crystalline oxide film

Abstract

The present invention provides an epitaxial film having a corundum structure with excellent crystal quality, which is useful for semiconductor devices, etc., and in which defects such as dislocations due to facet growth are reduced. The crystalline oxide film includes laterally grown regions of a corundum structure, in which the laterally grown regions are substantially free of facet growth regions, the crystal growth direction is along the c-axis or approximately the c-axis direction, and dislocation lines extend along the c-axis or approximately the c-axis direction, and the crystalline oxides whose crystal growth has spread along the c-axis or approximately the c-axis direction are joined to each other.

Description

[Technical Field]

[0001] The present invention relates to a crystalline oxide film useful for semiconductor devices. [Background technology]

[0002] Conventionally, cracks and lattice defects occur when growing crystals on heterogeneous substrates. To address this issue, methods such as matching the lattice constants and thermal expansion coefficients of the substrate and film have been studied. In addition, when mismatching occurs, film formation techniques such as ELO have also been considered.

[0003] Patent Document 1 describes a method of forming a buffer layer on a heterogeneous substrate and growing a zinc oxide-based semiconductor layer on the buffer layer. Patent Document 2 describes forming a nanodot mask on a heterogeneous substrate and then forming a single-crystal semiconductor material layer. Non-Patent Document 1 describes a method of growing GaN crystals on sapphire via GaN nanocolumns. Non-Patent Document 2 describes a method of growing GaN crystals on Si(111) using a periodic SiN intermediate layer to reduce defects such as pits.

[0004] However, with both techniques, the film formation speed is slow, and cracks, dislocations, warpage, etc. occur in the substrate, and dislocations, cracks, etc. occur in the epitaxial film, making it difficult to obtain a high-quality epitaxial film. These techniques also cause problems when increasing the diameter of the substrate and the thickness of the epitaxial film.

[0005] Furthermore, semiconductor devices using gallium oxide (Ga2O3), which has a large band gap, are attracting attention as next-generation switching elements that can achieve high breakdown voltage, low loss, and high heat resistance, and are expected to be applied to power semiconductor devices such as inverters. Furthermore, due to its wide band gap, it is also expected to be applied to light-emitting and receiving devices such as LEDs and sensors. According to Non-Patent Document 3, the band gap of gallium oxide can be controlled by mixing indium and aluminum, either individually or in combination, and it constitutes an extremely attractive material family as an InAlGaO-based semiconductor. Here, InAlGaO-based semiconductors are In X Al Y Ga Z O3 (0≦X≦2, 0≦Y≦2, 0≦Z≦2, X+Y+Z=1.5~2.5), and can be viewed as the same material family containing gallium oxide.

[0006] However, since the most stable phase of gallium oxide is the β-gallium structure, it is difficult to form a crystalline film with a corundum structure unless a special film formation method is used, and many issues still remain in terms of crystal quality, etc. In response to this, several studies are currently being conducted on the formation of a crystalline semiconductor film with a corundum structure. Patent Document 3 describes a method for producing an oxide crystal thin film by mist CVD using gallium or indium bromide or iodide. Patent Documents 4 to 6 describe multilayer structures in which a semiconductor layer having a corundum crystal structure and an insulating film having a corundum crystal structure are stacked on a base substrate having a corundum crystal structure.

[0007] Recently, studies have been conducted on ELO growth or the like of a gallium oxide film having a corundum structure, as described in Patent Documents 7 to 9 and Non-Patent Document 4. According to the methods described in Patent Documents 7 to 9, it is possible to obtain a gallium oxide film having a high-quality corundum structure, but when the crystalline film is actually examined, it tends to grow facets, and due to issues such as this facet growth, the method is still not satisfactory. Patent Documents 3 to 9 are all publications relating to patents or patent applications filed by the present applicant. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-232623 [Patent Document 2] Special Publication No. 2010-516599 [Patent Document 3] Patent No. 5397794 [Patent Document 4] Patent No. 5343224 [Patent Document 5] Patent No. 5397795 [Patent Document 6] Japanese Patent Application Laid-Open No. 2014-72533 [Patent Document 7] Japanese Patent Application Laid-Open No. 2016-100592 [Patent Document 8] Japanese Patent Application Laid-Open No. 2016-98166 [Patent Document 9] Japanese Patent Application Laid-Open No. 2016-100593 [Non-patent literature]

[0009] [Non-Patent Document 1] Kazuhide Kusakabe., et al., “Overgrowth of GaN layer on GaN nano-columns by RF-molecular beam epitaxy”, Journal of Crystal Growth 237-239 (2002) 988-992 [Non-patent document 2] KY Zang., et al., “Defect reduction by periodic SiNx interlayers in gallium nitride grown on Si (111)”, Journal of Applied Physics 101, 093502 (2007) [Non-patent document 3] Kentaro Kaneko, "Growth and Properties of Gallium Oxide-Based Alloy Thin Films with Corundum Structure," Doctoral Dissertation, Kyoto University, March 2013 [Non-patent document 4] Akio Takatsuka, Shinya Oda, Kentaro Kaneko, Shizuo Fujita, and Toshimi Hitora, "Selective Lateral Overgrowth (ELO) of α-type Gallium Oxide by Mist Epitaxy", 2015 62nd Spring Meeting of the Japan Society of Applied Physics, Tokai University, (March 11-14, 2015) 13a-P18-12. Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to provide an epitaxial film having a corundum structure with excellent crystal quality, which is useful for semiconductor devices and the like, in which defects such as dislocations due to facet growth are reduced. [Means for solving the problem]

[0011] As a result of extensive research to achieve the above object, the inventors have found that by using an m-plane sapphire substrate on the surface of which stripe-shaped ELO masks extending in the a-axis direction are arranged, and by performing ELO film formation under supply-limited conditions, facet growth can be suppressed and a crystalline oxide film can be obtained in which various defects that cause leakage current and the like are reduced. They also found that the crystalline oxide film obtained in this way can solve all of the above-mentioned conventional problems at once. Furthermore, after obtaining the above findings, the present inventors conducted further studies and have now completed the present invention.

