Method for forming crystalline metal oxide film

Abstract

The present invention is a film forming method for forming a crystalline metal oxide film by thermally reacting a misted raw material solution, the method for forming a crystalline metal oxide film comprising a misting step for atomizing or dropletizing the raw material solution to generate a mist, a mist conveying step for conveying the mist to a film forming unit by a carrier gas, and a film forming step for supplying the mist from a nozzle toward a film forming surface of a substrate in the film forming unit and thermally reacting the mist to form a film on the substrate, and in the film forming step, a film being formed while the substrate is moved parallel to a placement surface for the substrate, and the film formation being performed while satisfying MC / V < 3, where M [mg / s] is the speed at which the mist is supplied, C [mol / L] is the concentration of the metallic raw material in the raw material solution, and V [mm / s] is the movement speed of the substrate. Through this configuration, there is provided a film forming method for forming, on a large-diameter substrate, a crystalline metal oxide film in which mixing of other phases and deterioration of crystallinity are suppressed.

Description

Method for forming a crystalline metal oxide film

[0001] The present invention relates to a method for forming a crystalline metal oxide film.

[0002] As a next-generation switching element capable of achieving high breakdown voltage, low loss, and high heat resistance, a semiconductor device using gallium oxide (Ga ２ O ３ ) has attracted attention, and its application to power semiconductor devices such as inverters is expected. Moreover, applications as light-emitting and light-receiving devices such as LEDs and sensors are also expected due to its wide bandgap.

[0003] According to Non-Patent Document 1, gallium oxide can control its bandgap by forming mixed crystals with indium or aluminum, either individually or in combination, and constitutes an extremely attractive material system as an InAlGaO-based semiconductor. Here, the InAlGaO-based semiconductor refers to In Ｘ Al Ｙ Ga Ｚ O ３ (0 ≤ X ≤ 2, 0 ≤ Y ≤ 2, 0 ≤ Z ≤ 2, X + Y + Z = 1.5 to 2.5), and can be viewed as the same material system containing gallium oxide.

[0004] Patent Document 1 describes a method for producing an oxide crystal thin film of an InAlGaO-based semiconductor by using a bromide or iodide of gallium or indium and the mist CVD method, and c-plane sapphire is used as the substrate.

[0005] In Patent Documents 2 to 5, examples are described in which the electrical properties are improved by forming a crystalline oxide semiconductor film using a mist CVD apparatus of a tubular furnace type with a-plane sapphire, m-plane sapphire, or r-plane sapphire as the substrate instead of c-plane sapphire.

[0006] Japanese Patent No. 6152514, Japanese Patent No. 6967213, Japanese Patent No. 6770674, Japanese Patent No. 6701472, Japanese Patent No. 6761214, International Publication No. 2022 / 191230

[0007] Kentarou Kaneko, "Growth and Physical Properties of Corundum-Structured Gallium Oxide-Based Mixed Crystal Thin Films," Doctoral Thesis of Kyoto University, March 2013

[0008] The mist CVD method can form a film at a relatively low temperature unlike other CVD methods under atmospheric pressure, and can also produce a crystal structure of a metastable phase such as the corundum structure of α-Ga ２ O ３ with a quasi-stable phase.

[0009] However, when an oxide crystal thin film of an InAlGaO-based semiconductor is produced by the method described in Patent Document 1, although an oxide crystal thin film with excellent crystallinity can be obtained, it is not satisfactory in terms of electrical characteristics. In addition, the methods described in Patent Documents 2 to 5 are difficult to apply to large substrates and have problems in productivity.

[0010] Patent Document 6 describes a film formation method on a large-diameter c-plane sapphire substrate using a linear source type mist CVD apparatus. However, when the present inventors formed an α-(Al Ｘ Ga １－Ｘ ) ２ O ３ film (0 < X ≤ 1) or an α-Ga ２ O ３ film on an m-plane sapphire by the method described in Patent Document 6, the produced film had other crystal phases mixed in or poor crystallinity. It is considered that the optimum crystal growth conditions differ greatly between the c-plane and the m-plane due to physical property differences such as the thermal expansion coefficient. The mixing of other phases and the deterioration of crystallinity need to be suppressed because they cause deterioration of electrical characteristics.

[0011] The present invention has been made to solve the above problems, and an object thereof is to provide a film formation method for forming a crystalline metal oxide film with suppressed mixing of other phases and deterioration of crystallinity on a large-diameter substrate.

[0012] The present invention has been made to achieve the above objective, and provides a film-forming method for forming a crystalline metal oxide film by thermally reacting a atomized raw material solution, comprising: a atomization step of generating mist by atomizing or dropletizing the raw material solution; a mist transport step of transporting the mist to a film-forming section using a carrier gas; and a film-forming step of supplying the mist from a nozzle toward the film-forming surface of a substrate in the film-forming section, and forming a film on the substrate by thermally reacting the mist, wherein in the film-forming step, the substrate is moved parallel to the mounting surface of the substrate while the film is formed, and the method for forming a crystalline metal oxide film satisfies MC / V < 3 when the mist supply rate is M [mg / s], the concentration of the metal raw material in the raw material solution is C [mol / L], and the movement rate of the substrate is V [mm / s].

[0013] This method for forming crystalline metal oxide films allows for the formation of crystalline metal oxide films with excellent crystal quality on large-diameter substrates using the mist CVD method, while suppressing the inclusion of other phases and deterioration of crystallinity.

[0014] In this case, when the temperature at which the mist undergoes a thermal reaction in the film-forming process is T [°C], (T - 450) / MC ≥ 14.7 can be achieved.

[0015] This allows for better crystallinity to be maintained, and more effectively prevents foreign matter contamination and abnormal growth.

[0016] In this case, T can be set to 475°C or higher and 600°C or lower.

[0017] Within this temperature range, deterioration of crystallinity and contamination with other phases can be more effectively prevented in the fabricated film.

[0018] At this time, the area of ​​the discharge surface of the nozzle is S [cm²] ２ When H [cm] is the longest distance between a point in the discharge surface and the surface of the substrate, and Q [L / min] is the flow rate of the carrier gas supplied from the nozzle, then SHV / Q > 0.5 can be achieved.

[0019] This more effectively prevents the decrease in crystallinity caused by localized high gas supply, and allows for the maintenance of efficient film formation rates and productivity.

[0020] In this case, an m-plane sapphire substrate can be used as the substrate.

[0021] This makes it possible to fabricate crystalline metal oxide films with better electrical properties and lower costs.

