JP7105703B2 - Oxide semiconductor film, laminate, and method for manufacturing oxide semiconductor film - Google Patents

Description

The present invention relates to an oxide semiconductor film containing gallium as a main component, a laminate having the oxide semiconductor film, and a method for forming the oxide semiconductor film.

Conventionally, pulsed laser deposition (PLD), molecular beam epitaxy (MBE), sputtering method, etc. High vacuum film deposition equipment capable of realizing a non-equilibrium state has been developed. It has become possible to manufacture oxide semiconductors that could not be manufactured by the melt method or the like. In addition, a mist chemical vapor deposition (Mist CVD) method, in which crystals are grown on a substrate using atomized mist raw materials, has been developed. It has become possible to fabricate gallium oxide (α-Ga ₂ O ₃ ) with a corundum structure. As a semiconductor with a large bandgap, α-Ga ₂ O ₃ is expected to be applied to next-generation switching elements capable of achieving high withstand voltage, low loss and high heat resistance. Unlike other CVD methods, the mist CVD method does not require a high temperature and can produce a metastable phase crystal structure such as the corundum structure of α-gallium oxide.

Regarding the mist CVD method, Patent Document 1 describes a tubular furnace type mist CVD apparatus. Patent Document 2 describes a fine channel type mist CVD apparatus. Patent Document 3 describes a linear source type mist CVD apparatus. Patent Document 4 describes a tubular furnace 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. Patent Document 5 describes a mist CVD apparatus which is a rotating stage in which a substrate is placed above a mist generator and a susceptor is mounted on a hot plate.

JP-A-1-257337 Japanese Patent Application Laid-Open No. 2005-307238 JP 2012-46772 A Patent No. 5397794 JP 2014-63973 A

In order to use a semiconductor film as a semiconductor device, it is essential to form an electrode on the surface of the semiconductor film because of the necessity of inputting/outputting electric signals to/from an external circuit. At this time, ohmic contact is required between the semiconductor film and the electrode because the electrical signal must have a linear response. Ohmic contact characteristics (hereinafter simply referred to as “ohmic characteristics”) are also important from the viewpoint of reducing the power consumption of semiconductor devices.

Ohmic characteristics are generally believed to be achieved by adding a dopant at a high concentration. However, when the inventors of the present invention investigated an oxide semiconductor film containing gallium as a main component, such as gallium oxide (α-Ga ₂ O ₃ ) having a corundum structure, it was found that compared to the formation of a normal semiconductor film, , the dopant addition was found to be difficult to control. In addition, even if the dopant addition can be controlled, only the electrode contact portion needs to be highly doped, and the process is complicated because it takes time and effort to create regions with different densities in the plane. A problem arises.

The present invention has been made to solve the above problems, and an oxide semiconductor film containing gallium as a main component, which has excellent ohmic characteristics when an electrode is formed on the surface thereof, and a stack including the semiconductor film. An object of the present invention is to provide a film formation method for forming an oxide semiconductor film containing gallium as a main component and having excellent ohmic characteristics when an electrode is formed on the surface by a simple method.

The present invention has been made to achieve the above objects, and provides an oxide semiconductor film containing gallium as a main component, wherein the specular reflectance of the surface of the oxide semiconductor film is such that the incident light wavelength is 633 nm and the incident light wavelength is 633 nm. Provided is an oxide semiconductor film of 15% or less at an angle of 45°.

Such an oxide semiconductor film has excellent ohmic characteristics when an electrode is formed on the surface.

At this time, the oxide semiconductor film may have a corundum structure.

This results in a corundum-structured oxide semiconductor film having excellent ohmic characteristics.

At this time, the surface area of the oxide semiconductor film can be 100 mm ² or more.

Thereby, a large-area oxide semiconductor film having excellent ohmic characteristics can be obtained.

Further, the present invention provides a laminate of an oxide semiconductor film containing gallium as a main component and a substrate, wherein the specular reflectance of the surface of the oxide semiconductor film is an incident light wavelength of 633 nm and an incident angle of 45°. , 15% or less.

