JP6195986B2 - Method for manufacturing metal oxide semiconductor film and method for manufacturing thin film transistor - Google Patents

Description

The present invention relates to the production how the manufacturing method and the thin film transistor of the metal oxide semiconductor film.

A metal oxide semiconductor film has been put into practical use in the production by a vacuum film forming method and is currently attracting attention.
On the other hand, research and development relating to the production of metal oxide semiconductor films by liquid phase processes has been actively conducted for the purpose of forming metal oxide semiconductor films having high semiconductor characteristics at simple, low temperature and atmospheric pressure. .
In particular, the inkjet method is attracting attention because a necessary film can be formed at a necessary place in a liquid phase process and patterning is not necessary after the formation.

  For example, Japanese Patent Application Laid-Open No. 2010-283002 discloses a method of forming a metal oxide semiconductor by applying a solution containing a metal salt by an inkjet method. Since nitrate is inexpensive and can form a dense metal oxide film at low temperature, it can be suitably used in a solution process.

  Japanese Patent Application Laid-Open No. 2013-21289 discloses a method of manufacturing a metal oxide film by applying a solution containing a metal salt to a substrate by an ink-jet method, drying the solution, and then baking.

  In addition, in Japanese Patent Application Laid-Open Nos. 2010-182852 and 2010-171237, after a metal oxide semiconductor precursor solution or dispersion is applied on a substrate to form a metal oxide semiconductor precursor film, A method of converting into a metal oxide semiconductor film by a UV (ultraviolet) ozone method or the like is disclosed.

  On the other hand, when the film is formed by the ink jet method, a so-called coffee stain phenomenon is easily generated in which the center part of the film is recessed and the end part is raised (concave shape) due to the difference in the drying speed of the coating film. For example, in Appl. Mater. Interfaces 2013, 5, 3916-3920, when a silver nanoparticle ink is applied by an ink jet method to form a silver electrode, a coating film is formed due to a coffee stain phenomenon at low humidity during drying after ink jet application. Has been reported to be concave and convex at high humidity.

  As a semiconductor layer of a thin film transistor, when a metal oxide semiconductor film is formed through steps such as drying and heating after applying a coating solution containing a metal salt by an inkjet method, the thickness unevenness tends to increase due to the coffee stain phenomenon. Unevenness causes a decrease in electrical characteristics (mobility and electrical conductivity).

  For example, the method described in Appl. Mater. Interfaces 2013, 5, 3916-3920 may be applied to control the atmosphere (humidity) during drying after application by the ink jet method. It is difficult to control the thickness unevenness by controlling.

  In the method disclosed in JP2010-283002A, JP2013-21289A, JP2010-182852A, or JP2010-171237A, after a coating film is formed by an inkjet method. Although it is converted into a metal oxide film by heating in the atmosphere or UV irradiation, a thin film transistor having high mobility cannot be obtained even if a semiconductor layer is formed by these methods to form a thin film transistor.

The present invention has a small thickness unevenness, a method of manufacturing a metal oxide semiconductor film can be manufactured simply excellent metal oxide semiconductor film in electrical characteristics, and a manufacturing how excellent thin film transistor electrical characteristics The purpose is to provide.

In order to achieve the above object, the following invention is provided.
<1> A coating step in which a solution containing a metal nitrate and a solvent is applied by an inkjet method onto a substrate heated to a temperature equal to or higher than the boiling point of the solvent to form a coating film;
A conversion step of converting the coating film into a metal oxide semiconductor film having a thickness of 10 nm or less by performing ultraviolet irradiation in an atmosphere having an oxygen concentration of 80000 ppm or less;
The manufacturing method of the metal oxide semiconductor film containing this.
<2> The method for producing a metal oxide semiconductor film according to <1>, wherein the metal nitrate contains indium nitrate.
<3> Solvent is methoxyethanol <1> A process for producing a metal oxide semiconductor film according to <2>.
< 4 > The method for producing a metal oxide semiconductor film according to <1> or < 2>, wherein the solvent is methanol.
< 5 > The method for producing a metal oxide semiconductor film according to any one of <1> to < 4 >, wherein the ultraviolet rays include light having a wavelength of 300 nm or less.
< 6 > The method for producing a metal oxide semiconductor film according to any one of <1> to < 5 >, wherein in the conversion step, ultraviolet irradiation is performed while the substrate is heated.
< 7 > The metal oxide semiconductor film according to any one of <1> to < 6 >, including a step of performing a surface treatment on the surface of the substrate on which the coating film is formed before the coating step. Production method.
<8> as the surface treatment, ultraviolet ozone treatment, producing how the metal oxide semiconductor film according to an argon plasma treatment, or perform the nitrogen plasma treatment <7>.
< 9 > A method for producing a thin film transistor including a step of forming an oxide semiconductor layer by forming a metal oxide semiconductor film by the method for producing a metal oxide semiconductor film according to any one of <1> to < 8 >. Law.

According to the present invention, a small thickness unevenness, a method of manufacturing a metal oxide semiconductor film which can be easily manufactured excellent metal oxide semiconductor film in electrical properties, and the manufacturing side of excellent thin film transistor electrical characteristics Law is provided.

It is the schematic which shows the structure of an example (top gate-top contact type) of the thin-film transistor manufactured by this invention. It is the schematic which shows the structure of an example (top gate-bottom contact type) of the thin-film transistor manufactured by this invention. It is the schematic which shows the structure of an example (bottom gate-top contact type) of the thin-film transistor manufactured by this invention. It is the schematic which shows the structure of an example (bottom gate-bottom contact type) of the thin-film transistor manufactured by this invention. It is a schematic sectional drawing which shows a part of liquid crystal display device of embodiment. It is a schematic block diagram of the electrical wiring of the liquid crystal display device shown in FIG. It is a schematic sectional drawing which shows a part of organic EL display apparatus of embodiment. It is a schematic block diagram of the electrical wiring of the organic electroluminescence display shown in FIG. It is a schematic sectional drawing which shows a part of X-ray sensor array of embodiment. It is a schematic block diagram of the electrical wiring of the X-ray sensor array shown in FIG. It is a diagram showing, _V g -I _d characteristics of the simplified TFT fabricated in Examples 1 to 4 and Comparative Example 1. 4 is an electron micrograph of the TFT semiconductor layer produced in Comparative Example 1 in plan view. It is the electron micrograph which observed the cross section of the edge part (A location) of the semiconductor layer shown in FIG. It is the electron micrograph which observed the cross section of the center part (B location) of the semiconductor layer shown in FIG.

