Film formation method

Abstract

To provide a film formation method having excellent mass productivity.SOLUTION: The present disclosure provides a film formation method which uses at least one of a metal complex having two or more different ligands and a metal complex having same ligands and substituents.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for forming a thin film. [Background technology]

[0002] Thin films of metal oxides as insulators, metal oxides as conductors, and metal oxides as semiconductors (also called oxide semiconductors) are used in a variety of products, including semiconductor devices. In particular, semiconductor devices using gallium oxide (Ga2O3), which has a large bandgap, are attracting attention as next-generation switching elements that can achieve high voltage resistance, low loss, and high heat resistance, and are expected to be applied to power semiconductor devices such as inverters. Moreover, due to its wide bandgap, it is also expected to be applied to light-emitting and light-receiving devices such as LEDs and sensors.

[0003] In recent years, gallium oxide-based p-type semiconductors have been studied. For example, Patent Document 1 describes that when a β-Ga2O3-based crystal is formed by the FZ method using MgO (a p-type dopant source), a substrate exhibiting p-type conductivity can be obtained. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-340308 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a film deposition method that offers excellent mass productivity. [Means for solving the problem]

[0006] To solve the above problems, in one embodiment of the present invention, the film formation method uses at least one of a metal complex having two or more different ligands and a metal complex having the same ligand and substituent.

Advantages of the Invention

[0007] The film-forming method of the present invention is excellent in mass productivity.

Brief Description of the Drawings

[0008] [Figure 1] FIG. 1 is a schematic configuration diagram of a film-forming apparatus (mist CVD apparatus) used in the examples.

Embodiments for Carrying Out the Invention

[0009] The film-forming method of the present invention is a method for forming a metal film on a substrate, particularly a method for forming a metal oxide film. More specifically, it is characterized in that a metal complex or an aqueous solution of a metal complex is used for forming the metal oxide film. More specifically, for example, it is a method for forming a metal oxide film by using a solution in which a metal complex is dissolved and each film-forming method of an atomization method (mist CVD method) and a coating method. The film-forming method of the present invention is excellent in mass productivity. In this specification, "excellent in mass productivity" means that the time required to form a film with a desired thickness is short.

[0010] The metal complex or the aqueous solution of a metal complex used in the film-forming method of the present invention will be described below. In this specification, "metal complex" means a compound containing a central metal and a ligand coordinated to the central metal.

[0011] The metal complex used in the film-forming method of the present invention is at least one of a metal complex having two or more different ligands and a metal complex having the same ligand and a substituent. Although not wishing to be construed in a limiting sense, the above metal complex has a specific ligand or substituent, so that its solubility in a solution (especially water) is higher than that of a conventional metal complex. As a result, the concentration of the solution used for film formation can be relatively increased, and thus it is considered to be excellent in mass productivity.

[0012] In the present invention, the valence of the central metal in the metal complex is not particularly limited as long as it does not inhibit the object of the present invention, and it may be monovalent, divalent, trivalent, or tetravalent. In the present invention, it is preferable that the central metal contains a d-block metal of the periodic table or a Group 13 metal of the periodic table, and it is more preferable that it contains a Group 9 metal or a Group 13 metal of the periodic table.

[0013] Note that the "periodic table" means the periodic table defined by the International Union of Pure and Applied Chemistry (IUPAC). "d-block" refers to elements having electrons filling the 3d, 4d, 5d, and 6d orbitals.

[0014] The "Group 9 metal" may be any Group 9 metal of the periodic table. Examples of such Group 9 metals include iridium (Ir), cobalt (Co), rhodium (Rh), or two or more of these metals. The "Group 13 metal" is not particularly limited as long as it is a Group 13 metal of the periodic table. Examples of Group 13 metals include aluminum (Al), gallium (Ga), indium (In), thallium (Tl), or two or more of these metals. In the present invention, one or more selected from aluminum (Al), gallium (Ga), and indium (In) are preferable.

[0015] Specifically, as the central metal, a metal selected from 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), tantalum (Ta), zinc (Zn), lead (Pb), rhenium (Re), titanium (Ti), tin (Sn), magnesium (Mg), calcium (Ca), arsenic (As), germanium (Ge), and zirconium (Zr) can be used.

[0016] From the viewpoint of reactivity and availability, gallium (Ga), iridium (Ir), indium (In), and rhodium (Rh) are particularly preferred, and iridium (Ir) is especially preferred due to its solubility in aqueous solutions.

[0017] In the present invention, a metal complex can be used in which two or more different ligands are selected from the group consisting of acetylacetonate-derived ligands, ligands having a heterocyclic structure, and ligands represented by the following formula (1), and at least one of the metal complexes represented by the following formula (2) can be used in which the same ligand and substituent is present.

[0018] [ka]

[0019] In equation (1) above, the dotted line represents a coordinate bond, *1 indicates the coordinate bond position with the metal, and *2 indicates the bonding position with the metal. 1 and R 2 Each of these independently represents an alkyl group having 1 to 6 carbon atoms.

[0020] In equation (2) above, R 3 and R 4 Each of these independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, and a tolyl group, R 5 represents a halogen atom, formyl group, acetoxy group, sulfo group, mesyl group, nitro group, nitroso group, phosphoryl group, or an alkyl group having 1 to 6 carbon atoms. X represents the central metal.

[0021] Examples of ligands having a heterocyclic structure include pyridine, 2-methylpyridine, 2,4,6-trimethylpyridine, 4-dimethylaminopyridine, 2,6-lutidine, pyrimidine, pyridazine, pyrazine, oxazole, isoxazole, thiazole, isothiazole, imidazole, 1,2-dimethylimidazole, 3-(dimethylamino)propylimidazole, pyrazole, furazan, pyrazine, quinoline, isoquinoline, purine, 1H-indazole, quinazoline, sinnoline, quinoxaline, phthalazine, and pteridine. Examples include phenanthridine, 2,6-di-t-butylpyridine, 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridyl, 4,4'-dimethyl-2,2'-bipyridyl, 5,5'-dimethyl-2,2'-bipyridyl, 6,6'-t-butyl-2,2'-dipyridyl, 4,4'-diphenyl-2,2'-bipyridyl, 1,10-phenanthroline, 2,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline.

