JP2011009518A - Thin-film transistor, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve performance and production efficiency of a reduced thin-film transistor, and to reduce dispersion of characteristics due to it.SOLUTION: In this thin-film transistor including, on a substrate, a gate electrode, a gate insulating film and an oxide semiconductor thin film, at least a portion of the gate insulating film is an anodized film.

Description

  The present invention relates to a thin film transistor in which stability of semiconductor characteristics is improved and production efficiency is improved, and a manufacturing method thereof.

  A technique of a thin film transistor using an oxide semiconductor is disclosed (for example, Patent Documents 1 to 3 and Non-Patent Document 1). These thin film transistors have a gate insulating film formed mainly using a plasma CVD method. However, in the case of an insulating film formed by these methods, the carrier mobility of the thin film transistor is not sufficient. There are problems such as a large off current and a small on / off ratio.

  The present invention greatly improves these characteristics.

JP 2006-165527 A JP 2006-165528 A JP 2007-73735 A

IDW'07 (International Display Workshop 2007) p1783

  Accordingly, an object of the present invention is to improve the performance of the reduced thin film transistor and improve the production efficiency, and to reduce variation in characteristics due to this.

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

  1. A thin film transistor having a gate electrode, a gate insulating film, and an oxide semiconductor thin film on a substrate, wherein at least a part of the gate insulating film is an anodized film, and an insulating layer is provided at an end of the gate electrode A thin film transistor characterized by the above.

  2. 2. The thin film transistor according to 1 above, wherein an insulating layer is provided between the anodic oxide film and the oxide semiconductor thin film.

  3. 3. The thin film transistor according to 1 or 2 above, wherein the oxide semiconductor thin film is formed from a coating solution of a precursor solution or dispersion.

  4). 4. The thin film transistor according to 3 above, wherein the precursor includes one or more metal salts selected from metal nitrates, sulfates, phosphates, carbonates, acetates or oxalates.

  5. 5. The thin film transistor according to 4 above, wherein the metal salt contains at least a salt of In, Zn, or Sn.

  6). 6. The thin film transistor according to 4 or 5 above, wherein the metal salt contains at least a salt of Ga or Al.

  7. 7. The thin film transistor according to any one of 4 to 6, wherein the metal salt is a nitrate.

  8). 8. The thin film transistor according to any one of 1 to 7, wherein the oxide semiconductor thin film is made of an amorphous semiconductor.

  9. 9. A method for producing a thin film transistor, comprising producing the thin film transistor according to any one of 1 to 8 above.

  According to the present invention, the characteristics of the thin film transistor are improved, and improvement in production efficiency and reduction in variation in characteristics are achieved.

It is a cross-sectional schematic diagram which shows formation of the anodic oxide film of a gate electrode. It is a cross-sectional schematic diagram which shows each process about preparation of the thin-film transistor of this invention.

  Hereinafter, although the form for implementing this invention is demonstrated, this invention is not limited by this.

  The present invention is a thin film transistor having a gate electrode, a gate insulating film, and an oxide semiconductor thin film on a substrate, wherein at least a part of the gate insulating film is an anodic oxide film.

  These anodic oxide films are formed by anodic oxidation of a gate electrode metal material.

  The metal material is not particularly limited as long as it has conductivity at a practical level as an electrode and can be anodized. Nickel, chromium, copper, iron, tin, antimony lead, tantalum, indium, palladium, tellurium Aluminum, ruthenium, germanium, molybdenum, tungsten, antimony, zinc, magnesium / aluminum mixture, aluminum / aluminum oxide mixture, lithium / aluminum mixture and the like are used. Among them, preferable metals are aluminum, molybdenum, tantalum and the like, and particularly preferable metal is aluminum.

  The anodization can be performed by using an anodizing apparatus equipped with an electrolytic cell and means for supplying electricity to the electrolytic cell.

This anodizing treatment is described in US Pat. No. 1,412,768, a method of electrolyzing an aqueous solution containing sulfuric acid at a concentration of 10 to 50% as an electrolytic solution at a current density of 1 to 50 A / dm ² . Method of electrolysis at high current density in sulfuric acid, method of electrolysis using phosphoric acid described in JP 3,511,661, solution containing one or more kinds of chromic acid, oxalic acid, malonic acid, etc. And the like.

