a wide range of other technical fields. [Example]

[0157] Next, examples of the present invention will be described, but the present invention is not limited or restricted by the following examples.

[0158] [Example 1] Using the apparatus 500 configured as shown in FIG. 6, Group III element nitride crystals were produced as shown in FIG. 7. First, 12 g of metallic gallium (Ga) 110 was placed on the metal mounting portion 104, and a sapphire substrate (manufactured by Shinkosha Co., Ltd., 0.43 mm thick, 12 mm × 25 mm) 202 was attached to the substrate support portion 103. Next, N gas was introduced while the temperature of the entire apparatus was raised. Specifically, as shown in FIG. 7, 300 sccm of N gas 201a was introduced through the oxidizing gas introduction pipe 105, 1800 sccm of N gas 203e was introduced through the carrier gas introduction pipe 107c, 1200 sccm of N gas 203f was introduced through the oxygen-containing gas introduction pipe 107d, and 1200 sccm of N gas 203g was introduced from the outside of the oxygen-containing gas introduction pipe 107d. The temperature of the entire apparatus 500, including the nozzle section (oxidizing gas inlet pipe 105, carrier gas inlet pipe 107c, oxygen-containing gas inlet pipe 107d, and the outside of the oxygen-containing gas inlet pipe 107d), the source section (second container 102 and metal placement section 104), and the crystal growth section (substrate support section 103 and sapphire substrate 202), was raised to 1100°C, and then gas was continuously flowed under the conditions shown in Table 1 below to produce GaO crystals on the sapphire substrate. The growth took one hour to produce GaO crystals. In Table 1 below, "Line 1," "Line 2," "Line 3," and "Line 4" indicate that gases were passed in that order from the inside out. That is, "Line 1" represents gas 201a introduced from oxidizing gas introduction pipe 105, "Line 2" represents gas 203e introduced from carrier gas introduction pipe 107c, "Line 3" represents gas 203f introduced from oxygen-containing gas introduction pipe 107d, and "Line 4" represents gas 203g introduced from outside oxygen-containing gas introduction pipe 107d. In this example, metal gallium 110 (metal) was reacted with HO gas (oxidizer) contained in gas 201a (Line 1) to generate GaO gas (metal oxide gas) (metal oxide gas generation step), and then the GaO gas (metal oxide gas) was reacted with HO gas (oxygen-containing gas) contained in gas 203f (Line 3) on a sapphire substrate to generate GaO crystals (metal oxide crystal generation step), thereby producing the desired GaO crystals.

[0159] [Table 1]

[0160] Figure 27 shows an SEM (scanning electron microscope) photograph of the Ga2O3 crystals produced in this example. This SEM photograph was taken using a scanning electron microscope, VHX-D510 (product name) manufactured by Keyence Corporation. As shown in the SEM photograph in Figure 27, it was confirmed that in this example, Ga2O3 crystals with a uniform orientation (orientation direction) were grown on the sapphire substrate.

[0161] Figure 28 shows a Nomarski image (photograph) of the Ga2O3 crystals produced in this example. Similar to Figure 27, this Nomarski image was captured using a Keyence VHX-7000 (product name) scanning microscope. Enlarged photographs of portions (a), (b), (c), (d), and (e) in the upper center photograph are shown counterclockwise from the upper left. As shown in the Nomarski image in Figure 28, it was confirmed that Ga2O3 crystals with uniform orientation (direction) had grown over a wide area on the sapphire substrate.

[0162] Additionally, Figure 29 shows a photograph of the 2 μm thick Ga2O3 crystal growth area of ​​the Nomarski observation image in Figure 28. As shown in Figure 29, it was confirmed that Ga2O3 crystals with a uniform orientation (direction of orientation) had grown even in the relatively thick Ga2O3 crystal growth area of ​​2 μm or more.

[0163] Figure 30 shows a photograph of the area around the holding jig in the Nomarski image of Figure 28. Because the Ga2O3 crystal growth thickness is relatively thin near the holding jig, it is possible to clearly capture the shape of the grown Ga2O3 crystal. As shown in the photograph in Figure 30, it was confirmed that triangular Ga2O3 crystals had grown on the sapphire substrate in a plan view around the holding jig.