Such a laminate has excellent ohmic characteristics when electrodes are formed on the surface.

At this time, the oxide semiconductor film may have a corundum structure.

As a result, a laminate having a corundum structure semiconductor film with excellent ohmic characteristics is obtained.

At this time, the surface area of the oxide semiconductor film can be 100 mm ² or more.

As a result, a large-area laminate having excellent ohmic characteristics is obtained.

Further, according to the present invention, a mist generated by atomizing or dropletizing a raw material solution containing at least gallium is conveyed using a carrier gas, and the mist is heated to cause a thermal reaction of the mist on the substrate. Provided is a method for manufacturing an oxide semiconductor film in which the temperature of the substrate is changed during the film formation.

According to such a film formation method, an oxide semiconductor film having excellent ohmic characteristics when an electrode is formed on the surface can be formed by a very simple method.

At this time, the film formation method can be such that the temperature of the substrate is changed by 5° C. or more during the film formation.

Accordingly, an oxide semiconductor film having excellent ohmic characteristics when an electrode is formed on the surface can be formed more reliably and stably.

At this time, the film formation method may be such that the substrate having a film formation surface area of 100 mm ² or more is used.

Accordingly, a large-area oxide semiconductor film having excellent ohmic characteristics when an electrode is formed on the surface can be formed by a very simple method.

As described above, according to the oxide semiconductor film and laminate of the present invention, excellent ohmic characteristics are obtained when electrodes are formed. Further, according to the film forming method of the present invention, it is possible to form a semiconductor film having excellent ohmic characteristics when electrodes are formed by a very simple method.

It is a figure explaining the regular reflectance which concerns on this invention. 1 is a schematic configuration diagram showing an example of a film forming apparatus of the present invention; FIG. It is a figure explaining an example of the misting part used for this invention.

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

As described above, there has been a demand for a film forming method and a film forming apparatus that greatly improve the ohmic characteristics of an oxide semiconductor film.

As a result of intensive studies on the above problems, the present inventors have found that an oxide semiconductor film containing gallium as a main component has a regular reflectance of the surface of the oxide semiconductor film with an incident light wavelength of 633 nm and an incident angle of The inventors have found that an oxide semiconductor film having a thickness of 15% or less under the condition of 45° provides excellent ohmic characteristics when an electrode is formed on the surface, and completed the present invention.

Further, in a laminate of an oxide semiconductor film containing gallium as a main component and a substrate, the specular reflectance of the surface of the oxide semiconductor film is 15% or less under the conditions of an incident light wavelength of 633 nm and an incident angle of 45°. The inventors have found that the laminate has excellent ohmic characteristics when electrodes are formed on the surface thereof, and have completed the present invention.

Further, a mist generated by atomizing or dropletizing a raw material solution containing at least gallium is conveyed using a carrier gas, and the mist is heated to cause a thermal reaction of the mist on the substrate to form a film. In the method for manufacturing an oxide semiconductor film in which the temperature of the substrate is changed during the film formation, an excellent ohmic property is obtained when an electrode is formed on the surface by a very simple method. The inventors have found that an oxide semiconductor film having properties can be formed, and have completed the present invention.

Description will be made below with reference to the drawings.

(Oxide semiconductor film)
The oxide semiconductor film according to the present invention is characterized in that it contains gallium as a main component and has a regular reflectance of 15% or less under the conditions of an incident light wavelength of 633 nm and an incident angle of 45°. Generally, an oxide semiconductor film is composed of metal and oxygen, but in the oxide semiconductor film according to the present invention, gallium is the main component of the metal. The main component here means that 50 to 100% of the metal component is gallium. Metal components other than gallium may include, for example, one or more metals selected from iron, indium, aluminum, vanadium, titanium, chromium, rhodium, iridium, nickel and cobalt.

The oxide semiconductor film can contain a dopant depending on the application. The type of dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants such as copper, silver, tin, iridium and rhodium. The dopant concentration may be, for example, about 1×10 ¹⁶ /cm ³ to 1×10 ²² /cm ³ , and even at a low concentration of about 1×10 ¹⁷ /cm ³ or less, about 1×10 ²⁰ /cm ³ or higher.