[0012] That is, the present invention relates to the following inventions. [1] A crystalline oxide film comprising a laterally grown region of a corundum structure, wherein the laterally grown region is substantially free of facet-grown regions. [2] A crystalline oxide film including a laterally grown region of a corundum structure, characterized in that the crystal growth direction of the laterally grown region is the c-axis or approximately the c-axis direction. [3] The crystalline oxide film according to [1] or [2], wherein the laterally grown region is substantially free of dislocation lines. [4] A crystalline oxide film including a laterally grown region of a corundum structure, characterized in that in part or all of the laterally grown region, crystalline oxides whose crystal growth has spread in the c-axis or approximately c-axis direction are joined to each other. [5] A crystalline oxide film including a laterally grown region of a corundum structure, characterized in that in part or all of the laterally grown region, crystalline oxides whose crystal growth has spread at different crystal growth rates in the c-axis or approximately c-axis direction are bonded to each other. [6] A crystalline oxide semiconductor film including an epitaxial layer of a corundum structure, characterized in that the epitaxial layer is on a junction surface between crystalline oxides whose crystal growth extends in the c-axis or approximately c-axis direction. [7] A crystalline oxide semiconductor film including an epitaxial layer of a corundum structure, characterized in that the epitaxial layer is on a junction surface between crystalline oxides whose crystal growth has spread at different crystal growth rates in the c-axis or approximately c-axis direction. [8] The crystalline oxide film according to any one of [1] to [7] above, which contains at least one or more metals from Periods 4 to 6 of the periodic table. [9] The crystalline oxide film according to any one of [1] to [8] above, which contains at least gallium, indium, rhodium or iridium.

[10] The crystalline oxide film according to any one of [1] to [9] above, which contains α-Ga2O3 or a mixed crystal thereof as a main component.

[11] A semiconductor device comprising the crystalline oxide film according to any one of [1] to

[10] above.

[12] The semiconductor device according to

[11] , wherein the crystalline oxide film is a semiconductor film containing a dopant.

[13] The semiconductor device according to

[11] or

[12] , which is a power device.

[14] The semiconductor device according to

[11] or

[12] above, which is a power module, an inverter, or a converter.

[15] A semiconductor system including a semiconductor device, wherein the semiconductor device is the semiconductor device according to any one of

[11] to

[14] above. [Effects of the Invention]

[0013] The crystalline oxide film of the present invention has reduced defects such as dislocations due to facet growth, is useful for semiconductor devices, and has excellent crystal quality. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view schematically showing one embodiment of an uneven portion formed on the crystal growth surface of a crystal substrate used in the present invention. [Figure 2] 1 is a cross-sectional view schematically showing one embodiment of an uneven portion formed on the crystal growth surface of a crystal substrate used in the present invention. [Figure 3] 1 is a cross-sectional view schematically showing one embodiment of an uneven portion formed on the crystal growth surface of a crystal substrate used in the present invention. [Figure 4] 1 is a cross-sectional view schematically showing one embodiment of an uneven portion formed on the crystal growth surface of a crystal substrate used in the present invention. [Figure 5] 1 is a cross-sectional view schematically showing one embodiment of an uneven portion formed on the crystal growth surface of a crystal substrate used in the present invention. [Figure 6] 1 is a cross-sectional view schematically showing one embodiment of an uneven portion formed on the crystal growth surface of a crystal substrate used in the present invention. [Figure 7] 1 is a cross-sectional view schematically showing a crystalline layered structure of the present invention. [Figure 8] FIG. 1 is a cross-sectional view schematically showing a crystalline layered structure (with a buffer layer) of the present invention. [Figure 9] 1 is a schematic diagram illustrating the configuration of a film forming apparatus that is preferably used in the present invention. [Figure 10] FIG. 10 is a schematic diagram showing the configuration of a film forming apparatus (mist CVD) of another embodiment different from that of FIG. 9, which is preferably used in the present invention. [Figure 11] FIG. 1 is a diagram schematically illustrating a preferred example of a power supply system. [Figure 12] FIG. 1 is a diagram schematically illustrating a preferred example of a system device. [Figure 13] FIG. 2 is a circuit diagram showing a preferred example of a power supply circuit of the power supply device. [Figure 14] FIG. 1 is a diagram showing the results of microscopic observation of a membrane cross section in an example. [Figure 15] FIG. 10 is a diagram showing the results of microscopic observation of the upper surface of the film in the example. [Figure 16] FIG. 1 is a diagram showing the results of microscopic observation of a membrane cross section in an example. DETAILED DESCRIPTION OF THE INVENTION

[0015] The crystalline oxide film of the present invention is a crystalline oxide film containing laterally grown regions of a corundum structure and / or epitaxial layers of a corundum structure, and has any one of the following features (1) to (7). (1) The laterally grown region is substantially free of facet grown regions. (2) The crystal growth direction of the laterally grown region is the c-axis direction or approximately the c-axis direction. (3) The laterally grown region contains dislocation lines, which extend in the c-axis direction or substantially in the c-axis direction. (4) In part or all of the laterally grown region, crystalline oxides whose crystal growth has expanded in the c-axis or substantially c-axis direction are bonded to each other. (5) In part or all of the laterally grown region, crystalline oxides whose crystal growth has spread at different crystal growth rates in the c-axis or substantially c-axis direction are bonded to each other. (6) The epitaxial layer is an epitaxial layer on a junction surface between crystalline oxides whose crystal growth extends in the c-axis or substantially c-axis direction. (7) The epitaxial layer is an epitaxial layer on a junction surface between crystalline oxides whose crystal growth has spread at different crystal growth rates in the c-axis or approximately c-axis direction.

