Stacked structure, semiconductor device, and method for forming crystalline oxide film

Abstract

The present invention is a laminated structure that has at least a base substrate and a crystalline oxide film having gallium oxide as the main component, wherein the average reflectance of light at a wavelength of 400-800 nm is 16% or more on the crystalline oxide film side surface of the laminated structure. Thus, provided is a laminated structure that has a crystalline oxide film having gallium oxide as the main component, that has excellent crystallinity with very few crystal defects, and that has excellent semiconductor characteristics when applied to a semiconductor device.

Description

[Technical Field]

[0001] The present invention relates to a layered structure having a base substrate and a crystalline oxide film containing gallium oxide as a main component, a semiconductor device, and a method for forming a crystalline oxide film. [Background technology]

[0002] In recent years, gallium oxide (Ga2O3) has been attracting attention as a semiconductor material. Gallium oxide is known to have five crystal forms: α, β, γ, δ, and ε. Among these, the metastable phase α-Ga2O3 has an extremely large band gap of 5.3 eV, and is attracting attention as a material for power semiconductors.

[0003] For example, Patent Document 1 discloses a semiconductor device including a base substrate having a corundum crystal structure, a semiconductor layer having a corundum crystal structure, and an insulating film having a corundum crystal structure, and describes an example in which an α-Ga2O3 film is formed as a semiconductor layer on a sapphire substrate. Patent Document 2 also discloses a semiconductor device including an n-type semiconductor layer containing a crystalline oxide semiconductor having a corundum crystal structure as a main component, a p-type semiconductor layer containing an inorganic compound having a hexagonal crystal structure as a main component, and an electrode. An example of Patent Document 2 discloses the fabrication of a diode by forming an α-Ga2O3 film having a metastable corundum crystal structure as an n-type semiconductor layer and an α-Rh2O3 film having a hexagonal crystal structure as a p-type semiconductor layer on a c-plane sapphire substrate.

[0004] However, because α-Ga2O3 is a metastable phase, single-crystal substrates have not yet been put to practical use, and it is generally formed by heteroepitaxial growth on sapphire substrates, etc. In such cases, stress is applied to the semiconductor film due to the difference in lattice constant with sapphire, which can lead to the formation of numerous crystal defects or warping of the semiconductor film.

[0005] To reduce crystal defects in α-Ga2O3, a method of forming a buffer layer between sapphire and the α-Ga2O3 layer has been reported. For example, Non-Patent Document 1 describes a method of forming a buffer layer between sapphire and the α-Ga2O3 layer using Al x ,Ga 1-x By introducing the )2O3 layer (x=0.2~0.9), the edge dislocation and screw dislocation were increased to 3×10 8 / cm 2 and 6 x 10 8 / cm 2 An example is given of what is supposed to be the case. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-72533 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-25256 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-157878 [Non-patent literature]

[0007] [Non-Patent Document 1] Riena Jinno et al., Reduction IN edge dislocation density IN corundum-structured α-Ga2O3 layers on sapphire substrates with quasi-graded α-(Al,Ga)2O3 buffer layers, Applied Physics Express, Japan, tHE Japan Society of Applied Physics, June 1, 2016, vol.9, pages 071101-1 to 071101-4 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when crystalline oxide films primarily composed of gallium oxide, such as α-Ga2O3 films, are used in power semiconductors and other devices requiring high breakdown voltages, the breakdown field characteristics are affected by the amount of crystal defects, making further reduction of crystal defects desirable. Furthermore, α-Ga2O3 films can sometimes form mosaic crystals, in which domains with slightly different tilts (inclination of the crystal axis in the growth direction) and twists (rotation of the crystal axis within the surface plane) exist. This is thought to be due in part to the relatively low film formation temperature, resulting from the metastable phase of the α-Ga2O3 layer. However, when used in power semiconductors and other devices, the presence of grain boundaries between domains can degrade the breakdown field characteristics, making it desirable to suppress domain formation. Patent Document 3 discloses that the provision of a quantum well buffer layer reduces the rotational domains in α-Ga2O3 films and improves crystallinity, but the effect is insufficient.

[0009] The present invention has been made to solve the above problems, and aims to provide a stacked structure and a semiconductor device including a crystalline oxide film containing gallium oxide as a main component, which has significantly fewer crystal defects, excellent crystallinity, and excellent semiconductor properties when applied to a semiconductor device, as well as a method for forming the above crystalline oxide film. [Means for solving the problem]

[0010] The present invention has been made to achieve the above-mentioned object, and provides a laminated structure having at least a base substrate and a crystalline oxide film containing gallium oxide as a main component, wherein the average reflectance of the surface of the laminated structure facing the crystalline oxide film is 16% or more for light with a wavelength of 400 to 800 nm.

[0011] The crystalline oxide film constituting such a laminated structure has extremely few crystal defects and is excellent in crystallinity, and when applied to a semiconductor device, it has excellent semiconductor properties.