  Preferred examples of the metal that can be anodized include aluminum and tantalum, and the anodizing method is not particularly limited, and the known methods can be used. By performing the anodizing treatment, a metal oxide film is formed on the surface of the gate electrode formed on the substrate with these metal materials.

Any electrolyte solution that can form a metal oxide film can be used as the anodizing treatment. Generally, sulfuric acid, phosphoric acid, oxalic acid, chromic acid, boric acid, sulfamic acid, benzenesulfone, and the like can be used. An acid or the like, a mixed acid obtained by combining two or more of these, or a salt thereof can be used. The treatment conditions for anodization vary depending on the electrolyte used, and thus cannot be specified in general. In general, the electrolyte concentration is 1 to 80% by mass, the electrolyte temperature is 5 to 70 ° C., and the current density. A range of 0.5 to 60 A / dm ² , a voltage of 1 to 100 volts, and an electrolysis time of 10 seconds to 5 minutes is appropriate. A preferred anodizing treatment is a method in which an aqueous solution of sulfuric acid, phosphoric acid or boric acid is used as the electrolytic solution and the treatment is performed with a direct current, but an alternating current can also be used. The concentration of these acids is preferably 5 to 45% by mass, and is preferably subjected to electrolytic treatment at an electrolyte temperature of 20 to 50 ° C. and a current density of 0.5 to 20 A / dm ² for ²⁰ to 250 seconds.

  The formed anodic oxidation coating amount is 10 nm to 500 nm in terms of film thickness. The amount of anodic oxidation coating is, for example, immersed in a chromic phosphate solution (85% phosphoric acid solution: 35 ml, prepared by dissolving 20 g of chromium (IV) oxide in 1 L of water), dissolving the oxide film, and dissolving the coating of the plate It is obtained from the mass change measurement before and after.

  As the material of the anode, Ti mesh, platinum mesh or the like is used. Moreover, carbon or aluminum can be used as the material of the cathode.

  A method for forming an insulating film from an electrode metal by anodic oxidation is an efficient method for forming a gate insulating film, and a gate electrode can be formed together with the gate insulating film by patterning after anodic oxidation. The gate insulating film formed by anodic oxidation of the gate electrode seems to be because the interface with the electrode is uniform, but it constitutes a thin film transistor with high mobility and good performance.

  It is preferable to provide a separate insulating layer on the anodized film.

  As a result, a gate insulating film having a smooth surface and better characteristics can be obtained.

  The insulating layer formed on the anodized film is not limited, but an inorganic oxide film having a high relative dielectric constant is preferable. Inorganic oxides include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead lanthanum titanate, strontium titanate, Examples thereof include 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. Inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.

  These inorganic oxide film formation methods include vacuum deposition, molecular beam epitaxy, ion cluster beam, low energy ion beam, ion plating, CVD, sputtering, atmospheric pressure plasma, and other dry processes. And wet processes such as spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, die coating, and other methods such as printing and inkjet patterning. Can be used depending on the material.

  The wet process is a method of applying and drying a liquid in which fine particles of inorganic oxide are dispersed in an arbitrary organic solvent or water using a dispersion aid such as a surfactant as required, or an oxide precursor, for example, A so-called sol-gel method in which a solution of an alkoxide body is applied and dried is used. In addition, for example, Aquamica NN110 (perhydropolysilazane / xylene solution: manufactured by AZ Electronic Materials) can be used as a solvent system.

  Of these, the atmospheric pressure plasma method is preferred.

  Inorganic oxides such as silicon oxide and aluminum oxide formed by the atmospheric pressure plasma method are particularly preferable.

  In addition, as an organic compound film, polyimide, polyamide, polyester, polyacrylate, photo radical polymerization type, photo cation polymerization type photo curable resin, or a copolymer containing an acrylonitrile component, polyvinyl phenol, polyvinyl alcohol, novolac resin, Resins such as silicone rubber can also be used.

  The inorganic oxide film and the organic oxide film can be laminated and used together. The thickness of these insulating layers is generally 10 nm to 3 μm, preferably 20 nm to 1 μm.

  Due to the formation of the insulating layer, the insulating layer material enters the minute irregularities on the surface of the anodized film formed by anodic oxidation of the electrode material, and fills this, so that the film interface is closely joined, smooth surface protrusions, etc. Since a uniform insulating film is obtained, when this is used as a gate insulating layer, when a semiconductor thin film is formed in a thin film transistor or when an electrode is formed on the insulating film, the process resistance is further improved and the film is stable. It is considered that a thin film transistor having performance can be manufactured.

