JP2010283190A - Thin film transistor and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transistor which is formed at low temperature in a short period of time through simple processes, has superior transistor characteristics, and also has high repetitive stability and temporal stability, and to provide a method of manufacturing the thin film transistor. <P>SOLUTION: The thin film transistor has, on a substrate, a gate electrode, a gate insulating layer, a source electrode-a drain electrode, and a semiconductor layer including an oxide semiconductor, wherein at least one of the gate electrode, and the source electrode-drain electrode are formed of a conductive film that is pattern-formed of a solution or fluid dispersion, and the gate insulating layer is formed on the conductive film by being applied thereon. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thin film transistor that can be formed by a simple process at a low temperature and has high mobility and high stability, and a manufacturing method thereof.

  A field effect thin film transistor (TFT) using a thin film made of amorphous silicon or the like on a glass substrate and using it as an active layer, and an active matrix circuit using these are well known.

  However, since TFTs using amorphous silicon have low carrier mobility and unstable characteristics during continuous driving, a stable thin film transistor with high carrier mobility is required for use in an organic EL active matrix circuit or the like. It has been.

  A TFT using a polysilicon thin film has been developed as a high-mobility TFT, but the manufacturing process is complicated, such as the need for laser annealing that requires high-precision control, and performance variations between elements are also a problem. It has become.

  A TFT using an organic semiconductor is well known as a TFT to which a simple manufacturing process can be applied. However, since the carrier mobility is low, the performance deterioration during continuous driving and the variation between elements are large, an organic EL active matrix circuit. It has been found that it is insufficient for use in, for example. In recent years, TFTs using metal oxide semiconductors have been actively developed as high-mobility TFTs that can be applied with simple manufacturing processes, have high stability during continuous driving, high carrier mobility, and little variation between elements. It has been broken.

  In particular, it has been found that an amorphous metal oxide having a composition of In—Ga—Zn—O is excellent as a semiconductor of a thin film transistor (see, for example, Patent Documents 1 to 3).

  Furthermore, a method for forming an oxide semiconductor layer by a solution process that can be easily formed at low temperature and under atmospheric pressure is also disclosed (see, for example, Patent Document 4).

  However, many of these methods require high-temperature baking at 400 ° C. or higher in order to function as a semiconductor, and it is difficult to say that these methods can be applied to resin substrates. Similarly, the gate insulating layer, which is one of the components of thin film transistors, is formed by vacuum processes such as sputtering and CVD, and high-temperature processes such as thermal oxidation and baking at high temperatures. At present, few thin film transistors that can be formed on a necessary resin substrate by a simple process and have excellent transistor performance have been disclosed.

  Incidentally, several methods for forming a gate insulating layer by a solution process that can be formed at low temperature and atmospheric pressure are known. For example, a method of forming a polymer film such as polyimide or polyvinylphenol from a precursor solution, a method of drying after coating from a dispersion of fine inorganic oxide particles, an alkoxide such as tetraethoxysilane, polysilazane, polymetalloxane, etc. There is a method of drying and baking after applying the oxide precursor solution.

  Since the polymer film has concerns about solvent resistance, insulation, hardness, and the like, an inorganic oxide film is preferable. However, in order to obtain a level of insulating characteristics applicable to the gate insulating layer of the thin film transistor, the dry film needs to be fired at a higher temperature.

  In recent years, a method for obtaining an inorganic oxide film having good insulation by low-temperature treatment using a coating material such as polysilazane has been known (for example, see Patent Documents 5 and 6).

  Usually, a silica insulating film formed by converting polysilazane does not complete the reaction even when subjected to a high temperature treatment at 450 ° C. or higher, for example, so that unreacted substances, intermediates, by-products, etc. remaining inside the insulating film are present. It causes deterioration of insulation characteristics. In particular, when this insulating film is used for a gate insulating layer of a thin film transistor, it has been found that transistor characteristics such as an increase in off-current and a decrease in mobility greatly affect transistor characteristics.

  In particular, when an oxide semiconductor as described above is used for a semiconductor layer of a thin film transistor, the adverse effect is large. Probably, in the case of an organic thin film transistor using an organic semiconductor, the formation of the semiconductor layer is usually performed near room temperature or at a low temperature of 100 ° C. or less. I think that a heat treatment process such as the above is necessary and that it may have an adverse effect.

  For example, in the case of an oxide semiconductor layer formed by sputtering, it remains in the insulating film at the time of post-baking, and in the case of an oxide semiconductor layer formed by using a coating material made of an oxide semiconductor precursor, at the time of conversion baking. Performance degradation due to diffusion of nitrogen and other by-products such as ammonia generated by the conversion reaction of unreacted polysilazane and by-products originally remaining in the insulating film into the semiconductor layer It is predicted that it is causing.

  Although it has been found that a method of converting polysilazane by UV ozone oxidation as disclosed in Patent Documents 5 and 6 can provide a silica film having good insulation properties, all the insulating films are made of silica. In order to convert it into a long period of time, at least 2 to 3 hours or more is required. In particular, a film having a high resistivity as disclosed in Patent Document 6 is obtained only with a thin film of 100 nm or less. First, it is difficult to say that it is a practical technique for use as a gate insulating layer of a thin film transistor.

  In the present invention, it is preferable to use a polymer film such as polyimide that can be formed in a short time and with a simple process, or a coating type insulating film obtained by UV ozone oxidation of polysilazane as a gate insulating film of a transistor. When a coating-type insulating film as described above is formed on an electrode patterned by general photolithography or the like, an electric field concentrates on the electrode end portion, so that electric discharge breakdown easily occurs and a stable element cannot be obtained. It has been found that a new problem arises.

  Increasing the thickness of the insulating film in order to avoid such discharge breakdown is not preferable because it increases costs and decreases mobility. Further, in order to form the electrode in a tapered shape, a complicated vacuum process such as photolithography or vapor deposition is required, which is not a preferable method.

  A method for solving such discharge breakdown by a simple process has not been disclosed so far.

JP 2006-165527 A JP 2006-165528 A JP 2007-73705 A JP 2001-244464 A International Publication No. 06/19157 Pamphlet JP 2001-159824 A

  The present invention has been made in view of the above-described problems and circumstances, and the solution to the problem is that it can be formed by a simple process at a low temperature for a short time, has excellent transistor characteristics, and has high repeatability and stability over time. A thin film transistor and a method for manufacturing the same are provided.

  The above object of the present invention is achieved by the following configurations.

  1. A thin film transistor having a gate electrode, a gate insulating layer, a source / drain electrode, and a semiconductor layer containing an oxide semiconductor on a substrate, wherein at least one of the gate electrode or the source / drain electrode is a solution or dispersion A thin film transistor comprising a conductive film patterned from a liquid, wherein the gate insulating layer is formed by coating on the conductive film.

  2. 2. The thin film transistor according to 1 above, comprising a gate electrode and a gate insulating layer in this order on the substrate.

  3. 3. The thin film transistor according to 1 or 2 above, wherein the oxide semiconductor includes at least an oxide of In, Zn, or Sn.

  4). 4. The thin film transistor according to any one of 1 to 3, wherein the oxide semiconductor includes at least an oxide of Ga or Al.

  5. 5. The thin film transistor according to any one of claims 1 to 4, wherein the semiconductor layer includes a film formed using a solution or dispersion containing a precursor of an oxide semiconductor.

  6). 6. The thin film transistor according to any one of 1 to 5, wherein the semiconductor layer includes a film formed by irradiating microwaves on a film obtained by applying a precursor of an oxide semiconductor.

