Laminate, semiconductor device using same, and method for producing laminate

Abstract

The present invention is a laminate that includes a crystal substrate, a first crystal layer mainly composed of a first crystalline metal oxide semiconductor formed directly or via another layer on a main surface of the crystal substrate, and a second crystal layer mainly composed of a second crystalline metal oxide semiconductor formed directly or via another layer on the first crystal layer, wherein the laminate is characterized in that the second crystalline metal oxide semiconductor has the same composition as that of the first crystalline metal oxide semiconductor and has a crystal phase different from that of the first crystalline metal oxide semiconductor. Thus, provided are a laminate containing a crystalline metal oxide semiconductor having excellent physical properties and enabling the production of a high-performance semiconductor device and a production method for producing the laminate easily, inexpensively, and stably.

Description

Stacked body, semiconductor device using same, and method for manufacturing stacked body

[0001] The present invention relates to a laminate, a semiconductor device using the same, and a method for manufacturing the laminate.

[0002] As a method for forming a crystalline thin film at low temperature and under atmospheric pressure, a film formation technique using water particles, such as mist CVD, is known. This method has particularly attracted attention because it can form a metastable phase gallium oxide thin film suitable for power semiconductor devices, and recently, the development of the ε (or κ) phase applicable to high-frequency devices has been active. In this case, much research has been done on the crystal that serves as the base of the gallium oxide layer. For example, Non-Patent Document 1 describes ε-GaFeO ３ In addition, Patent Document 1 discloses an example in which an α-(Al ｘ Ga １－ｘ ) ２ O ３ An example using

[0003] Japanese Patent Application Laid-Open No. 2019-46984

[0004] ACS Omega 2020, 5, 29585-29592

[0005] However, the above-mentioned conventional methods have problems such as high production costs due to the expensive substrate itself and complicated processes, and the difficulty in controlling the electrical conductivity of the underlayer reduces the degree of freedom in device design, hindering the development of high performance.

[0006] The present invention has been made to solve the above problems, and aims to provide a low-cost laminate containing a crystalline metal oxide semiconductor that has excellent physical properties that enable the production of high-performance semiconductor devices, and a manufacturing method for easily, low-cost, and stably manufacturing the laminate.

[0007] The present invention has been made to achieve the above-mentioned object, and provides a laminate including a crystalline substrate, a first crystalline layer mainly composed of a first crystalline metal oxide semiconductor formed on a main surface of the crystalline substrate directly or via another layer, and a second crystalline layer mainly composed of a second crystalline metal oxide semiconductor formed on the first crystalline layer directly or via another layer, wherein the second crystalline metal oxide semiconductor has the same composition as the first crystalline metal oxide semiconductor and a different crystalline phase from that of the first crystalline metal oxide semiconductor.

[0008] Such a laminate containing a crystalline metal oxide semiconductor has excellent physical properties that enable the production of a high-performance semiconductor device.

[0009] In this case, the first crystalline metal oxide semiconductor and the second crystalline metal oxide semiconductor may be gallium oxide.

[0010] This results in a stack containing a crystalline metal oxide semiconductor having better physical properties.

[0011] In this case, the first crystalline metal oxide semiconductor may be alpha gallium oxide.

[0012] This results in a laminate containing a crystalline metal oxide semiconductor having even more excellent physical properties.

[0013] In this case, the second crystalline metal oxide semiconductor may be ε-gallium oxide or κ-gallium oxide.

[0014] This makes the laminate even more useful as a semiconductor device.

[0015] In this case, the electrical resistivity of the first crystal layer can be set to 5 Ωcm or less.

[0016] This results in a stack that can realize a semiconductor device with better characteristics.

[0017] In this case, the second crystal layer may have a higher electrical resistivity than the first crystal layer.

[0018] This results in a stack that can realize a semiconductor device with even better characteristics.

[0019] In this case, the other layer provided between the first crystal layer and the second crystal layer may include an intermediate layer.

[0020] This results in a higher quality laminate of the second crystal layer.

[0021] In this case, the crystal substrate may be sapphire.

[0022] This results in a laminate that is less expensive and more suitable for application to semiconductor devices.

[0023] In this case, the semiconductor device may include at least a semiconductor layer and an electrode, and the semiconductor layer may include the first crystal layer and the second crystal layer of the above-mentioned laminate.

[0024] This results in a semiconductor device with excellent electrical characteristics.

[0025] The present invention also provides a method for manufacturing a laminate including a crystalline metal oxide semiconductor, comprising the steps of: heating a crystal substrate; mixing a raw material solution mist containing an atomized metal oxide precursor with a carrier gas to form a first mixture; supplying the first mixture to the crystal substrate to form a first crystal layer mainly composed of a first crystalline metal oxide semiconductor; exposing the surface of the first crystal layer to a surface modification atmosphere to modify the surface; and supplying the first mixture to the crystal substrate with the modified surface of the first crystal layer to form a second crystal layer mainly composed of a second crystalline metal oxide semiconductor having the same composition as the first crystalline metal oxide semiconductor but a different crystalline phase from the first crystalline metal oxide semiconductor.

[0026] According to this method for manufacturing a laminate, a laminate having excellent physical properties suitable for a semiconductor device can be manufactured easily and at low cost.

[0027] In this case, the first crystalline metal oxide semiconductor and the second crystalline metal oxide semiconductor may be made of gallium oxide.

[0028] This makes it possible to easily produce a laminate containing a crystalline metal oxide semiconductor having superior physical properties at low cost.

[0029] In this case, the surface modification atmosphere may be an atmosphere containing any of nitrogen, carbon dioxide, oxygen, ozone, and water vapor.

[0030] This makes it possible to easily and inexpensively manufacture a laminate having excellent physical properties that enable the manufacture of high-performance semiconductor devices.

[0031] In this case, the substrate temperature in the step of modifying the surface of the first crystal layer can be set to a temperature equal to or lower than the substrate temperature in the step of forming the first crystal layer.

[0032] This makes it possible to more stably manufacture a high-quality laminate.

[0033] In this case, the substrate temperature in the step of modifying the surface of the first crystal layer can be set to 20° C. or higher and 500° C. or lower.

[0034] This makes it possible to more stably manufacture high-quality laminates.

[0035] In this case, in the step of forming the first crystal layer, a second mixture formed by mixing a carrier gas with a support agent mist containing an atomized acid solution can be supplied to the crystal substrate.

[0036] This reduces crystal defects in the first crystal layer and improves the quality of the second crystal layer formed thereon, making it possible to manufacture a higher quality stack.

[0037] In this case, in the step of forming the second crystal layer, a second mixture formed by mixing a carrier gas with a support agent mist containing an atomized acid solution can be supplied to the crystal substrate.

[0038] This makes it possible to manufacture a stack having a second crystal layer of higher quality.

[0039] At this time, in the step of forming the first crystal layer and the step of forming the second crystal layer, a second mixture formed by mixing a carrier gas with an assisting agent mist containing an atomized acidic solution can be supplied to the crystal substrate.

[0040] This makes it possible to manufacture a stack having a first crystal layer and a second crystal layer of higher quality.

[0041] In this case, the acidic solution may contain hydrochloric acid.

[0042] This allows a high-quality laminate to be produced more cheaply and stably.

