Laminated structure, semiconductor device, and ground substrate

Abstract

To provide a laminated structure having a crystalline oxide film with a smooth surface and a method for manufacturing the laminated structure.SOLUTION: A laminated structure comprises a ground substrate and a crystalline oxide film containing gallium oxide as a main component. Root-mean-square roughness on the surface of the crystalline oxide film is 0.2 μm or less. The diameter of the ground substrate is 50 mm or more. Surface roughness Ra on the surface on the opposite side of the laminated structure from the surface having the crystalline oxide film is 0.5 μm or less.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As a method for forming a highly crystalline gallium oxide-based thin film on a film-forming target, a film-forming technique using water fine particles such as mist CVD 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 fine particles. These raw material fine particles are supplied to the film-forming surface of the film-forming target by a carrier gas, and the raw material fine 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 target.

[0003] In order to form a semiconductor device using a gallium oxide-based thin film, it is essential to control the conductivity of the gallium oxide-based thin film. Patent Document 1 and Non-Patent Document 1 disclose techniques for doping impurities into an α-gallium oxide thin film.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] According to the methods of Patent Document 1 and Non-Patent Document 1, α-gallium oxide (hereinafter sometimes referred to as “α-Ga2O3”) thin films excellent in conductivity can be formed, but there are specific problems such as the film surface not being smooth. For use in semiconductor devices, it was still not satisfactory. Also, in order to smooth the film surface, surface treatment such as etching may be considered, but in this case, there were problems such as the thin film being etched away or the semiconductor characteristics being impaired.

[0007] Regarding 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 not sufficient, and the characteristics of semiconductor devices using the obtained film are also not satisfactory.

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

Means for Solving the Problems

[0009] The present invention has been made to achieve the above object, and provides a laminated structure having a lower base substrate and a crystalline oxide film containing gallium oxide as a main component, wherein the root mean square roughness of the surface of the crystalline oxide film is 0.2 μm or less, the diameter of the lower base substrate is 50 mm or more, and the TTV of the lower 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 characteristics are excellent.

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

[0012] Thereby, when applied to a semiconductor device, the semiconductor characteristics are excellent.

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

[0014] Thereby, the surface becomes smoother, and a laminated structure having more excellent semiconductor characteristics when applied to a semiconductor device can be obtained.

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

[0016] Thereby, when applied to a semiconductor device, the semiconductor characteristics are more excellent.

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

[0018] Thereby, a laminated structure having a gallium oxide film with more excellent crystallinity can be obtained.

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

[0020] As a result, a laminated structure having a gallium oxide film with a smoother surface and better crystallinity can be obtained.

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

[0022] Such a laminated structure is a laminated structure of high quality and suitable for manufacturing a semiconductor film device.

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

[0024] Such a laminated structure is a laminated structure of even higher quality and suitable for manufacturing a semiconductor film device.

[0025] Further, the present invention provides a semiconductor device including the laminated structure described above.

[0026] As a result, a semiconductor device having more excellent characteristics is obtained.

[0027] Further, the present invention provides a method for manufacturing a laminated structure, a mist generation step of generating a mist by mistifying a raw material solution containing gallium in a mistifying section; a carrier gas supply step of supplying a carrier gas for transporting the mist to the mistifying section; a transport step of transporting the mist from the mistifying section to the film forming chamber where a lower base substrate is installed through a supply pipe connecting the mistifying section and the film forming chamber by the carrier gas; a film forming step of heat-treating the transported mist to form a film on the lower base substrate and including providing a method for manufacturing a laminated structure using, as the lower base substrate, one having a diameter of 50 mm or more and a TTV of 30 μm or less.

[0028] According to the manufacturing method of such a laminated structure, a laminated structure including a crystalline oxide film having a smooth surface can be manufactured.

[0029] In addition, in the present invention, the underlying substrate having a thickness of 100 to 5000 μm can be used.

[0030] As a result, the surface becomes smoother, and a laminated structure having more excellent semiconductor characteristics when applied to a semiconductor device can be manufactured.

[0031] In addition, in the present invention, a single crystal can be used as the underlying substrate.

[0032] As a result, a laminated structure having a gallium oxide film with more excellent crystallinity can be manufactured.

[0033] In addition, in the present invention, any one of a sapphire substrate, a lithium tantalate substrate, or a lithium niobate substrate can be used as the underlying substrate.