[0022] The metal complex used in the present invention exhibits high solubility in aqueous solutions while also showing excellent thermal stability. Furthermore, aqueous solutions containing such metal complexes do not precipitate during long-term storage, thus demonstrating high quality stability.

[0023] In particular, metal complexes having the ligand shown in formula (1) above can be obtained by reacting a metal halide such as iridium trichloride with acetylacetonate in the presence of a water-soluble basic compound, such as ammonia or trimethylammonium hydride (TMAH).

[0024] Furthermore, it is preferable that the pH of the aqueous solution containing the metal complex is in the range of 4.0 to 7.5. If the pH of the aqueous solution is less than 6, ligand exchange of the metal complex occurs, reducing its solubility in the aqueous solution and tending to increase the amount of metal compound precipitated. If the pH of the aqueous solution is greater than 7.5, the formation of a thin film from the aqueous solution containing the metal complex tends to be poor.

[0025] Furthermore, it is preferable that the aqueous solution containing the metal complex of the present invention is substantially free of organic solvents. This is because the presence of organic solvents lowers the flash point, leading to restrictions on the location and method of use.

[0026] If an organic solvent is included, preferred organic solvents are those that are miscible with water, such as methanol, ethanol, and isopropyl alcohol. The amount of organic solvent used is 10% by mass or less of the total solvent amount in the aqueous solution, and more preferably 5% by mass or less.

[0027] In particular, the aforementioned metal is preferably iridium (Ir), and is a metal complex represented by the following formula (3) or formula (4).

[0028] [ka]

[0029] In the above equation (4), R 5 This group consists of a halogen atom, a C1 to C6 alkyl group, a formyl group, an acetoxy group, a sulfo group, a mesyl group, a nitro group, a nitroso group, and a phosphoryl group. Of these, the chlorine atom is particularly preferred from the viewpoint of the stability of the compound during synthesis.

[0030] The metal complex represented by formula (3) above is synthesized by alkaline treatment of iridium trichloride in an aqueous solution. It has been confirmed that compounds represented by formulas (3-1) and (4-1) below are also included as metal complexes other than formula (3). Therefore, the aqueous solution of the metal complex used in the present invention also contains at least one of the metal complexes of formula (3-1) or (4-1) below.

[0031] [ka]

[0032] The metal complex of the present invention may have a countercation in an aqueous solution. Examples of these countercations include hydrogen ions and ammonium ions, with ammonium ions being particularly preferred. Ammonium ions become the counterions of the metal complex through neutralization using an alkaline aqueous solution such as ammonia water during the synthesis of the metal complex. When neutralization is performed using an acidic aqueous solution such as hydrochloric acid, hydrogen ions become the counterions.

[0033] Examples of metal complexes containing such countercations include those represented by the following formulas (3-2) or (4-2).

[0034] [ka]

[0035] Next, a film formation method using the metal complex of the present invention will be described. Examples of film formation methods include atomization (mist CVD method) and coating method.

[0036] <Atomization method (mist CVD method)> The atomization method (mist CVD method) uses, for example, the film deposition apparatus shown in Figure 1. The atomization method (mist CVD method) comprises, for example, a step of atomizing or dropletizing a liquid containing the metal complex (atomization / dropletization step), a step of transporting the obtained mist or droplets to a substrate using a carrier gas (transportation step), and a step of forming a metal oxide film on the substrate by thermally reacting the mist or droplets near the substrate (film deposition step). According to the mist CVD method, a metal oxide film with excellent semiconductor properties and surface smoothness can be obtained.

[0037] (Atomization / dropletization process) In the atomization / droplet formation process, the liquid (raw material solution) containing the metal complex is atomized or dropletized. The atomization or droplet formation means for the raw material solution is not particularly limited as long as it can atomize or dropletize the raw material solution, and any known means may be used. However, in the present invention, an atomization or droplet formation means using ultrasound is preferred. The mist or droplets obtained using ultrasound are preferred because they have zero initial velocity and float in the air. For example, they are very suitable because they can be transported as a gas floating in space rather than being sprayed like a spray, so there is no damage due to collision energy. The mist particle size or droplet size is not particularly limited and may be several millimeters in size, but is preferably 50 μm or less, and more preferably 100 nm to 10 μm.

[0038] (Raw material solution) The raw material solution contains at least one metal complex having two or more different ligands and a metal complex having the same ligand and substituent, and is not particularly limited as long as it can be atomized or dropletized, and may contain inorganic materials or organic materials. In the present invention, the raw material solution may contain metal in the form of a complex other than the metal complex or in the form of a salt. Examples of other complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, hydride complexes, etc. Examples of salt forms include organometallic salts (e.g., metal acetates, metal oxalates, metal citric acids, etc.), metal sulfide salts, metal nitrate salts, metal phosphorylated salts, metal halide salts (e.g., metal chloride salts, metal bromide salts, metal iodide salts, etc.).

[0039] In addition, it is preferable to mix additives such as hydrohalic acids and oxidants into the raw material solution. Examples of the hydrohalic acid include hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. Among them, hydrobromic acid or hydrochloric acid is preferable, and hydrochloric acid is particularly preferable because a higher-quality film can be obtained. Examples of the oxidant include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), benzoyl peroxide ((C6H5CO)2O2), hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, organic acid oxides such as peracetic acid and nitrobenzene, etc. The content ratio of hydrochloric acid in the raw material solution when the additive is hydrochloric acid is preferably 1 to 20% by mass, and more preferably 3 to 10% by mass.

[0040] The raw material solution may contain a dopant. By including a dopant in the metal complex aqueous solution, doping can be performed well. The dopant is not particularly limited as long as it does not inhibit the object of the present invention. Examples of the dopant include p-type dopants such as Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, P, etc. The concentration of the dopant is usually about 1×10 16 / cm 3 ~1×10 22 / cm 3 and it may be such, or the concentration of the dopant may be made, for example, a low concentration of about 1×10 17 / cm 3 or less. Further, in the present invention, the dopant may be contained at a high concentration of about 1×10 20 / cm 3 or more.

