JP2013175648A - Field effect transistor and manufacturing method thereof - Google Patents

Abstract

A method of manufacturing a field effect transistor that is suitable in terms of materials and processes is provided.
A method of manufacturing a field effect transistor having at least a gate electrode, a source electrode, a drain electrode, a channel layer, and a gate insulating layer, using a metal salt-containing composition including a metal salt, an organic solvent, and water. Forming a channel layer, and heat-treating the metal salt-containing composition under an atmospheric gas containing an oxygen gas and an inert gas when the channel layer is formed. .
[Selection] Figure 2

Description

  The present invention relates to a field effect transistor and a manufacturing method thereof. More specifically, the present invention relates to a field effect transistor that can be used as a TFT and a method for manufacturing the same.

  With the widespread use of information terminals, there is an increasing need for flat panel displays as computer displays. In a flat panel display, generally, a display medium is formed using an element using liquid crystal, organic EL (organic electroluminescence), electrophoresis, or the like. In such display media, a technique using an active drive element (for example, a field effect transistor such as a TFT element) as an image drive element has become the mainstream in order to ensure uniformity of screen brightness, screen rewriting speed, and the like. The TFT is an abbreviation of “Thin Film Transistor” and is also referred to as a thin film transistor. For example, in a normal computer display, a TFT element is formed on a substrate, and a liquid crystal, an organic EL element and the like are sealed.

  Here, although it is mainly used a semiconductor such as a-Si (amorphous silicon) in the TFT element, since the mobility of a-Si is not as high as about 0.5, the large area of the display It is becoming difficult to cope with the trend toward higher speed and higher speed driving.

  Under such circumstances, metal oxide semiconductors have attracted attention as semiconductors that can be manufactured relatively easily with high characteristics. As a method for manufacturing such a semiconductor, a vacuum process such as a sputtering method or an ALD method or a solution method using a printing technique can be considered, but a method using a sputtering method has become the mainstream as a method for manufacturing an oxide semiconductor. Yes.

Japanese Patent Application No. 2010-290516 JP2011-77514

  A vacuum process such as sputtering requires a “vacuum device” as a matter of course, but the vacuum device itself is relatively expensive. In addition, the formation of a metal oxide semiconductor layer that becomes a channel layer of a TFT (particularly “a process for forming by a solution method using a printing technique”) generally requires a high temperature and an oxidizing atmosphere. In addition, heat resistance and oxidation resistance are required for electrodes and gate insulating materials. That is, other TFT elements such as a substrate, an insulating film, and an electrode material are limited in terms of material selection.

  On the other hand, even if a metal oxide layer is formed as the channel layer, the threshold voltage tends to shift if the oxidation of the metal oxide layer is insufficient. In such a case, even if the gate voltage is 0 V, current flows between the source electrode and the drain electrode, so-called “normally on” (see FIG. 25). A transistor in which a channel is formed and a drain current flows even when a gate voltage is not applied is not suitable as a thin film transistor used in a circuit.

  The present invention has been made in view of the above circumstances. That is, the main problem of the present invention is to provide a manufacturing method capable of forming a channel layer in a field effect transistor such as a thin film transistor by a suitable process, and accordingly, a stable and high performance field effect transistor (particularly “ It is an object of the present invention to provide a field effect transistor in which normally on is prevented.

In order to solve the above problems, in the present invention,
A method of manufacturing a field effect transistor having at least a gate electrode, a source electrode, a drain electrode, a channel layer, and a gate insulating layer,
A channel layer is formed from a metal salt-containing composition comprising a metal salt, an organic solvent, and water, and the metal salt-containing composition is formed under an atmospheric gas comprising an oxygen gas and an inert gas when forming the channel layer. There is provided a method of manufacturing a field effect transistor, characterized by heat-treating.

  One of the features of the present invention is that a “metal salt-containing composition comprising a metal salt, an organic solvent and water” is used in forming a channel layer of a field effect transistor, and such a metal salt-containing composition is used as “oxygen gas”. And heat treatment under an atmospheric gas containing an inert gas.

  In this specification, “atmospheric gas containing oxygen gas and inert gas” means a gas containing oxygen gas and inert gas as the name implies. However, it does not exclude the inclusion of trace amounts of impurities that may be inevitably or accidentally included. Therefore, in the present invention, the “atmosphere gas” means the trace amounts of impurities that are inevitably or accidentally included. Gas may also be included in some cases.

  In this specification, the “field effect transistor” means a transistor that controls the conductance of a current path (channel) by an electric field from a gate electrode. An example of such a field effect transistor is a thin film transistor (TFT).

  In a preferred embodiment, the oxygen gas concentration of the atmospheric gas is about 1 ppm to about 10,000 ppm. That is, the heat treatment of the metal salt-containing composition is performed in “substantially an inert gas atmosphere” in which a trace amount of oxygen gas is contained in the inert gas.

  In another preferred embodiment, the metal salt-containing composition is heat-treated in a state where the atmospheric gas is circulated. That is, the metal salt-containing composition is heat-treated while flowing “a gas containing oxygen gas and inert gas” through the metal salt-containing composition. In such an embodiment, it is preferable to perform heat treatment using a tubular furnace. In this case, it is preferable to distribute “a gas containing oxygen gas and inert gas” in the tubular furnace during the heat treatment of the metal salt-containing composition.

  In still another preferred embodiment, the heat treatment of the metal salt-containing composition is performed under positive pressure conditions. For example, when the heat treatment of the metal salt-containing composition is performed using a heating furnace such as a heating chamber, the inside of the heating furnace is set to a positive pressure condition.

  The inert gas contained in the atmospheric gas is preferably nitrogen gas and / or noble gas. More specifically, the inert gas is preferably one or more gases selected from the group consisting of nitrogen gas, helium, neon and argon.

  In a preferred embodiment, the metal salt-containing composition is heat-treated at a temperature of about 200 ° C to about 600 ° C. In other words, the metal salt-containing composition is subjected to a firing treatment at a heating temperature of about 200 ° C. to about 600 ° C. under an atmospheric gas containing oxygen gas and inert gas.

  The metal salt contained in the metal salt-containing composition may be one or more salt forms selected from the group consisting of nitrates, sulfates, carboxylates, halides, alkoxides and acetylacetone salts, preferably nitrates. It is.

  Metal salts resulting from such nitrates are Mg, Ca, Sr, Ba, Y, Ti, Zr, Hf, Nb, Ta, Cr, W, Fe, Ni, Cu, Ag, Zn, Al, Ga, In, Sn And one or more metal salts selected from the group consisting of Sb. Preferably, the metal salt contained in the metal salt-containing composition comprises one or more metal salts selected from In, Ga, and Zn.

  The “water” (or “water”) in the metal salt-containing composition preferably has a content of 0.05 to 50% by weight based on the entire composition.

The production method of the present invention may have the following steps (i) to (iv):
(I) forming a gate electrode on the substrate;
(Ii) forming a gate insulating layer on the substrate so as to cover the gate electrode;
(Iii) A “metal salt-containing composition comprising a metal salt, an organic solvent and water” is provided on the gate insulating layer to form a channel precursor layer, and the channel precursor layer is formed as “inert with oxygen gas”. A step of forming a channel layer by heating under an atmospheric gas containing a gas, and (iv) a step of forming a source electrode and a drain electrode so as to be in contact with the channel layer.