[0034] As a result, a laminated structure having a gallium oxide film with a smoother surface and more excellent crystallinity can be manufactured at a lower cost.

[0035] In addition, in the present invention, the surface roughness Ra of the surface on the side opposite to the film formation surface of the underlying substrate may be 0.5 μm or less.

[0036] With such a method, a laminated structure including a high-quality semiconductor film with excellent crystal orientation can be stably manufactured. In addition, since the damage to the transport system and the substrate carrier due to the back surface of the substrate is significantly reduced, the generation of dust in the apparatus is suppressed. In addition, since the degree of freedom of the material of the transport system and the substrate carrier increases, a laminated structure including a high-quality semiconductor film can be manufactured more stably and inexpensively.

[0037] In addition, in the present invention, the waviness Wa of the surface on the side opposite to the film formation surface of the underlying substrate may be 50 μm or less.

[0038] By doing so, the heat conduction is improved by increasing the contact area with the substrate, and the temperature drop on the substrate surface during film formation by the raw material mist for film formation is not significant and the crystal orientation of the semiconductor film does not deteriorate. Therefore, a high-quality laminated structure can be stably manufactured.

[0039] Further, in the present invention, in the film formation step, the underlying substrate is placed on a stage, and the surface roughness Ra of the contact surface of the stage with the underlying substrate may be 0.5 μm or less.

[0040] With such a method, it becomes possible to stably manufacture a laminate including a high-quality semiconductor film having excellent crystal orientation. In addition, since damage to the transport system and substrate carrier due to the back surface of the substrate is significantly reduced, dust generation in the apparatus is suppressed. In addition, since the degree of freedom in the material of the transport system and substrate carrier increases, a laminate including a semiconductor film having a high-quality corundum-type crystal structure can be manufactured more stably and inexpensively.

[0041] Further, in the present invention, in the film formation step, the underlying substrate is placed on a stage, and the waviness Wa of the contact surface of the stage with the underlying substrate may be 50 μm or less.

[0042] By doing so, the heat conduction is improved by increasing the contact area with the substrate, and the temperature drop on the substrate surface during film formation by the raw material mist for film formation is not significant and the crystal orientation of the semiconductor film does not deteriorate. Therefore, a high-quality laminated structure can be stably manufactured.

Effects of the Invention

[0043] As described above, according to the laminated structure of the present invention, it has a crystalline oxide film with a smooth surface, and when applied to a semiconductor device, it becomes a laminated structure with excellent semiconductor characteristics. Further, according to the method for manufacturing the laminated structure of the present invention, it is possible to manufacture a laminated structure having a crystalline oxide film with a smooth surface and excellent semiconductor characteristics when applied to a semiconductor device.

Brief Description of the Drawings

[0044]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0045] As described above, there has been a demand for providing a laminated structure including a crystalline oxide film having a smooth surface, and a method for manufacturing the laminated structure.

[0046] As a result of intensive studies on the above problems, the present inventors have found a laminated structure having 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 (2 inches) or more, and the TTV of the base substrate is 30 μm or less. A laminated structure having a crystalline oxide film with a smooth surface and excellent semiconductor characteristics when applied to a semiconductor device has been found, and the present invention has been completed.

[0047] Further, the present inventors have a method for manufacturing a laminated structure, In the mist generating unit, a mist generating step of generating a mist by mistifying a raw material solution containing gallium, A carrier gas supply step of supplying a carrier gas for transporting the mist to the mist generating unit, A transport step of transporting the mist by the carrier gas from the mist generating unit to the film forming chamber in which the base substrate is installed via a supply pipe connecting the mist generating unit and the film forming chamber, A film-forming step of heat-treating the transported mist to form a film on the lower base substrate including By the manufacturing method of a laminated structure characterized by using, as the lower base substrate, one having a diameter of 50 mm or more and a TTV of 30 μm or less, it has been found that a laminated structure having a crystalline oxide film with a smooth surface can be manufactured, and when applied to a semiconductor device, a laminated structure with excellent semiconductor characteristics can be obtained, thus completing the present invention.

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

[0049] Hereinafter, the present invention will be described in detail, 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 lower base substrate 101 and a crystalline oxide film 103 mainly composed of gallium oxide. The root mean square roughness of the surface 103c of the crystalline oxide film 103 is 0.2 μm or less, the diameter of the lower base substrate 101 is 50 mm (2 inches) or more, and the TTV of the lower base substrate 101 is 30 μm or less. Thereby, it has a crystalline oxide film 103 with a smooth surface, and when applied to a semiconductor device, it becomes a laminated structure 110 with excellent semiconductor characteristics.