[0012] In this case, the base substrate may be a single crystal, and the crystalline oxide film may be a single crystal or a uniaxially oriented film, forming a laminate structure.

[0013] This results in a laminated structure having a crystalline oxide film with better crystallinity.

[0014] In this case, the base substrate may be a laminated structure of a sapphire substrate, a lithium tantalate substrate, or a lithium niobate substrate.

[0015] This makes it possible to obtain a laminated structure having a crystalline oxide film with excellent crystallinity industrially and inexpensively.

[0016] In this case, the crystalline oxide film may be a laminated structure having a corundum structure.

[0017] The layered structure according to the present invention is suitable for such a crystalline oxide film having a corundum structure.

[0018] In this case, the crystalline oxide film having the corundum structure may be a laminated structure having an X-ray rocking curve half width of 5 to 20 seconds on the (006) plane.

[0019] As described above, the crystalline oxide film containing gallium oxide as a main component according to the present invention is a layered structure having a crystalline oxide film with superior crystallinity.

[0020] At this time, the surface area of ​​the base substrate having the crystalline oxide film is 100 mm 2 or larger, or a laminated structure having a diameter of 2 inches (50 mm) or larger.

[0021] This results in a laminated structure having a large-area crystalline oxide film with excellent crystallinity.

[0022] The present invention also provides a method for depositing a crystalline oxide film containing gallium oxide as a main component by a mist CVD method, in which a carrier gas containing mist is supplied from a nozzle to a base substrate placed in a deposition chamber, and the deposition is carried out while the temperature of the nozzle or the inner wall of the deposition chamber is kept higher than room temperature.

[0023] This makes it possible to obtain a crystalline oxide film with extremely few crystal defects and excellent crystallinity, which, when applied to a semiconductor device, provides excellent semiconductor properties.

[0024] At this time, the nozzle temperature can be set to 50 to 250°C.

[0025] This makes it possible to obtain a crystalline oxide film with better crystallinity.

[0026] The present invention also provides a semiconductor device comprising a crystalline oxide film containing gallium oxide as a main component as an insulating thin film or a conductive thin film, wherein the average reflectance of the surface on the crystalline oxide film side for light with a wavelength of 400 to 800 nm is 16% or more.

[0027] Such a crystalline oxide film has extremely few crystal defects and is excellent in crystallinity, and can be used as a semiconductor device having excellent semiconductor properties such as a high breakdown voltage. [Effects of the Invention]

[0028] As described above, the stacked structure of the present invention provides a crystalline oxide film with extremely few crystal defects and excellent crystallinity, which, when applied to a semiconductor device, provides excellent semiconductor properties. Furthermore, the method for forming a crystalline oxide film of the present invention provides a crystalline oxide film with extremely few crystal defects and excellent crystallinity, which, when applied to a semiconductor device, provides excellent semiconductor properties. Furthermore, the semiconductor device of the present invention provides a semiconductor device with excellent semiconductor properties, such as a high breakdown voltage. [Brief explanation of the drawings]

[0029] [Figure 1] FIG. 2 is a diagram showing an example of the reflectance spectra of the laminated structures according to Example 1 and Comparative Example 1. [Figure 2] FIG. 10 is a diagram showing an example of a reflectance spectrum of the laminated structure according to Example 2. [Figure 3] FIG. 10 is a diagram showing an example of a reflectance spectrum of a laminated structure according to Example 3. [Figure 4] 1 is a schematic diagram showing an example of a semiconductor device using a stacked structure according to the present invention; [Figure 5] 1 is a schematic diagram showing an example of a film-forming apparatus (mist CVD apparatus) suitably used for forming a film of a laminated structure according to the present invention. [Figure 6] FIG. 2 is a diagram illustrating an example of a mist-forming unit used in the present invention. [Figure 7] FIG. 10 is a diagram showing an example of a reflectance spectrum of a laminated structure according to Example 4. [Figure 8] FIG. 10 is a diagram showing an example of a reflectance spectrum of a laminated structure according to Example 5. [Figure 9] FIG. 10 is a diagram showing an example of a reflectance spectrum of a laminated structure according to Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described in detail below, but the present invention is not limited thereto.

[0031] As described above, there has been a demand for a stacked structure and a semiconductor device including a crystalline oxide film containing gallium oxide as a main component, which has significantly fewer crystal defects, excellent crystallinity, and excellent semiconductor characteristics when applied to a semiconductor device, as well as a method for forming the above crystalline oxide film.

[0032] As a result of extensive research into the above-mentioned problems, the inventors have found that a laminate structure having at least a base substrate and a crystalline oxide film containing gallium oxide as a main component, in which the average reflectance of light having a wavelength of 400 to 800 nm on the surface of the laminate structure facing the crystalline oxide film is 16% or more, results in a crystalline oxide film with significantly fewer crystal defects and excellent crystallinity, and when applied to a semiconductor device, has excellent semiconductor properties, and have completed the present invention.

