Crystalline metal oxide film, method for forming same, storage solution, laminated

Abstract

The present invention is a film-forming method for forming a crystalline metal oxide film on a substrate by heat-treating an atomized starting material solution and performing a thermal reaction on the substrate, the film-forming method being characterized in that: a starting material solution containing a metal starting material and a carboxylic acid is used as the starting material solution; the metal raw material contains at least a metal element constituting the crystalline metal oxide film. As a result, provided is a film formation method in which, when a film is formed on a substrate by heat-treating an atomized starting material solution, the formation of spherical foreign matter is suppressed, and a film having good surface smoothness can be formed.

Description

Technical Field

[0001] The present invention relates to a crystalline metal oxide film, a film forming method thereof, a raw material solution, a stacked structure, and a semiconductor device. Background Art

[0002] In the past, a high vacuum film-forming apparatus has been developed that can achieve a non-equilibrium state using methods such as pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and sputtering. This makes it possible to produce oxide semiconductors that have been previously impossible using melt deposition methods.

[0003] In addition, a mist chemical vapor deposition method (Mist Chemical Vapor Deposition: Mist CVD; hereinafter also referred to as "mist-CVD method") has been developed, which uses atomized mist-like raw materials to grow crystals on a substrate, and can produce gallium oxide (α-Ga2O3) with a corundum structure.

[0004] As a semiconductor with a large band gap, α-Ga2O3 is expected to be used in next-generation switching elements that can achieve high withstand voltage, low loss and high heat resistance.

[0005] Regarding the mist-CVD method, Patent Document 1 describes a tube furnace-type mist-CVD apparatus. Patent Document 2 describes a microchannel-type mist-CVD apparatus. Patent Document 3 describes a line source-type mist-CVD apparatus. Patent Document 4 describes a tube furnace-type mist-CVD apparatus, which differs from the mist-CVD apparatus described in Patent Document 1 in that a carrier gas is introduced into the mist generator.

[0006] Patent Document 5 describes a mist-CVD apparatus having a substrate placed above a mist generator and a rotating platform with an induction heater (susceptor) mounted on a hot plate.

[0007] Regarding the use of the mist-CVD method to produce an α-Ga2O3 film, the following example is described in Patent Document 6: a raw material solution prepared by adding hydrochloric acid to an aqueous solution of a metal raw material is used to stack multiple layers as α-(Al X Ga 1-X )2O3 film (0≤X≤1) buffer film, and a high-quality α-Ga2O3 film is stacked on the buffer film.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 01-257337

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2005-307238

[0012] Patent Document 3: Japanese Patent Application Laid-Open No. 2012-046772

[0013] Patent Document 4: Japanese Patent Application Laid-Open No. 2014-234337

[0014] Patent Document 5: Japanese Patent Application Laid-Open No. 2014-063973

[0015] Patent Document 6: Japanese Patent Application Laid-Open No. 2022-31108 Summary of the Invention

[0016] (1) Technical issues to be resolved

[0017] Unlike other CVD methods, the mist-CVD method can form films at relatively low temperatures and can produce quasi-stable crystal structures such as the corundum structure of α-Ga2O3.

[0018] However, when α-(Al X Ga 1-X After forming a )2O3 film or an α-Ga2O3 film, the inventors of this application observed a large number of spherical foreign matter, believed to be byproducts of the metal raw materials. Because films containing a large amount of foreign matter may cause a decrease in crystallinity and degrade device characteristics, it is preferable to remove the foreign matter.

[0019] Although foreign matter can be removed by polishing, removing foreign matter by polishing increases the number of steps required to manufacture a semiconductor device. Therefore, it is preferable to suppress the generation of foreign matter during film formation.

[0020] The present invention is made to solve the above-mentioned problems, and its purpose is to provide a film-forming method that suppresses the generation of spherical foreign matter when a raw material solution that has been atomized is heat-treated and a film is formed on a substrate, and can form a film with good surface smoothness, as well as a raw material solution used in the film-forming method, and a crystalline metal oxide film with good surface smoothness.

[0021] (2) Technical solution

[0022] The present invention is made to achieve the above-mentioned purpose, and provides a film-forming method, which forms a crystalline metal oxide film on the substrate by heat-treating an atomized raw material solution and causing a thermal reaction on the substrate. The film-forming method is characterized in that, as the raw material solution, a raw material solution containing a metal raw material and a carboxylic acid is used, and the metal raw material contains at least a metal element constituting the crystalline metal oxide film.

[0023] Thus, by using a solution containing carboxylic acid as the raw material solution, the metal raw material in the raw material solution is suppressed from forming foreign matter.

[0024] Therefore, when film formation is performed using mist-CVD, the generation of spherical foreign matter is suppressed, and a film having good surface smoothness can be formed.

[0025] As the carboxylic acid, a carboxylic acid having an acid dissociation constant with respect to water at 25° C. of 2.65 to 4.67 can be used.

[0026] By setting the acid dissociation constant to 2.65 or higher, the formation of foreign matter from the metal raw material can be reliably suppressed. Furthermore, by setting the acid dissociation constant to 4.67 or lower, the excess carboxylic acid required to suppress the formation of spherical foreign matter can be reliably prevented from remaining in the crystalline metal oxide film.

[0027] As the carboxylic acid, a carboxylic acid having 4 or less carbon atoms can be used.

[0028] Thus, by using a carboxylic acid having 4 or less carbon atoms, it is possible to suppress the carbon atoms in the carboxylic acid from remaining in the crystalline oxide film. Furthermore, since the carboxylic acid is easily soluble in water, the atomization efficiency is improved, and the film formation cost is excellent.

[0029] As the carboxylic acid, formic acid can be used.

[0030] Since formic acid is a carboxylic acid composed only of H, C, and O and has the smallest molecular weight, it is advantageous in suppressing incorporation of elements constituting the carboxylic acid into the crystalline oxide film.

[0031] The volume ratio of the carboxylic acid in the raw material solution can be set to 1 vol % or more and 50 vol % or less.

[0032] By setting the volume ratio to 1 vol% or more, the effect of suppressing foreign matter generated by carboxylic acid can be reliably exerted. In addition, by setting the volume ratio to 50 vol% or less, the effect of suppressing foreign matter generated by carboxylic acid can be fully exerted, and the carbon in the carboxylic acid can be suppressed from remaining in the crystalline oxide film.

[0033] The molar concentration of the carboxylic acid in the raw material solution can be set to 0.1 mol / L or more and 13.2 mol / L or less.

[0034] By setting the molar concentration of the carboxylic acid to 0.1 mol / L, the effect of suppressing foreign matter generated by the carboxylic acid can be reliably exerted. In addition, by setting the molar concentration to 13.2 mol / L or less, the effect of suppressing foreign matter generated by the carboxylic acid can be fully exerted, and the carbon in the carboxylic acid can be suppressed from remaining in the crystalline oxide film.

[0035] The molar concentration of the carboxylic acid in the raw material solution can be set to a concentration equal to or higher than the molar concentration of the metal raw material in the raw material solution.

[0036] By setting such a molar concentration, the effect of suppressing foreign matter generated by carboxylic acid can be fully exerted.

[0037] In addition, the present invention provides a film-forming method, which forms a crystalline metal oxide film on a substrate by heat-treating an atomized raw material solution and causing a thermal reaction on the substrate. The film-forming method is characterized in that, as the raw material solution, a raw material solution containing a metal raw material and an acid whose acid dissociation constant relative to water at 25°C is greater than -8 and less than 8.8 is used, and the metal raw material contains at least a metal element constituting the crystalline metal oxide film.

[0038] Thus, by using a solution containing an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25° C. as the raw material solution, the formation of foreign matter from the metal raw material in the raw material solution is suppressed.

[0039] Therefore, when film formation is performed using mist-CVD, the generation of spherical foreign matter is suppressed, and a film having excellent surface smoothness can be formed.

[0040] The metal raw material in the raw material solution may contain at least one of gallium or aluminum as a main component.

[0041] By including gallium or aluminum in the metal raw material, a crystalline oxide film of these metals can be formed. The main component mentioned here refers to the component with the largest atomic % among the metal elements in the metal raw material.

[0042] When the metal raw material contains at least one of gallium or aluminum as a main component, the metal raw material can be an acetylacetone complex.

[0043] By using an acetylacetone complex as the metal raw material, the metal element can be easily dissolved in the carboxylic acid in the raw material solution.

[0044] The raw material solution can be set to a solution of an acetylacetone complex containing aluminum. In this case, in the MS spectrum of the raw material solution, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.25.

[0045] By satisfying the above conditions, a raw material solution containing less structures in which the acetylacetone complex is cross-linked with ОH or acetylacetone, structures in which dimerization occurs, and structures in which acetylacetone is substituted with OH can be obtained, thereby reliably suppressing the generation of spherical foreign matter believed to be caused by these structures.

[0046] The temperature of the heat treatment can be set to 400° C. or higher and 550° C. or lower.

[0047] By setting the heat treatment temperature to 400°C or higher, the temperature required for thermal reaction can be ensured during film formation. By setting the heat treatment temperature to 550°C or lower, the atomized raw material can be reliably thermally reacted on the substrate.

[0048] The area of the substrate on which the crystalline metal oxide film can be formed is 10 cm 2 The above matrix.

[0049] By making the area of the film forming surface 10cm 2 As described above, a high-quality crystalline metal oxide film over a large area can be formed, and in particular, productivity can be improved.

[0050] In addition, the present invention provides a raw material solution, which is used for a film forming method of forming a crystalline metal oxide film on a substrate by heat treating the atomized raw material solution and causing a thermal reaction on the substrate. The raw material solution is characterized in that it contains: a metal raw material containing a metal element constituting the crystalline metal oxide film, and formic acid.

[0051] By using a solution containing formic acid as the raw material solution in this manner, the formation of foreign matter from the metal raw material in the raw material solution is suppressed.

[0052] Therefore, when film formation is performed using mist-CVD, the generation of spherical foreign matter is suppressed, and a film having excellent surface smoothness can be formed.

[0053] In addition, the present invention provides a raw material solution, which is used for forming a film on a substrate by heat-treating the atomized raw material solution and causing a thermal reaction on the substrate, characterized in that it contains: a metal raw material containing a metal element constituting the crystalline metal oxide film, and an acid having an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C.

[0054] If the raw material solution contains an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C, the metal raw material in the raw material solution is suppressed from forming foreign matter.

[0055] Therefore, when film formation is performed using mist-CVD, the generation of spherical foreign matter can be suppressed, and a film having good surface smoothness can be formed.

[0056] The metal raw material in the raw material solution may contain at least one of Ga and Al as a main component.

[0057] By including gallium or aluminum in the metal raw material, a crystalline oxide film thereof can be formed. The main component referred to here refers to the component with the largest atomic % among the metal elements in the metal raw material.

[0058] In the case where the metal raw material comprises gallium or aluminum, the metal raw material can be an acetylacetonate complex.

[0059] By using an acetylacetone complex as the metal raw material, the metal element can be easily dissolved in formic acid in the raw material solution.