  In the case where the gate insulating layer including the anodic oxide film is used, it is preferable to form the insulating layer at the end portion of the gate electrode.

  An anodization can efficiently form an insulating layer on the metal electrode layer. However, after anodization, it is necessary to pattern a gate electrode with an anodized film to form a gate electrode or a gate bus line pattern. Therefore, it is necessary to pattern a metal thin film on which an anodized metal oxide film is formed after anodization.

  For example, a method using a known photolithography method or a lift-off method, a method of forming and etching a resist, laser ablation, dry etching using plasma or the like can be used.

  These anodic oxide films are preferably patterned together with electrodes after forming a gate electrode pattern. Anodization may be performed after the gate electrode pattern is formed, but it is inefficient to individually anodize small patterns. Therefore, it is preferable in terms of production efficiency to form the gate electrode pattern after forming the anodized film.

  However, with this method, the metal is exposed at the etching end, that is, at the electrode end. Further, even when an insulating layer is further provided as described above, particularly when this is thin, the etching end is likely to be disturbed, and leakage is likely to occur.

  FIG. 1 is a schematic cross-sectional view showing the formation of an anodized film by anodic oxidation of a gate electrode. FIG. 1 (1) shows a state in which, for example, an aluminum layer 2 is uniformly formed on a glass substrate 1 and then anodized to form an aluminum oxide layer 3 by anodization.

  Next, a gate electrode pattern is formed by using, for example, dry etching (FIG. 1B). At this point, the aluminum layer 2 as a gate electrode is exposed at the electrode end.

  Therefore, in order to prevent leakage from the end (side) when forming the semiconductor layer and forming the thin film transistor by forming the source electrode, the drain electrode, etc., the insulating layer 4 is provided at the end as a leak preventing layer. (FIG. 1 (3)). As a result, the exposed surface of the electrode can be covered and leakage can be prevented.

  The insulating layer 4 can be formed as a bank (partition) on and around the gate electrode, for example (FIGS. 1 (3) and (5)), and a precursor solution is discharged there by, for example, an ink jet method or the like. Thus, the oxide semiconductor thin film 5 can be formed in the partition wall (FIG. 1 (4)).

  Further, if the insulating layer provided between the anodic oxide film and the oxide semiconductor thin film is formed in a wider area covering the anodic oxide film with a sufficient thickness to prevent leakage, the insulating layer can be used as a leakage preventing layer. I can do it.

  FIG. 1 (6) shows an example in which a thin film transistor is formed by providing the insulating layer 4 in a wide area covering the entire anodic oxide film and the gate electrode. In the figure, 5 represents an oxide semiconductor thin film, and 6 and 7 represent a source electrode and a drain electrode, respectively.

  Here, a silicon oxide film made of, for example, polysilazane is formed as the insulating film.

  Therefore, a preferred form in the present invention is a form in which after forming the gate electrode metal film, an anodized film is formed on the electrode surface by anodic oxidation, and then patterned by etching or the like to further form an insulating layer on the anodized film. Thus, both effects of preventing leakage and improving the characteristics of the insulating film can be obtained.

  The insulating layer disposed at the end portions of the gate electrodes may have a thickness that sufficiently covers the end portions, but is 40 nm to 3 μm, preferably 80 nm to 1 μm.

  As these insulating layers, the same material as the insulating layer material formed on the anodic oxide film is used.

  Next, the elements of the present invention other than the gate electrode and the insulating layer will be described.

  The oxide semiconductor thin film of the present invention may be fired and formed by sputtering or the like, but in the present invention, the oxide semiconductor thin film is formed from a precursor solution or a dispersion coating film. It is preferable.

  These precursors are metal salts, and preferably contain one or more metal salts selected from metal nitrates, sulfates, phosphates, carbonates, acetates or oxalates.

  In the present invention, the semiconductor is a metal oxide. In the present invention, a thin film of a metal salt containing a metal component of a metal oxide serving as a precursor of a metal oxide semiconductor is provided, and then the semiconductor conversion such as thermal oxidation is performed on the thin film. A treatment is performed to convert the metal oxide semiconductor into a semiconductor thin film.

  It is known to obtain a metal oxide semiconductor by thermally oxidizing a precursor of a metal oxide semiconductor. As a metal compound that can be used as a precursor of a metal oxide semiconductor, a very wide range of inorganic salts, organometallic compounds, organometallic complexes, and the like are known. In particular, organometallic compounds and metal chlorides are well known and used in Electrochemical and Solid-State Letters, 10 (5) H135-H138, Advanced Materials 2007, 19, 183-187, and the like.

