JP2009065012A - Thin film transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable thin film transistor (TFT element) having a high mobility and a small off-current, and to provide a fabrication process of thin film transistor exhibiting high productivity. <P>SOLUTION: In a thin film transistor where a thin film containing the precursor of a metal oxide semiconductor is formed on a substrate and a metal oxide semiconductor thin film formed by a process for oxidizing the thin film serves as an active layer, a gate insulating film is provided on the side of the metal oxide semiconductor thin film opposite to a support. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a thin film transistor having a metal oxide semiconductor thin film formed by oxidizing a precursor thin film as an active layer.

  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, an active matrix circuit using these, and the like 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 demanded. 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. 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 small variations between elements. It has been broken.

  As a technique for manufacturing a metal oxide semiconductor, for example, a method of forming an amorphous oxide by decomposing and oxidizing (heating, decomposition reaction) an organic metal is known (for example, Patent Document 1).

  In addition, a field effect transistor in which an oxide semiconductor is produced by applying a metal halide precursor solution such as zinc chloride on a substrate by an inkjet method or the like and then heat-treating it in the atmosphere to convert it into an oxide semiconductor to form an active layer. Is also known (for example, Non-Patent Document 1).

  Similarly, a method of obtaining a metal oxide semiconductor thin film by applying a metal halide solution such as zinc chloride or tin chloride on a substrate to form a thin film and then treating it at a temperature of several hundred degrees and thermally decomposing it. (For example, Non-Patent Document 2).

  Further, a method using metal oxidation is also known (for example, Patent Document 2).

  In either case, the precursor is thermally oxidized to obtain an oxide semiconductor. However, in the case of using thermal oxidation, the treatment is performed in a high temperature range of 300 ° C. or higher, so that the energy efficiency is low, and it is inexpensive and lightweight. It is difficult to apply to a resin substrate.

In addition, when forming a thin film of a metal oxide semiconductor by such a method, it is difficult to eliminate impurities, so that it is difficult to form a good oxide film depending on the configuration and process, and thus the mobility is low and the off current is large. The effect on the semiconductor characteristics becomes remarkable.
JP 2003-179242 A JP-A-8-264794 Advanced Materials 2007, 19, 843-847 Electrochemical and Solid-State Letters, 10 (5) H135-H138 (2007)

  Accordingly, an object of the present invention is to obtain a stable thin film transistor element (TFT element) with high mobility and low off current, and to provide a method for manufacturing a thin film transistor with high productivity.

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

  1. In a thin film transistor having a metal oxide semiconductor thin film formed by a step of forming a thin film containing a precursor of a metal oxide semiconductor on a substrate and then oxidizing the thin film as an active layer, the metal oxide semiconductor thin film support A thin film transistor, wherein a gate insulating film is provided on a side opposite to the gate electrode.

  2. 2. The thin film transistor according to 1 above, wherein at least one of a source electrode and a drain electrode is provided on a side opposite to the support of the metal oxide semiconductor thin film.

  3. 3. The thin film transistor according to 1 or 2 above, wherein the step of oxidizing the thin film containing the metal oxide semiconductor precursor is plasma oxidation.

  4). 4. The thin film transistor according to 3 above, wherein the step of oxidizing the thin film containing the metal oxide semiconductor precursor is performed by an atmospheric pressure plasma method.

  5). 5. The thin film transistor according to any one of 1 to 4, wherein the gate insulating film is formed by an atmospheric pressure plasma method.

  According to the present invention, a stably operating thin film transistor (TFT) element with high mobility, low off current, improved production efficiency, and the like can be obtained.

  The best mode for carrying out the present invention will be described below, but the present invention is not limited thereto.

  The present invention provides a thin film transistor having a metal oxide semiconductor thin film formed by a step of forming a thin film containing a precursor of a metal oxide semiconductor on a substrate and then oxidizing the thin film as an active layer. The present invention relates to a thin film transistor configured such that a gate insulating film is provided on a side opposite to a thin film support.

  Therefore, the element configuration of the present invention has a top gate type configuration in order to form a gate insulating film on the surface of the active layer (semiconductor layer) on the side opposite to the support.

  In the case of a semiconductor thin film formed by an oxidation process from a coated precursor thin film, it has been found that this configuration has a particularly good performance.