[0043] As described above, the laminate of the present invention provides a low-cost laminate containing a crystalline metal oxide semiconductor with excellent physical properties that enable the production of high-performance semiconductor devices. Furthermore, the method for producing a laminate of the present invention makes it possible to easily, low-cost, and stably produce a high-quality semiconductor laminate that can be used to produce high-performance semiconductor devices.

[0044] Fig. 1 is a diagram showing one embodiment of a stack including a crystalline metal oxide semiconductor according to the present invention. Fig. 2 is a diagram showing another embodiment of a stack including a crystalline metal oxide semiconductor according to the present invention. Fig. 3 is a diagram showing yet another embodiment of a stack including a crystalline metal oxide semiconductor according to the present invention. Fig. 4 is a diagram showing one embodiment of a method for manufacturing a stack including a crystalline metal oxide semiconductor according to the present invention. Fig. 5 is a diagram showing an example of a high electron mobility transistor according to the present invention.

[0045] The present invention will be described in detail below, but the present invention is not limited thereto.

[0046] As described above, there has been a demand for a laminate containing a crystalline metal oxide semiconductor having excellent physical properties that enable the production of high-performance semiconductor devices, and a manufacturing method for easily, inexpensively, and stably manufacturing such a laminate.

[0047] As a result of extensive research into the above-mentioned problems, the inventors have found that a laminate including a crystalline metal oxide semiconductor has excellent physical properties that enable the production of high-performance semiconductor devices, and has completed the present invention. The laminate includes a crystalline substrate, a first crystalline layer formed on a main surface of the crystalline substrate directly or via another layer and containing a first crystalline metal oxide semiconductor as a main component, and a second crystalline layer formed on the first crystalline layer directly or via another layer and containing a second crystalline metal oxide semiconductor as a main component, wherein the second crystalline metal oxide semiconductor has the same composition as the first crystalline metal oxide semiconductor but has a different crystalline phase from that of the first crystalline metal oxide semiconductor.

[0048] The present inventors have also discovered that a method for manufacturing a laminate containing a crystalline metal oxide semiconductor, the method comprising the steps of heating a crystal substrate, mixing a raw material solution mist containing an atomized metal oxide precursor with a carrier gas to form a first mixture, supplying the first mixture to the crystal substrate to form a first crystal layer mainly composed of a first crystalline metal oxide semiconductor, exposing the surface of the first crystal layer to a surface modification atmosphere to modify the surface, and supplying the first mixture to the crystal substrate with the modified surface of the first crystal layer to form a second crystal layer mainly composed of a second crystalline metal oxide semiconductor having the same composition as the first crystalline metal oxide semiconductor but a different crystalline phase from the first crystalline metal oxide semiconductor, enables the above-mentioned laminate to be manufactured easily, at low cost, and has completed the present invention.

[0049] The present invention will be described in detail below with reference to FIGS. 1, 2 and 3, but the present invention is not limited thereto.

[0050] One embodiment of a stack containing a crystalline metal oxide semiconductor (hereinafter, sometimes simply referred to as a stack) of the present invention is shown in Figure 1. As shown in Figure 1, a stack 100 containing a crystalline metal oxide semiconductor basically includes a crystalline substrate 101, a first crystalline layer 102, and a second crystalline layer 103.

[0051] Another embodiment of the stacked structure including the crystalline metal oxide semiconductor of the present invention is shown in Fig. 2. As shown in Fig. 2, the stacked structure 200 including the crystalline metal oxide semiconductor basically includes a crystalline substrate 201, a first crystalline layer 202, and a second crystalline layer 203, and includes a buffer layer 204 between the crystalline substrate 201 and the first crystalline layer 202.

[0052] Another embodiment of the stacked structure including the crystalline metal oxide semiconductor of the present invention is shown in Fig. 3. As shown in Fig. 3, the stacked structure 300 including the crystalline metal oxide semiconductor basically includes a crystalline substrate 301, a first crystalline layer 302, and a second crystalline layer 303, with a buffer layer 304 between the crystalline substrate 301 and the first crystalline layer 302 and an intermediate layer 305 between the first crystalline layer 302 and the second crystalline layer 303.

[0053] [Substrate] The crystalline substrates 101, 201, and 301 are not particularly limited as long as they contain a crystalline substance as a main component, and may be any known substrate. The shape of the substrate is not particularly limited, and may be circular, elliptical, or polygonal. They may be conductive substrates, semiconductor substrates, single-crystal substrates, or polycrystalline substrates, but are preferably, for example, sapphire substrates, which are high-quality and inexpensive.

[0054] Examples of sapphire substrates include c-plane sapphire substrates, m-plane sapphire substrates, a-plane sapphire substrates, and r-plane sapphire substrates. The sapphire substrate may have an off-axis angle. The off-axis angle is not particularly limited, but is preferably 0° to 15°. The thickness of the crystal substrate is not particularly limited, but is preferably about 200 to 800 μm from the viewpoint of cost.

[0055] [First Crystalline Layer] The first crystal layer 102, 202, 302 contains a crystalline metal oxide as a main component, and the crystalline metal oxide may have the crystalline structure that constitutes the crystalline substrate 101, 201, 301, and more preferably has the same crystalline structure as the crystalline substrate 101, 201, 301 and is single-oriented.

[0056] The crystalline metal oxide may be the same as or different from the main component of the crystalline substrates 101, 201, and 301.

[0057] The crystalline metal oxide may be a single metal oxide or a mixed crystal containing multiple metal elements, specifically, an oxide containing any of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium.

[0058] The crystal structure of the first crystal layers 102, 202, and 302 is not particularly limited and may have various crystal structures, but in the present invention, a corundum-type crystal is preferable. ２ O ３ , Ti ２ O ３ , V ２ O ３ , Cr ２ O ３ , Fe ２ O ３ , Ga ２ O ３ , Rh ２ O ３ , In ２ O ３ , Ir ２ O ３ The crystalline metal oxide has a structure such that, when two of the above metal elements are A and B, (A ｘ B １－ｘ ) ２ O ３ Binary metal oxides represented by (0≦x≦1), or when three of the above metal elements are A, B, and C, (A ｘ B ｙ C １－ｘ－ｙ ) ２ O ３ (0≦x≦1, 0≦y≦1) These metal oxides can have a corundum structure, and therefore the first crystal layers 102, 202, and 302 may have a corundum structure.

[0059] The crystalline metal oxide is gallium oxide (Ga ２ O ３ ), more preferably α-Ga ２ O ３ This results in a laminate containing a crystalline metal oxide semiconductor with better physical properties. ２ O３ has a crystalline phase having a peak at least near 2θ=40.3° in X-ray diffraction measurement.

[0060] In the present invention, the term "main component" means that the crystalline metal oxide is contained in an atomic ratio higher than any other component of the crystalline layer, preferably at 50% or more, and may be 100%. The above ratio can be quantified by known methods such as secondary ion mass spectrometry and X-ray fluorescence spectrometry.

[0061] The thickness of the first crystal layers 102, 202, 302 is determined appropriately depending on the design of the intended semiconductor device, but the lower limit can be set to 1 nm.

