JP7306640B2 - crystalline oxide film - Google Patents

Description

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

As a method for forming a highly crystalline gallium oxide-based thin film on a film-forming sample, a film-forming method using water fine particles such as a mist CVD method is known (Patent Document 1). In this method, a raw material solution is prepared by dissolving a gallium compound such as gallium acetylacetonate in an acid such as hydrochloric acid. A highly crystalline gallium oxide-based thin film is formed on the film-forming sample by supplying it to the film-forming surface of the film-forming sample and reacting the raw material mist to form a thin film on the film-forming surface.

In order to form a semiconductor device using a gallium oxide thin film, it is essential to control the conductivity of the gallium oxide thin film. Techniques for doing so are disclosed.

JP 2013-28480 A JP 2015-199649 A Electrical Conductive Corundum-Structured α-Ga2O3 Thin Films on Sapphire with Tin-Doping Grown by Spray-Assisted Mist Chemical Vapor Deposition (Japanese Journal of Applied Physics 51 (2012) 070203)

According to the methods of Patent Document 1 and Non-Patent Document 1, a highly conductive α-gallium oxide (hereinafter sometimes referred to as “α-Ga ₂ O ₃ ”) thin film can be formed. However, it has a unique problem that it is not smooth, and it is still not satisfactory for use in semiconductor devices. In order to smoothen the surface of the film, it may be possible to perform a surface treatment such as etching.

In response to this problem, Patent Document 2 discloses a method of reducing the average roughness (Ra). However, even if this method is used, the flatness of the surface cannot be said to be sufficient, and the characteristics of the semiconductor device using the obtained film are also unsatisfactory.

The present invention has been made to solve the above problems, and includes a crystalline oxide film having a corundum structure with a smooth surface, and provides a laminated structure with excellent semiconductor characteristics when applied to a semiconductor device. Furthermore, it is an object of the present invention to provide a laminated structure having a crystalline oxide film with reduced crystal defects, and to provide a method for manufacturing the laminated structure.

The present invention has been made to achieve the above objects, and provides a laminated structure having a base substrate and a crystalline oxide film having a corundum structure, wherein the crystalline oxide film contains impurities as Provided is a laminated structure containing at least carbon (C), wherein the crystalline oxide film has a root mean square roughness (RMS) of 0.1 μm or less.

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

At this time, a laminated structure can be obtained in which the C concentration in the crystalline oxide film is 2×10 ¹⁷ to 2×10 ²⁰ /cm ³ .

As a result, the surface becomes smoother, and the semiconductor characteristics become more excellent when applied to a semiconductor device.

At this time, the laminated structure can be obtained in which the thickness of the crystalline oxide film is 1 μm or more.

As a result, a multilayer structure having a smooth surface and a thick film is obtained.

At this time, the laminated structure may be such that the underlying substrate is a c-plane sapphire substrate.

As a result, a laminated structure including a crystalline oxide film having a corundum structure of better quality is obtained.

At this time, it is possible to obtain a laminated structure in which the area of the crystalline oxide film is 100 mm ² or more.

This results in a large area that is more useful for semiconductor devices.

Further, raw material fine particles generated by atomizing a raw material solution are conveyed to a substrate by a carrier gas, and the raw material fine particles are thermally reacted on the substrate to form a crystalline oxide film having a corundum structure. In the method for manufacturing a structure, the raw material solution is mixed with a surface smoothing agent containing at least carbon (C) to perform a doping process of C on the crystalline oxide film. It is possible to provide a method for manufacturing a laminated structure in which the root-mean-square roughness (RMS) of the surface of is 0.1 μm or less.

According to such a method for manufacturing a laminated structure, the laminated structure includes a crystalline oxide film having a corundum structure having a smooth surface, and the laminated structure has excellent semiconductor characteristics when applied to a semiconductor device. can be manufactured.

At this time, as the surface smoothing agent, one or more of alcohols and diketones can be used as the method for producing a laminated structure.

Thereby, a laminated structure having a smoother surface can be produced more effectively and stably.