  Further, at least one of a source electrode and a drain electrode is provided on the opposite side of the metal oxide semiconductor thin film support, that is, on the surface of the metal oxide semiconductor thin film formed on the support (substrate). A configuration in which the source and drain electrodes are in direct contact is preferable.

  Therefore, the thin film transistor of the present invention has a configuration in which a semiconductor thin film, a gate insulating layer, and a gate electrode are formed in order from the support.

  Hereinafter, the constituent features of the present invention will be sequentially described.

  In the present invention, examples of the metal oxide semiconductor precursor include metal atom-containing compounds, that is, metal salts, halides, and organometallic compounds containing metal atoms.

  Metals of metal salts, metal oxides, organometallic compounds, halogen metal compounds, metal hydrides 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.

  Among these metal salts, it is preferable to contain any of indium, tin, and zinc, and they may be used in combination. Moreover, it is preferable that a gallium or aluminum is included as another metal.

  As metal salts, nitrates, acetates and the like can be suitably used, and as halides, chlorides, iodides, bromides and the like can be suitably used.

  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. Further, a hydrogen atom in the alkyl group may be substituted with a fluorine atom. Examples of the group selected from the β-diketone complex group, β-ketocarboxylic acid ester complex group, β-ketocarboxylic acid complex group and 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, trimethylacetate Examples thereof include ethyl acetate, methyl trifluoroacetoacetate and the like, and examples of β-ketocarboxylic acid include , Acetoacetic acid, there may be mentioned trimethyl acetoacetate, and as Ketookishi, for example, can be exemplified acetoxy group (or an acetoxy group), a propionyloxy group, Buchirirokishi group, acryloyloxy group, a methacryloyloxy group. 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 of R ³ A metal compound having at least one group selected from a group (ketooxy complex group) is most preferable. Among the metal salts, nitrate is preferable. 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.

  As a thin film forming material used for forming the semiconductor film of the present invention, a metal atom-containing compound is preferable. Examples of the metal atom-containing compound include metal salts, organometallic compounds, halogen metal compounds, metal hydride compounds, and the like. Particularly preferred organometallic compounds include those represented by the general formula (I). Can be mentioned.

  Of the above precursors, metal nitrates, halides, and alkoxides are preferable. 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.

(Film formation method, patterning method)
As a method for forming the precursor thin film, it is preferable to form the thin film by coating a solution of the precursor and casting the solvent.

  Solvents include 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, diethylene glycol monomethyl ether, etc. Glycol ether, acetonitrile, aromatic hydrocarbon solvents such as xylene and toluene, aromatic solvents such as o-dichlorobenzene, nitrobenzene, and m-cresol, aliphatic carbonization such as hexane, cyclohexane, and tridecane Hydrogen solvents, α-terpineol, halogenated alkyl solvents such as chloroform and 1,2-dichloroethane, N-methylpyrrolidone, carbon disulfide and the like can be preferably used. Ethanol, alcohols such as, also, such as acetonitrile, can be used any be any solvent capable of dissolving the precursor.

  In the present invention, as a method of forming a thin film containing a metal oxide semiconductor precursor by applying a liquid containing a thin film forming material on a substrate, a spray coating method, a spin coating method, a blade coating method, Examples thereof include a dip coating method, a cast method, a roll coating method, a bar coating method, a die coating method, and a mist method, and a patterning method using a printing method such as a relief plate, an intaglio plate, a planographic printing method, a screen printing method, and an ink jet method. The coating film may be patterned by photolithography, laser ablation, or the like. Conventionally known methods can be applied to the formation and patterning of a thin film containing metal fine particles. Of these, the spray coating and mist methods that can apply a thin film are preferable.

  A preferred droplet forming method in the mist method will be described below.