The oxide semiconductor film may be single crystal or polycrystal. The crystal structure is not particularly limited, and may be a β-gallia structure, a corundum structure, or a mixture of multiple crystal structures.

FIG. 1 shows a conceptual diagram of regular reflectance. The specular reflectance is the incident light 304 and the incident light 304 when light is received by the light receiving probe 303 at the position of the reflection angle 307 which is the same as the incident angle 306 when light is incident on the surface of the sample 301 from the light source 302 and reflected. It is the energy ratio of the reflected light 305 . Since the oxide semiconductor film is transparent in the visible light range, the regular reflectance is about 20% when the surface is flat. The oxide semiconductor film according to the present invention has an uneven surface so that diffuse reflection is promoted and regular reflectance is reduced. That is, the inventors have found that extremely low contact resistance, that is, excellent ohmic characteristics can be achieved if the specular reflectance is 15% or less under the conditions of an incident light wavelength of 633 nm and an incident angle of 45°. . In order to achieve low contact resistance, the regular reflectance is preferably 12% or less, more preferably 10% or less. When the incident light is white light and the object is observed with the naked eye, the film looks white.

Light with a wavelength of 633 nm, which is incident light, can be obtained by, for example, a helium neon laser, but can also be used by spectrally dispersing a halogen lamp or a xenon lamp.

The thickness of the oxide semiconductor film according to the present invention is not particularly limited. For example, it may be 0.05 to 100 μm, preferably 0.1 to 50 μm, more preferably 0.5 to 20 μm.

Further, the oxide semiconductor film according to the present invention may be a self-supporting oxide semiconductor film alone or a laminate with a substrate. In the case of a stacked body, another layer may be interposed between the substrate and the oxide semiconductor film. The other layer is not particularly limited. Membranes are also applicable.

The oxide semiconductor film according to the present invention can be used for a semiconductor device by appropriately designing the structure. For example, Schottky barrier diode (SBD), metal semiconductor field effect transistor (MESFET), high electron mobility transistor (HEMT), metal oxide semiconductor field effect transistor (MOSFET), static induction transistor (SIT), junction field effect It can constitute a semiconductor layer in a transistor (JFET), an insulated gate bipolar transistor (IGBT), a light emitting diode (LED), and the like.

(Deposition device)
FIG. 2 shows an example of a film forming apparatus 101 that can be used for the film forming method 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 transfer section 109 that connects the misting section 120 and the film forming section 140 and transports the 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 the whole or part of the film forming apparatus 101 .

Here, the term "mist" as used in the present invention refers to a general term for fine particles of liquid dispersed in gas, and includes what is called mist, liquid droplets, and the like.

(Misting part)
The mist generating unit 120 adjusts the raw material solution 104a and mists the raw material solution 104a to generate mist. The misting means is not particularly limited as long as it can mist the raw material solution 104a, and may be a known misting means, but it is preferable to use a misting means using ultrasonic vibration. This is because mist can be made more stably.

An example of such a misting unit 120 is shown in FIG. For example, it may include a mist generation source 104 containing a raw material solution 104a, a container 105 containing a medium capable of transmitting ultrasonic vibrations, such as water 105a, and an ultrasonic transducer 106 attached to the bottom surface of the container 105. good. Specifically, a mist generation source 104, which is a container containing a raw material solution 104a, is contained in a container 105 containing water 105a using a support (not shown). An ultrasonic transducer 106 is provided at the bottom of the container 105, and the ultrasonic transducer 106 and the oscillator 116 are connected. When the oscillator 116 is operated, the ultrasonic vibrator 106 vibrates, ultrasonic waves propagate through the water 105a into the mist generation source 104, and the raw material solution 104a turns into mist.

(raw material solution)
The raw material solution 104a is not particularly limited as long as it contains a material that can be misted, and may be an inorganic material or an organic material. Metals or metal compounds are preferably used, and those containing one or more metals selected from gallium, iron, indium, aluminum, vanadium, titanium, chromium, rhodium, nickel and cobalt can be used.