  7). 7. The thin film transistor according to any one of 1 to 6, wherein the gate insulating layer is an inorganic film formed by converting a film formed from a precursor material.

  8). 8. The thin film transistor according to 7 above, wherein the precursor material is a solution or dispersion containing an inorganic polymer material.

  9. 9. The thin film transistor as described in 8 above, wherein the inorganic polymer material is polysilazane.

  10. The gate insulating layer is composed of a surface layer in contact with the semiconductor layer, and an inorganic insulating material layer having a composition or density different from that of the surface layer, and the surface layer is an inorganic material subjected to an oxidation treatment in the presence of oxygen. 10. The thin film transistor according to any one of 1 to 9, wherein the thin film transistor is a film.

  11. 11. The thin film transistor according to 10 above, wherein the oxidation treatment is performed by light irradiation in the presence of oxygen.

  12 12. The thin film transistor according to any one of 1 to 11, wherein an end shape of the gate electrode or the source electrode / drain electrode is a curved surface.

  13. 13. A method for producing a thin film transistor, comprising producing the thin film transistor according to any one of 1 to 12 above.

  By the above means of the present invention, it is possible to provide a thin film transistor that can be formed by a simple process at a low temperature for a short time, has excellent transistor characteristics, and has high repetitive stability and stability over time, and a method for manufacturing the same.

It is a figure which shows the typical element structure of the thin-film transistor element of this invention. It is a schematic equivalent circuit diagram showing an example of a thin film transistor sheet in which a plurality of thin film transistor elements are arranged. It is a cross-sectional schematic diagram explaining each process of thin-film transistor manufacture in embodiment.

  Hereinafter, the present invention will be described in detail.

  The present invention is a thin film transistor having a gate electrode, a gate insulating layer, a source electrode / drain electrode, and a semiconductor layer containing an oxide semiconductor on a substrate, wherein at least one of the gate electrode and the source electrode / drain electrode One is made of a conductive film patterned from a solution or a dispersion, and the gate insulating layer is formed by coating on the conductive film.

[Semiconductor layer]
The semiconductor layer according to the present invention preferably contains an oxide semiconductor.

  As an embodiment of the present invention, the oxide semiconductor is preferably an oxide semiconductor containing zinc or indium. In this case, the oxide semiconductor is preferably an oxide semiconductor containing any one of an oxide containing zinc and indium, an oxide containing zinc and gallium, or an oxide containing indium and gallium. The oxide semiconductor is more preferably an oxide semiconductor containing an oxide made of zinc, indium and gallium or an oxide made of indium and gallium.

  In this invention, it is preferable that the said semiconductor layer is an aspect comprised by the film | membrane formed by the solution process using the precursor of an oxide semiconductor. Moreover, it is preferable that the said semiconductor layer is an aspect comprised by the film | membrane formed by irradiating the film | membrane obtained by apply | coating the precursor of an oxide semiconductor with a microwave.

  Hereinafter, an oxide semiconductor that is a component of the semiconductor layer will be described in detail.

[Oxide semiconductor]
In the present invention, the oxide semiconductor is preferably formed from a solution or dispersion containing a precursor of an oxide semiconductor.

(Oxide semiconductor precursor)
In the present invention, a precursor of an oxide semiconductor is a material that is converted into a metal oxide semiconductor by heating or oxidative decomposition. Specific examples of the material include a metal atom-containing compound, and examples of the metal atom-containing compound include a metal salt containing a metal atom, a halogenated metal compound, and an organometallic compound.

  Metals of metal salts, halogen metal compounds, and organometallic compounds include Li, Be, B, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Cd, In, Ir, Sn, Sb, Cs, Ba, La, Hf, Ta, W, Tl, Pb, Bi, Ce, Pr Nd, Pm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the like.

  As metal salts, nitrates, sulfates, phosphates, carbonates, acetates or oxalates are preferred. Further, nitrates, acetates, etc. are used, and chlorides, iodides, bromides, etc. are suitably used as halogen metal compounds. be able to.

  Examples of the organometallic compound include those represented by the following general formula (I).

Formula (I) R ¹ _x MR ² _y R ³ _z
In the formula, M is a metal, R ¹ is an alkyl group, R ² is an alkoxy group, R ³ is a β-diketone complex group, a β-ketocarboxylic acid ester complex group, a β-ketocarboxylic acid complex group, and a ketooxy group (ketooxy complex group). X + y + z = m, x = 0 to m, or x = 0 to m−1, and y = 0 to m, z = 0. ~ M, each of which is 0 or a positive integer.

Examples of the alkyl group for R ¹ include a methyl group, an ethyl group, a propyl group, and a butyl group. Examples of the alkoxy group for R ² include a methoxy group, an ethoxy group, a propoxy group, a butoxy group, and a 3,3,3-trifluoropropoxy group. Moreover, what substituted the hydrogen atom of the alkyl group by the fluorine atom may be used.

Examples of the group selected from the β-diketone complex group, the β-ketocarboxylic acid ester complex group, the β-ketocarboxylic acid complex group, and the ketooxy group (ketooxy complex group) of R ³ include, for example, 2,4 -Pentanedione (also called acetylacetone or acetoacetone), 1,1,1,5,5,5-hexamethyl-2,4-pentanedione, 2,2,6,6-tetramethyl-3,5-heptanedione , 1,1,1-trifluoro-2,4-pentanedione, and the β-ketocarboxylic acid ester complex group includes, for example, acetoacetic acid methyl ester, acetoacetic acid ethyl ester, acetoacetic acid propyl ester, trimethyl Examples thereof include ethyl acetoacetate and methyl trifluoroacetoacetate. For example, acetoacetic acid, trimethylacetoacetic acid and the like can be mentioned, and examples of ketooxy include acetooxy group (or acetoxy group), propionyloxy group, butyryloxy group, acryloyloxy group, methacryloyloxy group and the like.

These groups preferably have 18 or less carbon atoms. Further, it may be linear or branched, or a hydrogen atom may be a fluorine atom. Among organometallic compounds, those having at least one oxygen in the molecule are preferable. As such, an organometallic compound containing at least one alkoxy group of R ² , a β-diketone complex group, a β-ketocarboxylic acid ester complex group, a β-ketocarboxylic acid complex group and a ketooxy group of R ³ ( Most preferred is a metal compound having at least one group selected from a ketooxy complex group.

  Of the metal salts, nitrate is preferred. Nitrate is easily available as a high-purity product and has high solubility in water, which is preferable as a medium for use. Examples of nitrates include indium nitrate, tin nitrate, zinc nitrate, and gallium nitrate.

  Of the above oxide semiconductor precursors, preferred are metal nitrates, metal halides, and alkoxides. Specific examples include indium nitrate, zinc nitrate, gallium nitrate, tin nitrate, aluminum nitrate, indium chloride, zinc chloride, tin chloride (divalent), tin chloride (tetravalent), gallium chloride, aluminum chloride, tri-i-. Examples include propoxyindium, diethoxyzinc, bis (dipivaloylmethanato) zinc, tetraethoxytin, tetra-i-propoxytin, tri-i-propoxygallium, and tri-i-propoxyaluminum.

  In particular, in the present invention, it is preferable to use a metal salt selected from nitrates, sulfates, phosphates, carbonates, acetates or oxalates as a precursor of the metal oxide semiconductor.

  In the present invention, by using a metal salt selected from nitrate, sulfate, phosphate, carbonate, acetate, or oxalate of the above metal as a precursor, the carrier mobility is high, and the TFT element is on / A metal oxide semiconductor having good characteristics with a large off ratio can be obtained.