  FIG. 1 is a schematic view of an ultrasonic sprayer used when a liquid containing a thin film forming material is applied as droplets on a substrate or supplied between electrodes. Thereby, a micro droplet (droplet) can be formed. In FIG. 1, 1 is an ultrasonic atomizer, 11 is an introduction tube for introducing nitrogen gas, 12 is a raw material reservoir for storing a liquid L containing a thin film forming material as a droplet raw material, 13 is an ultrasonic generator, 14 Is a power source connected to the ultrasonic wave generator 13, and 15 is a discharge tube for discharging the generated droplets. When nitrogen gas is introduced from the introduction pipe 11 into the raw material storage unit 12 and the power source 14 is turned on to generate ultrasonic waves from the ultrasonic wave generation unit 13, droplets are generated. The droplets generated in this manner are discharged to the outside of the ultrasonic sprayer 1 through the discharge tube 15, and the droplets are sprayed onto the substrate at an appropriate location of a coating apparatus (not shown), and a thin film is formed on the substrate. Is formed. The thin film is subjected to oxidation, for example, plasma oxidation in an atmospheric pressure plasma processing apparatus.

  FIG. 2 is a schematic diagram of a single-wafer type atmospheric pressure plasma processing apparatus equipped with an ultrasonic atomizer, whereby thin film formation by droplet spraying and plasma oxidation by atmospheric pressure plasma processing can be performed continuously or simultaneously. . In FIG. 2, reference numeral 1 denotes an ultrasonic sprayer similar to that shown in FIG. The droplets M sprayed downward from the ultrasonic sprayer 1 are applied onto the substrate S in the spray space A. Reference numeral 21 denotes a fixed first electrode, and reference numeral 22 denotes a second electrode that supports the substrate S and can be repeatedly moved in the direction of the arrow in the figure. The first electrode 21 and the second electrode 22 are provided to face each other with a predetermined gap, and this gap constitutes the discharge space D. The first electrode 21 and the second electrode 22 are connected to a filter 27A or 27B, which is a load, a matching box 26A or 26B, and a high-frequency power source 25A or 25B, respectively, and are grounded. The filter is inserted in order to superimpose two different types of high-frequency electric fields in the discharge space so that the high-frequency waves do not affect each other's power supply. The matching box is inserted to cancel the reactance component of the load and correct the impedance in order to effectively use the energy of the high-frequency power source.

  The first high-frequency electric field generated by the high-frequency power supply 25A and the second high-frequency electric field generated by the high-frequency power supply 25B satisfy the following relationship. The frequency ω2 of the second high-frequency electric field is higher than the frequency ω1 of the first high-frequency electric field, and the strength V1 of the first high-frequency electric field, the strength V2 of the second high-frequency electric field, and the strength of the discharge start electric field The relationship with IV satisfies V1 ≧ IV> V2 or V1> IV ≧ V2. As described above, by superimposing two types of high-frequency electric fields satisfying this relationship, a stable and high-density discharge state can be achieved even when a gas such as nitrogen having a high discharge starting electric field strength is used. High-quality film formation can be performed.

  For example, a high frequency with a frequency of 100 kHz is used as the first high frequency electric field, and a high frequency with a frequency of 13.56 MHz is used as the second high frequency electric field facing the first high frequency electric field. Between the electrodes, for example, a mixed gas of 0.1% by volume of oxygen gas is introduced into the nitrogen gas to form a discharge space.

  The substrate S such as glass is placed on the second electrode 22 and repeatedly moves between the spray space A and the discharge space D. In the spray space A, liquid droplets containing the thin film forming material are applied onto the substrate S. In the discharge space D, a discharge gas such as nitrogen is supplied, two kinds of high-frequency electric fields are superimposed, and high-density plasma is generated, and the substrate S to which droplets are applied is exposed. Plasma processing is performed by repeating this.

  FIG. 3 is also a schematic view of a roll-type atmospheric pressure plasma processing apparatus provided with an ultrasonic atomizer. In FIG. 3, the same reference numerals as those in FIG. 2 are the same as the members described in FIG. In FIG. 3, S is a long base material such as a plastic film. The base material S is wound around the roll electrode 22R that is the second electrode, and is conveyed in the direction of the arrow in the drawing. The droplet M containing the thin film forming material sprayed from the ultrasonic sprayer 1 is applied on the substrate S in the spray space A. Thereafter, when the base material S to which the droplet M is applied passes through the discharge space D formed between the first electrode 21 and the second electrode 22R, a thin film is formed.

As the first power supply (high frequency power supply) installed in the atmospheric pressure plasma processing apparatus,
Applied power symbol Manufacturer Frequency Product name A1 Shinko Electric 3kHz SPG3-4500
A2 Shinko Electric 5kHz SPG5-4500
A3 Kasuga Electric 15kHz AGI-023
A4 Shinko Electric 50kHz SPG50-4500
A5 HEIDEN Research Laboratories 100kHz * PHF-6k
A6 Pearl Industry 200kHz CF-2000-200k
A7 Pearl Industry 400kHz CF-2000-400k
And the like, and any of them can be used.