[0022] In this case, the substrate has a diameter of 10 cm (4 inches) or more or a surface area of ​​75 cm². ２ The above can be used.

[0023] A substrate of this size is preferable because it allows for the production of a large-area film in a single deposition, resulting in excellent productivity.

[0024] In this case, a raw material solution containing gallium or aluminum can be used.

[0025] This makes it possible to fabricate large-diameter gallium-containing oxide films or aluminum-containing oxide films with superior crystal quality, as the inclusion of other phases and deterioration of crystallinity are more suppressed.

[0026] As described above, the method for forming a crystalline metal oxide film according to the present invention makes it possible to form a crystalline metal oxide film with excellent crystal quality on a large-diameter substrate using the mist CVD method, while suppressing the inclusion of other phases and deterioration of crystallinity.

[0027] This shows an example of the process flow of the method for forming a crystalline metal oxide film according to the present invention. This is a schematic diagram showing an example of a film-forming apparatus suitably used in the present invention. This is a diagram illustrating an example of a misting section. This is a diagram illustrating an example of a film-forming section. This is a diagram illustrating an example of a nozzle. This is a diagram illustrating an example of a film-forming section equipped with multiple nozzles. This is a diagram illustrating an example of a nozzle equipped with multiple discharge surfaces. This is a diagram illustrating an example of a nozzle. This is a diagram illustrating an example of a substrate movement mechanism. This is a diagram illustrating an example of a movement mechanism that reciprocates near the nozzle. This is a diagram illustrating an example of a rotational movement mechanism that moves in one direction near the nozzle. This is a diagram showing the results of X-ray diffraction analysis of the film produced in Example 1. This is a diagram showing the results of X-ray diffraction analysis of the film produced in Comparative Example 1. This is a diagram showing the evaluation results of the films produced in the Example and Comparative Example. This is a diagram showing the evaluation results of the film produced in the Example. This is a diagram showing the evaluation results of the film produced in the Example.

[0028] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0029] As described above, there was a need for a film deposition method that could produce crystalline metal oxide films on large-diameter substrates while suppressing the inclusion of other phases and deterioration of crystallinity.

[0030] In order to solve the above problems, the present inventors have further investigated the method of Patent Document 6 and have found a film-forming method for forming a crystalline metal oxide film by thermal reaction of a atomized raw material solution, comprising: an atomization step of generating mist by atomizing or dropletizing the raw material solution; a mist transport step of transporting the mist to a film-forming section using a carrier gas; and a film-forming step of supplying the mist from a nozzle toward the film-forming surface of a substrate in the film-forming section and forming a film on the substrate by thermal reaction of the mist, wherein the film-forming step includes In this method of forming a crystalline metal oxide film, in which the substrate is moved parallel to the mounting surface of the substrate while the film is formed, and the mist supply rate is M [mg / s], the concentration of the metal raw material in the raw material solution is C [mol / L], and the substrate movement rate is V [mm / s], and the film is formed while satisfying MC / V < 3, we have found that in the mist CVD method, a crystalline metal oxide film with excellent crystal quality, in which the inclusion of other phases and deterioration of crystallinity are suppressed, can be formed on a large-diameter substrate, thus completing the present invention.

[0031] [Film Forming Apparatus] The method for forming a crystalline metal oxide film according to the present invention will be described below with reference to the drawings. Figure 2 shows a schematic configuration diagram of an example of a film forming apparatus 101 that can be suitably used in the film forming method according to the present invention.

[0032] The film-forming apparatus 101 includes a misting unit 120 that atomizes the raw material solution 104a to generate mist, a carrier gas supply unit 130 that supplies a carrier gas to transport the mist, a film-forming unit 140 that heat-reacts the mist to form a film on the substrate 110, a transport unit 109 that connects the misting unit 120 and the film-forming unit 140 and transports the mist by the carrier gas, a nozzle 150 for supplying the rectified mist onto the substrate 110, and a moving mechanism 160 that moves the substrate 110 near the nozzle 150.

[0033] Furthermore, the operation of the film-forming apparatus 101 may be controlled by a control unit (not shown) that controls the whole or a part of the film-forming apparatus 101.

[0034] (Misting section) In the misting section 120, the raw material solution 104a is atomized to generate mist. The misting means is not particularly limited as long as it can atomize the raw material solution 104a, and any known misting means may be used, but it is preferable to use a misting means using ultrasonic vibration, because it can atomize more stably.

[0035] An example of such a misting unit 120 is shown in Figure 3. The misting unit 120 may include, for example, a mist generating source 104 in which a raw material solution 104a is contained, a container 105 in which a medium capable of transmitting ultrasonic vibrations, such as water 105a is contained, and an ultrasonic transducer 106 attached to the bottom surface of the container 105.

[0036] In detail, a mist generating source 104, which consists of a container containing the raw material solution 104a, is housed in a container 105 containing water 105a using a support (not shown).

[0037] An ultrasonic transducer 106 is installed at the bottom of the container 105, and the ultrasonic transducer 106 is connected to an oscillator 116. When the oscillator 116 is activated, the ultrasonic transducer 106 vibrates, and ultrasonic waves are transmitted through the water 105a into the mist generation source 104, causing the raw material solution 104a to be atomized.

[0038] Furthermore, a crystalline metal oxide film made of two or more metals (for example, α-(Al Ｘ Ga １－Ｘ ) ２ O ３ When forming a film (0 < X ​​< 1), the raw material solution 104a, which is a mixture of each metal raw material solution, may be contained in the mist generating source 104 of a single misting unit 120 and atomized, or multiple misting units may be provided, and each metal raw material solution may be atomized in a different misting unit.

[0039] If multiple misting units are provided, a mist mixer may be provided to mix each of the misted raw material solutions, or the solutions may be supplied separately to the film-forming chamber without a mist mixer (not shown).

[0040] (Carrier gas supply unit) The carrier gas supply unit 130 has a carrier gas source 102a for supplying carrier gas, and may also be equipped with a flow control valve 103a for adjusting the flow rate of carrier gas sent out from the carrier gas source 102a.

[0041] Furthermore, the system may also be equipped with a dilution carrier gas source 102b for supplying dilution carrier gas as needed, and a flow control valve 103b for adjusting the flow rate of dilution carrier gas discharged from the dilution carrier gas source 102b.

[0042] The type of carrier gas is not particularly limited and can be appropriately selected depending on the film to be deposited. Examples include inert gases such as oxygen, ozone, nitrogen, and argon, or reducing gases such as hydrogen gas and foaming gas. Furthermore, there may be one type of carrier gas or two or more types. For example, a dilution gas obtained by diluting the same gas as the first carrier gas with another gas (for example, diluted 10 times) may be used as the second carrier gas, and air can also be used. In addition, there may be two or more locations for supplying the carrier gas, not just one.