  These metal salts have less energy of oxidation reaction, which is expected to include hydrolysis and dehydration reactions, compared to the use of other inorganic salts and organometallic compounds, and the decomposition products generated during the oxide formation process are more efficient. It is presumed that good semiconductor characteristics can be obtained because it is not easily left in the film because it is well vaporized and discharged, and there are few impurity components such as carbon present in the generated oxide.

  Among the above metal salts, nitrates are most preferable from the viewpoint of reducing impurities and improving semiconductor characteristics.

  The effect of improving the semiconductor properties obtained with metal salts, particularly nitrates, is particularly remarkable in an amorphous metal oxide semiconductor obtained at a heating temperature of 100 ° C. or higher and 400 ° C. or lower. It has not been known so far that a good state of an amorphous oxide semiconductor can be obtained by a semiconductor thin film using a metal salt as a raw material, which can be said to be a remarkable effect.

  Use of these salts is preferable because the irradiation time can be shortened when the semiconductor conversion process is performed with electromagnetic waves (microwaves) at a substantially low temperature.

(Method for depositing oxide semiconductor precursor thin film)
In order to form a thin film containing these metal oxide semiconductor precursors, a known film formation method, vacuum deposition method, molecular beam epitaxial growth method, ion cluster beam method, low energy ion beam method, ion plating method are used. The CVD method, the sputtering method, the atmospheric pressure plasma method, and the like can be used. In the present invention, a solution obtained by dissolving the above-described metal oxide semiconductor precursor in an appropriate solvent is used to coat the substrate. It is preferable that the productivity can be greatly improved.

  The solvent for dissolving the precursor of the metal oxide semiconductor is not particularly limited as long as it dissolves the metal compound in addition to water, but water, alcohols such as ethanol, propanol, and ethylene glycol, Ethers such as tetrahydrofuran and dioxane, esters such as methyl acetate and ethyl acetate, ketones such as acetone, methyl ethyl ketone and cyclohexanone, glycol ethers such as diethylene glycol monomethyl ether, acetonitrile, and further aromatic carbonization such as xylene and toluene Hydrogen solvents, aromatic solvents such as o-dichlorobenzene, nitrobenzene, m-cresol, aliphatic hydrocarbon solvents such as hexane, cyclohexane, tridecane, α-terpineol, chloroform, 1,2-dichloroethane, etc. Halogenated alkyl solvents, N- methylpyrrolidone, can be preferably used carbon disulfide and the like.

  Among these, water and lower alcohols are preferable from the viewpoint of solubility of metal salts and the like and drying properties after coating, and among these lower alcohols, methanol, ethanol, and propanol (1-propanol and isopropanol) are preferable from the viewpoint of drying properties. Moreover, a lower alcohol may be used alone as a solvent, or may be used by mixing with water at an arbitrary ratio. From the viewpoint of solubility, solution stability, and drying properties, it is preferable to prepare an “aqueous solution” according to the present invention by mixing water and these lower alcohols. It is preferable to prepare an aqueous solution by mixing a lower alcohol, since the surface tension can be lowered without causing a large change in composition, and the light emission is improved in inkjet coating or the like.

  The aqueous solution according to the present invention is a mixed solvent having a water content of 30% by mass or more in the solvent and water (water content = 100% by mass) and a solute (in the present invention, a metal salt and other necessary additions). It means a solution in which (additive) is dissolved. From the viewpoint of solubility of solutes such as metal salts and solution stability, the water content is preferably 50% by mass or more, more preferably 70% by mass or more.

  In addition, when considering semiconductor characteristics such as drying characteristics, inkjet emission characteristics, and thin film transistor characteristics, it is preferable to add a lower alcohol with a solvent ratio of 5% by mass or more, and satisfy any characteristics (drying, emission characteristics and solution stability). The water / lower alcohol ratio is preferably 5/5 to 95/5.

  Further, as an effect of adding alcohols, an effect of improving semiconductor characteristics is recognized. For example, improvement in characteristics such as mobility, on / off ratio, and threshold value of the thin film transistor is recognized. Although the cause of this effect is not clear, it is presumed that it has an influence on the oxide formation process by heating.

  When a metal halide and / or metal alkoxide is used, a solvent having a relatively high polarity is preferable. Among them, water having a boiling point of 100 ° C. or less, alcohols such as ethanol and propanol, acetonitrile, or a mixture thereof is used. Since the drying temperature can be lowered, it can be applied to the resin substrate, which is more preferable. In particular, the solvent preferably contains 50% by mass or more of water or alcohols.

  Addition of metal alkoxide and various ligands such as alkanolamine, α-hydroxyketone, β-diketone and other chelating ligands in the solvent stabilizes the metal alkoxide and increases the solubility of carboxylate. It is preferable to add in a range that can be increased and does not cause adverse effects.

  As a method of forming a thin film by applying a liquid containing a precursor material of an oxide semiconductor on a substrate, a spin coating method, a spray coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, Bar coat method, die coat method. Examples thereof include a mist method, a printing method such as a relief printing plate, an intaglio plate, a lithographic printing method, a screen printing method, and an ink jet printing method in a broad sense, and a method for patterning by this. The coating film may be patterned by photolithography, laser ablation, or the like. Among these, preferred are an ink jet method and a spray coat method which can apply a thin film.

  For example, when forming a film using the inkjet method, the metal salt solution is dropped and the solvent (water) is volatilized at about 80 to 150 ° C., thereby forming a semiconductor precursor layer thin film containing the metal salt. In addition, when dropping the solution, it is preferable that the substrate itself is heated to about 80 to 150 ° C. because two processes of coating and drying can be performed simultaneously and the film forming property of the precursor film is good.

  Moreover, the film thickness of the thin film containing the metal used as a precursor is 1-200 nm, More preferably, it is 5-100 nm.

(Composition ratio of metal)
As a preferable metal composition ratio, when the metal A is 1, the metal B composition ratio is 0.2 to 5, preferably 0.5 to 2, and the metal C is 0 to 5, preferably 0 to 2. It is. Metal A; In or Sn, metal B; Ga or Al metal C; Zn.

  Among these, it is preferable that either In (indium) or Zn (zinc) is included, and it is preferable that other metals include Ga (gallium). Specifically, an oxide semiconductor having an In—Ga—Zn—O composition (In: Ga: Zn = 1: 2: 1) or an In—Ga—O composition (In: Ga = 1: 1) is preferably used. .

(Amorphous oxide)
As the oxide semiconductor formed by thermal oxidation, any state of single crystal, polycrystal, and amorphous can be used, but an amorphous thin film is preferable.

The electron carrier concentration of an amorphous oxide, which is a metal oxide according to the present invention, formed from a metal compound material that becomes a precursor of an oxide semiconductor only needs to be less than 10 ¹⁸ / cm ³ .

The electron carrier concentration is a value when measured at room temperature. The room temperature is, for example, 25 ° C., specifically a temperature appropriately selected from a range of about 0 ° C. to 40 ° C. Note that the electron carrier concentration of the amorphous oxide according to the present invention does not need to satisfy less than 10 ¹⁸ / cm ³ in the entire range of 0 ° C. to 40 ° C. For example, a carrier electron density of less than 10 ¹⁸ / cm ³ may be realized at 25 ° C. Further, when the electron carrier concentration is further reduced to 10 ¹⁷ / cm ³ or less, more preferably 10 ¹⁶ / cm ³ or less, a normally-off thin film transistor can be obtained with a high yield.