As the second power source (high frequency power source),
Applied power supply symbol Manufacturer Frequency Product name B1 Pearl Industry 800kHz CF-2000-800k
B2 Pearl Industry 2MHz CF-2000-2M
B3 Pearl Industry 13.56MHz CF-5000-13M
B4 Pearl Industry 27MHz CF-2000-27M
B5 Pearl Industry 150MHz CF-2000-150M
And the like, and any of them can be preferably used.

  Of the above power supplies, * indicates a HEIDEN Laboratory impulse high-frequency power supply (100 kHz in continuous mode). Other than that, it is a high-frequency power source that can apply only a continuous sine wave.

In the present invention, the electric power applied between the electrodes facing each other supplies power (power density) of 1 W / cm ² or more to the second electrode (second high-frequency electric field) to excite the discharge gas to generate plasma. Then, energy is applied to the thin film forming droplet and plasma oxidation is performed. The upper limit value of the power supplied to the second electrode is preferably 50 W / cm ² , more preferably 20 W / cm ² . The lower limit is preferably 1.2 W / cm ² . The discharge area (cm ² ) refers to an area in a range where discharge occurs in the electrode.

Further, by supplying power (output density) of 1 W / cm ² or more to the first electrode (first high frequency electric field), the output density is improved while maintaining the uniformity of the second high frequency electric field. be able to. Thereby, a further uniform high-density plasma can be generated, and a further improvement in film forming speed and an improvement in film quality can be achieved. Preferably it is 5 W / cm ² or more. The upper limit value of the power supplied to the first electrode is preferably 50 W / cm ² .

  Here, the waveform of the high-frequency electric field is not particularly limited. There are a continuous sine wave continuous oscillation mode called a continuous mode, an intermittent oscillation mode called ON / OFF intermittently called a pulse mode, and either of them may be adopted, but at least the second electrode side (second The high-frequency electric field is preferably a continuous sine wave because a denser and better quality film can be obtained.

  Accordingly, the liquid containing the thin film forming material is preferably applied as droplets by spraying or the like on the substrate. The average particle size of the droplets is 5 μm or less, preferably 1 μm or less. The average particle size of the droplets can be measured by simply irradiating the droplet group with laser light and calculating the particle size distribution from the intensity distribution pattern of the diffracted / scattered light emitted from it. The company's LDSA-1500A can be used.

  In this invention, after forming the thin film containing the metal used as the precursor of a metal oxide semiconductor in this way, a metal oxide semiconductor is manufactured by performing plasma oxidation with respect to this thin film.

  As a method for oxidizing a thin film formed of a metal material which is a precursor of a metal oxide semiconductor, it is preferable to use plasma oxidation as described above in the present invention.

  As the plasma oxidation, an atmospheric pressure plasma method using the atmospheric pressure plasma processing apparatus is preferable. In plasma oxidation, the substrate on which the thin film containing the precursor is formed is preferably heated in the range of 150 ° C to 300 ° C.

  In the atmospheric pressure plasma method, an inert gas such as argon gas or nitrogen gas is used as a discharge gas under atmospheric pressure, and a reactive gas (a gas containing oxygen) is introduced into the discharge space and a high frequency electric field is applied. The plasma oxidation is performed by exciting the discharge gas, generating plasma, bringing it into contact with the reaction gas, generating oxygen plasma, and exposing the substrate surface to this. Under atmospheric pressure represents a pressure of 20 to 110 kPa, preferably 93 to 104 kPa.

  When an oxygen plasma is generated using a gas containing oxygen as a reactive gas by the atmospheric pressure plasma method, the gas to be used varies depending on the type of thin film, but basically a discharge gas (inert gas) and an oxidizing gas. It is a mixed gas. When performing plasma oxidation, it is preferable to contain 0.01-10 volume% of oxygen gas with respect to mixed gas as oxidizing 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, WO2006 / 129461, and the like.

  In the plasma oxidation, it is preferable to heat the substrate in the range of 150 ° C. to 300 ° C.