In another preferred embodiment, the production method of the present invention may have the following steps (i) ′ to (vi) ′:
(I) 'preparing a metal foil,
(Ii) 'forming a gate insulating layer on the metal foil;
(Iii) 'A “metal salt-containing composition comprising a metal salt, an organic solvent and water” is provided on the gate insulating layer to form a channel precursor layer, and the channel precursor layer is made “inert with oxygen gas” A step of forming a channel layer by heating under an atmospheric gas comprising a gas,
(Iv) forming a source electrode and a drain electrode in contact with the channel layer;
(V) 'a step of forming a sealing layer so as to cover the channel layer, the source electrode and the drain electrode; and (vi)' a step of etching the metal foil to form a gate electrode.

The present invention also provides a field effect transistor that can be obtained by the above manufacturing method. Such a field effect transistor of the present invention comprises:
Channel layer,
Gate electrode,
A gate insulating layer positioned at least between the channel layer and the gate electrode, and a source electrode and a drain electrode disposed in contact with the channel layer,
The channel layer comprises a metal oxide, and the metal oxide contains a metal salt comprising a metal salt, an organic solvent and water by “heating under an atmospheric gas comprising an oxygen gas and an inert gas”. It is an oxide formed from the “composition”, and the carrier concentration of the channel layer is about 10 ¹⁶ / cm ³ to about 10 ¹⁸ / cm ³ .

In the field effect transistor of the present invention, since the carrier concentration of the metal oxide is about 10 ¹⁶ / cm ³ to about 10 ¹⁸ / cm ³ , a channel layer contributing to “normally off” is provided.

  In this specification, the “gate insulating layer located at least between the channel layer and the gate electrode” substantially means an aspect in which at least a part of the gate insulating film exists between the channel layer and the gate electrode. (See Fig. 1)

  In a preferred embodiment, the arithmetic average roughness Ra of the surface in the channel layer is about 10 nm or less, preferably about 5 nm or less, more preferably about 1 nm or less. That is, the arithmetic average roughness Ra of the surface in the channel layer (upper surface in the drawing) is 0 (excluding 0) to about 10 nm, preferably 0 (excluding 0) to about 5 nm, more preferably 0 (excluding 0). ˜about 1 nm, and the channel layer is substantially flat.

  In another preferred embodiment, the channel layer metal oxide is an amorphous oxide. Further, although depending on the metal salt of the raw material composition, the metal oxide of the channel layer is an oxide of one or more metals selected from the group consisting of In, Ga and Zn.

  According to the production method of the present invention, since “a paste-like metal salt-containing composition comprising a metal salt, an organic solvent and water” is used as the channel layer material, the paste material is applied, printed and heated. Through this, a channel layer can be formed. This means that the field effect transistor can be manufactured by a simple process. Therefore, the productivity is improved and the cost is reduced.

  In particular, in the present invention, the metal salt-containing composition is heated using “atmospheric gas containing oxygen gas and inert gas”, whereby a dense and stable channel layer can be obtained. Further, the oxidation resistance required for the material by the conventional solution method is not necessary, and “a material susceptible to oxidation” such as copper can be positively used for manufacturing the thin film transistor.

  Furthermore, in the present invention, a channel layer of a metal oxide film that is “normally off” can be obtained as a result. In general, it is considered that “the heating in an inert atmosphere makes the oxidation state of the metal oxide insufficient and the threshold voltage easily shifts”. In the present invention, “this can be regarded as a substantially inert gas”. Even under “atmosphere” conditions, a channel layer that is “normally off” can be obtained. In other words, in the present invention, a stable and high-performance thin film transistor is obtained through a process of heat-treating a “metal salt-containing composition comprising a metal salt, an organic solvent and water” in an atmosphere of “deemed inert gas”. Can do.

Sectional drawing which shows the structure of the thin-film transistor in 1st Embodiment of this invention. Schematic diagram showing an example (embodiment using a tubular furnace) of "heating of a metal salt-containing composition under an atmospheric gas containing oxygen gas and inert gas" in the present invention Schematic diagram showing an example (an embodiment using a heating chamber) of “heating of a metal salt-containing composition under an atmosphere gas containing oxygen gas and inert gas” in the present invention Process sectional drawing which shows the manufacturing process of the thin-film transistor in 1st Embodiment of this invention. Process sectional drawing which shows another manufacturing process of the thin-film transistor in 1st Embodiment of this invention. Sectional drawing which shows the structure of the thin-film transistor in 2nd Embodiment of this invention. Process sectional drawing which shows the manufacturing process of the thin-film transistor in 2nd Embodiment of this invention. Sectional drawing which shows the structure of the thin-film transistor in 3rd Embodiment of this invention. Process sectional drawing which shows the manufacturing process of the thin-film transistor in 3rd Embodiment of this invention. External perspective view showing the overall appearance of the image display device Thin film transistor structure in a modified form of the invention Thin film transistor structure in a modified form of the invention Thin film transistor structure in a modified form of the invention Results of film surface observation by AFM Illustration of arithmetic mean roughness Ra Graph of X-ray reflectivity measurement results Illustration of transistor characteristics confirmation test Graph of results of transistor characteristic confirmation test Schematic showing product application example (TV image display part) of field effect transistor Schematic diagram showing a product application example (image display part of a mobile phone) of a field effect transistor Schematic diagram showing a field effect transistor product application example (image display part of a mobile computer or notebook computer) Schematic diagram showing a product application example of a field effect transistor (image display part of a digital still camera) Schematic diagram showing a product application example (camcorder image display part) of a field effect transistor Schematic diagram showing product application example (image display part of electronic paper) of field effect transistor Graph to explain “normally on” (prior art)

  Next, the manufacturing method of the field effect transistor of the present invention will be described with reference to the drawings. The field effect transistor will also be described in the form accompanying the description of the manufacturing method.

<Metal salt-containing composition>
The manufacturing method of the present invention is a method of manufacturing a field effect transistor 100 (see FIG. 1) including a gate electrode 20, a source electrode 40, a drain electrode 50, a channel layer 10, and a gate insulating layer 30. In the production method of the present invention, a metal salt-containing composition containing a metal salt, an organic solvent and water is heat-treated under an atmospheric gas containing an oxygen gas and an inert gas, thereby containing the metal salt-containing composition. A channel layer of a field effect transistor is formed from the composition.

  The oxygen gas concentration in the atmospheric gas is preferably from about 1 ppm to about 10,000 ppm, more preferably from about 2 ppm to about 1000 ppm, even more preferably from about 3 ppm to about 150 ppm (for example, from 3 to 100 ppm, 4 to 20 ppm, or 6 to 15 ppm). possible). As described above, since the oxygen concentration of the atmospheric gas is low, the atmospheric gas used in the present invention can be regarded as a “substantially inert gas atmosphere”. The “oxygen concentration” / “oxygen gas concentration” as used in the present invention is a value obtained by measurement using, for example, a zirconia oxygen analyzer “SA25NW / LD-300 (manufactured by Toray Engineering Co., Ltd.)”. It means that.