  The electron carrier concentration can be measured by Hall effect measurement.

  The film thickness of the semiconductor that is a metal oxide is not particularly limited, but the characteristics of the obtained transistor are often greatly influenced by the film thickness of the semiconductor film, and the film thickness varies depending on the semiconductor, but is generally 1 μm or less. In particular, 10 to 300 nm is preferable.

In the present invention, the precursor material, composition ratio, production conditions, and the like are controlled so that, for example, the electron carrier concentration is 10 ¹² / cm ³ or more and less than 10 ¹⁸ / cm ³ . More preferably, it is in the range of 10 ¹³ / cm ³ or more and 10 ¹⁷ / cm ³ or less, more preferably 10 ¹⁵ / cm ³ or more and 10 ¹⁶ / cm ³ or less.

(Conversion from precursor to oxide semiconductor)
Examples of the semiconductor conversion treatment described above, that is, a method of converting a precursor thin film formed from a precursor material into a metal oxide semiconductor include an oxidation treatment such as an oxygen plasma method, a thermal oxidation method, and a UV ozone method. Moreover, the microwave irradiation mentioned later can be used.

  In the present invention, the temperature for heating the precursor material can be arbitrarily set within the range of the temperature of the thin film surface containing the precursor in the range of 50 to 1000 ° C., but from the viewpoint of the characteristics of the electronic device and the production efficiency, 100 It is preferable to set it to -400 degreeC.

  The temperature of the thin film surface, the temperature of the substrate, etc. can be measured by a surface thermometer using a thermocouple, a radiation thermometer capable of measuring the radiation temperature, a fiber thermometer, or the like. The heating temperature can be controlled by the output of electromagnetic waves, the irradiation time, and the number of irradiations. Moreover, although the time which heats precursor material can be set arbitrarily, the range of 1 second or more and 60 minutes or less is preferable from a viewpoint of the characteristic and production efficiency of an electronic device. More preferably, it is 5 to 30 minutes.

  Further, the semiconductor conversion treatment can be performed at a relatively low temperature by using a metal salt selected from nitrate, sulfate, phosphate, carbonate, acetate or oxalate.

  Further, the formation of the metal oxide can be detected by ESCA or the like, and the conditions under which the conversion to the semiconductor is sufficiently performed can be selected in advance.

  Further, it is preferable to use an atmospheric pressure plasma method as the oxygen plasma method. In the oxygen plasma method and the UV ozone method, the substrate is preferably heated in the range of 50 to 300 ° C.

  In the atmospheric pressure plasma method, an inert gas such as argon gas is used as a discharge gas under atmospheric pressure, and a reaction gas (a gas containing oxygen) is introduced into the discharge space, and a high frequency electric field is applied to the discharge gas. Is excited, is brought into contact with a reaction gas to generate a plasma containing oxygen, and the substrate surface is exposed to this to perform an oxygen plasma treatment. Under atmospheric pressure represents a pressure of 20 to 110 kPa, preferably 93 to 104 kPa.

  Using the atmospheric pressure plasma method, oxygen-containing gas is used as a reactive gas, oxygen plasma is generated, and the precursor thin film containing the metal salt is exposed to the plasma space to oxidize and decompose the precursor thin film by plasma oxidation. A layer of metal oxide is formed.

The high frequency power source is 0.5 kHz or more and 2.45 GHz or less, and the power supplied between the counter electrodes is preferably 0.1 W / cm ² or more and 50 W / cm ² or less.

  The gas used is basically a mixed gas of a discharge gas (inert gas) and a reaction gas (oxidizing gas). The reaction gas is preferably oxygen gas and is preferably contained in an amount of 0.01 to 10% by volume with respect to the mixed gas. Although it is more preferable that it is 0.1-10 volume%, More preferably, it is 0.1-5 volume%.

  Examples of the inert gas include Group 18 elements of the periodic table, specifically, helium, neon, argon, krypton, xenon, radon, nitrogen gas, and the like, in order to obtain the effects described in the present invention. For this, helium, argon, or nitrogen gas is preferably used.

  In order to introduce the reaction gas between the electrodes which are the discharge space, normal temperature and normal pressure may be used.

  The plasma method under atmospheric pressure is described in JP-A-11-61406, JP-A-11-133205, JP-A-2000-121804, JP-A-2000-147209, JP-A-2000-185362, and the like. .

  In addition, the UV ozone method is a method of irradiating ultraviolet light in the presence of oxygen to advance the oxidation reaction. It is preferable to irradiate so-called vacuum ultraviolet light having a wavelength of ultraviolet light of 100 to 450 nm, particularly preferably about 150 to 300 nm. As the light source, a low-pressure mercury lamp, a deuterium lamp, a xenon excimer lamp, a metal halide lamp, an excimer laser, or the like can be used.

The output of the lamp ^{400W~30kW, 100mW / cm 2 ~100kW /} cm 2 as illuminance, preferably 10~5000mJ / cm ² as irradiation energy, 100 to 2000 mJ / cm ² is more preferable.

The illuminance upon ultraviolet irradiation is preferably 1 mW / cm ^{2 to} 10 W / cm ² .

  In the present invention, it is preferable to perform a heat treatment after the oxidation treatment or simultaneously with the oxidation treatment in addition to the oxidation treatment. Thereby, oxidative decomposition can be promoted.

  Further, after oxidizing the thin film containing the precursor material, the base material is preferably heated in the range of 50 to 200 ° C., preferably 80 to 150 ° C., and the heating time in the range of 1 minute to 10 hours. .

  The heat treatment may be performed at the same time as the oxidation treatment, and can be rapidly converted into a metal oxide semiconductor by oxidation.

  After the conversion to a metal oxide semiconductor, the thickness of the formed semiconductor thin film is preferably 1 to 200 nm, more preferably 5 to 100 nm.

  In this invention, it is preferable that the process of microwave (0.3-50 GHz) irradiation is included as said semiconductor conversion process. In addition, it is preferable to irradiate microwaves in the presence of oxygen in order to advance the oxidation reaction of the metal oxide semiconductor precursor in a short time.

(Microwave irradiation)
In the present invention, it is preferable to use microwave irradiation as a method of converting a thin film formed from the metal inorganic salt material, which is a precursor of a metal oxide semiconductor, into a semiconductor.

  That is, after forming a thin film containing the metal salt material to be a precursor of these metal oxide semiconductors, the thin film is irradiated with electromagnetic waves, particularly microwaves (frequency: 0.3 to 50 GHz).

  By irradiating the thin film containing the metal salt material, which is the precursor of the metal oxide semiconductor, with microwaves, the electrons in the metal oxide precursor vibrate and heat is generated to uniformly heat the thin film from the inside. The Since substrates such as glass and resin have almost no absorption in the microwave region, the substrate itself hardly generates heat, and it is possible to selectively heat only the thin film portion and convert it to thermal oxidation or a metal oxide semiconductor. Become.

  In microwave heating, as is generally the case, microwave absorption concentrates on strongly absorbing substances, and it is possible to raise the temperature in a very short time. The material itself is hardly affected by heating by electromagnetic waves, and only the precursor thin film can be heated to a temperature at which an oxidation reaction occurs in a short time, and the metal oxide precursor can be converted into a metal oxide. Further, the heating temperature and the heating time can be controlled by the output of the microwave to be irradiated and the irradiation time, and can be adjusted according to the precursor material and the substrate material.