Furthermore, a laminated structure including a first crystalline oxide film having a corundum structure and a second crystalline oxide film having a corundum structure, wherein Provided is a laminated structure having the first crystalline oxide film, wherein the second crystalline oxide film contains at least carbon (C) as an impurity.

In such a laminated structure, since the surface of the second crystalline oxide film having a corundum structure is smooth, the crystal defects of the first crystalline oxide film having a corundum structure are reduced. . Such a laminated structure has very excellent semiconductor properties.

At this time, a laminated structure can be obtained in which the C concentration in the second crystalline oxide film is 2×10 ¹⁷ to 2×10 ²⁰ /cm ³ .

As a result, the surface becomes smoother, and the semiconductor characteristics become more excellent when applied to a semiconductor device.

At this time, it is possible to obtain a laminated structure in which the film thickness of the first crystalline oxide film is 1 μm or more. Furthermore, a laminated structure in which the area of the first crystalline oxide film is 100 mm ² or more can be obtained.

This makes the semiconductor device more useful.

At this time, a semiconductor device including the stacked structure described above can be obtained.

As a result, a semiconductor device having excellent characteristics can be obtained.

As described above, according to the laminated structure of the present invention, it has a crystalline oxide film having a smooth surface and a corundum structure, and when applied to a semiconductor device, the laminated structure has excellent semiconductor characteristics. Further, according to the method for manufacturing a laminated structure of the present invention, a laminated structure having a crystalline oxide film having a corundum structure with a smooth surface and having excellent semiconductor characteristics when applied to a semiconductor device is manufactured. becomes possible. Furthermore, according to the laminated structure of the present invention, the laminated structure includes a crystalline oxide film having a corundum structure in which crystal defects in the film are reduced, and has excellent semiconductor characteristics when applied to a semiconductor device. .

1 is a schematic configuration diagram showing an example of a film forming apparatus used in a film forming method according to the present invention; FIG. 1 is a schematic configuration diagram showing an example of a laminated structure according to the present invention; FIG.

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

As described above, a laminated structure including a crystalline oxide film having a corundum structure with a smooth surface and having excellent semiconductor characteristics when applied to a semiconductor device, a method for producing the laminated structure, and crystal defects in the film It has been desired to provide a laminated structure that includes a crystalline oxide film having a corundum structure with a reduced E and has excellent semiconductor characteristics when applied to a semiconductor device.

As a result of intensive studies on the above problems, the inventors of the present invention have found a laminated structure having a base substrate and a crystalline oxide film having a corundum structure, wherein the crystalline oxide film contains at least as impurities A semiconductor device having a crystalline oxide film with a smooth surface by a laminated structure containing carbon (C) and having a root mean square roughness (RMS) of 0.1 μm or less of the crystalline oxide film. The present inventors have completed the present invention based on the finding that a laminated structure having excellent semiconductor characteristics can be obtained by applying the composition.

In addition, the present inventors conveyed the raw material fine particles generated by atomizing the raw material solution to a substrate by a carrier gas, and thermally reacted the raw material fine particles on the substrate to obtain a crystalline oxide having a corundum structure. A method for manufacturing a laminated structure for forming a film, wherein the raw material solution is mixed with a surface smoothing agent containing at least carbon (C) to dope the crystalline oxide film with C, It has a crystalline oxide film with a smooth surface and is applied to a semiconductor device by a method for manufacturing a laminated structure in which the root mean square roughness (RMS) of the surface of the crystalline oxide film is 0.1 μm or less. The inventors have found that a laminated structure having excellent semiconductor characteristics can be produced in some cases, and have completed the present invention.

Furthermore, the present inventors have found a laminated structure comprising a first crystalline oxide film having a corundum structure and a second crystalline oxide film having a corundum structure, wherein the second crystallinity A laminated structure having the first crystalline oxide film on the oxide film, and the second crystalline oxide film containing at least carbon (C) as an impurity prevents crystal defects in the film. The present inventors have found that a laminated structure having a crystalline oxide film with a reduced polycrystalline oxide film and having excellent semiconductor characteristics when applied to a semiconductor device has been completed.