Hereinafter, the present invention will be specifically described with reference to the accompanying drawings.
In the drawings, members (components) having the same or corresponding functions are denoted by the same reference numerals and description thereof is omitted as appropriate. Further, in the present specification, when a numerical range is indicated by the symbol “to”, numerical values described as the lower limit value and the upper limit value are included.

<Method for producing metal oxide film>
The method for producing a metal oxide film according to the present disclosure includes a coating step of forming a coating film by applying a solution containing a metal nitrate and a solvent on a heated substrate by an inkjet method, and an oxygen concentration with respect to the coating film. Is converted to a metal oxide film by performing ultraviolet irradiation in an atmosphere of 80000 ppm or less.

(Coating process)
A solution containing a metal nitrate and a solvent (metal nitrate solution) is applied on a heated substrate by an inkjet method to form a coating film.

-Metal nitrate solution-
The metal nitrate solution used in the present disclosure is obtained, for example, by preparing a predetermined amount of a solute such as metal nitrate, adding a solvent so as to have a predetermined concentration, stirring and dissolving. The stirring time is not particularly limited as long as the solute is sufficiently dissolved. The metal nitrate may be a hydrate.

The metal nitrate solution may contain other metal-containing compounds. Examples of the metal-containing compound include metal salts other than metal nitrates, metal halides, and organometallic compounds.
Examples of metal salts other than metal nitrates include sulfates, phosphates, carbonates, acetates, and oxalates. Examples of metal halides include chlorides, iodides, bromides, and the like. Examples thereof include metal alkoxides, organic acid salts, and metal β-diketonates.

  The metal nitrate solution preferably contains at least indium nitrate. By using indium nitrate, an indium-containing oxide film can be easily formed, and high electrical conductivity can be obtained. In addition, in the process of converting the metal oxide precursor film into the metal oxide film, indium nitrate is efficiently decomposed by the ultraviolet light when irradiated with ultraviolet light, and an indium-containing oxide film can be easily formed.

The metal nitrate solution preferably contains a compound (metal-containing compound) containing one or more metal elements selected from zinc, tin, gallium, and aluminum as a metal element other than indium. By including an appropriate amount of the above metal element other than indium, when an oxide semiconductor film is formed as a semiconductor layer of a thin film transistor, the threshold voltage of the obtained oxide semiconductor film can be controlled to a desired value, and The electrical stability can be improved.
As an oxide semiconductor or an oxide conductor containing indium and a metal element other than indium, In—Ga—Zn—O, In—Zn—O, In—Ga—O, In—Sn—O, and In—Sn— Zn-O etc. are mentioned.

  The concentration of the metal nitrate in the solution may be selected according to the viscosity of the solution, the target film thickness, the electrical properties, etc., but the indium content in the solution is 50 atom% of the metal component contained in the solution. The above is preferable. By using a solution containing indium in the above concentration range, a metal oxide film in which 50 atom% or more of the metal components in the film is indium can be obtained, and a metal oxide film having excellent electrical characteristics can be manufactured.

  The concentration of the metal component in the solution (the sum of the mole fractions of each metal when multiple metals are included) can be arbitrarily selected depending on the viscosity and the desired film thickness, but the metal oxide film From the viewpoint of flatness and productivity, the concentration of the metal component in the solution is preferably 0.01 mol / L or more and 1.0 mol / L or less, preferably 0.01 mol / L or more and 0.5 mol / L or less. It is more preferable.

  The solvent used in the metal nitrate solution is not particularly limited as long as it is a solvent in which the metal nitrate to be used and other metal-containing compounds to be added as required are dissolved. Water, alcohol solvents (methanol, ethanol, propanol, ethylene glycol) Etc.), amide solvents (N, N-dimethylformamide etc.), ketone solvents (acetone, N-methylpyrrolidone, sulfolane, N, N-dimethylimidazolidinone etc.), ether solvents (tetrahydrofuran, methoxyethanol etc.), nitrile solvents (Acetonitrile, etc.) and other heteroatom-containing solvents other than the above.

  In particular, methanol and methoxyethanol can be suitably used from the viewpoints of solubility, paintability, and boiling point.

-Board-
In the present disclosure, the shape, structure, size, and the like of the substrate on which the metal oxide film is formed are not particularly limited and can be appropriately selected according to the purpose.
For example, the structure of the substrate may be a single layer structure or a laminated structure.

  As a material constituting the substrate, a substrate made of an inorganic material such as glass or YSZ (Yttria-Stabilized Zirconia), a resin, a resin composite material, or the like can be used. Among these, a substrate made of a resin or a resin composite material is preferable in terms of light weight and flexibility. Specifically, polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polystyrene, polycarbonate, polysulfone, polyethersulfone, polyarylate, allyl diglycol carbonate, polyamide, polyimide, polyamideimide, polyetherimide, Fluorine resin such as polybenzazole, polyphenylene sulfide, polycycloolefin, norbornene resin, polychlorotrifluoroethylene, liquid crystal polymer, acrylic resin, epoxy resin, silicone resin, ionomer resin, cyanate resin, crosslinked fumaric acid diester, cyclic polyolefin, Substrates made of synthetic resins such as aromatic ethers, maleimide-olefins, cellulose, episulfide compounds, A substrate composed of a composite plastic material of the above-mentioned synthetic resin and the like and silicon oxide particles, a substrate composed of a composite plastic material of the above-described synthetic resin and the like and metal nanoparticles, inorganic oxide nanoparticles or inorganic nitride nanoparticles, A substrate made of a composite plastic material of the above-described synthetic resin and the like and carbon fiber or carbon nanotube, a substrate made of a composite plastic material of the above-described synthetic resin and the glass flake, glass fiber or glass bead, the above-mentioned synthetic resin Etc. and a substrate made of a composite plastic material of clay mineral or particles having a mica-derived crystal structure, a laminated plastic substrate having at least one bonding interface between a thin glass and any of the aforementioned synthetic resins, an inorganic layer, and By alternately laminating organic layers (the aforementioned synthetic resins), at least one bonding interface Improve surface insulation by applying oxidation treatment (for example, anodization treatment) to a substrate made of a composite material having barrier performance, a stainless steel substrate, a metal multilayer substrate in which stainless steel and a dissimilar metal are laminated, an aluminum substrate or the surface. An aluminum substrate with an oxide film, a silicon substrate with an oxide film, or the like can be used.

