Stacked structure, semiconductor device, and method for manufacturing stacked structure

Abstract

The present invention provides a multilayer structure which is characterized by comprising a base substrate and a crystalline oxide film that is mainly composed of gallium oxide, while being also characterized in that: the root mean square roughness of the surface of the crystalline oxide film is 0.2 μm or less; the diameter of the base substrate is 50 mm or more; and the TTV of the base substrate is 30 μm or less. Consequently, the present invention provides: a multilayer structure which comprises a crystalline oxide film having a smooth surface; and a method for producing this multilayer structure.

Description

[Technical field]

[0001] The present invention relates to a laminated structure, a semiconductor device, and a method for manufacturing the laminated structure. [Background technology]

[0002] As a method for forming a highly crystalline gallium oxide-based thin film on a film-forming sample, a film-forming technique using water particles such as a mist CVD method is known (Patent Document 1). In this method, a gallium compound such as gallium acetylacetonate is dissolved in an acid such as hydrochloric acid to prepare a raw material solution, and the raw material solution is atomized to generate raw material particles, which are then supplied to the film-forming surface of the film-forming sample by a carrier gas, and the raw material particles are reacted to form a thin film on the film-forming surface, thereby forming a highly crystalline gallium oxide-based thin film on the film-forming sample.

[0003] In order to form a semiconductor device using a gallium oxide-based thin film, it is essential to control the electrical conductivity of the gallium oxide-based thin film. Patent Document 1 and Non-Patent Document 1 disclose a technique for doping an α-gallium oxide thin film with an impurity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-028480 A [Patent Document 2] JP 2015-199649 A [Non-patent literature]

[0005] [Non-Patent Document 1] Electrical Conductive Corundum-Structured α-Ga2O3 Thin Films on Sapphire with Tin-Doping Grown by Spray-Assisted Mist Chemical Vapor Deposition(Japanese Journal of Applied Physics 51(2012)070203) Summary of the Invention [Problem to be solved by the invention]

[0006] According to the methods of Patent Document 1 and Non-Patent Document 1, a thin film of α-gallium oxide (hereinafter, sometimes referred to as "α-Ga2O3") having excellent electrical conductivity can be formed, but there is a particular problem that the film surface is not smooth, and it is still not satisfactory for use in semiconductor devices. In addition, in order to smooth the film surface, it is possible to perform surface treatment such as etching, but in this case, there are problems such as the thin film being scraped off or the semiconductor properties being impaired.

[0007] To address this problem, Patent Document 2 discloses a method for reducing the average roughness (Ra). However, even when this method is used, the surface flatness is still not sufficient, and the characteristics of the semiconductor device using the obtained film are also unsatisfactory.

[0008] The present invention has been made to solve the above problems, and has an object to provide a laminated structure including a crystalline oxide film having a smooth surface, and to provide a method for manufacturing the laminated structure. [Means for solving the problem]

[0009] The present invention has been made to achieve the above-mentioned object, and provides a laminated structure comprising a base substrate and a crystalline oxide film mainly composed of gallium oxide, wherein the root-mean-square roughness of the surface of the crystalline oxide film is 0.2 μm or less, the diameter of the base substrate is 50 mm or more, and the TTV of the base substrate is 30 μm or less.

[0010] Such a laminated structure has a crystalline oxide film with a smooth surface, and when applied to a semiconductor device, the semiconductor properties are excellent.

[0011] In the present invention, the crystalline oxide film may be a single crystal or a uniaxially oriented film.

[0012] As a result, when applied to a semiconductor device, the semiconductor properties become excellent.

[0013] In the present invention, the base substrate preferably has a thickness of 100 to 5000 μm.

[0014] This makes the surface smoother, and when applied to a semiconductor device, the laminated structure has superior semiconductor properties.

[0015] In the present invention, the crystalline oxide film may have a thickness of 1 to 100 μm.

[0016] This results in superior semiconductor properties when applied to a semiconductor device.

[0017] In the present invention, the base substrate is preferably a single crystal.

[0018] This makes it possible to obtain a laminated structure having a gallium oxide film with excellent crystallinity.

[0019] In the present invention, the base substrate is preferably any one of a sapphire substrate, a lithium tantalate substrate, and a lithium niobate substrate.

[0020] This makes it possible to obtain a laminated structure having a gallium oxide film with a smoother surface and better crystallinity.

[0021] In the present invention, the surface of the laminated structure opposite to the surface having the crystalline oxide film may have a surface roughness Ra of 0.5 μm or less.

[0022] Such a laminated structure is of high quality and is suitable for the manufacture of semiconductor film devices.

[0023] In the present invention, the surface of the laminated structure opposite to the surface having the crystalline oxide film may have a waviness Wa of 50 μm or less.

[0024] Such a laminate structure has a higher quality and is suitable for manufacturing semiconductor film devices.

[0025] The present invention also provides a semiconductor device including the above-described laminated structure.

[0026] This results in a semiconductor device with better characteristics.

[0027] The present invention also provides a method for producing a laminated structure, comprising the steps of: a mist generating step of misting a raw material solution containing gallium in a mist generating section to generate mist; A carrier gas supplying 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 unit to the deposition chamber in which a base substrate is placed by the carrier gas through a supply pipe connecting the mist generating unit and the deposition chamber; a film forming step of forming a film on the base substrate by heat-treating the transported mist; Including, The present invention provides a method for producing a laminated structure using a base substrate having a diameter of 50 mm or more and a TTV of 30 μm or less.