[0060] The raw material solution can be set to a solution of an acetylacetone complex containing aluminum. In this case, in the MS spectrum of the raw material solution, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.25.

[0061] By satisfying the above conditions, a raw material solution containing less structure (I2) in which the acetylacetone complex is cross-linked by ОH or acetylacetone, less structure (I3) in which the acetylacetone complex is dimerized, and less structure (I4) in which acetylacetone is substituted by OH can be obtained, thereby reliably suppressing the formation of spherical foreign matter that is believed to be caused by these structures.

[0062] Furthermore, the present invention provides a crystalline metal oxide film containing at least one of gallium or aluminum as a main component, wherein the crystalline metal oxide film is characterized in that the number density of spherical foreign matter or agglomerates of spherical foreign matter present on the surface of the crystalline metal oxide film is 621 pieces / cm 2 the following.

[0063] Such a crystalline metal oxide film has excellent film smoothness and can therefore be suitably used in semiconductor devices.

[0064] In this case, the number density of the spherical foreign matter or the aggregate of the spherical foreign matter on the surface of the crystalline metal oxide film can be set to 54 pieces / cm 2 the following.

[0065] The crystalline metal oxide film described above has further improved film smoothness and can therefore be more preferably used in semiconductor devices.

[0066] In this case, the crystalline metal oxide film can have a corundum structure.

[0067] The crystalline metal oxide film described above becomes a crystalline metal oxide film having a corundum structure with excellent smoothness.

[0068] At this time, the surface area of the crystalline metal oxide film can be 10 cm 2 above.

[0069] The crystalline metal oxide film described above has excellent smoothness and covers a large area, and therefore can be preferably used in semiconductor devices.

[0070] In this case, a stacked structure including a substrate and the crystalline metal oxide film formed on the substrate via a buffer layer can be produced.

[0071] The laminated structure described above has excellent film smoothness and can therefore be suitably used in semiconductor devices.

[0072] In this case, a semiconductor device including at least one of the crystalline metal oxide film and the stacked structure can be manufactured.

[0073] The semiconductor device described above has excellent film smoothness and therefore has good electrical characteristics.

[0074] In this case, the semiconductor device is any one of a semiconductor laser, a diode, or a transistor.

[0075] The semiconductor device described above is formed into a semiconductor laser, a diode, or a transistor having excellent electrical characteristics.

[0076] (3) Beneficial effects

[0077] As described above, according to the film forming method of the present invention, when heat-treating an atomized raw material solution and forming a film on a substrate, the generation of spherical foreign matter is suppressed, and a film having a smooth surface can be formed.

[0078] Furthermore, according to the raw material solution of the present invention, when the atomized raw material solution is heat-treated and a film is formed on a substrate, the generation of spherical foreign matter can be suppressed, and a film having good surface smoothness can be formed.

[0079] Therefore, the mist-CVD method can form a film with few spherical foreign matter on the surface and good smoothness by a simple method.

[0080] Furthermore, the crystalline metal oxide film of the present invention has excellent film smoothness and can therefore be suitably used in semiconductor devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 An example of a film forming apparatus used in the film forming method of the present invention is shown.

[0082] Figure 2 An example of the atomizing unit of the film forming apparatus used in the film forming method of the present invention is shown.

[0083] Figure 3 Another example of the film forming apparatus used in the film forming method of the present invention is shown.

[0084] Figure 4 Represents α-(Al X Ga 1-X An example of an SEM image of spherical foreign matter on a )2O3 film (0≤X≤1).

[0085] Figure 5 Represents α-(Al X Ga 1-X ) Another example of SEM image of spherical foreign matter on a )2O3 film (0≤X≤1).

[0086] Figure 6 The relationship between the amount of formic acid added in the raw material solution and the foreign matter density in Examples and Comparative Examples is shown.

[0087] Figure 7 The relationship between the acid dissociation constant of carboxylic acid contained in the raw material solution with respect to water and the foreign matter density in Examples and Comparative Examples is shown.

[0088] Figure 8 The MS spectrum of the raw material solution used in Example 1 is shown.

[0089] Figure 9 The MS spectrum of the raw material solution used in Comparative Example 1 is shown.

[0090] Figure 10 The MS spectrum of the raw material solution used in Comparative Example 2 is shown.

[0091] Figure 11 This is a diagram showing one embodiment of the structure of the laminated structure of the present invention.

[0092] Figure 12 This is a diagram showing an example of the Schottky barrier diode of the present invention.

[0093] Figure 13 A diagram showing an example of a high electron mobility transistor according to the present invention.

[0094] Figure 14 This is a diagram showing an example of the semiconductor electric field effect transistor of the present invention.

[0095] Figure 15 A diagram showing an example of the insulated gate bipolar transistor of the present invention.

[0096] Figure 16 This is a diagram showing an example of a light-emitting diode according to the present invention.

[0097] Figure 17 The relationship between the foreign matter density and the yield in Examples and Comparative Examples (semiconductor devices with a withstand voltage of 600 V or higher) is shown.

[0098] Figure 18 The relationship between the foreign matter density and the yield in Examples and Comparative Examples is shown (semiconductor devices with a withstand voltage of 1200 V or higher). DETAILED DESCRIPTION

[0099] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0100] As described above, a film forming method is sought that can suppress the generation of spherical foreign matter and form a film with good surface smoothness when an atomized raw material solution is heat-treated and a film is formed on a substrate, as well as a raw material solution used in the film forming method and a crystalline metal oxide film with good surface smoothness.

[0101] The inventors of the present application have conducted careful research on the above-mentioned technical problems, and as a result, have discovered a film-forming method, by which the generation of spherical foreign matter can be suppressed and a film with good surface smoothness can be formed when an atomized raw material solution is heat-treated and a film is formed on a substrate, thereby completing the present invention. The film-forming method forms a crystalline metal oxide film on the substrate by heat-treating an atomized raw material solution and causing a thermal reaction on the substrate. The film-forming method is characterized in that, as the raw material solution, a raw material solution containing a metal raw material and a carboxylic acid is used, and the metal raw material contains at least a metal element constituting the crystalline metal oxide film.

[0102] In addition, the inventors of the present application have conducted careful research on the above-mentioned technical problems, and as a result, have discovered a film-forming method, by which the generation of spherical foreign matter can be suppressed and a film with good surface smoothness can be formed when the atomized raw material solution is heat-treated and a film is formed on a substrate, thereby completing the present invention. The film-forming method forms a crystalline metal oxide film on the substrate by heat-treating the atomized raw material solution and causing a thermal reaction on the substrate. The film-forming method is characterized in that, as the raw material solution, a raw material solution containing a metal raw material and an acid with an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C is used, and the metal raw material contains at least a metal element constituting the crystalline metal oxide film.

[0103] In addition, the inventors of the present application have conducted careful research on the above-mentioned technical problems, and as a result, they have discovered a raw material solution, by which the generation of spherical foreign matter can be suppressed and a film with good surface smoothness can be formed when the atomized raw material solution is heat-treated and a film is formed on a substrate, thereby completing the present invention. The raw material solution is used in a film-forming method for forming a crystalline metal oxide film on the substrate by heat-treating the atomized raw material solution and causing a thermal reaction on the substrate. The raw material solution is characterized in that it contains: a metal raw material containing a metal element constituting the crystalline metal oxide film, and formic acid.

[0104] In addition, the inventors of the present application have conducted careful research on the above-mentioned technical problems, and as a result, they have discovered a raw material solution, by which the generation of spherical foreign matter can be suppressed and a film with good surface smoothness can be formed when the atomized raw material solution is heat-treated and a film is formed on a substrate, thereby completing the present invention. The raw material solution is used in a film-forming method for forming a crystalline metal oxide film on the substrate by heat-treating the atomized raw material solution and causing a thermal reaction on the substrate. The raw material solution is characterized in that it contains: a metal raw material containing a metal element constituting the crystalline metal oxide film, and an acid having an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C.

[0105] Furthermore, the inventors of the present application have diligently studied the above-mentioned technical problems and, as a result, have discovered a crystalline metal oxide film that has excellent film smoothness and is therefore suitably usable in semiconductor devices, thereby completing the present invention. The crystalline metal oxide film contains at least one of gallium or aluminum as a main component, and the crystalline metal oxide film is characterized in that the number density of spherical foreign particles or aggregates of spherical foreign particles present on the surface of the crystalline metal oxide film is 621 pieces / cm 2 the following.

[0106] Hereinafter, the present invention will be described with reference to the accompanying drawings.

[0107] First, refer to Figure 1 , an example of a film forming apparatus 100 used in the film forming method of the present invention will be described.

[0108] (Film forming device)

[0109] Figure 1 shows an example of a film-forming apparatus 100 that can be used in the film-forming method of the present invention. Film-forming apparatus 100 includes an atomizing unit 120 that atomizes a 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-treats the mist and forms a film on a substrate, and a transport unit 109 that connects atomizing unit 120 and film-forming unit 140 and transports the mist via a carrier gas. Furthermore, film-forming apparatus 100 may also include a control unit (not shown) that controls all or part of film-forming apparatus 100 to control its operation.

[0110] (Atomization part)

[0111] In the atomizing unit 120, the raw material solution 104a is atomized to generate mist. The atomization method is not particularly limited as long as the raw material solution 104a can be atomized, and any known atomization method may be used. However, an atomization method based on ultrasonic vibration is preferably used because it can achieve more stable atomization.

[0112] exist Figure 2 1 shows an example of an atomizing unit 120 using ultrasonic vibrations. The atomizing unit 120 may include, for example, a mist generating source 104 containing a raw material solution 104a, a container 105 containing a medium capable of transmitting ultrasonic vibrations (e.g., water 105a), and an ultrasonic vibrator 106 mounted on the bottom surface of the container 105.

[0113] Specifically, a mist generating source 104, consisting of a container containing a raw material solution 104a, is housed in a container 105 containing water 105a using a support (not shown). An ultrasonic vibrator 106 is attached to the bottom of container 105 and connected to an oscillator 116. The system is configured such that when oscillator 116 is activated, ultrasonic vibrator 106 vibrates, propagating ultrasound through water 105a into mist generating source 104, thereby atomizing raw material solution 104a.

[0114] In addition, in the case of a crystalline metal oxide film composed of two or more metals (e.g., α-(Al X Ga 1-X)2O3 film (0≤X<1)) is formed, the raw material solution 104a mixed with each metal raw material solution can be accommodated in the mist generating source 104 of an atomizing part 120 for atomization, or it can be atomized like Figure 3 As shown in the figure, a plurality of atomizing sections are provided, and each metal raw material solution is contained in the mist generation source 204a, 204c of each different atomizing section and atomized separately.

[0115] When multiple atomizing units are provided, Figure 3 As shown, a mist mixer 213 is provided to mix the atomized raw material solutions. Alternatively, the mist mixer 213 may not be provided and the raw material solutions may be supplied separately to the film forming chamber 207 (not shown).