[0041] The solvent of the raw material solution 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, it is preferable that the solvent contains water, more preferably water or a mixed solvent of water and alcohol, and even more preferably water.

[0042] (Conveying process) In the transport process, the mist or droplets obtained in the atomization / dropletization process are transported to the substrate using a carrier gas. The type of carrier gas is not particularly limited as long as it does not hinder the objective of the present invention. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, or reducing gases such as hydrogen gas and foaming gas, but oxygen gas and / or ozone gas are particularly preferred. There may be one type of carrier gas, or there may be two or more types, and a dilution gas with a changed carrier gas concentration (e.g., a 10-fold dilution gas) may be used as a second carrier gas. There may also be two or more locations for supplying the carrier gas, not just one. The flow rate of the carrier gas is not particularly limited, but is preferably 0.01 L / min to 20 L / min, and more preferably 0.1 to 10 L / min.

[0043] The substrate is not particularly limited as long as it can support the metal film, but it is preferable that it has a corundum structure. The material of the substrate may be a known substrate, and may be an organic compound or an inorganic compound. Suitable examples of substrate materials include sapphire, α-type gallium oxide, and other metal oxides having a corundum structure. It is preferable that at least a portion of the substrate, including the crystal growth surface, contains gallium as the main component. "Main component" means that, in terms of atomic ratio, it is preferably present in 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the substrate, and may be 100%.

[0044] The shape of the substrate can be any shape and is effective for any shape, such as a flat plate or disc (hereinafter also referred to as "substrate"), a fibrous shape, a rod shape, a cylindrical shape, a prismatic shape, a tubular shape, a spiral shape, a spherical shape, a ring shape, etc., but in the present invention, a substrate is preferred. The thickness of the substrate is not particularly limited in the present invention.

[0045] A substrate having a corundum structure is preferred as the substrate. Specifically, examples include a sapphire substrate and an α-type gallium oxide substrate. Here, the main surface of the substrate is preferably a surface inclined from the c-plane, and more preferably the m-plane.

[0046] (Film forming process) In the film formation process, the mist or droplets transported in the transport process are subjected to a thermal reaction near the substrate to form a metal oxide film on the substrate. The metal oxide film is formed by the formation of metal oxide crystals or mixed crystals through the thermal reaction. The upper limit of the thermal reaction temperature is preferably 900°C or less, and more preferably less than 600°C. In the film formation method of the present invention, a metal oxide film can be formed even at a relatively low temperature of less than 600°C. Furthermore, the film formation process may be carried out under any atmosphere, such as vacuum, non-oxygen atmosphere, reducing gas atmosphere, or oxidizing atmosphere, as long as it does not hinder the objective of the present invention, and may also be carried out under any conditions, such as atmospheric pressure, pressurized pressure, or reduced pressure. However, in the present invention, it is preferable to carry out the process under an oxidizing atmosphere, preferably under atmospheric pressure, and more preferably under both an oxidizing atmosphere and atmospheric pressure. The term "oxidizing atmosphere" is not particularly limited as long as it is an atmosphere in which metal oxide crystals or mixed crystals can be formed, and is acceptable as long as oxygen or an oxygen-containing compound is present. For example, an atmosphere containing 1% or more oxygen in an inert gas, or the use of an oxygen-containing carrier gas or an oxidizing agent can be considered an oxidizing atmosphere. The film thickness can be set by adjusting the film formation time. In the present invention, the film thickness is preferably 50 nm or more, more preferably 100 nm or more, and most preferably 1.0 μm or more. There is no particular upper limit to the film thickness, but it is preferably 1 mm, and more preferably 100 μm. In addition, in the present invention, the metal complex may be subjected to this process with a p-type dopant included, and the metal oxide having the corundum structure may be p-doped. Examples of the p-type dopant include Mg, H, Li, Na, K, Rb, Cs, Fr, Be, Ca, Sr, Ba, Ra, Mn, Fe, Co, Ni, Pd, Cu, Ag, Au, Zn, Cd, Hg, Tl, Pb, N, P, and two or more of these elements. In the present invention, the p-type dopant is preferably a Group 1 or Group 2 metal of the periodic table, more preferably a Group 2 metal, and most preferably magnesium (Mg). Furthermore, in the present invention, the metal oxide film obtained in this step may be annealed.

[0047] <Application Method> The coating method involves applying a liquid containing a metal complex onto a substrate and drying it to form a metal oxide film.

[0048] The liquid containing the metal complex (coating solution) is the main compound raw material for forming a metal oxide film on the substrate. The content of the metal complex in the liquid is preferably in the range of 1 to 30% by mass, and more preferably 5 to 20% by mass. If the content is higher than 30% by mass, the metal complex is more likely to precipitate, which can reduce the stability of the coating solution, or the resulting metal oxide film may become too thick, leading to cracking.

[0049] If necessary, a small amount of one or more of the following may be added to the coating solution: an organotin compound, an organotin compound, or an organozinc compound. Furthermore, an organic binder may be added to the coating solution if necessary. Adding an organic binder improves the wettability to the substrate and simultaneously adjusts the viscosity of the coating solution. The organic binder is preferably made of a material that burns or decomposes during heat treatment, and cellulose derivatives, acrylic resins, etc., are effective such materials.

[0050] Examples of cellulose derivatives used in organic binders include methylcellulose, ethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, ethylhydroxyethylcellulose, carboxymethylcellulose, carboxyethylcellulose, carboxyethylmethylcellulose, and nitrocellulose. Among these, hydroxypropylcellulose (hereinafter sometimes referred to as "HPC") is preferred.

[0051] Furthermore, many types of the above-mentioned cellulose derivatives and acrylic resins are commercially available with different molecular weights. For example, HPC has high molecular weight, medium molecular weight, and low molecular weight types, and the higher the molecular weight, the higher the viscosity of the metal complex aqueous solution containing the metal complex blended as a binder. The selection of the molecular weight type and the determination of the blending amount need to be optimized as needed, depending on the applicability of the coating solution, the coating method, and the coating film thickness.