[0033] The inventors have also discovered that a method for forming a crystalline oxide film containing gallium oxide as a main component by a mist CVD method in which a carrier gas containing mist is supplied from a nozzle to a base substrate placed in a film formation chamber, and film formation is carried out while the temperature of the nozzle or the inner wall of the film formation chamber is kept higher than room temperature, can produce a crystalline oxide film with significantly fewer crystal defects and excellent crystallinity, which will have excellent semiconductor properties when applied to a semiconductor device, and have completed the present invention.

[0034] The present inventors further discovered that a semiconductor device having a crystalline oxide film containing gallium oxide as a main component as an insulating thin film or a conductive thin film, in which the average reflectance of light having a wavelength of 400 to 800 nm on the surface facing the crystalline oxide film is 16% or more, results in a semiconductor device with excellent semiconductor properties such as a high breakdown voltage, and thus completed the present invention.

[0035] The following description will be made with reference to the drawings.

[0036] (Laminated structure) Fig. 4 shows a preferred example of a semiconductor device 100 using a layered structure 110 according to the present invention. As shown in Fig. 4, the layered structure 110 according to the present invention has a base substrate 101 and a crystalline oxide film 103 containing at least gallium oxide as a main component. The average reflectance of light with a wavelength of 400 to 800 nm on a surface 103c on the crystalline oxide film side is 16% or more.

[0037] This results in significantly fewer crystal defects and excellent crystallinity, resulting in excellent semiconductor properties when applied to a semiconductor device. The reflectance is thought to reflect the refractive index of the crystalline oxide film produced. If the reaction is incomplete, hydroxyl groups and the like remain in the film, lowering the refractive index and resulting in a decrease in reflectance. Conversely, if an ideal reaction occurs, unintended hydroxyl groups will no longer be present in the film, increasing the refractive index of the film and the reflectance of the laminate structure. This means that the reflectance of the laminate structure is higher than the reflectance when the film is removed and only the substrate is left.

[0038] Here, the point defined by the light reflectance in the laminate structure according to the present invention will be explained. The wavelength range of 400 to 800 nm of reflected light is a range in which the spectrum changes relatively slowly, and by adopting the average value of this wavelength range of reflected light, the crystallinity of the film can be evaluated stably and accurately. Since the refractive index of gallium oxide when an ideal reaction occurs is approximately 2.0, the upper limit of the reflectance is estimated to be approximately 19%. Conversely, when the reaction is incomplete, the refractive index of gallium oxide is lower than 2.0, and the reflectance also decreases correspondingly. A reflectance of 16% or less corresponds to a refractive index of 1.9 or less, which means poor crystallinity and the expected properties of gallium oxide cannot be obtained. Thus, a high average reflectance of light with a wavelength of 400 to 800 nm indicates that residues such as hydroxyl groups in the film are suppressed, crystal defects are significantly reduced, and crystallinity is excellent, indicating that an ideal film formation reaction has occurred.

[0039] The upper limit of reflectance also depends on the starting substrate, which will be described later. When the starting substrate is sapphire, the upper limit of reflectance is approximately 19%, as mentioned above, but when the starting substrate is lithium tantalate, the upper limit of reflectance is approximately 35%.

[0040] The reflectance can be calculated from the results of measuring the reflectance spectrum using, for example, a spectrophotometer. Reflectance includes specular reflectance, diffuse reflectance, and total reflectance, which is a combination of these. Either can be used, but it is preferable to evaluate using total reflectance. This is because it is less susceptible to the influence of surface conditions due to differences in film formation conditions, such as surface irregularities.

[0041] A spectrophotometer has at least an integrating sphere for detecting light reflected from a sample. Total reflectance is measured by irradiating the sample with light at an incident angle of approximately 10 degrees or less, and measuring not only diffusely reflected light but also specularly reflected light with the integrating sphere. When measuring, a baseline measurement is first performed. The reflectance is measured with a standard white plate such as barium sulfate attached to the integrating sphere, and this is used as the baseline. Once the baseline is obtained, the standard white plate is removed and the sample is attached, allowing the reflectance spectrum to be measured.

[0042] Another layer may be interposed between the substrate and the crystalline oxide film. The another layer is a layer having a different composition from the substrate and the outermost crystalline oxide film, and is also called a buffer layer. The buffer layer may be any of a crystalline oxide film, a semiconductor film, an insulating film, a metal film, etc., and suitable materials include Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, and Ir2O3. The thickness of the buffer layer is preferably 0.1 μm to 2 μm.

[0043] (Base substrate) The base substrate in the laminate structure of the present invention is not particularly limited as long as it can serve as a support for the crystalline oxide film. The material is not particularly limited, and known substrates can be used, including organic and inorganic compounds. Examples include polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, quartz, glass, calcium carbonate, gallium oxide, and ZnO. In addition, single-crystal substrates such as silicon, sapphire, lithium tantalate, lithium niobate, SiC, GaN, iron oxide, and chromium oxide are also suitable. These single-crystal substrates are desirable for the laminate structure of the present invention. These substrates enable the production of higher-quality crystalline oxide films. In particular, sapphire substrates, lithium tantalate substrates, and lithium niobate substrates are relatively inexpensive and industrially advantageous.