Description will be made below with reference to the drawings.

The present inventors have made intensive studies to achieve the above object, and found that a crystalline multilayer structure having a smooth surface of a crystalline oxide film can be obtained by doping treatment using a surface smoothing agent. The present invention was completed by repeating the above.

According to the first aspect of the present invention, a base substrate and a crystalline oxide film having a corundum structure directly or via another layer are provided thereon, and the root mean square roughness of the crystalline oxide film is Provided is a crystalline laminated structure having a thickness (RMS) of 0.1 μm or less.

Further, according to the second aspect of the present invention, at least a first crystalline oxide film having a corundum structure and a second crystalline oxide film having a corundum structure are provided, and the second crystallinity A first crystalline oxide film is provided on the oxide film, and the second crystalline oxide film provides a crystalline multilayer structure containing at least carbon (C) as an impurity.

The root mean square roughness (RMS) is not particularly limited as long as it is 0.1 μm or less, preferably 30 nm or less, more preferably 10 nm or less. The root-mean-square roughness (RMS) is calculated based on JIS B0601 (equivalent to Rq in the same standard) using the surface shape measurement results of a 10 μm square region with an atomic force microscope (AFM). value.

A laminated structure according to the present invention is a structure including one or more layers of crystalline oxide films. For example, it may be a laminate of one or more layers of a crystalline oxide film and a base substrate or thin film. A film (layer) (eg, an amorphous layer) other than the crystalline oxide film may be included. It may also be a laminate composed of a plurality of films (layers) from which the underlying substrate has been removed.

The crystalline oxide film may be annealed, whereby a metal oxide film in which the ohmic electrode is oxidized may be formed between the crystalline oxide film and the ohmic electrode. . Examples of ohmic electrodes include indium and titanium.

The underlying substrate is not particularly limited as long as it serves as a support for the crystalline oxide film. The material is not particularly limited, and a known substrate can be used, and it may be an organic compound or an inorganic compound. For example, polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, iron, aluminum, stainless steel, metals such as gold, silicon, sapphire, quartz, glass, calcium carbonate, oxide Gallium, SiC, ZnO, GaN and the like can be mentioned, but are not limited to these. A substrate having a corundum structure is preferred in the laminated structure according to the present invention. Substrates having a corundum structure include sapphire substrates (eg, c-plane sapphire substrates) and α-type gallium oxide substrates. In particular, it is preferable to use a c-plane sapphire substrate. This is because a crystalline oxide film having a better corundum structure can be obtained. Although the thickness of the underlying substrate is not particularly limited, it is preferably 10 to 2000 μm, more preferably 50 to 800 μm. Its area is preferably 100 mm ² or more, and more preferably its aperture (diameter) is 2 inches (50 mm) or more.

The crystalline oxide film is not particularly limited as long as it is a thin film having a corundum structure and containing an oxide semiconductor as a main component. Further, the crystalline oxide film is preferably single crystal, but may be polycrystal. In the composition of the crystalline oxide film, the total atomic ratio of gallium, indium, aluminum and iron in the metal elements contained in the film is preferably 0.5 or more. It is more preferable that the atomic ratio of gallium in is 0.5 or more. This preferred atomic ratio is specifically, for example, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and within a range between any two of the numerical values exemplified here may be In the present invention, it is more preferable that the atomic ratio of gallium in the metal element is 0.5 or more. This is because the surface roughness of the crystalline oxide film can be further reduced.

Further, the _composition of the crystalline oxide film _{is ,} for example _, the general formula: _{InXAlYGaZFeVO3} (0≤X≤2.5, 0≤Y≤2.5, 0≤Z≤2.5 , 0≦V≦2.5, X+Y+Z+V=1.5 to 2.5), more preferably 1≦Z. In this general formula, preferred X, Y, Z and V are specifically, for example, 0, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0 .5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1 .8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5. Moreover, preferable X+Y+Z+V is specifically, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4 , 2.5. The above X, Y, Z and V and X+Y+Z+V may each be within a range between any two of the numerical values exemplified here. In addition, the above general formula expresses the composition of atoms on the lattice points forming the corundum structure, and as is clear from the fact that "X + Y + Z + V = 2" is not described, non-stoichiometric oxidation substances, which may also include metal-poor oxides, oxygen-poor oxides.