[0016] In the present invention, the crystalline oxide film preferably contains at least one or more metals from periods 4 to 6 of the periodic table, more preferably at least gallium, indium, rhodium, or iridium, and most preferably contains α-Ga2O3 or a mixed crystal thereof as a main component. Such a preferred crystalline oxide film is more suitable for semiconductor devices and exhibits superior semiconductor properties. The crystalline oxide film also preferably contains a dopant. Examples of the dopant include tin, germanium, silicon, titanium, zirconium, vanadium, and niobium. The dopant concentration is typically about 1×10 16 / cm 3 ~1×10 22 / cm 3 Alternatively, the dopant concentration may be, for example, about 1×10 17 / cm 3 Furthermore, according to the present invention, the dopant may be present in a concentration as low as about 1×10 20 / cm 3 It may be contained in a concentration higher than this.

[0017] The crystalline oxide film can be obtained by, for example, the following suitable film formation method. That is, it is a method for forming an epitaxial film directly or via another layer on the crystal growth surface of a crystal substrate having a corundum structure, in which an uneven portion consisting of recesses or protrusions is formed on the crystal growth surface of the crystal substrate, and the film formation is carried out under conditions that are supply-rate-limiting.

[0018] <Crystal substrate> The crystalline substrate is not particularly limited as long as it has a corundum structure, and may be a known substrate. It may be an insulating substrate, a conductive substrate, or a semiconductor substrate. It may be a single crystal substrate or a polycrystalline substrate. An example of the crystalline substrate is a substrate containing a crystalline material having a corundum structure as a main component. The term "main component" refers to a substrate containing 50% or more of the crystalline material, preferably 70% or more, and more preferably 90% or more, in terms of composition ratio in the substrate. Examples of the crystalline substrate having a corundum structure include a sapphire substrate and an α-type gallium oxide substrate.

[0019] The crystal substrate is preferably a sapphire substrate. Examples of the sapphire substrate include a c-plane sapphire substrate, an m-plane sapphire substrate, and an a-plane sapphire substrate. The sapphire substrate may have an off-angle. The off-angle is not particularly limited, but is preferably 0° to 15°. In an embodiment of the present invention, the sapphire substrate is preferably an m-plane sapphire substrate. The thickness of the crystal substrate is not particularly limited, but is preferably 10 to 2000 μm, and more preferably 50 to 1000 μm.

[0020] <Uneven part> The uneven portion is not particularly limited as long as it is composed of convex portions or concave portions. It may be an uneven portion composed of convex portions, an uneven portion composed of concave portions, or an uneven portion composed of convex portions and concave portions. That is, the uneven portion may be any portion as long as it includes concave portions or convex portions. Furthermore, the uneven portion may be formed of regular convex portions or concave portions, or irregular convex portions or concave portions. The uneven portion is preferably formed periodically, and more preferably is patterned periodically and regularly. The shape of the uneven portion is not particularly limited and includes, for example, a stripe shape, a dot shape, a mesh shape, or a random shape. A stripe shape or a dot shape is preferred, and a stripe shape is more preferred. When the uneven portion is formed in a dot shape, the uneven portions may be periodically and regularly arranged at lattice positions such as a square lattice, an orthorhombic lattice, a triangular lattice, a hexagonal lattice, or a hexagonal lattice, and the like. The cross-sectional shape of the concave or convex portions of the uneven portion is not particularly limited, but examples thereof include a U-shape, an inverted U-shape, a wave shape, or a polygonal shape such as a triangle, a quadrangle (e.g., a square, a rectangle, or a trapezoid), a pentagon, or a hexagon.

[0021] The material constituting the protrusions is not particularly limited and may be a known material. The material constituting the protrusions may be an insulating material, a conductive material, or a semiconductor material, but is preferably a material that can inhibit vertical crystal growth. The material constituting the protrusions may be amorphous, single crystal, or polycrystalline. Examples of the material constituting the protrusions include oxides, nitrides, or carbides of Si, Ge, Ti, Zr, Hf, Ta, Sn, etc., carbon, diamond, metals, and mixtures thereof. More specifically, examples of the material constituting the protrusions include Si-containing compounds containing SiO2, SiN, or polycrystalline silicon as a main component, and metals having a melting point higher than the crystal growth temperature of the crystalline semiconductor (e.g., noble metals such as platinum, gold, silver, palladium, rhodium, iridium, and ruthenium). The content of the material in the protrusions is preferably 50% or more, more preferably 70% or more, and most preferably 90% or more, in terms of composition ratio.

[0022] The means for forming the convex portions may be known means, for example, known patterning processing means such as photolithography, electron beam lithography, laser patterning, and subsequent etching (e.g., dry etching or wet etching), etc. In the present invention, the convex portions are preferably in the form of stripes or dots, and more preferably in the form of stripes.