[0044] The thickness of the base substrate is preferably 100 to 5000 μm, as this range makes it easy to handle and reduces thermal resistance during film formation, making it easier to obtain a high-quality film.

[0045] There is no particular limitation on the size of the base substrate, but the surface area of ​​the base substrate on which the crystalline oxide film is formed is 100 mm 2 A diameter of 2 inches (50 mm) or more is preferred because a large-area film with good crystallinity can be obtained. The upper limit of the area of ​​the base substrate is not particularly limited, but it is preferably 100,000 mm 2 It can be as follows:

[0046] (crystalline oxide film) The crystalline oxide film in the layered structure according to the present invention is a crystalline oxide film containing gallium oxide as its main component. Generally, oxide films are composed of metal and oxygen, but the crystalline oxide film in the layered structure according to the present invention may contain gallium as its main component. In the present invention, "containing gallium as its main component" means that 50 to 100% of the metal components are gallium. The metal components other than gallium may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt.

[0047] The crystalline oxide film may contain a dopant element. Examples of the dopant include, but are not limited to, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, tin, iridium, rhodium, and magnesium. The dopant concentration is, for example, about 1×10 16 / cm 3 ~1×10 22 / cm 3 may be about 1 x 10 17 / cm 3 Even at a low concentration of less than 1 × 10 20 / cm 3 A concentration higher than this may be used.

[0048] The crystal structure of the crystalline oxide film is not particularly limited, and may be a β-gallium structure, a corundum structure, or an orthorhombic crystal. Multiple crystal structures may be mixed, or the film may be polycrystalline; however, a single crystal or uniaxially oriented film is preferred. Whether the film is single crystal or uniaxially oriented can be confirmed using an X-ray diffraction device or an electron beam diffraction device. When the film is irradiated with X-rays or electron beams, a diffraction pattern corresponding to the crystal structure is obtained, and in the case of uniaxial orientation, only a specific peak appears. This indicates that the film is uniaxially oriented. Furthermore, the crystalline oxide film according to the present invention preferably has a corundum structure. In this case, the half-width of the (006) plane of the X-ray diffraction rocking curve can be 5 to 20 seconds.

[0049] The thickness of the crystalline oxide film is not particularly limited, but is preferably 1 μm or more. There is no particular upper limit. For example, it may be 100 μm or less, preferably 50 μm or less, and more preferably 20 μm or less.

[0050] (Semiconductor Devices) The semiconductor device according to the present invention includes a crystalline oxide film containing gallium oxide as a main component as an insulating thin film or a conductive thin film. The average reflectance of the surface on the crystalline oxide film side for light with a wavelength of 400 to 800 nm is 16% or more. Such a crystalline oxide film has significantly fewer crystal defects and excellent crystallinity, resulting in a semiconductor device with excellent semiconductor properties such as a high breakdown voltage.

[0051] (Configuration example of semiconductor device) In the example of a semiconductor device 100 shown in FIG. 4, a crystalline oxide film 103 is formed on an underlying substrate 101. The crystalline oxide film 103 is configured by laminating an insulating thin film 103a and a conductive thin film 103b in this order from the underlying substrate 101 side. A gate insulating film 105 is formed on the conductive thin film 103b. A gate electrode 107 is formed on the gate insulating film 105. Furthermore, source-drain electrodes 109 are formed on the conductive thin film 103b so as to sandwich the gate electrode 107. With this configuration, it is possible to control the depletion layer formed in the conductive thin film 103b by applying a gate voltage to the gate electrode 107, enabling transistor operation (FET device).

[0052] Examples of semiconductor devices formed using the stacked structure according to the present invention include transistors such as MIS, HEMT, and IGBT, TFTs, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements. The stacked structure according to the present invention is useful for improving the characteristics of these devices.

[0053] The above-described laminated structure can be formed by known methods such as vapor deposition, MBE, sputtering, CVD, mist CVD, and liquid phase epitaxy.

[0054] The method for manufacturing a laminated structure according to the present invention will be described below using the mist CVD method as an example. Here, the term "mist" as used in the present invention refers to a general term for fine particles of liquid dispersed in a gas, and includes what is called fog, droplets, etc.

[0055] (Film forming equipment) First, a film formation apparatus (mist CVD apparatus) used in the mist CVD method suitable for manufacturing the laminated structure according to the present invention will be described. Fig. 5 shows an example of a film formation apparatus 201 used in the mist CVD method. The film formation apparatus 201 includes at least a mist-forming unit 220 that generates mist by misting a raw material solution 204a, a carrier gas supply unit 230 that supplies a carrier gas that transports the mist, a supply pipe 209 that connects the mist-forming unit 220 to a film formation chamber 207 and transports the mist by the carrier gas, and the film formation chamber 207 that heat-treats the mist supplied from the supply pipe 209 together with the carrier gas to form a film on a base substrate 210.