The crystalline oxide film may be formed directly on the underlying substrate, or may be formed via another layer. Another layer includes a crystalline film having a different composition of corundum structure, a crystalline film other than corundum structure, an amorphous film, and the like. For example, it is possible to form a laminated structure in which a C-undoped crystalline oxide film is interposed between a C-doped crystalline oxide film whose surface is smoothed and an underlying substrate.

At least part of the crystalline oxide film (more specifically, part of its thickness) is preferably doped with an impurity. It may have a layered structure. In the case of a multi-layer structure, the crystalline oxide film is configured by laminating an insulating thin film and a conductive thin film, for example, but the present invention is not limited to this. When an insulating thin film and a conductive thin film are laminated to form a multilayer structure, the compositions of the insulating thin film and the conductive thin film may be the same or different from each other. The ratio of the thicknesses of the insulating thin film and the conductive thin film is not particularly limited. Preferably, 0.1 to 5 is more preferable. This more preferred ratio is specifically, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 3, 4, 5 and exemplified here It may be in a range between any two of the numbers.

The conductive thin film may be doped with impurities to impart conductivity. By adjusting the conductivity as appropriate, a crystalline oxide semiconductor film can be obtained. The doping concentration of the impurity for imparting conductivity is appropriately determined depending on the properties required for the conductive thin film, but is preferably 1×10 ¹⁵ /cm ³ to 1×10 ²² /cm ³ . The type of doping impurity is not particularly limited, but for example, a dopant made of at least one selected from Ge, Sn, Si, Ti, Zr, Hf, V, Nb, Rh, Ag, and Cu. mentioned. The insulating thin film generally does not require impurity doping, but may be doped to such an extent that conductivity does not appear.

The thickness of the crystalline oxide film is not particularly limited, and may be 1 μm or less or 1 μm or more. and more preferably 1 to 50 μm. By setting such a preferable film thickness, it is possible not only to improve the surface smoothness without impairing the semiconductor characteristics, but also to reduce the electrical resistance during the annealing treatment, thereby improving the semiconductor characteristics. Obtainable.

In the laminated structure according to the present invention, raw material fine particles produced by atomizing a raw material solution are supplied to a film forming chamber by a carrier gas, and a crystalline oxidation having a corundum structure is provided on a base substrate placed in the film forming chamber. When the crystalline oxide film is formed, the root mean square roughness (RMS), which is the surface roughness of the crystalline oxide film, is reduced to 0 by performing doping treatment on the crystalline oxide film using a surface smoothing agent. .1 μm or less.

FIG. 1 shows an example of a film forming apparatus 101 that can be used for manufacturing a laminated structure according to the present invention. The film forming apparatus 101 includes a mist forming unit 120 that forms mist from a raw material solution to generate mist, a carrier gas supply unit 130 that supplies a carrier gas for transporting the mist, and a heat treatment of the mist to form a film on a substrate. It has a film forming section 140 and a conveying section 109 that connects the atomizing section 120 and the film forming section 140 and conveys mist by a carrier gas. Further, the operation of the film forming apparatus 101 may be controlled by including a control unit (not shown) that controls all or part of the film forming apparatus 101 . The details of the film forming apparatus 101 will be described in Examples below.

More specifically, the crystalline oxide film is formed by supplying raw material fine particles generated from a raw material solution in which a raw material compound is dissolved into a film forming chamber, and reacting the raw material compound in the film forming chamber. be able to. The solvent of the raw material solution is preferably water or hydrogen peroxide solution. When the thin film is to be doped with impurities, the raw material compound is thermally reacted in the presence of the dopant raw material. The dopant source is preferably included in the source solution and micronized along with the source compound. In the present application, in addition to the n-type dopant and p-type dopant for exhibiting conductivity, an element that brings about a surface smoothing effect is also referred to as a dopant.