[0028] According to such a method for producing a laminated structure, it is possible to produce a laminated structure including a crystalline oxide film having a smooth surface.

[0029] In the present invention, the base substrate may have a thickness of 100 to 5000 μm.

[0030] This makes the surface smoother, and when applied to a semiconductor device, a laminated structure having superior semiconductor properties can be manufactured.

[0031] In the present invention, the base substrate may be a single crystal.

[0032] This makes it possible to manufacture a laminated structure having a gallium oxide film with excellent crystallinity.

[0033] In the present invention, the base substrate may be any one of a sapphire substrate, a lithium tantalate substrate, and a lithium niobate substrate.

[0034] This makes it possible to manufacture a laminated structure having a gallium oxide film with a smoother surface and better crystallinity at a lower cost.

[0035] In the present invention, the surface roughness Ra of the surface of the base substrate opposite to the film-forming surface may be 0.5 μm or less.

[0036] This method makes it possible to stably manufacture a laminated structure including a high-quality semiconductor film with excellent crystal orientation. In addition, damage to the transfer system and substrate carrier caused by the rear surface of the substrate is significantly reduced, which suppresses dust generation within the device and increases the freedom in materials for the transfer system and substrate carrier, making it possible to more stably and inexpensively manufacture a laminated structure including a high-quality semiconductor film.

[0037] In the present invention, the waviness Wa of the surface of the base substrate opposite to the film-forming surface may be set to 50 μm or less.

[0038] In this way, the contact area with the substrate is increased, thereby improving thermal conduction, and the temperature drop on the substrate surface during film formation due to the film-forming raw material mist is not significant, so that the crystal orientation of the semiconductor film does not deteriorate, making it possible to stably produce a high-quality laminated structure.

[0039] In the present invention, in the film forming step, the base substrate may be placed on a stage, and a surface roughness Ra of the stage at a contact surface with the base substrate may be set to 0.5 μm or less.

[0040] This method makes it possible to stably manufacture a laminate including a high-quality semiconductor film with excellent crystal orientation. In addition, damage to the transport system and the substrate carrier caused by the back surface of the substrate is greatly reduced, so that dust generation in the device is suppressed, and the degree of freedom in the materials of the transport system and the substrate carrier is increased, so that a laminate including a high-quality semiconductor film having a corundum-type crystal structure can be manufactured more stably and inexpensively.

[0041] In the present invention, in the film forming step, the base substrate may be placed on a stage, and a waviness Wa of a contact surface of the stage with the base substrate may be set to 50 μm or less.

[0042] In this way, the contact area with the substrate is increased, thereby improving thermal conduction, and the temperature drop on the substrate surface during film formation due to the film-forming raw material mist is not significant, so that the crystal orientation of the semiconductor film does not deteriorate, making it possible to stably produce a high-quality laminated structure. Effect of the Invention

[0043] As described above, the laminate structure of the present invention has a crystalline oxide film with a smooth surface, and when applied to a semiconductor device, the laminate structure has excellent semiconductor properties. Also, the method for manufacturing the laminate structure of the present invention makes it possible to manufacture a laminate structure having a crystalline oxide film with a smooth surface, and when applied to a semiconductor device, the laminate structure has excellent semiconductor properties. [Brief description of the drawings]

[0044] [Figure 1] 1 is a schematic diagram showing an example of a semiconductor device according to the present invention; [Diagram 2] 1 is a schematic diagram showing an example of a film forming apparatus used in a method for producing a laminated structure according to the present invention. [Diagram 3] FIG. 1 is a graph showing the relationship between the TTV of a base substrate according to the present invention and the root-mean-square roughness of a crystalline oxide film surface. [Figure 4] FIG. 2 is a schematic diagram showing an example of a mist generating unit used in the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] As described above, there has been a need to provide a laminate structure including a crystalline oxide film having a smooth surface, and a method for producing the laminate structure.

[0046] As a result of extensive research into the above-mentioned problems, the inventors have discovered that a laminate structure having a base substrate and a crystalline oxide film mainly composed of gallium oxide, characterized in that the root mean square roughness of the surface of the crystalline oxide film is 0.2 μm or less, the diameter of the base substrate is 50 mm (2 inches) or more, and the TTV of the base substrate is 30 μm or less, has a crystalline oxide film with a smooth surface, and becomes a laminate structure with excellent semiconductor properties when applied to a semiconductor device, thereby completing the present invention.

[0047] The present inventors also discovered a method for producing a laminated structure, comprising the steps of: a mist generating step of misting a raw material solution containing gallium in a mist generating section to generate mist; A carrier gas supplying 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 unit to the deposition chamber in which a base substrate is placed by the carrier gas through a supply pipe connecting the mist generating unit and the deposition chamber; a film forming step of forming a film on the base substrate by heat-treating the transported mist; Including, The present inventors have found that a method for manufacturing a laminated structure, which is characterized by using a base substrate having a diameter of 50 mm or more and a TTV of 30 μm or less, makes it possible to manufacture a laminated structure having a crystalline oxide film with a smooth surface and having excellent semiconductor properties when applied to a semiconductor device, thereby completing the present invention.