[0023] The material constituting the recesses is not particularly limited, but may be the same as the material constituting the protrusions, or may be a crystal substrate. The recesses are preferably dot-shaped, and more preferably, dot-shaped recesses are provided in a mask layer made of the silicon-containing compound. The recesses can be formed by the same means as the protrusion-forming means described above. It is also preferable that the recesses are a void layer provided on the crystal growth surface of the crystal substrate. The void layer can be formed on the crystal growth surface of the crystal substrate by providing grooves in the crystal substrate using known groove processing means. The groove width, groove depth, terrace width, etc. of the void layer are not particularly limited and can be set appropriately as long as they do not impede the objectives of the present invention. The void layer may also contain air or an inert gas, etc.

[0024] In the present invention, it is preferable that an uneven portion consisting of recesses or protrusions is formed on the crystal growth surface of the crystal substrate in a direction perpendicular or approximately perpendicular to the c-axis. By forming such uneven portions, facet growth can be further suppressed, and film formation more suitable for semiconductor devices can be achieved. In the present invention, "perpendicular or approximately perpendicular to the c-axis" usually means that the angle formed with the c-axis direction is within a range of 90 degrees ± 10 degrees, and preferably within a range of 90 degrees ± 5 degrees.

[0025] A more preferred embodiment of the film forming method of the present invention will be described below with reference to the drawings. Figure 1 shows one embodiment of the unevenness provided on the crystal growth surface of the crystal substrate. The unevenness in Figure 1 is formed from a crystal substrate 1 and protruding portions 2a on the crystal growth surface 1a. The protruding portions 2a are striped, and the striped protruding portions 2a are periodically arranged on the crystal growth surface 1a of the crystal substrate 1. The protruding portions 2a are made of a silicon-containing compound such as SiO2, and can be formed using known means such as photolithography.

[0026] FIG. 2 shows one embodiment of a concave-convex portion provided on the crystal growth surface of a crystal substrate, and shows an embodiment different from that of FIG. 1. As in FIG. 1, the concave-convex portion of FIG. 2 is formed from a crystal substrate 1 and convex portions 2a provided on the crystal growth surface 1a. The convex portions 2a are dot-shaped, and the dot-shaped convex portions 2a are periodically and regularly arranged on the crystal growth surface 1a of the crystal substrate 1. The convex portions 2a are made of a silicon-containing compound such as SiO2, and can be formed using known means such as photolithography.

[0027] FIG. 3 shows one embodiment of an uneven portion provided on the crystal growth surface of a crystal substrate. FIG. 3 has recesses 2b instead of protrusions. The recesses in FIG. 3 are formed from a crystal substrate 1 and a mask layer 4. The mask layer is formed on the crystal growth surface 1 and has dot-shaped holes. The crystal substrate 1 is exposed through the dot holes in the mask layer 4, and dot-shaped recesses 2b are formed on the crystal growth surface 1a. The recesses 2b can be obtained by forming the mask layer 4 using a known method such as photolithography. The mask layer 4 is not particularly limited as long as it is a layer that can inhibit vertical crystal growth. Examples of materials that can be used to form the mask layer 4 include known materials such as silicon-containing compounds such as SiO2.

[0028] Figure 4 shows one embodiment of a concave-convex portion provided on the crystal growth surface of a crystal substrate. The concave-convex portion in Figure 4 is formed from a crystal substrate 1 and a void layer. The void layer is striped, and striped recesses 2b are periodically arranged on the crystal growth surface 1a of the crystal substrate 1. The recesses 2b can be formed by known groove processing means.

[0029] 5 also shows one embodiment of an uneven portion provided on the crystal growth surface 1a of the crystal substrate 1. The uneven portion in FIG. 5 differs from that in FIG. 4 in that the spacing between the recesses 2b is smaller. In other words, the terrace width of the recesses 2b is wider in FIG. 4 and narrower in FIG. 5. Like the recesses in FIG. 4, the recesses 2b in FIG. 5 can also be formed using known groove processing means.

[0030] 6, like FIGS. 4 and 5, shows one embodiment of an uneven portion provided on the crystal growth surface of a crystal substrate, and the uneven portion in FIG. 6 is formed from a crystal substrate 1 and a void layer. Unlike FIGS. 4 and 5, the void layer is dot-shaped, and dot-shaped recesses 2b are periodically and regularly arranged on the crystal growth surface 1a of the crystal substrate 1. The recesses 2b can be formed by known groove processing means.

[0031] The width and height of the convex portions of the uneven portion, the width and depth of the concave portions, and the spacing between them are not particularly limited, but in the present invention, each is, for example, within the range of about 10 nm to about 1 mm, preferably about 10 nm to about 300 μm, more preferably about 10 nm to about 1 μm, and most preferably about 100 nm to about 1 μm.

[0032] In addition, other layers such as a buffer layer or a stress relaxation layer may be provided on the crystal substrate. When other layers are provided, the uneven portion may be formed on or under the other layers, but the uneven portion is usually formed on the other layers.

[0033] As described above, an uneven portion consisting of recesses or protrusions is formed on the crystal growth surface of the crystal substrate directly or via another layer. After the uneven portion is formed, film formation is performed under supply-rate-limiting conditions, thereby realizing lateral growth without facet growth on the uneven portion, and forming an epitaxial layer containing as a main component a crystalline semiconductor with a high-quality corundum structure.

[0034] The epitaxial crystal growth method is not particularly limited and may be any known method as long as it does not impede the objectives of the present invention. Examples of the epitaxial crystal growth method include CVD, MOCVD, MOVPE, mist CVD, mist epitaxy, MBE, HVPE, and pulse growth. In the present invention, the epitaxial crystal growth method is preferably mist CVD, mist epitaxy, or HVPE, and more preferably mist CVD or mist epitaxy.