  The atmospheric gas preferably does not contain water, hydrogen, or the like. The inert gas and the oxygen gas may be introduced into the heat treatment apparatus in a premixed state, or they may be introduced separately into the heat treatment apparatus. The inert gas used is preferably nitrogen or a rare gas such as helium, neon, or argon. In such a case, the purity of nitrogen introduced into the heat treatment apparatus or the rare gas such as helium, neon, or argon is 5N (99 .999%) or more, preferably 6N (99.9999%) or more.

  Here, when the channel layer is formed by heating a metal salt-containing composition containing a metal salt, an organic solvent, and water in the above atmospheric gas, the inventors of the present application have a low oxygen concentration in the atmospheric gas. However, it has been found that the carrier concentration of the channel layer to be formed is not increased, and only the channel resistance value resulting from the application of the gate voltage during TFT operation is reduced. If the oxygen concentration in the atmospheric gas is too small, the channel layer (metal oxide film) can be a high resistance body. Therefore, the lower limit value of the oxygen gas concentration in the atmospheric gas is preferably the value shown above.

  The type of metal salt contained in the metal salt-containing composition may be one or more salt forms selected from the group consisting of nitrates, sulfates, carboxylates, halides, alkoxides, and acetylacetone salts. Nitrate is preferable in terms of impurity residue components and process simplicity.

  Metal salts contained in the metal salt-containing composition used for forming the channel layer are Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), Y (yttrium), Ti (titanium), Zr ( Zirconium), Hf (hafnium), Nb (niobium), Ta (tantalum), Cr (chromium), W (tungsten), Fe (iron), Ni (nickel), Cu (copper), Ag (silver), Zn ( It is preferably a salt of one or more metals selected from the group consisting of zinc), Al (aluminum), Ga (gallium), In (indium), Sn (tin) and Sb (antimony). This is because these metal salt oxides can be converted into semiconductors by becoming single or complex oxides.

  With regard to channel layer formation in particular, the metal salt contained in the metal salt-containing composition is preferably a salt comprising at least In, Ga, and Zn (zinc). This is because oxides of these metal salts can be suitable for field effect transistors (for example, thin film transistors) in terms of mobility and stability.

  The content (concentration) of the metal salt in the metal salt-containing composition is not particularly limited as long as the metal salt itself dissolves in the solvent, and is appropriately determined according to the thickness of the metal oxide film to be formed. Can be adjusted. For example, the content (concentration) of the metal salt in the metal salt-containing composition may range from about 0.005 mol / L to about 1 mol / L (based on the total composition at room temperature).

  In particular, when a composition containing a salt containing Zn, a salt containing In and a salt containing Ga is used for forming the channel layer, each may be used in an equimolar amount, for example, about 0.01 to 0.5 mol / L. The concentration may preferably be about 0.05 to 0.15 mol / L (about 0.1 mol / L, for example) (based on the entire composition at room temperature).

  The organic solvent contained in the metal salt-containing composition is not particularly limited as long as it can stably dissolve the metal salt. For example, as an organic solvent, methanol, ethanol, ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 3-methoxymethylbutanol (for example, 3-methoxy-3-methyl-1-butanol) One or more organic solvents selected from the group consisting of N-methylpyrrolidone, terpineol, and the like. The content of such an organic solvent is not particularly limited, but may be, for example, about 50 to 90% by weight, preferably about 60 to 85% by weight (based on the whole composition).

  The metal salt-containing composition contains water (or moisture). Such water content is preferably from about 0.05% to about 50%, more preferably from about 1% to about 50%, more preferably about 5% by weight, based on the total composition. To about 30% by weight (eg, it may be about 5% to about 20% by weight). There is no restriction | limiting in particular in the form of the water contained in a metal salt containing composition, Any form may be sufficient. For example, although water in a simple substance form may be typically contained in a metal salt-containing composition, the organic solvent itself may contain water, or water as a hydrate of a metal salt. May be included. Regardless of which form is included, it is desirable that the total water content based on the entire composition be in the above numerical range.

  In the present invention, the metal salt-containing composition is heat-treated in an atmospheric gas containing oxygen gas and inert gas. The heating temperature under atmospheric gas is preferably about 200 ° C. to about 600 ° C., more preferably about 300 ° C. to about 500 ° C. Through such heat treatment, the metal salt-containing composition is subjected to firing, and as a result, a channel layer is obtained from the metal salt-containing composition. In the present invention, the “heating temperature” refers to the temperature of the “metal salt-containing composition” itself to be heated, but alternatively or simply can be regarded as the temperature of the “atmosphere gas” itself. Alternatively, it may be regarded as a set temperature of the heating means.

  The heat treatment under the atmospheric gas is preferably performed in a state in which the atmospheric gas is circulated as shown in FIG. That is, it is preferable to perform the heat treatment of the metal salt-containing composition in an environment in which “a gas containing oxygen gas and inert gas” flows from one to the other. The flow rate of the gas flow is preferably about 0.5 SLM to about 100 SLM, more preferably about 1 SLM to about 50 SLM, and even more preferably about 5 SLM to about 20 SLM (SLM: Gas). The amount of gas supplied in one minute in the standard state of 1 in liters).

  In the heating under the circulation of the atmospheric gas, it is preferable to use a tubular furnace 200 as shown in FIG. That is, it is preferable to heat the metal salt-containing composition provided inside the tubular furnace 200 while flowing “a gas containing oxygen gas and inert gas” through the tubular furnace 200. The term “tubular furnace” as used herein refers to a heating furnace in which the furnace has a cylindrical shape, gas can be flowed from one furnace end, and supply gas can be discharged from the other furnace end. Meaning. When such a tubular furnace is used, it is possible to heat the entire area around the pipe, contribute to uniform heating, and a gas component ratio (oxygen) around the metal salt-containing composition due to continuous gas supply. Variation in gas concentration can be reduced. That is, in a tubular furnace, both “desired temperature” and “desired concentration” are easily produced.

  Further, as shown in FIG. 3, a heating furnace such as a heating chamber 300 may be used for the heat treatment under atmospheric gas. In such a case, it is preferable to heat the metal salt-containing composition under conditions that allow the inside of the heating furnace to be in a positive pressure state. "Positive pressure" here means substantially the differential pressure between the internal space of the heating furnace and the surrounding ambient atmosphere. Therefore, the “positive pressure” can be represented by, for example, the difference between the pressure in the internal space of the heating chamber 300 and the atmospheric pressure. For example, the inside of the heating furnace is, for example, a positive pressure state of 0 (excluding 0) to about 10 kPa, preferably 0 (excluding 0) to a positive pressure state of about 1 kPa, and more preferably 0 (0 The atmospheric gas conditions are preferably such that a positive pressure state of about 500 Pa is excluded. In such a “positive pressure state”, impurities from the outside can be prevented from being mixed, so that fluctuations in the component ratio (oxygen gas concentration) of the furnace gas can be prevented. In order to maintain the “positive pressure state”, it is generally preferable to continue supplying gas from the outside, and in order to avoid the pressure in the furnace from becoming higher than necessary, the gas in the heating furnace is required. Is preferably discharged. From this point of view, it can be said that the “mode using the tubular furnace 200” can correspond to the “mode in which the inside of the heating furnace 300 is in a positive pressure state”.