[0048] Here, the mist in the present invention refers to a general term for fine particles of liquid dispersed in a gas, and includes what are called fog, droplets, etc. Hereinafter, the present invention will be described with reference to the drawings.

[0049] The present invention will be described in detail below, but the present invention is not limited thereto.

[0050] (Laminated structure) Fig. 1 shows a semiconductor device 100 including a laminated structure 110 of the present invention. As shown in Fig. 1, the laminated structure 110 of the present invention has a base substrate 101 and a crystalline oxide film 103 mainly composed of gallium oxide, the root mean square roughness of a surface 103c of the crystalline oxide film 103 is 0.2 µm or less, the diameter of the base substrate 101 is 50 mm (2 inches) or more, and the TTV of the base substrate 101 is 30 µm or less. This results in a laminated structure 110 having a crystalline oxide film 103 with a smooth surface and excellent semiconductor characteristics when applied to a semiconductor device.

[0051] (Base substrate) Conventionally, as the diameter of the base substrate 101 increases, the root mean square roughness of the surface of the crystalline oxide film 103 deteriorates significantly, and in particular, a roughness of 0.2 μm or less could not be obtained for a substrate with a diameter of 50 mm or more. The inventors of the present invention conducted an intensive investigation and found that, as shown in FIG. 3, the RMS of the surface of the crystalline oxide film increases rapidly from the point where the TTV of the base substrate exceeds 30 μm. As described later, this is believed to be caused by a deterioration in thermal contact with the heater and an increase in thermal resistance. Therefore, in the present invention, the TTV is set to 30 μm or less. Even if a substrate with a diameter of 50 mm (2 inches) or more is used, the root mean square roughness of the surface 103c of the crystalline oxide film 103 is 0.2 μm or less by setting the TTV of the base substrate 101 to 30 μm or less.

[0052] The base substrate for the laminated structure of the present invention has a diameter of 50 mm (2 inches) or more and a TTV of 30 μm or less. The upper limit of the diameter is not particularly limited, but can be, for example, 300 mm or less. The lower limit of the TTV is not particularly limited, but can be, for example, 0.1 μm or more.

[0053] TTV is an abbreviation for total thickness variation, and is the difference between the maximum and minimum heights measured in the thickness direction on the entire surface of the wafer, with the back surface of the wafer as the reference surface. In the present invention, the TTV of the base substrate is 30 μm or less. The TTV of the laminated structure obtained in this case is also 30 μm or less. TTV can be measured using a micrometer, a capacitance method, an optical interference method, a laser confocal method, or the like.

[0054] The surface of the laminated structure opposite to the surface 103c having the crystalline oxide film may have a roughness Ra of 0.5 μm or less. The smaller the surface roughness Ra, the more preferable it is, and the lower limit is not particularly limited, but it can be, for example, 0.1 nm or more. If the surface roughness Ra is 0.5 μm or less, the contact area with the base substrate 101 is not reduced, so that heat conduction is not deteriorated, and the temperature of the substrate surface during film formation is not lowered by the mist of the film-forming raw material, so that the crystal orientation of the semiconductor film is not deteriorated.

[0055] The waviness Wa of the surface of the laminated structure opposite to the surface 103c having the crystalline oxide film may be 50 μm or less. The smaller the waviness Wa, the more preferable, and the lower limit is not particularly limited, but it can be, for example, 0.5 μm or more. If Wa is 50 μm or less, the contact area with the base substrate 101 increases, improving thermal conduction, and the temperature drop of the substrate surface during film formation due to the mist of film-forming raw material is not significant, so that the crystal orientation of the semiconductor film does not deteriorate.

[0056] Waviness Wa is defined as "the magnitude of deviation of a planar shape from a geometrically correct plane". Waviness Wa may be measured on one or more arbitrary straight lines on the mounting surface that are appropriately determined according to the shape of the mounting surface. For example, if the mounting surface is circular, the measurement length can be the diameter of two straight lines that intersect at right angles at the center of the circle. Waviness Wa refers to a value calculated based on JIS B 0601 using the results of surface shape measurement using a stylus method, an atomic force microscope (AFM) method, or a non-contact measurement method using a laser microscope or a confocal microscope, such as an optical interference method, a confocal method, or an image synthesis method using focal movement.

[0057] The thickness of the base substrate is preferably 100 to 5000 μm. If the thickness falls within this range, handling is easy, heat resistance during film formation is small, and a good quality film can be obtained.

[0058] The base substrate is not particularly limited as long as it can be a support for the crystalline oxide film. The material is not particularly limited, and a known substrate can be used, and may be an organic compound or an inorganic compound. For example, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, quartz, glass, calcium carbonate, gallium oxide, ZnO, and the like can be mentioned. In addition to these, single crystal substrates such as silicon, sapphire, α-type gallium oxide, lithium tantalate, lithium niobate, SiC, GaN, iron oxide, and chromium oxide can be mentioned. As the base substrate for the laminated structure of the present invention, the above-mentioned single crystal substrate is desirable. With these, a better quality crystalline oxide film can be obtained. In particular, the sapphire substrate, the lithium tantalate substrate, and the lithium niobate substrate are relatively inexpensive and industrially advantageous.