[0116] (Carrier gas supply unit)

[0117] exist Figure 1 The carrier gas supply unit 130 shown in FIG. 1 includes a carrier gas source 102 a for supplying a carrier gas, and may include a flow control valve 103 a for adjusting the flow rate of the carrier gas delivered from the carrier gas source 102 a. Furthermore, as needed, the unit may include a dilution carrier gas source 102 b for supplying a dilution carrier gas, and a flow control valve 103 b for adjusting the flow rate of the dilution carrier gas delivered from the dilution carrier gas source 102 b.

[0118] The type of carrier gas is not particularly limited and can be appropriately selected depending on the film to be formed. Examples thereof include inert gases such as oxygen, ozone, nitrogen, and argon, and reducing gases such as hydrogen and forming gas.

[0119] The carrier gas may be one or more types. For example, a diluted gas obtained by diluting the same gas as the first carrier gas with another gas (for example, by 10 times) may be used as the second carrier gas. Air may also be used.

[0120] The carrier gas may be supplied not only at one location but also at two or more locations.

[0121] The flow rate of the carrier gas is not particularly limited. For example, when forming a film on a substrate with a diameter of 4 inches, it is preferably set to 1 to 80 L / min, and more preferably 4 to 40 L / min. In addition, the flow rate of the carrier gas in the present invention is set to the measured value at 20°C and normal pressure. When measuring at other temperatures and pressures or when measuring different types of flow rates (mass flow rate, etc.), the volume flow rate at 20°C and normal pressure can be converted using the state equation of the gas.

[0122] (Film forming section)

[0123] In the film forming unit 140, the mist is heated to generate a thermal reaction, thereby forming a film on a portion or the entire surface of the substrate 110 (crystalline substrate). The film forming unit 140 includes, for example, a film forming chamber 107, in which the substrate (crystalline substrate) 110 is placed, and may include a hot plate 108 for heating the substrate (crystalline substrate) 110.

[0124] like Figure 1 As shown, the hot plate 108 may be provided outside or inside the film forming chamber 107. In addition, an exhaust port 112 for exhaust gas may be provided in the film forming chamber 107 at a position that does not affect the supply of mist to the base (crystalline substrate) 110.

[0125] In addition, the base (crystalline substrate) 110 can be placed on the upper surface of the film forming chamber 107, etc., in a face-down state, or the base (crystalline substrate) 110 can be placed on the bottom surface of the film forming chamber 107, in a face-up state. Figure 1 The face-up situation is illustrated in FIG.

[0126] As for the thermal reaction, as long as the mist reacts by heating, the reaction conditions and the like are not particularly limited. It can be set appropriately according to the raw material or the film-forming object. Specifically, during film formation, the lower limit of the temperature at which the mist is heat-treated, that is, the lower limit of the temperature at which the mist is heated by the electric hot plate 108, is the temperature at which the mist reacts by heating. The upper limit of the temperature for heat treatment is the temperature at which the mist reacts reliably on the substrate 110 without undergoing a gas phase reaction or the like. More specifically, the heat treatment temperature is above 120°C and below 600°C, preferably in the range of above 200°C and below 600°C, and can more preferably be set in the range of above 400°C and below 550°C.

[0127] The thermal reaction can be carried out in any of the following atmospheres: vacuum, non-oxygen atmosphere, reducing gas atmosphere, air atmosphere, and oxygen atmosphere, and can be appropriately set according to the film to be formed. Furthermore, the reaction pressure can be carried out under any of atmospheric pressure, increased pressure, or reduced pressure. However, film formation under atmospheric pressure is preferred because it simplifies the apparatus configuration.

[0128] (Transportation Department)

[0129] The transport unit 109 connects the atomizing unit 120 and the film forming unit 140. The mist is transported from the mist generating source 104 of the atomizing unit 120 to the film forming chamber 107 of the film forming unit 140 via the transport unit 109 through the carrier gas. The transport unit 109 can be formed into, for example, a supply tube 109a. For example, a quartz tube or a resin tube can be used as the supply tube 109a.

[0130] (Raw material solution)

[0131] The raw material solution 104a is not particularly limited as long as it contains a metal raw material containing at least a metal element constituting the crystalline metal oxide film, and a carboxylic acid or an acid having an acid dissociation constant with respect to water at 25°C greater than -8 and less than 8.8, and may be either an inorganic material or an organic material. A solution of a metal or a metal compound can be suitably used for the raw material solution 104a, and a solution containing one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel, and cobalt can be used.

[0132] By including the above-mentioned metals, crystalline metal oxide films of these metals can be formed. In particular, by using at least one of gallium or aluminum as the main component, crystalline oxide films of gallium or aluminum, such as α-Ga2O3 films or α-Al2O3 films, can be formed. The main component here refers to the component with the largest atomic percentage among the metal elements in the metal raw material.

[0133] The raw material solution 104a is not particularly limited as long as the metal solution can be atomized. A solution obtained by dissolving or dispersing a metal in the form of a complex or salt in an organic solvent or water can be used as the raw material solution 104a. A solution obtained by dissolving a metal complex in water is preferred because of its excellent atomization efficiency and cost.

[0134] Examples of the complex form include acetylacetone complexes, carbonyl complexes, ammonia complexes, and hydride complexes.

[0135] In particular, when the metal raw material contains at least one of gallium and aluminum as a main component, the metal raw material can be an acetylacetone complex.

[0136] By using an acetylacetone complex as the metal raw material, the metal element can be easily dissolved in the carboxylic acid in the raw material solution 104 a .

[0137] Examples of the salt form include metal chlorides, metal bromides, and metal iodides. In addition, solutions prepared by dissolving the above metals in hydrobromic acid, hydrochloric acid, hydroiodic acid, and the like can also be used as the salt aqueous solution.

[0138] The raw material concentration of the metal raw material as the solute can be 0.01 mol / L to 1 mol / L, preferably 0.05 mol / L to 0.5 mol / L, and more preferably 0.08 mol / L to 0.30 mol / L. Within this range, a sufficient film formation rate is maintained and the formation of foreign matter can be more effectively suppressed.

[0139] In addition, the raw material solution 104a of the present invention contains a carboxylic acid or an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C. By containing such an acid, it is possible to suppress the generation of side reactions of the metal raw material, such as Figure 4 Such spherical foreign bodies, such as Figure 5 Therefore, when using mist-CVD for film formation, the generation of spherical foreign matter can be suppressed and a film with good surface smoothness can be formed.

[0140] in addition, Figure 4 and Figure 5 In order to form a film of α-(Al X Ga 1-X )2O3 film (0≤X<1)) when the foreign matter formed on the film.

[0141] In addition, for Figure 4 or Figure 5 Such a spherical foreign body, except Figure 4 and Figure 5 In addition to the SEM shown in the figure, it is also possible to observe the shape or conduct a quantitative investigation by using an electron microscope such as TEM, an optical microscope, a surface inspection device that detects defects based on light and dark differences, a surface inspection device that performs machine learning and detection on defects using image recognition AI, etc., to determine the shape or quantity, but the observation method and the counting method are not particularly limited.

[0142] The formation mechanism of spherical foreign matter and the mechanism by which carboxylic acid or an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C can inhibit the formation of spherical foreign matter are not certain, but the following mechanism is considered.

[0143] First, according to the results of ionizing the raw material solution 104a and measuring the MS spectrum, the raw material dimer was observed in the raw material solution 104a without the addition of carboxylic acid or an acid with an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C, and the raw material dimer was almost not observed in the raw material solution 104a with the addition of carboxylic acid or an acid with an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C.

[0144] Furthermore, when using an acid (such as hydrochloric acid) that is stronger than carboxylic acid or an acid with an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C, structures formed by coordination of hydroxides or strong acids were observed. It is speculated that at the heat treatment temperatures mentioned above, these raw material components formed by coordination of dimers, hydroxides, and strong acids do not form a crystalline metal oxide film on the substrate, but instead form foreign matter.

[0145] For example, when the MS spectrum of the raw material solution 104a containing aluminum acetylacetonate as the metal raw material is measured, [Al(acac)2], which is considered to be formed by the separation of one acac from the raw material Al(acac)3, appears particularly strongly in the solution to which carboxylic acid or an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C is added. + ], on the other hand, in the solution without adding carboxylic acid or acid with acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C, a peak such as [Al(acac)2 + ] [Al(acac)2-OH-Al(acac)2 + ]、[Al(acac)2-acac-Al(acac)2 + ] The structures formed by dimerization of such raw materials have m / z=467, m / z=549, etc.

[0146] Furthermore, when hydrochloric acid (acid dissociation constant of -8) as a strong acid was added, the + ] is replaced by OH to form [Al(acac)(OH) + ] m / z=143, etc.

[0147] It is speculated that these dimers, hydroxides, and raw material components coordinated with strong acids do not form a crystalline metal oxide film on the substrate, but instead form spherical foreign matter. The above reason is considered to be the formation mechanism of spherical foreign matter.

[0148] Furthermore, in raw material solution 104a to which carboxylic acid or an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C was added, peaks due to raw material components formed by dimers, hydroxides, or strong acid coordination were hardly observed. Therefore, it is speculated that the formation of these components is suppressed by the carboxylic acid or the acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C, thereby suppressing the formation of foreign matter. This is believed to be the mechanism by which carboxylic acid or an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C can suppress the formation of spherical foreign matter.

[0149] In the mechanism described above, since it is believed that carboxylic acids or acids having an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C can suppress the formation of spherical foreign matter, it is preferred that, in particular, the raw material solution 104a containing aluminum acetylacetonate as the metal raw material, the less the raw material components formed by dimers, hydroxides, and strong acid coordination, the more the formation of foreign matter is suppressed.

[0150] Therefore, when the raw material solution 104a is set to a solution of an acetylacetone complex containing aluminum, in the MS spectrum of the raw material solution 104a, it is preferred that when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.25.

[0151] More preferably, (I2+I3+I4) / I1<0.1, further preferably (I2+I3+I4) / I1<0.05, and most preferably (I2+I3+I4) / I1=0 (I1, I3, I4 are all less than the detection limit of 5.0×10 3 ).

[0152] Therefore, by using a raw material solution 104a containing less acetylacetone complex crystal ОH or a structure formed by cross-linking acetylacetone (m / z=467), a structure formed by dimerization (m / z=549), and a structure formed by acetylacetone substituted with OH (m / z=143), the formation of spherical foreign matter believed to be caused by these structures can be reliably suppressed.

[0153] The method for acquiring the MS spectrum and the ionization method are not particularly limited. Examples of ionization methods include electron ionization, chemical ionization, high-speed atom bombardment, matrix-assisted laser desorption ionization, and electrospray ionization.

[0154] The type of carboxylic acid in the present invention is not particularly limited. It can be a saturated monocarboxylic acid (formic acid, acetic acid, propionic acid, butyric acid, valeric acid, etc.), an unsaturated monocarboxylic acid (acrylic acid, crotonic acid, methacrylic acid, etc.), a dicarboxylic acid with two carboxyl groups (oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, etc.), a tricarboxylic acid with three carboxyl groups (citric acid, etc.), a hydroxy acid having a hydroxyl group in addition to a carboxyl group (lactic acid, malic acid, tartaric acid, glycolic acid, etc.), an aromatic carboxylic acid having a phenyl group (benzoic acid, isophthalic acid, terephthalic acid, etc.), or a carboxylic acid having a carbonyl group (glyoxylic acid, levulinic acid, etc.).