  The resin substrate is preferably excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, workability, low air permeability, low moisture absorption, and the like. The resin substrate may include a gas barrier layer for preventing permeation of moisture and oxygen, an undercoat layer for improving the flatness of the resin substrate and adhesion with the lower electrode, and the like.

  Further, a lower electrode or an insulating film may be provided on the substrate. In that case, the metal oxide film of the present disclosure is formed on the lower electrode or the insulating film on the substrate.

-Surface treatment-
The metal nitrate solution is applied by an ink jet method while the substrate is heated, but may include a step of performing a surface treatment on the surface of the substrate on which the coating film is formed before the applying step. For example, when a thin film transistor is manufactured, if it is left in an indoor environment for a long time after the formation of a gate insulating film, the surface of the insulating film is adversely affected (operational stability) due to contamination with moisture, carbon, organic components, etc. there is a possibility. Therefore, it is preferable to perform a surface treatment for removing moisture and dirt on the substrate as a pretreatment for applying the metal nitrate solution to the substrate. Examples of the substrate surface treatment include ultraviolet (UV) ozone treatment, argon plasma treatment, and nitrogen plasma treatment.
As the UV ozone treatment, for example, a UV ozone treatment apparatus (Model 144AX-100 manufactured by Jelight-company-Inc) is used and is performed for about 1 to 3 minutes under the following conditions and wavelengths.
-Conditions: atmospheric pressure, in air-Wavelength: 254 nm (30 mW / cm ² ), 185 nm (3.3 mW / cm ² )

-Application by inkjet method-
After the substrate is subjected to UV ozone treatment as necessary, a metal nitrate solution is applied by an inkjet method while the substrate is heated.

The heating temperature of the substrate is selected according to the heat resistance of the substrate, the solvent contained in the metal nitrate solution to be applied, the target thickness unevenness, and the like, but is preferably equal to or higher than the boiling point of the solvent contained in the metal nitrate solution. The active layer composed of a semiconductor film is particularly susceptible to adverse effects on electrical properties, but the process is performed by discharging the solution onto the substrate heated above the boiling point of the solvent by the ink jet method and drying almost simultaneously with landing. Time can be shortened and uneven thickness of the coating film can be suppressed, and a semiconductor film with improved electrical characteristics can be formed in the next conversion step.
The present invention is not limited to the active layer, and is suitable for forming a conductive film other than the active layer. For example, the configuration of the bottom gate TFT shown in FIG. 3 has a configuration in which a gate electrode 22, a gate insulating film 20, an active layer 14, and source / drain electrodes 16 and 18 are stacked on a substrate 12. Further, a channel protective layer, an interlayer insulating film, and the like are formed on the TFT. Therefore, for example, when the gate electrode 22 is formed by inkjet, when the thickness of the gate electrode 22 is large due to the coffee stain phenomenon, the insulation characteristics are deteriorated due to the coverage of the next formed gate insulating film 20 or the coffee stain shape. There is a high possibility that a short circuit will occur. However, by forming the gate electrode 22 according to the present disclosure, the thickness unevenness can be reduced, and the deterioration of the insulating characteristics and the occurrence of a short circuit can be suppressed. Further, by applying the present disclosure to the formation of source / drain electrodes and gate electrodes in TFTs having other structures, thickness unevenness is suppressed and influence on the upper layer is suppressed, so that the same effect can be obtained.

The heating temperature of the substrate is, for example, about 65 ° C. or more when the solvent contained in the metal nitrate solution is methanol (boiling point: 64.7 ° C.), and about 125 ° C. or more when methoxyethanol (boiling point: 124 ° C.) is used. It is preferable that the temperature is lower than the heat-resistant temperature of the substrate, for example, when the resin substrate is used, the temperature is lower than the softening point.
If the surface temperature of the substrate is too high, the shape of the metal nitrate solution droplets may be disturbed when ejected onto the substrate, and the energy cost required for heating also increases. The boiling point of the solvent is preferably 20 ° C. or lower, more preferably the boiling point of the solvent + 10 ° C. or lower. The substrate temperature is measured by using a Si wafer with a thermocouple.

  There is no restriction on the heating time of the substrate, and the heat conduction of the substrate may be taken into consideration. Moreover, there is no restriction | limiting in the heating method of a board | substrate, A board | substrate may be arrange | positioned on the heated stage, a heater may be installed separately from a stage, and lamp heating may be performed. From the viewpoint of shortening the heating time, it is preferable that the substrate is in direct contact with the heating portion.

  The atmosphere in the coating step is not particularly limited, but is preferably an inert atmosphere (nitrogen, argon, etc.) from the viewpoint of eliminating influences other than water and oxygen solutions.

  While the surface of the substrate is heated to a target temperature, a metal nitrate solution is applied by an inkjet method. By heating the substrate preferably above the boiling point of the solvent, the solvent in the coating solution formed on the substrate quickly volatilizes, and the shape of the semiconductor film formed after conversion is determined and uneven thickness is suppressed. .

According to the ink jet method, it is not necessary to perform a photolithography process, and a coating film can be formed at a necessary portion.
In addition, according to the ink jet method, it is possible to cope with a pattern alignment shift due to a thermal factor in the process when a flexible substrate is used, and it is possible to form a coating film with high accuracy by confirming a formation position in advance. it can.
In the present invention, since the solution is applied by the ink jet method while the substrate is heated, the droplets of the metal nitrate solution are discharged and dried almost simultaneously, and it is not necessary to perform a separate drying step after the application.
Further, when the entire substrate is dried after patterning by the ink jet method, the solvent may be volatilized little by little, which may make shape control difficult. Moreover, the pattern accuracy before and after application may deteriorate.
Further, if UV irradiation is performed under heating without performing a drying step after patterning by inkjet, the film may be damaged.
On the other hand, in this invention, since it apply | coats by the inkjet method in the state which heated the board | substrate, the pattern with high uniformity of a dimension (especially thickness) can be formed in the part applied initially and the part applied last.

(Conversion process)
After a metal nitrate solution is applied by an inkjet method while the substrate is heated to form a coating film, the coating film is subjected to an atmosphere having an oxygen concentration of 80000 ppm or less (hereinafter referred to as “low oxygen concentration atmosphere”). .) Is converted into a metal oxide film by irradiating with ultraviolet rays.

  The coating film can be converted into a metal oxide film at a lower temperature by irradiating with ultraviolet light in a low oxygen concentration atmosphere, and a conductor film or a semiconductor film having excellent electrical characteristics can be formed. .