[0052] Using the above-mentioned HPC, sufficient wettability can usually be obtained with a content of 5% by mass or less, while simultaneously allowing for significant viscosity adjustment. Furthermore, since the combustion start temperature of HPC is around 300°C, combustion occurs when the heat treatment is performed at a heating temperature of 300°C or higher, preferably 350°C or higher. This does not inhibit the grain growth of the generated conductive particles, and a metal oxide film with good conductivity can be produced. If the HPC content exceeds 5% by mass, it tends to become gel-like and remain in the coating liquid, forming an extremely porous metal film, which severely impairs transparency and conductivity.

[0053] Here, if ethylcellulose is used as a cellulose derivative, for example, instead of HPC, the viscosity of the coating solution can usually be set lower than when HPC is used. However, in screen printing methods and the like, where a high viscosity coating solution is preferred, the pattern printability is slightly reduced.

[0054] The solvent of the coating solution 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, it is preferable that the solvent contains water, more preferably that it is water or a mixed solvent of water and alcohol, and even more preferably that it is water.

[0055] The aforementioned coating solution may contain organic solvents other than the water and alcohol mentioned above. The solvent added to lower the viscosity of the coating solution or improve its applicability should be compatible with solutions containing various organometallic compounds and cellulose derivatives or acrylic resins. Other solvents include, for example, ketone solvents such as acetone, methyl ethyl ketone (MEK), methyl propyl ketone, methyl isobutyl ketone (MIBK), cyclohexanone, and isophorone; ethyl acetate, butyl acetate, amyl formate, isoamyl acetate, butyl propionate, isopropyl butyrate, ethyl butyrate, butyl butyrate, methyl lactate, and ethyl lactate. Methyl oxyacetate, ethyl oxyacetate, butyl oxyacetate, methyl methoxyacetate, ethyl methoxyacetate, butyl methoxyacetate, methyl ethoxyacetate, ethyl ethoxyacetate, methyl 3-oxypropionate, ethyl 3-oxypropionate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, methyl 2-oxypropionate, ethyl 2-oxypropionate, propyl 2-oxypropionate, methyl 2-methoxypropionate, methyl 2-methyl 2-meth Ester solvents such as ethyl xypropionate, propyl 2-methoxypropionate, methyl 2-ethoxypropionate, ethyl 2-ethoxypropionate, methyl 2-oxy-2-methylpropionate, ethyl 2-oxy-2-methylpropionate, methyl 2-methoxy-2-methylpropionate, ethyl 2-ethoxy-2-methylpropionate, methyl pyruvate, ethyl pyruvate, propyl pyruvate, methyl acetoacetate, ethyl acetoacetate, methyl 2-oxobutanoate, ethyl 2-oxobutanoate, and ethylene glycol mono Methyl ether (MCS), ethylene glycol monoethyl ether (ECS), ethylene glycol isopropyl ether (IPC), ethylene glycol monobutyl ether (BCS), ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol methyl ether (PGM), propylene glycol ethyl ether (PE), propylene glycol methyl ether acetate (PGM-AC), propylene glycol ethyl ether acetate (PE-AC),Examples of glycol derivatives include, but are not limited to, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, and dipropylene glycol monobutyl ether; benzene derivatives such as toluene, xylene, mesitylene, and dodecylbenzene; formamide (FA), N-methylformamide, dimethylformamide (DMF), dimethylacetamide, dimethyl sulfoxide (DMSO); ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butylene glycol, pentamethylene glycol, 1,3-octylene glycol, tetrahydrofuran (THF), chloroform, mineral spirits, terpineol, and several mixtures thereof.

[0056] The viscosity of the coating solution can be adjusted according to the molecular weight and content of the organic binder and the type of solvent, so it can be adjusted to a viscosity suitable for various coating methods such as inkjet printing, screen printing, gravure printing, offset printing, flexographic printing, dispenser printing, slit coating, die coating, doctor blade coating, wire bar coating, spin coating, and spray coating.

[0057] High-viscosity coating solutions (approximately 5,000 to 50,000 mPa·s) can be prepared by including 5% by mass or less, preferably 2 to 4% by mass, of a high-molecular-weight organic binder. Low-viscosity solutions (approximately 5 to 500 mPa·s) can be prepared by including 5% by mass or less, preferably 0.1 to 2% by mass, of a low-molecular-weight organic binder and diluting it with a low-viscosity diluent. Medium-viscosity coating solutions (500 to 5,000 mPa·s) can be prepared by mixing a high-viscosity coating solution with a low-viscosity coating solution.

[0058] The coating method comprises, more specifically, a step of applying the coating liquid onto a substrate to form a coating film (coating step), a step of drying the coating film to form a dried coating film (drying step), and a step of heat-treating the dried coating film in an oxygen-containing atmosphere with a low dew point temperature to form an inorganic film (heat treatment step).

[0059] Various methods for coating onto a substrate include inkjet printing, screen printing, gravure printing, offset printing, flexographic printing, dispenser printing, slit coating, die coating, doctor blade coating, wire bar coating, spin coating, and spray coating.

[0060] These coatings should preferably be applied in a clean environment with controlled temperature and humidity, such as a cleanroom. Typical temperatures are room temperature (around 25°C) and humidity between 40-60% RH.

[0061] The aforementioned substrate is described in the section on atomization (mist CVD method) above.

[0062] In the drying process, the substrate coated with the coating solution is usually held in the air at 80 to 180°C for 1 to 30 minutes, preferably 2 to 10 minutes, to dry the coating film and produce a dried coating film.

[0063] The drying conditions (drying temperature, drying time) can be appropriately selected depending on the type of substrate used, the coating thickness, etc., and are not limited to the above drying conditions. However, considering productivity, it is desirable to shorten the drying time to the minimum necessary so as not to deteriorate the quality of the resulting dried coating film.

[0064] Furthermore, the drying temperature must be below the heat resistance temperature of the substrate used. For example, with the PEN film mentioned above, the temperature needs to be set to around 200°C or lower (depending on the drying time). If necessary, vacuum drying (ultimate pressure: usually 1 kPa or less) can be used instead of air drying. In vacuum drying, the applied solvent is forcibly removed under reduced pressure, allowing for drying at lower temperatures compared to air drying. This is useful when using substrates made of materials with poor heat resistance or solvent resistance.