  In the present invention, the metal oxide semiconductor precursor is preferably selected from nitrates, sulfates, phosphates, carbonates, acetates or oxalates among metal salts.

  As the metal in the metal salt, 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.

  In the present invention, these metal salts preferably contain one or more of any of indium (In), tin (Sn), and zinc (Zn), and may be used in combination.

  Moreover, it is preferable that the other metal contains a salt of either gallium (Ga) or aluminum (Al).

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

  These metal salts are less likely to remain in the membrane due to the low energy of the oxidation reaction, which is expected to include hydrolysis and dehydration reactions, and the decomposition products generated during the oxide formation process are efficiently vaporized and discharged. Since there are few impurity components such as carbon present in the oxide, it is presumed that good semiconductor characteristics can be obtained.

  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 temperature range 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 with a semiconductor thin film made of a metal salt as a raw material, which can be said to be a remarkable effect obtained by the present invention.

  Use of these salts is also preferable because the irradiation time can be shortened when the semiconductor conversion treatment is performed at substantially low temperatures by electromagnetic waves (microwaves).

(Precursor thin film formation method, patterning method)
In order to form a thin film containing a metal salt that is a precursor of these metal oxide semiconductors, a known film formation method, vacuum deposition method, molecular beam epitaxial growth method, ion cluster beam method, low energy ion beam method, An ion plating method, a CVD method, a sputtering method, an atmospheric pressure plasma method, and the like can be used. In the present invention, a metal salt selected from the nitrates, sulfates, phosphates, carbonates, acetates or oxalates. Is preferably coated on a substrate using a solution in which the solvent is dissolved in an appropriate solvent, which can greatly improve productivity.

  The solvent for dissolving the metal salt is not particularly limited as long as it dissolves the metal compound to be used in addition to water, such as water, alcohols such as ethanol, propanol and ethylene glycol, tetrahydrofuran, dioxane and the like. Ether type, ester type such as methyl acetate and ethyl acetate, ketone type such as acetone, methyl ethyl ketone and cyclohexanone, glycol ether type such as diethylene glycol monomethyl ether, acetonitrile and the like, further aromatic solvents such as xylene and toluene, hexane, It is possible to use α-terpineol such as cyclohexane and tridecane, halogenated alkyl solvents such as chloroform and 1,2-dichloroethane, N-methylpyrrolidone, carbon disulfide and the like.

  The solvent used in the metal salt solution of the present invention is not particularly limited as long as the metal salt is soluble, but water and lower alcohol are preferable from the viewpoint of solubility of the metal salt and drying property after coating. Among these, methanol, ethanol, and propanol (1-propanol and isopropanol) are preferable from the viewpoint of dryness. 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 viewpoints of solubility, solution stability, and drying properties, it is preferable to prepare “aqueous solution” of the present invention by mixing water and these lower alcohols. When an aqueous solution is prepared by mixing a lower alcohol, the surface tension can be lowered without greatly changing the composition.

  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.

  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.

  The aqueous solution of 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) as a solute (in the present invention, a metal salt and other additives added as necessary. ) Is dissolved. From the viewpoints of solubility of solutes such as metal salts and solution stability, the water content is preferably 50% by mass or more, and more preferably 70% by mass or more.

  Among the metal salts according to the present invention, nitrates having the most excellent properties in performance such as degradation, decomposition, and easy dissolution in water and deliquescence are most preferable.

  In the present invention, a solution containing a metal salt is applied onto a substrate to form a thin film containing a metal oxide semiconductor precursor.

  As a method of forming a precursor thin film of a metal oxide semiconductor by applying a solution containing a metal salt on a substrate, a spray coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll Examples include a coating method, a bar coating method, a die coating method, 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. Etc. The coating film may be patterned by photolithography, laser ablation, or the like. Among these, the ink jet method, spray coating method, etc. which can apply | coat a thin film are preferable.

  For example, when forming a film using an inkjet method, a semiconductor precursor layer thin film containing a metal salt is formed by dropping a metal salt solution and volatilizing a solvent (water) at about 80 ° C. to 100 ° C. In addition, when dropping the solution, it is preferable that the substrate itself is heated to about 80 ° C. 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.