[0035] Furthermore, it is preferable to perform the film formation by atomizing a raw material solution containing a metal (atomization step), suspending the droplets, transporting the atomized droplets to the vicinity of the crystal substrate with a carrier gas (transport step), and then thermally reacting the atomized droplets (film formation step). By forming the film in this manner, lateral growth without facet growth can be more easily achieved.

[0036] (Raw material solution) The raw material solution contains a metal as a film-forming raw material, and is not particularly limited as long as it can be atomized, and may contain an inorganic material or an organic material. The metal may be a simple metal or a metal compound, and is not particularly limited as long as it does not impede the object of the present invention. Examples of the metal include gallium (Ga), iridium (Ir), indium (In), rhodium (Rh), aluminum (Al), gold (Au), silver (Ag), platinum (Pt), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), palladium (Pd), cobalt (Co), ruthenium (Ru), chromium (Cr), molybdenum (Mo), tungsten (W), titanium (Ti), and the like. Examples of suitable metals include one or more metals selected from the group consisting of talc (Ta), zinc (Zn), lead (Pb), rhenium (Re), titanium (Ti), tin (Sn), gallium (Ga), magnesium (Mg), calcium (Ca), and zirconium (Zr). In the present invention, the metal preferably includes at least one or more metals from periods 4 to 6 of the periodic table, and more preferably includes at least gallium, indium, rhodium, or iridium. The use of such preferred metals allows for the deposition of epitaxial films that are suitable for use in semiconductor devices and the like.

[0037] In the present invention, the raw material solution can be suitably prepared by dissolving or dispersing the metal in the form of a complex or salt in an organic solvent or water. Examples of the complex include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of the salt include organic metal salts (e.g., metal acetates, metal oxalates, and metal citrates), metal sulfides, metal nitrates, metal phosphates, and metal halides (e.g., metal chlorides, metal bromides, and metal iodides).

[0038] The solvent for the raw material solution is not particularly limited as long as it does not impair the object of the present invention, and may be an inorganic solvent such as water, an organic solvent such as alcohol, or a mixed solvent of an inorganic solvent and an organic solvent. In the present invention, the solvent preferably contains water.

[0039] The raw material solution may also contain additives such as hydrohalic acids and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid. Examples of oxidizing agents include peroxides such as hydrogen peroxide (HO), sodium peroxide (NaO), barium peroxide (BaO), and benzoyl peroxide (CHCO)O, as well as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0040] The raw material solution may contain a dopant. The dopant is not particularly limited as long as it does not impede the object of the present invention. Examples of the dopant include tin, germanium, silicon, titanium, zirconium, vanadium, and niobium. The concentration of the dopant is usually about 1×10 16 / cm 3 ~1×10 22 / cm 3 Alternatively, the dopant concentration may be, for example, about 1×10 17 / cm 3 Furthermore, according to the present invention, the dopant may be present in a concentration as low as about 1×10 20 / cm3 It may be contained in a concentration higher than this.

[0041] (Atomization process) The atomization step involves preparing a raw material solution containing a metal, atomizing the raw material solution, and suspending the droplets to generate atomized droplets. The blending ratio of the metal is not particularly limited, but is preferably 0.0001 mol / L to 20 mol / L relative to the total raw material solution. The atomization means is not particularly limited as long as it can atomize the raw material solution, and may be any known atomization means. However, in the present invention, an atomization means using ultrasonic vibration is preferred. The mist used in the present invention is airborne, and is preferably a mist that floats in space with an initial velocity of zero and can be transported as a gas, rather than being sprayed like a spray. The droplet size of the mist is not particularly limited, and may be droplets of about several mm, but is preferably 50 μm or less, more preferably 1 to 10 μm.

[0042] (Transportation process) In the transport step, the atomized droplets are transported to the substrate by the carrier gas. The type of carrier gas is not particularly limited as long as it does not impede the object of the present invention, and suitable examples include oxygen, ozone, an inert gas (e.g., nitrogen or argon), or a reducing gas (e.g., hydrogen gas or forming gas). The type of carrier gas may be one type, or two or more types. A diluted gas with a different carrier gas concentration (e.g., a 10-fold diluted gas) may also be used as a second carrier gas. The number of carrier gas supply locations may be one or more. The flow rate of the carrier gas is not particularly limited, but is preferably a flow rate that limits the transport rate. More specifically, a flow rate of 1 LPM or less is preferred, and 0.1 to 1 LPM is more preferred.

[0043] (Film forming process) In the film-forming step, the atomized droplets are reacted to form a film on the uneven surface. The reaction is not particularly limited as long as it forms a film from the atomized droplets, but a thermal reaction is preferred in the present invention. The thermal reaction may be any reaction that heats the atomized droplets to react, and the reaction conditions are not particularly limited as long as they do not impede the objectives of the present invention. In this step, the thermal reaction is typically carried out at a temperature equal to or higher than the evaporation temperature of the solvent in the raw material solution, but is preferably not too high, more preferably 650°C or lower. The thermal reaction may be carried out under any of the following conditions: vacuum, oxygen-free, reducing gas, and oxygen, as long as it does not impede the objectives of the present invention. Furthermore, the thermal reaction may be carried out under any of the following conditions: atmospheric pressure, pressurized, and reduced pressure. However, in the present invention, atmospheric pressure is preferred because it simplifies the calculation of the evaporation temperature and simplifies the equipment. The film thickness can be set by adjusting the film-forming time.