  According to the present invention, a normally off channel layer can be obtained even under conditions that can be regarded as an inert gas atmosphere. More specifically, it is possible to obtain a channel layer in which “normally on” (FIG. 25) exhibiting the characteristic that the rising voltage is shifted to the negative side in the gate voltage-drain current correlation graph is prevented. (See also FIG. 18 to be described later). In addition, the metal oxide obtained by “heating under an atmosphere gas containing oxygen gas and inert gas” according to the present invention has good stability to the subsequent heat treatment. That is, good characteristics as the channel layer can be maintained regardless of the subsequent heat treatment.

<Manufacturing process>
First Embodiment Next, a manufacturing process of the thin film transistor (TFT) 100 shown in FIG. 1 is illustrated with reference to FIGS.

  In manufacturing the thin film transistor 100, first, the step (i) is performed. That is, the gate electrode 20 is formed on the substrate 60 as shown in FIG.

  Examples of the material of the substrate 60 include glass, alumina, glass-alumina composite material, silicon, epoxy resin, polyimide resin, stainless steel, and copper. In this embodiment, a glass substrate is used as the substrate 60. The thickness of the substrate 60 is preferably in the range of about 50 μm to about 1800 μm, more preferably in the range of about 200 μm to about 800 μm (eg, about 700 μm).

The gate electrode 20 is formed at a predetermined position on the substrate. The material of the gate electrode 20 is gold (Au), silver (Ag), copper (Cu), nickel (Ni), chromium (Cr), cobalt (Co), magnesium (Mg), calcium (Ca), platinum ( Metal materials such as Pt), molybdenum (Mo), iron (Fe) and / or zinc (Zn), or tin oxide (SnO ₂ ), indium tin oxide (ITO), fluorine-containing tin oxide (FTO), ruthenium oxide Examples thereof include conductive oxides such as (RuO ₂ ), iridium oxide (IrO ₂ ), and platinum oxide (PtO ₂ ). The formation method of the gate electrode is not particularly limited, and a conventional electrode formation method may be employed. For example, the gate electrode may be formed by a printing method / printing process, or may be formed by a vacuum deposition method, a sputtering method, or the like. In this embodiment, the gate electrode is formed by depositing ITO by a sputtering method using a mask. The thickness of the gate electrode 20 is preferably in the range of about 10 nm to about 100 nm, more preferably in the range of about 15 nm to about 50 nm (eg, about 30 nm).

  Subsequent to step (i), step (ii) is performed. That is, as shown in FIG. 4B, the gate insulating layer 30 is formed on the substrate 60 so as to cover the gate electrode 20.

The gate insulating layer 30 may be a resin-based or inorganic insulating-based insulating film. Examples of the resin-based insulating film include films made of epoxy resin, polyimide (PI) resin, polyphenylene ether (PPE) resin, polyphenylene oxide resin (PPO), polyvinyl pyrrolidone (PVP) resin, and the like. On the other hand, examples of the inorganic insulating insulating film include, for example, tantalum oxide (Ta ₂ O ₅ etc.), aluminum oxide (Al ₂ O ₃ etc.), silicon oxide (SiO ₂ etc.), zeolite oxide (ZrO). ₂ ), titanium oxide (TiO ₂ etc.), yttrium oxide (Y ₂ O ₃ etc.), lanthanum oxide (La ₂ O ₃ etc.), hafnium oxide (HfO ₂ etc.), Examples thereof include films made of such metal nitrides. A film made of a dielectric material such as barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), calcium titanate (CaTiO ₃ ) can be given.

The gate insulating layer 30 may be formed by a printing method or a printing process, or a vacuum deposition method, a sputtering method, or the like may be used. Especially in the case of forming a resin-based insulating film, a coating agent (which may be a resist containing a photosensitive agent) in which a resin material is mixed with a medium is applied to a formation position, followed by drying, and heat treatment. The gate insulating layer 30 can be formed by applying and curing. On the other hand, in the case of an inorganic insulator system, the gate insulating layer 30 can be formed by a thin film forming method using a mask (such as sputtering). In this embodiment, a tantalum oxide film (Ta ₂ O ₅ ) is formed by sputtering to form the gate insulating layer 30. The thickness of the gate insulating layer 30 is preferably in the range of about 0.1 μm to about 2 μm, more preferably in the range of about 0.2 μm to about 1 μm (eg, about 0.3 μm).

  Subsequent to step (ii), step (iii) is performed. That is, after forming a channel precursor layer 11 by applying a metal salt-containing composition on the gate insulating layer 30 as shown in FIG. 4C, the channel precursor layer is shown in FIG. 11 is heat-treated to obtain the channel layer 10.

  Since the metal salt-containing composition has a paste form, the application method thereof is, for example, a technique such as spray coating, spin coating, screen printing, gravure coating, bar coating, roll coating, die coating, or inkjet. Can do. What is necessary is just to select these coating methods suitably according to the viscosity of a metal salt containing composition, and, thereby, uniform precursor layer thickness (namely, uniform film thickness) can be formed. The thickness of the channel precursor layer 11 is preferably in the range of about 30 μm to about 300 μm, more preferably in the range of about 50 μm to about 150 μm (eg, about 70 μm).

  The precursor layer is subjected to baking through heat treatment of the channel precursor layer 11, whereby the channel layer 10 is formed from the precursor layer 11. Such heat treatment is preferably performed in two stages, a primary heating process and a secondary heating process. The primary heating step is mainly intended for the drying treatment of the channel precursor layer (ie, the applied metal salt-containing composition), while the secondary heating step is mainly for the substantial firing treatment of the precursor layer. Is intended. In the present invention, it is preferable to carry out at least the secondary heating step of the channel precursor layer under “atmospheric gas containing oxygen gas and inert gas”.

  Specifically, after the channel precursor 11 is dried at a temperature of about 100 ° C. to about 200 ° C. for about 1 to 15 minutes as a primary heating step, a baking treatment is performed at a temperature of about 200 ° C. to about 600 ° C. as a secondary heating step. It is preferable to carry out at a temperature of about 10 ° C. (more preferably about 300 ° C. to about 500 ° C.) for about 10 to about 120 minutes. This is because when the heat treatment at about 400 ° C. or higher is performed without passing through the primary heating step, the resulting metal oxide film is likely to be non-uniform, and spots and the like are likely to occur. When such “non-uniformity” occurs, the characteristics of the thin film transistor cannot be stabilized, and the practical value is impaired.

  The temperature of the primary heating step may be appropriately selected according to the type of the organic solvent contained in the metal salt-containing composition. However, since the metal salt-containing composition contains moisture, the temperature is about 100 ° C. or higher from that viewpoint. Preferably there is. On the other hand, if the temperature of the primary heating step becomes higher than necessary, the intermediate oxide film formed after the primary heating step is difficult to be uniform. Therefore, the upper limit temperature of the primary heating step is preferably 200 ° C. from this viewpoint.

  The atmospheric gas in the primary heating process is not particularly limited, and the pressure condition in the primary heating process is not particularly limited. Therefore, the primary heating may be performed under atmospheric pressure conditions, for example.

  As a heating means in the primary heating step, for example, a heating furnace may be used. By providing the “substrate 60 including the gate electrode 20, the gate insulating layer 30, and the channel precursor layer 11” in the heating furnace, a channel precursor is provided. The body layer can be heat-treated as a whole.