The method for forming the crystalline oxide film is not particularly limited, but examples include gallium compounds, iron compounds, indium compounds, aluminum compounds, vanadium compounds, titanium compounds, chromium compounds, rhodium compounds, iridium compounds, nickel compounds and cobalt compounds. It can be formed by thermally reacting a raw material compound in which one or two or more metals selected from are combined according to the composition of the crystalline oxide film. Thereby, a crystalline oxide film can be crystal-grown on the underlying substrate from the underlying substrate side. As the above metal compounds, organometallic complexes (e.g., acetylacetonate complexes, carbonyl complexes, ammine complexes, hydride complexes) and halides (fluoride, chloride, bromide, or iodide) for each metal are also available. Alternatively, for example, metal gallium or metal indium may be used as a starting material and changed into a gallium compound and an indium compound immediately before film formation. A solution obtained by dissolving metallic gallium in an acid such as hydrochloric acid or hydrobromic acid can also be used as the gallium compound.

Furthermore, an acid may be mixed in the raw material solution. Examples of the acid include hydrogen halides such as hydrobromic acid, hydrochloric acid, and hydroiodic acid, hypochlorous acid, chlorous acid, hypobromous acid, bromous acid, hypoiodic acid, iodic acid, and the like. halogen oxoacids, formic acid, nitric acid, and the like. Moreover, a base may be mixed in the raw material solution. Examples of the base include potassium hydroxide, sodium hydroxide, ammonia, calcium hydroxide, barium hydroxide, magnesium hydroxide, copper hydroxide, iron hydroxide and the like. Among them, ammonia is particularly preferred because it has a low boiling point and leaves no residue when the solution is heated.

In the layered structure and the method for manufacturing the layered structure according to the present invention, the doping treatment is performed by including a surface smoothing agent in the raw material solution. By performing doping treatment with the raw material solution containing a surface smoothing agent, it is possible to efficiently and industrially advantageously produce a crystalline multilayer structure having a crystalline oxide film with a surface roughness of 0.1 μm or less. can.

The surface smoothing agent is not particularly limited as long as it can make the root mean square roughness (RMS) of the crystalline oxide film 0.1 μm or less. is preferred, and alcohols or diketones are more preferred. A laminate structure having a smoother surface can be produced more effectively and stably. Examples of alcohols include methanol, ethanol, propanol, diols such as ethylene glycol, propylene glycol and diethylene glycol, and triols such as glycerin. Examples of diketones include diacetyl, acetylacetone, 2,5-hexanedione, dimedone, and the like, and any of them may be used.

When alcohol or diketone is used as the surface smoothing agent, C is introduced into the film and deterioration of surface roughness can be suppressed. It is considered that C enters between crystal lattices and has an effect of alleviating lattice strain. It is also conceivable that surface smoothing agent molecules induce steric hindrance on the substrate surface, promoting planar crystal growth.

The surface smoothing agent may be added directly to the aqueous solution in which the raw material compound is dissolved, or the surface smoothing agent may be dissolved in water in advance to adjust the pH, and then added to the aqueous solution in which the raw material compound is dissolved.

In the laminated structure according to the present invention, the content of C in the crystalline oxide film is preferably 2×10 ¹⁷ to 2×10 ²⁰ (atoms/cm ³ ), more preferably 3× ^{10 17} to 2×10 20 (atoms/cm 3 ). It is more preferably 1×10 ²⁰ (atoms/cm ³ ), most preferably 4×10 ¹⁷ to 8×10 ¹⁹ (atoms/cm ³ ).

Moreover, in the method for producing a laminated structure according to the present invention, it _is most preferable to use methanol or _{acetylacetone} as the surface smoothing agent. The surface of the crystalline oxide film containing as can be made very smooth. The amount of the surface smoothing agent added is not particularly limited, but it is preferably 10% or less, more preferably 7% or less, and in the range of 3 to 0.001% by volume in the raw material solution. is most preferred. By using it in such a preferable range, it can function as a surface smoothing agent, so that the surface of the crystalline oxide film can be smoothed.