[0044] A film formation apparatus 19 suitable for use in the present invention will be described below with reference to the drawings. The film formation apparatus 19 shown in Fig. 9 includes a carrier gas source 22a for supplying a carrier gas, a flow rate control valve 23a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 22a, a carrier gas (dilution) source 22b for supplying a carrier gas (dilution), a flow rate control valve 23b for adjusting the flow rate of the carrier gas (dilution) delivered from the carrier gas (dilution) source 22b, a mist generation source 24 for containing a raw material solution 24a, a container 25 for containing water 25a, an ultrasonic vibrator 26 attached to the bottom of the container 25, a film formation chamber 30, a quartz supply pipe 27 connecting the mist generation source 24 to the film formation chamber 30, and a hot plate (heater) 28 installed in the film formation chamber 30. A substrate 20 is placed on the hot plate 28.

[0045] As shown in FIG. 9 , the raw material solution 24a is placed in the mist source 24. The substrate 20 is then placed on the hot plate 28, which is then operated to raise the temperature inside the film formation chamber 30. The flow control valves 23 (23a, 23b) are then opened to supply carrier gas from the carrier gas source 22 (22a, 22b) into the film formation chamber 30. The atmosphere in the film formation chamber 30 is then thoroughly replaced with the carrier gas, and the flow rates of the carrier gas and the carrier gas (dilution) are then adjusted. The ultrasonic vibrator 26 is then vibrated, and the vibrations are propagated to the raw material solution 24a through the water 25a, thereby atomizing the raw material solution 24a and generating atomized droplets 24b. The atomized droplets 24b are then introduced into the film formation chamber 30 by the carrier gas and transported to the substrate 20. The atomized droplets 24b then undergo a thermal reaction in the film formation chamber 30 under atmospheric pressure, forming a film on the substrate 20.

[0046] It is also preferable to use a mist CVD apparatus (film formation apparatus) 19 shown in Fig. 10. The mist CVD apparatus 19 in Fig. 10 includes a susceptor 21 on which a substrate 20 is placed, a carrier gas supply means 22a for supplying a carrier gas, a flow rate control valve 23a for adjusting the flow rate of the carrier gas delivered from the carrier gas supply means 22a, a carrier gas (dilution) supply means 22b for supplying a carrier gas (dilution), a flow rate control valve 23b for adjusting the flow rate of the carrier gas delivered from the carrier gas (dilution) supply means 22b, a mist generating source 24 that contains a raw material solution 24a, a container 25 that contains water 25a, an ultrasonic vibrator 26 attached to the bottom of the container 25, a supply pipe 27 made of a quartz tube with an inner diameter of 40 mm, a heater 28 installed around the supply pipe 27, and an exhaust port 29 for discharging mist, droplets, and exhaust gas after the thermal reaction. The susceptor 21 is made of quartz, and the surface on which the substrate 20 is placed is inclined from the horizontal. By making both the supply pipe 27, which serves as the film formation chamber, and the susceptor 21 out of quartz, impurities originating from the apparatus are prevented from being mixed into the film formed on the substrate 20. This mist CVD apparatus 19 can be used in the same manner as the above-mentioned film formation apparatus 19.

[0047] By using the above-described suitable film-forming apparatus, it is possible to more easily form an epitaxial layer on the crystal growth surface of the crystal substrate. The epitaxial layer is usually formed by epitaxial crystal growth.

[0048] Furthermore, according to the preferred film formation method, the crystalline oxide film of the present invention can usually be obtained as a crystalline layered structure together with the crystal substrate. The crystalline layered structure is characterized in that an uneven portion consisting of recesses or protrusions in a direction perpendicular or nearly perpendicular to the c-axis is formed on the crystal growth surface of a crystal substrate having a corundum structure, either directly or via another layer, and an epitaxial layer including a laterally grown region of the corundum structure is formed on the uneven portion, and the crystal growth direction of the laterally grown region is parallel or nearly parallel to the crystal growth surface of the crystal substrate. In an embodiment of the present invention, it is preferable that an uneven portion including recesses or protrusions in the a-axis direction is formed on the crystal growth surface of the crystal substrate directly or via another layer.

[0049] A "crystalline layered structure" is a structure including one or more crystalline layers, and may also include layers other than crystalline layers (e.g., amorphous layers). The crystalline layer is preferably a single crystalline layer, but may also be a polycrystalline layer. In the present invention, "parallel or approximately parallel to the crystal growth surface" generally means a direction that forms an angle within a range of ±10 degrees with respect to the direction parallel to the crystal growth surface (main surface) of the crystalline substrate, and preferably within a range of ±5 degrees.

[0050] FIG. 7 shows a cross-sectional view of the crystalline layered structure. The crystalline layered structure of FIG. 7 has protrusions 2a formed on a crystal substrate 1, and an epitaxial layer 3 formed by crystal growth. The protrusions 2a cause the epitaxial film having a corundum structure to grow laterally in the epitaxial layer 3. The resulting crystalline film having a corundum structure is a high-quality crystalline film, completely different from a crystalline film having a corundum structure without any protrusions or recesses. FIG. 8 also shows an example in which a buffer layer is provided. The crystalline layered structure of FIG. 8 has a buffer layer 5 formed on a crystal substrate 1, and protrusions 2a formed on the buffer layer 5. The epitaxial layer 3 is then formed on the protrusions 2a. Similar to FIG. 7, the crystalline layered structure of FIG. 8 also has a protrusion 2a causing the crystalline film having a corundum structure to grow laterally, resulting in a high-quality crystalline film having a corundum structure.