  After performing the drying process in the primary heating process, the baking process is performed as the secondary heating process. In the present invention, at least the secondary heating step is performed under “atmosphere gas containing oxygen gas and inert gas”. More specifically, “the oxygen gas concentration in the inert gas is preferably about 1 to 10,000 ppm, more preferably about 2 to 1000 ppm, still more preferably about 3 to 150 ppm (for example, 3 to 100 ppm, 4 to 20 ppm, or 6 to 6 ppm). The channel precursor layer after drying is subjected to a heat treatment under a substantially inert gas atmosphere (approximately 15 ppm).

  The temperature of the secondary heating process promotes the formation of the metal oxide film, but if the temperature becomes lower than necessary, the residue in the metal oxide film increases and the semiconductor characteristics of the channel layer are likely to deteriorate. Therefore, the temperature is preferably about 200 ° C. or higher from that viewpoint. On the other hand, the upper limit temperature of the secondary heating process may be appropriately determined depending on the heat-resistant temperature of the substrate 60 and the properties of the metal oxide film. For example, when a glass substrate is used as the substrate, about 500 ° C. can be the upper limit temperature of the secondary heating step. Even when a substrate with high heat resistance is used, if it exceeds about 600 ° C., a metal oxide film (for example, an In—Ga—Zn-based amorphous metal oxide film) is crystallized to reduce reliability. From this viewpoint, the upper limit temperature of the secondary heating step is preferably about 600 ° C.

  In the secondary heating step, the above-described tubular furnace 200 (FIG. 2) may be used, and the field effect transistor precursor 100 ′, that is, “gate electrode 20, gate insulating layer 30” is included in the tubular furnace 200. And the substrate 60 "provided with the channel precursor layer 11", the channel precursor layer 11 may be subjected to a heat treatment. In such a case, the flow rate of the gas flowing into the tubular furnace may be, for example, about 5 SLM to 20 SLM. Further, in the secondary heating step, a heating chamber 300 as shown in FIG. 3 may be used, and the field effect transistor precursor 100 ′, that is, “the gate electrode 20, the gate insulating layer 30, and the channel is included in the heating chamber 300. By providing the substrate 60 "with the precursor layer 11, the channel precursor layer 11 can be heat-treated.

  The channel precursor layer 11 is subjected to baking by the heat treatment in the step (iii), and as a result, the channel layer 10 is formed from the channel precursor layer 11. The final thickness of the channel layer 10 can preferably be in the range of about 8 nm to about 50 nm, more preferably in the range of about 10 nm to about 20 nm (eg, about 15 nm).

  In addition, the heat treatment (particularly “secondary heating”) of the channel precursor layer in the step (iii) can be performed by laser irradiation in addition to the above-described baking.

  Subsequent to step (iii), step (iv) is performed. That is, as shown in FIG. 4E, the source electrode 40 and the drain electrode 50 are formed so as to be in contact with the channel layer 10. As a material of the source / drain electrodes, a metal having good conductivity is preferable, and for example, copper (Cu), nickel (Ni), aluminum (Al), stainless steel (SUS), or the like can be used. The formation of the source electrode 40 and the drain electrode 50 is not particularly limited, and a conventional electrode forming method may be employed. That is, the source electrode and the drain electrode may be formed by a printing method / printing process, or a vacuum deposition method, a sputtering method, or the like may be used. As this embodiment, a source electrode and a drain electrode are obtained by forming an aluminum electrode by performing a vacuum evaporation method. Each thickness of the source electrode 40 and the drain electrode 50 is preferably in the range of about 0.02 μm to about 10 μm, more preferably in the range of about 0.03 μm to about 1 μm (eg, about 0.1 μm).

  After the formation of the source and drain electrodes, a channel layer sealing step and a wiring layer are formed as necessary.

  Through the steps (i) to (iv) as described above, the thin film transistor 100 as shown in FIG. 4E or FIG. 1 can be obtained. In such a manufacturing process, a “semiconductor film made of a metal oxide” constituting the channel layer 10 is formed by heating in an atmospheric gas. Therefore, a high-performance thin film transistor can be obtained at a low cost without using an expensive vacuum device or the like for channel formation, and the selection of materials such as a substrate, an electrode, and an insulating layer is not greatly limited.

As shown in FIG. 1, the obtained thin film transistor 100 is disposed in contact with the channel layer 10, the gate electrode 20, the gate insulating layer 30 positioned at least between the channel layer 10 and the gate electrode 20, and the channel layer 10. The source electrode 40 and the drain electrode 50 are formed. In the thin film transistor 100, the channel layer 10 is made of a metal oxide, and the metal oxide is an oxide formed from the above-described metal salt-containing composition. Particularly due to the fact that the metal salt-containing composition was formed by heating in the atmospheric gas, the channel layer 10 has a substantially stable carrier concentration. The carrier concentration of the channel layer 10 is 10 ¹⁶ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less, preferably 10 ¹⁷ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less (as a result, the off current is small and the thin film transistor is formed). Incidentally, the carrier concentration of the channel layer obtained by the prior art process which is not “substantially heated under inert gas” is approximately 10 ²² cm ⁻³ ). Further, in the thin film transistor 100, the metal oxide of the channel layer 10 is preferably an amorphous oxide.

In the present invention, the channel layer is formed using a metal salt-containing composition including a salt of one or more metals selected from the group consisting of, for example, In (indium), Ga (gallium), and Zn (zinc). In this case, the obtained channel layer 10 has a film form made of a metal oxide containing In, Ga and / or Zn. Here, in particular, when the channel layer has a film form made of a metal oxide containing In, Ga, and Zn, the density of the channel layer 10 is about 4.0 to 5.5 g / cm ³ , for example, 4.3. It can be about ˜4.8 g / cm ³ (film thickness is about 10 nm to 40 nm). Further, the flatness of the channel layer 10 can be improved. For example, the arithmetic average roughness Ra of the surface of the channel layer is about 10 nm or less, preferably about 5 nm or less, more preferably about 1 nm or less (for example, about 0.5 nm or less). It has become.

Modification of the First Embodiment Next, with reference to FIGS. 5A to 5E, a modification of the thin film transistor manufacturing method of the first embodiment will be described. The description of the same points as in the manufacturing process described above will be omitted.

  First, as shown in FIG. 5A, the gate electrode 20 and the gate insulating layer 30 are formed on the substrate 60.

  Next, as shown in FIG. 5B, the metal salt-containing composition is applied so as to cover substantially the entire gate insulating layer 30 to form the channel precursor layer 11. Subsequently, as shown in FIG. 5C, the channel precursor layer 11 is heat-treated to form a metal oxide film 12 from the precursor layer 11. More specifically, the channel layer 10 is formed through a process of heating “a metal salt-containing composition containing a metal salt, an organic solvent and water” under “atmospheric gas containing oxygen gas and inert gas”. (This step can be carried out in the mode described in the above “first embodiment”).

  Next, as shown in FIG. 5D, the metal oxide film 12 is partially removed, and the channel layer 10 is formed at a position facing the gate electrode 20. Such partial removal of the metal oxide film can be performed, for example, by dry etching or wet etching.

  Finally, as shown in FIG. 5E, the thin film transistor 100 is completed by forming the source electrode 40 and the drain electrode 50 in contact with the channel layer 10.

Second Embodiment Next, a manufacturing process of a thin film transistor (TFT) 100 as shown in FIG. 6 is illustrated with reference to FIGS. This manufacturing process corresponds to the steps (i) ′ to (vi) ′ described in [Summary of the Invention]. A description of the same points as in the manufacturing process described above will be omitted.