Examples of the ultraviolet light source include a UV lamp and a laser, and a UV lamp is preferable from the viewpoint of uniformly irradiating ultraviolet rays with a cheap facility with a large area.
Examples of UV lamps include excimer lamps, deuterium lamps, low pressure mercury lamps, high pressure mercury lamps, ultrahigh pressure mercury lamps, metal halide lamps, helium lamps, carbon arc lamps, cadmium lamps, electrodeless discharge lamps, etc. Use of a mercury lamp is preferable because conversion from a precursor film to an oxide film can be easily performed. Laser light having a wavelength of 266 nm may be used.

In the conversion step, it is preferable that the film surface of the metal oxide precursor film is irradiated with ultraviolet light including light having a wavelength of 300 nm or less at an illuminance of 10 mW / cm ² or more. By irradiating ultraviolet light in a wavelength range of 300 nm or less with an illuminance of 10 mW / cm ² or more, conversion from the metal oxide precursor film to the metal oxide film can be performed in a shorter time.

The ultraviolet irradiation in the conversion step is performed in a low oxygen concentration atmosphere having an oxygen concentration of 80000 ppm (8%) or less.
By performing UV irradiation on the coating film on the substrate in a low oxygen concentration atmosphere having an oxygen concentration of 80000 ppm or less, the carrier density of the oxide semiconductor can be easily controlled, and a metal oxide film having high electron transfer characteristics can be obtained. From the viewpoint of enhancing the electron transfer characteristics, the oxygen concentration in the atmosphere in which the ultraviolet irradiation is performed is preferably 30000 ppm or less (3% or less).

  In addition, as a means for adjusting the oxygen concentration in the atmosphere at the time of ultraviolet irradiation to 80000 ppm or less, for example, nitrogen gas supplied to the processing chamber for heating and ultraviolet irradiation of the metal oxide precursor film on the substrate or the like Examples include a method for adjusting the flow rate of the inert gas, a method for adjusting the oxygen concentration in the gas supplied to the processing chamber, and a method for evacuating the processing chamber in advance and filling the gas with a desired oxygen concentration therein. .

When UV irradiation is performed in a low oxygen concentration atmosphere on the coating film on the substrate in the conversion step, ultraviolet irradiation may be performed while the substrate is heated. If UV irradiation and substrate heating are performed, the metal oxide film is converted in a shorter time, and the processing time can be shortened.
When UV irradiation is performed by heating the substrate in the conversion step, it is preferable that the highest temperature reached by the substrate is 120 ° C. or higher. When the temperature is 120 ° C. or higher, a dense metal oxide film can be easily obtained.
On the other hand, if the substrate temperature in the conversion step is maintained at 200 ° C. or lower, an increase in thermal energy can be suppressed and the manufacturing cost can be reduced, and application to a resin substrate with low heat resistance is facilitated.

The heating means for the substrate in the conversion step is not particularly limited, and may be selected from hot plate heating, electric furnace heating, infrared heating, microwave heating, and the like.
The substrate temperature during the ultraviolet treatment may be radiant heat from the ultraviolet lamp to be used, or the substrate temperature may be controlled by a heater or the like. When radiant heat from an ultraviolet lamp is used, it can be controlled by adjusting the lamp-substrate distance and the lamp output.

Although the ultraviolet irradiation time depends on the illuminance of the ultraviolet rays, it is preferably 5 seconds or longer and 120 minutes or shorter from the viewpoint of productivity.
Further, the film thickness of the metal oxide film produced according to the present disclosure is not particularly limited and may be selected according to the application. However, when the semiconductor layer of the thin film transistor is formed according to the present disclosure, the film thickness is preferably 50 nm or less. More preferably, it is about 10 nm.

Through the above steps, a metal oxide film having conductor or semiconductor characteristics can be easily produced.
The manufacturing method of the metal oxide film of this indication can obtain easily the metal oxide film which has a conductor or a semiconductor characteristic with a low-temperature process of 200 degrees C or less. In addition, the device manufacturing cost can be greatly reduced because it is not necessary to use a large vacuum apparatus, an inexpensive resin substrate with low heat resistance can be used, and the raw material is inexpensive.
Moreover, since the manufacturing method of the metal oxide film of this indication is applicable also to a resin substrate with low heat resistance, it becomes possible to produce flexible electronic devices, such as a flexible display, at low cost.

  Further, by using the metal oxide film manufacturing method of the present disclosure, it is possible to form a conductive film or a semiconductor film with small thickness unevenness and excellent electrical characteristics, for example, excellent process suitability and high electron mobility. A semiconductor element exhibiting electrical characteristics can be manufactured at low cost.

<Thin film transistor>
In the present disclosure, a metal oxide film having small thickness unevenness and conductivity or semiconductivity can be manufactured. Therefore, a method for manufacturing a metal oxide film of the present disclosure includes a thin film transistor (TFT) electrode (source electrode, It can be suitably used for forming a drain electrode or a gate electrode) or an oxide semiconductor layer (active layer).

  Hereinafter, although the form which applies the manufacturing method of the metal oxide film of this indication to formation of the semiconductor layer (oxide semiconductor film) of TFT is mainly demonstrated, this invention is limited to formation of the semiconductor layer of TFT. is not.

The element structure of the TFT according to the present disclosure is not particularly limited, and may be any of a so-called reverse stagger structure (also referred to as a bottom gate type) and a stagger structure (also referred to as a top gate type) based on the position of the gate electrode. Also good. Further, based on the contact portion between the semiconductor layer and the source and drain electrodes (referred to as “source / drain electrodes” as appropriate), either a so-called top contact type or bottom contact type may be employed.
The top gate type is a form in which a gate electrode is disposed on the upper side of the gate insulating film and a semiconductor layer is formed on the lower side of the gate insulating film when the substrate on which the TFT is formed is the lowermost layer. The bottom gate type is a form in which a gate electrode is disposed below a gate insulating film and a semiconductor layer is formed above the gate insulating film. The bottom contact type is a mode in which the source / drain electrodes are formed before the semiconductor layer, and the lower surface of the semiconductor layer is in contact with the source / drain electrodes. The top contact type is the type in which the semiconductor layer is source / drain. In this embodiment, the upper surface of the semiconductor layer is in contact with the source / drain electrodes.