[0043] (Film Forming Section) In the film forming section 140, mist is heated to generate a thermal reaction, and a film is formed on part or all of the surface of the substrate (crystalline substrate) 110.

[0044] The film-forming section 140 may include, for example, a film-forming chamber 107, in which a substrate (crystalline substrate) 110 is installed, and a hot plate 108 for heating the substrate (crystalline substrate) 110.

[0045] The hot plate 108 may be located inside the film-forming chamber 107, as shown in Figure 2, or it may be located outside the film-forming chamber 107.

[0046] Furthermore, the film-forming chamber 107 may be provided with an exhaust gas outlet 111 in a position that does not affect the supply of mist to the substrate (crystalline substrate) 110. In addition, the film-forming section 140 includes a nozzle 150 for rectifying the mist and a moving mechanism 160 for transporting (moving) the substrate (crystalline substrate) 110. Details of these will be described later.

[0047] Alternatively, the substrate (crystalline substrate) 110 may be placed on the upper surface of the film-forming chamber 107 to form a face-down structure, or the substrate (crystalline substrate) 110 may be placed on the bottom surface of the film-forming chamber 107 to form a face-up structure.

[0048] (Nozzle) As shown in Figure 4, the film-forming section 140 is equipped with a nozzle 150 for supplying mist to the substrate (crystalline substrate) 110. The nozzle 150 rectifies the mist that flows into the nozzle 150 from the transport section 109 and supplies it onto the substrate (crystalline substrate) 110.

[0049] An example of the nozzle 150 is shown in Figure 5. The nozzle 150 is a box-shaped member having a connection part 151 that connects to the transport part 109, an internal space (not shown) for straightening the mist flow, and a nozzle discharge surface 152 that discharges the mist toward the substrate (crystalline substrate) 110. Here, straightening means that the direction of the flow of the discharged mist and carrier gas is aligned at the nozzle discharge surface.

[0050] The installation position of the nozzle 150 is not particularly limited. As shown in Figure 2, the substrate (crystalline substrate) 110 may be installed on the lower surface of the film-forming chamber 107 and the nozzle 150 may be mounted vertically above the substrate (crystalline substrate) 110, thus forming a face-up configuration. Alternatively, the substrate (crystalline substrate) 110 may be installed on the upper surface of the film-forming chamber 107 and the nozzle 150 may be mounted vertically below the substrate, thus forming a face-down configuration.

[0051] The number of nozzles 150 and the number of nozzle discharge surfaces 152 are not particularly limited, as long as there is one or more. As shown in Figure 6, there may be multiple nozzles 150a and 150b, and as shown in Figure 7, one nozzle 150c may have multiple nozzle discharge surfaces 152.

[0052] Furthermore, the angle between the plane containing the nozzle discharge surface 152 and the plane containing the film-forming surface of the substrate (crystalline substrate) 110 is not particularly limited. As shown in Figure 8, a nozzle 150d may be provided with a nozzle discharge surface 152 that is inclined to facilitate mist flow in a specific direction, and as shown in Figure 9, a nozzle 150e may be provided with a part of the nozzle discharge surface 152 inclined. However, as shown in Figures 2 and 5, it is preferable that the substrate (crystalline substrate) 110 and the nozzle discharge surface 152 be arranged parallel to each other. This is because a uniform film can be formed even on a large-diameter substrate with a simpler structure.

[0053] Furthermore, the nozzle 150 may be equipped with a nozzle position adjustment mechanism (not shown) that can appropriately adjust the longest distance H [cm] between a point within the nozzle discharge surface 152 and the surface of the substrate (crystalline substrate) 110.

[0054] The above H is not particularly limited, but is preferably 0.1 cm or more and less than 10 cm, more preferably 0.5 cm or more and less than 6 cm, and more preferably 0.8 cm or more and 3 cm or less. Within this range, it is possible to effectively prevent a decrease in productivity due to a decrease in the film formation rate, and an increase in the linear velocity of the gas flowing over the substrate 110, which would increase the removal of heat from the substrate 110 by the gas and reduce crystallinity, and a more uniform film can be formed even on a large-diameter substrate.

[0055] The shape of the nozzle discharge surface 152 is not particularly limited. It can be a polygon, circle, ellipse, etc., but is preferably a quadrilateral and more preferably a rectangle.

[0056] The area of ​​the nozzle discharge surface 152 is S [cm²] ２ When this is the case, the area S of the nozzle discharge surface 152 is 0.1 cm². ２ More than 400cm ２ Less than 4 cm is good. ２ More than 100cm ２ A value less than is preferable. If it is too small, it becomes difficult to form a uniform film over the entire surface of the substrate 110, and if it is too large, the mist will be supplied to the outside of the substrate 110, resulting in poor productivity.

[0057] Furthermore, the area of ​​the nozzle discharge surface 152 is S [cm²] ２], the area of ​​the base 110 described later is A [cm²] ２ When this is the case, S / A ≤ 0.3 is preferred, and more preferably 0.004 ≤ S / A ≤ 0.15. If S / A ≤ 0.3, a film with good crystallinity and greater uniformity can be produced.

[0058] Furthermore, at this time, the area A of the base 110 is 75 cm². ２ Preferably, the above conditions apply, and if the substrate 110 is circular, it is preferable that the diameter be 4 inches or more. This is because a film with good crystallinity can be formed over a larger area. Furthermore, there is no particular upper limit to A, but it can be, for example, less than or equal to the area of ​​a circle with a diameter of 12 inches. The larger the area of ​​the substrate, the larger the area of ​​the film that can be obtained in a single deposition, making it suitable for mass production.

[0059] Furthermore, the characteristic length L [cm] of the nozzle discharge surface 152, as shown in Figure 5, is not particularly limited. It can be appropriately determined according to the size of the substrate (crystalline substrate) 110, but it is preferable that the characteristic length L [cm] of the nozzle discharge surface 152 is longer than the characteristic length R [cm] of the substrate (crystalline substrate) 110.

[0060] In this invention, "representative length" refers to the diameter in the case of a circle, the length of the major axis in the case of an ellipse, and the length of the longest side in the case of a polygon. For example, if the substrate (crystalline substrate) 110 is a circle with a diameter of 4 inches, R is approximately 10 cm, and if the nozzle discharge surface is a rectangle with a long side of 15 cm and a short side of 2 cm, L is 15 cm. By setting L and R to these conditions, a stable and uniform film can be formed even on a large-diameter substrate.