As a dopant raw material for making the crystalline oxide film exhibit electrical conductivity, there are single metals or compounds (eg, halides, oxides, hydroxides) of impurities to be doped. Electronic conductivity can be controlled by n-type dopants such as Ge, Sn, Si, Ti, Zr, Hf, V, Nb and p-type dopants such as Cu, Ir, Rh, Sn, Ag, but not limited to these. .

The thermal reaction is not particularly limited as long as the raw material fine particles react by heating, and the reaction conditions are not particularly limited. It can be appropriately set according to the raw material and the film-formed material. For example, the heating temperature can be in the range of 100-600°C, preferably in the range of 200-600°C, more preferably in the range of 300-550°C.

The thermal reaction may be performed under vacuum, under a non-oxygen atmosphere, under a reducing gas atmosphere, under an air atmosphere, or under an oxygen atmosphere, and may be appropriately set according to the film to be deposited. In addition, the reaction pressure may be under atmospheric pressure, under increased pressure or under reduced pressure, but film formation under atmospheric pressure is preferable because the apparatus configuration can be simplified.

A crystalline oxide film having a root-mean-square roughness (RMS) of 0.1 μm or less as described above can be used as a buffer layer. That is, the first crystalline oxide film is further formed on the substrate on which the second crystalline oxide film having a root-mean-square roughness (RMS) of 0.1 μm or less is formed. Since the surface of the second crystalline oxide film is flat, defects and dislocations in films formed on this film are greatly reduced. A semiconductor device having excellent semiconductor characteristics can be obtained by using the obtained first crystalline oxide film in a semiconductor device. The C concentration in the second crystalline oxide film is preferably 2×10 ¹⁷ to 2×10 ²⁰ (atoms/cm ³ ). On the other hand, the C concentration in the first crystalline oxide film is not particularly limited. That is, the C concentration in the first crystalline oxide film may be 2×10 ¹⁷ to 2×10 ²⁰ (atoms/cm ³ ), or may be 2×10 ¹⁷ (atoms/cm ³ ) or less. I do not care. This is because C is necessary for exhibiting surface flatness, but is not particularly necessary for exhibiting excellent semiconductor properties.

The crystalline oxide according to the present invention may be annealed after film formation. The annealing temperature is not particularly limited, but is preferably 600° C. or lower, more preferably 550° C. or lower, and most preferably 500° C. or lower. By performing the annealing treatment at such a preferable temperature, the electrical resistance of the crystalline oxide film can be more preferably reduced. The annealing treatment time is not particularly limited, but is preferably 10 seconds to 10 hours, more preferably 10 seconds to 1 hour.

In the laminated structure according to the present invention, the crystalline oxide film may be separated from the underlying substrate. The peeling means is not particularly limited, and known means may be used. Examples of peeling means include means for applying mechanical impact to peel, means for applying heat and utilizing thermal stress for peeling, means for peeling by applying vibration such as ultrasonic waves, and means for peeling by etching. etc. By the peeling, the crystalline oxide film can be obtained as a self-supporting film.

(Configuration example of crystalline laminated structure)
FIG. 2 shows a preferred example of a laminated structure according to the present invention and a semiconductor device using the same. In the example of FIG. 2, a crystalline oxide film 203 is formed on the underlying substrate 201 . The crystalline oxide film 203 is formed by stacking an insulating thin film 203a and a conductive thin film 203b in order from the underlying substrate 1 side. A gate insulating film 205 is formed on the conductive thin film 203b. A gate electrode 207 is formed on the gate insulating film 205 . Source/drain electrodes 209 are formed on the conductive thin film 203b so as to sandwich the gate electrode 207 therebetween. According to such a configuration, the depletion layer formed in the conductive thin film 203b can be controlled by the gate voltage applied to the gate electrode 207, enabling transistor operation (FET device).

Semiconductor devices formed using the laminated structure according to the present invention include transistors and TFTs such as MIS, HEMT, and IGBT, Schottky barrier diodes utilizing semiconductor-metal junctions, PN or PIN diodes and light emitting/receiving elements are included. The laminated structure according to the present invention is useful for improving the characteristics of these devices.