[0062] Although FIG. 1 shows a configuration in which the first crystal layer 102 is formed directly on the crystal substrate 101, the present invention is not limited to this, and the first crystal layer 102 may be formed via another layer. For example, in cases where it is desirable to avoid the formation of defects due to crystal lattice mismatch between the crystal substrate and the first crystal layer, the first crystal layer 202 may be formed via, for example, a buffer layer 204, as shown in FIG.

[0063] In this case, it is preferable that the lattice constant of the buffer layer 204 changes continuously or stepwise in the growth direction of the buffer layer 204 from a value close to or the same as the lattice constant of the substrate 201 to a value close to or the same as the lattice constant of the first crystal layer 202. For example, ２ O ３ α-Ga on the substrate ２ O ３ When crystalline regions of (Al ｘ Ga １－ｘ ) ２ O ３ (0≦x≦1), where the x value decreases from the substrate 201 side toward the first crystal layer 202 side. Alternatively, the film may be a superlattice structure film in which films of different compositions are alternately stacked.

[0064] The buffer layer 204 may be a sacrificial layer for peeling the stack from the substrate, and in this case, the buffer layer 204 may have, for example, different optical properties than the first crystal layer 202, lower mechanical fragility, or solubility in a specific chemical solution.

[0065] The first crystal layers 102, 202, and 302 may be conductive. In this case, the first crystal layers 102, 202, and 302 may be doped with impurities to impart conductivity. For example, when the first crystal layers 102, 202, and 302 contain at least gallium, the impurities may include n-type dopants such as silicon, germanium, tin, magnesium, titanium, zirconium, vanadium, and niobium, or p-type dopants such as iron, copper, silver, cobalt, iridium, rhodium, magnesium, and nickel. The electrical resistivity imparted to the first crystal layers 102, 202, and 302 by doping with impurities depends on the design of the intended semiconductor device, but is preferably 5 Ω·cm or less, and more preferably 1 Ω·cm or less, for example, in the case of a high electron mobility transistor described below. The lower limit is not particularly limited, but can be 0.01 Ω·cm. This results in a stack that can realize a semiconductor device with superior characteristics.

[0066] [Second Crystalline Layer] The crystalline metal oxide semiconductor that is the main component of the second crystal layers 103, 203, and 303 has the same composition but a different crystalline phase from the crystalline metal oxide semiconductor that is the main component of the first crystal layers 102, 202, and 302. Such a stacked body can be a stacked body containing a crystalline metal oxide semiconductor that has excellent physical properties that enable the manufacture of a high-performance semiconductor device.

[0067] The crystalline metal oxide semiconductor that is the main component of the second crystalline layers 103, 203, and 303 is preferably gallium oxide. ２ O ３ In this case, the crystalline metal oxide semiconductor that is the main component of the second crystalline layer 103, 203, 303 is preferably β-Ga ２ O ３ , ε (or κ)-Ga ２ O ３ In the present invention, more preferably ε (or κ)-Ga ２ O ３ This results in a stacked body including a crystalline metal oxide semiconductor having better physical properties.

[0068] The ε phase and the κ phase are not clearly classified at present due to their structural similarity, but here they refer to crystalline phases that have a peak at least near 2θ = 38.9° in X-ray diffraction measurement.

[0069] The second crystalline layers 103, 203, 303 may contain a part of amorphous material, or may be partly or entirely polycrystalline, but are preferably entirely single-crystal or uniaxially oriented films oriented in one crystal axis.

[0070] The above describes a configuration in which the second crystal layers 103, 203 are formed directly on the first crystal layers 102, 202, but the present invention is not limited to this. As shown in Figure 3, the second crystal layer 303 may be formed on the first crystal layer 302 via another layer (intermediate layer 305).

[0071] The intermediate layer 305 may be a crystalline or amorphous layer, or a mixture of these, containing the constituent elements of the first crystalline layer 302. The intermediate layer 305 may also be a layer containing an element that terminates the surface of the first crystalline layer 302, and specifically may contain any of hydrogen, oxygen, carbon, nitrogen, chlorine, bromine, and iodine, and may be a layer of about one atomic layer or several atomic layers.

[0072] The formation of such an intermediate layer 305 is believed to prevent the extension of dislocation defects in the first crystal layer 302, resulting in a higher quality second crystal layer 303. The dislocation defects and their density can be evaluated by known methods such as the TEM method and the etch-pit method.

[0073] The second crystal layer 103, 203, 303 may be conductive. In this case, impurities for imparting conductivity may be added to the second crystal layer 103, 203, 303. When the second crystal layer 103, 203, 303 contains gallium oxide, the impurities may include n-type dopants such as silicon, germanium, tin, magnesium, titanium, zirconium, vanadium, or niobium, or p-type dopants such as iron, copper, silver, cobalt, iridium, rhodium, magnesium, or nickel.

[0074] The electrical resistivity imparted to the second crystal layer 103, 203, 303 by doping with impurities depends on the design of the target semiconductor device, but for example, in a high electron mobility transistor described later, it is preferable that the electrical resistivity is higher than that of the first crystal layer, and is 5 Ω cm or more, more preferably 10 Ω cm or more. This results in a stack that can realize a semiconductor device with even better characteristics.

[0075] The electrical resistance or carrier density of the film alone and the laminate can be evaluated by known methods such as the four-probe method, spreading resistance method, eddy current method, scanning capacitance microscopy, and scanning microwave microscopy.

[0076] [Semiconductor Device Comprising the Laminate of the Present Invention] The laminate of the present invention containing the crystalline metal oxide semiconductor has excellent electrical properties and is industrially useful. Such a laminate containing the crystalline metal oxide semiconductor is useful for semiconductor devices, particularly power devices.

[0077] In the semiconductor device of the present invention, the crystalline metal oxide semiconductor film may be formed as is, or may be formed as a film peeled from a substrate or the like by known means. When used after peeling, the peeled film can be used by transferring it onto a support substrate, for example. In this case, the peeled film and the support substrate can be fixed by known bonding techniques, for example, by using an adhesive or pressure-sensitive adhesive, or by bonding via a surface activated by plasma treatment.

[0078] The support substrate is not particularly limited as long as it can support the release film without any problems in the process after the bonding, and a wide variety of substrates can be used, including ceramic, glass, metal, semiconductor, and resin substrates.

[0079] The laminate containing the crystalline metal oxide semiconductor of the present invention can be classified into a horizontal element (horizontal device) in which an electrode is formed on one side of the semiconductor layer, and a vertical element (vertical device) in which an electrode is formed on both the front and back sides of the semiconductor layer. The present invention is suitable for both horizontal and vertical devices, but is particularly suitable for lateral devices. Specifically, it is suitable for use in, for example, high electron mobility transistors (HEMTs).

[0080] Hereinafter, preferred examples in which the semiconductor film containing the crystalline metal oxide of the present invention is applied to an n-type semiconductor layer (such as an n+ type semiconductor or an n- type semiconductor layer) will be described with reference to the drawings, but the present invention is not limited to these examples. Note that the semiconductor devices exemplified below may further include other layers (such as an insulator layer, a semi-insulator layer, a conductor layer, a semiconductor layer, or other intermediate layers), and buffer layers may be omitted as appropriate.