[0164] The graph in Figure 31 shows the XRD (X-ray diffraction) spectrum of the Ga2O3 crystal produced in this example. In this figure, the horizontal axis represents 2θ (°) and the vertical axis represents the relative intensity of the peaks. The XRD spectrum in this figure was measured using a Smartlab (product name) manufactured by Rigaku Corporation. As shown in the figure, diffractions were obtained from the 20-1, 40-2, and 60-3 planes of the β-phase Ga2O3 crystal, and peaks from the sapphire substrate (Al2O3 crystal) were also confirmed.

[0165] [Example 2] A Ga2O3 crystal (Ga2O3 epitaxial crystal) was produced by epitaxial growth (homoepitaxy) on the Ga2O3 crystal substrate in the same manner as in Example 1, except that a Ga2O3 crystal substrate (0.43 mm thick, 1.0 cm × 2.5 cm) 202 was used instead of the sapphire substrate 202. In this way, a laminate (metal oxide epitaxial crystal laminated substrate) was produced in which the Ga2O3 epitaxial crystal was laminated on the Ga2O3 crystal substrate.

[0166] The graph in Figure 32 shows the XRD spectra of the Ga2O3 crystal of Example 1 (produced by heteroepitaxy) and the Ga2O3 crystal of this Example (produced by homoepitaxy). In this figure, the horizontal axis represents 2θ (°), and the vertical axis represents the relative peak intensity. The XRD spectra in this figure were measured using a Smartlab (product name) manufactured by Rigaku. In this figure, the Ga2O3 crystal substrate used in this Example is presumed to have a (20-1) orientation. In this Example, diffractions attributable to (20-1), (40-2), (60-3), and (80-4) were confirmed after crystal production, confirming that Ga2O3 crystals were produced. Furthermore, in Example 1 (heteroepitaxy) using a sapphire substrate, diffractions attributable to (20-1) and (60-3) were observed, consistent with those in this Example (homoepitaxy), confirming that Ga2O3 crystals were produced. In addition, it is presumed that another diffraction was detected near (40-2) and (80-4) in the Ga2O3 crystal of Example 1, because there was a difference in the diffraction angle from this example (homoepitaxy). This other diffraction may be the diffraction of polycrystals.

[0167] Figure 33 shows the XRD spectrum of the metal oxide epitaxial crystal laminate substrate (a laminate consisting of Ga2O3 epitaxial crystals laminated on a Ga2O3 crystal substrate) produced in this example. To evaluate the crystal, rocking curve measurements (2θ-ω scans) were performed at each diffraction angle detected by XRD for the Ga2O3 crystal obtained by homoepitaxy shown in Figure 33. As shown in Figure 34, in this example, the rocking curve half-widths were in the 20-second range for the (20-1), (40-2), and (60-3) diffractions, demonstrating that highly oriented Ga2O3 crystals were produced, retaining the quality of the seed crystal (the Ga2O3 crystal substrate). However, the (80-4) diffraction in Figure 34 is weak in intensity, making it difficult to accurately evaluate the crystal quality from the half-width.

[0168] [Example 3] Ga2O3 crystals were produced in the same manner as in Example 1, except that a Ga2O3 crystal substrate (thickness 0.43 mm, diameter 2.54 cm) 202 was used instead of the sapphire substrate 202, and the crystal growth conditions (gas flow rate) after heating were changed as shown in Table 2 below.

[0169] [Table 2]

[0170] Figure 34 shows SEM images (photographs) of the Ga2O3 crystals produced in this example. The upper left image in Figure 34 is a full-body SEM image, the upper right image is a surface SEM image (500x magnification), and the lower image is a cross-sectional SEM image (2000x magnification). As shown in the full-body SEM image, surface SEM image, and cross-sectional SEM images in Figure 34, it was confirmed that Ga2O3 crystals with irregularities were grown on flat Ga2O3 seed crystals in this example. Furthermore, the grown film thickness of the Ga2O3 crystals produced in this example was approximately 18 to 24 μm.