EXAMPLES The present invention will be described in detail below with reference to examples, but these are not intended to limit the present invention.

(Example 1)
A film forming apparatus 101 used in this example will be described with reference to FIG. The film forming apparatus 101 includes a hot plate 108 on which a substrate 110, which is a film-forming sample such as an underlying substrate, is placed and heated, carrier gas sources 102a and 102b for supplying carrier gas, and carrier gas sources 102a and 102b. flow control valves 103a and 103b for adjusting the flow rate of the carrier gas supplied, the particle generation source 104 containing the raw material solution 104a, the container 105 containing water 105a, and the ultrasonic wave attached to the bottom surface of the container 105. A vibrator 106 and a film forming chamber 107 made of quartz are provided. By fabricating the film forming chamber 107 from quartz, it is possible to prevent impurities derived from the apparatus from entering the thin film formed on the substrate 110 .

An aqueous solution of gallium bromide and tin chloride was prepared so that the atomic ratio of tin to gallium was 1:0.05. The concentration of gallium bromide was set to 0.1 mol/L. At this time, 10% by volume of a 48% hydrobromic acid solution was added to promote the dissolution of tin chloride. Furthermore, 0.016% of methanol was mixed as a surface smoothing agent.

As the substrate 110, a c-plane sapphire substrate with a diameter of 4 inches (100 mm) was placed on the hot plate 108 and heated to raise the substrate temperature to 500.degree. Next, the flow control valves 103a and 103b are opened to supply the carrier gas from the carrier gas sources 102a and 102b into the film forming chamber 107. After sufficiently replacing the atmosphere in the film forming chamber 107 with the carrier gas, the carrier gas is supplied. Total flow rate was adjusted to 26 L/min. Oxygen gas was used as the carrier gas.

Next, the ultrasonic vibrator 106 was oscillated at 2.4 MHz, and the vibration was propagated to the raw material solution 104a through the water 105a, thereby micronizing the raw material solution 104a to generate raw material microparticles. The raw fine particles were introduced into the film formation chamber 107 by a carrier gas, and a thin film was formed on the film formation sample 110 by the CVD reaction on the film formation surface of the film formation sample 110 . The film formation time was 180 minutes.

The phases of the deposited thin film were identified. Identification was performed using a thin film XRD diffractometer and performing 2θ/ω scans at angles from 15° to 95°. The measurement was performed using CuKα rays. As a result, the thin film formed was α-Ga ₂ O ₃ having a corundum structure. Further, when the film thickness of the thin film of this example was measured using an interferometric film thickness meter, the film thickness was 6.0 μm.

(Comparative example)
Film formation was carried out without mixing the raw material solution with methanol. Specifically, with respect to 0.1 mol/L gallium bromide, the aqueous solution was adjusted so that the atomic ratio of tin chloride to gallium was 1:0.05, and the volume ratio of 48% hydrobromic acid solution was adjusted. was included at 10%. A film was formed in the same manner as in Example 1, except that this was used as the raw material solution. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 5.8 μm.

(Example 2)
As a raw material solution, an aqueous solution was prepared so that the atomic ratio of tin chloride to gallium was 1:0.007 for 0.02 mol/L gallium iodide, and a 35% hydrochloric acid solution was added at a volume ratio of 2. % was included. Furthermore, 0.003% of methanol was mixed as a surface smoothing agent. A film was formed in the same manner as in Example 1, except that this was used as the raw material solution. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 1.3 μm.

(Example 3)
As a raw material solution, metallic gallium was dissolved in hydrochloric acid to prepare a solution with a gallium concentration of 0.05 mol/L. On the other hand, the aqueous solution of tin chloride was adjusted so that the atomic ratio of tin to gallium was 1:0.01, and 1% by volume of 35% hydrochloric acid solution was included. Furthermore, 0.008% of methanol was mixed as a surface smoothing agent. A film was formed in the same manner as in Example 1, except that this was used as the raw material solution. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 3.1 μm.