  Generally, a microwave refers to an electromagnetic wave having a frequency of 0.3 to 50 GHz, and is used in 0.8 GHz and 1.5 GHz bands, 2 GHz bands, amateur radio, aircraft radar, etc. used in mobile communication. .2 GHz band, microwave oven, local radio, 2.4 GHz band used for VICS, 3 GHz band used for ship radar, etc., and 5.6 GHz used for other ETC communications are all electromagnetic waves in the microwave category. is there. In addition, oscillators such as 28 GHz and 50 GHz are available on the market.

  Compared to a normal heating method using an oven or the like, a better metal oxide semiconductor layer can be obtained by using the heating method by electromagnetic wave (microwave) irradiation according to the present invention. In producing a metal oxide semiconductor from a metal oxide semiconductor precursor material, an effect other than conduction heat, for example, an effect suggesting direct action of electromagnetic waves on the metal oxide semiconductor precursor material is obtained. Although the mechanism has not been clarified sufficiently, it is presumed that the conversion of the metal oxide semiconductor precursor material into a metal oxide semiconductor by dehydration, decomposition, oxidation, or the like was promoted by electromagnetic waves.

  The method of performing semiconductor conversion treatment by irradiating the semiconductor precursor layer containing the metal salt with microwaves is a method of allowing the oxidation reaction to proceed selectively in a short time. Note that irradiation with microwaves in the presence of oxygen is preferable in order to advance the oxidation reaction of the metal oxide semiconductor precursor in a short time.

  However, heat is transferred to the base material not only by heat conduction, so in the case of a base material with low heat resistance such as a resin substrate, the precursor can be controlled by controlling the microwave output, the irradiation time, and the number of times of irradiation. It is preferable to process so that the surface temperature of the thin film containing a body may be 100 degreeC or more and less than 400 degreeC. The temperature of the thin film surface, the temperature of the substrate, and the like can be measured by a surface thermometer using a thermocouple or a non-contact surface thermometer.

  In addition, when a strong electromagnetic wave absorber such as ITO is present in the vicinity (for example, a gate electrode), this also absorbs microwaves and generates heat, so that the adjacent region can be heated in a shorter time. .

[Gate insulation layer]
In the present invention, the gate insulating layer is formed from a solution. However, the type of the gate insulating layer is not particularly limited as long as the material can be formed from a solution. Examples of the material for forming the gate insulating layer include inorganic oxides and organic compound films, but inorganic oxides are more preferable in terms of solvent resistance, insulation, hardness, and the like.

  Inorganic insulating materials for forming the gate insulating layer include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead titanate Examples include inorganic oxides such as lanthanum, strontium titanate, barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, and yttrium trioxide. Of these, silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide are preferable, and silicon oxide is most preferable.

  As a method of forming an inorganic oxide film from a solution, a method of applying and drying a liquid in which inorganic oxide fine particles are dispersed in an arbitrary organic solvent or water using a dispersion aid such as a surfactant as necessary. Alternatively, a so-called sol-gel method in which an oxide precursor, for example, an alkoxide body solution is applied and dried can be used. In the present invention, as these gate insulating layers, M-O-Si (M is A thin film of an inorganic polymer material such as polymetalloxane containing a (metal) bond or polysilazane containing a Si—N bond is formed by a coating method (in a broad sense), and this is subjected to heat treatment to produce silicon oxide and / or oxidation. What converted into the inorganic film | membrane which contains titanium as a main component is preferable.

  As an example of the polymetalloxane which is an inorganic polymer material, polysiloxane containing Si—O—Si bond in which M is Si, polytitanometalloxane containing Ti or the like, and the like can be given. These inorganic polymer materials, for example, polysilazane (perhydropolysilazane) are commercially available as AZ Electronic Materials Co., Ltd., Aquamica NP110, NN110, and the like.

  In addition, as the organic compound film, polyimide, polyamide, polyester, polyacrylate, photo radical polymerization type, photo cation polymerization type photo curable resin, copolymer containing acrylonitrile component, polyvinyl phenol, polyvinyl alcohol, novolac resin Etc. can also be used.

  The gate insulating layer is preferably composed of a surface layer in contact with the semiconductor layer and an inorganic insulating material layer having a composition or density different from that of the surface layer. The surface layer is subjected to light irradiation treatment or plasma irradiation in the presence of oxygen. More preferably, the inorganic film is treated.

  These film formation methods include spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, die coating, and other coating methods, and printing and inkjet patterning. Examples of the application process include a method.

  The thickness of these insulating films is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.

  Hereinafter, each component in the case where the gate insulating layer is composed of a surface layer in contact with the semiconductor layer and an inorganic insulating material layer having a composition or density different from the surface layer will be described.

(Surface layer of gate insulating layer)
As a preferred embodiment of the present invention, the surface layer constituting the surface of the gate insulating layer is made of an inorganic film that has been subjected to light irradiation treatment or plasma irradiation treatment in the presence of oxygen. In particular, it is preferable to form a precursor film using a coating material that can be formed as described above, and then convert it into an inorganic film by performing light irradiation treatment or plasma irradiation treatment in the presence of oxygen.

In the present invention, the surface layer is preferably an inorganic film having a high density (high density surface layer). The film density is preferably 2.2 g / cm ³ or more, and more preferably 2.3 g / cm ³ or more.

  It is more preferable to perform light irradiation treatment or plasma irradiation treatment in the presence of oxygen in combination with heat treatment. Specifically, it is preferable to perform oxidation treatment while heating the substrate in the range of 50 to 300 ° C.

  For the plasma irradiation treatment in the presence of oxygen in the present invention, the above-described atmospheric pressure plasma method is preferably used.

  In the present invention, the conversion reaction from the precursor film to the inorganic film is preferably subjected to light irradiation treatment in the presence of oxygen. The light in the light irradiation treatment in the presence of oxygen is more preferably ultraviolet light. By irradiating with ultraviolet light, ozone is generated and the oxidation reaction further proceeds. It is preferable to irradiate so-called vacuum ultraviolet light having a wavelength of ultraviolet light of 100 to 450 nm, particularly preferably about 150 to 300 nm.

As the light source, a low-pressure mercury lamp, a deuterium lamp, a xenon excimer lamp, a metal halide lamp, an excimer laser, or the like can be used. The output of the lamp ^{400W~30kW, 100mW / cm 2 ~100kW /} cm 2 as illuminance, preferably 10~5000mJ / cm ² as irradiation energy, 100 to 2000 mJ / cm ² is more preferable. The illuminance upon ultraviolet irradiation is preferably 1 mW / cm ^{2 to} 10 W / cm ² .

(Inorganic insulating material layer of gate insulating layer)
In the present invention, the inorganic insulating material layer constituting the gate insulating layer other than the surface layer is not particularly limited as long as it is an insulating layer made of an inorganic film, but is preferably made of an inorganic oxide film as described above. The inorganic insulating material layer may be formed by a vapor phase method such as sputtering, CVD, or vapor deposition, but the solution process as described above is more preferable.

(Measurement of film density)
In the present invention, the density of the gate insulating layer (surface layer, inorganic insulating material layer) can be determined by the X-ray reflectometry method as the film density.

  Specifically, the X-ray generation source targets copper and operates at 50 kV-300 mA. X-rays monochromatized with a multilayer mirror and a Ge (111) channel cut monochromator are used. The measurement was performed using the software ATX-Crystal Guide Ver. 6.5.3.4, halved, after alignment adjustment, 2θ / ω = 0 ° to 1 ° from 0.002 ° / step to 0.05 ° / min. Scan with. After measuring the reflectance curve under the above measurement conditions, GXRR Ver. It can be determined using 2.1.0.0 analysis software.