[0081] 5 shows an example of a HEMT to which a stacked layer including a crystalline metal oxide semiconductor according to the present invention is applied. The HEMT 500 includes an n-type semiconductor layer (electron supply layer) 501 having a wide band gap, an n-type semiconductor layer (electron transit layer) 502 having a narrow band gap, and an n-type semiconductor layer (electron conduction layer) 503 having a narrow band gap. ＋ The device includes a semiconductor layer 503 , a support substrate 504 , a buffer layer 505 , a gate electrode 506 , a source electrode 507 and a drain electrode 508 .

[0082] The wide bandgap n-type semiconductor layer (electron supply layer) 501 corresponds to the first crystal layer in the present invention, and the narrow bandgap n-type semiconductor layer (electron transit layer) 502 corresponds to the second crystal layer in the present invention. In this case, it is preferable that a two-dimensional electron gas is formed inside the narrow bandgap n-type semiconductor layer (electron transit layer) 502, and for this purpose, it is preferable that the resistivity of the narrow bandgap n-type semiconductor layer (electron transit layer) 502 is at least higher than that of the wide bandgap n-type semiconductor layer (electron supply layer) 501.

[0083] Examples of materials for each electrode include metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium, and Ag, and alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene, and polypyrrole; and mixtures thereof.

[0084] The method for forming the electrode film is not particularly limited, and the electrode is formed on the substrate according to a method appropriately selected from wet methods such as printing, spraying, and coating; physical methods such as vacuum deposition, sputtering, and ion plating; and chemical methods such as CVD and plasma CVD, taking into consideration the suitability for the material.

[0085] As described above, a semiconductor device including the first and second crystalline layers of the laminate containing the crystalline metal oxide semiconductor of the present invention is a semiconductor device with excellent electrical characteristics.

[0086] [Method for Producing Laminate] Hereinafter, an example of a method for producing the laminate of the present invention (embodiment of FIG. 1) will be described with reference to FIG. 4, but the present invention is not limited thereto.

[0087] The method for producing a laminate of the present invention basically uses a mist CVD apparatus 400 .

[0088] [Step of Heating the Crystal Substrate] The crystal substrate 404 is heated by a heat source 407 in a film-forming chamber 406. The temperature of the crystal substrate 404 is appropriately optimized depending on the raw materials used and the target formation. ２ O ３ When forming the crystal, it is generally preferable to set the temperature at 300° C. or higher and 600° C. or lower. If the temperature is 300° C. or higher, it is expected that the crystal will be more crystalline than amorphous, and if the temperature is 600° C. or lower, the metastable phase can be maintained more stably.

[0089] [Step of forming first gas mixture] The film-forming raw material solution 421 is misted in the atomizer 402a. The type of raw material solution 421 is not particularly limited as long as it can be misted, and a solution in which a metal is dissolved or dispersed in the form of a complex or salt in an organic solvent or water can be used.

[0090] The metal may be any metal capable of forming a semiconductor, and examples of such metals include aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium. The content of the metal in the raw material solution is not particularly limited, but is preferably 0.001 mol / L to 50 mol / L, and more preferably 0.01 mol / L to 5 mol / L.

[0091] Examples of the salt form include halide salts such as metal chlorides, metal bromides, and metal iodides. Furthermore, the above metals can also be used as salt solutions in which they are dissolved in hydrogen halides such as hydrochloric acid, hydrobromic acid, and hydroiodic acid.

[0092] Examples of the form of the complex include an acetylacetone complex, a carbonyl complex, an ammine complex, a hydride complex, etc. An acetylacetonate complex can also be formed by mixing acetylacetone with the above salt solution.

[0093] The crystalline metal oxide semiconductor that is the main component of the first and second crystal layers is preferably gallium oxide, which makes it possible to easily manufacture a stack including the crystalline metal oxide semiconductor with superior physical properties.

[0094] The impurity raw material when doping to impart conductivity to at least a portion of the first crystal layer is not particularly limited, but for example, when the metal contains at least gallium, examples include n-type dopants such as silicon, germanium, tin, magnesium, titanium, zirconium, vanadium, or niobium, or p-type dopants such as iron, copper, silver, cobalt, iridium, rhodium, magnesium, or nickel. These compounds may be mixed in a raw material solution at 0.001 to 10 atomic percent, more preferably 0.01 to 1 atomic percent.

[0095] The solvent of the raw material solution 421 is not particularly limited, 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, but in the present invention, it is preferable that the solvent is water.

[0096] Next, the valve 411a is opened, and the carrier gas delivered from the carrier gas source 401a is mixed with the mist from the atomizer 402a to form a first mixture 431. The type of carrier gas is not particularly limited, and suitable examples include air, oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. One type of carrier gas may be used, but two or more types may also be used. The flow rate of the carrier gas varies depending on the substrate size and the size of the deposition chamber, but is generally about 0.01 to 40 L / min.

[0097] Although not shown in the figure, a gas similar to the carrier gas may be supplied as a dilution gas, for example, downstream of the atomizer 402a. The dilution gas may be the same as the carrier gas, or a different gas may be used. In this case, the flow rate of the dilution gas varies depending on the film formation conditions, but is generally preferably 0.1 to 10 times the flow rate of the carrier gas per minute.

[0098] [Step of forming first crystal layer] Next, the first gas mixture 431 is transported through the pipe 403a into the film formation chamber 406. The first gas mixture 431 introduced into the film formation chamber 406 reacts with the crystal substrate 404 heated by the heat source 407 in the film formation chamber 406, and a film (first crystal layer) is formed on the crystal substrate 404.

[0099] The shape and material of the film formation chamber 406 are not particularly limited, and metals such as aluminum and stainless steel may be used, or quartz or silicon carbide may be used when film formation is performed at a higher temperature than the heat-resistant temperature of these metals. 405 denotes a susceptor.

[0100] The film formation may be carried out under any of atmospheric pressure, elevated pressure, and reduced pressure, but is preferably carried out under atmospheric pressure from the viewpoint of equipment cost and productivity. The film thickness can be appropriately set by adjusting the film formation time.

[0101] In this step, the supporting agent mist obtained by atomizing the acid solution may be mixed with the raw material solution mist and supplied to the crystal substrate 404 placed in the film formation chamber 406 through the pipe 403b. In this case, the atomizer 402b may be filled with the acid solution 422, and the mist obtained by atomizing the acid solution 422 may be mixed with the carrier gas sent out from the carrier gas source 401b to form the second gas mixture 432, which may be supplied to the film formation chamber together with the first gas mixture 431.

[0102] The acid solution 422 may be hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, hydrofluoric acid, an aqueous solution of ammonium fluoride, hydrogen peroxide, a carboxylic acid, or a mixture thereof, but preferably contains hydrochloric acid from the viewpoint of production cost and process stability. By using hydrochloric acid, a high-quality laminate can be produced more inexpensively and stably.

[0103] The type of solvent for the acid solution 422 is not particularly limited, 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, but water is preferred in the present invention. The concentration of the acid in this case is determined appropriately depending on the film formation conditions, but can generally be 0.01 mol / L to 2 mol / L.

[0104] The type of carrier gas mixed into the second gas mixture 432 is not particularly limited, and suitable examples include air, oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. The carrier gas used may be the same as or different from the carrier gas mixed into the first gas mixture 431. The flow rate of the second gas mixture 432 may be adjusted appropriately depending on the desired film and its film formation conditions, but it is generally preferable that the molar ratio of the second gas mixture 432 be 2 to 50 times the molar ratio of the metal elements in the first gas mixture.