[0155] In addition, derivatives of the above-mentioned acids in which some of the hydrogen atoms are substituted with electron-attracting functional groups such as halogen, vinyl, cyano, and nitro groups can also be used. For example, in the case of acetic acid (CH3COOH), there are monochloroacetic acid (CH2ClCOOH), dichloroacetic acid (CHCl2COOH), and trichloroacetic acid (CCl3COOH) in which the hydrogen atoms of CH3 are substituted with chlorine. That is, the "carboxylic acid" mentioned in the present invention also includes derivatives.

[0156] Similarly, other derivatives include fluoroacetic acid obtained by substituting a portion of hydrogen atoms of the above-mentioned acids with fluorine, bromoacetic acid obtained by substituting with bromine, iodoacetic acid obtained by substituting with iodine, cyanoacetic acid obtained by substituting with a cyano group, vinylacetic acid obtained by substituting with a vinyl group, nitroacetic acid obtained by substituting with a nitro group, etc. The acidity of the -COOH portion can be increased by substituting with an electron-attracting functional group.

[0157] Alternatively, a carboxylic acid may be produced by hydrolyzing an acyl halide obtained by substituting the OH portion of the carboxyl group of the above-mentioned acid with a halogen, or a carboxylate obtained by neutralizing the above-mentioned acid with a base such as NaOH or ammonia. However, the use of a carboxylic acid is preferred because this method does not make the process more complicated than necessary and can simply suppress the generation of foreign matter.

[0158] The carboxylic acid of the present invention may be used directly as a liquid at room temperature and pressure, or may be mixed with an organic solvent or water. Furthermore, when using a solid carboxylic acid at room temperature and pressure, a solution thereof dissolved in an organic solvent or water may be used, but dissolution in water is preferred because of its good atomization efficiency and cost-effectiveness.

[0159] The carboxylic acid of the present invention is, for example, a carboxylic acid having 5 or less carbon atoms, but is preferably a carboxylic acid having 4 or less carbon atoms. The fewer carbon atoms there are, the less residual carbon atoms in the crystalline metal oxide film can be achieved, and the more easily it is soluble in water, the easier it is to atomize, resulting in an excellent film formation cost.

[0160] Furthermore, the carboxylic acid in the present invention is preferably a carboxylic acid composed only of H, C, and O. This is because it is possible to suppress incorporation of undesired impurities into the crystalline metal oxide film.

[0161] Among them, the carboxylic acid of the present invention is preferably formic acid.

[0162] Formic acid consists only of H, C, and O and is the carboxylic acid with the smallest molecular weight. Therefore, the elements in the carboxylic acid are less likely to be incorporated into the crystalline oxide film than carboxylic acids with larger molecular weights, which is advantageous in suppressing incorporation.

[0163] Furthermore, the carboxylic acid in the present invention preferably has an acid dissociation constant of 2.65 or more and 4.67 or less with respect to water at 25° C. When the acid dissociation constant is within the above range, OH can be effectively suppressed. - and can effectively inhibit the residual carbon atoms in the film.

[0164] By setting the acid dissociation constant to 2.65 or higher, the formation of foreign matter from the metal raw material can be more reliably suppressed. Furthermore, by setting the acid dissociation constant to 4.67 or lower, the carboxylic acid necessary to suppress the formation of spherical foreign matter can be reliably prevented from becoming excessive and remaining in the crystalline metal oxide film.

[0165] In addition, the acid dissociation constant represents the negative common logarithm pKa of the equilibrium constant Ka of the dissociation reaction in which hydrogen ions are released from an acid. In addition, the acid dissociation constant relative to water described in the present invention is set to the value recorded in a chemical handbook. In the case of performing a multi-step ionization of a carboxylic acid, it is set to the acid dissociation constant of the first step. If not recorded, it can be experimentally obtained by neutralization titration, absorptiometry, capillary electrophoresis, etc.

[0166] Examples of carboxylic acids having an acid dissociation constant of 2.65 to 4.67 include formic acid (3.55), acetic acid (4.56), propionic acid (4.67), butyric acid (4.63), valeric acid (4.64), acrylic acid (4.26), malonic acid (2.65), succinic acid (4.00), glutaric acid (4.13), adipic acid (4.26), citric acid (2.87), lactic acid (3.66), malic acid (3.24), and tartaric acid. (D-isomer is 2.82, L-isomer is 2.99), glycolic acid (3.63), benzoic acid (4.20), isophthalic acid (3.50), terephthalic acid (3.54), glyoxylic acid (3.18), levulinic acid (4.44), chloroacetic acid (2.68), 2-chloropropionic acid (2.71), 3-chloropropionic acid (3.92), vinylacetic acid (4.12), bromoacetic acid (2.72), iodoacetic acid (2.98), etc., but are not limited to these. In addition, the numbers in parentheses represent the acid dissociation constants of the first step.

[0167] The concentration of the carboxylic acid in the present invention is not particularly limited as long as it is within a range in which the foreign matter suppression effect of the carboxylic acid can be exerted and carbon is unlikely to remain in the crystalline oxide film.

[0168] For example, the concentration of the carboxylic acid of the present invention is 60 vol% or less, more preferably 1 vol% or more and 50 vol% or less, and even more preferably 5 vol% or more and 40 vol% or less, in terms of volume ratio relative to the entire solution.

[0169] By setting the volume ratio to 1 vol% or more, the foreign matter suppression effect of the carboxylic acid can be more reliably exerted. In addition, by setting the volume ratio to 50 vol% or less, the foreign matter suppression effect of the carboxylic acid can be more fully exerted, and the carbon in the carboxylic acid can be suppressed from remaining in the crystalline oxide film.

[0170] The molar concentration of the carboxylic acid in the raw material solution of the present invention is not particularly limited, but is, for example, 15.8 mol / L or less, preferably 0.1 mol / L or more and 13.2 mol / L or less, and more preferably 1.3 mol / L or more and 10.5 mol / L or less.

[0171] By setting the molar concentration of the carboxylic acid to 0.1 mol / L or higher, the foreign matter suppression effect of the carboxylic acid can be reliably exerted. In addition, by setting the molar concentration to 13.2 mol / L or lower, the foreign matter suppression effect of the carboxylic acid can be fully exerted, and the carbon in the carboxylic acid can be suppressed from remaining in the crystalline oxide film.

[0172] Furthermore, the molar concentration of the carboxylic acid in the raw material solution is preferably equal to or higher than the molar concentration of the metal raw material in the raw material solution 104 a .

[0173] This is because the foreign matter suppressing effect of the carboxylic acid can be fully exhibited by setting the molar concentration as described above.

[0174] In addition, the acid of the present invention having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25°C is not particularly limited as long as the acid dissociation constant is greater than -8 and less than 8.8. It is preferably greater than 0.77 and less than 8.8, and more preferably greater than 2.0 and less than 7.53. As the acid described above, in addition to the carboxylic acids described above, hypobromous acid (7.53), hypochlorous acid (7.53), chlorous acid (2.53), carbonic acid (6.35), fluoric acid (3.17), iodic acid (0.77), phosphinic acid (1.23), phosphonic acid (1.5), phosphoric acid (2.15), diphosphoric acid (0.8), tripolyphosphoric acid (2.0), hydrogen sulfide (7.02), sulfurous acid (1.91), etc. can also be listed, but are not limited thereto.

[0175] By using an acid having an acid dissociation constant within the above-mentioned range, the formation of foreign matter from the metal raw material can be suppressed.

[0176] Furthermore, 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, and p-type dopants such as copper, silver, tin, iridium, and rhodium. The concentration of the dopant may be, for example, approximately 1.0×10 -9 ~1.0mol / L, which can be set to about 1.0×10 -7 The concentration may be as low as 0.01 mol / L or less, or as high as 0.01 mol / L or more.

[0177] (Matrix)

[0178] Figure 1The substrate 110 shown in the figure has a surface on which a crystalline metal oxide film can be formed. It is not particularly limited as long as it can support the formed metal oxide film. It can be a known substrate. It can be an insulator, a conductor, or a semiconductor, and can be single crystal or polycrystalline.

[0179] Specific examples of the substrate 110 include, but are not limited to, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron or aluminum, stainless steel, gold, silicon, sapphire, quartz, glass, gallium oxide, lithium niobate, and lithium tantalate.

[0180] Furthermore, it is preferable to use a substrate 110 in which aluminum is the largest metal element in terms of atomic % among the metal elements contained in the substrate 110. Among them, it is preferable to use a sapphire wafer from the viewpoints of quality and cost.

[0181] The orientation of the principal surface of the substrate 110 is not particularly limited. In the case of a sapphire wafer, for example, a principal surface such as the c-plane, m-plane, or a-plane can be used. Furthermore, the substrate 110 may have an inclination angle relative to the reference plane. The inclination angle is not particularly limited, but is preferably 0° to 15°.

[0182] The thickness of the substrate 110 is not particularly limited, but is preferably about 200 to 800 μm from the perspective of cost. In addition, the area of the main surface of the substrate 110 (the surface on which the crystalline metal oxide film is formed) can be 10 cm 2 The area is preferably an area greater than the area of a circle with a diameter of about 5 cm (2 inches) or more, and more preferably an area greater than the area of a circle with a diameter of about 10 cm (4 inches). The upper limit of the area is not particularly limited and can be 750 cm 2 The area below can be an area with a diameter of 12 inches (300 mm) or less in the case of a circle.

[0183] Therefore, if the base 110 is set to 10 cm 2 The above-mentioned large-area substrate can form a high-quality crystalline metal oxide film on the large-area substrate 110, especially with high productivity. In the present invention, the shape of the substrate 110 is not particularly limited.

[0184] The crystalline metal oxide film can be formed directly on the substrate 110 or laminated on an intermediate layer (buffer film or release film) formed on the substrate 110. The intermediate layer is not particularly limited as long as it is a metal oxide that can produce a corundum structure. For example, it can contain an oxide of any one of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium as a main component.

[0185] More specifically, the intermediate layer is Al2O3, Ti2O3, V2O3, Cr2O3, Fe2O3, Ga2O3, Rh2O3, In2O3, Ir2O3. In addition, when two elements selected from the above metal elements are set as A and B, it can be set as (A x B 1-x )2O3(0<x<1) is a binary metal oxide, or when three elements selected from the above metal elements are set as A, B, and C, it can be set as (A x B y C 1-x-y )2O3(0<x<1, 0<y<1) is a ternary metal oxide represented by.

[0186] In the film formation method of the present invention, an annealing treatment may be performed after the crystalline metal oxide film is formed. The annealing temperature is not particularly limited, but is preferably 600°C or lower, more preferably 550°C or lower. This is to prevent the crystallinity of the film from being impaired. The annealing time is not particularly limited, but is preferably 10 seconds to 10 hours, more preferably 10 seconds to 1 hour.