[0061] (Moving mechanism) As shown in Figure 10, the film-forming section 140 may be equipped with a moving mechanism 160 for moving the substrate (crystalline substrate) 110 in the vicinity of the nozzle 150. The direction in which the substrate 110 is moved is parallel to the mounting surface of the substrate 110.

[0062] Figures 11 and 12 show a view of the film-forming section 140, equipped with moving mechanisms 160a and 160b, from vertically above the substrate (crystalline substrate) 110. The moving mechanism 160a shown in Figure 11 has the substrate (crystalline substrate) 110 and the hot plate 108 on it, and moves back and forth near the nozzle 150 together with the substrate (crystalline substrate) 110 and the hot plate 108.

[0063] The moving mechanism 160b shown in Figure 12 has a substrate (crystalline substrate) 110 and a hot plate 108 on it, and rotates and moves together with the substrate (crystalline substrate) 110 and the hot plate 108 in the vicinity of the nozzle 150. In addition, a mechanism for rotating the substrate 110 may be provided, and the substrate 110 may be rotated at this time.

[0064] (Conveying section) The conveying section 109 connects the atomizing section 120 and the film-forming section 140. Through the conveying section 109, mist is transported by carrier gas from the mist source 104 of the atomizing section 120 to the film-forming chamber 107 of the film-forming section 140. The conveying section 109 can be, for example, a supply pipe 109a. For the supply pipe 109a, for example, a quartz tube or a resin tube can be used.

[0065] [Raw Material Solution] The raw material solution (aqueous solution) 104a is not particularly limited as long as it contains a material that can be atomized, and may be an inorganic material or an organic material. A metal or metal compound solution is preferably used for the raw material solution 104a, and can contain one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt.

[0066] In the film-forming method of the present invention, a raw material solution 104a containing gallium or aluminum can be suitably used. This makes it possible to produce a large-diameter gallium-containing oxide film or an aluminum-containing oxide film with excellent crystal quality, while suppressing the inclusion of other phases and deterioration of crystallinity.

[0067] The raw material solution 104a is not particularly limited as long as it can atomize the above-mentioned metal solution, but it is preferable to use a raw material solution 104a in which the metal is dissolved or dispersed in an organic solvent or water in the form of a complex or salt.

[0068] Examples of complex forms include acetylacetonate complexes, carbonyl complexes, ammine complexes, and hydride complexes. Examples of salt forms include metal chloride salts, metal bromide salts, and metal iodide salts. Furthermore, aqueous solutions of the above metals dissolved in hydrobromic acid, hydrochloric acid, hydroiodic acid, etc., can also be used as salt solutions.

[0069] The solute concentration C [mol / L] is preferably 0.01 to 1 mol / L, more preferably 0.05 to 0.5 mol / L, and more preferably 0.08 to 0.30 mol / L. Within this concentration range, it is possible to effectively prevent the deterioration of productivity due to a decrease in film formation rate at low concentrations, the decrease in crystallinity at high concentrations, and the contamination of foreign matter and abnormal growth due to side reactions and precipitation of excess raw materials.

[0070] Furthermore, the raw material solution 104a may be mixed with a halogen-containing substance (for example, a hydrohalic acid). Examples of hydrohalic acids include hydrobromic acid, hydrochloric acid, and hydroiodic acid, but hydrobromic acid or hydroiodic acid are preferred.

[0071] Furthermore, an oxidizing agent may be added to the raw material solution 104a. Examples of oxidizing agents include hydrogen peroxide (H ２ O ２ ), sodium peroxide (Na ２ O ２ ), barium peroxide (BaO ２ ), benzoyl peroxide (C ６ H ５ CO) ２ O ２ Examples include peroxides such as hypochlorous acid (HClO), perchloric acid, nitric acid, ozonated water, peracetic acid, and nitrobenzene, as well as other organic peroxides.

[0072] Furthermore, if the film is a semiconductor, the raw material solution 104a may contain a dopant. The dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, or p-type dopants such as copper, silver, tin, iridium, or rhodium.

[0073] The dopant concentration is, for example, approximately 1.0 × 10⁻⁶ －９ It may be up to 1.0 mol / L, and approximately 1.0 × 10 －７ The concentration can be as low as mol / L or less, or as high as approximately 0.01 mol / L or higher.

[0074] [Substrate] The substrate (crystalline substrate) 110 according to the present invention is not particularly limited as long as it has a surface on which a crystalline metal oxide film can be formed and can support the formed metal oxide film.

[0075] The material of the substrate (crystalline substrate) 110 is not particularly limited, and known substrates can be used, and may be organic compounds or inorganic compounds. Examples include, but are not limited to, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, silicon, sapphire, quartz, glass, gallium oxide, lithium niobate, and lithium tantalate.

[0076] Furthermore, the base 110 may have an off-angle. The off-angle is preferably 0.2 to 12.0°, and preferably 0.5 to 5.0°, as this can further improve the electrical characteristics.

[0077] In the film-forming method of the present invention, it is preferable to use a substrate (crystalline substrate) 110 in which the most abundant metal element in atomic percent is aluminum. In particular, it is preferable to use an m-plane sapphire substrate. This makes it possible to form a crystalline metal oxide film with good electrical properties and excellent cost performance.

[0078] The thickness of the substrate (crystalline substrate) 110 is not particularly limited, but from a cost standpoint, it is preferably about 200 to 800 μm.

[0079] Furthermore, in the film-forming method of the present invention, the substrate (crystalline substrate) 110 is, as described above, a diameter of approximately 10 cm (4 inches) or more, or a main surface area (the surface on which the crystalline metal oxide film is formed) of 75 cm². ２ It is preferable to use the above-mentioned materials, and more preferably to use materials with a diameter of approximately 15 cm (6 inches) or more. There is no particular upper limit to the area, but it can be, for example, less than or equal to the area of ​​a circle with a diameter of approximately 30 cm (12 inches). Such a size of substrate is preferable because a large area film can be obtained in a single film formation, resulting in excellent productivity.

[0080] The shape of the substrate (crystalline substrate) 110 can be any shape having a film-forming surface (a film-forming surface on which a crystalline metal oxide film is formed) and a back surface thereof. For example, it can be a plate shape such as a flat plate or disc, a rod shape, a cylindrical shape, a prismatic shape, a tubular shape, a ring shape, etc., but it is preferably a plate shape.