[0171] The graph in Figure 35 shows the XRD spectrum of the metal oxide epitaxial crystal laminate substrate (a laminate in which Ga2O3 epitaxial crystals are laminated on a Ga2O3 crystal substrate) produced in this example. In the graph on the left side of the figure, the horizontal axis is 2θ / ω, and the vertical axis is peak intensity (relative value). In the graph on the right side, the horizontal axis is ω, and the vertical axis is peak intensity (relative value). From the 2θ-ω scan of the graph on the left side of Figure 35, 020 plane diffraction was confirmed. This confirmed that the Ga2O3 crystal produced in this example was homoepitaxially grown in the same orientation as the (010) plane gallium oxide seed crystal. The graph on the right side of Figure 35 is a profile obtained by ω scan with 2θ fixed at the diffraction angle of the 020 plane, and indicates the quality of the crystal. As shown in this graph, the Ga2O3 crystal produced in this example exhibits some peak splitting, but the half-width is approximately 99 seconds, confirming high orientation.

[0172] [Example 4] A Ga2O3 crystal (Ga2O3 epitaxial crystal) was produced on the Ga2O3 crystal substrate by epitaxial growth (homoepitaxy) in the same manner as in Example 1, except that a GaN crystal substrate (manufactured by SINO NITRIDE, thickness 0.43 mm, 12 mm × 25 mm) was used instead of the sapphire substrate 202, and the crystal growth conditions (gas flow rate) after heating were changed as shown in Table 3 below. In this way, a laminate (metal oxide epitaxial crystal laminated substrate) was produced in which the Ga2O3 epitaxial crystal was laminated on the Ga2O3 crystal substrate.

[0173] [Table 3]

[0174] Figure 36 shows an SEM image (photograph) of the Ga2O3 crystals produced in this example. The image on the left side of Figure 36 is a whole SEM image, and the image on the right side is a surface SEM image (5000x magnification). The enlarged SEM image on the right side of Figure 36 confirmed that Ga2O3 crystals oriented with the same plane orientation were obtained in this example.

[0175] Figure 37 shows the XRD spectrum of the metal oxide epitaxial crystal laminated substrate (a laminate in which Ga2O3 epitaxial crystals are laminated on a GaN crystal substrate) produced in this example. In the graph on the left side of the figure, the horizontal axis is 2θ / θ, and the vertical axis is peak intensity (relative value). As shown in the figure, in addition to the diffraction of the GaN crystal seed crystal, -201, -402, and -603 diffraction peaks were confirmed, confirming that β-gallium oxide crystals with a -201 plane orientation were obtained in this example.

[0176] [Example 5] Ga2O3 crystals were produced in the same manner as in Example 1, except that the crystal growth conditions (gas flow rate) after heating were changed as shown in Table 4 below. In this example, the gas serving as the Group VI element source was changed from water to a mixed gas with a nitrogen (N2):oxygen (O2) molar ratio of 4:1 (air ratio). In other words, this mixed gas corresponds to dry air.

[0177] [Table 4]

[0178] An SEM photograph of the sapphire substrate surface after one hour of crystal growth is shown in Figure 38. As shown in the figure, deposits were confirmed on the sapphire substrate, and these deposits were subjected to elemental analysis using SEM-EDS.

[0179] Figure 39 shows SEM-EDS mapping images (photographs) of the deposit in Figure 38. The upper left of Figure 39 is an FE-SEM image (photograph). The upper right of Figure 39 is an OK image (photograph). The lower left of Figure 39 is an Al-K image (photograph). The lower right of Figure 39 is a Ga-L image (photograph). As shown in the figures, gallium and oxygen were detected in the deposit area, which indicates that the deposit is gallium oxide, confirming the generation of gallium oxide in this example. Additionally, aluminum was detected in areas other than the deposit, which is presumed to be derived from the sapphire substrate.

[0180] The graph in Figure 40 shows the results of elemental analysis (EDS line analysis) by the SEM-EDS described above. In this graph, the horizontal axis represents the distance [μm] on the line shown in the upper photograph, and the vertical axis represents peak intensity (relative value). In this graph, the top spectrum is the Al-K spectrum. The middle spectrum is the OK spectrum. The bottom spectrum is the Ga-L spectrum. As shown in Figure 40, the gallium intensity increased in the deposit area, which indicated that this deposit was gallium oxide, confirming the generation of gallium oxide in this example.