[0051] The epitaxial layer typically includes a laterally grown region of a corundum structure that is substantially free of facet growth regions. However, in the present invention, the crystal growth direction of the laterally grown region is preferably the c-axis or approximately c-axis direction. According to the preferred film formation method described above, crystalline oxides whose crystal growth spreads at different crystal growth rates along the c-axis or approximately c-axis direction are bonded to each other. In the present invention, the term "c-axis or approximately c-axis" typically refers to an angle with the c-axis direction within a range of ±10 degrees, preferably within a range of ±5 degrees. It is also preferred that the laterally grown region contains dislocation lines that extend parallel or approximately parallel to the crystal growth surface of the crystal substrate. It is more preferred that the dislocation lines extending parallel or approximately parallel to the crystal growth surface of the crystal substrate in the laterally grown region are more numerous than the dislocation lines extending in other axial directions. Such an epitaxial layer can be easily formed by the preferred film formation method described above.

[0052] In the present invention, the laterally grown region of the corundum structure preferably contains, as its main component, a metal oxide containing at least one or more metals from periods 4 to 6 of the periodic table, and more preferably, the metal contains at least gallium, indium, rhodium, or iridium. For example, when the metal oxide contained in the lateral region is α-Ga2O3, the "main component" may be α-Ga2O3, so long as the atomic ratio of gallium among the metal elements in the lateral region is 0.5 or more. In the present invention, the atomic ratio of gallium among the metal elements in the lateral region is preferably 0.7 or more, and more preferably 0.8 or more.

[0053] In the present invention, it is also preferable to further deposit an epitaxial film on the epitaxial layer of the crystalline layered structure. By depositing an additional film in this manner, it is possible to more easily obtain a crystalline layered structure in which an uneven portion consisting of recesses or protrusions in a direction perpendicular or substantially perpendicular to the c-axis is formed on the crystal growth surface of a crystal substrate having a corundum structure, directly or via another layer, and an epitaxial layer including laterally grown regions of the corundum structure is formed on the uneven portion, and the crystal growth direction of the laterally grown regions is parallel or substantially parallel to the crystal growth surface of the crystal substrate. Furthermore, by depositing an additional film in this manner, it is possible to easily obtain a crystalline oxide semiconductor film including an epitaxial film of the corundum structure, which is an epitaxial layer on a junction surface between crystalline oxides whose crystal growth extends in the c-axis or substantially c-axis direction. Furthermore, by forming further films in this manner, it is possible to more easily obtain a crystalline oxide semiconductor film including an epitaxial film with a corundum structure, which is an epitaxial layer on the junction surface between crystalline oxides whose crystal growth spreads at different crystal growth rates in the c-axis or approximately c-axis direction. With a crystalline oxide film of this configuration, even if it is an epitaxial film with a corundum structure, the laterally grown region does not substantially include a facet region, and the dislocation density can be further reduced. When forming further epitaxial films on the epitaxial layer of the crystalline stacked structure, it is preferable to form a concave-convex portion on the epitaxial layer (first crystal layer) before forming the epitaxial film (second crystal layer), as this can more effectively reduce the dislocation density.

[0054] In the present invention, it is preferable that crystalline oxides whose crystal growth extends in the c-axis or approximately c-axis direction are bonded to each other on the uneven portion, and it is also preferable that the epitaxial layer is substantially free of dislocation lines or contains dislocation lines extending parallel or approximately parallel to the crystal growth surface of the crystal substrate. It is also preferable that the epitaxial layer is substantially free of facet growth regions. Such an epitaxial layer can be easily formed by the above-mentioned preferred film formation means.

[0055] In the present invention, the corundum-structured epitaxial layer preferably contains, as its main component, a metal oxide containing at least one or more metals from periods 4 to 6 of the periodic table, and more preferably, the metal contains at least gallium, indium, rhodium, or iridium. The term "main component" refers to, for example, when the metal oxide contained in the epitaxial layer is α-Ga2O3, and the gallium atomic ratio of the metal elements in the epitaxial layer is 0.5 or more. In the present invention, the gallium atomic ratio of the metal elements in the epitaxial layer is preferably 0.7 or more, and more preferably 0.8 or more.

[0056] The crystalline laminated structure is useful for semiconductor devices. Examples of semiconductor devices formed using the crystalline laminated structure include transistors such as MIS and HEMT, TFTs, Schottky barrier diodes using semiconductor-metal junctions, JBS, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements. In the present invention, the crystalline laminated structure can be used in a semiconductor device as is or after the crystal substrate and the crystalline oxide film are separated.

[0057] In addition to the above features, the semiconductor device of the present invention can be suitably used as a power module, inverter, or converter using known means, and further suitably used in, for example, a semiconductor system using a power supply device. The power supply device can be fabricated from or as the semiconductor device by connecting it to a wiring pattern or the like using known means. FIG. 11 shows an example of a power supply system. FIG. 11 shows a power supply system 170 configured using multiple power supply devices 171 and 172 and a control circuit 173. As shown in FIG. 12, the power supply system can be used in a system device 180 by combining an electronic circuit 181 and a power supply system 182. FIG. 13 shows an example of a power supply circuit diagram for a power supply device. FIG. 13 shows the power supply circuit of the power supply device, which consists of a power circuit and a control circuit. DC voltage is switched at high frequency by an inverter 192 (comprising MOSFETs A to D) to convert it to AC, then insulated and transformed by a transformer 193, rectified by rectifying MOSFETs 194 (A to B'), smoothed by a DCL 195 (smoothing coils L1 and L2) and a capacitor, and output as a DC voltage. At this time, a voltage comparator 197 compares the output voltage with a reference voltage, and a PWM control circuit 196 controls the inverter 192 and rectifying MOSFET 194 so as to obtain a desired output voltage.