[0081] Furthermore, the substrate (crystalline substrate) 110 may be polished to an optically mirror-like surface, or it may be subjected to a roughening process, but it is preferable that both the film-forming surface and its back surface are polished to a mirror-like surface.

[0082] More specifically, in the present invention, it is preferable that the surface roughness Ra of the film-forming surface and the back surface is 1 μm or less. Furthermore, it is preferable that the warp (hereinafter referred to as "Wa") is 50 μm or less.

[0083] The smaller the surface roughness Ra, the better. The lower limit is not particularly limited, but it can be, for example, 0.1 nm or more. The surface roughness Ra may be measured at one or more arbitrary locations on the surface of the film to be deposited, with a measurement length of, for example, 10 μm or more.

[0084] The waviness Wa is preferably as small as possible, and can be, for example, 50 μm or less. The lower limit is not particularly limited, but can be, for example, 0.5 μm or more. The waviness Wa may be measured on one or more arbitrary straight lines on the film-forming surface, which are appropriately determined according to the shape of the substrate (crystalline substrate) 110. For example, in the case of a disc-shaped substrate with a diameter of 4 inches, the measurement length can be any length on two straight lines that intersect at right angles at the center of the substrate.

[0085] Furthermore, surface roughness Ra and waviness Wa refer to values ​​calculated in accordance with JIS B 0601, using surface shape measurement results obtained by non-contact measurement methods using laser microscopes or confocal microscopes, such as the stylus method, atomic force microscopy (AFM) method, or optical interferometry, confocal method, or image synthesis method with focus shift.

[0086] Such a substrate 110 is of high quality and allows for the processing of a laminate by light irradiation from the back surface of the substrate (crystalline substrate) 110, thus increasing the design flexibility of semiconductor devices. Furthermore, by combining it with a hot plate 108 having a smooth substrate mounting surface and forming a film, it is possible to create a laminate with a high-quality semiconductor film that exhibits excellent crystal orientation even when a thick film is formed.

[0087] Such surface smoothness of the substrate 110 can be easily achieved, for example, in the case of sapphire, by lapping the surface of a substrate obtained by processing a crystal with diamond abrasive grains, and then further applying a mirror finish by chemical mechanical polishing (CMP) using colloidal silica.

[0088] [Method for forming a crystalline metal oxide film] Figure 1 shows an example of the process flow of the method for forming a crystalline metal oxide film according to the present invention. As shown in Figure 1, the method for forming a crystalline metal oxide film according to the present invention includes a misting step (S1) in which a raw material solution is atomized or dropletized to generate mist, a mist transport step (S2) in which the mist is transported to the film-forming section by a carrier gas, and a film-forming step (S3) in which the mist is supplied from a nozzle toward the film-forming surface of a substrate in the film-forming section, and the mist is subjected to a thermal reaction to form a film on the substrate.

[0089] Furthermore, in the film formation process (S3), the substrate is moved parallel to the mounting surface while forming the film, and when the mist supply rate is M [mg / s], the concentration of the metal raw material in the raw material solution is C [mol / L], and the substrate movement rate is V [mm / s], the film is formed while satisfying MC / V < 3.

[0090] The MC / V ratio should be less than 3, preferably between 0.01 and 3, more preferably between 0.01 and 2.5, and even more preferably between 0.05 and 2. If MC / V < 3, a film with good crystallinity will be formed. When MC / V ≥ 3, crystallinity decreases due to an excessive amount of raw materials supplied locally, and the excess raw materials can cause side reactions and precipitation, foreign matter contamination, and abnormal growth, making it difficult to form a uniform film. If MC / V ≥ 0.01, an efficient film formation rate and productivity can be maintained.

[0091] This method for forming crystalline metal oxide films allows for the formation of crystalline metal oxide films with excellent crystal quality on large-diameter substrates using the mist CVD method, while suppressing the inclusion of other phases and deterioration of crystallinity.

[0092] An example of the film-forming method of the present invention will be described below with reference to Figure 2. First, the raw material solution 104a is placed in the mist generating source 104 of the misting unit 120, the substrate (crystalline substrate) 110 is placed on the hot plate 108, and the hot plate 108 is operated.

[0093] Next, flow control valves 103a and 103b are opened to supply carrier gas from carrier gas source 102a (main carrier gas) and dilution carrier gas source 102b (dilution carrier gas) into the film-forming chamber 107, thereby sufficiently replacing the atmosphere in the film-forming chamber 107 with carrier gas, and the flow rates of the main carrier gas and dilution carrier gas are adjusted and controlled, respectively.

[0094] The carrier gas flow rate Q [L / min] is preferably 1 to 80 L / min, and more preferably 4 to 40 L / min, when depositing a film on a substrate with a diameter of 4 inches. Within this flow rate range, it is possible to effectively suppress the deterioration of productivity due to a decrease in film deposition rate when the flow rate is low, and the decrease in crystallinity due to a decrease in substrate temperature when the flow rate is high.

[0095] In the film-forming method of the present invention, the carrier gas flow rate is measured at 20°C and atmospheric pressure. If measurements are taken at other temperatures and pressures, or if different types of flow rates (such as mass flow rate) are measured, they can be converted to volumetric flow rates at 20°C and atmospheric pressure using the ideal gas law.

[0096] In the misting process (S1), the ultrasonic transducer 106 is vibrated, and the vibrations are transmitted to the raw material solution 104a through the water 105a, thereby atomizing the raw material solution 104a and generating mist.

[0097] Next, in the mist transport process (S2) in which the mist is transported by a carrier gas, the mist is transported by the carrier gas from the atomization section 120 through the transport section 109 to the film formation section 140, and introduced into the nozzle 150 in the film formation chamber 107.

[0098] Then, in the film formation process (S3), the substrate (crystalline substrate) 110 placed on the hot plate 108 is moved parallel to the mounting surface, and mist is supplied from the nozzle 150 toward the film formation surface of the substrate (crystalline substrate) 110. The mist undergoes a thermal reaction in the film formation chamber 107 due to the heat of the hot plate 108, and a film is formed on the substrate (crystalline substrate) 110.

[0099] The mist supply rate M [mg / s] in the film formation process (S3) can be calculated by dividing the weight of the raw material solution 104a supplied in the film formation process (S3) by the film formation time. The mist supply rate M [mg / s] is preferably between 1 and 100, and more preferably between 8 and 50. Within this range of supply rate M, an efficient film formation rate can be maintained, and when M is high, heat removal from the substrate 110 by the mist can be effectively suppressed, effectively preventing deterioration of crystallinity due to a decrease in the surface temperature of the substrate.