[0187] [Crystalline metal oxide film]

[0188] The crystalline metal oxide film of the present invention is a crystalline metal oxide film containing at least one of gallium or aluminum as a main component, and is characterized in that the number density of spherical foreign matter or agglomerates of spherical foreign matter present on the surface of the crystalline metal oxide film is 621 pieces / cm 2 the following.

[0189] Such a crystalline metal oxide film has excellent film smoothness and can therefore be suitably used in semiconductor devices.

[0190] In addition, the surface of the crystalline metal oxide film in the present invention refers to one of the front surface and the back surface of the crystalline metal oxide film.

[0191] Typically, crystalline metal oxide films are composed of a metal and oxygen. However, in the crystalline metal oxide film of the present invention, the metal is primarily composed of at least one of gallium or aluminum. The term "primary component" herein means that 50 to 100 atomic percent of the metal component is gallium or aluminum.

[0192] As the metal component other than gallium, for example, one or two or more metals selected from the group consisting of iron, indium, vanadium, titanium, chromium, rhodium, iridium, nickel, and cobalt may be included.

[0193] The crystalline metal oxide film preferably has a number density of spherical foreign matter or aggregates of spherical foreign matter present on the film surface of 100 pieces / cm 2Below, more preferably 54 pieces / cm 2 Below, more preferably 8 / cm 2 There is no particular lower limit for spherical foreign matter. It can be 0.01 pieces / cm 2 above.

[0194] The crystalline metal oxide film described above has further improved film smoothness and can therefore be more preferably used in semiconductor devices.

[0195] In addition, as described later, the spherical foreign matter of the present invention is an amorphous particle formed during film formation. Therefore, if it is attached to the surface of the film or embedded in the film, it will be crystallized by heat. However, at this time, it is not the α phase, but the γ phase of aluminum oxide crystals or gallium oxide crystals or their mixed crystals that grow. Therefore, if a voltage is applied to the film in which the spherical foreign matter is observed, the electric field is concentrated on the grain boundary portion of the α phase and the γ phase, which is likely to cause insulation breakdown. If the number density of the spherical foreign matter or the agglomerate of the spherical foreign matter is 621 / cm 2 Below, it is possible to sufficiently suppress dielectric breakdown due to the formation of grain boundaries.

[0196] Furthermore, the crystalline metal oxide film can be configured to have a corundum structure.

[0197] The crystalline metal oxide film described above is a crystalline metal oxide film having a corundum structure and excellent smoothness.

[0198] The spherical foreign matter described in the present invention refers to the spherical foreign matter from the metal raw material. Figure 4 The formation mechanism of spherical foreign matter is still uncertain, but it is believed that it is caused by the evaporation of water in the mist during film formation, which leads to the precipitation of metal raw materials, and the formation of metal oxides due to side reactions of the metal raw materials in the gas phase.

[0199] The term "spherical" as used herein refers to a shape that at least partially resembles a sphere, and includes not only spheres but also oblate spheroids obtained by rotating an ellipse about its minor axis, or prolate spheroids obtained by rotating an ellipse about its major axis. Furthermore, shapes such as hemispheres, which are formed by plane-dividing a sphere, oblate spheroid, or prolate spheroid, are also included.

[0200] The spherical equivalent diameter of a spherical foreign body is between submicron and 10 μm. The spherical equivalent diameter here refers to the radius of the spherical foreign body if it were considered a sphere. There are no specific limitations on the method for calculating the spherical equivalent diameter. For example, it can be calculated by photographing the spherical foreign body using an electron microscope such as an SEM and measuring the radius.

[0201] Furthermore, the main component of the spherical foreign matter is amorphous aluminum oxide or gallium oxide.

[0202] The analysis method of the composition is not particularly limited. It can be examined by EDX, Auger electron spectroscopy, SIMS, etc. In addition, the analysis method of the crystal structure is also not particularly limited. It can be investigated by conventional methods such as electron beam diffraction.

[0203] In addition, the aggregate of spherical foreign matter refers to Figure 5 The foreign matter shown here is a collection of about 2 to 100 spherical foreign matter.

[0204] In addition, for spherical foreign matter or spherical foreign matter aggregates, except for Figure 4 and Figure 5 In addition to the SEM shown in the figure, it is also possible to observe the shape or conduct a quantitative investigation by using an electron microscope such as TEM, an optical microscope, a surface inspection device that detects defects by light and dark contrast, a surface inspection device that performs machine learning and detection of defects using image recognition AI, etc., to determine the shape or quantity, but the observation method and the counting method are not particularly limited.

[0205] In addition, the method for determining the shape of the spherical foreign matter is not particularly limited. It can be determined by an electron microscope, an optical microscope, a surface inspection device that performs machine learning and detection on defects identified by humans, etc., among which determination by an electron microscope is preferred. This is because, under an optical microscope, it is difficult to distinguish by the direction and angle of light. In addition, a surface inspection device of a machine learning type with a review function based on an electron microscope is particularly preferred. In addition to being able to determine by an electron microscope, it is also automatic and can selectively count spherical foreign matter, so the inspection can be made with high precision and shortened.

[0206] The crystalline metal oxide film may contain a dopant depending on the application. The dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium, or niobium, and p-type dopants such as copper, silver, tin, iridium, or rhodium. The concentration of the dopant can be, for example, approximately 1.0×10 16 ~1.0×10 22 / cm 3 , which can be set to about 1.0×10 17 / cm 3 The following low concentration can also be set to about 1.0×10 20 / cm 3 Above high concentration.

[0207] The film thickness of the crystalline metal oxide film of the present invention is not particularly limited, but may be, for example, 0.05 to 100 μm, preferably 0.1 to 50 μm, and more preferably 0.5 to 20 μm.

[0208] The crystalline metal oxide film can be formed directly on the substrate or as Figure 11 The intermediate layer 252 (buffer film or release film) is laminated on the substrate 253. The intermediate layer is not particularly limited as long as it is a metal oxide that can form a corundum structure. For example, it can contain an oxide of any one of aluminum, titanium, vanadium, chromium, iron, gallium, rhodium, indium, and iridium as a main component.

[0209] More specifically, when the intermediate layer is Al2O3, Ti2O3, V2O3, Cr2O3, Fe2O3, Ga2O3, Rh2O3, In2O3, or Ir2O3, and two elements selected from the above metal elements are set as A and B, it can be set as (A x B 1-x )2O3(0<x<1) is a binary metal oxide, or when three elements selected from the above metal elements are set as A, B, and C, it can be set as (A x B y C 1-x-y )2O3(0<x<1, 0<y<1) is a ternary metal oxide represented by.

[0210] The surface area of the crystalline metal oxide film is preferably 10 cm 2 In the case of a circular shape, the area is preferably equivalent to an area of 2 inches (50 mm) or more in diameter. The upper limit of the area is not particularly limited and can be 750 cm 2 In the case of a circle, the area may be equivalent to a diameter of 12 inches (300 mm) or less.

[0211] The crystalline metal oxide film described above has excellent smoothness and can be preferably used in semiconductor devices due to its large area.

[0212] The crystalline metal oxide film of the present invention can be utilized in a semiconductor device by appropriately designing its structure. Examples of semiconductor devices will be described in detail later.

[0213] (Method for producing crystalline metal oxide film)

[0214] As described above, the crystalline metal oxide film of the present invention can be obtained by appropriately selecting a substrate or an intermediate layer for film formation. As described above, the film formation method can be performed by mist-CVD using an appropriate raw material solution.

[0215] (Laminated structure)

[0216] Figure 11This figure shows one embodiment of the structure of the stacked structure of the present invention. The stacked structure 250 having a crystalline metal oxide film of the present invention basically comprises a substrate 253 and a crystalline metal oxide film 251. In this case, an intermediate layer 252 serving as the buffer layer described above may be included between the substrate 253 and the crystalline metal oxide film 251.

[0217] The laminated structure described above has excellent film smoothness and can therefore be suitably used in semiconductor devices.

[0218] The crystalline metal oxide film of the present invention can be utilized in semiconductor devices by appropriately designing its structure. For example, it can constitute the semiconductor layer of a Schottky barrier diode (SBD), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), a metal oxide semiconductor field effect transistor (MOSFET), a static induction transistor (SIT), a junction field effect transistor (JFET), an insulated gate bipolar transistor (IGBT), a light emitting diode (LED), and the like.

[0219] (Semiconductor Device)

[0220] In addition, the semiconductor device of the present invention includes at least one of the above-mentioned crystalline metal oxide film or the above-mentioned stacked structure. For example, a semiconductor device (semiconductor element) such as a semiconductor laser, a diode or a transistor can be provided. The semiconductor device described above may include a substrate or may be removed. The semiconductor device of the present invention uses a high-quality crystalline metal oxide film with good flatness and is a high-quality semiconductor device with excellent electrical properties. Application examples (specific examples) of the semiconductor device are described below.

[0221] (Examples of Applicable Semiconductor Devices)

[0222] The crystalline metal oxide film or the stacked structure having the crystalline metal oxide film has good flatness and excellent electrical properties, and is useful in industry. The crystalline metal oxide film or the stacked structure having the crystalline metal oxide film can be suitably used in various semiconductor devices, etc., and is particularly useful in power devices.

[0223] In addition, the semiconductor device can be classified into a horizontal element (horizontal device) having an electrode on a single-sided side of the crystalline metal oxide film, and a vertical element (vertical device) having an electrode on the front and back sides of the crystalline metal oxide film. The semiconductor device of the present invention can be suitably used in a horizontal device, and can also be suitably used in a vertical device, preferably in a vertical device. As a semiconductor device, for example, a Schottky barrier diode (SBD), a metal semiconductor field effect transistor (MESFET), a high electron mobility transistor (HEMT), a semiconductor field effect transistor (MOSFET), a junction field effect transistor (JFET), an insulated gate bipolar transistor (IGBT) or a light emitting diode (LED) can be listed.

[0224] (Method for Manufacturing Semiconductor Device)

[0225] First, a crystalline metal oxide film is formed on the main surface of the substrate directly or through other layers to obtain a stacked structure of the present invention. Then, a semiconductor device is manufactured by forming an electrode or the like on the crystalline metal oxide film. At this time, the stacked structure comprising the substrate and the crystalline metal oxide film can be used directly, or the substrate can be removed, retaining the intermediate layer and the crystalline oxide semiconductor film, or the substrate and the intermediate layer can be removed, retaining only the crystalline oxide semiconductor film. By proceeding in the above manner, a high-performance semiconductor device can be manufactured, which uses a high-quality crystalline metal oxide film with good flatness.

[0226] The following describes preferred examples of applying the crystalline metal oxide film of the present invention to an n-type semiconductor layer (e.g., an n+-type semiconductor or an n--type semiconductor layer) using the accompanying drawings, but the present invention is not limited to these examples. Furthermore, the semiconductor elements exemplified below may further include other layers (e.g., an insulator layer or a conductor layer), and intermediate layers or buffer layers (buffer layers) may be omitted as appropriate.

[0227] Figure 12 The SBD 300 is an example of an SBD of the present invention. The SBD 300 includes an n-type semiconductor layer 301 a doped at a relatively low concentration, an n+ type semiconductor layer 301 b doped at a relatively high concentration, a Schottky electrode 302 , and an ohmic electrode 303 .