[0051] (Lower base substrate) Conventionally, when the diameter of the lower base substrate 101 increases, the deterioration of the root mean square roughness of the surface of the crystalline oxide film 103 becomes remarkable. In particular, for those with a diameter of 50 mm or more, those with a roughness of 0.2 μm or less could not be obtained. Therefore, as a result of the intensive investigation by the present inventors, as shown in FIG. 3, it was found that the RMS of the surface of the crystalline oxide film rapidly increases from around where the TTV of the lower base substrate exceeds 30 μm. As will be described later, it is considered to be due to the deterioration of the thermal contact with the heater and the increase in thermal resistance. Therefore, in the present invention, the TTV is set to 30 μm or less. As in the present invention, even when using a lower base substrate 101 with a diameter of 50 mm (2 inches) or more, by setting the TTV of the lower base substrate 101 to 30 μm or less, the root mean square roughness of the surface 103c of the crystalline oxide film 103 becomes 0.2 μm or less.

[0052] The lower base substrate according to 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 value of the diameter is not particularly limited, but for example, it can be 300 mm or less. Also, the lower limit value of the TTV is not particularly limited, but for example, it can be 0.1 μm or more.

[0053] TTV is an abbreviation for total thickness variation, and is the difference between the maximum value and the minimum value of the height measured in the thickness direction with the back surface of the wafer as the reference plane over the entire surface of the wafer. In the present invention, the TTV of the lower base substrate is 30 μm or less. At this time, the TTV of the obtained laminated structure also becomes 30 μm or less. TTV can be measured by a micrometer, a capacitance method, an optical interference method, a laser confocal method, or the like.

[0054] The Ra of the surface of the laminated structure on the side opposite to the surface 103c having the crystalline oxide film may be 0.5 μm or less. The smaller the surface roughness Ra, the better. The lower limit value is not particularly limited, but for example, it can be 0.1 nm or more. If the surface roughness Ra is 0.5 μm or less, the contact area with the lower base substrate 101 does not decrease, so heat conduction does not deteriorate, and the temperature drop of the substrate surface during film formation due to the film-forming raw material mist does not occur, and the crystal orientation of the semiconductor film does not deteriorate.

[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 it is, and the lower limit is not particularly limited, but for example, it can be 0.5 μm or more. If Wa is 50 μm or less, the heat conduction is improved by increasing the contact area with the underlying substrate 101, and the temperature drop of the substrate surface during film formation by the film-forming raw material mist is not significant, and the crystal orientation of the semiconductor film does not deteriorate.

[0056] The waviness Wa is defined as "the magnitude of the deviation from a geometrically correct plane of the planar shape". The waviness Wa may be measured on one or more arbitrary straight lines on the placement surface appropriately determined according to the shape of the placement surface. For example, when the placement surface is circular, on two straight lines intersecting at right angles at the center of the circle, the diameter of the circle can be used as the measurement length. The waviness Wa refers to a value obtained by calculating based on JIS B 0601 using the surface shape measurement results by a non-contact measurement method using a laser microscope or a confocal microscope such as a contact needle method, an atomic force microscope (AFM) method, or an optical interference method, a confocal method, or an image synthesis method by focus movement.

[0057] The thickness of the underlying substrate is preferably 100 to 5000 μm. Within this range, the handling is good, the thermal resistance is small during film formation, and a high-quality film can be obtained.

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

[0059] Note that the RMS of the lower base substrate surface is preferably 0.1 μm or less. By using such a substrate, it becomes easier to obtain a crystalline oxide film with an RMS of 0.2 μm or less. Also, the particle density of 0.5 μm or more on the lower base substrate is preferably 50 / cm 2 or less, and the metal impurity density is preferably 1×10 11 / cm 2 or less. By using such a lower base substrate, it becomes easier to obtain a crystalline oxide film with good crystallinity. Once it becomes a laminated structure, it is difficult to evaluate the RMS of the surface of such a lower base substrate, the particle density on the lower base substrate, the metal impurity density, etc.

[0060] (Crystalline Oxide Film) The crystalline oxide film according to 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 value of the root mean square roughness is not particularly limited, but it can be, for example, 0.0001 μm or more.