The raw material solution 104a is not particularly limited as long as the metal can be misted. As the raw material solution 104a, the metal is preferably dissolved or dispersed in an organic solvent or water in the form of a complex or a salt. can be used for Examples of forms of the complex include acetylacetonate complexes, carbonyl complexes, ammine complexes, hydride complexes, and the like. Salt forms include, for example, metal chloride salts, metal bromide salts, and metal iodide salts. Further, a solution obtained by dissolving the above metal in hydrobromic acid, hydrochloric acid, hydroiodic acid, or the like can also be used as an aqueous salt solution.

Also, the raw material solution 104a may be mixed with an acid. 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, carboxylic acids such as formic acid, nitric acid, and the like. From the viewpoint of cost, metal gallium dissolved in hydrochloric acid or an aqueous solution of gallium chloride is most preferable.

Furthermore, the raw material solution can contain a dopant depending on the design of the film to be formed. The dopant is not particularly limited. Examples include n-type dopants such as tin, germanium, silicon, titanium, zirconium, vanadium or niobium, or p-type dopants such as copper, silver, tin, iridium and rhodium. The dopant concentration may be, for example, about 1×10 ¹⁶ /cm ³ to 1×10 ²² /cm ³ , and even at a low concentration of about 1×10 ¹⁷ /cm ³ or less, about 1×10 ²⁰ /cm ³ or higher.

(Carrier gas supply unit)
Refer to FIG. 2 again. The carrier gas supply unit 130 has a carrier gas source 102a that supplies carrier gas, and may include a flow control valve 103a for adjusting the flow rate of the carrier gas sent from the carrier gas source 102a. In addition, a carrier gas source 102b for dilution that supplies a carrier gas for dilution and a flow control valve 103b for adjusting the flow rate of the carrier gas for dilution sent from the carrier gas source 102b for dilution can also be provided as necessary. .

The type of carrier gas is not particularly limited, and can be appropriately selected according to the film to be deposited. Examples thereof include oxygen, ozone, inert gases such as nitrogen and argon, and reducing gases such as hydrogen gas and forming gas. Also, the number of carrier gases may be one, or two or more. For example, a diluent gas obtained by diluting the same gas as the first carrier gas with another gas (for example, diluted 10 times) may be further used as the second carrier gas, and air may also be used. The flow rate of the carrier gas is appropriately determined depending on the size of the deposition chamber and the substrate, and is generally 1 to 20 L/min, preferably 2 to 10 L/min.

(Deposition part)
In the film forming section 140 , the mist is heated to cause a thermal reaction to form a film on part or all of the surface of the substrate 110 . The film forming section 140 includes, for example, a film forming chamber 107, a substrate 110 is installed in the film forming chamber 107, and a heating means for heating the substrate 110, such as a hot plate 108, can be provided. . The hot plate 108 may be provided outside the film forming chamber 107 as shown in FIG. 2, or may be provided inside the film forming chamber 107 . In addition to the hot plate, it is also possible to heat the substrate by light or the like that can be absorbed by the substrate and generate heat. Further, the deposition chamber 107 is provided with an exhaust port 112 for exhaust gas at a position that does not affect the supply of mist to the substrate 110 . Note that the substrate 110 may be placed on the top surface of the film formation chamber 107 to face down, or the substrate 110 may be placed on the bottom surface of the film formation chamber 107 to face up.

(substrate)
The substrate 110 is not particularly limited as long as it can form a film and can support a film. The material of the substrate 110 is also not particularly limited, and a known substrate can be used, and it may be an organic compound or an inorganic compound. Examples include polysulfone, polyethersulfone, polyphenylene sulfide, polyetheretherketone, polyimide, polyetherimide, fluororesin, metals such as iron, aluminum, stainless steel, and gold, silicon, sapphire, quartz, glass, and gallium oxide. Examples include, but are not limited to. The shape of the substrate may be any shape, and it is effective for all shapes. The substrate may have a cylindrical shape, a spiral shape, a spherical shape, a ring shape, or the like, and a plate-like substrate is preferable in the present invention. The thickness of the plate-shaped substrate is not particularly limited, but preferably 10 to 2000 μm, more preferably 50 to 800 μm. When the substrate is plate-shaped, its area is preferably 100 mm ² or more, and its diameter is more preferably 2 inches (50 mm) or more.