[0056] (Mist generating section) The mist generating section 220 generates mist by turning the raw solution 204a into mist. The mist generating means is not particularly limited as long as it can turn the raw solution 204a into mist, and any known mist generating means may be used, but it is preferable to use a mist generating means that uses ultrasonic vibrations, as this allows for more stable mist generation.

[0057] An example of such a mist-generating unit 220 is shown in FIG. 6. The mist-generating unit 220 may include a mist source 204 containing raw solution 204a, a container 205 containing a medium capable of transmitting ultrasonic vibrations, such as water 205a, and an ultrasonic vibrator 206 attached to the bottom of the container 205. Specifically, the mist source 204, which is a container containing raw solution 204a, may be housed in the container 205 containing water 205a using a support (not shown). The bottom of the container 205 may be equipped with an ultrasonic vibrator 206, or the ultrasonic vibrator 206 may be connected to an oscillator 216. When the oscillator 216 is activated, the ultrasonic vibrator 206 vibrates, and ultrasonic waves propagate through the water 205a into the mist source 204, thereby misting the raw solution 204a.

[0058] (Raw material solution) The raw material solution 204a contains gallium and may contain any material, inorganic or organic, as long as it can be misted. Other than gallium, metals or metal compounds are preferably used, including, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt. The raw material solution may be a solution in which a metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt. Examples of salts include halide salts such as metal chlorides, metal bromides, and metal iodides. Furthermore, solutions in which the above metals are dissolved in hydrogen halides such as hydrobromic acid, hydrochloric acid, and hydroiodic acid can also be used. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. An acetylacetonate complex can also be formed by mixing acetylacetone with the aforementioned salt solution. The metal concentration in the raw material solution 204a is not particularly limited, and can be set to 0.005 to 1 mol / L, etc. The temperature during mixing and dissolution is preferably 20° C. or higher.

[0059] The raw material solution may contain additives such as hydrohalic acid and oxidizing agents. Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, with hydrobromic acid and hydroiodic acid being preferred. Examples of oxidizing agents include peroxides such as hydrogen peroxide (HO), sodium peroxide (NaO), barium peroxide (BaO), and benzoyl peroxide (CHCO)O, as well as hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0060] The raw material solution may contain a dopant. The dopant is not particularly limited. Examples of the dopant include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, and niobium, and p-type dopants such as copper, silver, iridium, rhodium, and magnesium.

[0061] (Carrier gas supply unit) 5, the carrier gas supply unit 230 has a carrier gas source 202a that supplies a carrier gas. In this case, a flow rate control valve 203a for adjusting the flow rate of the carrier gas sent out from the carrier gas source 202a may be provided. In addition, if necessary, a dilution carrier gas source 202b for supplying a dilution carrier gas and a flow rate control valve 203b for adjusting the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 202b may also be provided.

[0062] The type of carrier gas is not particularly limited and can be selected appropriately depending on the film to be formed. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen gas and forming gas. The type of carrier gas may be one or more. For example, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (e.g., diluted 10 times) may be used as the second carrier gas, or air may be used. The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a substrate with a diameter of 2 inches (approximately 50 mm), the flow rate of the carrier gas is preferably 0.05 to 50 L / min, and more preferably 5 to 20 L / min.

[0063] (supply pipe) The film forming apparatus 201 has a supply pipe 209 that connects the mist generating unit 220 and the film forming chamber 207. In this case, the mist is carried by a carrier gas from the mist generating source 204 of the mist generating unit 220 through the supply pipe 209 and supplied into the film forming chamber 207. The supply pipe 209 may be, for example, a quartz tube, a glass tube, or a resin tube.

[0064] (Film forming chamber) A substrate 210 is placed in the film formation chamber 207, and a heater 208 for heating the substrate 210 may be provided. The heater 208 may be provided outside the film formation chamber 207 as shown in FIG. 5, or may be provided inside the film formation chamber 207. The mist supplied from a supply pipe 209 passes through piping in the film formation chamber 207 and is ejected from a nozzle toward the substrate 210 together with the carrier gas. The film formation chamber 207 may also be provided with an exhaust gas outlet 212 at a position that does not affect the supply of mist to the substrate 210. The substrate 210 may be placed face-down, for example, on the top surface of the film formation chamber 207, or may be placed face-up, for example, on the bottom surface of the film formation chamber 207.

[0065] (Film forming method) 5 and 6, an example of a method for manufacturing a laminated structure according to the present invention will be described. The mist CVD method generally comprises a mist generating step of misting a raw material solution containing gallium in a mist generating section to generate mist, a carrier gas supply step of supplying a carrier gas for transporting the mist to the mist generating section, a transport step of transporting the mist from the mist generating section to the film forming chamber by the carrier gas via a supply pipe connecting the mist generating section to the film forming chamber, and a film forming step of heat-treating the transported mist to form a film on a base substrate.