[0105] Such an assisting agent has the effect of suppressing the occurrence and growth (abnormal growth) of crystals of a crystal phase different from the desired crystal on the surface of the growing film, or stabilizing the crystal growth of the desired crystal phase, thereby enabling the stable formation of a high-quality first crystal layer.

[0106] 4, the first gas mixture 431 and the second gas mixture 432 are supplied independently to the film formation chamber 406, but the present invention is not limited to this, and the first gas mixture 431 and the second gas mixture 432 may be mixed before entering the film formation chamber 406 and then supplied to the film formation chamber 406. In this case, although not shown in the figure, for example, mist may be supplied to the film formation chamber via a mist mixing container for mixing and stirring the first gas mixture and the second gas mixture.

[0107] Film formation is stopped by stopping the supply of first gas mixture 431 after a predetermined time has elapsed since the start of supply of first gas mixture 431. The method for stopping the supply of first gas mixture 431 is not particularly limited, and the supply of first gas mixture 431 may be stopped simply by stopping the atomization of the raw material, by closing valve 411a while continuing the atomization of the raw material and stopping the supply of carrier gas from carrier gas source 401a, or by both stopping the atomization of the raw material and closing valve 411a.

[0108] [Surface modification step] Next, valve 411c is opened and the surface modification gas sent from surface modification gas source 401c is supplied to crystal substrate 404 placed in film formation chamber 406 through pipe 403c, and the surface of the first crystal layer is maintained in an atmosphere of surface modification gas to perform a modification process on the surface of the first crystal layer.

[0109] The surface modification gas preferably contains at least one of nitrogen, carbon dioxide, oxygen, ozone, and water vapor, or may be air, which makes it possible to easily produce a laminate having excellent physical properties that enable the production of high-performance semiconductor devices.

[0110] This step may be performed while the crystal substrate 404 remains in the film formation chamber, or the crystal substrate 404 may be transferred to another container not shown in the figure, or to an open atmosphere, particularly when the surface modification gas is atmospheric air, and then processed.

[0111] When the crystal substrate 404 is placed in a container for surface treatment, the container may be sealed after replacing the atmosphere in the container with a surface-modifying gas, or the surface-modifying gas may be introduced continuously or intermittently. In this case, it is sufficient that the surface of the first crystal layer is sufficiently exposed to the atmosphere of the surface-modifying gas. Therefore, the flow rate of the surface-modifying gas may be determined appropriately depending on the volume of the container or space in which the surface-modifying treatment is performed and the size of the substrate. However, particularly when the surface-modifying treatment is performed in a container, it is preferable to set the flow rate of the surface-modifying gas to about 2 to 10 times the volume of the container per minute.

[0112] In addition, the temperature of the crystal substrate 404 at this time is generally preferably set to be equal to or lower than the substrate temperature during the formation of the first crystal layer, and more preferably between 20° C. and 500° C. By exposing the crystal substrate 404 to an atmosphere of the surface-modifying gas at such a temperature, molecules derived from the surface-modifying gas can be efficiently fixed to the surface of the first crystal layer.

[0113] The surface state of the first crystal layer at this time varies depending on the substrate temperature, the surface modifying gas, and the mixing conditions of the acid solution mist described below. The surface state of the first crystal layer may disappear when the second crystal layer is formed, or may remain on the first crystal layer as an intermediate layer. For example, the α-Ga ２ O ３ When an intermediate layer is formed on the surface, a mixture of ozone or oxygen and hydrochloric acid mist is preferably used as the surface modifying gas.

[0114] The processing time for surface modification is appropriately determined depending on the type of the first crystal layer, the type of the second crystal layer, and the conditions of the gas and acidic mist used for surface modification, and is not particularly limited, but from the viewpoint of productivity, it can be, for example, several tens of minutes to several days.

[0115] The above describes an example of a form in which the surface of a growing film is modified using only the above gas, but the present invention is not limited to this. The second mixture 432 may be used instead of the surface modification gas, or a mixture of the second support agent mist atomized by an atomizer (not shown) and the surface modification gas may be supplied to the crystal substrate 404.

[0116] For the second support agent mist, hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, hydrofluoric acid, ammonium fluoride aqueous solution, hydrogen peroxide solution, carboxylic acid, or a mixture thereof can be used, but from the viewpoint of production cost and process stability, it is more preferable to use hydrochloric acid.

[0117] The type of solvent for these acid solutions is not particularly limited, 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, but water is preferred in the present invention. The concentration of the acid in this case is determined appropriately depending on the film formation conditions, but can generally be 0.01 mol / L to 2 mol / L.

[0118] The surface modifying gas and the supporting agent mist may be supplied under the same conditions throughout this step, or the gas type, solution type, or their mixing ratio may be changed during the step.

[0119] After a predetermined processing time has elapsed, the valve 411c is closed to stop the supply of the surface modifying gas.

[0120] [Step of forming second crystalline layer] Next, the second crystalline layer is formed. Valve 411a is opened, and carrier gas delivered from carrier gas source 401a is mixed with the raw material mist from atomizer 402a to form first gas mixture 431, which is then supplied to deposition chamber 406. The raw material solution 421 at this time may be prepared under the same conditions as those used to form the first crystalline layer, or may be different within the range of conditions described above as applicable raw material solutions, but must have the same composition as the first crystalline layer.

[0121] The composition and flow rate of the carrier gas may be the same as or different from those used when forming the first crystal layer. For example, in addition to air, oxygen, and ozone, inert gases such as nitrogen and argon, or reducing gases such as hydrogen gas and forming gas are preferably used. One type of carrier gas may be used, but two or more types may also be used. The flow rate of the carrier gas varies depending on the substrate size and the size of the deposition chamber, but can be approximately 0.01 to 40 L / min.

[0122] The impurity raw material used when doping to impart conductivity to at least a portion of the second crystal layer is not particularly limited, but when the raw material solution contains at least gallium, examples thereof include n-type dopants such as silicon, germanium, tin, magnesium, titanium, zirconium, vanadium, and niobium, and p-type dopants such as iron, copper, silver, cobalt, iridium, rhodium, magnesium, and nickel. These compounds may be mixed into the raw material solution at 0.0001 to 0.1 atomic percent, more preferably 0.0001 to 0.01 atomic percent.

[0123] Furthermore, by opening the valve 411 b , the carrier gas delivered from the carrier gas source 401 b can be mixed with the support agent mist from the atomizer 402 b to form a second mixture 432 , which can be supplied to the film formation chamber 406 .

[0124] The second gas mixture 432 may be a gas mixture containing a support agent mist obtained by misting the acid solution 422. That is, the second gas mixture 432 may be a gas mixture formed by mixing a carrier gas with the mist obtained by atomizing the acid solution 422. The acid solution 422 may be hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, carboxylic acid, or a mixture thereof, but from the viewpoints of production cost and process stability, it is more preferable to use hydrochloric acid.

[0125] The type of solvent for the acid solution 422 is not particularly limited, 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, but water is preferred in the present invention. The concentration of the acid at this time is determined appropriately depending on the film formation conditions, but can generally be 0.01 mol / L to 2 mol / L.