[0181] Figure 41 shows SEM-EDS mapping images (photographs) of a region on the sapphire substrate of Figure 38 that is different from those in Figures 39 and 40 (a region where thin deposits were observed on the surface). The upper left of Figure 41 is an FE-SEM image (photograph). The upper right of Figure 41 is an Al-K image (photograph). The lower left of Figure 41 is a Ga-L image (photograph). The lower right of Figure 41 is an OK image (photograph). As shown in the figures, gallium was detected even in the region where thin deposits were observed on the surface, confirming that the deposits were gallium oxide and that gallium oxide was produced. [Industrial Applicability]

[0182] As described above, the present invention can provide a method for producing a metal oxide crystal that uses halogen-free raw materials and enables high-speed crystal growth, a method for producing a metal oxide epitaxial crystal multilayer substrate, a method for producing a semiconductor device, a metal oxide crystal, a metal oxide epitaxial crystal multilayer substrate, a semiconductor device, and a metal oxide crystal production apparatus. The metal oxide crystal of the present invention can be used, for example, in optical devices such as light-emitting diodes and laser diodes; electronic devices such as rectifiers and bipolar transistors; and semiconductor sensors such as temperature sensors, pressure sensors, radiation sensors, and visible-ultraviolet light detectors. However, the present invention is not limited to the aforementioned uses and can be applied in a wide range of fields. [Explanation of symbols]

[0183] 100, 300, 500 Manufacturing equipment used in the manufacturing method of metal oxide crystals 101 First Container 102, 301 Second container 103 Substrate support 104 Metal placement section 105 Oxidizing gas introduction pipe 106 Metal oxidation product gas outlet pipe 107a, 107b gas introduction pipes 107c Carrier gas inlet tube 107d Oxygen-containing gas introduction tube 108 Exhaust pipe 109a, 109b First heating means 200a, 200b Second heating means 201a, 201b, 401a, 401b Oxidizing gas or reducing gas 111a, 111b Metal oxide gas 202 Substrate 203a, 203b, 203c, 203f Nitrogen-containing gases 203d exhaust gas 203e, 203g carrier gas 204 Metal oxide crystal (Ga2O3 crystal) 205 Solid Carbon (Graphite) 302 Metal introduction pipe 402, 110 metal

Claims

1. A method for producing metal oxide crystals, comprising: a metal oxide gas generating step of reacting a metal with an oxidizing agent under heating to generate a metal oxide gas; a metal oxide crystal generating step of generating the metal oxide crystal by reacting the metal oxide gas with an oxygen-containing gas; A manufacturing method comprising:

2. 2. The method according to claim 1, wherein in the metal oxide crystallization step, the ratio of partial pressures of the metal oxide gas to the oxygen-containing gas is in the range of 1000:1 to 1:1000.

3. 3. The method according to claim 1, wherein the partial pressure of the oxygen-containing gas in the metal oxide crystal generating step is equal to or higher than the dissociation pressure of the metal oxide crystal.

4. 4. The method according to claim 1, wherein the metal element in the metal oxide crystal is at least one selected from the group consisting of Group I elements, Group II elements, Group III elements, Group IV elements, and lanthanoids.

5. 4. The manufacturing method according to claim 1, wherein the metal element in the metal oxide crystal is at least one selected from the group consisting of Li, Na, K, Rb, Cs, Fr, Cu, Ag, Au, Be, Mg, Ca, Sr, Ba, Ra, Zn, Cd, Hg, Al, Ga, In, Ti, Zr, Hf, Ge, Sn, Pb, and Ir.

6. The metal oxide crystal is α-Ga ２ O ３ , α-In ２ O ３ , α-Ir ２ O ３ , α-Al ２ O ３ , β-Ga ２ O ３ , β-In ２ O ３ , β-Ir ２ O ３ , β-Al ２ O ３ , ε-Ga ２ O ３ , ε-In ２ O ３ , ε-Ir ２ O ３ , ε-Al ２ O ３ , c-Ga ２ O ３ , c-In ２ O ３ , c-Ir ２ O ３ , c-Al ２ O ３ 6. The method according to claim 1, wherein the crystal is formed of a crystal of Li—Cs—B—O, Li—B—O, Sr—O, or two or more thereof.