(Conveyor)
The conveying section 109 connects the mist forming section 120 and the film forming section 140 . Mist is transported by the carrier gas from the mist generation source 104 of the mist generating unit 120 to the film forming chamber 107 of the film forming unit 140 via the transport unit 109 . The transport section 109 can be, for example, a supply pipe 109a. As the supply pipe 109a, for example, a quartz pipe or a resin tube can be used.

(Film formation method)
Next, an example of the film forming method according to the present invention will be described below with reference to FIG.
First, the raw material solution 104a is accommodated in the mist generation source 104 of the mist generating section 120, the substrate 110 is placed on the hot plate 108 directly or through the wall of the film forming chamber 107, and the hot plate 108 is operated.

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 to sufficiently replace the atmosphere in the film forming chamber 107 with the carrier gas, and the main carrier gas and the flow rate of the carrier gas for dilution are adjusted to control the carrier gas flow rate.

Next, mist is generated. By vibrating the ultrasonic oscillator 106 and propagating the vibration to the raw material solution 104a through the water 105a, the raw material solution 104a is misted to generate mist. Next, the mist generated in the mist generating section 120 is conveyed from the mist generating section 120 to the film forming section 140 via the conveying section 109 and introduced into the film forming chamber 107 by the carrier gas. The mist introduced into the film formation chamber 107 is heat-treated by the heat of the hot plate 108 in the film formation chamber 107 and thermally reacts to form a film on the substrate 110 .

The thermal reaction may be carried out under any of a non-oxygen atmosphere, a reducing gas atmosphere, an air atmosphere, and 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.

Moreover, the thermal reaction is not particularly limited as long as the mist reacts by heating. 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 120-600°C, preferably in the range of 200-600°C, more preferably in the range of 300-550°C.

The film formation method according to the present invention is characterized in that the substrate temperature is changed during film formation (hereinafter also referred to as "substrate temperature change step"). In the substrate temperature changing step, the substrate temperature is preferably changed by 3° C. or more, more preferably by 5° C. or more. The time for changing the substrate temperature is not particularly limited, but is preferably 5 seconds or longer, more preferably 10 seconds or longer. By setting such a temperature difference and time, it is possible to more effectively obtain a surface structure with a low specular reflectance.

For example, when the substrate set temperature is 500° C., the substrate temperature is changed so as to include a time period when the temperature is 497° C. or lower during film formation. Conversely, it is also possible to change the substrate temperature so as to include a period of time when the substrate temperature is set to 500° C. and the temperature rises to 503° C. or higher during film formation. The temperature change step may be performed once during film formation, or may be performed multiple times. It suffices that the regular reflectance, which is affected by the uneven structure of the surface, can be kept within a certain range by changing the crystal growth mode during film formation to change the uneven structure of the surface.

The substrate temperature changing step can be realized by changing the set temperature of the heating means, for example. The change of the set temperature may be controlled automatically by creating a program, or may be adjusted manually. The simplest method is to temporarily stop heating. In the mist CVD method, mist, that is, a liquid phase material is always supplied during film formation, so that the latent heat of vaporization of the mist can rapidly lower the temperature of the substrate.

When the temperature change step as described above is performed, the preferential growth direction of the crystal at the time of film formation is partially changed, and a size corresponding to the wavelength of visible light (submicron size) is distributed throughout the plane. Unevenness is formed. Good ohmic characteristics are achieved by forming an electrode on a semiconductor film having such a surface structure.