[0065] The prepared dried coating film is obtained by volatilizing and removing the aforementioned organic solvent from the coating solution, and is composed of organic components such as the above-mentioned organometallic compounds (organoindium compounds, organotin compounds, and organozinc compounds, which may be added in small amounts as needed), and organic binders.

[0066] In the heat treatment process, the dried coating film prepared in the drying process is heat-treated in an oxygen-containing atmosphere with a low dew point temperature. The organometallic compounds in the dried coating film, or the organometallic compounds including a small amount of added organometallic compounds, and organic components such as organic binders are mineralized by thermal decomposition and combustion (oxidation), forming a dense inorganic film (a metal oxide film as a layer of densely packed metal oxide nanoparticles) consisting mainly of inorganic components (metal oxides).

[0067] In other words, as the heating temperature increases during the heating process, the organometallic compounds in the dried coating film (including those containing small amounts of organometallic compounds) are gradually thermally decomposed and burned (oxidized), first resulting in a conversion to an amorphous state (here, this refers to a state of very fine particles with a crystallite size of less than 3 nm, as determined by X-ray diffraction), known as mineralization. Subsequently, if the heating temperature rises further and exceeds the usual range of 300-330°C, or if the heating time is extended even if the temperature remains within the 300-330°C range, crystallization of the metal oxide occurs, and further crystal growth occurs to form metal oxide nanoparticles, which become the final components of the metal oxide film.

[0068] It should be noted that the temperature range of 300-330°C represents a general temperature range in which the above-mentioned mineralization and crystallization are likely to occur. For example, if the heating time is long, mineralization, crystallization, and crystal growth of the above-mentioned metal oxide may occur even at around 270°C. Therefore, the heating temperature in the heat treatment process of the present invention is not limited to 300°C or higher.

[0069] Similarly, organic binders also gradually undergo thermal decomposition and combustion (oxidation) during the heating process, but are mainly converted into carbon dioxide (CO2) and volatilize into the atmosphere, disappearing from the film (depending on the type of organic binder, for example, the aforementioned HPC almost disappears at around 300-350°C), so ultimately almost none remains in the metal oxide film. It should be noted that a large amount of organic binder remains in the initial stages of the heating process (for example, at a certain stage in the heating process, when heating from room temperature to 300°C), and the organic binder is uniformly interposed between the amorphous metal oxides, suppressing crystallization. However, as the heating process progresses further, the organic binder component gradually disappears, and it is thought that crystallization of the metal oxide occurs.

[0070] The heat treatment process will be explained in more detail below.

[0071] In the heat treatment process of the dried coating film of the present invention, by first applying an oxygen-containing atmosphere with a low dew point temperature, i.e., a low water vapor content, to the atmosphere during the heating process, the crystallization of metal oxides due to mineralization that occurs in the initial stages of the heat treatment process as described above, as well as crystal growth, are suppressed, and a film structure of the metal oxide nanoparticle layer of the present invention, in which metal oxide nanoparticles are densely packed, can be obtained. The mechanism by which the metal oxide nanoparticles are densely packed is not entirely clear, but for example, it can be considered as follows.

[0072] In other words, at least until the point in time when crystallization of the metal oxide occurs due to mineralization during the heating process (the initial stage of the heating process; usually around 300-330°C in this invention), the film structure in which the organic binder is uniformly interposed between the amorphous metal oxides is maintained. This film structure has flexibility due to the action of the organic binder, which is an organic substance, and allows the film to shrink (densify) perpendicular to the substrate. Therefore, when the heating process is carried out by raising the temperature in an air atmosphere with a low dew point temperature, it is presumed that the crystallization of the metal oxide is suppressed up to the heating temperature just before the organic binder disappears (up to about 300-350°C), allowing the above-mentioned shrinkable film structure to be obtained, which leads to film densification.

[0073] <Metal oxide film> The metal oxide film obtained by the above preferred formation method is industrially useful and has excellent electrical properties. More specifically, the mobility is typically 1.0 cm². 2 The mobility is greater than or equal to / V·s. The mobility refers to the mobility obtained by Hall effect measurement, and in this invention, the mobility is 3.0 cm 2 It is preferable that the carrier density of the metal oxide film is 8.0 × 10⁻¹⁰. 20 / cm 3 It is also preferable that the above is true. Here, the carrier density refers to the carrier density in the semiconductor film obtained by Hall effect measurement. The lower limit of the carrier density is not particularly limited, but is approximately 1.0 × 10⁻⁶. 15 / cm 3 The above is preferable, approximately 1.0 × 10 17 / cm3 The above is more preferable. In the present invention, by adjusting the type and amount of dopant or the material and content of the mixed crystal, the carrier density can be increased to 1.0 × 10⁻⁶. 16 / cm 3 ~1.0×10 20 / cm 3 It can be easily controlled within that range.

[0074] Furthermore, if the metal oxide film contains a mixed crystal, it is also preferable that the metal oxide contains iridium and a Group 2 metal, a Group 9 metal other than iridium, or a Group 13 metal of the periodic table. By using such preferred metal oxides, a band gap of 2.4 eV or more, and even 4.5 eV or more, can be obtained, thus enabling the p-type oxide semiconductor to exhibit a wider band gap and superior electrical properties. The "Group 2 metal" can be any Group 2 metal of the periodic table, and examples of Group 2 metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), or two or more of these metals.

[0075] The metal oxide film obtained as described above can be suitably used as a p-type semiconductor layer using known means. In the present invention, the film may be formed directly on the substrate, or other layers such as a semiconductor layer different from the p-type semiconductor layer (e.g., an n-type semiconductor layer, an n+-type semiconductor layer, an n--type semiconductor layer, etc.), an insulating layer (including a semi-insulating layer), or a buffer layer may be laminated on the substrate, and then the film may be formed on the substrate via the other layers. Examples of semiconductor layers and insulating layers include semiconductor layers and insulating layers containing the Group 13 metal. Suitable examples of buffer layers include semiconductor layers, insulating layers, or conductive layers containing a corundum structure. Examples of semiconductor layers containing a corundum structure include α-Fe2O3, α-Ga2O3, and α-Al2O3. The means for laminating the buffer layer is not particularly limited and may be the same as the means for forming the p-type oxide semiconductor.