(Composition ratio of metal)
By the method of the present invention, a thin film of a metal oxide semiconductor containing a single metal atom or a plurality of metal atoms selected from the metal atoms described above is produced. As the metal oxide semiconductor, any state of single crystal, polycrystal, and amorphous can be used, but an amorphous thin film is preferably used.

  The metal atom contained in the formed metal oxide semiconductor preferably contains any one of indium (In), tin (Sn), and zinc (Zn), as described in the description of the precursor. It is preferable to contain gallium (Ga) or aluminum (Al).

  When preparing a precursor solution containing these metals as components, the preferred metal composition ratio is as follows: a metal (metal A) contained in a salt selected from metal salts of In and Sn, and metal salts of Ga and Al The molar ratio (metal A: metal B: metal C) of metal (metal B = metal C) contained in the metal salt (metal B) contained in the salt selected from the following relational expression: It is preferable to satisfy.

Metal A: Metal B: Metal C = 1: 0.2-1.5: 0-5
It is.

  As the metal salt, nitrate is most preferable. Therefore, the molar ratio (A: B: C) of In, Sn (metal A), Ga, Al (metal B), and Zn (metal C) is as described above. It is preferable to form a precursor thin film containing a metal inorganic salt by coating using a coating solution in which nitrate of each metal is dissolved and formed in a solvent containing water as a main component so as to satisfy the formula.

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

(Amorphous oxide)
As the metal oxide semiconductor to be formed, any state of single crystal, polycrystal, and amorphous can be used, but an amorphous thin film is preferably used. Being amorphous can be confirmed by X-ray diffraction or electron diffraction, and can be regarded as amorphous if a diffraction pattern unique to the crystal is not observed.

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 is a precursor of a metal 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 certain temperature appropriately selected from the 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 TFT 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. Generally, 1 μm or less, particularly 10 to 300 nm is preferable.

In the present invention, the precursor material (metal salt), 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, and more preferably 10 ¹⁵ / cm ³ or more and 10 ¹⁶ / cm ³ or less.

  Examples of the semiconductor conversion treatment, that is, a method of converting a precursor thin film formed from a metal inorganic salt into a metal oxide semiconductor include oxidation treatments 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 at which the precursor material is heated can be arbitrarily set within the range of the temperature of the thin film surface containing the precursor in the range of 50 ° C to 1000 ° C. From a viewpoint, it is preferable to set it as 100 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. The time for heating the precursor material can be set arbitrarily, but is preferably in the range of 1 second to 60 minutes from the viewpoint of the characteristics of the electronic device and production efficiency. More preferably, it is 5 minutes to 30 minutes.

  By using the metal salt, the semiconductor conversion treatment can be performed at a relatively low temperature.

  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 ° C 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 to generate plasma, and contact with a reactive gas to generate plasma containing oxygen, and the substrate surface is exposed to this to perform oxygen plasma treatment. Under atmospheric pressure represents a pressure of 20 to 110 kPa, preferably 93 to 104 kPa.

  Using an atmospheric pressure plasma method, oxygen plasma is generated as a reactive gas, oxygen plasma is generated, and the precursor thin film containing a metal salt is exposed to the plasma space, so that the precursor thin film is oxidized and decomposed by plasma oxidation. A layer made of a 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.

  The UV ozone method is a method in which an ultraviolet light is irradiated in the presence of oxygen to advance an oxidation reaction. It is preferable to irradiate so-called vacuum ultraviolet light having a wavelength of ultraviolet light of 100 nm 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 at the time of ultraviolet irradiation is preferably 1 mW 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.

  Moreover, after oxidizing the thin film containing a metal salt, the substrate may be heated in the range of 50 ° C. to 200 ° C., preferably in the range of 80 ° C. to 150 ° C., and the heating time in the range of 1 minute to 10 hours. preferable.

  The heat treatment may be performed at the same time as the oxidation treatment, and can be quickly 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 the present invention, the semiconductor conversion process preferably includes a microwave (0.3 to 50 GHz) irradiation step. 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.

  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 GHz 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. Is done. Since substrates such as glass and resin have almost no absorption in the microwave region, the substrate itself hardly generates heat, and only the thin film portion can be selectively heated to be thermally oxidized and converted into a metal oxide semiconductor. Become.