  FIG. 1 is a schematic diagram illustrating an example of a top contact type TFT according to the present disclosure having a top gate structure. In the TFT 10 shown in FIG. 1, the above-described oxide semiconductor film is stacked as the semiconductor layer 14 on one main surface of the substrate 12. A source electrode 16 and a drain electrode 18 are disposed on the semiconductor layer 14 so as to be separated from each other, and a gate insulating film 20 and a gate electrode 22 are sequentially stacked.

  FIG. 2 is a schematic diagram illustrating an example of a TFT according to the present disclosure having a top gate structure and a bottom contact type. In the TFT 30 shown in FIG. 2, the source electrode 16 and the drain electrode 18 are disposed on one main surface of the substrate 12 so as to be separated from each other. Then, the above-described oxide semiconductor film, the gate insulating film 20, and the gate electrode 22 are sequentially stacked as the semiconductor layer 14.

  FIG. 3 is a schematic diagram showing an example of a top contact type TFT according to the present disclosure having a bottom gate structure. In the TFT 40 shown in FIG. 3, the gate electrode 22, the gate insulating film 20, and the above-described oxide semiconductor film as the semiconductor layer 14 are sequentially stacked on one main surface of the substrate 12. A source electrode 16 and a drain electrode 18 are disposed on the surface of the semiconductor layer 14 so as to be separated from each other.

  FIG. 4 is a schematic diagram illustrating an example of a bottom contact type TFT according to the present disclosure having a bottom gate structure. In the TFT 50 shown in FIG. 4, the gate electrode 22 and the gate insulating film 20 are sequentially stacked on one main surface of the substrate 12. Then, the source electrode 16 and the drain electrode 18 are provided on the surface of the gate insulating film 20 so as to be separated from each other, and the above-described oxide semiconductor film is stacked as the semiconductor layer 14.

  In the following embodiment, the top gate type thin film transistor 10 shown in FIG. 1 will be mainly described. However, the thin film transistor according to the present disclosure is not limited to the top gate type, and may be a bottom gate type thin film transistor.

(substrate)
The shape, structure, size, etc. of the substrate on which the TFT is formed are not particularly limited, and can be appropriately selected from the above-described substrates according to the purpose.
Moreover, there is no restriction | limiting in particular in the thickness of the board | substrate used by this indication, However, It is preferable that they are 50 micrometers or more and 500 micrometers or less.
When the thickness of the substrate is 50 μm or more, the flatness of the substrate itself is further improved. Further, when the thickness of the substrate is 500 μm or less, the flexibility of the substrate itself is further improved, and the use as a flexible device substrate becomes easier. For example, in the manufacturing process of a flexible device, after forming a thin-film transistor on the flexible substrate temporarily fixed to the glass substrate, the form which peels a flexible substrate from a glass substrate may be sufficient.

(Semiconductor layer)
When the thin film transistor 10 of the present embodiment is manufactured, the surface of the substrate 12 on the side where the TFT is formed is subjected to UV ozone treatment as necessary, and then the metal nitrate solution is applied to the semiconductor layer by the inkjet method while the substrate 12 is heated. Then, the coating film is formed into a metal oxide semiconductor film by irradiation with ultraviolet rays in an atmosphere having an oxygen concentration of 80000 ppm or less.

  The thickness of the semiconductor layer 14 is preferably 5 nm or more and 50 nm or less from the viewpoint of flatness and time required for film formation.

(Protective layer)
A protective layer (not shown) for protecting the semiconductor layer 14 is preferably formed on the semiconductor layer 14 when the source / drain electrodes 16 and 18 are etched. There is no particular limitation on the method for forming the protective layer, and the protective layer may be formed after the metal oxide semiconductor film.
The protective layer is preferably an insulator, and the material constituting the protective layer may be an inorganic material or an organic material such as a resin. The protective layer may be removed after the source electrode 16 and the drain electrode 18 (referred to as “source / drain electrodes” as appropriate) are formed.

(Source / drain electrodes)
Source / drain electrodes 16 and 18 are formed on a semiconductor layer 14 formed of a metal oxide semiconductor film. The source / drain electrodes 16 and 18 each have a high electrical conductivity functioning as an electrode, for example, metals such as Al, Mo, Cr, Ta, Ti, Ag, Au, Al—Nd, Ag alloy, tin oxide, oxidation A metal oxide conductive film such as zinc, indium oxide, indium tin oxide (ITO), zinc indium oxide (IZO), or In—Ga—Zn—O can be used.

  When the source / drain electrodes 16 and 18 are formed, a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, a CVD (chemical vapor deposition), or a plasma CVD method. The film may be formed according to a method appropriately selected in consideration of suitability with a material to be used from among chemical methods such as the above.

  The film thickness of the source / drain electrodes 16 and 18 is preferably 10 nm or more and 1000 nm or less, preferably 50 nm or more and 100 nm or less in consideration of film forming properties, patterning properties by etching or lift-off methods, conductivity, and the like. More preferred.

  The source / drain electrodes 16 and 18 may be formed by patterning into a predetermined shape by, for example, etching or a lift-off method after forming a conductive film, or may be directly formed by an inkjet method or the like. At this time, it is preferable to pattern the source / drain electrodes 16 and 18 and wiring (not shown) connected to these electrodes simultaneously.

(Gate insulation film)
After the source / drain electrodes 16 and 18 and the wiring (not shown) are formed, the gate insulating film 20 is formed. The gate insulating film 20 is preferably made of a material having high insulating properties. For example, an insulating film such as SiO ₂ , SiN _x , SiON, Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , HfO ₂ , or a compound thereof is used. The insulating film may include two or more types, and may have a single layer structure or a stacked structure.
The gate insulating film 20 can be formed from a printing method, a wet method such as a coating method, a physical method such as a vacuum deposition method, a sputtering method or an ion plating method, or a chemical method such as a CVD or plasma CVD method. The film may be formed according to a method appropriately selected in consideration of suitability with the material to be used. The gate insulating film 20 may be an organic insulating film or an inorganic insulating film as long as it has gate insulating characteristics.

  The gate insulating film 20 needs to have a thickness for reducing leakage current and improving voltage resistance. On the other hand, if the thickness of the gate insulating film 20 is too large, the driving voltage is increased. Although the gate insulating film 20 depends on the material, the thickness of the gate insulating film 20 is preferably 10 nm to 10 μm, more preferably 50 nm to 1000 nm, and particularly preferably 100 nm to 400 nm.