(Oxidation process)
As a method (process) for oxidizing a thin film formed from a metal material that is a precursor of a metal oxide semiconductor, other methods such as a thermal oxidation method may be used in addition to the plasma oxidation described above, and a UV ozone method may be used. Can also be used. The UV ozone method is a method of irradiating ultraviolet light 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. It is preferable to heat the substrate in the range of 50 ° C to 400 ° C, preferably 100 ° C to 250 ° C. As described above, a precursor solution is applied by various coating methods (coating methods), for example, an ink jet method, printing or spraying method, mist method, etc., and a solvent is cast on a substrate to form a thin film and then oxidized. Process.

  In the present invention, the precursor of the metal oxide semiconductor may be a metal, a thin film containing metal formed by coating a thin film containing metal using a method such as vapor deposition or sputtering, or by using a metal fine particle dispersion. A metal oxide semiconductor can be obtained by oxidation treatment by the above method.

  Although a metal thin film formed by vapor deposition, sputtering, or the like may be used as the thin film containing metal, a method of forming from a dispersion of metal fine particles can form a uniform thin film by a coating method such as an inkjet method or printing. preferable.

  As the material of the metal fine particles, silver, nickel, chromium, copper, iron, tin, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, zinc, gallium, or the like can be used. .

  Among these, it is preferable that any one of indium, zinc, and tin is included, and it is preferable that gallium is further included.

  It is preferable to form an electrode using a dispersion in which fine particles made of these metals are dispersed in water or a dispersion medium that is an arbitrary organic solvent using a dispersion stabilizer mainly made of an organic material.

  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, Japanese Patent No. 2561537, etc. It is a dispersion of fine metal particles produced by a gas evaporation method.

  The average particle diameter of the metal fine particles is preferably 1 to 300 nm, and can promote the fusion described later and facilitate the conversion to an amorphous oxide semiconductor when an oxidation treatment is performed.

(Composition ratio of metal)
The metal preferably contains any one of In, Zn, and Sn, and further preferably contains Ga or Al. However, when the metal contains In, the composition ratio of the metal when In is set to 1, Zn _y Sn _1-y (where y is a positive number from 0 to ₁ ) is preferably from 0.2 to 5, more preferably from 0.5 to 2. Moreover, when In is set to 1, the composition ratio of Ga and Al is preferably 0 to 5, more preferably 0.5 to 2, respectively.

(Film formation method, patterning method)
As a method for forming a thin film containing metal fine particles, a dispersion liquid such as a spray coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, a bar coating method, or a die coating method is applied as described above. Examples thereof include a coating method in a broad sense such as a printing method such as a relief printing plate, an intaglio printing plate, a planographic printing plate, a screen printing, and an inkjet, and a patterning method thereby. The coating film may be patterned by photolithography, laser ablation, or the like. Conventionally known methods can be applied to the formation and patterning of a thin film containing metal fine particles.

  In addition, a dispersion of metal fine particles is dropped by, for example, ink jet and the dispersion medium is volatilized to form a thin film. Further, by heating the thin film made of the metal fine particles, the fine particles can be fused to obtain a metal thin film.

  The thickness of the formed metal thin film is 1 to 200 nm, more preferably 5 to 100 nm.

  Moreover, the metal thin film formed from the metal fine particles can be subjected to a heat treatment before the oxidation treatment. The metal fine particles may be fused together by heat treatment. The degree of fusion can be arbitrarily adjusted, and the thin film can be oxidized from any fusion state. Fusion can be performed at a low temperature of 400 ° C. or lower in the case of metal fine particles having a particle size of 300 nm or less.

  The metal fine particles are preferably dispersed in a dispersion medium using a dispersant from the viewpoint of dispersion stability. However, the thin film containing the metal fine particles is formed, before the fusion, and before the oxidation step. In addition, it is preferable to perform cleaning by a dry cleaning process such as oxygen plasma or UV ozone cleaning, and to decompose and clean organic substances contained in the thin film such as a dispersant to exclude organic substances other than metal components.

  The precursor thin film formed by these can be made into an oxide semiconductor by using the oxidation treatment method.

(Oxide semiconductor thin film)
By the method of the present invention, a metal oxide semiconductor thin film 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.