  As is generally the case with microwave heating, microwave absorption concentrates on strongly absorbing substances and can be raised in a very short time, so when this method is used in the present invention, The base material itself is hardly affected by heating by electromagnetic waves, and only the precursor thin film can be heated to a temperature at which the 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 GHz 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 a heating method by electromagnetic wave (microwave) irradiation. In producing a metal oxide semiconductor from a metal oxide semiconductor precursor material, effects other than conduction heat, for example, an effect suggesting direct action of electromagnetic waves on the metal oxide semiconductor precursor material are obtained. Although the mechanism has not been fully clarified, it is presumed that the conversion of the metal oxide semiconductor precursor material into a metal oxide semiconductor by hydrolysis, 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, since heat is transferred to the base material not only by heat conduction, 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, 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, etc. can be measured by a surface thermometer using a thermocouple or a non-contact surface thermometer.

  Further, 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 a region adjacent thereto can be heated in a shorter time.

  The metal oxide semiconductor thin film formed from the metal salt according to the present invention can be used for various semiconductor elements such as transistors and diodes, and electronic circuits, and by applying a solution of a precursor material on a substrate. A metal oxide semiconductor material layer can be produced by a low-temperature process, and can be preferably applied to the manufacture of semiconductor elements such as thin film transistor elements (TFT elements) using a resin substrate.

  The metal oxide semiconductor of the present invention can be used for a diode or a photosensor. For example, a Schottky diode or a photodiode can be manufactured by overlapping a metal thin film made of an electrode material described later.

  Next, other elements constituting the TFT element will be described.

(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. Platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony lead, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin oxide / antimony, indium tin oxide (ITO), fluorine-doped zinc oxide, zinc, carbon, graphite, glassy carbon, silver paste and carbon paste, lithium, beryllium, sodium, magnesium, potassium, calcium, scandium, titanium, manganese, zirconium, gallium, niobium, sodium Beam, sodium - potassium alloy, magnesium, lithium, aluminum, magnesium / copper mixture, a magnesium / silver mixture, a magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide mixture, a lithium / aluminum mixture, or the like is used.

  For the gate electrode, materials such as aluminum and tantalum that are easily oxidized are preferable.

  Moreover, as a conductive material, a conductive polymer, metal fine particles, or the like can be suitably used. As the dispersion containing metal fine particles, for example, a known conductive paste may be used, but a dispersion containing metal fine particles having a particle diameter of 1 nm to 50 nm, preferably 1 nm to 10 nm is preferable. 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 an electrode using a known photolithographic method or a lift-off method, using a conductive thin film formed by a method such as vapor deposition or sputtering using the above as a raw material, or a metal foil such as aluminum or copper There is a method in which a resist is formed and etched by thermal transfer, ink jet or the like. 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 or laser ablation. 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.

  As a method of forming an electrode such as a source, drain, or gate electrode, a gate, or a source bus line without patterning a metal thin film using a photosensitive resin such as etching or lift-off, there is a method by an electroless plating method. Are 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 inkjet printing), a plating agent is brought into contact with a portion where an electrode is provided. If it does so, electroless plating will be performed to the said part by the contact of the said catalyst and a plating agent, and an electrode pattern will be formed.

  The application of the electroless plating catalyst and the plating agent may be reversed, and the pattern formation may be performed either. However, 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, planographic printing, letterpress printing, intaglio printing, printing by ink jet printing, or the like is used.

(Gate insulation layer)
Although the gate insulating layer of the thin film transistor of the present invention includes the anodic oxide film of the gate electrode, various insulating films can be used as the insulating layer used in addition to the anodic oxide film. In particular, an inorganic oxide film having a high relative dielectric constant is preferable. Inorganic oxides include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead lanthanum titanate, strontium titanate, Examples thereof include 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. Inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.

  Examples of the method for forming the film include a vacuum process, a molecular beam epitaxial growth method, an ion cluster beam method, a low energy ion beam method, an ion plating method, a CVD method, a sputtering method, an atmospheric pressure plasma method, and a spray process. Examples include wet processes such as coating methods, spin coating methods, blade coating methods, dip coating methods, casting methods, roll coating methods, bar coating methods, die coating methods, and other methods such as printing and ink jet patterning. Can be used depending on the material.

  The wet process is a method of applying and drying a liquid in which fine particles of inorganic oxide are dispersed in an arbitrary organic solvent or water using a dispersion aid such as a surfactant as required, or an oxide precursor, for example, A so-called sol-gel method in which a solution of an alkoxide body is applied and dried is used.