[0126] The type of carrier gas mixed into the second gas mixture 432 is not particularly limited, and suitable examples include air, oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. The carrier gas used may be the same as or different from the carrier gas mixed into the first gas mixture 431. The flow rate of the second gas mixture 432 may be adjusted appropriately depending on the desired film and its film formation conditions, but it is generally preferable that the molar ratio of the second gas mixture 432 be 2 to 50 times the molar ratio of the metal elements in the first gas mixture.

[0127] Such an assisting agent has the effect of suppressing the occurrence and growth (abnormal growth) of crystals of a crystal phase different from the desired crystal on the surface of the growing film, or stabilizing the crystal growth of the desired crystal phase, thereby enabling the stable formation of a high-quality second crystal layer.

[0128] Furthermore, it is preferable to supply such an assisting agent mist to the crystal substrate 404 in both the step of forming the first crystal layer and the step of forming the second crystal layer, thereby enabling the manufacture of a laminate having a first crystal layer and a second crystal layer of even higher quality.

[0129] The first gas mixture 431 and the second gas mixture 432 introduced into the film formation chamber 406 react with the crystal substrate 404 heated by the heat source 407 in the film formation chamber 406, and a second crystal layer is formed on the first crystal layer.

[0130] The temperature of the crystal substrate 404 is optimized as appropriate depending on the raw material used and the intended product, but when forming a metastable crystalline phase of, for example, gallium oxide in the second crystalline layer, it is generally best to set the temperature at 300° C. or higher and 600° C. or lower. If the temperature is 300° C. or higher, it is expected that more crystals will be produced than amorphous, and if the temperature is 600° C. or lower, the metastable phase can be maintained more stably.

[0131] At this time, the second crystalline layer has a different crystalline phase from the first crystalline layer, which is thought to be due to the interaction between the molecules attached to the surface of the first crystalline layer by the surface modification treatment and the molecules originating from the mist contained in the mixed gas, which promotes nucleation of the second crystalline layer. In contrast, the intermediate layer is thought to be in a state where at least a part of it is bonded to the surface of the first crystalline layer by the surface modification treatment.

[0132] The deposition chamber 406 for forming the second crystalline layer may be the same as or different from that used for forming the first crystalline layer. In the latter case, the shape and material of the deposition chamber 406 are not particularly limited, and metals such as aluminum and stainless steel may be used. In the case of deposition at higher temperatures exceeding the heat resistance temperatures of these metals, quartz or silicon carbide may also be used.

[0133] The film formation may be carried out under any of atmospheric pressure, elevated pressure, and reduced pressure, but is preferably carried out under atmospheric pressure from the viewpoint of equipment cost and productivity. The film thickness can be appropriately set by adjusting the film formation time.

[0134] Film formation is stopped by stopping the supply of raw material mist after a predetermined time has elapsed since the start of supply of first gas mixture 431. The method for stopping the supply of raw material mist is not particularly limited, and may be achieved by simply stopping the atomization of the raw material, by closing valves 411a and 411b while continuing the atomization of the raw material and stopping the supply of carrier gas from carrier gas sources 401a and 401b, or by both stopping the atomization of the raw material and closing valves 411a and 411b.

[0135] According to this method for manufacturing a laminate, a high-performance laminate suitable for a semiconductor device can be manufactured easily, at low cost, and stably.

[0136] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0137] Example 1 [Step of Heating Crystal Substrate and Step of Forming First Gas Mixture] A laminate according to the present invention was produced using a mist CVD apparatus similar to that shown in Figure 4. Two quartz atomizers (atomizer 402a, atomizer 402b) and a quartz film-forming chamber were prepared. Compressed dry air was used as the surface modification gas. The compressed dry air supply source and the atomizers 402a and 402b were connected to the film-forming chamber via quartz piping.

[0138] Next, hydrochloric acid was added at a ratio of 0.2 mol / L to a 0.05 mol / L aqueous solution of gallium acetylacetonate, and the mixture was stirred for 60 minutes using a stirrer to obtain a raw material solution. This precursor was then filled into the atomizer 402a. Hydrochloric acid was mixed with pure water at a ratio of 0.6 mol / L and filled into the atomizer 402b.

[0139] Next, a c-plane sapphire substrate having a diameter of 10 cm and a thickness of 0.65 mm was placed on a susceptor installed in the film formation chamber and heated to a substrate temperature of 450°C.

[0140] Next, ultrasonic vibrations were propagated through the water to the precursors in the atomizers 402a and 402b by a 2.4 MHz ultrasonic vibrator, thereby atomizing (misting) the precursors. Nitrogen gas was added to the atomizer 402a at a flow rate of 5 L / min to form a mixture of the atomized raw material solution and nitrogen gas (first mixture).

[0141] [Step of forming a first crystalline layer] The obtained first mixture was supplied to the film formation chamber. Dry air was added to the atomizer 402b at a flow rate of 5 L / min, and a mixture of atomized hydrochloric acid (support agent mist) and dry air was supplied simultaneously with the first mixture. After supplying the mixture for 20 minutes, atomization by the atomizers 402a and 402b was stopped, and all gas supplies were stopped.

[0142] [Surface Modification Step] Next, the substrate was removed from the film formation chamber and cooled to about room temperature, and then transferred to a thermostatic chamber, which was then purged with dry air and left at 30° C. for 30 minutes.

[0143] [Step of Forming Second Crystalline Layer] After that, the substrate was taken out of the thermostatic chamber and placed on the susceptor again installed in the film formation chamber, and heated to a substrate temperature of 450°C.

[0144] Next, ultrasonic vibrations were propagated through the water by a 2.4 MHz ultrasonic vibrator to the precursors in the atomizers 402a and 402b, atomizing the raw material solution.

[0145] Next, nitrogen gas was added to the atomizer 402a at a flow rate of 10 L / min, and a mixture of the atomized raw material solution and nitrogen gas (first mixture) was supplied to the film formation chamber. Dry air was added to the atomizer 402b at a flow rate of 5 L / min, and a mixture of the atomized hydrochloric acid (support agent mist) and dry air was supplied simultaneously with the first mixture. After the mixture was supplied for 60 minutes, atomization by the atomizers 402a and 402b was stopped, and all gas supplies were stopped.

[0146] The heating of the substrate was stopped, and the substrate was cooled to about room temperature, and then removed from the film formation chamber.

[0147] [Evaluation] The formed laminate showed peaks at 2θ=38.9° and 40.3° in 2θ / ω scan by X-ray diffraction using CuKα radiation, and was therefore determined to be ε-Ga ２ O ３ and α-Ga ２ O ３ Furthermore, EBSD analysis of the cross section revealed that the substrate was composed of α-Ga. ２ O ３ is formed, and ε-Ga is further formed on it. ２ O ３ From the cross-sectional observation of the laminate, it was found that the thickness of each layer was α-Ga ２ O ３ is about 200 nm, ε-Ga ２ O ３ was about 1200 nm.

[0148] Next, the dislocation density of the laminated film was evaluated by quantification using a TEM method using a sample obtained by cutting a longitudinal section of the laminated film into a thin slice having a thickness of 100 nm.

[0149] (Example 2) Film formation was performed in the same manner as in Example 1, except that the support agent mist formed by the atomizer 402b was not used in the step of forming the second crystalline layer (a mixture of hydrochloric acid mist and dry air was not supplied).