[0058] Example 1 1. Film deposition equipment In this example, a film forming apparatus 19 shown in FIG. 9 was used.

[0059] 2. Preparation of the stock solution To a 0.1 M aqueous solution of gallium bromide (GaBr3), 20% by volume of hydrobromic acid (HBr) was added, and this was used as a raw material solution.

[0060] 3. Preparation for film deposition The raw material solution 24a obtained in 2 above was placed in the mist generating source 24. Next, an m-plane sapphire substrate with a stripe pattern mask applied in the a-axis direction was used as the substrate 20, and it was placed on the hot plate 28. The hot plate 28 was operated to raise the substrate temperature to 550°C. Next, the flow rate control valves 23a and 23b were opened, and carrier gas was supplied from the carrier gas supply means 22a and 22b, which serve as the carrier gas sources, into the film formation chamber 30. After the atmosphere in the film formation chamber 30 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 1 L / min so that it became the supply rate-limiting gas. Nitrogen was used as the carrier gas.

[0061] 4. Film formation Next, ultrasonic vibrator 26 was vibrated at 2.4 MHz, and the vibrations were propagated through water 25a to raw material solution 24a, atomizing the raw material solution 24a and generating mist (atomized droplets) 24b. This mist 24b was then introduced into film-forming chamber 30 via supply pipe 27 by a carrier gas. The mist reacted thermally on substrate 20 at 550°C under atmospheric pressure, forming a film on substrate 20. The film-forming time was 2 hours. The resulting film was identified using an X-ray diffraction system and found to be an α-GaO single crystal film. The cross-sectional shape of the resulting film was also observed under a microscope. A microscopic image is shown in Figure 14. For reference, a microscopic image of the top surface is shown in Figure 15. As is clear from Figures 14 and 15, no particular facet growth was observed, and a highly-quality, approximately c-axis ELO film without dislocations was formed.

[0062] (Comparative Example 1) The film was formed in the same manner as in Example 1, except that the carrier gas flow rate was set to 4 L / min so as not to become rate-limiting, and the carrier gas (dilution) flow rate was set to 0.5 L / min. The obtained film was an α-Ga2O3 film, and a triangular facet structure was confirmed. Furthermore, screw dislocations were obliquely inserted inside the facets.

[0063] Example 2 1. Formation of the first crystal layer A first crystalline layer was formed in the same manner as in Example 1, except that the film formation temperature was set to 600° C. The obtained film was identified using an X-ray diffractometer and was found to be an α-Ga2O3 single crystal film.

[0064] 2. Formation of the second crystal layer A striped pattern of SiO2 was formed in the a-axis direction on the first crystalline film obtained in step 1 above. The pattern was formed so that openings were provided on the bonding surfaces between the crystalline oxides in the first crystalline layer. A second crystalline layer was formed on the patterned first crystalline film in the same manner as in step 1 above. The obtained film was identified using an X-ray diffraction device and was found to be an α-Ga2O3 single crystalline film.

[0065] 3. Evaluation The cross-sectional shape of the obtained film was observed using a microscope. The microscope image is shown in Figure 16. As is clear from Figure 16, crystalline oxides with crystal growth extending in the c-axis or approximately c-axis direction are bonded together, and an epitaxial layer with a corundum structure is formed on the bonded surface. Furthermore, TEM observation of the obtained film revealed no particular facet growth. Furthermore, when the dislocation density was measured, it was found to be reduced by more than two orders of magnitude compared to when a film was formed using a substrate without a pattern mask. [Industrial Applicability]

[0066] The crystalline oxide film of the present invention can be used in a wide range of fields, including semiconductors (e.g., compound semiconductor electronic devices), electronic and electrical equipment components, optical and electrophotographic related devices, and industrial materials, but is particularly useful in semiconductor devices and their components. [Explanation of symbols]

[0067] 1. Crystal substrate 1a Crystal growth plane 2a Convex part 2b Recess 3 Epitaxial layer 4 Mask Layer 5. Buffer layer 19 Film deposition equipment 20 PCB 21 Susceptor 22a Carrier gas supply means 22b Carrier gas (dilution) supply means 23a Flow control valve 23b Flow control valve 24 Mist source 24a Raw material solution 25 Container 25a water 26 Ultrasonic vibrator 27 Supply pipe 28 Heater 29 Exhaust port 30 Deposition chamber 170 Power System 171 Power supply 172 Power supply 173 Control Circuit 180 System Unit 181 Electronic circuit 182 Power System 192 inverter 193 Trans 194 Rectifier MOSFET 195 DCL 196 PWM control circuit 197 Voltage Comparator

Claims

1. A crystalline oxide film comprising laterally grown regions of a corundum structure, wherein the laterally grown regions do not include facet-grown regions.

2. 2. The crystalline oxide film according to claim 1, which contains at least one or more metals from periods 4 to 6 of the periodic table.

3. 3. The crystalline oxide film according to claim 1, which contains at least gallium, indium, rhodium or iridium.

4. α-Ga ２ O ３ 4. The crystalline oxide film according to claim 1, which contains, as a main component, a mixed crystal thereof.

5. A semiconductor device comprising the crystalline oxide film according to any one of claims 1 to 4.

6. 6. The semiconductor device according to claim 5, wherein the crystalline oxide film is a semiconductor film containing a dopant.

7. 7. The semiconductor device according to claim 5, which is a power device.

8. 7. The semiconductor device according to claim 5, which is a power module, an inverter, or a converter.

9. A semiconductor system comprising a semiconductor device, wherein the semiconductor device is the semiconductor device according to any one of claims 5 to 8.

Images