  Of these, the atmospheric pressure plasma method described above is preferable.

  Examples of organic compound films include polyimides, polyamides, polyesters, polyacrylates, photo-radical polymerization-type, photo-cation polymerization-type photo-curing resins, copolymers containing acrylonitrile components, polyvinyl phenol, polyvinyl alcohol, novolac resins, etc. Can also be used.

  An inorganic oxide film and an organic oxide film can be laminated and used together. The thickness of these insulating layers is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.

(Substrate)
Various materials can be used as the material constituting the substrate (substrate or support). For example, ceramic substrates such as glass, quartz, aluminum oxide, sapphire, silicon nitride, silicon carbide, silicon, germanium, gallium A semiconductor substrate such as arsenic, gallium phosphide, gallium nitrogen, paper, non-woven fabric or the like can be used. In the present invention, the support is preferably made of a resin, for example, a plastic film sheet can be used. Examples of plastic films include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), and cellulose. Examples include films made of triacetate (TAC), cellulose acetate propionate (CAP), and the like. By using a plastic film, the weight can be reduced as compared with the case of using a glass substrate, the portability can be improved, and the resistance to impact can be improved.

  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 thin film transistor and the manufacturing method thereof according to the present invention will be described in detail.

Example 1
The production of the thin film transistor of the present invention will be described with reference to cross-sectional schematic diagrams of each step in FIG.

<Production of Thin Film Transistor 1>
A gate electrode 302 is formed using a non-alkali glass substrate having a thickness of 0.7 mm as the support 301. An aluminum film having a thickness of 200 nm was formed on one surface by sputtering, and then etched by photolithography to form the gate electrode 2 (FIG. 2 (1)).

(Anodized film forming process)
The gate electrode 2 formed from an aluminum film was used as an anode, platinum was used as a cathode, and connected to a constant current voltage power source. Then, a 3% tartaric acid: ethylene glycol = 1: 9 solution was used as an electrolyte, and 0.2 mA / cm. ^A voltage was applied so that a constant current of ² was obtained.

  Then, after confirming that the voltage rose to 100V, the voltage was applied at a constant 100V and held for 10 minutes.

  Next, it was washed with pure water, dried and baked at 180 ° C. for 1 hour, and an anodic oxide film 303 having a thickness of 150 nm was formed (FIG. 2 (2)).

  Further, a silicon oxide film having a thickness of 30 nm was formed thereon by continuous atmospheric pressure plasma treatment (AGP) under the following conditions. As the atmospheric pressure plasma processing apparatus, an apparatus according to FIG. 6 described in Japanese Patent Application Laid-Open No. 2003-303520 was used (the silicon oxide film is omitted in the drawing).

(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)
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 rectangular stainless steel pipe was coated with the same dielectric as described above under the same conditions.

(Glass substrate temperature) 200 ° C
Next, a silicone resin film having a thickness of 3 μm was formed as an insulating film 304 covering the edge of the gate electrode by screen printing (FIG. 2 (3)).

  Next, a 10 mass% aqueous solution in which indium nitrate, zinc nitrate, and gallium nitrate are mixed at a metal ratio of 1: 1: 1 (gram atomic ratio) is used as ink, and between the insulating films 4 using a piezo ink jet apparatus. Ink was discharged in accordance with a semiconductor layer pattern (substantially gate electrode pattern) to form a semiconductor precursor material thin film 305 '(FIG. 2 (4)).

  An average film thickness of the precursor material thin film 305 ′ formed by heat treatment at 100 ° C. and drying was 30 nm.

  Further, the semiconductor layer was irradiated with microwaves while maintaining the substrate temperature at 200 ° C. That is, irradiation with microwaves (2.45 GHz) was performed at an output of 30 W under an atmospheric pressure condition where the partial pressure of oxygen and nitrogen was 1: 1. The precursor material was converted into an oxide semiconductor, and an IGZO-based oxide semiconductor layer 305 was formed on the gate insulating film so as to face the gate electrode (FIG. 2 (5)).

  Next, a silver fine particle dispersion (CCI-300 (silver content 20 mass%) manufactured by Cabot) is ejected from a piezo-type inkjet head, and printing is performed on the source electrode and drain electrode portions including the exposed regions of the semiconductor layer. gave. Next, heat treatment was performed at 200 ° C. for 30 minutes to form a source electrode 306 and a drain electrode 307 (FIG. 2 (6)). Each size is 40 μm wide, 100 μm long (channel width), and 100 nm thick, and the distance (channel length) between the source electrode 306 and the drain electrode 307 is 20 μm. A thin film transistor 1 was prepared.