[0061] Generally, a crystalline oxide film is composed of a metal and oxygen. However, in the crystalline oxide film according to the laminate structure of the present invention, it is only necessary that gallium be the main component as the metal. In the present invention, "gallium as the main component" means that 50 to 100% of the metal components are gallium. As metal components other than gallium, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt may be included.

[0062] A dopant element may be included in the crystalline oxide film. For example, 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, magnesium, etc. may be mentioned and are not particularly limited. The concentration of the dopant is, for example, about 1×10 16 / cm 3 ~1×10 22 / cm 3 may be sufficient, or may be a low concentration of about 1×10 17 / cm 3 or less, or a high concentration of about 1×10 20 / cm 3 or more.

[0063] The crystal structure of the crystalline oxide film is not particularly limited, and may be a β-gallia structure, a corundum structure, or a cubic crystal. A plurality of crystal structures may be mixed, or it may be polycrystalline, but it is preferably a single crystal or a uniaxially oriented film. Whether it is a single crystal or a uniaxially oriented film can be confirmed by an X-ray diffractometer, an electron beam diffractometer, etc. When the film is irradiated with X-rays or an electron beam, a diffraction image corresponding to the crystal structure is obtained, but when it is uniaxially oriented, only specific peaks appear. Thus, it can be determined that it 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) is a value obtained by using the surface shape measurement results of a 10 μm square region by an atomic force microscope (AFM) and calculating based on JIS B 0601 (corresponding to Rq in the same standard). The arithmetic mean roughness (Ra) is a value obtained by using the surface shape measurement results of a 10 μm square region by an atomic force microscope (AFM) and calculating based on JIS B 0601.

[0065] The film thickness of the crystalline oxide film is not particularly limited, but it 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 film thickness in this way, when applied to a semiconductor device, semiconductor characteristics such as improved withstand voltage become more excellent.

[0066] Also, another layer may be interposed between the underlying substrate and the crystalline oxide film. Another layer is a layer having a different composition from the underlying substrate and the outermost crystalline oxide film, 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. As the material, for example, Al2O3, Ga2O3, Cr2O3, Fe2O3, In2O3, Rh2O3, V2O3, Ti2O3, Ir2O3, etc. are preferably used. The thickness of the buffer layer is preferably 0.1 μm to 2 μm.

[0067] (Film-forming apparatus) FIG. 2 shows an example of a film-forming apparatus 201 according to the method for manufacturing a laminated structure of the present invention. The film-forming apparatus 201 includes a mist-forming unit 220 that atomizes a raw material solution 204a containing gallium to generate a mist, a carrier gas supply unit 230 that supplies a carrier gas for transporting the mist, a supply pipe 209 that connects the mist-forming unit 220 and the film-forming chamber 207 and through which the mist is transported by the carrier gas, and a film-forming chamber 207 that heat-treats the mist supplied together with the carrier gas from the supply pipe 209 to form a film on the underlying substrate 210, and has at least these components.

[0068] (Atomization section) In the atomization section 220, a raw material solution 204a containing gallium is atomized to generate mist. The atomization means is not particularly limited as long as it can atomize the raw material solution 204a containing gallium, and it may be a known atomization means. However, it is preferable to use an atomization means by ultrasonic vibration. This is because mist can be atomized more stably.

[0069] An example of such an atomization section 220 is shown in FIG. 4. The atomization section 220 may include a mist generation source 204 that houses the raw material solution 204a containing gallium, a container 205 into which a medium capable of transmitting ultrasonic vibration, for example, water 205a, is placed, and an ultrasonic vibrator 206 attached to the bottom surface of the container 205. Specifically, the mist generation source 204, which is a container housing the raw material solution 204a containing gallium, can be housed in the container 205 containing water 205a using a support (not shown). An ultrasonic vibrator 206 may be provided at the bottom of the container 205, and the ultrasonic vibrator 206 and the oscillator 216 may be connected. Then, when the oscillator 216 is operated, the ultrasonic vibrator 206 vibrates, ultrasonic waves propagate into the mist generation source 204 through the water 205a, and the raw material solution 204a containing gallium can be configured to be atomized.