[0228] The materials of the Schottky electrode 302 and the ohmic electrode 303 can be well-known electrode materials. Examples of such electrode materials include metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium or silver, or alloys of these metals; metal oxide conductive films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO); organic conductive compounds such as polyaniline, polythiophene or polypyrrole; or mixtures of these substances and stacks thereof.

[0229] The Schottky electrode 302 and the ohmic electrode 303 can be formed by a known method such as vacuum evaporation or sputtering. More specifically, when the Schottky electrode is formed using two of the above-mentioned metals, namely a first metal and a second metal, the Schottky electrode can be formed by laminating a layer composed of the first metal and a layer composed of the second metal, and patterning the layer composed of the first metal and the layer composed of the second metal using photolithography.

[0230] When a reverse bias is applied to the SBD 300, a depletion layer (not shown) diffuses in the n-type semiconductor layer 301a, resulting in a high-voltage SBD. Furthermore, when a forward bias is applied, electrons flow from the ohmic electrode 303 to the Schottky electrode 302. Therefore, the SBD of the present invention excels in high-voltage and high-current applications, with fast switching speeds, and excellent voltage resistance and reliability.

[0231] Figure 13 HEMT 400 is an example of a HEMT according to the present invention. It includes a wide-bandgap n-type semiconductor layer 401 , a narrow-bandgap n-type semiconductor layer 402 , an n+-type semiconductor layer 403 , a semi-insulator layer 404 , a buffer layer 405 , a gate electrode 406 , a source electrode 407 , and a drain electrode 408 .

[0232] Figure 14 MOSFET 500 is an example of a MOSFET of the present invention. MOSFET 500 includes an n-type semiconductor layer 501 , n+ type semiconductor layers 502 and 503 , a gate insulating film 504 , a gate electrode 505 , a source electrode 506 , and a drain electrode 507 .

[0233] Figure 15 The IGBT 600 is an example of an IGBT of the present invention and includes an n-type semiconductor layer 601 , an n-type semiconductor layer 602 , an n+ type semiconductor layer 603 , a p-type semiconductor layer 604 , a gate insulating film 605 , a gate electrode 606 , an emitter electrode 607 , and a collector electrode 608 .

[0234] Figure 16It is an example of the LED of the present invention. LED700 includes a first electrode 701, an n-type semiconductor layer 702, a light-emitting layer 703, a p-type semiconductor layer 704, a translucent electrode 705, and a second electrode 706. As the material of the translucent electrode. Conductive materials containing indium or titanium oxides can be listed. More specifically, for example, In2O3, ZnO, SnO2, Ga2O3, TiO2, CeO2 or mixed crystals of two or more of these oxides or materials doped in these oxides can be listed. By processing these materials in a known manner such as sputtering, a translucent electrode can be formed. In addition, after the translucent electrode is formed, thermal annealing for the purpose of making the translucent electrode transparent can be performed.

[0235] As materials for the first electrode 701 and the second electrode 706, for example, metals such as aluminum, molybdenum, cobalt, zirconium, tin, niobium, iron, chromium, tantalum, titanium, gold, platinum, vanadium, manganese, nickel, copper, hafnium, tungsten, iridium, zinc, indium, palladium, neodymium or silver or alloys of these metals, metal oxide conductive films such as tin oxide, zinc oxide, rhenium oxide, indium oxide, indium tin oxide (ITO), zinc indium oxide (IZO), organic conductive compounds such as polyaniline, polythiophene or polypyrrole, or mixtures of these compounds can be listed. The film forming method of the electrode is not particularly limited. It can be formed on the substrate according to a method appropriately selected from wet methods such as printing, spraying, and coating, physical methods such as vacuum evaporation, sputtering, and ion plating, and chemical methods such as CVD and plasma CVD, taking into account the compatibility with the above materials.

[0236] (Film Formation Method)

[0237] Below, while referring to Figure 1 An example of the film forming method of the present invention will be described. First, a raw material solution 104a is placed in the mist generating source 104 of the mist generating unit 120, and a base (crystalline substrate) 110 is placed on the hot plate 108, which is then turned on.

[0238] Next, open the flow regulating valves 103a and 103b, and supply carrier gas from the carrier gas source 102a (main carrier gas) and the dilution carrier gas source 102b (dilution carrier gas) into the film forming chamber 107, use the carrier gas to fully replace the atmosphere of the film forming chamber 107, and at the same time adjust and control the flow of the main carrier gas and the flow of the dilution carrier gas respectively.

[0239] Specifically, the ultrasonic vibrator 106 is vibrated, and the vibration is transmitted to the raw material solution 104a through the water 105a, thereby atomizing the raw material solution 104a to generate mist.

[0240] Next, the mist is transported by the carrier gas. Specifically, the mist is transported from the atomizing unit 120 to the film forming unit 140 via the transport unit 109 by the carrier gas, and is introduced into the film forming chamber 107 .

[0241] Then, film formation is performed. Specifically, mist is supplied onto a substrate 110 placed on a hot plate 108. Heat from the hot plate 108 causes a thermal treatment in the film formation chamber 107, resulting in a thermal reaction and the formation of a crystalline metal oxide film on the substrate 110. Annealing can be performed as needed after film formation.

[0242] (peel off)

[0243] After film formation, the substrate 110 can be peeled from the crystalline metal oxide film. The peeling method is not particularly limited and can be any known method. Examples include peeling by mechanical impact, peeling by applying heat and utilizing thermal stress, peeling by applying vibrations such as ultrasound, peeling by etching, and peeling by laser lift-off. By such peeling, a crystalline metal oxide film can be obtained as a free-standing film.

[0244] Example

[0245] Hereinafter, the present invention will be described in detail with reference to examples, but these examples do not limit the present invention.

[0246] Raw material solutions containing various ratios of metal raw materials and various carboxylic acids were atomized and heat-treated to form crystalline metal oxide films on substrates. The number of spherical foreign matter particles generated on the surface of the films was compared with that formed using raw material solutions that did not contain carboxylic acids. Furthermore, the MS spectra of the raw material solutions were compared. The specific procedure is as follows.

[0247] (Example 1)

[0248] 1. Formation of crystalline metal oxide films

[0249] use Figure 1 The film forming apparatus 100 shown in FIG. 1 forms a crystalline metal oxide film according to the following procedure.

[0250] 1-1. Process for preparing raw material solution 104a

[0251] To a solution of aluminum acetylacetonate as a metal raw material added to water, 15 vol% formic acid as a carboxylic acid was added, and the solution was stirred at 60°C for 120 minutes to dissolve the metal raw material. This aqueous solution with a solute concentration of 0.1 mol / L of the metal raw material was prepared as raw material solution 104a. The resulting raw material solution 104a was placed in mist generation source 104. The solution temperature at this point was 25°C.

[0252] 1-2. Heating process

[0253] Next, in the film forming chamber 107, a circular sapphire substrate with a diameter of 4 inches (100 mm) and a main surface of the c-plane as the base 110 is placed on the hot plate 108, and the hot plate 108 is started to increase the temperature to 500°C.

[0254] 1-3. Carrier gas supply process

[0255] Next, open the flow regulating valves 103a and 103b, and supply nitrogen as a carrier gas from the carrier gas source 102a (main carrier gas) and the dilution carrier gas source 102b (dilution carrier gas) into the film forming chamber 107. Use the above-mentioned carrier gases to fully replace the atmosphere of the film forming chamber 107, and at the same time adjust the flow rate of the main carrier gas to 12L / min and the flow rate of the dilution carrier gas to 12L / min, respectively.

[0256] 1-4. Film Formation Process

[0257] Next, the ultrasonic vibrator 106 is vibrated at 2.4 MHz, and the vibration is transmitted to the raw material solution 104 a through the water 105 a , thereby atomizing the raw material solution 104 a to generate mist.

[0258] The mist is transported to the film forming chamber 107 through the supply pipe 109 a using a carrier gas, and the mist is supplied onto the substrate 110 .

[0259] Then, gas was exhausted from the exhaust port 112 at atmospheric pressure and 500°C, and the mist was thermally reacted within the film-forming chamber 107, forming a film of α-Al₂O₃ having a corundum structure on the substrate 110. The film-forming time was set to 150 minutes. At this time, a refill mechanism (not shown) was used to replenish the raw material solution 104a in the mist generating source 104, so that the water level during the film formation was constant.

[0260] (Example 2 to Example 5)

[0261] The film was formed in the same manner as in Example 1, except that in the preparation process of 1-1. raw material solution 104a, the amount of formic acid added to the raw material solution 104 was set to 0.5 vol% (Example 2), 1 vol% (Example 3), 5 vol% (Example 4), and 25 vol% (Example 5).

[0262] (Comparative Example 1)

[0263] Film formation was performed in the same manner as in Example 1, except that 1 vol % of hydrochloric acid (acid dissociation constant: −8) was added instead of formic acid in the step 1-1. of preparing the raw material solution 104 a .

[0264] (Example 6 to Example 9)

[0265] The film was formed in the same manner as in Example 1, except that in the preparation process of 1-1. raw material solution 104a, the concentration of aluminum acetylacetonate was set to 0.30 mol / L, the amount of formic acid added was set to 20 vol% (Example 6), 40 vol% (Example 7), 50 vol% (Example 8), 60 vol% (Example 9), and the film formation temperature was set to 440°C.

[0266] (Example 10)

[0267] Film formation was performed in the same manner as in Example 1, except that 15 vol % of acetic acid (having an acid dissociation constant of 4.56 with respect to water) was added instead of formic acid in the step 1-1. of preparing the raw material solution 104a.

[0268] (Example 11)

[0269] Film formation was performed in the same manner as in Example 1 except that 15 vol % of propionic acid (having 3 carbon atoms and having an acid dissociation constant with respect to water of 4.67) was added instead of formic acid in the step 1-1. preparing the raw material solution 104a.

[0270] (Example 12)

[0271] Film formation was performed in the same manner as in Example 1 except that a 15 vol % saturated aqueous solution of malonic acid (acid dissociation constant with respect to water: 2.65) was added instead of formic acid in the step 1-1. preparing the raw material solution 104a.

[0272] (Example 13)

[0273] Film formation was performed in the same manner as in Example 1 except that 15 vol % of a 50 wt % aqueous solution of glyoxylic acid (acid dissociation constant with respect to water: 3.18) was added instead of formic acid in the step 1-1. preparing the raw material solution 104a.

[0274] (Comparative Example 2)

[0275] Film formation was performed in the same manner as in Example 1, except that 15 vol % of hydrochloric acid (acid dissociation constant: −8) was added instead of formic acid in the step 1-1. of preparing the raw material solution 104 a .

[0276] (Comparative Example 3)

[0277] The film was formed in the same manner as in Example 1 except that 15 vol % of hydrobromic acid (acid dissociation constant: −9) was added instead of formic acid in the step 1-1. of preparing the raw material solution 104 a .

[0278] (Comparative Example 4)

[0279] Film formation was performed in the same manner as in Example 1, except that 15 vol % of acetylacetone (acid dissociation constant: 8.8) was added instead of formic acid in the step 1-1. of preparing the raw material solution 104a.