[0150] The formed laminate showed peaks at 2θ=38.9° and 40.3° in X-ray diffraction measurement, indicating that it was ε-Ga ２ O ３ and α-Ga ２ O ３Furthermore, EBSD analysis of the cross section revealed that the substrate was composed of α-Ga. ２ O ３ is formed, and ε-Ga is further formed on it. ２ O ３ From the cross-sectional observation of the laminate, it was found that the thickness of each layer was α-Ga ２ O ３ is about 200 nm, ε-Ga ２ O ３ Next, in the same manner as in Example 1, the dislocation densities of the first and second crystal layers were evaluated.

[0151] (Example 3) Film formation was performed in the same manner as in Example 1, except that the support agent mist formed by the atomizer 402b was not used in the step of forming the first crystal layer (a mixture of hydrochloric acid mist and dry air was not supplied).

[0152] The formed laminate showed peaks at 2θ=38.9° and 40.3° in X-ray diffraction measurement, indicating that it was ε-Ga ２ O ３ and α-Ga ２ O ３ Furthermore, EBSD analysis of the cross section revealed that the substrate was composed of α-Ga. ２ O ３ is formed, and ε-Ga is further formed on it. ２ O ３ From the cross-sectional observation of the laminate, it was found that the thickness of each layer was α-Ga ２ O ３ is about 200 nm, ε-Ga ２ O ３ Next, in the same manner as in Example 1, the dislocation densities of the first and second crystal layers were evaluated.

[0153] (Example 4) Film formation was performed in the same manner as in Example 1, except that the support agent mist formed by the atomizer 402b was not used in either the step of forming the first crystal layer or the step of forming the second crystal layer (a mixture of hydrochloric acid mist and dry air was not supplied).

[0154] The formed laminate showed peaks at 2θ=38.9° and 40.3° in X-ray diffraction measurement, indicating that it was ε-Ga ２ O ３ and α-Ga ２ O ３ Furthermore, EBSD analysis of the cross section revealed that the substrate was composed of α-Ga. ２ O ３ is formed, and ε-Ga is further formed on it. ２ O ３ From the cross-sectional observation of the laminate, it was found that the thickness of each layer was α-Ga ２ O ３ is about 200 nm, ε-Ga ２ O ３ Next, in the same manner as in Example 1, the dislocation densities of the first and second crystal layers were evaluated.

[0155] Example 5 After forming the first crystal layer in the same manner as in Example 1, the substrate was held at 450° C. in the film formation chamber.

[0156] Next, a mixed gas obtained by adding 10% by volume of ozone to nitrogen to hydrochloric acid (0.6 mol / L) atomized by the atomizer 402b at a flow rate of 5 L / min was added, and the resulting mixture was supplied to the substrate for 30 minutes to perform surface modification.

[0157] Thereafter, a second crystal layer was formed in the same manner as in Example 1.

[0158] The formed laminate showed peaks at 2θ=38.9° and 40.3° in X-ray diffraction measurement, indicating that it was ε-Ga ２ O ３ and α-Ga ２ O ３ Furthermore, EBSD analysis of the cross section revealed that the substrate was composed of α-Ga. ２ O ３ is formed, and ε-Ga is further formed on it. ２ O ３ From the cross-sectional observation of the laminate, it was found that the thickness of each layer was α-Ga ２ O ３ is about 200 nm, ε-Ga ２ O ３The thickness of the first and second crystal layers was about 1200 nm, and an oxygen-rich intermediate layer having a thickness of 1 to 2 nm was observed between these layers. Next, in the same manner as in Example 1, the dislocation densities of the first and second crystal layers were evaluated.

[0159] Comparative Example Film formation was carried out in the same manner as in Example 1, except that the surface modification treatment was not carried out after the formation of the first crystal layer.

[0160] The formed laminate was found to be α-Ga, as a peak appeared around 2θ=40.3° in X-ray diffraction measurement. ２ O ３ It was confirmed that this is the case.

[0161] (Example 6) As the raw material solution in the step of forming the first crystal layer (electron supply layer), a solution was prepared by adding hydrochloric acid at a ratio of 0.2 mol / L to an aqueous solution of gallium acetylacetonate at a ratio of 0.05 mol / L, stirring the solution with a stirrer for 60 minutes, and then mixing tin (II) chloride dihydrate to obtain a Sn / Ga ratio of 0.1%. Furthermore, as the raw material solution in the step of forming the second crystal layer (electron transit layer), a solution was prepared by adding hydrochloric acid at a ratio of 0.25 mol / L to an aqueous solution of gallium acetylacetonate at a ratio of 0.1 mol / L, stirring the solution with a stirrer for 60 minutes, and then mixing tin (II) chloride dihydrate to obtain a Sn / Ga ratio of 0.001%. Other than these, film formation was performed in the same manner as in Example 1.

[0162] The manufactured laminate showed peaks at 2θ=38.9° and 40.3° in the 2θ / ω scan of the X-ray diffraction method using CuKα radiation, which indicated that it was ε-Ga ２ O ３ and α-Ga ２ O ３ Furthermore, EBSD analysis of the cross section revealed that the substrate was composed of α-Ga. ２ O ３ is formed, and ε-Ga is further formed on it. ２ O ３ From the cross-sectional observation of the laminate, it was found that the thickness of each layer was α-Ga ２ O ３ is about 200 nm, ε-Ga ２ O ３ was about 1200 nm.

[0163] Next, the resistivity of each layer was evaluated by the spreading resistance method, and the resistivity was found to be 0.2 Ω cm for the first crystal layer and 14.2 Ω cm for the second crystal layer. In addition, the dislocation densities of the first and second crystal layers were evaluated in the same manner as in Example 1.

[0164] The results of Examples 1 to 6 and the Comparative Example are shown in Table 1.

[0165] As shown in Table 1, the film forming method of the present invention provided laminates of the same composition but with different crystal phases. Furthermore, the obtained laminates were useful as electronic devices.

[0166] In contrast, in the film formation by the conventional method (comparison example), no phase transition of crystals occurred, and only a film of a single crystal layer was formed.

[0167]

[0168] From the above results, it can be seen that the method for manufacturing a laminate containing a crystalline metal oxide semiconductor of the present invention makes it possible to easily manufacture a high-quality laminate using a low-cost, low-temperature process, which was not possible with conventional techniques.