(Gate electrode)
After forming the gate insulating film 20, a gate electrode 22 is formed. The gate electrode 22 is made of a material having high conductivity, for example, metal such as Al, Cu, Mo, Cr, Ta, Ti, Ag, Au, Al—Nd, Ag alloy, tin oxide, zinc oxide, indium oxide, indium oxide. A metal oxide conductive film such as tin (ITO), indium zinc oxide (IZO), or In—Ga—Zn—O can be used. As the gate electrode 22, these conductive films can be used as a single layer structure or a stacked structure of two or more layers.

The gate electrode 22 is made of a material used from a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method or an ion plating method, or a chemical method such as a CVD or plasma CVD method. The film is formed according to a method appropriately selected in consideration of the suitability of the above.
The film thickness of the metal film for forming the gate electrode 22 is preferably 10 nm or more and 1000 nm or less, preferably 50 nm or more and 200 nm or less in consideration of film forming properties, patterning properties by etching or lift-off methods, conductivity, and the like. More preferably.
After the film formation, the gate electrode 22 may be formed by patterning into a predetermined shape by an etching or lift-off method, or the pattern may be formed directly by an inkjet method, a printing method, or the like. At this time, it is preferable to pattern the gate electrode 22 and the gate wiring (not shown) at the same time.

The use of the thin film transistor 10 of the present embodiment described above is not particularly limited, but since a thin film transistor having high transport characteristics can be produced at a low temperature, it can be applied to production of various electronic devices, particularly flexible electronic devices. it can. Specifically, it is suitable for manufacturing a flexible display using a driving element in a display device such as a liquid crystal display device, an organic EL (Electro Luminescence) display device, and an inorganic EL display device, and a resin substrate having low heat resistance.
Furthermore, the thin film transistor manufactured according to the present disclosure is suitably used as a driving element (driving circuit) in various electronic devices such as various sensors such as an X-ray sensor and an image sensor, and a MEMS (Micro Electro Mechanical System).

<Liquid crystal display device>
FIG. 5 shows a schematic sectional view of a part of a liquid crystal display device according to an embodiment of the present invention, and FIG. 6 shows a schematic configuration diagram of electrical wiring.

  As shown in FIG. 5, the liquid crystal display device 100 according to the present embodiment includes a top contact type TFT 10 having the top gate structure shown in FIG. 1 and a pixel lower electrode on the gate electrode 22 protected by the passivation layer 102 of the TFT 10. 104 and a liquid crystal layer 108 sandwiched between the counter upper electrode 106 and an R (red) G (green) B (blue) color filter 110 for developing different colors corresponding to each pixel. In this configuration, polarizing plates 112a and 112b are provided on the substrate 12 side and the RGB color filter 110, respectively.

  As shown in FIG. 6, the liquid crystal display device 100 according to the present embodiment includes a plurality of gate lines 112 that are parallel to each other and data lines 114 that are parallel to each other and intersect the gate lines 112. Here, the gate wiring 112 and the data wiring 114 are electrically insulated. The TFT 10 is provided in the vicinity of the intersection between the gate wiring 112 and the data wiring 114.

  The gate electrode 22 of the TFT 10 is connected to the gate wiring 112, and the source electrode 16 of the TFT 10 is connected to the data wiring 114. The drain electrode 18 of the TFT 10 is connected to the pixel lower electrode 104 through a contact hole 116 provided in the gate insulating film 20 (a conductor is embedded in the contact hole 116). The pixel lower electrode 104 forms a capacitor 118 together with the grounded counter upper electrode 106.

<Organic EL display device>
FIG. 7 shows a schematic sectional view of a part of an active matrix organic EL display device according to an embodiment of the present invention, and FIG. 8 shows a schematic configuration diagram of electrical wiring.

  The active-matrix organic EL display device 200 of the present embodiment includes the TFT 10 having the top gate structure shown in FIG. 1 as a driving TFT 10a and a switching TFT 10b on a substrate 12 having a passivation layer 202. , 10b is provided with an organic EL light emitting element 214 composed of an organic light emitting layer 212 sandwiched between a lower electrode 208 and an upper electrode 210, and the upper surface is also protected by a passivation layer 216.

  As shown in FIG. 8, the organic EL display device 200 of this embodiment includes a plurality of gate wirings 220 that are parallel to each other, and data wirings 222 and driving wirings 224 that are parallel to each other and intersect the gate wirings 220. ing. Here, the gate wiring 220, the data wiring 222, and the drive wiring 224 are electrically insulated. The gate electrode 22 of the switching TFT 10 b is connected to the gate wiring 220, and the source electrode 16 of the switching TFT 10 b is connected to the data wiring 222. The drain electrode 18 of the switching TFT 10b is connected to the gate electrode 22 of the driving TFT 10a, and the driving TFT 10a is kept on by using the capacitor 226. The source electrode 16 of the driving TFT 10 a is connected to the driving wiring 224, and the drain electrode 18 is connected to the organic EL light emitting element 214.

  In the organic EL display device shown in FIG. 7, the upper electrode 210 may be a top emission type using a transparent electrode, or the lower electrode 208 and each electrode of a TFT may be a bottom emission type using a transparent electrode.

<X-ray sensor>
FIG. 9 shows a partial schematic cross-sectional view of an X-ray sensor according to an embodiment of the present invention, and FIG. 10 shows a schematic configuration diagram of electrical wiring.

  The X-ray sensor 300 of this embodiment includes the TFT 10 and the capacitor 310 formed on the substrate 12, the charge collection electrode 302 formed on the capacitor 310, the X-ray conversion layer 304, and the upper electrode 306. Composed. A passivation film 308 is provided on the TFT 10.

  The capacitor 310 has a structure in which an insulating film 316 is sandwiched between a capacitor lower electrode 312 and a capacitor upper electrode 314. The capacitor upper electrode 314 is connected to one of the source electrode 16 and the drain electrode 18 (the drain electrode 18 in FIG. 9) of the TFT 10 through a contact hole 318 provided in the insulating film 316.

The charge collection electrode 302 is provided on the capacitor upper electrode 314 in the capacitor 310 and is in contact with the capacitor upper electrode 314.
The X-ray conversion layer 304 is a layer made of amorphous selenium, and is provided so as to cover the TFT 10 and the capacitor 310.
The upper electrode 306 is provided on the X-ray conversion layer 304 and is in contact with the X-ray conversion layer 304.