[0070] (Raw material solution containing gallium) The raw material solution 204a containing gallium can be atomized, and the material contained in the solution is not particularly limited as long as it contains gallium, and it may be an inorganic material or an organic material. Metals or metal compounds are preferably used. For example, those containing 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, those in which a metal is dissolved or dispersed in an organic solvent or water in the form of a complex or a salt can be preferably used. Examples of the salt form include halogenated salts such as metal chloride salts, metal bromide salts, and metal iodide salts. In addition, those in which the above metals are dissolved in hydrohalic acids such as hydrobromic acid, hydrochloric acid, and hydroiodic acid can also be used as salt solutions. Examples of the complex form include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. An acetylacetonate complex can also be formed by mixing acetylacetone with the salt solution described above. The metal concentration in the raw material solution 204a containing gallium is not particularly limited, and can be, for example, 0.005 to 1 mol / L.

[0071] Additives such as hydrohalic acids and oxidants may be mixed into the raw material solution 204a containing gallium. Examples of the hydrohalic acid include hydrobromic acid, hydrochloric acid, and hydroiodic acid, among which hydrobromic acid or hydroiodic acid is preferred. Examples of the oxidant include peroxides such as hydrogen peroxide (H2O2), sodium peroxide (Na2O2), barium peroxide (BaO2), benzoyl peroxide (C6H5CO)2O2, hypochlorous acid (HClO), perchloric acid, nitric acid, ozone water, organic 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, magnesium, etc. can be mentioned.

[0073] (Carrier gas supply unit) As shown in FIG. 2, the carrier gas supply unit 230 has a carrier gas source 202a that supplies carrier gas. At this time, a flow rate adjustment valve 203a for adjusting the flow rate of the carrier gas sent out from the carrier gas source 202a may be provided. Further, a dilution carrier gas source 202b that supplies dilution carrier gas as necessary, and a flow rate adjustment 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.

[0074] The type of carrier gas is not particularly limited and can be appropriately selected according to the film-forming material. For example, oxygen, ozone, an inert gas such as nitrogen or argon, or a reducing gas such as hydrogen gas or forming gas can be mentioned. Also, the type of carrier gas may be one type or two or more types. 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) substrate, the flow rate of the carrier gas is preferably 0.05 to 50 L / min, and 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 unit 220 and the film-forming chamber 207. In this case, the mist is conveyed by the carrier gas through the supply pipe 209 from the mist generating source 204 of the mist generating unit 220 and supplied into the film-forming chamber 207. The supply pipe 209 can use, for example, a quartz tube, a glass tube, a resin tube, or the like.

[0076] (Film-forming chamber) Inside the film formation chamber 207, a lower base plate 210 is installed, and a heater 208 for heating the lower base plate 210 can 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. Further, an exhaust port 212 for exhaust gas may be provided in the film formation chamber 207 at a position that does not affect the supply of mist to the lower base plate 210. Also, the lower base plate 210 may be installed on the upper surface of the film formation chamber 207 to be face-down, or the lower base plate 210 may be installed on the bottom surface of the film formation chamber 207 to be face-up. Note that a stage for placing the lower base plate 210 may be installed inside the film formation chamber 207. At this time, the surface roughness Ra of the stage surface may be 0.5 μm or less. The smaller the surface roughness Ra, the more preferable, and the lower limit is not particularly limited, but for example, it can be 0.1 nm or more. If the surface roughness Ra is 0.5 μm or less, the contact area with the lower base plate 210 does not decrease, so heat conduction does not deteriorate, and the temperature drop on the substrate surface during film formation by the film formation raw material mist does not occur, and 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 for example, it can be 0.5 μm or more. If Wa is 50 μm or less, the contact area with the lower base plate 210 increases, so heat conduction improves, and the temperature drop on the substrate surface during film formation by the film formation raw material mist does not become significant, and the crystal orientation of the semiconductor film does not deteriorate.

[0077] (Method for manufacturing a laminated structure) Next, an example of the method for manufacturing 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 the raw material to reach the substrate surface in a liquid state. For this reason, the temperature of the substrate surface drops significantly. At this time, if the TTV of the substrate is greater than 30 μm, the thermal contact between the substrate and the heater deteriorates. At the same time, in the thick part of the substrate, the thermal resistance is relatively large. Due to these effects, the decrease in the substrate surface temperature becomes even greater. This is particularly significant for diameters of 50 mm or more. When film formation is performed in this state, abnormal growth occurs on the film surface, and the surface roughness of the obtained film becomes extremely large, exceeding 0.2 μm. Therefore, in the method for manufacturing 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 root mean square surface roughness of 0.2 μm or less on the film surface can be obtained in the as-grown state.