Moreover, it is preferable that the film density of the surface layer in this invention is 2.2 g / cm < ³ > or more. In general, the film density of a silicon oxide film obtained by thermally oxidizing a silicon wafer is about 2.2 g / cm ³ , and it can be said that the surface of the gate insulating layer according to the present invention has a density comparable to that of a thermal oxide film. .

(Measurement of elemental composition percentage)
In the present invention, the elemental composition of the gate insulating layer (surface layer, inorganic insulating material layer) can be determined by X-ray electron spectroscopy (XPS).

  In the present invention, the nitrogen atoms detected from the surface layer are preferably 10 at% or less, more preferably 5 at% or less, and most preferably 1 at% or less in terms of elemental composition percentage.

  Subsequently, an element structure of the thin film transistor will be described.

(Element structure)
FIG. 1 is a diagram showing a typical element configuration of a thin film transistor element using a metal oxide semiconductor according to the present invention.

  Several structural examples of thin film transistors are shown in cross-sectional views in FIGS. In FIG. 1, a source electrode 102 and a drain electrode 103 are connected to a semiconductor layer 101 made of a metal oxide semiconductor as a channel.

  FIG. 5A shows a bottom gate and top contact type. After forming a gate electrode 104 on a support 106, a gate insulating layer 105 is formed, a semiconductor layer 101 is formed thereon, and then a source electrode 102 is formed. And the drain electrode 103 is formed.

  FIG. 4B shows a bottom gate and top contact type, and the formation method is the same as that in FIG. 1A. In FIG. 1A, all of the gate electrode 104, the source electrode 102, and the drain electrode 103 are formed. Whereas the end shape is curved, only the gate electrode 104 has a curved end shape in FIG.

  FIG. 4C shows a bottom gate and bottom contact type. After forming a gate electrode 104 on a support 106, a gate insulating layer 105 is formed, and a source electrode 102 and a drain electrode 103 are formed thereon, A semiconductor layer 101 is formed between the electrodes.

  FIG. 4D shows a top gate, top contact type. First, a semiconductor layer 101 is formed on a support 106, and then a source electrode 102, a drain electrode 103, and an insulating layer 105 are formed, and then a gate electrode 104. Form.

  FIG. 4E shows a top gate / bottom contact type, in which a source electrode 102 and a drain electrode 103 are formed on a support 106, a semiconductor layer 101 is formed between the electrodes, and then a gate insulating layer 105 is formed. Then, the gate electrode 104 is formed.

  Note that, except for the source electrode 102 and the drain electrode 103 in FIG. 5B, the end shapes of all the other gate electrodes 104, the source electrode 102, and the drain electrode 103 are curved.

  FIG. 2 is a schematic equivalent circuit diagram showing an example of a thin film transistor sheet in which a plurality of thin film transistor elements are arranged.

  The thin film transistor sheet 120 includes a large number of thin film transistor elements 124 arranged in a matrix. 121 is a gate bus line of the gate electrode of each thin film transistor element 124, and 122 is a source bus line of the source electrode of each thin film transistor element 124.

  An output element 126 is connected to the drain electrode of each thin film transistor element 124. The output element 126 is, for example, a liquid crystal or an electrophoretic element, and constitutes a pixel in the display device. In the illustrated example, the output element 126 is shown by an equivalent circuit in which liquid crystal is composed of a resistor and a capacitor. Reference numeral 125 denotes a storage capacitor, 127 denotes a vertical drive circuit, and 128 denotes a horizontal drive circuit. The present invention can be used to manufacture the source, drain electrode, gate electrode, and the like of each transistor element in the thin film transistor sheet 120, as well as the gate bus line, source bus line, and circuit wiring.

  Next, other elements constituting the thin film transistor will be described below.

〔electrode〕
In the present invention, the conductive material used for the electrodes such as the source electrode, the drain electrode, and the gate electrode constituting the TFT element is not particularly limited as long as it has conductivity at a practical level as an electrode. , Gold, silver, nickel, chromium, copper, iron, tin, lead antimony, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, and also, for example, antimony tin oxide, oxide Electrode materials with electromagnetic wave absorbing ability such as indium tin (ITO), fluorine-doped zinc oxide, zinc, carbon, graphite, glassy carbon, silver paste and carbon paste, lithium, beryllium, sodium, magnesium, potassium, calcium, scandium, Titanium, manganese, Luconium, gallium, niobium, sodium, sodium-potassium alloy, magnesium, lithium, aluminum, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide mixture, lithium / aluminum mixture, etc. Is used.

  Moreover, a conductive polymer, metal microparticles, etc. can be used suitably as a conductive material.

  For example, a known conductive paste may be used as the dispersion containing the metal fine particles, but the dispersion preferably contains metal fine particles having a particle diameter of 1 to 50 nm, preferably 1 to 10 nm. In order to form an electrode from metal fine particles, the above-described method can be used in the same manner, and the metal described above can be used as the material of the metal fine particles.

(Method for forming electrodes, etc.)
As a method for forming an electrode, a method for forming the electrode by using a method such as vapor deposition or sputtering through a mask using the above as a raw material, or forming a conductive thin film formed by a method such as vapor deposition or sputtering using a known photolithography method or lift-off method. There are a method of forming an electrode using a method, and a method of forming a resist on a metal foil such as aluminum or copper by thermal transfer, ink jet or the like and etching.

  Alternatively, a conductive polymer solution or dispersion, a dispersion containing metal fine particles, or the like may be directly patterned by an ink jet method, or may be formed from a coating film by lithography, laser ablation, or the like. Further, a method of patterning a conductive ink or conductive paste containing a conductive polymer or metal fine particles by a printing method such as relief printing, intaglio printing, planographic printing or screen printing can also be used.

  Further, as a method of forming a source, drain, gate electrode, etc., and a gate bus line, source bus line, etc. without patterning a metal thin film using a photosensitive resin such as etching or lift-off, a method by an electroless plating method It has been known.

  Regarding the method of forming an electrode by electroless plating, as described in Japanese Patent Application Laid-Open No. 2004-158805, a liquid containing a plating catalyst that causes electroless plating by acting with a plating agent on a portion where an electrode is provided After patterning, for example, by a printing method (including ink jet printing), a plating agent is brought into contact with a portion where an electrode is provided. Then, electroless plating is performed by contact between the catalyst and the plating agent, and an electrode pattern is formed.

  The application of the electroless plating catalyst and the plating agent may be reversed, and the pattern formation may be performed by either method, but a method of forming a plating catalyst pattern and applying the plating agent to this is preferable.

  As the printing method, for example, screen printing, lithographic printing, letterpress printing, intaglio printing, ink jet printing, or the like is used.

  The electrode material of the source or drain electrode and the formation method according to the present invention are preferably formed using a fluid electrode material that can be easily formed by a wet process such as coating or printing.

  As the fluid electrode material, a known conductive paste or the like may be used, but a metal fine particle dispersion having an average particle size of 1 to 300 nm is preferable, and among them, a particle size of 1 to 50 nm, preferably 1 to 10 nm is preferable. Examples thereof include a metal nanoparticle dispersion liquid that is a dispersion containing metal particles. Moreover, a conductive polymer solution, a dispersion liquid, etc. can be used suitably.