[0076] In the present invention, it is preferable to form an n-type semiconductor layer before or after the formation of the p-type semiconductor layer. More specifically, it is preferable that the method for manufacturing the semiconductor device includes a step of stacking at least a p-type semiconductor layer and an n-type semiconductor layer. The means for forming the n-type semiconductor layer are not particularly limited and may be known means, but in the present invention, the mist CVD method is preferred. The n-type semiconductor layer is preferably mainly composed of an oxide semiconductor, and more preferably mainly composed of an oxide semiconductor containing a Group 13 metal of the periodic table (e.g., Al, Ga, In, Tl, etc.). Furthermore, the n-type semiconductor layer is also preferably mainly composed of a crystalline oxide semiconductor, more preferably mainly composed of a crystalline oxide semiconductor containing Ga, and most preferably mainly composed of a crystalline oxide semiconductor having a corundum structure and containing Ga. In addition, in the present invention, it is preferable that the difference in lattice constants between the oxide semiconductor, which is the main component of the n-type semiconductor, and the p-type oxide semiconductor be 1.0% or less, as this allows for the formation of a good pn junction, and more preferably 0.3% or less.

[0077] Here, "lattice constant difference" is defined as the absolute value (%) of the value obtained by subtracting the lattice constant of the p-type oxide semiconductor from the lattice constant of the oxide semiconductor that is the main component of the n-type semiconductor, and then dividing that value by the lattice constant of the p-type oxide semiconductor, multiplying by 100. An example of a case where the lattice constant difference is 1.0% or less is when the p-type oxide semiconductor has a corundum structure, and the oxide semiconductor that is the main component of the n-type semiconductor also has a corundum structure. More preferably, the p-type oxide semiconductor is a single crystal or mixed crystal of Ir2O3, and the oxide semiconductor that is the main component of the n-type semiconductor is a single crystal or mixed crystal of Ga2O3. Note that "main component" means that the oxide semiconductor is preferably present in an atomic ratio of 50% or more, more preferably 70% or more, and even more preferably 90% or more of the total components of the n-type semiconductor layer, and may be 100%. Furthermore, in the present invention, the p-type oxide semiconductor may be a single crystal, a polycrystalline, or the like.

[0078] The metal oxide films obtained by the various metal oxide film formation methods described above can be used as p-type semiconductor layers in semiconductor devices, and are particularly useful in power devices. By using the metal oxide film in a semiconductor device, roughness scattering can be suppressed, and the channel mobility of the semiconductor device can be improved. Semiconductor devices can be classified into horizontal devices, where electrodes are formed on one side of the semiconductor layer, and vertical devices, where electrodes are formed on both the front and back sides of the semiconductor layer. In the present invention, the metal oxide film can be suitably used in both horizontal and vertical devices, but it is especially preferable to use it in vertical devices. Examples of the semiconductor device include Schottky barrier diodes (SBDs), metal-semiconductor field-effect transistors (MESFETs), high electron-mobility transistors (HEMTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), electrostatic induction transistors (SITs), junction field-effect transistors (JFETs), insulated-gate bipolar transistors (IGBTs), and light-emitting diodes. [Examples]

[0079] The present invention will be described in detail below based on examples. The present invention is not limited to these examples.

[0080] [Film deposition by mist CVD method] In this example, film deposition was performed using the mist CVD method.

[0081] (Example 1) 1. Manufacturing equipment Using Figure 1, the mist CVD apparatus (cold wall type) used in the embodiment will be explained. The mist CVD apparatus 1 includes a carrier gas source 2a for supplying carrier gas, a flow control valve 3a for adjusting the flow rate of carrier gas discharged from the carrier gas source 2a, a carrier gas (dilution) source 2b for supplying carrier gas (dilution), a flow control valve 3b for adjusting the flow rate of carrier gas (dilution) discharged from the carrier gas (dilution) source 2b, a mist generation source 4 containing the raw material solution 4a which is a precursor solution, a container 5 into which water 5a is placed, an ultrasonic transducer 6 attached to the bottom of the container 5, a film deposition chamber 7, a supply pipe 9 connecting the mist generation source 4 to the film deposition chamber 7, a hot plate 8 installed in the film deposition chamber 7, and an exhaust port 11 for discharging atomized droplets 4b and exhaust gas after the thermal reaction. A substrate 10 is installed on the hot plate 8.

[0082] 2. Preparation of raw material solution An aqueous solution was prepared by mixing an aqueous solution containing iridium complexes represented by the following formulas (3) and (4) (iridium (Ir) concentration 0.01 mol / L) with hydrochloric acid to a total concentration of 3% by mass, and an aqueous solution of gallium acetylacetonate (gallium (Ga) concentration 0.01 mol / L) with hydrochloric acid to a total concentration of 3% by mass. This mixture was used as the raw material solution.

[0083] [ka]

[0084] 3. Preparation for film deposition The raw material solution 4a obtained in step 2 above was placed in the mist generating source 4. Next, an m-plane sapphire substrate was placed on the hot plate 8 as the substrate 10, and the temperature of the hot plate 8 was increased to raise the substrate 10 to 500°C. Next, the flow control valves 3a and 3b were opened, and carrier gas was supplied into the deposition chamber 7 from the carrier gas source 2a and the carrier gas (dilution) source 2b, which are the carrier gas sources. After the atmosphere in the deposition chamber 7 was sufficiently replaced with carrier gas, the flow rate of the carrier gas was adjusted to 1.0 L / min, and the flow rate of the carrier gas (dilution) was adjusted to 1.0 L / min. Oxygen was used as the carrier gas.

[0085] 4.Membrane formation Next, the ultrasonic transducer 6 was vibrated, and the vibrations were transmitted to the raw material solution 4a through the water 5a, thereby atomizing the raw material solution 4a and generating atomized droplets 4b. These atomized droplets 4b were transported to the deposition chamber 7 by a carrier gas, and under atmospheric pressure and at a temperature of 500°C, the atomized droplets 4b underwent a thermal reaction on the surface of the substrate 10 to form a film on the substrate 10. The deposition time was 60 minutes. The film thickness was 130 nm.