(Separation of substrate and semiconductor film)
In the layered product obtained as described above, the substrate and the semiconductor film can be separated to obtain a single semiconductor film. For example, the substrate may be separated from the laminate. A peeling method is not particularly limited, and a known method can be adopted. For example, there are a method of applying a mechanical impact to peel, a method of applying heat and using thermal stress to peel, a method of applying vibration such as ultrasonic waves to peel, and a method of etching and peeling the intermediate layer. be done. Alternatively, the substrate itself can be etched to be dissolved and removed to form a single semiconductor film. In this manner, a self-supporting semiconductor film can be obtained.

(electrode)
When applying the semiconductor film according to the present invention to a semiconductor device and forming an electrode, a general method can be used as the method for forming the electrode. In other words, there are no particular limitations on the method such as vapor deposition, sputtering, CVD, plating, or a printing method for adhering together with a resin or the like. Al, Ag, Ti, Pd, Au, Cu, Cr, Fe, W, Ta, Nb, Mn, Mo, Hf, Co, Zr, Sn, Pt, V, Ni, Ir, Zn, In , Nd, etc., metal oxide conductive films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), zinc indium oxide (IZO), organic conductive compounds such as polyaniline, polythiophene or polypyrrole, etc. , regardless of material type. An alloy or mixture of two or more of these may also be used. The thickness of the electrode is preferably 1-1000 nm, more preferably 10-500 nm.

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 gallium oxide (hereinafter referred to as “α-Ga ₂ O ₃ ”) film having a corundum structure was formed as an oxide semiconductor film containing gallium as a main component based on the above-described film formation method.

Specifically, first, an aqueous solution of 0.1 mol/min of gallium bromide was prepared, and then a 48% hydrobromic acid solution was added so as to be 10% by volume, and this was used as the raw material solution 104a.
The raw material solution 104 a obtained as described above was accommodated in the mist generation source 104 . Next, a 4-inch (100 mm diameter) c-plane sapphire substrate as the substrate 110 was placed adjacent to the hot plate 108 in the deposition chamber 107, and the hot plate 108 was operated to raise the temperature to 500°C. did.

Note that the temperature of the hot plate 108 is monitored by a temperature measuring device built into the hot plate 108 . Since the substrate 110 is installed adjacent to the hot plate 108, it has good temperature followability, and it has been confirmed in advance that the monitored temperature of the hot plate 108 and the temperature of the substrate 110 are substantially equal.

Subsequently, the flow control valves 103a and 103b are opened to supply oxygen gas as a carrier gas from the carrier gas sources 102a and 102b into the film forming chamber 107 to sufficiently replace the atmosphere in the film forming chamber 107 with the carrier gas, The flow rate of the main carrier gas was adjusted to 2 L/min, and the flow rate of the diluent carrier gas was adjusted to 5 L/min. That is, the carrier gas total flow rate was set to 7 L/min.

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 misting the raw material solution 104a to generate mist. This mist was introduced into the film forming chamber 107 through the supply pipe 109a by the carrier gas. Then, an α-Ga ₂ O ₃ film was formed on the substrate 110 by thermally reacting the mist in the film forming chamber 107 under the conditions of 500° C. under atmospheric pressure. The film formation time was 30 minutes. During the film formation, as a substrate temperature change step, the set temperature was set to 497° C. for 5 minutes and then returned to 500° C. again.

When the surface of the obtained film was observed with the naked eye, it was found that the film tended to be slightly cloudy. The specular reflectance of the surface of this film was measured using a specular reflectance measurement system (manufactured by Ocean Photonics, OP-FLMS-RF-ST1). When measured under the conditions of an incident light wavelength of 633 nm and an incident angle of 45°, the regular reflectance was 14%.

Next, in order to determine the contact resistance by the TLM method, Ti was vapor-deposited as an electrode in the form of parallel lines with a width of 1 mm and a period of 5 mm on the obtained α-Ga ₂ O ₃ film. The film thickness was set to 1 μm. The resulting laminate was diced into 1 cm width pieces, and the contact resistance was determined by successively measuring the resistance between the electrodes. The contact resistance was calculated to be 15 mΩcm ² .