[0100] The film-forming time referred to here is the time during which the heat reaction occurred in the film-forming process (S3), and more specifically, the time during which the substrate 110 was heated on the hot plate 108 and mist of the raw material solution 104a was supplied onto the substrate 110.

[0101] The speed V [mm / s] and range of movement of the substrate (crystalline substrate) 110 are not particularly limited as long as MC / V < 3 is satisfied, but the number of times a single substrate 110 passes under the nozzle 150 is preferably 0.1 times or more, more preferably 0.5 times or more, and more preferably 1 time or more per minute. With such a number, it is possible to effectively prevent the surface temperature of the substrate from decreasing and the crystallinity from deteriorating due to the supply of a large amount of gas locally.

[0102] Furthermore, while there is no particular upper limit on the number of rotations, increasing the rotational speed makes the base unstable due to centrifugal force, so 120 rotations or less is preferable, and 60 rotations or less is even better.

[0103] More specifically, in the case of a moving mechanism as shown in Figure 11, the moving speed of the base body V [mm / s] is such that the width D [mm] of movement of the base body 110 is 60V / D is preferably 0.1 or more, preferably 0.5 to 120, and more preferably 1 to 60 times.

[0104] The width D over which the substrate 110 moves is not particularly limited. It is preferable that it is greater than or equal to the characteristic length R [mm] of the substrate 110 (for a substrate 110 with a diameter of 4 inches, D ≥ 100 mm). There is no particular upper limit. If it is increased, a large number of substrates can be formed on one nozzle. However, since the film formation speed per substrate decreases, it is preferable to set the number of substrates to be formed per nozzle to 1000 mm or less for efficient productivity.

[0105] The width D of the movement of the base 110 represents the length of movement of the center of the base 110. For example, in the case of a rotary type moving mechanism 160b as shown in Figure 12, the distance between the rotation center of the moving mechanism 160b and the center of the base 110 is l [mm], and D can be calculated as D = 2πl [mm].

[0106] The moving speed V of the base 110 is not particularly limited as long as MC / V < 3 is satisfied. It is preferably 0.5 mm / s or more and 500 mm / s or less, more preferably 1 mm / s or more and 200 mm / s or less, and more preferably 2.5 mm / s or more and 50 mm / s or less. In the case of a rotary type moving mechanism 160b as shown in Figure 12, the rotational speed ω [rpm] of the base 110 is preferably 0.1 rpm or more, more preferably 0.5 to 120 rpm, and more preferably 1 to 60 rpm.

[0107] In this invention, the moving speed V of the base 110 represents the speed at which the center of the base 110 moves. In the case of a rotary moving mechanism 160b as shown in Figure 12, when the distance between the rotation center of the moving mechanism 160b and the center of the base 110 is l [mm] and the rotation speed is ω [rpm], the moving speed V of the base 110 can be calculated as V = 60lω [mm / s].

[0108] The thermal reaction in the film formation process (S3) only requires that the mist react upon heating, and the reaction conditions are not particularly limited. They can be set appropriately depending on the raw materials and the resulting film. For example, when forming a film of α-gallium oxide, the film formation temperature T [°C] is preferably in the range of 450°C to 650°C, more preferably in the range of 475°C to 600°C, and even more preferably in the range of 500°C to 550°C. Within this temperature range, deterioration of crystallinity and amorphous formation at low temperatures, and the inclusion of the β phase (most stable phase) at high temperatures can be effectively prevented.

[0109] The thermal reaction may be carried out under any of the following conditions: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, or oxygen atmosphere, and should be set appropriately depending on the material to be deposited. The reaction pressure may also be atmospheric pressure, pressurized pressure, or reduced pressure, but deposition under atmospheric pressure is preferred because it simplifies the apparatus configuration.

[0110] Furthermore, the temperature T [°C] at which the thermal reaction occurs in the film formation process (S3) should preferably be (T - 450) / MC ≥ 3. (T - 450) / MC is preferably 3 or more and 1500 or less, preferably 5 or more and 1000 or less, and more preferably 14.7 or more and 600 or less.

[0111] If (T-450) / M ≥ 3, a film with better crystallinity will be produced. If (T-450) / MC ≥ 14.7, an efficient amount of raw material will be supplied, allowing good crystallinity to be maintained, and foreign matter contamination and abnormal growth due to side reactions and precipitation of excess raw material can be effectively prevented. If (T-450) / MC ≤ 1500, an efficient film formation rate and productivity can be maintained.

[0112] Furthermore, the area of ​​the nozzle discharge surface 152 is S [cm²] ２ When H [cm] is the longest distance between a point in the discharge surface 152 and the surface of the substrate 110, and Q [L / min] is the flow rate of the carrier gas supplied from the nozzle 150, it is preferable to set SHV / Q ≥ 0.25. SHV / Q is preferably 0.25 or more and 100 or less, preferably more than 0.5 and 50 or less, and preferably 1.0 or more and 30 or less. A higher value results in a film with better crystallinity, but within this range, it is possible to effectively prevent a decrease in crystallinity due to the supply of a large amount of gas locally and maintain an efficient film formation rate and productivity.

[0113] The crystalline metal oxide film may be formed directly on the substrate (crystalline substrate) 110, or it may be laminated on an intermediate layer (buffer film or release film) formed on the substrate (crystalline substrate) 110. The intermediate layer is not particularly limited as long as it is a metal oxide capable of taking on a corundum structure, and for example, it can be mainly composed of an oxide containing any of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, or iridium.

[0114] More specifically, the middle layer is, for example, Al ２ O ３ Ti ２ O ３、 V ２ O ３ , Cr ２ O ３ Fe ２ O ３ Ga ２ O ３ , Rh ２ O ３ In ２ O ３ , Ir ２ O ３And if two elements selected from the above metal elements are A and B, then (A ｘ B １－ｘ ) ２ O ３ A binary metal oxide represented by (0 < x < 1), or when three elements selected from the above metal elements are A, B, and C, (A ｘ B ｙ C １－ｘ－ｙ ) ２ O ３ It can be a ternary metal oxide represented by (0 < x < 1, 0 < y < 1).

[0115] In the present invention, annealing treatment may be performed after film formation. The temperature of the annealing treatment is not particularly limited, but is preferably 600°C or lower, and more preferably 550°C or lower, in order to avoid impairing the crystallinity of the film. The treatment time for the annealing treatment is not particularly limited, but is preferably 10 seconds to 10 hours, and more preferably 10 seconds to 1 hour.