7. The method according to any one of claims 1 to 6, wherein the metal oxide crystal is a laminate of two or more crystal layers having different metal element compositions or electrical conductivities.

8. In the metal oxide crystallization step, the oxygen-containing gas is ２ , H ２ O, CO ２ , CO, NO ２ , NO, N ２ The method according to any one of claims 1 to 7, wherein the hydroxyl group is at least one selected from the group consisting of hydroxyl groups, hydroxypropyl ...

9. In the metal oxide gas generating step, the oxidizing agent is O ２ , H ２ O, CO ２ , CO, NO ２ , NO, N ２ The method according to any one of claims 1 to 8, wherein the hydroxyl group is at least one selected from the group consisting of hydroxyl groups, hydroxypropyl groups, and alcohols.

10. The method according to claim 1 , wherein the reaction between the metal and the oxidizing agent is carried out at 650° C. or higher in the metal oxide gas generating step.

11. Further, H ２ , N ２ The method according to any one of claims 1 to 10, wherein at least one selected from the group consisting of air and a rare gas is allowed to coexist.

12. The method according to any one of claims 1 to 11, wherein a dopant is further present in the reaction system.

13. The manufacturing method according to claim 12, wherein the dopant is at least one selected from the group consisting of a simple substance of an element other than the metal oxide crystal, an oxide of the element, a hydride of the element, and an organic compound.

14. The method according to any one of claims 1 to 13, wherein the metal oxide crystal is a semiconductor.

15. The method according to claim 14, wherein the metal oxide crystal is at least one of an n-type semiconductor and a p-type semiconductor.

16. A method for producing a metal oxide crystal, comprising epitaxially growing the metal oxide crystal on a crystal substrate by the production method according to any one of claims 1 to 15, and then separating the metal oxide crystal from the crystal substrate to form a free-standing crystal.

17. A method for manufacturing a metal oxide epitaxial crystal laminated substrate in which metal oxide epitaxial crystals are laminated on a crystal substrate, comprising: The metal oxide epitaxial crystal is a metal oxide crystal produced by the production method according to any one of claims 1 to 15, A manufacturing method, comprising epitaxially growing the metal oxide epitaxial crystal on the crystal substrate by the manufacturing method according to any one of claims 1 to 15.

18. 18. The method according to claim 17, wherein the crystal substrate is a crystal substrate formed of the same material as the metal oxide epitaxial crystal or a crystal substrate formed of a material different from that of the metal oxide epitaxial crystal.

19. The method according to claim 18, wherein the metal oxide epitaxial crystal is a β-gallium oxide single crystal.

20. The method according to claim 18, wherein the metal oxide epitaxial crystal is an α-gallium oxide single crystal.

21. A method for manufacturing a semiconductor device including a metal oxide crystal or metal oxide epitaxial crystal laminated substrate, comprising: A manufacturing method characterized by manufacturing the metal oxide crystal by the manufacturing method described in any one of claims 1 to 20, or manufacturing the metal oxide epitaxial crystal laminated substrate by the manufacturing method described in any one of claims 17 to 20.

22. A metal oxide crystal manufacturing apparatus used in the manufacturing method according to any one of claims 1 to 21, a reaction vessel, a metal oxide gas supply mechanism, and an oxygen-containing gas supply mechanism; the metal oxide gas supply mechanism is capable of continuously supplying the metal oxide gas into the reaction vessel; the oxygen-containing gas supply mechanism can continuously supply the oxygen-containing gas into the reaction vessel; A metal oxide crystal manufacturing apparatus characterized in that the metal oxide gas generation process is carried out in the reaction vessel by reacting the metal and the oxidizing agent in a heated state to generate the metal oxide gas, and the metal oxide crystal generation process is carried out by reacting the metal oxide gas with the oxygen-element-containing gas.

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