(Example 2)
Film formation and evaluation were carried out under the same conditions as in Example 1, except that as the substrate temperature change step, heating was stopped for 12 seconds during the film formation, and then the heating was restarted and the temperature was raised to 500° C. again. In Example 2, the substrate temperature decreased to 495° C. during the substrate temperature change step. The specular reflectance was 9% and the contact resistance was calculated to be 4 mΩcm ² .

(Example 3)
Film formation and evaluation were carried out under the same conditions as in Example 1, except that as the substrate temperature change step, heating was stopped for 60 seconds during the film formation, and then the heating was restarted to 500° C. again. In Example 3, the substrate temperature decreased to 475° C. during the substrate temperature change step. The specular reflectance was 7% and the contact resistance was calculated to be 3 mΩcm ² .

(Example 4)
Film formation and evaluation were carried out under the same conditions as in Example 1, except that as the substrate temperature change step, the heating was stopped for 12 seconds during the film formation, and then the heating was restarted and the temperature was raised to 500° C. again three times. rice field. In Example 4, the substrate temperature decreased to 495° C. during the substrate temperature change step. The specular reflectance was 5% and the contact resistance was calculated to be 1 mΩcm ² .

When the surface of the film was observed with the naked eye, the tendency of clouding became stronger in the order of Examples 2, 3 and 4.

(Comparative example)
Film formation and evaluation were performed under the same conditions as in Example 1, except that the substrate temperature changing step was not performed and the film formation was performed while heating to a constant temperature of 500° C. all the time. When the surface of the obtained film was observed with the naked eye, it was found to be glossy. The specular reflectance was 19%. Also, the contact resistance was calculated to be 95 mΩcm ² .

Table 1 shows a summary of the above results.

As is clear from Table 1, Examples 1 to 3 have extremely low contact resistances and good ohmic characteristics as compared to Comparative Examples. Furthermore, it can be seen that the contact resistance correlates with the regular reflectance, and good ohmic characteristics can be obtained in the case of an oxide semiconductor film in which the regular reflectance of the surface is set to 15% or less. As a result, it has become possible to form good ohmic characteristics by a simple method.

It should be noted that the present invention is not limited to the above embodiments. 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... Mist 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,
110... Substrate, 112... Exhaust port, 116... Oscillator,
DESCRIPTION OF SYMBOLS 120... Misting part, 130... Carrier gas supply part, 140... Film-forming part,
301... Sample, 302... Light source, 303... Light receiving probe, 304... Incident light,
305... Reflected light, 306... Incidence angle, 307... Reflection angle.

Claims (7)

An oxide semiconductor film containing gallium as a main component,
The specular reflectance of the surface of the oxide semiconductor film is 15% or less under the conditions of an incident light wavelength of 633 nm and an incident angle of 45° ,
1. An oxide semiconductor film, wherein the oxide semiconductor film has a corundum structure and a submicron-sized uneven surface structure . The oxide semiconductor film according to claim 1, wherein the surface area of the oxide semiconductor film is 100 mm ² or more. A laminate of an oxide semiconductor film containing gallium as a main component and a substrate, wherein the regular reflectance of the surface of the oxide semiconductor film is 15% or less under the conditions of an incident light wavelength of 633 nm and an incident angle of 45°. the law of nature,
The layered product, wherein the oxide semiconductor film has a corundum structure and a submicron-sized uneven surface structure . 4. The laminate according to claim 3, wherein the surface area of the oxide semiconductor film is 100 mm< ² > or more. Oxidation in which a mist generated by atomizing or dropletizing a raw material solution containing at least gallium is transported using a carrier gas, the mist is heated, and the mist is thermally reacted on a substrate to form a film. A method for manufacturing a semiconductor film, comprising:
A method for producing an oxide semiconductor film, wherein the temperature of the substrate is changed by stopping heating and restarting heating during the film formation. 6. The method of manufacturing an oxide semiconductor film according to claim 5 , wherein the temperature of said substrate is changed by 5[deg.] C. or more during said film formation. 7. The method for producing an oxide semiconductor film according to claim 5 , wherein the substrate has a film formation surface area of 100 mm< ² > or more.

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