(Composition ratio of metal)
The metal atom contained in the formed metal oxide semiconductor preferably contains any of indium, tin, and zinc, and further preferably contains gallium or aluminum, as described in the description of the precursor.

As a preferred composition ratio, when In is 1, Zn _y Sn _1-y (where y is a positive number from 0 to ₁ ) is preferably 0.2 to 5, more preferably 0.5 to 2. . Moreover, when In is set to 1, the composition ratio of Ga or Al is preferably 0 to 5, more preferably 0.5 to 2.

  The film thickness of the semiconductor thin film is preferably 1 to 200 nm, more preferably 5 to 100 nm.

In the present invention, the oxidation conditions, the temperature and time for thermal oxidation, the oxygen concentration for the UV ozone method, the irradiation conditions such as the energy, temperature and time for ultraviolet irradiation, and the plasma In the case of oxidation, the manufacturing conditions such as precursor material and composition ratio, gas composition ratio in plasma oxidation, flow rate, electrode conditions (frequency, potential, etc.) are controlled, 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.

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

  The oxide semiconductor thin film according to the present invention can be used for a field effect transistor (thin film transistor: TFT).

  In the structure of the present invention, since the oxide semiconductor thin film is uniformly formed on the substrate prior to the gate insulating layer and the source / drain electrodes, the electrode or insulating layer formed on the uniform surface is formed. It is considered that it exhibits stable and good properties with no disturbance at the interface.

  In addition, since the diffusion of impurities from the substrate surface to the thin film is small, variations in the performance of the semiconductor thin film formed thereon are reduced, and a semiconductor thin film having excellent mobility and a small off current is formed.

  Further, it is considered that a thin film transistor having stable characteristics can be obtained because damage to other elements such as an electrode and an insulating film is small due to oxidation treatment conditions in semiconductor formation.

  FIG. 4 shows a preferred configuration example of the thin film transistor of the present invention.

  FIG. 4A shows a metal oxide semiconductor thin film 104 according to the present invention formed on a substrate 101, a source electrode 105, a drain electrode 106, and a gate insulating film 103 formed thereon, and a gate insulating film 103 on the gate insulating film 103. A top-gate thin film transistor having the structure of the present invention in which the electrode 102 is formed is shown. Reference numeral 108 denotes an undercoat layer.

  In FIG. 4B, a source electrode 105 and a drain electrode 105 are first formed on a substrate 101, and then a metal oxide semiconductor thin film 104 according to the present invention is formed, and then a gate insulating film 103 and a gate electrode are formed. Another example of a top-gate thin film transistor will be described.

  The structure of the thin film transistor of the present invention in which the gate insulating film is provided on the side opposite to the metal oxide semiconductor thin film support is preferable, and what is the metal oxide semiconductor thin film support? The configuration of FIG. 4A in which a source electrode and a drain electrode are provided on the opposite side is more preferable.

  FIG. 5 is a schematic equivalent circuit diagram of an example of a thin film transistor sheet 120 in which a plurality of thin film transistor elements of the present invention are arranged.

  The thin film transistor sheet 120 has a large number of thin film transistor elements 124 arranged in a matrix. Reference numeral 21 denotes a gate bus line of the gate electrode of each thin film transistor element 24, and reference numeral 122 denotes a source bus line of the source electrode of each thin film transistor element 24. 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, a liquid crystal is shown as an output element 126 by an equivalent circuit 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 thin film transistor element of the present invention can be used for producing such a thin film transistor sheet in which TFT elements are two-dimensionally arranged on a support.

(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, antimony lead, tantalum, indium, palladium, tellurium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin / antimony oxide, 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 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.

  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 from a conductive thin film formed by using 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 for 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, a method by an electroless plating method is used. 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 is applied to a portion where the electrode is provided. For example, after patterning 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 film)
Although various insulating films can be used as the gate insulating film of the thin film transistor of the present invention, an inorganic oxide film having a high relative dielectric constant is particularly 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.

  It is also preferable that the gate insulating film (layer) is composed of an anodized film or the anodized film and an insulating film. The anodized film is preferably sealed. The anodized film is formed by anodizing a metal that can be anodized by a known method.

  Examples of the metal that can be anodized include aluminum and tantalum, and the anodizing method is not particularly limited, and a known method can be used.

  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 films is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.