  As a method for producing such a dispersion of metal fine particles, metal ions are reduced in a liquid phase, such as a physical generation method such as gas evaporation method, sputtering method, and metal vapor synthesis method, colloid method, and coprecipitation method. Examples of the chemical production method for producing metal fine particles include those described in JP-A-11-76800, JP-A-11-80647, JP-A-11-319538, JP-A-2000-239853, and the like. The colloid method described in Japanese Patent Application Laid-Open No. 2001-254185, 2001-53028, 2001-35255, 2000-124157, 2000-123634, and Japanese Patent No. 2561537. It is a dispersion of fine metal particles produced by a gas evaporation method.

  A method of applying a conductive ink or conductive paste containing a conductive polymer or metal fine particles by a printing method such as relief printing, intaglio printing, planographic printing, or screen printing can be used.

  After being applied on the substrate by printing or the like, by performing a baking treatment at a temperature of 150 to 450 ° C., fusion proceeds and a low resistance electrode is obtained.

〔substrate〕
Various materials can be used as the material constituting the substrate, for example, ceramic substrates such as glass, quartz, aluminum oxide, sapphire, silicon nitride, silicon carbide, silicon, germanium, gallium arsenide, gallium phosphide, gallium. A semiconductor substrate such as nitrogen, paper, non-woven fabric and the like can be used. In the present invention, the substrate (support) is preferably made of a resin, and for example, a resin (plastic) film sheet can be used.

  Examples of the resin (plastic) film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide (PPS), polyarylate, polyimide ( Examples thereof include films made of PI), polyamideimide (PAI), polycarbonate (PC), cellulose triacetate (TAC), cellulose acetate propionate (CAP), and the like. By using a resin (plastic film), the weight can be reduced as compared with the case of using a glass substrate, and the portability can be improved and the resistance to impact can be improved.

  In addition, an element protective layer can be provided on the thin film transistor element of the present invention. Examples of the protective layer include the inorganic oxides and inorganic nitrides described above, and it is preferable to form the protective layer by the atmospheric pressure plasma method described above.

  Hereinafter, embodiments of the method for manufacturing a thin film transistor of the present invention will be described in detail.

Example 1
<< Production of Thin Film Transistor Element 1 >>
Each step of manufacturing a thin film transistor in a preferred embodiment of the present invention will be described with reference to a schematic cross-sectional view of FIG.

A polyimide film (200 μm) was used as the support 301, and a corona discharge treatment was first performed on the polyimide film under the condition of 50 W / m ² / min. Thereafter, an undercoat layer was formed in order to improve adhesion as follows.

(Formation of undercoat layer)
A coating solution having the following composition was applied to a dry film thickness of 2 μm, dried at 90 ° C. for 5 minutes, and then cured for 4 seconds from a distance of 10 cm under a 60 W / cm high-pressure mercury lamp.

Dipentaerythritol hexaacrylate monomer 60g
Dipentaerythritol hexaacrylate dimer 20g
Dipentaerythritol hexaacrylate trimer or higher component 20g
Diethoxybenzophenone UV initiator 2g
Silicone surfactant 1g
75g of methyl ethyl ketone
Methyl propylene glycol 75g
Further, a silicon oxide film having a thickness of 50 nm was formed on the layer by continuous atmospheric pressure plasma treatment under the following conditions, and these layers were used as an undercoat layer (barrier layer) 310 (FIG. 3 (1)). . In addition, the atmospheric pressure plasma processing apparatus used the apparatus according to FIG. 6 as described in Unexamined-Japanese-Patent No. 2003-303520.

(Used gas)
Inert gas: helium 98.25% by volume
Reactive gas: oxygen gas 1.5 volume%
Reactive gas: Tetraethoxysilane vapor (bubbled with helium gas) 0.25% by volume
(Discharge conditions)
High frequency power supply: 13.56 MHz
Discharge output: 10 W / cm ² .

(Electrode condition)
The electrode is coated with 1 mm of alumina by ceramic spraying on a stainless steel jacket roll base material having cooling means with cooling water, and then a solution obtained by diluting tetramethoxysilane with ethyl acetate is applied and dried, and then sealed by ultraviolet irradiation. This is a roll electrode having a dielectric (relative permittivity of 10) that has been subjected to hole treatment and has a smooth surface and an Rmax of 5 μm, and is grounded. On the other hand, as the application electrode, a hollow square stainless steel pipe was covered with the same dielectric as described above under the same conditions.

[Formation of gate electrode]
Next, a silver fine particle dispersion (CCI-300 manufactured by Cabot (silver content 20% by mass)) was ejected from a piezo-type inkjet head, and printing was performed. Next, heat treatment was performed at 200 ° C. for 30 minutes to form the gate electrode 302 (FIG. 3A).

[Formation of gate insulating layer]
Aquamica NN110-20 (perhydropolysilazane, 10% by mass xylene solution, manufactured by AZ Electronic Materials Co., Ltd.) was applied on the support on which the gate electrode was formed by spin coating (2000 rpm × 30 sec), and dried. A precursor layer was formed. Next, by performing UV ozone oxidation treatment at 200 ° C. for 30 minutes, 20 nm from the surface is made of a silicon oxide film (surface layer) converted from polysilazane, and its lower layer 180 nm is from an inorganic insulating material layer containing unconverted products. A gate insulating layer (200 nm in total) was formed (FIG. 3 (2)).

  When the element composition analysis in the film thickness direction was performed by XPS on the gate insulating film produced here, the element composition percentage detected at the position of 20 nm in the depth direction from the surface layer was Si = 33.2 at%, O = 64.5 at%, N = 2.3 at%. On the other hand, the element composition percentages detected at a position of 150 nm in the depth direction from the surface layer were Si = 45.7 at%, O = 26.3 at%, and N = 27.9 at%.

Further, the film density of the surface layer portion determined by X-ray reflectometry is 2.3 g / cm ^3, the film density of the inner layer obtained by etching a surface portion (near the substrate surface) is 1.5 g / cm ³ met It was.

[Formation of semiconductor layer]
The support is heated to 100 ° C. using ink as a 10 mass% water / ethanol (9/1) solution in which indium nitrate, zinc nitrate, and gallium nitrate are mixed at a metal ratio of 1: 1: 1 (molar ratio). In this state, the ink was ejected by the ink jet device to form a semiconductor precursor material thin film 306 ′ (FIG. 3 (3)).

  Subsequently, the polyimide support was attached to the ITO film side of the glass substrate on which a 110 nm-thick ITO film was formed on one side by sputtering so that the back surface side (side on which the semiconductor layer was not formed) was in close contact. (Not shown). Next, microwave irradiation was performed from the back side of the glass substrate. That is, treatment was performed at 200 ° C. for 20 minutes by irradiating with microwaves (2.45 GHz) at an output of 500 W under an atmospheric pressure condition where the partial pressure of oxygen and nitrogen was 1: 1.

  The precursor material was converted to an oxide semiconductor by heat generation by microwave absorption of the ITO film on the glass substrate, and an oxide semiconductor layer 306 was formed on the gate insulating film so as to face the gate electrode (FIG. 3 (4)). ). After forming the oxide semiconductor layer by microwave irradiation, the glass substrate described above was peeled from the polyimide support.

[Formation of source electrode and drain electrode]
Next, a silver fine particle dispersion (CCI-300 manufactured by Cabot (silver content 20 mass%)) was ejected from a piezo-type inkjet head, and printing was performed on the source and drain electrode portions including the exposed regions of the semiconductor layer. . Next, heat treatment was performed at 200 ° C. for 30 minutes to form a source electrode 304 and a drain electrode 305 (FIG. 3 (5)). Each size was 40 μm wide, 100 μm long (channel width), and 100 nm thick, and the distance (channel length) between the source electrode 304 and the drain electrode 305 was 20 μm.