  First, a metal foil 90 is prepared as a step (i) ′, and then a gate insulating layer 30 is formed on the metal foil 90 as a step (ii) ′ (see FIG. 7A).

  Although the metal foil 90 functions as a member that supports the gate insulating layer 30 and the channel layer 10, it is finally used as an electrode material. Therefore, the metal constituting the metal foil 90 is preferably a metal having conductivity and a relatively high melting point, such as copper (Cu, melting point: 1083 ° C.), nickel (Ni, melting point: 1453 ° C.), Aluminum (Al, melting point: 660 ° C.) and stainless steel (SUS) can be used.

  The gate insulating layer 30 can be formed by the same method as in the first embodiment. In other words, the gate insulating layer 30 may be formed by a thin film forming method (such as sputtering) using a mask or the like, or by applying and heat-treating a metal salt-containing composition for the gate insulating layer. May be formed.

  Subsequent to the step (ii) ', the step (iii)' is performed. That is, after forming a channel precursor layer 11 by applying a metal salt-containing composition on the gate insulating layer 30 as shown in FIG. 7B, the channel precursor layer is shown in FIG. 7C. 11 is heated to form the channel layer 10. More specifically, the channel layer 10 is formed through a process of heating “a metal salt-containing composition containing a metal salt, an organic solvent and water” under “atmospheric gas containing oxygen gas and inert gas”. (This step can be carried out in the mode described in the above “first embodiment”).

  Subsequently, step (iv) 'is performed. That is, as shown in FIG. 7D, the source electrode 40 and the drain electrode 50 are formed so that both ends thereof are in contact with the channel layer 10 and the metal foil 90. The source electrode 40 and the drain electrode 50 can be formed by the same method as in the first embodiment. That is, the source electrode and the drain electrode may be formed by a printing method / printing process, or a vacuum deposition method, a sputtering method, or the like may be used.

  Next, step (v) 'is performed. That is, the sealing layer 70 is formed so as to cover the channel layer 10, the source electrode 40, and the drain electrode 50 (see FIG. 7E). As a material constituting the sealing layer 70, a resin material having flexibility after curing is preferable. Examples of such resin materials include epoxy resins, polyimide (PI) resins, acrylic resins, polyethylene terephthalate (PET) resins, polyethylene naphthalate (PEN) resins, polyphenylene sulfide (PPS) resins, and polyphenylene ether (PPE) resins. And composites thereof. These resin materials are excellent in properties such as flexibility and dimensional stability, and are preferable in terms of imparting flexibility to the obtained thin film transistor.

  The method for forming the sealing layer 70 is not particularly limited. For example, a method of applying an uncured liquid resin by spin coating or the like, a method of bonding an uncured resin to the upper surface of the metal foil 90, or a film For example, a method of applying an adhesive material to the surface of the sealing layer 70 and bonding the adhesive material to the upper surface of the metal foil 90 through the adhesive material can be employed. In such bonding, a technique of applying pressure while heating by roll lamination, vacuum lamination, hot press, or the like can be appropriately employed.

  Finally, step (vi) 'is performed. That is, as shown in FIG. 7F, the gate electrode 20 and the extraction electrodes 80a and 80b are formed by etching the metal foil 90 functioning as a support. Etching is not particularly limited, and may be performed by a conventional method (for example, etching using photolithography).

  Through the steps (i) ′ to (vi) ′ as described above, the thin film transistor 100 as shown in FIG. 6 to FIG. 7F can be obtained. Even in such a process mode, the “semiconductor film made of a metal oxide” constituting the channel layer 10 is formed by heating in an atmospheric gas. Therefore, a low-cost and high-performance thin film transistor can be obtained without using an expensive vacuum apparatus or the like for channel formation, and the material selection of the substrate, electrode, and insulating layer is not greatly limited.

  Moreover, according to the manufacturing method of this embodiment, since the support body of the transistor 100 becomes the flexible resin sealing layer 70, a thin film transistor having flexibility can be obtained relatively easily. Furthermore, according to the manufacturing method of this embodiment, after forming the gate insulating film 30, the channel layer 10, the source electrode 40, and the drain electrode 50 on the upper surface of the metal foil 90 as a support, the metal foil 90 is formed on the metal foil 90. Since the sealing layer 70 is formed, not only the channel layer 10 but also the fabrication of the gate insulating film 30, the source electrode 40, and the drain electrode 50 can be performed by a baking process higher than the heat resistance temperature of the sealing resin. .

  As shown in FIG. 6, the obtained thin film transistor 100 includes a gate electrode 20, a channel layer 10, a gate insulating layer 30, a source electrode 40, a drain electrode 50, a sealing layer 70, an extraction electrode 80a, 80b. Specifically, the gate electrode 20 and the extraction electrodes 80a and 80b formed by etching the metal foil, the channel layer 10, the gate insulating film 30 formed therebetween, the channel layer 10 and the extraction electrode A source electrode 40 and a drain electrode 50 that are in contact with 80a and 80b, respectively, and a sealing layer 70 that seals the channel layer 10, the source electrode 40, and the drain electrode 50 are provided. Since the gate electrode 20 and the extraction electrodes 80a and 80b are formed from the same metal foil, they are located on the same plane as shown in the figure. One end of each of the source electrode 40 and the drain electrode 50 extends to the outside of the outer edges of the channel layer 10 and the gate insulating layer 30, and the channel layer 10 and the extraction electrodes 80a and 80b are electrically connected to each other. .

Even in the thin film transistor 100 of the second embodiment, the channel layer 10 is made of a metal oxide, and the metal oxide is an oxide formed from the above-described metal salt-containing composition. The carrier concentration is substantially stable in the channel layer 10 particularly due to the fact that it is formed from the metal salt-containing composition by heating under the atmospheric gas. The carrier concentration of the channel layer 10 is 10 ¹⁶ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less, preferably 10 ¹⁷ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less (as a result, the off current is small and the thin film transistor is formed). Incidentally, the carrier concentration of the channel layer obtained by the prior art process which is not “substantially heated under inert gas” is approximately 10 ²² cm ⁻³ ). Furthermore, also in the thin film transistor 100 of the second embodiment, the metal oxide of the channel layer 10 is preferably an amorphous oxide. For example, when the channel layer is formed using a metal salt-containing composition containing a salt of one or more metals selected from the group consisting of In (indium), Ga (gallium), and Zn (zinc) The channel layer 10 has a film form made of a metal oxide containing In, Ga and / or Zn. In particular, when the channel layer 10 has a film form formed of a metal oxide containing In, Ga, and Zn, the density of the channel layer 10 is about 4.0 to 5.5 g / cm ³ , for example, 4. It can be about ³ to 4.8 g / cm ³ (film thickness is about 10 nm to 40 nm). Further, the flatness of the channel layer 10 is improved. For example, the arithmetic average roughness Ra of the channel layer surface is about 10 nm or less, preferably about 5 nm or less, more preferably about 1 nm or less (for example, about 0.5 nm). Below).

Although not shown, another protective layer that seals at least the channel layer 10 may be formed on the channel layer 10. With such a protective layer, damage to the channel layer due to the sealing process can be prevented, leading to further stabilization of the back channel, so that transistor characteristics can be improved and stabilized more suitably. As a material for the protective layer, for example, a thermosetting resin such as a fluororesin or a polyimide resin, an oxide such as SiO ₂ or Al ₂ O ₃ , or a nitride such as SiN can be used.