[0066] The raw material solution 204a mixed as described above is placed in the mist generation source 204, the substrate 210 is placed in the film formation chamber 207, and the heater 208 is activated. Next, the flow rate control valves 203a and 203b are opened to supply carrier gas from the carrier gas sources 202a and 202b into the film formation chamber 207, and after the atmosphere in the film formation chamber 207 is sufficiently replaced with the carrier gas, the flow rate of the carrier gas and the flow rate of the dilution carrier gas are each adjusted.

[0067] Next, in the mist generating step, the ultrasonic vibrator 206 is vibrated, and the vibration is propagated to the raw material solution 204a through the water 205a, thereby turning the raw material solution 204a into mist and generating the mist.

[0068] Next, in the carrier gas supply step, a carrier gas for transporting the mist is supplied to the mist-forming section 220.

[0069] Next, in the transport step, the mist is transported by a carrier gas from the mist-generating section 220 to the film-forming chamber 207 via the supply pipe 209 connecting the mist-generating section 220 and the film-forming chamber 207.

[0070] Next, in the film formation process, the mist transported to the film formation chamber 207 is heated to cause a thermal reaction, thereby forming a film on a part or the entire surface of the substrate 210 .

[0071] Thermal reactions require heating to promote the reaction of gallium and other elements contained in the mist. Therefore, the substrate surface temperature during the reaction must be at least 400°C or higher. Unlike other CVD methods, mist CVD requires the raw materials to reach the substrate surface in a mist-like liquid state. This significantly reduces the substrate surface temperature. Therefore, the substrate surface temperature during the reaction differs from the temperature set in the equipment. It is preferable to measure and control the substrate surface temperature during the reaction. However, if this is difficult, the reaction can be simulated by introducing only carrier gas or water mist without solute, and the temperature can be measured instead.

[0072] Furthermore, the thermal reaction also depends on the temperature of the environment around the substrate. Therefore, when a carrier gas containing mist is supplied from a nozzle to a base substrate placed in a film formation chamber to form a crystalline oxide film mainly composed of gallium oxide by mist CVD, the film formation is carried out with the temperature of the nozzle or the inner wall of the film formation chamber set higher than room temperature. This is to stabilize the thermal reaction. For example, the nozzle temperature is preferably set to 50 to 250°C. This allows for the production of a crystalline oxide film with better crystallinity.

[0073] The thermal reaction may be carried out under any of the following atmospheres: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and may be appropriately set depending on the film to be formed. The reaction pressure may be atmospheric pressure, elevated pressure, or reduced pressure, but film formation under atmospheric pressure is preferred because it simplifies the device configuration.

[0074] (Buffer layer formation) As described above, a buffer layer may be appropriately provided between the substrate and the crystalline oxide film. The buffer layer can be formed by any known method, such as sputtering or vapor deposition. However, the mist CVD method described above allows for easy formation by simply changing the source solution. Specifically, a solution prepared by dissolving or dispersing one or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium in water in the form of a complex or salt can be used as the source aqueous solution. Examples of complexes include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salts include metal chlorides, metal bromides, and metal iodides. Furthermore, solutions of the above metals in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. can also be used as salt aqueous solutions. In this case, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is preferably 20°C or higher. The buffer layer can be formed under the same conditions as described above. After the buffer layer is formed to a predetermined thickness, film formation is carried out by the above-mentioned method.

[0075] In a special case of the buffer layer formation method, the same material as that of the crystalline oxide film is used. In this case, the deposition temperature of the buffer layer may be higher than that of the crystalline oxide film. For example, the deposition temperature of the buffer layer may be 450°C and that of the crystalline oxide film may be 400°C, or the buffer layer may be deposited at 500°C and the crystalline oxide film at 450°C. This further improves the crystallinity of the crystalline oxide film.

[0076] (Heat treatment) The laminated structure according to the present invention may also be heat-treated at 200 to 600°C. This further removes unreacted species from the film, resulting in a higher quality laminated structure. The heat treatment may be carried out in air or an oxygen atmosphere, or in an inert gas atmosphere such as nitrogen or argon. The heat treatment time can be determined as appropriate, but may be, for example, 5 to 240 minutes.

[0077] (peeling) In the layered structure according to the present invention, the crystalline oxide film may be peeled off from the base substrate. The peeling means is not particularly limited and may be any known means. Examples of peeling methods include peeling by applying mechanical impact, peeling by applying heat and using thermal stress, peeling by applying vibration such as ultrasonic waves, and peeling by etching. By such peeling, the crystalline oxide film can be obtained as a free-standing film.