[0079] The raw material solution 204a containing gallium mixed by the above method is accommodated in the mist generation source 204, the base substrate 210 is placed in the film formation chamber 207, and the heater 208 is operated. Next, the flow 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. After sufficiently replacing the atmosphere in the film formation chamber 207 with the carrier gas, the flow rate of the carrier gas and the flow rate of the carrier gas for dilution are adjusted respectively.

[0080] Next, as the mist generation step, the ultrasonic vibrator 206 is vibrated, and the vibration is propagated through the water 205a to the raw material solution 204a containing gallium, thereby atomizing the raw material solution 204a containing gallium to generate mist.

[0081] Next, as the carrier gas supply step, a carrier gas for transporting the mist is supplied to the mist generation section 220.

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

[0083] Next, as a film forming step, the mist conveyed to the film forming chamber 207 is heated to cause a thermal reaction, and a film is formed on a part or all of the surface of the underlying substrate 210.

[0084] For the thermal reaction, it is only necessary that the mist reacts by heating, and the reaction conditions and the like are not particularly limited. They can be appropriately set according to the raw materials and the film to be formed. For example, the heating temperature ranges from 120 to 600 °C, preferably from 200 °C to 600 °C, and more preferably from 300 °C to 550 °C.

[0085] Note that the thermal reaction may be carried out in any atmosphere such as under vacuum, in a non-oxygen atmosphere, in a reducing gas atmosphere, in an air atmosphere, and in an oxygen atmosphere, and may be appropriately set according to the film to be formed. Also, the reaction pressure may be carried out under any conditions of atmospheric pressure, under pressure, or under reduced pressure, but atmospheric pressure film formation is preferable because the device configuration can be simplified.

[0086] (Buffer layer) In the above film formation, a buffer layer may be appropriately provided between the underlying substrate and the film. The method for forming the buffer layer is not particularly limited, and it can be formed by a known method such as sputtering or vapor deposition. However, when using the mist CVD method as described above, it can be formed simply by appropriately changing the raw material solution containing gallium. Specifically, a raw material aqueous solution obtained 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 a salt can be preferably used. Examples of the form of the complex include acetylacetonate complex, carbonyl complex, ammine complex, and hydride complex. Examples of the form of the salt include metal chloride, metal bromide, and metal iodide. Also, a solution obtained by dissolving the above metal in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. can also be used as an aqueous salt solution. In this case as well, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is 20 °C or higher. Regarding other conditions, a buffer layer can be formed in the same manner as above. After forming the buffer layer to a predetermined thickness, a crystalline oxide film is formed.

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

[0088] (Peeling) In the laminated structure of the present invention, the crystalline oxide film may be peeled from the underlying substrate. The peeling means is not particularly limited and may be a known means. Examples of the method of the peeling means include means for peeling by applying mechanical impact, means for peeling by applying heat and utilizing thermal stress, means for peeling by applying vibration such as ultrasonic waves, and means for peeling by etching. By the peeling, the crystalline oxide film can be obtained as a free-standing film.

[0089] (Configuration example of semiconductor device) A preferred example of a semiconductor device 100 using the laminated structure of the present invention is shown in FIG. 1. In the example of FIG. 1, a crystalline oxide film 103 is formed on an underlying substrate 101. The crystalline oxide film 103 is composed of an insulating thin film 103a and a conductive thin film 103b laminated in 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. Also, on the conductive thin film 103b, source / drain electrodes 109 are formed so as to sandwich the gate electrode 107. According to such a configuration, the control of the depletion layer formed in the conductive thin film 103b becomes possible by the gate voltage applied to the gate electrode 107, and transistor operation (FET device) becomes 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 and light-receiving elements. The laminated structure of the present invention is useful for improving the characteristics of these devices.

[0091] (Manufacturing System of Laminated Structure) Next, an example of a manufacturing system for the 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, in the mist CVD method, it is necessary to reach the surface of the substrate with the raw material in a liquid state. For this reason, the temperature of the substrate surface drops significantly. At this time, if the TTV of the substrate is greater than 30 μm, the thermal contact between the substrate and the heater deteriorates. At the same time, in a thick portion of the substrate, the thermal resistance becomes relatively large. Due to these effects, the decrease in the substrate surface temperature becomes even greater. This is particularly significant when the diameter is 50 mm or more. When film formation is performed in this state, abnormal growth occurs on the film surface, and the surface roughness of the obtained film becomes extremely large, exceeding 0.2 μm. Therefore, in the manufacturing system of 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 root mean square surface roughness of 0.2 μm or less on the film surface can be obtained in an as-grown state.