(Example 4)
In Example 1, film formation was performed using ethanol instead of methanol. A film was formed in the same manner as in Example 1 except for this. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 6.1 μm.

(Example 5)
In Example 1, film formation was performed using oxalic acid instead of methanol. A film was formed in the same manner as in Example 1 except for this. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 6.3 μm.

(Example 6)
In Example 1, film formation was performed using acetylacetone instead of methanol. A film was formed in the same manner as in Example 1 except for this. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 6.0 μm.

(Example 7)
In Example 6, film formation was performed with the concentration of acetylacetone set to 2.9%. A film was formed in the same manner as in Example 1 except for this. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 5.9 μm.

(Example 8)
An acetylacetone/ammonia aqueous solution was prepared in advance such that the molar ratio of acetylacetone:ammonia was 1:1. This aqueous solution was used as acetylacetone in Example 7 to form a film. A film was formed in the same manner as in Example 1 except for this. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 6.4 μm.

(Example 9)
A film was formed in the same manner as in Example 1, except that the film forming time was 20 minutes. As a result of evaluation, it was confirmed to be α-Ga ₂ O ₃ having a corundum structure, and the film thickness was 0.55 μm.

(evaluation)
The root-mean-square surface roughness (RMS) of the α-Ga ₂ O ₃ thin film samples obtained in Examples 1 to 9 and Comparative Example was measured using an atomic force microscope (AFM). Also, using SIMS, the content of C in the film was examined. Table 1 shows the results.

As shown in Table 1, the sample without the surface smoothing agent had large irregularities, while the film with the surface smoothing agent exhibited an RMS value of several nm, indicating excellent surface smoothness. At the same time, the C concentration in the film was extremely high, and it is believed that this brought about the surface smoothing effect.

(Example 10)
A film was formed in the same manner as in Example 1 except that the film forming time was set to 10 minutes, and the obtained film was used as a second crystalline oxide film. Subsequently, film formation was carried out by changing the raw material solution to one containing no methanol, and an α-Ga ₂ O ₃ film having a thickness of 5.4 μm was formed as the first crystalline oxide film. The obtained sample was subjected to X-ray diffraction measurement to evaluate the crystallinity. Specifically, the rocking curve of the (0006) plane diffraction peak of α-Ga ₂ O ₃ was measured, and the full width at half maximum was obtained. The resulting full width at half maximum was 11 seconds, confirming that the film was extremely excellent in crystallinity.

In addition, this invention is not limited to the said embodiment. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

101... Film forming apparatus, 102a... Carrier gas source,
102b... carrier gas source for dilution, 103a... flow control valve,
103b... Flow control valve, 104... Fine particle generation source, 104a... Raw material solution,
DESCRIPTION OF SYMBOLS 105... Container 105a... Water 106... Ultrasonic oscillator 107... Film-forming chamber,
108...Hot plate, 109...Conveyor, 109a...Supply pipe,
DESCRIPTION OF SYMBOLS 110... Substrate (crystalline substrate), 112... Exhaust port, 116... Oscillator,
120... atomization section, 130... carrier gas supply section, 140... film forming section,
201... Base substrate, 203... Crystalline oxide film, 203a... Insulating thin film,
203b... conductive thin film, 205... gate insulating film, 207... gate electrode,
209... Source/drain electrodes.

Claims (3)

A crystalline oxide film having a corundum structure,
the crystalline oxide film contains at least carbon (C) as an impurity,
The crystalline oxide film has a root-mean-square roughness (RMS) of 0.1 μm or less,
The crystalline oxide film contains a metal element in the film, and the atomic ratio of gallium in the metal element is 0.5 or more,
A crystalline oxide film, wherein the C concentration in the crystalline oxide film is 2×10 ¹⁷ to 2×10 ²⁰ /cm ³ . 2. The crystalline oxide film according to claim 1, wherein the crystalline oxide film has a thickness of 1 [mu]m or more. 3. The crystalline oxide film according to claim 1, wherein the crystalline oxide film has an area of 100 mm ² or more.

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