[0059] The RMS of the base substrate surface is preferably 0.1 μm or less. By using such a substrate, it is easy to obtain a crystalline oxide film with an RMS of 0.2 μm or less. In addition, the particle density of 0.5 μm or more on the base substrate is 50 / cm 2 The metal impurity density is preferably 1×10 11 / cm 2 It is preferable that the thickness of the substrate is less than 100 nm. By using such a substrate, it is easy to obtain a crystalline oxide film with good crystallinity. Once a laminate structure is formed, it is difficult to evaluate the RMS of the substrate surface, the particle density, the metal impurity density, and the like on the substrate.

[0060] (Crystalline oxide film) The crystalline oxide film of the laminated structure of the present invention is a crystalline oxide film mainly composed of gallium oxide, and the root mean square roughness of the surface of the crystalline oxide film mainly composed of gallium oxide is 0.2 μm or less. The lower limit of the root mean square roughness is not particularly limited, but can be, for example, 0.0001 μm or more.

[0061] Generally, a crystalline oxide film is composed of metal and oxygen, but in the crystalline oxide film of the laminated structure of the present invention, the metal may be gallium as the main component. In the present invention, "mainly composed of gallium" 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.

[0062] 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, or niobium, or p-type dopants such as copper, silver, nickel, tin, iridium, rhodium, cobalt, or 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.

[0063] The crystal structure of the crystalline oxide film is not particularly limited, and may be a β-gallium structure, a corundum structure, or a rectangular crystal. A mixture of multiple crystal structures or polycrystals is acceptable, but a single crystal or uniaxially oriented film is preferable. Whether the film is single crystal or uniaxially oriented can be confirmed by an X-ray diffraction device or an electron beam diffraction device. When the film is irradiated with X-rays or electron beams, a diffraction image according to the crystal structure is obtained, and if the film is uniaxially oriented, only a specific peak appears. This allows it to be determined that the film is uniaxially oriented.

[0064] The root mean square roughness (RMS) is not particularly limited as long as it is 0.2 μm or less. The root mean square roughness (RMS) refers to a value calculated based on JIS B 0601 (corresponding to Rq in the standard) using the surface shape measurement results for a 10 μm square area by an atomic force microscope (AFM). The arithmetic mean roughness (Ra) refers to a value calculated based on JIS B 0601 using the surface shape measurement results for a 10 μm square area using an atomic force microscope (AFM).

[0065] The thickness of the crystalline oxide film is not particularly limited, but is preferably 1 μm or more. The upper limit is not particularly limited. For example, it may be 100 μm or less, preferably 50 μm or less, and more preferably 20 μm or less. By setting the thickness in this range, when the crystalline oxide film is applied to a semiconductor device, the semiconductor characteristics, such as improved breakdown voltage, are improved.

[0066] In addition, another layer may be interposed between the base substrate and the crystalline oxide film. The other layer is a layer having a different composition from the base substrate and the crystalline oxide film of the outermost layer, and is also called a buffer layer. The buffer layer may be any of an oxide semiconductor film, an insulating film, a metal film, etc., and examples of the material that can be used 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.

[0067] (Film forming equipment) 2 shows an example of a film forming apparatus 201 according to the method for producing a laminated structure of the present invention. The film forming apparatus 201 has at least a mist generating section 220 that generates mist by turning a raw material solution 204a containing gallium into mist, a carrier gas supply section 230 that supplies a carrier gas for transporting the mist, a supply pipe 209 that connects the mist generating section 220 to a film forming chamber 207 and transports the mist by the carrier gas, and the film forming 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.

[0068] (Mist generating section) In the mist generating section 220, the raw solution 204a containing gallium is turned into mist to generate mist. The mist generating means is not particularly limited as long as it can turn the raw solution 204a containing gallium into mist, and any known mist generating means may be used, but it is preferable to use a mist generating means using ultrasonic vibration, as this allows for more stable mist generation.

[0069] An example of such a mist generating unit 220 is shown in FIG. 4. The mist generating unit 220 may include a mist generating source 204 in which a raw solution 204a containing gallium is accommodated, a medium capable of transmitting ultrasonic vibration, for example, a container 205 in which water 205a is accommodated, and an ultrasonic vibrator 206 attached to the bottom surface of the container 205. In detail, the mist generating source 204 consisting of a container in which the raw solution 204a containing gallium is accommodated can be accommodated in the container 205 in which the water 205a is accommodated, using a support (not shown). The bottom of the container 205 may be equipped with an ultrasonic vibrator 206, or the ultrasonic vibrator 206 and an oscillator 216 may be connected. Then, when the oscillator 216 is operated, the ultrasonic vibrator 206 vibrates, and ultrasonic waves are propagated into the mist generating source 204 through the water 205a, and the raw solution 204a containing gallium can be configured to be misted.