[0093] The raw material solution 204a containing gallium mixed by the above method is housed in the mist generation source 204, the base substrate 210 is placed in the film formation chamber 207, and the heater 208 is operated. Next, the flow 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. After sufficiently replacing the atmosphere in the film formation chamber 207 with the carrier gas, the flow rate of the carrier gas and the flow rate of the carrier gas for dilution are adjusted respectively.

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

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

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

[0097] Next, as a film forming mechanism, the mist transported to the film forming chamber 207 is heated to cause a thermal reaction, and a film is formed on a part or all of the surface of a base substrate 210.

[0098] For the thermal reaction, it is sufficient that the mist reacts upon heating, and the reaction conditions and the like are not particularly limited. They can be appropriately set according to the raw materials 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] Note that the thermal reaction may be carried out under any atmosphere of vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and can be appropriately set according to the film to be formed. Also, the reaction pressure may be under any condition of atmospheric pressure, pressurization, or depressurization, but atmospheric pressure film formation is preferable because the apparatus configuration can be simplified.

[0100] (Buffer layer) In the above film formation, a buffer layer may be appropriately provided between the underlying substrate and the film. The method for forming the buffer layer is not particularly limited, and it can be formed by known methods such as sputtering and vapor deposition. However, when using the mist CVD method as described above, it can be formed simply by appropriately changing the raw material solution containing gallium. Specifically, a raw material aqueous solution in which 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 a salt can be preferably used. Examples of the form of the complex include acetylacetonate complex, carbonyl complex, ammine complex, and hydride complex. Examples of the form of the salt include metal chloride, metal bromide, and metal iodide. Also, a solution in which the above metal is dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc. can be used as an aqueous solution of the salt. Also in this case, the solute concentration is preferably 0.005 to 1 mol / L, and the dissolution temperature is 20°C or higher. Regarding other conditions, the buffer layer can be formed in the same manner as above. After forming the buffer layer to a predetermined thickness, a crystalline oxide film is formed.

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

[0102] (Peeling) In the laminate structure of the present invention, the crystalline oxide film may be peeled from the underlying substrate. The peeling means is not particularly limited, and known means may be used. Examples of the method of the peeling means include means for peeling by applying mechanical impact, means for peeling by applying heat and utilizing thermal stress, means for peeling by applying vibration such as ultrasonic waves, and means for peeling by etching. By the above peeling, the crystalline oxide film can be obtained as a free-standing film.

[0103] Further, in the present invention, prior to installing the lower base substrate in the film forming chamber, it is preferable that the manufacturing system of the laminated structure is such that when the diameter of the lower base substrate is 50 mm or more, the TTV is confirmed to be 30 μm or less.

Example

[0104] Hereinafter, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited thereto.

[0105] (Example 1) Referring to FIG. 2, the film forming apparatus 201 used in this example will be described. The film forming apparatus 201 includes a carrier gas source 202a that supplies a carrier gas, a flow rate regulating valve 203a for regulating the flow rate of the carrier gas sent out from the carrier gas source 202a, a dilution carrier gas source 202b that supplies a dilution carrier gas, a flow rate regulating valve 203b for regulating the flow rate of the dilution carrier gas sent out from the dilution carrier gas source 202b, a mist generation source 204 that stores a raw material solution 204a containing gallium, a container 205 that stores 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 that connects the mist generation source 204 to the film forming chamber 207.

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

[0107] (Raw material solution containing gallium) Next, a raw material solution containing gallium was prepared. The solvent was ultrapure water and the solute was gallium bromide. The gallium concentration was 0.1 mol / L, and this was used as the 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 generation source 204. Subsequently, the flow 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 sufficiently replacing the atmosphere in the film formation chamber 207 with the carrier gas, the flow rate of the carrier gas was adjusted to 2 L / min and the flow rate of the carrier gas for dilution was adjusted to 6 L / min. Nitrogen was used as the carrier gas.