Third Embodiment With reference to FIGS. 9A to 9F, a manufacturing process of a thin film transistor (TFT) 100 as shown in FIG. 8 will be exemplified. A description of the same points as in the manufacturing process described above will be omitted.

  First, as shown in FIG. 9A, a metal foil 90 is prepared, and a gate insulating layer 30 is formed thereon. The gate insulating layer 30 may be formed by a thin film formation method using a mask (sputtering method, etc.), or the gate insulating layer 30 is formed by applying and heat-treating a metal salt-containing composition for the gate insulating layer. May be.

  Next, as shown in FIG. 9B, the source electrode 40 and the drain electrode 50 are formed so that both ends thereof are in contact with the channel layer 10 and the metal foil 90. The source / drain electrodes may be formed by vacuum deposition or sputtering, or the source / drain electrodes may be formed by applying a metal salt-containing composition for the source / drain electrodes and heat treatment. .

  Next, as shown in FIG. 9C, “a metal salt-containing composition containing at least a metal salt, an organic solvent and water” is applied on the gate insulating layer 30 so as to be in contact with the source electrode 40 and the drain electrode 50. Thus, the channel precursor layer 11 is formed. Then, as shown in FIG. 9 (d), the channel layer 10 is formed through a process of heating the channel precursor layer 11 under “atmosphere gas containing oxygen gas and inert gas”. This process is performed in the mode described in the above “first embodiment”.

  Next, as illustrated in FIG. 9E, a sealing layer 70 is formed on the upper surface of the metal foil 90 so as to cover the channel layer 10, the gate insulating layer 30, the source electrode 40 and the drain electrode 50. Such a sealing layer 70 may be formed by the same method as in the second embodiment.

  Finally, as shown in FIG. 9F, the metal foil 90 functioning as a support is etched to form the gate electrode 20 and the extraction electrodes 80a and 80b, thereby completing the thin film transistor 100.

As shown in FIG. 8, the obtained thin film transistor 100 includes a gate electrode 20, a channel layer 10, a gate insulating layer 30, a source electrode 40, a drain electrode 50, a sealing layer 70, an extraction electrode 80a, 80b. More specifically, the gate electrode 20 and the extraction electrodes 80a and 80b formed by etching the metal foil, the channel layer 10, the gate insulating film 30 formed therebetween, the channel layer 10 and the extraction. A source electrode 40 and a drain electrode 50 that are in contact with the electrodes 80a and 80b, respectively, and a sealing layer 70 that seals the channel layer 10 and the source / drain electrodes 40 and 50 are provided. Also in the thin film transistor 100 of the third embodiment, the channel layer 10 is made of a metal oxide, and the metal oxide is an oxide formed from the above-described metal salt-containing composition. The carrier concentration is substantially stable in the channel layer 10 particularly due to the fact that it is formed from the metal salt-containing composition by heating under the atmospheric gas. The carrier concentration of the channel layer 10 is 10 ¹⁶ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less, preferably 10 ¹⁷ cm ⁻³ or more and 10 ¹⁸ cm ⁻³ or less (as a result, the off current is small and the thin film transistor is formed). Incidentally, the carrier concentration of the channel layer obtained by the prior art process which is not “substantially heated under inert gas” is approximately 10 ²² cm ⁻³ ). Furthermore, also in the thin film transistor 100 of the third embodiment, the metal oxide of the channel layer 10 is preferably an amorphous oxide. For example, when the channel layer is formed using a metal salt-containing composition containing a salt of one or more metals selected from the group consisting of In (indium), Ga (gallium), and Zn (zinc) The channel layer 10 has a film form made of a metal oxide containing In, Ga and / or Zn. In particular, when the channel layer 10 has a film form formed of a metal oxide containing In, Ga, and Zn, the density of the channel layer 10 is about 4.0 to 5.5 g / cm ³ , for example, 4. It can be about ³ to 4.8 g / cm ³ (film thickness is about 10 nm to 40 nm). Further, the flatness of the channel layer 10 is improved. For example, the arithmetic average roughness Ra of the channel layer surface is about 10 nm or less, preferably about 5 nm or less, more preferably about 1 nm or less (for example, about 0.5 nm). Below).

<Image display device>
FIG. 10 shows an example of the image display apparatus 1000. FIG. 10 shows the overall appearance of the image display apparatus 1000.

  The image display apparatus 1000 is an organic EL display, for example. As shown in the figure, the image display apparatus 1000 includes a TFT unit 1100, a driver unit (1200, 1300), and an EL unit 1400. Each pixel of the TFT unit 1100 is related to the first to third embodiments. A thin film transistor 100 is included.

  Specifically, the thin film transistor 100 is formed under the organic EL element included in the EL portion 1400, and the drain electrode 50 of the driving TFT element including the thin film transistor 100 is connected to the organic EL element. A transparent electrode is formed on the organic EL element. In addition, a protective film (for example, a resin film such as PET or PEN) is formed thereon.

  Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will readily understand that various modifications can be made.

For example, the thin film transistor according to the present invention can be realized in various forms. For example, a thin film transistor 100 having a form as shown in FIGS.

In the thin film transistor 100 shown in FIG. 11, the source electrode 40 and the drain electrode 50 are formed on the substrate 60, and the channel layer 10 is formed so as to be in contact with the source electrode 40 and the drain electrode 50, respectively. Yes. The gate insulating layer 30 is formed so as to cover the channel layer 11 and the source / drain electrodes 40 and 50. A gate electrode 20 is formed on the gate insulating layer 30 at a position facing the channel layer 10. The channel layer 10, the gate insulating layer 30, the source electrode 40, and the drain electrode 50 can be formed by the method described in the first embodiment.

In the thin film transistor 100 shown in FIG. 12, the gate electrode 20 and the gate insulating film 30 are formed in this order on the substrate 60. A source electrode 40 and a drain electrode 50 are formed on the gate insulating film 30, and the channel layer 10 is in a position facing the gate electrode 20 on the gate insulating film 30 so as to be in contact with the source electrode 40 and the drain electrode 50. Is formed. The channel layer 10, the gate insulating layer 30, the source electrode 40, and the drain electrode 50 can be formed by the method described in the first embodiment.

In the thin film transistor 100 shown in FIG. 13, the channel layer 10 is formed on the substrate 60, and the source electrode 40 and the drain electrode 50 are formed on the channel layer 10 so as to be in contact with the channel layer 10. The gate insulating layer 30 is formed so as to cover the channel layer 11 and the source / drain electrodes 40 and 50. A gate electrode 20 is formed on the gate insulating layer 30 at a position facing the channel layer 10. The channel layer 10, the gate insulating layer 30, the source electrode 40, and the drain electrode 50 can be formed by the method described in the first embodiment.