[0169] This specification includes the following aspects. [1]: A laminate including a crystalline substrate, a first crystalline layer mainly composed of a first crystalline metal oxide semiconductor formed on a main surface of the crystalline substrate directly or via another layer, and a second crystalline layer mainly composed of a second crystalline metal oxide semiconductor formed on the first crystalline layer directly or via another layer, wherein the second crystalline metal oxide semiconductor has the same composition as the first crystalline metal oxide semiconductor and a different crystalline phase from that of the first crystalline metal oxide semiconductor. [2]: The laminate of [1] above, wherein the first crystalline metal oxide semiconductor and the second crystalline metal oxide semiconductor are gallium oxide. [3]: The laminate of [1] or [2] above, wherein the first crystalline metal oxide semiconductor is α-gallium oxide. [4]: ​​The laminate of [1], [2], or [3] above, wherein the second crystalline metal oxide semiconductor is ε-gallium oxide or κ-gallium oxide. [5]: The laminate of [1], [2], [3] or [4] above, wherein the electrical resistivity of the first crystal layer is 5 Ωcm or less. [6]: The laminate of [1], [2], [3], [4] or [5] above, wherein the second crystal layer has a higher electrical resistivity than the first crystal layer. [7]: The laminate of [1], [2], [3], [4], [5] or [6] above, wherein the other layer provided between the first crystal layer and the second crystal layer includes an intermediate layer. [8]: The laminate of [1], [2], [3], [4], [5], [6] or [7] above, wherein the crystal substrate is sapphire. [9]: A semiconductor device including at least a semiconductor layer and an electrode, wherein the semiconductor layer includes the first crystal layer and the second crystal layer of the laminate of [1], [2], [3], [4], [5], [6], [7] or [8].

[10] : A method for manufacturing a laminate including a crystalline metal oxide semiconductor, the method comprising the steps of heating a crystal substrate, mixing a raw material solution mist including an atomized metal oxide precursor with a carrier gas to form a first mixture, supplying the first mixture to the crystal substrate to form a first crystal layer mainly composed of a first crystalline metal oxide semiconductor, exposing the surface of the first crystal layer to a surface-modifying atmosphere to modify the surface, and supplying the first mixture to the crystal substrate with the modified surface of the first crystal layer to form a second crystal layer mainly composed of a second crystalline metal oxide semiconductor having the same composition as the first crystalline metal oxide semiconductor but a different crystalline phase from the first crystalline metal oxide semiconductor.

[11] : A method for manufacturing the laminate according to

[10] , including using gallium oxide as the first crystalline metal oxide semiconductor and the second crystalline metal oxide semiconductor.

[12] : A method for manufacturing the laminate of

[10] or

[11] above, comprising setting the surface modification atmosphere to an atmosphere containing any of nitrogen, carbon dioxide, oxygen, ozone, and water vapor.

[13] : A method for manufacturing the laminate of

[10] ,

[11] , or

[12] above, comprising setting the substrate temperature in the step of surface-modifying the surface of the first crystal layer to a temperature equal to or lower than the substrate temperature in the step of forming the first crystal layer.

[14] : A method for manufacturing the laminate of

[10] ,

[11] ,

[12] , or

[13] above, comprising setting the substrate temperature in the step of surface-modifying the surface of the first crystal layer to 20°C or higher and 500°C or lower.

[15] : A method for manufacturing the laminate of

[10] ,

[11] ,

[12] ,

[13] , or

[14] above, comprising, in the step of forming the first crystal layer, further supplying to the crystal substrate a second mixture formed by mixing a carrier gas with a support agent mist containing an atomized acidic solution.

[16] : A method for manufacturing a laminate according to

[10] ,

[11] ,

[12] ,

[13] ,

[14] or

[15] , which further comprises, in the step of forming the second crystal layer, supplying to the crystal substrate a second mixture formed by mixing a carrier gas with an assisting agent mist containing an atomized acidic solution.

[17] : The method for manufacturing the laminate of

[10] ,

[11] ,

[12] ,

[13] ,

[14] ,

[15] or

[16] , wherein in the step of forming the first crystal layer and the step of forming the second crystal layer, a second mixture formed by mixing a carrier gas with an assisting agent mist containing an atomized acidic solution is supplied to the crystal substrate.

[18] : The method for manufacturing the laminate of

[15] ,

[16] or

[17] , wherein the acidic solution contains hydrochloric acid.

[0170] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention.

Claims

1. A laminate comprising: a crystal substrate; a first crystal layer composed mainly of a first crystalline metal oxide semiconductor formed directly or through another layer on a main surface of the crystal substrate; and a second crystal layer composed mainly of a second crystalline metal oxide semiconductor formed directly or through another layer on the first crystal layer, wherein the second crystalline metal oxide semiconductor has the same composition as the first crystalline metal oxide semiconductor and has a different crystal phase from the first crystalline metal oxide semiconductor.

2. The laminate according to claim 1, wherein the first crystalline metal oxide semiconductor and the second crystalline metal oxide semiconductor are gallium oxide.

3. The laminate according to claim 1, wherein the first crystalline metal oxide semiconductor is alpha gallium oxide.

4. The stack according to claim 1, wherein the second crystalline metal oxide semiconductor is ε-gallium oxide or κ-gallium oxide.

5. The laminate according to claim 1, wherein the electrical resistivity of the first crystal layer is 5 Ωcm or less.

6. The laminate according to claim 1, wherein the second crystal layer has a higher electrical resistivity than the first crystal layer.

7. The laminate according to claim 1, further comprising an intermediate layer as the other layer provided between the first crystal layer and the second crystal layer.

8. The laminate according to claim 1, wherein the crystal substrate is sapphire.

9. A semiconductor device including at least a semiconductor layer and an electrode, the semiconductor layer comprising the first crystal layer and the second crystal layer of a laminate according to any one of claims 1 to 8.

10. A method for manufacturing a laminate including a crystalline metal oxide semiconductor, comprising the steps of: heating a crystal substrate; mixing a raw material solution mist including an atomized metal oxide precursor with a carrier gas to form a first mixture; supplying the first mixture to the crystal substrate to form a first crystal layer mainly composed of a first crystalline metal oxide semiconductor; exposing a surface of the first crystal layer to a surface modification atmosphere to modify the surface; and supplying the first mixture to the crystal substrate with the modified surface of the first crystal layer to form a second crystal layer mainly composed of a second crystalline metal oxide semiconductor having the same composition as the first crystalline metal oxide semiconductor and a different crystal phase from the first crystalline metal oxide semiconductor.

11. The method for producing a laminate according to claim 10, wherein the first crystalline metal oxide semiconductor and the second crystalline metal oxide semiconductor are gallium oxide.

12. The method for producing a laminate according to claim 10, wherein the surface modification atmosphere is an atmosphere containing any one of nitrogen, carbon dioxide, oxygen, ozone, and water vapor.

13. The method for manufacturing a laminate according to claim 10, wherein the substrate temperature in the step of modifying the surface of the first crystal layer is set to a temperature equal to or lower than the substrate temperature in the step of forming the first crystal layer.

14. The method for producing a laminate according to claim 13, wherein the substrate temperature in the step of modifying the surface of the first crystal layer is set to 20° C. or higher and 500° C. or lower.

15. A method for manufacturing a laminate as described in claim 10, characterized in that in the step of forming the first crystal layer, a second mixture formed by mixing a carrier gas with an assistant mist containing an atomized acidic solution is further supplied to the crystal substrate.

16. A method for manufacturing a laminate as described in claim 10, characterized in that in the step of forming the second crystal layer, a second mixture formed by mixing a carrier gas with an assistant mist containing an atomized acidic solution is supplied to the crystal substrate.

17. A method for manufacturing a laminate as described in claim 10, characterized in that in the step of forming the first crystal layer and the step of forming the second crystal layer, a second mixture formed by mixing a carrier gas with an assistant mist containing an atomized acidic solution is further supplied to the crystal substrate.

18. The method for producing a laminate according to any one of claims 15, 16 and 17, characterized in that the acidic solution contains hydrochloric acid.

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