[0070] (Gallium-containing raw material solution) The raw material solution 204a containing gallium can be turned into mist, and the material contained in the solution is not particularly limited as long as it contains gallium, and may be an inorganic material or an organic material. Metals or metal compounds are preferably used, and for example, one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt may be used. As such a raw material solution, a solution in which a metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt can be preferably used. Examples of the salt form include halide salts such as metal chloride salts, metal bromide salts, and metal iodide salts. In addition, a solution in which the above metal is dissolved in a hydrogen halide such as hydrobromic acid, hydrochloric acid, or hydroiodic acid can also be used as a salt solution. Examples of the complex form include an acetylacetonate complex, a carbonyl complex, an ammine complex, and a hydride complex. An acetylacetonate complex can also be formed by mixing acetylacetone with the above-mentioned salt solution. The metal concentration in the raw material solution 204a containing gallium is not particularly limited, and may be, for example, 0.005 to 1 mol / L.

[0071] Additives such as hydrohalic acid and oxidizing agents may be mixed into the raw material solution 204a containing gallium. Examples of hydrohalic acid 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 (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), and benzoyl peroxide (C6H5CO)2O2, hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, and organic peroxides such as peracetic acid and nitrobenzene.

[0072] The raw material solution 204a containing gallium may contain a dopant. The dopant is not particularly limited. For example, n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopants such as copper, silver, iridium, rhodium, or magnesium may be used.

[0073] (Carrier gas supply unit) 2, the carrier gas supply unit 230 has a carrier gas source 202a for supplying a carrier gas. In this case, a flow rate control valve 203a for adjusting the flow rate of the carrier gas sent from the carrier gas source 202a may be provided. In addition, a dilution carrier gas source 202b for supplying a dilution carrier gas as required, and a flow rate control valve 203b for adjusting the flow rate of the dilution carrier gas sent from the dilution carrier gas source 202b may also be provided.

[0074] The type of carrier gas is not particularly limited and can be appropriately selected depending on the film to be formed. For example, oxygen, ozone, inert gas such as nitrogen or argon, or reducing gas such as hydrogen gas or forming gas can be used. The type of carrier gas may be one or more. For example, as the second carrier gas, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (for example, diluted 10 times) may be further used, or air may be used. The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a 50 mm (2 inch) base substrate, the flow rate of the carrier gas is preferably 0.05 to 50 L / min, more preferably 5 to 20 L / min.

[0075] (supply pipe) The film forming apparatus 201 has a supply pipe 209 that connects the mist generating section 220 and the film forming chamber 207. In this case, the mist is transported by a carrier gas from the mist generating source 204 of the mist generating section 220 via the supply pipe 209, and is 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.

[0076] (Film forming chamber) A base substrate 210 is installed in the film formation chamber 207, and a heater 208 for heating the base substrate 210 may be provided. The heater 208 may be provided outside the film formation chamber 207 as shown in FIG. 2, or may be provided inside the film formation chamber 207. In addition, the film formation chamber 207 may be provided with an exhaust gas exhaust port 212 at a position that does not affect the supply of mist to the base substrate 210. In addition, the base substrate 210 may be placed face-down on the top surface of the film formation chamber 207, or the base substrate 210 may be placed face-up on the bottom surface of the film formation chamber 207. A stage for placing the base substrate 210 may be installed in the film formation chamber 207. In this case, the surface roughness Ra of the stage may be 0.5 μm or less. The smaller the surface roughness Ra, the more preferable it is, and the lower limit is not particularly limited, but it can be, for example, 0.1 nm or more. If the surface roughness Ra is 0.5 μm or less, the contact area with the base substrate 210 is not reduced, so that heat conduction is not deteriorated, and the temperature drop of the substrate surface during film formation due to the film formation raw material mist does not occur, so that the crystal orientation of the semiconductor film does not deteriorate. Also, the waviness Wa may be 50 μm or less. The smaller the waviness Wa, the more preferable, and the lower limit is not particularly limited, but it can be, for example, 0.5 μm or more. If Wa is 50 μm or less, the contact area with the base substrate 210 increases, improving thermal conduction, and the temperature drop of the substrate surface during film formation due to the film-forming raw material mist is not significant, so that the crystal orientation of the semiconductor film does not deteriorate.

[0077] (Method of manufacturing laminated structure) Next, an example of a method for producing a laminated structure of the present invention will be described below with reference to Fig. 2. The present invention is characterized in that in mist CVD, the diameter of the substrate is 50 mm or more and the TTV is 30 µm or less.

[0078] Unlike other CVD methods, the mist CVD method requires that the raw material reach the substrate surface in a liquid state. This results in a large drop in the temperature of the substrate surface. If the TTV of the substrate is greater than 30 μm, the thermal contact between the substrate and the heater is poor. At the same time, the thermal resistance is relatively high in areas where the substrate is thick. Due to these effects, the drop in substrate surface temperature is even greater. This is particularly noticeable when the diameter is 50 mm or more. If a film is formed in this state, abnormal growth occurs on the film surface, and the surface roughness of the resulting film becomes very large, exceeding 0.2 μm. Therefore, in the method for producing a laminated structure of the present invention, by using a base substrate with a diameter of 50 mm or more and a TTV of 30 μm or less, a laminated structure with a film surface root mean square roughness of 0.2 μm or less can be obtained in an as-grown state.

[0079] The raw material solution 204a containing gallium mixed by the above-mentioned method is placed in the mist generating source 204, the base substrate 210 is placed in the film formation chamber 207, and the heater 208 is operated. 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.