[0078] (Other manufacturing methods) Although the method for producing the laminated structure according to the present invention has been described above using the mist CVD method as an example, the laminated structure according to the present invention can also be produced using methods other than the mist CVD method by controlling the temperature during deposition of the crystalline oxide film, particularly the temperature of the substrate surface. When it is difficult to accurately measure the temperature of the substrate, etc., it is also possible to obtain the laminated structure according to the present invention by producing samples of multiple laminated structures under different temperature conditions, measuring their reflectance spectra, and selecting those having the desired properties. [Example]

[0079] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0080] [Example 1] 5, a film formation apparatus 201 used in this example will be described. The film formation apparatus 201 includes a carrier gas source 202a for supplying a carrier gas, a flow rate control valve 203a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 202a, a dilution carrier gas source 202b for supplying a dilution carrier gas, a flow rate control valve 203b for adjusting the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 202b, a mist generation source 204 containing a raw material solution 204a, a container 205 containing water 205a, an ultrasonic vibrator 206 attached to the bottom of the container 205, a film formation chamber 207 equipped with a heater 208, and a quartz supply pipe 209 connecting the mist generation source 204 to the film formation chamber 207.

[0081] (Preliminary temperature measurement) First, film formation conditions were simulated using a dummy substrate and water mist, and the temperature of the substrate surface was measured. Specifically, the raw material solution 204a was pure water, and the dummy substrate was a c-plane sapphire substrate with a diameter of 4 inches (100 mm). This substrate was placed in the film formation chamber 207, and the heater 208 was set to 450°C, the temperature was raised, and the chamber was left for 30 minutes to stabilize the temperature inside the film formation chamber. Next, the flow rate control valves 203a and 203b were opened to supply carrier gas from the carrier gas sources 202a and 202b into the film formation chamber 207. After the atmosphere in the film formation chamber 207 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 2 L / min and the flow rate of the dilution carrier gas was adjusted to 6 L / min. Compressed air was used as the carrier gas. Next, ultrasonic vibrator 206 was vibrated at 2.4 MHz, and the vibrations were propagated through water 205a to raw material solution 204a (pure water), thereby misting the pure water and generating mist. This mist was introduced into film formation chamber 207 via supply pipe 209 using a carrier gas. At this time, temperatures at various locations within the film formation chamber were measured using thermocouples. As a result, the temperature of the substrate surface was 424°C, the temperature at the nozzle tip was 146°C, and the temperature of the film formation chamber wall was 43°C.

[0082] (Gallium oxide film formation) Subsequently, a gallium oxide film was formed. A 4-inch (100 mm) c-plane sapphire substrate was prepared as the substrate 210. This substrate was placed in the film formation chamber 207, and the heater 208 was set to 450°C, the temperature was raised, and the chamber was left for 30 minutes to stabilize the temperature inside the film formation chamber, including the nozzle.

[0083] The raw material solution 204a used ultrapure water as a solvent and gallium bromide as a solute. The gallium concentration in the raw material solution was 0.1 mol / L. This raw material solution 204a was placed in the mist generation source 204. Next, the flow rate control valves 203a and 203b were opened to supply carrier gas from the carrier gas sources 202a and 202b into the film formation chamber 207. After the atmosphere in the film formation chamber 207 was sufficiently replaced with the carrier gas, the flow rate of the carrier gas was adjusted to 2 L / min and the flow rate of the dilution carrier gas was adjusted to 6 L / min. Nitrogen was used as the carrier gas.

[0084] Next, ultrasonic vibrator 206 was vibrated at 2.4 MHz, and the vibrations were propagated to raw material solution 204a through water 205a, thereby misting raw material solution 204a and generating mist. This mist was introduced into film formation chamber 207 via supply pipe 209 by a carrier gas, and the mist was thermally reacted on substrate 210 to form a thin film of gallium oxide on substrate 210. The film formation time was 30 minutes. It is estimated that the temperatures at various locations in the film formation chamber at this time were the temperatures obtained in the above-mentioned preliminary temperature measurement.

[0085] (evaluation) X-ray diffraction confirmed the formation of α-Ga2O3 in the thin film formed on the substrate 210. Measurement of the rocking curve of the (006) plane of α-Ga2O3 revealed excellent crystallinity, with a half-width of 6 seconds. The rocking curve measurement was performed using a four-crystal monochromator combining two channel-cut crystals to enhance the monochromaticity of the X-rays and achieve higher accuracy. Next, a JASCO V-770 spectrophotometer was used to measure the reflectance spectrum of the film-coated side of the resulting laminated structure. The sample was mounted on an integrating sphere, and the total reflectance was measured with the measurement light at an incident angle of approximately 5°. A barium sulfate white standard plate was used to obtain the baseline. The results are shown in Figure 1. The average reflectance from 400 to 800 nm was calculated to be 17.1%. The film thickness was measured using an optical interference film thickness meter, resulting in a film thickness of 179 nm.

[0086] [Comparative Example 1] During deposition of a gallium oxide film similar to that of Example 1, the heater 208 was set to 500°C, and deposition was performed without stabilizing the temperature after heating. Other than this, deposition and evaluation were performed under the same conditions as in Example 1. As a result, the rocking curve half-width of the (006) plane of α-Ga2O3 was 102 seconds, indicating poor crystallinity. The reflectance spectrum is shown in Figure 1, along with that of Example 1. A decrease in reflectance was confirmed, with the average reflectance from 400 to 800 nm being 11.6%.