[0086] The film obtained in step 4 above was identified using an X-ray diffraction apparatus, and it was determined to be an α-(Ir,Ga)2O3 film. The ratio of Ir in the metal elements in the film was 9.1%, and the ratio of Ga was 90.9%. The band gap of the film is estimated to be approximately 5.0 eV. The obtained film was subjected to Hall effect measurement to confirm that it is a p-type semiconductor. Furthermore, acceptor concentration evaluation was performed from the CV measurement results, and the carrier density was found to be 1 × 10⁻⁶. 19 (cm -3 ) was the result. Furthermore, the evaluation result for the <Evaluation of Mass Producibility> below was "B".

[0087] (Example 2) A film was obtained in the same manner as in Example 1, except that the iridium (Ir) concentration of the aqueous solution containing the iridium complex shown in formula (3) above was set to 0.03 mol / L. The film thickness was 380 nm. The obtained film was identified using an X-ray diffraction apparatus, and it was determined to be an α-(Ir,Ga)2O3 film. The ratio of Ir to the metal elements in the film was 10.5%, and the ratio of Ga was 89.5%. The band gap of the film was estimated to be approximately 4.9 eV. The obtained film was subjected to Hall effect measurement to confirm that it was a p-type semiconductor. Furthermore, when the acceptor concentration was evaluated from the CV measurement results, the carrier density was found to be similar to that of the film obtained in Example 1. In addition, the evaluation result in the <Evaluation of Mass Producibility> below was "A".

[0088] (Comparative Example 1) In an attempt to carry out the same procedure as in Example 1, except that iridium acetylacetonate was used instead of the iridium complex shown in formulas (3) and (4) below, the iridium acetylacetonate did not dissolve in water, and it was not possible to prepare an aqueous solution of iridium acetylacetonate at the same concentration as in Example 1 (iridium concentration 0.01 mol / L). Therefore, the experiment was carried out with a system at one-tenth the concentration. Specifically, an aqueous solution was prepared by mixing an aqueous solution of iridium acetylacetonate (iridium (Ir) concentration 0.001 mol / L) with hydrochloric acid to a total of 3% by mass, and an aqueous solution of gallium acetylacetonate (gallium (Ga) concentration 0.001 mol / L) with hydrochloric acid to a total of 3% by mass, and this was used as the starting solution. Film deposition was carried out in the same manner as in Example 1, except for the starting solution and film deposition time. When the obtained film was identified using an X-ray diffraction apparatus, the obtained film was found to be an α-(Ir,Ga)2O3 film. The film deposition time was 180 minutes, and the film thickness was 90 nm. Furthermore, the evaluation result for <Evaluation of Mass Producibility> below was "C".

[0089] (Example 3) An aqueous solution was prepared by adding hydrochloric acid to a starting material containing the iridium complex shown in formula (3) above (iridium concentration 0.05 mol / L) and ultrapure water to a total concentration of 3% by mass, and this was used as the starting material solution. Film deposition was carried out in the same manner as in Example 1, except for the starting material solution. The film thickness was 800 nm.

[0090] The film obtained in Example 3 was identified using an X-ray diffraction apparatus, and it was determined to be an α-Ir2O3 film. Hall effect measurements were performed on the obtained film to confirm that it is a p-type semiconductor. Furthermore, the evaluation result in the <Evaluation of Mass Producibility> section below was "A".

[0091] <Evaluation of mass production capabilities> The film deposition progress was evaluated using the mist CVD method over a 60-minute deposition period. A thicker film formed in 60 minutes indicates superior mass productivity. The film thickness of the metal oxide film obtained after the 60-minute deposition reaction was measured using a spectroscopic ellipsometer (SEMILAB, model SE-2000). If the film thickness was in the range of 250 nm or more, it was considered excellent and given an "A" rating. If the film thickness was in the range of over 100 nm and less than 250 nm, it was considered good and given a rating of "B". If the film thickness was in the range of 100 nm or less, the deposition rate was considered poor and was graded "C".

[0092] [Film formation by coating method] In this example, film formation was performed by a coating method.

[0093] (Example 4) 1. Preparation of the coating solution The aqueous solution containing the iridium complex used in Example 1 (iridium concentration 0.01 mol / L) was used as the coating solution.

[0094] 2. Preparation of metal oxide films The above coating solution was spin-coated (1000 rpm × 60 sec) over the entire surface of a sapphire substrate at 25°C and atmospheric pressure, and then dried in air at 150°C for 10 minutes to obtain a dried coating film (film thickness: approximately 300 nm). This coating film was then heat-treated in air at 550°C for 6 hours to obtain a metal oxide film. The evaluation result for the surface roughness of the metal oxide film, as shown below, was "A".

[0095] (Comparative Example 2) A metal oxide film was prepared in the same manner as in Example 4, except that the coating solution used was an aqueous solution containing iridium acetylacetonate (iridium concentration 0.001 mol / L), as used in Comparative Example 1. The evaluation result for the surface roughness of the metal oxide film, as shown below, was "C".

[0096] <Evaluation of surface roughness of metal oxide films> The surface roughness (Ra) of the obtained films was observed using an AFM (Scanning Atomic Force Microscope, Bruker Dimension Fastscan / Icon). The following criteria were used for evaluation. Surface roughness values ​​within the range of 1 nm to less than 3 nm were considered excellent and rated "A". Surface roughness values ​​between 3 nm and less than 5 nm were considered good and rated as "B". If the surface roughness value was in the range of 5 nm or more, the surface roughness was considered poor and was graded "C".

[0097] The results from the examples and comparative examples show that the metal oxide films obtained by the formation method of the present invention are industrially useful because they have excellent film quality, such as surface smoothness and crystallinity, and also have excellent electrical properties, such as mobility.