[0080] Next, in the mist generating step, the ultrasonic vibrator 206 is vibrated and the vibration is propagated through the water 205a to the raw solution 204a containing gallium, thereby turning the raw solution 204a containing gallium into mist and generating the mist.

[0081] Next, in the carrier gas supplying step, a carrier gas for transporting the mist is supplied to the mist generating section 220.

[0082] Next, in a transport step, the mist is transported from the mist generating section 220 to the film forming chamber 207 by a carrier gas through the supply pipe 209 connecting the mist generating section 220 and the film forming chamber 207 .

[0083] Next, in the film-forming step, the mist transported to the film-forming chamber 207 is heated to cause a thermal reaction, thereby forming a film on a part or the whole of the surface of the base substrate 210 .

[0084] The thermal reaction is not particularly limited as long as the mist reacts by heating. The reaction conditions can be appropriately set according to the raw material and the film to be formed. For example, the heating temperature can be in the range of 120 to 600°C, preferably in the range of 200°C to 600°C, and more preferably in the range of 300°C to 550°C.

[0085] 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 according to the film to be formed. The reaction pressure may be under any of atmospheric pressure, pressurized pressure, and reduced pressure, but film formation under atmospheric pressure is preferred because the apparatus configuration can be simplified.

[0086] (Buffer layer) In forming the film, a buffer layer may be provided between the base substrate and the film. The method of forming the buffer layer is not particularly limited, and the film can be formed by known methods such as sputtering and vapor deposition. However, when the mist CVD method is used, the buffer layer can be formed simply by appropriately changing the raw material solution containing gallium. Specifically, one or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium are dissolved or dispersed in water in the form of a complex or salt, and the raw material aqueous solution can be suitably used. Examples of the complex include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of the salt include metal chlorides, metal bromides, and metal iodides. In addition, the above metals can be dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, and the like, and the aqueous solution of the salt can also be used. In this case, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is 20° C. or higher. The buffer layer can be formed by keeping the other conditions the same as above. After the buffer layer is formed to a predetermined thickness, a crystalline oxide film is formed.

[0087] (Heat treatment) The film obtained by the film forming method according to the method for producing a laminated structure of the present invention may be heat-treated at 200 to 600°C. This removes unreacted species in the film, and a higher quality laminated structure can be obtained. The heat treatment may be performed in air or an oxygen atmosphere, or in an inert gas atmosphere such as nitrogen or argon. The heat treatment time is appropriately determined, and may be, for example, 5 to 240 minutes.

[0088] (peeling) In the laminated structure of 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 a known means. Examples of the peeling means include a means for peeling off by applying a mechanical shock, a means for peeling off by applying heat and using thermal stress, a means for peeling off by applying vibration such as ultrasonic waves, and a means for peeling off by etching. By the peeling, the crystalline oxide film can be obtained as a free-standing film.

[0089] (Example of the configuration of a semiconductor device) FIG. 1 shows a preferred example of a semiconductor device 100 using the laminated structure of the present invention. In the example of FIG. 1, a crystalline oxide film 103 is formed on a base 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 base 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. In addition, 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 the gate voltage applied to the gate electrode 107, and a transistor operation (FET device) is possible.

[0090] Examples of semiconductor devices formed using the laminated structure of the present invention include transistors such as MIS, HEMT, IGBT, and TFT, Schottky barrier diodes using semiconductor-metal junctions, PN or PIN diodes combined with other P layers, and light-emitting / receiving elements. The laminated structure of the present invention is useful for improving the characteristics of these devices.

[0091] (Laminated structure manufacturing system) Next, an example of a manufacturing system for a laminated structure of the present invention will be described below with reference to Fig. 2. The present invention is characterized in that in mist CVD, the diameter of the substrate is 50 mm or more and the TTV is 30 µm or less.

[0092] Unlike other CVD methods, the mist CVD method requires that the raw material reach the substrate surface in a liquid state. This results in a large drop in the temperature of the substrate surface. If the TTV of the substrate is greater than 30 μm, the thermal contact between the substrate and the heater is poor. At the same time, the thermal resistance is relatively high in areas where the substrate is thick. Due to these effects, the drop in substrate surface temperature is even greater. This is particularly noticeable when the diameter is 50 mm or more. If a film is formed in this state, abnormal growth occurs on the film surface, and the surface roughness of the resulting film becomes very large, exceeding 0.2 μm. Therefore, in the manufacturing system for the laminated structure of the present invention, by using a base substrate with a diameter of 50 mm or more and a TTV of 30 μm or less, a laminated structure with a film surface root mean square roughness of 0.2 μm or less can be obtained in an as-grown state.

[0093] The raw material solution 204a containing gallium mixed by the above-mentioned method is placed in the mist generating source 204, the base substrate 210 is placed in the film formation chamber 207, and the heater 208 is operated. 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.

[0094] Next, as a mist generating mechanism, ultrasonic vibrator 206 is vibrated and the vibration is propagated to raw solution 204a containing gallium through water 205a, thereby turning raw solution 204a containing gallium into mist and generating the mist.

[0095] Next, a carrier gas for transporting the mist is supplied to the mist generating section 220 as a carrier gas supply mechanism.

[0096] Next, the mist is transported by a carrier gas from the mist generating section 220 to the film forming chamber 207 via a supply pipe 209 that connects the mist generating section 220 and the film forming chamber 207, which serves as a transport mechanism.