  As shown in FIG. 10, the X-ray sensor 300 of this embodiment includes a plurality of gate wirings 320 that are parallel to each other and a plurality of data wirings 322 that intersect with the gate wirings 320 and are parallel to each other. Here, the gate wiring 320 and the data wiring 322 are electrically insulated. The TFT 10 is provided in the vicinity of the intersection between the gate wiring 320 and the data wiring 322.

  The gate electrode 22 of the TFT 10 is connected to the gate wiring 320, and the source electrode 16 of the TFT 10 is connected to the data wiring 322. The drain electrode 18 of the TFT 10 is connected to the charge collecting electrode 302, and the charge collecting electrode 302 is connected to the capacitor 310.

  In the X-ray sensor 300 of this embodiment, X-rays enter from the upper electrode 306 side in FIG. 9 and generate electron-hole pairs in the X-ray conversion layer 304. By applying a high electric field to the X-ray conversion layer 304 by the upper electrode 306, the generated charge is accumulated in the capacitor 310 and read out by sequentially scanning the TFT 10.

  Note that the liquid crystal display device 100, the organic EL display device 200, and the X-ray sensor 300 of the above embodiment include a top gate TFT, but are not limited to the top gate TFT. A TFT having the structure shown in FIG.

Examples will be described below, but the present invention is not limited to the following examples.
In addition, in order to show the effect of this case, the effect was confirmed with the simple structure. In the present embodiment, “Examples 1, 2, 8” are read as “Reference Examples 1, 2, 8”.

<Example 1>
(Metal nitrate solution)
Indium nitrate (In (NO ₃ ) ₃ xH ₂ O, purity: 4N, manufactured by High Purity Chemical Laboratory Co., Ltd.) is dissolved in 2-methoxyethanol (special grade reagent, boiling point: 124 ° C., manufactured by Wako Pure Chemical Industries, Ltd.) To prepare a solution having an indium nitrate concentration of 0.5 mol / L.
The substrate was a p-type Si substrate with a thermal oxide film (film thickness 100 nm). The gate electrode is p-type Si, and the gate insulating film is a thermal oxide film Si.

  Before discharging the indium nitrate solution by inkjet, the substrate was subjected to UV ozone treatment for about 3 minutes using a UV ozone treatment apparatus (Model 144AX-100 manufactured by Jelight-company-Inc).

(Coating process)
As the ink jet apparatus, a material printer DMP-2831 manufactured by FUJIFILM Corporation was used. In this ink jet apparatus, the temperature of the ink cartridge and the stage can be adjusted independently, and the temperature of the ink cartridge is set to 25 ° C. On the other hand, a silicon rubber heater was attached on the substrate stage so that the substrate on the stage could be heated at a higher temperature, and a mechanism capable of heating to 60 degrees or more was provided. The temperature calibration was performed on a Si wafer with a thermocouple, and the temperature was adjusted so that the substrate surface temperature was accurate.

  The substrate was placed on a stage set at 60 ° C., heated for 5 minutes, and then a line-shaped coating film having a length of about 3 mm was formed on the substrate by inkjet (sometimes abbreviated as “IJ”).

(Conversion process)
Next, the coating film formed by inkjet was irradiated with ultraviolet rays in an atmosphere in which the oxygen concentration was controlled.
As a UV irradiation device, VUE-3400-F manufactured by Oak Manufacturing Co., Ltd. was used. This UV irradiation apparatus includes a substrate heating mechanism (maximum 300 ° C.), a gas (N ₂ , O ₂ ) introduction port, and a UV irradiation mechanism (low pressure mercury lamp: peak wavelength 254 nm).
The conditions in the conversion process are shown below.
Substrate heating temperature: 150 ° C (temperature calibrated: TC wafer with thermocouple)
Peak wavelength: 254 nm
Irradiation power: 20 mW / cm ² (measured with UV-M10 manufactured by Oak Manufacturing Co., Ltd.)
Irradiation time: 30 min Atmosphere: _N 2, 1atm (1013.25hPa)

  Prior to setting the sample on the stage in the UV irradiation apparatus, the stage was heated to 150 ° C. in advance, and after the stage temperature reached 150 ° C., the sample was placed on the stage.

Next, after flowing from the N ₂ introduction port at an amount of 10 L / min for about 5 minutes, UV irradiation was started. Note that the N ₂ flow was continued during UV irradiation. After 30 minutes of UV irradiation set time, a sample was taken out from the apparatus.

  Next, source / drain electrodes were formed on the semiconductor film. Here, a metal mask having two 1 mm square holes (distance 0.2 mm) for the source and drain electrodes is used in order to easily manufacture a TFT and eliminate the influence on the semiconductor film by photolithography or the like. Depending on conditions, Ti was sputtered to a thickness of about 50 nm to form source / drain electrodes.

Apparatus: MPS-6000C manufactured by ULVAC
Ultimate vacuum: 2 × 10 ⁻⁵ Pa
Deposition pressure: 0.25 Pa
Input power: DC100W
Deposition time: 8 minutes

  A source / drain electrode was formed by Ti film formation, thereby completing a bottom-gate type simplified TFT.

<Examples 2 to 4>
A TFT was produced in the same manner as in Example 1 except that the substrate surface temperature in the coating process was changed as shown in Table 1.

<Comparative Example 1>
A coating process was performed in the same manner as in Example 1 except that the substrate was not heated, and then dried at 60 ° C. for 1 minute using a hot plate. After drying, the conversion step was performed in the same manner as in Example 1.

<Comparative example 2>
The coating process was performed in the same manner as in Example 1 except that the substrate was not heated, and the conversion process was performed without drying. In the conversion process, cracks were generated in the coating film of the sample, so that the subsequent evaluation could not be performed (described as “NG” in Table 1). It is estimated that the crack of the coating film in the comparative example 2 was generated by heating and UV irradiation in a state where the coating film formed by inkjet was not sufficiently dried.

[Evaluation]
(Electrical characteristics)
The TFT prepared in the above Examples and Comparative Examples, using a semiconductor parameter analyzer 4156C (manufactured by Agilent Technologies), were measured transistor characteristics _(V g -I _d characteristics).
Measurement of V _g -I _d characteristics, the drain voltage _{(V d)} is fixed to + 1V, the gate voltage _{(V g)} is changed within the range of -15V~ + 15V, the drain current at gate voltages _(I d) Was measured, and the mobility, which is an important characteristic of the TFT, was calculated. The transistor characteristics are shown in FIG. 11 and the mobility calculated from FIG. 11 is shown in Table 1.
From FIG. 11 and Table 1, the mobility which shows a transistor characteristic has increased compared with the comparative example 1, and the characteristic improvement was able to be confirmed.