[0116] (Detachment) The substrate (crystalline substrate) 110 may be detached from the crystalline metal oxide film. The detachment method is not particularly limited and may be a known method. Examples include detachment by mechanical impact, detachment by applying heat and utilizing thermal stress, detachment by applying vibration such as ultrasound, detachment by etching, and laser lift-off. The crystalline metal oxide film can be obtained as a self-supporting film by the detachment.

[0117] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0118] [Example 1] The method for forming a crystalline metal oxide film in this example will be described with reference to Figure 2.

[0119] (1-1. Preparation of raw material solution) Gallium iodide was added to water to prepare a 0.05 mol / L aqueous solution. This was designated as raw material solution 104a. The raw material solution 104a obtained as described above was placed inside the mist generating source 104. The temperature of the solution at this time was 25°C.

[0120] (1-2. Heating Process) Next, a 4-inch diameter m-plane sapphire substrate was used as the substrate (crystalline substrate) 110. It was placed on a hot plate 108 in the film deposition chamber 107, and the hot plate 108 was operated to raise the temperature to 550°C.

[0121] (1-3. Carrier gas supply process) Next, flow control valves 103a and 103b were opened to supply nitrogen gas as carrier gas into the film-forming chamber 107 from the carrier gas source 102a (main carrier gas) and the dilution carrier gas supply source 102b (dilution carrier gas), thereby sufficiently replacing the atmosphere in the film-forming chamber 107 with these carrier gases, and the flow rate of the main carrier gas was adjusted to 12 L / min, and the flow rate of the dilution carrier gas was also adjusted to 12 L / min.

[0122] (1-4. Film Forming Process) Next, the ultrasonic transducer 106 was vibrated at 2.4 MHz, and the vibration was transmitted to the raw material solution 104a through the water 105a, thereby atomizing the raw material solution 104a and generating mist.

[0123] Then, under atmospheric pressure and at 550°C, while exhausting gas from the exhaust port 111, the substrate 110 is moved back and forth below the nozzle 150 by the substrate movement mechanism 160 in the film formation chamber 107, causing the mist to undergo a thermal reaction, and α-Ga is deposited onto the substrate (crystalline substrate) 110. ２ O ３ A film was formed.

[0124] As the nozzle 150, a nozzle 150 with a rectangular discharge surface 152 is used, and the area of ​​the discharge surface 152 of the nozzle is S [cm²]. ２ When the carrier gas flow rate is Q [L / min] and the longest distance between a point on the nozzle discharge surface 152 and the surface of the substrate (crystalline substrate) 110 is H [cm], the parameters were adjusted so that S = 6.0, H = 2.0, and Q = 24.

[0125] In this process, the substrate (crystalline substrate) 110 was moved so that it passed under the nozzle 150 once per minute. At this time, the movement width D of the substrate was 150 mm, and the movement speed V of the substrate was 2.5 mm / s.

[0126] When the mist supply rate is M [mg / s], the concentration of the metal raw material in the raw material solution 104a is C [mol / L], and the substrate migration rate is V [mm / s], M was 33 [mg / s], and MC / V = 0.66.

[0127] When the temperature at which the thermal reaction in the film formation process takes place is T [°C], (T - 450) / MC = 60.6.

[0128] Furthermore, the area of ​​the nozzle discharge surface 152 is S [cm²] ２ When the longest distance between a point in the discharge surface 152 and the surface of the substrate 110 is H [cm], and the flow rate of the carrier gas supplied from the nozzle 150 is Q [L / min], SHV / Q = 1.25. These conditions are summarized in Table 1. In the α single-phase column of Table 1, ○ indicates that only the α phase is formed, and × indicates that other phases are also formed.

[0129]

[0130] During the film formation process, the raw material solution 104a in the mist source 104 was periodically replenished using a replenishment mechanism (not shown) to maintain a constant water level during film formation.

[0131] [Example 2] Film formation was carried out in the same manner as in Example 1, except that various conditions were changed as shown in Table 1.

[0132] [Example 3] Film formation was carried out in the same manner as in Example 1, except that various conditions were changed as shown in Table 1 and gallium bromide was used as a raw material.

[0133] [Examples 4-6] Film formation was carried out in the same manner as in Example 1, except that various conditions were changed as shown in Table 1.

[0134] [Example 7] Film deposition was carried out in the same manner as in Example 1, except that a 6-inch diameter m-plane sapphire substrate was used as the base material (crystalline substrate) 110, and various conditions were changed as shown in Table 1.

[0135] [Comparative Examples 1-3] Film formation was carried out in the same manner as in Example 1, except that various conditions were changed as shown in Table 1.

[0136] [Evaluation 1: Crystalline Phase and Crystallinity Evaluation] The crystal structure of the films prepared in the Examples and Comparative Examples was evaluated by XRD 2θ-ω scanning. Figure 13 shows the X-ray diffraction analysis results of the film prepared in Example 1, and Figure 14 shows the X-ray diffraction analysis results of the film prepared in Comparative Example 1.

[0137] All of the films prepared in the examples were α-Ga ２ O ３ A peak was observed around 2θ = 64°, originating from the (300) plane. On the other hand, the film prepared in Comparative Example 1 showed a peak around 2θ = 64° as well as a peak around 2θ = 62°. The attribute of this peak is uncertain, but α-Ga ２ O ３ Since the peak does not originate from another phase (Ga other than the α phase) ２ O ３ It was suspected that the product contained other substances (such as GaOOH).

[0138] Next, the ω-scan locking curve of the (300) plane was measured, and the full width at half maximum of the (300) plane peak was determined.

[0139] The results of the examples and comparative examples are shown in Table 1. Figures 15 to 17 show the plotted full width at half maximum for each parameter (MC / V, (T-450) / MC, SHV / Q).

[0140] Table 1 and Figure 15 show that films fabricated with MC / V ≥ 3 exhibit contamination with other phases, whereas films with MC / V < 3 yield a single α-phase without contamination with other phases. Furthermore, these films exhibit excellent crystallinity.

[0141] Figure 16 shows that films fabricated satisfying (T-450) / MC ≥ 14.7 are better crystalline films with a (300) full width at half maximum of 2500 s or less. Such films exhibit superior mobility when used to fabricate devices.

[0142] Figure 17 shows that films fabricated satisfying SHV / Q > 0.5 have a narrower (300) full width at half maximum and improved crystallinity. Such films exhibit superior mobility when used to fabricate devices.

[0143] The measurement point was the center of the substrate. The measurement conditions are shown below. Note that since the radiation source was not monochromatized in this measurement, diffraction peaks from other radiation sources appear below 61°.