[0098] <Note> [Section 1] A method for forming a film using a metal complex having two or more different ligands and a metal complex having the same ligand and substituent. [Section 2] The two or more distinct ligands are at least two ligands selected from the group consisting of ligands derived from acetylacetonate, ligands having a heterocyclic structure, and ligands represented by the following formula (1). The method for forming a film according to item 1, wherein the metal complex having the same ligand and substituent is a metal complex represented by the following formula (2). [ka] (In equation (1), the dotted line indicates a coordination bond, *1 indicates the coordination bond position with the metal, and *2 indicates the bonding position with the metal. 1 and R 2 Each of these independently represents an alkyl group having 1 to 6 carbon atoms. In formula (2), R 3 and R 4 Each of these independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a phenyl group, or a tolyl group. 5 (where X represents a halogen atom, formyl group, acetoxy group, sulfo group, mesyl group, nitro group, nitroso group, phosphoryl group, or alkyl group having 1 to 6 carbon atoms. X represents the central metal.) [Section 3] The method for forming a film according to item 2 above, wherein the central metal to which the metal complex having two or more different ligands is coordinated, and the central metal represented by X in the metal complex represented by formula (2), contains a d-block metal or a group 13 metal of the periodic table. [Section 4] The method for forming a film according to item 3, wherein the central metal contains a Group 9 or Group 13 metal of the periodic table. [Section 5] The method for forming a film according to any one of the above items 2 to 4, wherein the central metal is iridium. [Section 6] The method for forming a film according to item 5, wherein the iridium-centered metal complex is a metal complex represented by the following formula (3) or formula (4). [ka] (In formula (4), R 5(This represents a halogen atom, a formyl group, an acetoxy group, a sulfo group, a mesyl group, a nitro group, a nitroso group, a phosphoryl group, or an alkyl group having 1 to 6 carbon atoms.) [Section 7] The method for forming a metal oxide film according to any one of the above items 1 to 6, wherein the metal complex is used as a raw material. [Section 8] The method for forming a film according to item 7 above, wherein the metal oxide film comprises a crystalline oxide semiconductor. [Section 9] The method for forming a film according to any one of the above items 1 to 8, wherein the metal complex is supplied onto a substrate having a corundum structure. [Section 10] The method for forming a film according to item 9 above, wherein at least a portion of the substrate, including the crystal growth surface, contains gallium as the main component. [Section 11] A method for forming a film according to any one of items 1 to 10, comprising the steps of: atomizing or dropletizing a liquid containing the metal complex; transporting the obtained mist or droplets to a substrate with a carrier gas; and causing a thermal reaction of the mist or droplets near the substrate to form a metal oxide film on the substrate. [Section 12] A film-forming method according to any one of items 1 to 10, comprising the step of coating a substrate with a liquid containing the metal complex and drying it to form a metal oxide film on the substrate. [Section 13] The aforementioned metal complex is contained in the liquid raw material, The method for forming a film according to any one of the above items 1 to 12, wherein the raw material further comprises gallium. [Section 14] The aforementioned metal complex is contained in the liquid raw material, The method for forming a film according to any one of the above items 1 to 12, further comprising a p-type dopant as the raw material. [Explanation of symbols]

[0099] 1. Mist CVD apparatus 2a Carrier gas source 2b Carrier gas (dilution) source 3a Flow control valve 3b Flow control valve 4. Mist source 4a Raw material solution 4b Atomized droplets 5 containers 5a water 6. Ultrasonic transducer 7 Deposition chamber 8. Hot plate 9 Supply pipe 10 Base 11 Exhaust vent

Claims

1. A method for forming a film using a metal complex having two or more different ligands and a metal complex having the same ligand and substituent, The two or more distinct ligands are at least two ligands selected from the group consisting of ligands derived from acetylacetonate, ligands having a heterocyclic structure, and ligands represented by the following formula (1). A method for forming a film in which the metal complex having the same ligand and substituent is a metal complex represented by the following formula (2). 【Chemistry 1】 (In equation (1), the dotted line indicates a coordination bond, *1 indicates the coordination bond position with the metal, and *2 indicates the bonding position with the metal. R １ and R ２ Each of these independently represents an alkyl group having 1 to 6 carbon atoms. In formula (2), R ３ and R ４ Each of these independently represents a hydrogen atom, a halogen atom, a C1 to C6 alkyl group, a phenyl group, or a tolyl group. ５ (where X represents a halogen atom, formyl group, acetoxy group, sulfo group, mesyl group, nitro group, nitroso group, phosphoryl group, or C1 to C6 alkyl group. X represents the central metal.)

2. The method for forming a film according to claim 1, wherein the central metal to which the metal complex having two or more different ligands is coordinated, and the central metal represented by X in the metal complex represented by formula (2), contains a d-block metal or a group 13 metal of the periodic table.

3. The method for forming a film according to claim 2, wherein the central metal contains a Group 9 or Group 13 metal of the periodic table.

4. The method for forming a film according to claim 2 or 3, wherein the central metal is iridium.

5. The method for forming a film according to claim 4, wherein the iridium-centered metal complex is a metal complex represented by the following formula (3) or formula (4). 【Chemistry 2】 (In formula (4), R ５ (This represents a halogen atom, a formyl group, an acetoxy group, a sulfo group, a mesyl group, a nitro group, a nitroso group, a phosphoryl group, or an alkyl group having 1 to 6 carbon atoms.)

6. The method for forming a film according to claim 1 or claim 2, wherein a metal oxide film is formed using the aforementioned metal complex as a raw material.

7. The method for forming a film according to claim 6, wherein the metal oxide film includes a crystalline oxide semiconductor.

8. The method for forming a film according to claim 1 or claim 2, wherein the metal complex is supplied onto a substrate having a corundum structure.

9. The method for forming a film according to claim 8, wherein at least a portion of the substrate, including the crystal growth surface, contains gallium as the main component.

10. A method for forming a film according to claim 1 or claim 2, comprising the steps of: atomizing or dropletizing a liquid containing the metal complex; transporting the obtained mist or droplets to a substrate using a carrier gas; and causing a thermal reaction of the mist or droplets near the substrate to form a metal oxide film on the substrate.

11. The method for forming a film according to claim 1 or claim 2, further comprising the step of coating a substrate with a liquid containing the metal complex and drying it to form a metal oxide film on the substrate.

12. The aforementioned metal complex is contained in the liquid raw material, The method for forming a film according to claim 1 or claim 2, wherein the raw material further comprises gallium.

13. The aforementioned metal complex is contained in the liquid raw material, The method for forming a film according to claim 1 or claim 2, wherein the raw material further comprises a p-type dopant.

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