[0280] (Example 14)

[0281] The film was formed in the same manner as in Example 1, except that in the preparation process of 1-1. raw material solution 104a, the concentration of aluminum acetylacetonate was set to 0.08 mol / L, 1 vol% of a 50 wt% aqueous solution of glyoxylic acid (the acid dissociation constant relative to water is 3.18) was added instead of formic acid, and the film formation temperature was set to 400°C.

[0282] (Example 15)

[0283] Film formation was performed in the same manner as in Comparative Example 1, except that 15 vol % of formic acid was further added in the step of 1-1. preparing the raw material solution 104 a .

[0284] (Example 16)

[0285] The film is formed in the same manner as in Example 1, except that a sapphire substrate with a diameter of 6 inches (150 mm) is used as the base 110, a 0.1 mol / L solution of gallium acetylacetonate is used as the metal raw material in the preparation process of 1-1. Raw material solution 104a, the film forming temperature is set to 550°C, and the supply amount of the carrier gas is set to 2 times.

[0286] (Example 17)

[0287] 2. AlGaO film formation

[0288] use Figure 3 The film forming apparatus 200 shown in FIG. 2 forms an AlGaO film according to the following procedure: In Example 17, a c-plane sapphire substrate having a diameter of 4 inches (100 mm) is first used as the base 210 .

[0289] 2-1. Raw material solution preparation process

[0290] To a solution of gallium acetylacetonate, one of the metal raw materials, added to water, 15 vol% formic acid, a carboxylic acid, was added and stirred at 60°C for 120 minutes to dissolve the solution. This aqueous solution, with a raw material concentration of 0.1 mol / L, was prepared as Ga raw material solution 204b. The resulting Ga raw material solution 204b was placed in mist generation source 204a. The solution temperature at this point was 25°C.

[0291] Next, 15 vol% formic acid (a carboxylic acid) was added to a solution of aluminum acetylacetonate (a metal raw material) in water. The solution was stirred at 60°C for 120 minutes to dissolve the metal raw material. This aqueous solution with a raw material concentration of 0.1 mol / L was prepared as Al raw material solution 204d. The Al raw material solution 204d obtained in this manner was placed in mist generation source 204c. The solution temperature at this time was 25°C.

[0292] 2-2. Substrate heating step

[0293] Next, in the film forming chamber 207 of the film forming unit 240 , a c-plane sapphire substrate with a diameter of 4 inches (100 mm) is placed on the hot plate 208 , which is then turned on to raise the temperature to 440° C.

[0294] 2-3. Carrier gas supply process

[0295] Next, open the flow regulating valves 203a, 203b, 203c, and 203d, and supply oxygen as a carrier gas from the carrier gas source 202a (main carrier gas of Ga) of the carrier gas supply section 230a, the dilution carrier gas supply source 202b (dilution carrier gas of Ga), the carrier gas source 202c (main carrier gas of Al) of the carrier gas supply section 230b, and the dilution carrier gas supply source 202d (dilution carrier gas of Al) into the film forming chamber 207, and use these carrier gases to fully replace the atmosphere of the film forming chamber 207. At the same time, adjust the flow rate of the main carrier gas of Ga to 2 L / min, the flow rate of the dilution carrier gas of Ga to 10 L / min, the flow rate of the main carrier gas of Al to 10 L / min, and the flow rate of the dilution carrier gas of Al to 2 L / min, respectively.

[0296] 2-4. Film Formation Process

[0297] Next, using oscillators 216a and 216b, ultrasonic vibrators 206a and 206b are vibrated at 2.4 MHz, and the vibration is transmitted to Ga raw material solution 204b and Al raw material solution 204d through water 205b and 205d in containers 205a and 205c, thereby atomizing Ga raw material solution 204b and Al raw material solution 204d to generate mist.

[0298] The mist is transported by carrier gas through the transport pipes 209a and 209b of the transport unit 209 to the mist mixer 213, where the mists of the Ga raw material solution 204b and the Al raw material solution 204d are mixed. The mist mixed in the mist mixer 213 is transported by carrier gas through the supply pipe 209c of the transport unit 209 to the film forming chamber 207, where the mist is supplied onto the substrate 210.

[0299] Then, the gas is exhausted from the exhaust port 212 at 440°C under atmospheric pressure, and the mist is thermally reacted in the film forming chamber 207 to form an AlGaO film (α-Al2O3) having a corundum structure on the substrate 210. x Ga 1-x )2O3 (0≤x<1) thin film. The film formation time was set to 150 minutes. At this time, a refill mechanism (not shown) was used to appropriately refill the Ga raw material solution 204b and Al raw material solution 204d in the mist generating source 204a and 204c, so that the water level during film formation remained constant.

[0300] (Comparative Example 5)

[0301] A film was formed in the same manner as in Example 17 except that 1 vol % of HCl was added in place of formic acid in the step 2-1. preparing the raw material solution.

[0302] (evaluate)

[0303] 1. Crystal structure evaluation

[0304] The crystal structure of the prepared films was evaluated by XRD 2θ-ω scanning. It was confirmed that the films obtained in Examples 1 to 15 and Comparative Examples 1 to 4 were α-Al2O3, the film obtained in Example 16 was α-Ga2O3, and the film obtained in Example 17 and Comparative Example 5 was α-(Al x Ga 1-x )2O3(0<x<1).

[0305] 2. Determination of the number of foreign matter

[0306] The number of foreign matter in the crystalline metal oxide films formed in Examples 1 to 17 and Comparative Examples 1 to 5 was counted using an optical microscope at a dark field magnification of 20. 2 Observe the visual field area and calculate 1cm 2 The number of foreign matter inside (= foreign matter density).

[0307] The film forming conditions and foreign matter density of Examples 1 to 17 and Comparative Examples 1 to 5 are shown in Table 1. In addition, the relationship between the foreign matter density and the amount of formic acid for Examples 1 to 9 and Comparative Examples 1 to 4 is shown in Table 1. Figure 6 The relationship between the foreign matter density and the acid dissociation constant when 15 vol% of various acids are added (Examples 1, 10 to 13, Comparative Examples 2 to 4) is shown in FIG. Figure 7 .

[0308] [Table 1]

[0309]

[0310] As can be seen from Table 1, the foreign matter density of Examples 1 to 17 in which carboxylic acid was added to the raw material solution was significantly lower than that of Comparative Examples 1 to 5 in which no carboxylic acid was added to the raw material solution.

[0311] In addition, if Figure 6 As shown, the relationship between the amount of formic acid added and the foreign matter density varies depending on the raw material concentration of the metal raw material. However, in the addition amount range of 1 to 60 vol% in Examples 1 to 9, the foreign matter density is significantly lower than that in Comparative Examples 1 to 4 in which no carboxylic acid is added.

[0312] Further, if Figure 7 As shown in FIG. 1 , the relationship between the acid dissociation constant of the added acid with respect to water and the foreign matter density indicates that within the range of the acid dissociation constants of Examples 1 and 10 to 13, the foreign matter density is significantly lower than that of Comparative Examples 2 to 4 in which no carboxylic acid is added.

[0313] From the above results, it is understood that by adding a carboxylic acid to the raw material solution, a smooth crystalline metal oxide film with suppressed generation of foreign matter can be obtained.

[0314] 3. MS Spectrum Measurement

[0315] The MS spectrum of the raw material solution 104a used in Example 1, Comparative Example 1, and Comparative Example 2 was measured by electrospray ionization (ESI). The measurement conditions were set as follows.

[0316]

[0317] Sample pretreatment: The sample is directly used as the measurement sample.

[0318] Measurement device: Triple TOF 5600+ (manufactured by AB SCIEX Pte. Ltd.)

[0319] Ionization method: ESI

[0320] IonSpray Voltage Floating: 5.5 kV (Positive mode), 4.5 kV (Negative mode)

[0321] Mass range: m / z 50-1500

[0322] The results of the detection of cationic species in the Positive mode are shown in Figures 8-10 Table 2 shows the relationship between the peak intensities I1, I2, I3, and I4 at m / z = 225, 467, 549, and 143 of Example 1, Comparative Example 1, and Comparative Example 2 and (I2+I3+I4) / I1.

[0323] [Table 2]

[0324]

[0325] like Figure 8 As shown in Table 2, in the raw material solution used in Example 1, the peak at m / z = 225 is prominent and strong, and almost only the peak at m / z = 225 can be observed. This is considered to be the result of the separation of one acac from the Al(acac)3 as the raw material [Al(acac)2 + ] peak.

[0326] On the other hand, Figure 9 As shown in Table 2, in addition to m / z=225, peaks at m / z=467 and m / z=549 were observed in the raw material solution used in Comparative Example 1. This is believed to be [Al(acac)2 + ] [Al(acac)2-OH-Al(acac)2 + ] or [Al(acac)2-acac-Al(acac)2 + ]The peak of the structure formed by dimerization of such raw materials.

[0327] In addition, if Figure 10 As shown in Table 2, in the raw material solution used in Comparative Example 2, m / z=143 was also observed in addition to m / z=225. This is believed to be [Al(acac)2 + ] is replaced by OH to form [Al(acac)(OH) + In addition, for the solution of Comparative Example 2, ionization is hindered by the high concentration of hydrochloric acid, and the peak intensity is low.

[0328] As shown in Table 2, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, in Example 1, (I2+I3+I4) / I1=0.03, and in Comparative Examples 1 and 2, (I2+I3+I4) / I1≥0.25.

[0329] In addition, the raw material solutions of Examples 2-15, 17, and Comparative Examples 3 and 4 were analyzed in the same manner. The results showed that, in the examples, (I2+I3+I4) / I1<0.25 was obtained, and the minimum was 0 (I2, I3, and I4 were all less than the detection limit of 5.0×10 3 On the other hand, in both Comparative Examples 3 and 4, (I2+I3+I4) / I11≥0.25.

[0330] As shown in the above MS spectrum measurement results, compared to the comparative examples without carboxylic acid addition, Examples 1 to 17, in which carboxylic acid was added, had a lower (I2+I3+I4) / I1 ratio. Peaks derived from structures formed by crosslinking the metal raw material with OH or acetylacetone (m / z=467), dimerization (m / z=549), and substitution of acetylacetone with OH (m / z=143) were almost undetectable, resulting in a low foreign matter density. On the other hand, these peaks were detected in Comparative Examples 1 to 5, in which carboxylic acid was not added, and the foreign matter density was higher than that of Examples 1 to 17.

[0331] Therefore, it is suggested that the structures of the metal raw materials represented by m / z = 467, m / z = 549, and m / z = 143 are the cause of the generation of foreign matter. In addition, it is suggested that the carboxylic acid suppresses the generation of these structures, thereby suppressing the generation of foreign matter.

[0332] 4.Electrical characteristics evaluation

[0333] Using the crystalline metal oxide film obtained in the above manner, a Figure 12 The semiconductor device (SBD) shown.

[0334] Schottky Electrode Formation

[0335] A Pt layer, a Ti layer, and an Au layer were stacked on the n-type semiconductor layer by electron beam evaporation.