(substrate)
Various materials can be used as the support 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. In addition, a semiconductor substrate such as gallium nitrogen, paper, and non-woven fabric 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.

  In the thin film transistor element of the present invention, when the support is a plastic film, it preferably has at least one of an undercoat layer containing a compound selected from inorganic oxides and inorganic nitrides, and an undercoat layer containing a polymer.

  Examples of the inorganic oxide contained in the undercoat layer include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, titanate Examples thereof include lead lanthanum, strontium titanate, barium titanate, barium fluoride magnesium, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, and yttrium trioxide. Examples of the inorganic nitride include silicon nitride and aluminum nitride.

  Of these, silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, and silicon nitride are preferable.

  In the present invention, the undercoat layer containing a compound selected from inorganic oxides and inorganic nitrides is preferably formed by the atmospheric pressure plasma method.

  As the polymer used for the undercoat layer containing a polymer, various polymers such as polyester resin, polycarbonate resin, cellulose resin, acrylic resin, polyurethane resin, polyethylene resin, polypropylene resin, polystyrene resin, phenoxy resin, norbornene resin, epoxy resin , Vinyl chloride-vinyl acetate copolymer, vinyl chloride resin, vinyl acetate resin, copolymer of vinyl acetate and vinyl alcohol, partially hydrolyzed vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, Vinyl polymers such as vinyl chloride-acrylonitrile copolymer, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, chlorinated polyvinyl chloride, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, polyamide resin, D Len - butadiene resin, butadiene - rubber resin such as acrylonitrile resin, silicone resin, and fluorine resins.

  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 the protective layer is preferably formed by the atmospheric pressure plasma method described above.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

Example 1
A manufacturing process of a thin film transistor will be described with reference to the schematic diagram illustrated in FIGS.

A polyethylene naphthalate resin film (200 μm) was used as the resin support 11, and first, a corona discharge treatment was performed thereon 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 the undercoat layer 108 (FIG. 6 (1)). As the atmospheric pressure plasma processing apparatus, an apparatus according to FIG. 6 described in JP-A No. 2003-303520 was used.

(Used gas)
Inert gas: Helium 98.25% by volume
Reactive gas: 1.5% by volume of oxygen gas
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) having a pore treatment, smoothing the surface and having R _{max 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.

  Tetra-i-propoxytin and diethoxyzinc were dissolved in toluene at a molar ratio of 1: 1 to prepare a 5% by mass solution. This solution was discharged onto the undercoat layer of the support using an ink jet apparatus, and the solvent was cast to form a thin film having an average film thickness of 40 nm.

  Furthermore, it was exposed to oxygen plasma using an atmospheric pressure plasma method, and plasma oxidation treatment was performed at a film temperature of 140 ° C. under the following conditions. The cast thin film turned transparent and was converted into a thin film 104 made of a metal oxide semiconductor having a thickness of about 50 nm.

  The plasma oxidation treatment was performed under the following conditions using the same atmospheric pressure plasma apparatus as described above.

(Used gas)
Inert gas: Helium 99.5% by volume
Reactive gas: Oxygen gas 0.5% by volume
(Discharge conditions)
High frequency power supply: 13.56 MHz
Discharge output: 10 W / cm ²
Next, the source electrode 105 and the drain electrode 106 were formed on the surface of the metal oxide semiconductor thin film 104 by heating and vapor-depositing gold through a mask. Each size is 10 μm wide, 50 μm long (channel width) and 50 nm thick, and the distance (channel length) between the source electrode 15 and the drain electrode 16 is 15 μm (FIG. 6 (3)).

  Further, a silicon oxide film having a thickness of 200 nm was provided by the above-described atmospheric pressure plasma method at a film temperature of 150 ° C. to form a gate insulating film 103 (FIG. 6 (4)).

(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
Next, a gate electrode is formed. An aluminum film having a thickness of 300 nm was formed on one surface by sputtering, and then etched by photolithography to form the gate electrode 102 (FIG. 6 (5)).

The thin film transistor manufactured by the above method was driven well and showed n-type enhancement operation. An increase in drain current (transfer characteristics) was observed when the drain bias was 10 V and the gate bias was swept from -10 V to +20 V. The carrier mobility estimated from the saturation region was 3 cm ² / Vs, the on / off ratio was 6 digits, and the threshold was 5V.