[0097] Next, the mist conveyed to the film-forming chamber 207 is heated to cause a thermal reaction, thereby forming a film on a part or the whole of the surface of the base substrate 210 as a film-forming mechanism.

[0098] The thermal reaction is not particularly limited as long as the mist reacts by heating. The reaction conditions can be appropriately set according to the raw material and the film to be formed. For example, the heating temperature can be in the range of 120 to 600°C, preferably in the range of 200°C to 600°C, and more preferably in the range of 300°C to 550°C.

[0099] 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 according to the film to be formed. The reaction pressure may be under any of atmospheric pressure, pressurized pressure, and reduced pressure, but film formation under atmospheric pressure is preferred because the apparatus configuration can be simplified.

[0100] (Buffer layer) In forming the film, a buffer layer may be provided between the base substrate and the film. The method of forming the buffer layer is not particularly limited, and the film can be formed by known methods such as sputtering and vapor deposition. However, when the mist CVD method is used, the buffer layer can be formed simply by appropriately changing the raw material solution containing gallium. Specifically, one or more metals selected from aluminum, gallium, chromium, iron, indium, rhodium, vanadium, titanium, and iridium are dissolved or dispersed in water in the form of a complex or salt, and the raw material aqueous solution can be suitably used. Examples of the complex include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of the salt include metal chlorides, metal bromides, and metal iodides. In addition, the above metals can be dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, and the like, and the aqueous solution of the salt can also be used. In this case, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is 20° C. or higher. The buffer layer can be formed by keeping the other conditions the same as above. After the buffer layer is formed to a predetermined thickness, a crystalline oxide film is formed.

[0101] (Heat treatment) The film obtained by the film forming system according to the laminated structure manufacturing system of the present invention may be heat-treated at 200 to 600°C. This removes unreacted species in the film, and a higher quality laminated structure can be obtained. The heat treatment may be performed in air or an oxygen atmosphere, or in an inert gas atmosphere such as nitrogen or argon. The heat treatment time is appropriately determined, and may be, for example, 5 to 240 minutes.

[0102] (peel off) In the laminated structure of 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 a known means. Examples of the peeling means include a means for peeling off by applying a mechanical shock, a means for peeling off by applying heat and using thermal stress, a means for peeling off by applying vibration such as ultrasonic waves, and a means for peeling off by etching. By the peeling, the crystalline oxide film can be obtained as a free-standing film.

[0103] Furthermore, the present invention is preferably a system for manufacturing a laminated structure, which confirms, prior to placing the base substrate in the film formation chamber, that the TTV is 30 μm or less when the diameter of the base substrate is 50 mm or more. EXAMPLES

[0104] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0105] Example 1 The film forming apparatus 201 used in this embodiment will be described with reference to Fig. 2. The film forming apparatus 201 includes a carrier gas source 202a for supplying a carrier gas, a flow rate control valve 203a for controlling the flow rate of the carrier gas sent 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 controlling the flow rate of the dilution carrier gas sent from the dilution carrier gas source 202b, a mist generating source 204 containing a raw material solution 204a containing gallium, a container 205 containing water 205a, an ultrasonic vibrator 206 attached to the bottom surface of the container 205, a film forming chamber 207 equipped with a heater 208, and a quartz supply pipe 209 connecting the mist generating source 204 to the film forming chamber 207.

[0106] (Base substrate) A c-plane sapphire substrate having a diameter of 100 mm (4 inches) was prepared as the base substrate 210. The TTV was measured by an optical interference flatness tester and found to be 16 μm. The substrate was placed in the film formation chamber 207, and the heater 208 was operated to raise the temperature to 500° C.

[0107] (Gallium-containing raw material solution) Next, a raw material solution containing gallium was prepared. The solvent was ultrapure water, and the solute was gallium bromide. The gallium concentration was set to 0.1 mol / L, and this was used as raw material solution 204a containing gallium.

[0108] (film formation) The raw material solution 204a containing gallium obtained as described above was placed in the mist generating 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 forming chamber 207, and the atmosphere in the film forming chamber 207 was sufficiently replaced with the carrier gas, and then 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.

[0109] Next, the ultrasonic vibrator 206 was vibrated at 2.4 MHz, and the vibration was propagated to the raw material solution 204a containing gallium through the water 205a, thereby misting the raw material solution 204a containing gallium to generate mist. This mist was introduced into the film formation chamber 207 through the supply pipe 209 by the carrier gas. Then, the mist was thermally reacted in the film formation chamber 207 under atmospheric pressure and at 500° C. to form a thin film of gallium oxide on the base substrate 210. The film formation time was 30 minutes.

[0110] (evaluation) It was confirmed by X-ray diffraction that the thin film formed on the base substrate 210 was α-Ga2O3. Next, the root mean square roughness RMS of the film surface was measured by AFM. The result was that the RMS was 8 nm. The film thickness was measured with a Filmetrics reflectance spectroscopic film thickness meter F50 and was found to be 0.52 μm.