(Film thickness)
The thickness of the semiconductor layer in the fabricated TFT was measured by observation with a transmission electron microscope (Hitachi H-9000NAR). FIG. 12 shows a photomicrograph of the TFT produced in Comparative Example 1. If it can be seen at a similar density, it may be considered as a comparable thickness. In FIG. 12, the concentration is different between both edges and the center of the semiconductor layer, and both edges are darker, and the lower thermal oxide film (black) can be seen through the center. This is due to the difference in the film thickness of the semiconductor layer, and it can be seen that the central part is thinner than both edges.

In order to actually confirm the film thickness, each cross-sectional observation of the edge (A location) and the central portion (B location) of the semiconductor layer in FIG. 12 was performed with a transmission electron microscope (Hitachi H-9000NAR). The A part is shown in FIG. 13 and the B part is shown in FIG.
The film thickness at the A location of the semiconductor layer was about 30 nm, and the film thickness at the B location was about 2 nm. In addition, in the semiconductor portion at the location A, a location presumed to be a defect (a location where the color in the semiconductor layer is light) was observed.

  Thus, the semiconductor layer of Comparative Example 1 has a large difference in film thickness (thickness unevenness). Further, a defect that is considered to cause deterioration in transistor characteristics is present at the edge (A portion), and the defect portion is not at the thermal oxide film interface but at a position of about 10 nm from the thermal oxide film interface. This is considered because impurities or the like cannot be completely removed in the conversion process to the semiconductor film. That is, it can be estimated that reducing the thickness unevenness of the semiconductor film and keeping it within about 10 nm (after conversion) is a factor for reducing defects.

  The film thicknesses of the semiconductor layers in Examples 1 to 4 were similarly confirmed, and the results are shown in Table 1.

  As shown in Table 1, compared with Comparative Example 1, in Examples 1 to 4, the difference in film thickness (thickness unevenness) at the A and B locations is reduced, and the substrate surface temperature in the coating process is reduced by the solvent. In Examples 3 and 4 having a boiling point (124 ° C.) or higher, the difference was 1 nm or less.

  In addition, high mobility was obtained in the TFTs of Examples 1 to 4 applied by inkjet while the substrate was heated, and the difference in film thickness at the A and B locations of the semiconductor layer (metal oxide film) was small. In particular, in Examples 3 and 4 where the substrate surface temperature was higher than the boiling point of the solvent, higher mobility was obtained.

<Example 5>
Indium nitrate (In (NO ₃ ) ₃ xH ₂ O, purity: 4N, manufactured by High Purity Chemical Laboratory Co., Ltd.) is dissolved in methanol (special grade reagent, boiling point: 64.7 ° C., manufactured by Wako Pure Chemical Industries, Ltd.). A solution having an indium nitrate concentration of 0.5 mol / L was prepared.
A coating film was formed by inkjet in the same manner as in Example 1 using the indium nitrate solution on a Si substrate with a thermal oxide film whose substrate surface temperature was adjusted to 65 ° C.

After forming the coating film, the bottom gate type TFT was produced by performing ultraviolet irradiation under nitrogen atmosphere (oxygen concentration: 50 ppm or less) and forming source / drain electrodes in the same manner as in Example 1.
About the produced TFT, it carried out similarly to Example 1, and measured the mobility and the film thickness of the semiconductor layer.

<Examples 6 to 8, Comparative Example 3>
A TFT was produced and evaluated in the same manner as in Example 5 except that the substrate surface temperature in the coating process was changed as shown in Table 2.
The results are summarized in Table 2.

  Even when the solvent was changed to methanol, high mobility was obtained in the TFTs of Examples 5 to 8 applied by inkjet while the substrate was heated, and the difference in film thickness at the A and B locations of the semiconductor layer was Comparative Example 3. Was smaller than. In particular, in Examples 5 to 7 in which the substrate surface temperature was higher than the boiling point of the solvent (64.7 ° C.), higher mobility was obtained.

<Examples 9 and 10, Comparative Examples 4 and 5>
A TFT was produced in the same manner as in Example 4 except that the oxygen concentration in the atmosphere during UV irradiation in the conversion step of Example 4 was changed as shown in Table 3 below, and the mobility was evaluated. The results are shown in Table 3 together with Example 4.

  High mobility was obtained when the oxygen concentration in the atmosphere during UV irradiation in the conversion step was 80000 ppm or less, but the mobility was low in Comparative Example 4 at 110000 ppm, and TFT characteristics were not exhibited in Comparative Example 5 at 200000 ppm.

The entire disclosure of Japanese Patent Application No. 2014-113319 is incorporated herein by reference.
All documents, patents, patent applications, and technical standards mentioned in this specification are specifically and individually described as individual documents, patents, patent applications, and technical standards are incorporated by reference. To the same extent, it is incorporated herein by reference.

Claims (9)

A coating step of forming a coating film by applying a solution containing a metal nitrate and a solvent on a substrate heated to a temperature equal to or higher than the boiling point of the solvent by an inkjet method;
A conversion step of converting the coating film into a metal oxide semiconductor film having a thickness of 10 nm or less by performing ultraviolet irradiation in an atmosphere having an oxygen concentration of 80000 ppm or less;
The manufacturing method of the metal oxide semiconductor film containing this. The method for producing a metal oxide semiconductor film according to claim 1, wherein the metal nitrate contains indium nitrate. The method for producing a metal oxide semiconductor film according to claim 1, wherein the solvent is methoxyethanol. The method for producing a metal oxide semiconductor film according to claim 1, wherein the solvent is methanol. The method for producing a metal oxide semiconductor film according to claim 1, wherein the ultraviolet light includes light having a wavelength of 300 nm or less. The method for producing a metal oxide semiconductor film according to claim 1, wherein in the conversion step, ultraviolet irradiation is performed in a state where the substrate is heated. The metal oxide semiconductor film according to any one of claims 1 to 6, further comprising a step of performing a surface treatment on a surface of the substrate on which the coating film is formed before the coating step. Production method. The method for producing a metal oxide semiconductor film according to claim 7, wherein an ultraviolet ozone treatment, an argon plasma treatment, or a nitrogen plasma treatment is performed as the surface treatment. A method for manufacturing a thin film transistor, including a step of forming an oxide semiconductor layer by forming a metal oxide semiconductor film by the method for manufacturing a metal oxide semiconductor film according to claim 1.