<< Production of Thin Film Transistor Element 2 >>
In the production of the thin film transistor element 1, a thin film transistor element 2 was produced in the same manner except that the source electrode and the drain electrode were formed as follows.

[Formation of source electrode and drain electrode]
An aluminum film having a thickness of 100 nm was formed on one surface by sputtering, and then etched by photolithography to form patterned source and drain electrodes.

<< Production of Thin Film Transistor Element 3 >>
A thin film transistor element 3 was produced in the same manner as in the production of the thin film transistor element 1 except that the gate insulating layer was formed as follows.

[Formation of gate insulating layer]
A 1% by mass N-methylpyrrolidone solution of a polyimide precursor compound (manufactured by Kyocera Chemical Co., Ltd., CT4112) is applied onto a substrate on which a gate electrode is formed by spin coating, and then heated at 180 ° C. for 30 minutes to form a gate insulating layer. Formed.

<< Production of Thin Film Transistor Element 4 >>
In the manufacture of the thin film transistor element 1, after forming a gate insulating layer, a source electrode and a drain electrode were formed, and further a semiconductor layer was formed, whereby a thin film transistor element 4 was manufactured.

<< Production of Thin Film Transistor Element 5 >>
In the production of the thin film transistor element 1, a thin film transistor element 5 was produced in the same manner except that the semiconductor layer was formed as follows.

[Formation of semiconductor layer]
Subsequently, a semiconductor layer was formed by a sputtering method. A composite oxide (IGZO) with an In: Ga: Zn composition ratio of 1: 1: 1 was used as a sputtering target, and a film was formed by a DC magnetron type sputtering apparatus. For patterning, a normal photolithography etching method was used, and for the etchant, a commercially available product for ITO was used. The average thickness of the formed oxide semiconductor layer 306 (FIG. 3D) was 30 nm.

<< Production of Thin Film Transistor Element 6 >>
A thin film transistor element 6 was produced in the same manner except that the semiconductor layer was formed as follows in the production of the thin film transistor element 1.

[Formation of semiconductor layer]
The support is heated to 100 ° C. using ink as a 10 mass% water / ethanol (9/1) solution in which indium nitrate and gallium nitrate are mixed at a metal ratio of 1: 0.5 (molar ratio). In this state, the ink was ejected by the ink jet device to form a semiconductor precursor material thin film 306 ′ (FIG. 3 (3)).

<< Production of Thin Film Transistor Element 7 >>
In the production of the thin film transistor element 1, after forming the undercoat layer, the semiconductor layer, the source / drain electrodes, the gate insulating layer, and the gate electrode were formed in this order, and the thin film transistor element 7 was produced.

<< Production of Thin Film Transistor Element 8 >>
In the fabrication of the thin film transistor element 1, after forming the undercoat layer, the source / drain electrodes, the semiconductor layer, the gate insulating layer, and the gate electrode were formed in this order, and the thin film transistor element 8 was fabricated.

<< Production of Thin Film Transistor Element 9 (Comparative) >>
A thin film transistor element 9 was produced in the same manner except that the gate electrode was formed as follows in the production of the thin film transistor element 1.

[Formation of gate electrode]
An aluminum film having a thickness of 200 nm was formed on one surface by sputtering, and then etched by photolithography to form a patterned gate electrode.

<< Production of Thin Film Transistor Element 10 (Comparison) >>
A thin film transistor element 10 was produced in the same manner as in the production of the thin film transistor element 7 except that the source electrode and the drain electrode were formed by the patterning method by sputtering and photolithography described in the thin film transistor element 2.

[Evaluation of thin film transistor element]
With respect to the thin film transistor element manufactured above, as a transistor performance, mobility (cm ² / Vs) from a saturation region in an increase (transfer characteristic) of drain current when a drain bias is +10 V and a gate bias is swept from −10 V to +40 V. ) Was estimated and the on / off ratio was evaluated. Further, the threshold voltage Vth (V) was obtained. These are all averages for 10 elements.

  Furthermore, each transistor characteristic after 20 times continuous drive was also evaluated. The results are shown in Table 1.

  From these results, the comparative thin film transistor elements 9 and 10 in which the gate electrode or the source electrode / drain electrode (SD electrode) is patterned by photolithography and then the gate insulating film is formed by coating have no problem in the initial characteristics. It has been found that, when continuously driven repeatedly, discharge breakdown occurs, and a stable element cannot be obtained.

  When the cross-sectional profile of the thin film transistor elements 9 and 10 was observed with an SEM (scanning electron microscope), the end portion of the gate electrode in the thin film transistor element 9 and the end portion of the source / drain electrode (SD electrode) in the thin film transistor element 10 were almost It was confirmed that it was a right angle.

  On the other hand, the thin film transistor element of the present invention, which has a gate electrode or a source / drain electrode (SD electrode) formed by a solution process and has a gate insulating layer formed by coating, has both repeated stability and stability over time. It turned out to be very good. This is because the gate electrode formed by the solution process according to the present invention, or the end shape of the source electrode / drain electrode (SD electrode) is curved (confirmed from the cross-sectional profile by SEM), so that an electric field is applied to the gate electrode. Even if this is continued, the concentration of the electric field at the end of the electrode film is hindered, so that the discharge breakdown does not occur, and it is considered that a stable element is obtained.

DESCRIPTION OF SYMBOLS 101 Semiconductor layer 102 Sort electrode 103 Drain electrode 104 Gate electrode 105 Gate insulating layer 301 Support body 302 Gate electrode 303 Gate insulating film 304 Source electrode 305 Drain electrode 306 Oxide semiconductor layer 306 ′ Precursor material thin film

Claims (13)

  A thin film transistor having a gate electrode, a gate insulating layer, a source / drain electrode, and a semiconductor layer containing an oxide semiconductor on a substrate, wherein at least one of the gate electrode or the source / drain electrode is a solution or dispersion A thin film transistor comprising a conductive film patterned from a liquid, wherein the gate insulating layer is formed by coating on the conductive film.   2. The thin film transistor according to claim 1, further comprising a gate electrode and a gate insulating layer in this order on the substrate.   3. The thin film transistor according to claim 1, wherein the oxide semiconductor includes an oxide of at least one of In, Zn, and Sn.   The thin film transistor according to claim 1, wherein the oxide semiconductor includes at least an oxide of Ga or Al.   5. The thin film transistor according to claim 1, wherein the semiconductor layer includes a film formed using a solution or dispersion containing a precursor of an oxide semiconductor.   The thin film transistor according to claim 1, wherein the semiconductor layer includes a film formed by irradiating a film obtained by applying a precursor of an oxide semiconductor with microwaves. .   The thin film transistor according to claim 1, wherein the gate insulating layer is an inorganic film formed by converting a film formed from a precursor material.   The thin film transistor according to claim 7, wherein the precursor material is a solution or dispersion containing an inorganic polymer material.   9. The thin film transistor according to claim 8, wherein the inorganic polymer material is polysilazane.   The gate insulating layer is composed of a surface layer in contact with the semiconductor layer, and an inorganic insulating material layer having a composition or density different from that of the surface layer, and the surface layer is an inorganic material subjected to an oxidation treatment in the presence of oxygen. The thin film transistor according to claim 1, wherein the thin film transistor is a film.   The thin film transistor according to claim 10, wherein the oxidation treatment is performed by light irradiation in the presence of oxygen.   The thin film transistor according to claim 1, wherein an end shape of the gate electrode or the source electrode / drain electrode is a curved surface.   A method for producing a thin film transistor, comprising producing the thin film transistor according to claim 1.

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