[0144] (2θ / ω scan analysis conditions) Measurement method: Out-of-Plane XRD method (2θ / ω scan) X-ray generation unit: Opposite cathode Cu: Output 45kV 200mA Detection unit: Semiconductor detector Incident optical system: Parallel beam method (slit collimation) Solar slit: Incident side 5.0°: Receiver side 5.0° Slit: Incident side IS = 1 (mm): Longitudinal limit 10 (mm): Receiver side RS1 = 1 RS2 = 1.1 (mm) Filter: Ni Scanning conditions: Scanning axis 2θ / ω: Scanning mode Continuous scan: Scanning range 55-80°: Step width 0.02°: Integration time 3° / min

[0145] (ω scan analysis conditions) Measurement method: Rocking curve measurement (ω scan) X-ray generation unit: Opposite cathode Cu: Output 45kV 200mA Detection unit: Semiconductor detector Incident optical system: Parallel beam method (slit collimation) Solar slit: Incident side 5.0°: Receiver side 5.0° Slit: Incident side IS = 1 (mm): Longitudinal limit 10 (mm): Receiver side RS1 = 1 RS2 = 1.1 (mm) Scanning conditions: Evaluation analysis surface α-Ga ２ O ３ (300) : Scanning axis ω : Scanning mode Continuous scanning : Scanning range 23-29° : Step width 0.02° : Accumulation time 3° / min

[0146] [Evaluation 2: Crystallinity Evaluation] The full width at half maximum (FWHM) measurement from Evaluation 1 was performed at nine in-plane points. The measurement points were defined as nine points in a (r, θ) coordinate system with the center of the substrate as the origin, where R is the radius of the substrate, and are represented by (r, θ) = (0, 0), (2R / 3, 0), (2R / 3, π / 4), (2R / 3, π / 2), (2R / 3, 3π / 4), (2R / 3, π), (2R / 3, 5π / 4), (2R / 3, 3π / 2), (2R / 3, 7π / 4).

[0147] For the nine measurement points, the variability [%], standard deviation [arcsec], and coefficient of variation [-] were calculated. The calculation methods for each were as follows. The calculation results are summarized in Table 2. Note that the full width at half maximum in Table 2 refers to the value in Table 1 measured at the center of the substrate. • Variability = (Maximum value - Minimum value) / 2 / Mean value × 100 • Standard deviation σ • Coefficient of variation = Standard deviation / Mean

[0148]

[0149] The results in Table 2 show that, compared to the film-forming methods of Examples 1 to 7, it is possible to stably obtain films with higher uniformity and better crystallinity.

[0150] As described above, according to the embodiments of the present invention, it was possible to deposit a crystalline metal oxide film with excellent crystal quality on a large-diameter substrate using the mist CVD method, while suppressing the inclusion of other phases and deterioration of crystallinity.

[0151] This specification encompasses the following embodiments: [1]: A method for forming a crystalline metal oxide film by thermally reacting a atomized raw material solution, comprising: a atomization step of generating mist by atomizing or dropletizing the raw material solution; a mist transport step of transporting the mist to a film-forming section with a carrier gas; and a film-forming step of supplying the mist from a nozzle toward the film-forming surface of a substrate in the film-forming section, and thermally reacting the mist to form a film on the substrate, wherein in the film-forming step, the substrate is moved parallel to the mounting surface of the substrate while the film is formed, and the film is formed while satisfying MC / V < 3, where the mist supply rate is M [mg / s], the concentration of the metal raw material in the raw material solution is C [mol / L], and the movement speed of the substrate is V [mm / s]. [2]: The method for forming a crystalline metal oxide film according to [1], wherein the temperature at which the mist is thermally reacted in the film-forming step is T [°C], and (T - 450) / MC ≥ 14.7. [3]: The method for forming a crystalline metal oxide film according to [2], wherein T is 475°C or more and 600°C or less. [4]: ​​The area of ​​the discharge surface of the nozzle is S [cm²]. ２ A method for forming a crystalline metal oxide film according to [1], [2], or [3] above, wherein the longest distance between a point in the discharge surface and the surface of the substrate is H [cm], and the flow rate of the carrier gas supplied from the nozzle is Q [L / min], and SHV / Q > 0.5. [5]: A method for forming a crystalline metal oxide film according to [1], [2], [3], or [4] above, wherein the substrate is an m-plane sapphire substrate. [6]: The substrate is a substrate with a diameter of 10 cm (4 inches) or more or a surface area of ​​75 cm². ２ A method for forming a crystalline metal oxide film according to [1], [2], [3], [4], or [5] above, comprising using the above. [7]: A method for forming a crystalline metal oxide film according to [1], [2], [3], [4], [5], or [6] above, comprising using a raw material solution containing gallium or aluminum.

[0152] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention.

Claims

1. A method for forming a crystalline metal oxide film by thermally reacting a atomized raw material solution, comprising: a atomization step of generating mist by atomizing or dropletizing the raw material solution; a mist transport step of transporting the mist to a film-forming section using a carrier gas; and a film-forming step of supplying the mist from a nozzle toward the film-forming surface of a substrate in the film-forming section, and thermally reacting the mist to form a film on the substrate, wherein in the film-forming step, the substrate is moved parallel to the mounting surface of the substrate while the film is formed, and the film is formed while satisfying MC / V < 3, where the mist supply rate is M [mg / s], the concentration of the metal raw material in the raw material solution is C [mol / L], and the movement speed of the substrate is V [mm / s].

2. The method for forming a crystalline metal oxide film according to claim 1, characterized in that, when the temperature at which the mist is thermally reacted in the film-forming step is T [°C], (T - 450) / MC ≥ 14.

7.

3. The method for forming a crystalline metal oxide film according to claim 2, characterized in that the temperature T is 475°C or higher and 600°C or lower.

4. The area of ​​the discharge surface of the nozzle is S [cm²] ２ The method for forming a crystalline metal oxide film according to claim 1, characterized in that when H [cm] is the longest distance between a point in the discharge surface and the surface of the substrate, and Q [L / min] is the flow rate of the carrier gas supplied from the nozzle, SHV / Q > 0.

5.

5. The method for forming a crystalline metal oxide film according to claim 1, characterized in that an m-plane sapphire substrate is used as the substrate.

6. The substrate has a diameter of 10 cm (4 inches) or more, or a surface area of ​​75 cm². ２ A method for forming a crystalline metal oxide film according to claim 1, characterized by using the above.

7. A method for forming a crystalline metal oxide film according to any one of claims 1 to 6, characterized in that the raw material solution contains gallium or aluminum.

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