[0111] (Examples 2 and 3) As the base substrate 210, c-plane sapphire substrates with a diameter of 100 mm (4 inches) and different TTVs were prepared. Specifically, substrates with TTVs of 3 and 26 μm were prepared, and films were formed and evaluated under the same conditions as in Example 1 except for this. As a result, the RMS were 2 and 8 nm, respectively. The film thicknesses were 0.49 and 0.51 μm, respectively.

[0112] (Comparative Examples 1 and 2) As the base substrate 210, a c-plane sapphire substrate having a diameter of 100 mm (4 inches) and a TTV of 41 and 61 μm was prepared. Other than this, film formation and evaluation were performed under the same conditions as in Example 1. As a result, the RMS were 245 and 303 nm, respectively. The film thicknesses were 0.47 and 0.46 μm, respectively.

[0113] Example 4 Except for changing the film formation time to 60 minutes, film formation and evaluation were performed under the same conditions as in Example 1. As a result, the film thickness was 1.1 μm and the RMS was 11 nm.

[0114] Example 5 Except for changing the film formation time to 480 minutes, film formation and evaluation were performed under the same conditions as in Example 1. As a result, the film thickness was 8.5 μm and the RMS was 15 nm.

[0115] Example 6 In Example 1, film formation and evaluation were performed under the same conditions as in Example 1, except that the Ra of the non-film-forming surface of the substrate was 0.41 μm. As a result, the RMS was 7 nm. The film thickness was 0.51 μm.

[0116] Example 7 In Example 1, film formation and evaluation were performed under the same conditions as in Example 1, except that the Wa of the non-film-forming surface of the substrate was set to 47.7 μm. As a result, the RMS was 10 nm. The film thickness was 0.53 μm.

[0117] Example 8 In Example 1, a copper plate (stage) was placed on the heater, and the film was formed and evaluated under the same conditions as in Example 1, except that the Ra of the copper plate was set to 0.45 μm. As a result, the RMS was 5 nm. The film thickness was 0.48 μm.

[0118] Example 9 In Example 1, a copper plate (stage) was placed on the heater, and the film was formed and evaluated under the same conditions as in Example 1, except that the Wa of the copper plate was set to 48.2 μm. As a result, the RMS was 6 nm. The film thickness was 0.50 μm.

[0119] A graph summarizing Examples 1, 2, and 3 and Comparative Examples 1 and 2 is shown in Figure 3. It can be seen that when the TTV of the base substrate exceeds 30 μm, the RMS of the surface of the crystalline oxide film increases rapidly. As mentioned above, this is thought to be due to the deterioration of thermal contact with the heater and the increase in thermal resistance.

[0120] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A laminated structure comprising a base substrate and a crystalline oxide film mainly composed of gallium oxide, the crystalline oxide film having a surface root mean square roughness of 0.2 μm or less, the base substrate having a diameter of 50 mm or more, and the base substrate having a total thickness variation (TTV) of 30 μm or less.

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

3. 3. The laminated structure according to claim 1, wherein the thickness of the base substrate is 100 to 5000 μm.

4. 4. The laminated structure according to claim 1, wherein the crystalline oxide film has a thickness of 1 to 100 μm.

5. 5. The laminated structure according to claim 1, wherein the base substrate is a single crystal.

6. 6. 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.

7. 7. The laminate structure according to claim 1, wherein the surface of the laminate structure opposite to the surface having the crystalline oxide film has a surface roughness Ra of 0.5 μm or less.

8. 8. The laminated structure according to claim 1, wherein a waviness Wa of a surface of the laminated structure opposite to a surface having a crystalline oxide film is 50 μm or less.

9. A semiconductor device comprising the laminated structure according to any one of claims 1 to 8.

10. A method for manufacturing a laminated structure, comprising the steps of: a mist generating step of misting a raw material solution containing gallium in a mist generating section to generate mist; A carrier gas supplying 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 unit to the deposition chamber in which a base substrate is placed by the carrier gas through a supply pipe connecting the mist generating unit and the deposition chamber; a film forming step of forming a film on the base substrate by heat-treating the transported mist; Including, A method for producing a laminated structure, comprising using as the base substrate a substrate having a diameter of 50 mm or more and a total thickness variation (TTV) of 30 μm or less.

11. 11. The method for producing a laminated structure according to claim 10, wherein the underlying substrate has a thickness of 100 to 5000 μm.

12. 12. The method for producing a laminated structure according to claim 10, wherein the base substrate is a single crystal substrate.

13. 13. The method for manufacturing a laminated structure according to claim 10, wherein the base substrate is any one of a sapphire substrate, a lithium tantalate substrate, and a lithium niobate substrate.

14. 14. The method for producing a laminated structure according to claim 10, wherein the surface of the base substrate opposite to the film-forming surface has a surface roughness Ra of 0.5 μm or less.

15. 15. The method for producing a laminated structure according to claim 10, wherein the waviness Wa of the surface of the base substrate opposite to the film-forming surface is set to 50 [mu]m or less.

16. 16. The method for manufacturing a laminated structure according to claim 10, wherein in the film formation step, the base substrate is placed on a stage, and a surface roughness Ra of the contact surface of the stage with the base substrate is set to 0.5 μm or less.

17. 17. The method for manufacturing a laminated structure according to claim 10, wherein in the film forming step, the base substrate is placed on a stage, and a waviness Wa of a contact surface of the stage with the base substrate is set to 50 μm or less.

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