Example 2
In Example 1, the process of forming the silicon oxide film by atmospheric pressure plasma was changed as follows.

  That is, after forming the anodic oxide coating 303 on the gate electrode, a polysilazane solution (NN110: manufactured by AZ Electronic Materials) was applied on the substrate to form a polysilazane thin film.

  The obtained polysilazane thin film was dried at 150 ° C. for 10 minutes, and then subjected to 30 conditions under the conditions of a flow rate of 0.6 L / min and a substrate temperature of 200 ° C. using a UV ozone irradiator (UV-1: manufactured by Samco). UV ozone irradiation treatment 15 was performed for a minute, and the polysilazane thin film was converted into an insulating film (thickness 15 nm) containing silicon oxide.

  After the formation of the insulating film 304 covering the end of the gate electrode, the thin film transistor 2 was formed in the same manner.

Example 3
A thin film transistor 3 was prepared in the same manner as in Example 1 except that the step of forming the silicon oxide film by atmospheric pressure plasma was omitted.

Example 4
A thin film transistor 304 was formed in the same manner as in Example 2. However, the gate electrode was formed by forming an aluminum film by sputtering (thickness 200 nm) and performing an anodic oxidation process in the same manner, and then etching it at once to form an anodic oxide film and a gate electrode pattern. .

Comparative Example 1
A thin film transistor 5 was similarly formed in Example 1 except that the silicon oxide film having a thickness of 30 nm by atmospheric pressure plasma treatment and the insulating film 304 covering the end portion of the gate electrode made of a silicone resin film were removed.

Comparative Example 2
In Example 1, an aluminum film having a thickness of 100 nm was formed on the entire surface by sputtering, and then etched by photolithography to form the gate electrode 302. Then, the anodic oxide film was not formed. Instead, A gate insulating film (thickness 150 nm) made of silicon oxide was formed by the same atmospheric pressure plasma treatment (AGP). Next, the formation of the semiconductor layer, the formation of the source electrode and the drain electrode were performed in the same manner as in Example 1, and the thin film transistor 5 was created.

For the fabricated thin film transistors 1 to 5, the drain bias was set to 10 V, the gate bias was swept from −10 V to +20 V, and an increase in drain current (transfer characteristics) was observed. The mobility (cm ² / Vs) was estimated from the saturation region of each transfer characteristic, and the on / off ratio was also estimated. The threshold value Vg (ON) is a gate bias value obtained by extrapolating √Id = 0 in relation to the square root √Id of the drain current value (Id) with respect to the gate bias (Vg).

  The results are shown in Table 1.

  It can be seen that the thin film transistor of the present invention exhibits good mobility and on / off ratio. The threshold is also low and good.

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Aluminum layer 3 Aluminum oxide layer 4 Insulating layer 5 Oxide semiconductor thin film 6 Source electrode 7 Drain electrode 301 Support body 302 Gate electrode 303 Anodized film 304 Insulating film 305 ′ Precursor material thin film 305 Semiconductor layer 306 Source electrode 307 Drain electrode

Claims (9)

  A thin film transistor having a gate electrode, a gate insulating film, and an oxide semiconductor thin film on a substrate, wherein at least a part of the gate insulating film is an anodized film, and an insulating layer is provided at an end of the gate electrode A thin film transistor characterized by the above.   2. The thin film transistor according to claim 1, wherein an insulating layer is provided between the anodic oxide film and the oxide semiconductor thin film.   3. The thin film transistor according to claim 1, wherein the oxide semiconductor thin film is formed from a coating solution of a precursor solution or dispersion.   4. The thin film transistor of claim 3, wherein the precursor includes one or more metal salts selected from metal nitrates, sulfates, phosphates, carbonates, acetates, and oxalates.   The thin film transistor according to claim 4, wherein the metal salt includes at least a salt of In, Zn, or Sn.   The thin film transistor according to claim 4 or 5, wherein the metal salt includes at least a salt of Ga or Al.   The thin film transistor according to claim 4, wherein the metal salt is a nitrate.   The thin film transistor according to claim 1, wherein the oxide semiconductor thin film is made of an amorphous semiconductor.   A method for producing a thin film transistor, comprising producing the thin film transistor according to claim 1.

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