[0109] Next, the ultrasonic oscillator 206 was vibrated at 2.4 MHz, and the vibration was propagated through the water 205a to the raw material solution 204a containing gallium, thereby atomizing 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, under the conditions of atmospheric pressure and 500 °C, the mist was thermally reacted in the film formation chamber 207 to form a gallium oxide thin film on the underlying substrate 210. The film formation time was 30 minutes.

[0110] (Evaluation) Regarding the thin film formed on the underlying substrate 210, it was confirmed by X-ray diffraction that α-Ga2O3 was formed. Next, the root mean square roughness RMS of the film surface was measured by AFM. As a result, RMS was 8 nm. Also, when the film thickness was measured with a reflection spectroscopic film thickness meter F50 from Filmmetrics, it was 0.52 μm.

[0111] (Examples 2 and 3) As the underlying substrate 210, c-plane sapphire substrates with different total thickness variations (TTV) and a diameter of 100 mm (4 inches) were prepared. Specifically, substrates with TTV of 3 and 26 μm were prepared, and film formation and evaluation were performed under the same conditions as in Example 1. As a result, RMS was 2 and 8 nm, respectively. Also, the film thicknesses were 0.49 and 0.51 μm, respectively.

[0112] (Comparative Examples 1 and 2) As the lower base plate 210, a c-plane sapphire substrate with a diameter of 100 mm (4 inches) and a TTV of 41 and 61 μm was prepared. Film formation and evaluation were carried out under the same conditions as in Example 1 except for this. As a result, the RMS values were 245 and 303 nm respectively. Also, the film thicknesses were 0.47 and 0.46 μm respectively.

[0113] (Example 4) Film formation and evaluation were carried out under the same conditions as in Example 1 except that the film formation time was set to 60 minutes. As a result, the film thickness was 1.1 μm and the RMS was 11 nm.

[0114] (Example 5) Film formation and evaluation were carried out under the same conditions as in Example 1 except that the film formation time was set to 480 minutes. 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 carried out under the same conditions as in Example 1 except that the Ra of the non-film-forming surface of the substrate was set to 0.41 μm. As a result, the RMS was 7 nm. Also, the film thickness was 0.51 μm.

[0116] (Example 7) In Example 1, film formation and evaluation were carried out 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. Also, the film thickness was 0.53 μm.

[0117] (Example 8) In Example 1, a copper plate (stage) was laid on the heater, and film formation and evaluation were carried out 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. Also, the film thickness was 0.48 μm.

[0118] (Example 9) In Example 1, a copper plate (stage) was laid on the heater, and film formation and evaluation were carried out 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. Also, the film thickness was 0.50 μm.

[0119] A graph summarizing Examples 1, 2, 3 and Comparative Examples 1, 2 is shown in FIG. 3. It can be seen that when the TTV of the underlying substrate exceeds 30 μm, the RMS of the surface of the crystalline oxide film increases rapidly. As described above, it is considered to be caused by the deterioration of the thermal contact with the heater and the increase in thermal resistance.

[0120] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are illustrative, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Claims

1. A laminated structure having a lower 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 lower base substrate is 50 mm or more, and the surface roughness Ra of the surface of the laminated structure on the side opposite to the surface having the crystalline oxide film is 0.5 μm or less.

2. A laminated structure having a lower 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 lower base substrate is 50 mm or more, and the waviness Wa of the surface of the laminated structure on the side opposite to the surface having the crystalline oxide film is 50 μm or less.

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

4. The laminated structure according to claim 2, wherein the surface roughness Ra of the surface of the laminated structure on the side opposite to the surface having the crystalline oxide film is 0.5 μm or less.

5. The laminated structure according to any one of claims 1 to 4, wherein the crystalline oxide film is a single crystal or a uniaxially oriented film.

6. The laminated structure according to any one of claims 1 to 5, wherein the thickness of the lower base substrate is 100 to 5000 μm.

7. The laminated structure according to any one of claims 1 to 6, wherein the film thickness of the crystalline oxide film is 1 to 100 μm.

8. The laminated structure according to any one of claims 1 to 7, wherein the lower base substrate is a single crystal.

9. The laminated structure according to any one of claims 1 to 8, wherein the lower base substrate is any one of a sapphire substrate, a lithium tantalate substrate, or a lithium niobate substrate.

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

11. A lower base substrate for forming a crystalline oxide film mainly composed of gallium oxide having a root mean square roughness of the surface of 0.2 μm or less, wherein the diameter of the lower base substrate is 50 mm or more, and the TTV of the lower base substrate is 30 μm or less.

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