[0336] <Formation of Ohmic Electrode>

[0337] A Ti layer and an Au layer were stacked on the n+ type semiconductor layer by electron beam deposition.

[0338] <Evaluation>

[0339] The current-voltage characteristics of the obtained semiconductor devices were evaluated. By measuring the current-voltage characteristics in the reverse direction, the voltage at which insulation breakdown occurs was adjusted. Semiconductor devices with a withstand voltage of 600V or more were considered qualified products. The number of qualified products / the total number of semiconductor devices produced = the yield [%], and the yield was calculated. The foreign matter density calculated in Evaluation 2. was plotted against the yield to obtain a graph. Figure 17 In addition, semiconductor devices with a withstand voltage of 1200V or more are considered qualified products, and the yield rate is calculated as the number of qualified products / total number of semiconductor devices produced = yield rate [%]. For the foreign matter density calculated in Evaluation 2., the yield rate is plotted in the following graph: Figure 18 .

[0340] Comparison of Examples 1 to 17 with Comparative Examples 1 to 5 suggests that the crystalline metal oxide film of the present invention has excellent smoothness and can produce semiconductor devices with a high withstand voltage with excellent yield. However, as the withstand voltage increases, insulation damage caused by spherical foreign matter is more likely to occur.

[0341] The following protocols are included in this specification.

[0342] [1]: A film forming method for forming a crystalline metal oxide film on a substrate by heat-treating an atomized raw material solution and causing a thermal reaction on the substrate, wherein the film forming method is characterized in that:

[0343] As the raw material solution, a raw material solution containing a metal raw material and a carboxylic acid is used, wherein the metal raw material contains at least a metal element constituting the crystalline metal oxide film.

[0344] [2]: The film forming method according to [1] above, wherein the carboxylic acid used is one having an acid dissociation constant of 2.65 to 4.67 with respect to water at 25°C.

[0345] [3]: The film forming method according to [1] or [2] above, wherein the carboxylic acid is a carboxylic acid having 4 or less carbon atoms.

[0346] [4]: The film forming method according to any one of [1] to [3] above, characterized in that formic acid is used as the carboxylic acid.

[0347] [5]: The film forming method according to any one of [1] to [4] above, characterized in that the volume ratio of the carboxylic acid in the raw material solution is set to 1 vol% or more and 50 vol% or less.

[0348] [6]: The film forming method according to any one of [1] to [5] above, characterized in that the molar concentration of the carboxylic acid in the raw material solution is set to 0.1 mol / L or more and 13.2 mol / L or less.

[0349] [7]: The film forming method according to any one of the above [1] to [6] is characterized in that the molar concentration of the carboxylic acid in the raw material solution is set to a concentration greater than the molar concentration of the metal raw material in the raw material solution.

[0350] [8]: A film forming method for forming a crystalline metal oxide film on a substrate by heat-treating an atomized raw material solution and causing a thermal reaction on the substrate, wherein the film forming method is characterized in that:

[0351] As the raw material solution, a raw material solution containing a metal raw material and an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25° C. is used, the metal raw material containing at least a metal element constituting the crystalline metal oxide film.

[0352] [9]: The film forming method according to any one of [1] to [8] above, characterized in that the metal raw material in the raw material solution contains at least one of gallium or aluminum as a main component.

[0353]

[10] : The film forming method according to any one of [1] to [9] above, characterized in that the metal raw material is an acetylacetone complex.

[0354]

[11] : The film forming method according to any one of [1] to

[10] , characterized in that:

[0355] The raw material solution is a solution containing an acetylacetone complex of aluminum,

[0356] In the MS spectrum of the raw material solution, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.25.

[0357]

[12] : The film forming method according to any one of [1] to

[11] above, characterized in that the temperature of the heat treatment is set to 400°C or higher and 550°C or lower.

[0358]

[13] : The film forming method according to any one of [1] to

[12] , wherein the area of the surface on which the crystalline metal oxide film is formed as the substrate is 10 cm 2The above matrix.

[0359]

[14] : A raw material solution used in a film forming method for forming a crystalline metal oxide film on a substrate by heat-treating the atomized raw material solution and causing a thermal reaction on the substrate, wherein the raw material solution is characterized in that it contains: a metal raw material containing a metal element constituting the crystalline metal oxide film, and formic acid.

[0360]

[15] : A raw material solution used in a film forming method for forming a crystalline metal oxide film on a substrate by heat-treating the atomized raw material solution and causing a thermal reaction on the substrate, wherein the raw material solution is characterized in that it contains: a metal raw material containing a metal element constituting the crystalline metal oxide film, and an acid having an acid dissociation constant greater than -8 and less than 8.8 relative to water at 25°C.

[0361]

[16] : The raw material solution according to

[14] or

[15] above, characterized in that the metal raw material in the raw material solution contains at least one of Ga and Al as a main component.

[0362]

[17] : The raw material solution according to any one of

[14] to

[16] above, wherein the metal raw material is an acetylacetone complex.

[0363]

[18] : The raw material solution according to any one of

[14] to

[17] above, wherein the raw material solution is a solution of an acetylacetone complex containing aluminum, characterized in that, in the MS spectrum of the raw material solution, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.25.

[0364]

[19] : A crystalline metal oxide film having at least one of gallium or aluminum as a main component, wherein the number density of spherical foreign matter or agglomerates of spherical foreign matter present on the surface of the crystalline metal oxide film is 621 pieces / cm 2 the following.

[0365]

[20] : The crystalline metal oxide film according to

[19] above, characterized in that the number density of spherical foreign matter or agglomerates of spherical foreign matter present on the surface of the crystalline metal oxide film is 54 pieces / cm 2 the following.

[0366]

[21] : The crystalline metal oxide film according to

[19] or

[20] above, characterized in that it has a corundum structure.

[0367]

[22] : The crystalline metal oxide film according to any one of

[19] to

[21] , wherein the surface area of the crystalline metal oxide film is 10 cm 2 above.

[0368]

[23] : A laminated structure comprising a substrate and a crystalline metal oxide film according to any one of

[19] to

[22] formed on the substrate via a buffer layer.

[0369]

[24] : A semiconductor device comprising at least one of the crystalline metal oxide film described in any one of

[19] to

[22] above or the stacked structure described in

[23] above.

[0370]

[25] : The semiconductor device according to

[24] above is characterized in that the semiconductor device is any one of a semiconductor laser, a diode or a transistor.

[0371] The present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any technical solution having substantially the same structure and exhibiting the same function and effect as the technical concept described in the claims of the present invention is within the technical scope of the present invention.

Claims

1. A film forming method for forming a crystalline metal oxide film on a substrate by heat-treating an atomized raw material solution and causing a thermal reaction on the substrate, wherein the film forming method is characterized in that: As the raw material solution, a raw material solution containing a metal raw material and a carboxylic acid is used, wherein the metal raw material contains at least a metal element constituting the crystalline metal oxide film.

2. The film forming method according to claim 1, wherein As the carboxylic acid, one having an acid dissociation constant with respect to water at 25° C. of 2.65 to 4.67 is used.

3. The film forming method according to claim 1, wherein As the carboxylic acid, a carboxylic acid having 4 or less carbon atoms is used.

4. The film forming method according to claim 1, wherein As the carboxylic acid, formic acid was used.

5. The film forming method according to claim 1, wherein The volume ratio of the carboxylic acid in the raw material solution is set to 1 vol % or more and 50 vol % or less.

6. The film forming method according to claim 1, wherein The molar concentration of the carboxylic acid in the raw material solution is set to 0.1 mol / L or more and 13.2 mol / L or less.

7. The film forming method according to claim 1, wherein The molar concentration of the carboxylic acid in the raw material solution is set to a concentration equal to or higher than the molar concentration of the metal raw material in the raw material solution.

8. A film forming method comprising: heat-treating an atomized raw material solution to cause a thermal reaction on a substrate, thereby forming a crystalline metal oxide film on the substrate, wherein: As the raw material solution, a raw material solution containing a metal raw material and an acid having an acid dissociation constant greater than -8 and less than 8.8 with respect to water at 25° C. is used, the metal raw material containing at least a metal element constituting the crystalline metal oxide film.

9. The film forming method according to any one of claims 1 to 8, wherein: The metal raw material in the raw material solution contains at least one of gallium and aluminum as a main component.

10. The film forming method according to claim 9, wherein: The metal raw material is an acetylacetone complex.

11. The film forming method according to claim 10, wherein: The raw material solution is a solution containing an acetylacetone complex of aluminum, In the MS spectrum of the raw material solution, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.

25.

12. The film forming method according to claim 1 or 8, characterized in that: The temperature of the heat treatment is set to 400° C. or higher and 550° C. or lower.

13. The film forming method according to claim 1 or 8, characterized in that: The area of the substrate on which the crystalline metal oxide film was formed was 10 cm 2 The above matrix.

14. A raw material solution for use in a film forming method for forming a crystalline metal oxide film on a substrate by heat-treating the atomized raw material solution to cause a thermal reaction on the substrate, the raw material solution comprising: A metal raw material containing a metal element constituting the crystalline metal oxide film, and Formic acid.

15. A raw material solution for use in a film forming method for forming a crystalline metal oxide film on a substrate by heat-treating the atomized raw material solution to cause a thermal reaction on the substrate, the raw material solution comprising: A metal raw material containing a metal element constituting the crystalline metal oxide film, and Acids with a dissociation constant relative to water at 25°C greater than -8 and less than 8.

8.

16. The raw material solution according to claim 14 or 15, characterized in that The metal raw material in the raw material solution contains at least one of Ga and Al as a main component.

17. The raw material solution according to claim 16, wherein The metal raw material is an acetylacetone complex.

18. The raw material solution according to claim 17, wherein the raw material solution is a solution containing an acetylacetone complex of aluminum, wherein: In the MS spectrum of the raw material solution, when the peak intensity of m / z=225 is set to I1, the peak intensity of m / z=467 is set to I2, the peak intensity of m / z=549 is set to I3, and the peak intensity of m / z=143 is set to I4, (I2+I3+I4) / I1<0.

25.

19. A crystalline metal oxide film containing at least one of gallium or aluminum as a main component, wherein the number density of spherical foreign matter or agglomerates of spherical foreign matter present on the surface of the crystalline metal oxide film is 621 pieces / cm 2 the following.

20. The crystalline metal oxide film according to claim 19, wherein The number density of spherical foreign matter or agglomerates of spherical foreign matter present on the surface of the crystalline metal oxide film was 54 pieces / cm 2 the following.

21. The crystalline metal oxide film according to claim 19, wherein It has a corundum structure.

22. The crystalline metal oxide film according to claim 19, wherein The surface area of the crystalline metal oxide film is 10 cm 2 above. 23 . A laminated structure comprising a substrate and the crystalline metal oxide film according to claim 19 formed on the substrate via a buffer layer. 24 . A semiconductor device comprising at least one of the crystalline metal oxide film according to claim 19 or the multilayer structure according to claim 23 .

25. The semiconductor device according to claim 24, wherein The semiconductor device is any one of a semiconductor laser, a diode or a transistor.

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