Example 2
In Example 1, a thin film transistor was manufactured by changing the element configuration by reversing the process of manufacturing the semiconductor thin film 104, the source electrode 105, and the drain electrode 106 (FIG. 6 (6)).

  That is, after forming the source electrode 105 and the drain electrode 106 on the undercoat layer 108 of the support, the thin film 104 made of a metal oxide semiconductor is formed in the same manner, and the gate insulating film 103 and the gate electrode 102 are formed in the same manner. did.

The thin film transistor manufactured by the above method was driven well and showed n-type enhancement operation. An increase in drain current (transfer characteristics) was observed when the drain bias was 10 V and the gate bias was swept from -10 V to +20 V. The carrier mobility estimated from the saturation region was 1 cm ² / Vs, the on / off ratio was 5 digits, and the threshold was 20V.

Comparative Example The process order is changed to a conventional bottom gate configuration (FIG. 6 (7)).

  That is, after the undercoat layer 108 made of a silicon oxide film is formed, the gate electrode 12 is formed by the same method as in Example 1, and further an anodic oxide film (thickness 120 nm) and a silicon oxide film (thickness 30 nm) are combined. After the 150 nm gate insulating film 103 was formed, a metal oxide semiconductor thin film 14 (average film thickness: 100 nm) was further formed.

  Next, a source electrode 105 and a drain electrode 106 were formed by gold vapor deposition using a mask in the same manner as in Example 1 to fabricate a thin film transistor having the same size (FIG. 3 (7)).

The comparative thin film transistor fabricated by the above method showed n-type enhancement operation. An increase in drain current (transfer characteristics) was observed when the drain bias was 10 V and the gate bias was swept from -10 V to +20 V. The carrier mobility estimated from the saturation region was 0.2 cm ² / Vs, the on / off ratio was 3 digits, and the threshold was 35V.

  Thus, in a thin film transistor in which a metal oxide semiconductor thin film is formed by oxidation treatment from a precursor and the thin film is used as an active layer, the gate insulating film (and hence the gate electrode), and at least the source electrode and the drain electrode It can be seen that the structure in which one electrode is provided on the side opposite to the support as viewed from the metal oxide semiconductor thin film has more preferable characteristics.

It is the schematic which shows an example of an ultrasonic atomizer. It is the schematic which shows an example of a single wafer type atmospheric pressure plasma processing apparatus. It is the schematic which shows an example of a roll-type atmospheric pressure plasma processing apparatus. It is sectional drawing which shows the preferable structural example of a thin-film transistor. It is a schematic equivalent circuit diagram of an example of a thin-film transistor sheet. The schematic diagram of a thin-film transistor manufacturing process is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrasonic sprayer 11 Introducing pipe 12 Raw material storage part 13 Ultrasonic wave generation part 14 Power supply 15 Release pipe 21 1st electrode 22, 32 2nd electrode 22R, 35 Roll rotation electrode 25A, 25B High frequency power supply 26A, 26B Matching box 27A, 27B Filter 101 Substrate 102 Gate electrode 103 Gate insulating film 104 Thin film 105 Source electrode 106 Drain electrode 120 Thin film transistor sheet 121 Gate bus line 122 Source bus line 124 Thin film transistor element 125 Storage capacitor 126 Output element 127 Vertical drive circuit 128 Horizontal drive circuit

Claims (5)

In a thin film transistor having a metal oxide semiconductor thin film formed by a step of forming a thin film containing a precursor of a metal oxide semiconductor on a substrate and then oxidizing the thin film as an active layer, the metal oxide semiconductor thin film support A thin film transistor, wherein a gate insulating film is provided on a side opposite to the gate electrode. 2. The thin film transistor according to claim 1, wherein at least one of a source electrode and a drain electrode is provided on a side opposite to the support of the metal oxide semiconductor thin film. 3. The thin film transistor according to claim 1, wherein the step of oxidizing the thin film containing the metal oxide semiconductor precursor is plasma oxidation. 4. The thin film transistor according to claim 3, wherein the step of oxidizing the thin film containing the metal oxide semiconductor precursor is performed by an atmospheric pressure plasma method. The thin film transistor according to any one of claims 1 to 4, wherein the gate insulating film is formed by an atmospheric pressure plasma method.

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