[0087] [Example 2] Film formation and evaluation were carried out in the same manner as in Example 1, except that an AlGaO film was formed as a buffer layer and the thickness of the gallium oxide film was 3 μm. The rocking curve half-width was a good 15 seconds. The reflectance spectrum is shown in Figure 2. The average reflectance from 400 to 800 nm was 17.1%.

[0088] [Example 3] Film formation and evaluation were carried out in the same manner as in Example 2, except that the thickness of the gallium oxide film was 6 μm. The rocking curve half width was a good 18 seconds. The reflectance spectrum is shown in Figure 3. The average reflectance from 400 to 800 nm was 17.0%.

[0089] [Example 4] When depositing a gallium oxide film similar to that in Example 1, the heater 208 was set to 430°C, and other conditions were the same as in Example 1, whereby film deposition and evaluation were carried out. The rocking curve half-width was a good 9 seconds. The reflectance spectrum is shown in Figure 7. The average reflectance from 400 to 800 nm was 16.4%.

[0090] [Example 5] When depositing a gallium oxide film similar to that in Example 1, the heater 208 was set to 550°C, and other conditions were the same as in Example 1, whereby film deposition and evaluation were carried out. The half-width of the rocking curve was a good 6 seconds. The reflectance spectrum is shown in Figure 8. The average reflectance from 400 to 800 nm was 18.3%.

[0091] Comparative Example 2 When forming a gallium oxide film similar to that in Example 1, the heater 208 was set to 550°C, and film formation was performed without stabilizing the temperature after heating. Film formation and evaluation were performed under the same conditions as in Example 1. As a result, the rocking curve half-width was 88 seconds, indicating poor crystallinity. The reflectance spectrum is shown in Figure 9. The average reflectance from 400 to 800 nm was 15.1%.

[0092] As described above, when the average reflectance of the obtained layered structure in the range of 400 to 800 nm is high, the crystallinity of the obtained film is good. If a semiconductor device is formed using the layered structure according to the present invention, it is useful for improving the characteristics of the semiconductor device.

[0093] 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 laminated structure having at least a base substrate and a crystalline oxide film containing gallium oxide as a main component, A laminate structure characterized in that, when measured by irradiating the surface of the laminate structure facing the crystalline oxide film with light at an incident angle of 10 degrees or less, the average total reflectance of light having a wavelength of 400 to 800 nm on the surface of the laminate structure facing the crystalline oxide film is 16% or more.

2. 2. The laminated structure according to claim 1, wherein the base substrate is a single crystal, and the crystalline oxide film is a single crystal or uniaxially oriented film.

3. 2. The laminated structure according to claim 1, wherein the base substrate is any one of a sapphire substrate, a lithium tantalate substrate, and a lithium niobate substrate.

4. 3. The laminated structure according to claim 2, wherein the base substrate is any one of a sapphire substrate, a lithium tantalate substrate, and a lithium niobate substrate.

5. 5. The laminate structure according to claim 1, wherein the crystalline oxide film has a corundum structure.

6. 6. The laminated structure according to claim 5, wherein the crystalline oxide film having the corundum structure has an X-ray rocking curve half width of 5 to 20 seconds in the (006) plane.

7. The surface area of ​​the base substrate having the crystalline oxide film is 100 mm ２ 5. The laminated structure according to claim 1, wherein the laminated structure has a diameter of 2 inches (50 mm) or more.

8. The surface area of ​​the base substrate having the crystalline oxide film is 100 mm ２ 6. The laminated structure according to claim 5, wherein the laminated structure has a diameter of 2 inches (50 mm) or more.

9. The surface area of ​​the base substrate having the crystalline oxide film is 100 mm ２ 7. The laminated structure according to claim 6, wherein the laminated structure has a diameter of 2 inches (50 mm) or more.

10. A method for depositing a crystalline oxide film containing gallium oxide as a main component by a mist CVD method by supplying a carrier gas containing mist from a nozzle to a base substrate placed in a film deposition chamber, the method comprising: placing a base substrate in a film formation chamber, setting the temperature of a heater for heating the base substrate to a film formation temperature, and increasing the temperature to stabilize the temperature inside the film formation chamber including the nozzle; A method for forming a crystalline oxide film, characterized in that the temperatures of the nozzle and the inner wall of the film formation chamber are made higher than room temperature, and film formation is carried out in a state where the temperature of the nozzle is set to 50 to 250°C.

11. A semiconductor device comprising a crystalline oxide film containing gallium oxide as a main component as an insulating thin film or a conductive thin film, The semiconductor device is characterized in that, when light is irradiated onto the surface of the semiconductor device facing the crystalline oxide film at an incident angle of 10 degrees or less and measured, the average total reflectance of light having a wavelength of 400 to 800 nm on the surface facing the crystalline oxide film is 16% or more.

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