<Characteristic confirmation test of metal oxide thin film>
[Example 1]
Zinc nitrate hexahydrate, 3-methoxy-3-methyl-1-butanol (MMB: product name Solfit Fine Grade, manufactured by Kuraray Co., Ltd.) and pure water (10% by weight) are mixed, and an ultrasonic bath is used. Sonication was performed for 5 to 30 minutes to prepare a solution having a metal salt content of 0.3 mol / L. Similarly, a solution having a content of each metal salt of about 0.3 mol / L was prepared using indium nitrate x hydrate and gallium nitrate x hydrate. The 3-methoxy-3-methyl-1-butanol (MMB) used for the preparation contained about 0.05% by weight of water. Next, each prepared solution is mixed, and each of the metal salt contents of In, Ga, and Zn is 0.1 mol / L, and the total metal salt content is 0.3 mol / L. A “metal salt-containing composition containing water” was prepared.

  The prepared metal salt-containing composition was spin-coated (4000 rpm × 30 seconds) on a Si wafer (100) to obtain a test substrate. Subsequently, the substrate (metal salt-containing composition) is primarily heated on a hot plate at 100 ° C. for 10 minutes, and then the nitrogen and oxygen gas flow rates are adjusted so that the oxygen concentration in the tubular furnace becomes 10 ppm. After raising the temperature to 550 ° C. over 2 hours, the substrate (metal salt-containing composition) was secondarily heated in the same tube furnace under the condition of 550 ° C. × 30 minutes (that is, the metal salt-containing composition was fired) Attached). The positive pressure conditions were set to 100 Pa (before heating) to 5 kPa (before heating). The metal oxide film formed on the substrate surface had a thickness of about 0.01 μm to about 0.02 μm.

<< Atomic force microscope image of substrate surface >>
The flatness of the metal oxide film was confirmed. Specifically, the film surface of the metal oxide film produced in Example 1 was observed by AFM (atomic force microscope). As the apparatus, nano-R2 (Pacific Nanotechnology Co., Ltd.) was used.

  The result of film surface observation by AFM is shown in FIG. It was found that the substrate surface of Example 1 was uniform and a dense and flat metal oxide film could be produced. Specifically, the arithmetic average roughness Ra of the surface of the metal oxide film was 0.43 nm. The arithmetic average roughness Ra is a value calculated by using a scanning probe image processor “SPIP” (manufactured by Image Metrology Co., Ltd.) (see also FIG. 15 for “Ra”).

《Membrane density confirmation test》
The film density of the metal oxide film according to the present invention was confirmed. Specifically, the density of the film obtained by applying and heating the metal salt-containing composition was examined under the following conditions.

Measurement method: XRR (X-ray reflectivity measurement method)
・ Apparatus: X-ray diffractometer (manufactured by BRUKER), Cu-Kα ray ・ Calculation of film density by fitting with software (Leptos) ・ Raw material coating solution: Metal salt of In, Ga and Zn (equal molar ratio of 0.1M each) : Total concentration 0.3M), mixed solution containing MMB and 10% by weight of water Metal oxide film: Metal oxide film prepared in Example 1. Specifically, a raw material coating solution is spin-coated (4000 rpm) on a Si (100) wafer, dried at 100 ° C. for 10 minutes, and then nitrogen and oxygen gas so that the oxygen concentration in the tubular furnace becomes 10 ppm. While adjusting the flow rate, the temperature was raised to 550 ° C. over 2 hours and then subjected to secondary heating in the tubular furnace at 550 ° C. for 30 minutes (positive pressure condition: (heating Before) 100 Pa to (during heating) 5 kPa).

The X-ray reflectance measurement results are shown in FIG. The following items could be confirmed by this confirmation test, and it was found that the metal oxide film (that is, the channel layer, etc.) obtained according to the present invention was dense.

Film density determined by fitting: 4.748 g / cm ³ (film thickness determined by fitting: 11.2 nm)
-Density of metal oxide film examined using several lots of coating solution: about 4.5 g / cm ³ to about 5.3 g / cm ³
<Confirmation test of carrier concentration>

The carrier concentration of the metal oxide film according to the present invention was confirmed. Specifically, the carrier concentration of the film obtained by applying and heating the metal salt-containing composition was examined under the following conditions.

・ Measurement method: Hall effect measurement method ・ Device: Hall measurement device (manufactured by BIO-RAD)
Raw material coating solution: In, Ga and Zn metal salts (equal molar ratio of 0.1M each: total concentration 0.3M), mixed solution containing MMB and 10% by weight of water Metal oxide film: Example 1 Metal oxide film produced in Specifically, a raw material coating solution is spin-coated (4000 rpm) on a Si (100) wafer, dried at 100 ° C. for 10 minutes, and then nitrogen and oxygen gas so that the oxygen concentration in the tubular furnace becomes 10 ppm. While adjusting the flow rate, the temperature was raised to 550 ° C. over 2 hours and then subjected to secondary heating in the tubular furnace at 550 ° C. for 30 minutes (positive pressure condition: (heating Before) 100 Pa to (during heating) 5 kPa).

The following items were confirmed by this confirmation test.

-Carrier concentration of metal oxide film: 4.20 × 10 ¹⁷ / cm ³
-Density of metal oxide film examined using several lots of coating solution: about 3.7 to about 4.8 g / cm ³

<Confirmation test of transistor characteristics>
[Example 2]
In order to confirm the characteristics of the transistor obtained by the present invention, a test was performed based on the following method (see FIG. 17):

-The raw material coating solution used in Example 1 was applied on a Si substrate with a thermal oxide film having a thickness of 300 nm by spin coating (4000 rpm), dried at 100 ° C for 10 minutes, and then subjected to a tube furnace. The temperature was raised to 550 ° C. over 2 hours while adjusting the nitrogen and oxygen gas flow rates so that the oxygen concentration was 0.1, 10, 100 ppm and 20%, and then the substrate was placed in the tube furnace at 550 ° C. for 30 minutes. Was subjected to secondary heating (firing). A semiconductor film was formed by baking at 550 ° C. for 30 minutes.

-Source and drain electrodes were formed by mask deposition of aluminum.

-Semiconductor characteristics were measured using a silicon substrate as the gate electrode.

-Semiconductor characteristics were measured using a semiconductor parameter analyzer (B1500A, manufactured by Agilent Technologies).

-The drain current (Id) when the drain voltage (Vd) was set to 10 V and the gate voltage (Vg) was changed was measured.

  The resulting graph is shown in FIG. From the graph of FIG. 18, formed by “heating under an atmospheric gas containing oxygen gas and inert gas” using “a metal salt-containing composition containing a metal salt, an organic solvent, and water” according to the present invention. It was found that the formed semiconductor film exhibited normally-off characteristics and was suitable as a channel layer of a thin film transistor.

《Secondary heating temperature》
The secondary heating needs to be a temperature of 200 ° C. or higher, and is 550 ° C. in the above example. The upper limit temperature of the secondary heating is preferably determined by the heat resistant temperature of the substrate. For example, if the substrate has a lower heat resistant temperature than the slide glass, it is preferable to perform secondary heating at a temperature close to 400 ° C. Conversely, if the substrate has a higher heat resistant temperature than the slide glass, the substrate is close to the heat resistant temperature of the substrate. It can be said that secondary heating is possible.

  The manufacturing method of the present invention is excellent in the productivity of field effect transistors. Note that the obtained field effect transistor can be used for various image display units, and can also be used for electronic paper, digital paper, and the like. For example, a television image display unit as shown in FIG. 19, an image display unit of a mobile phone or a smartphone as shown in FIG. 20, an image display unit of a mobile personal computer or notebook computer as shown in FIG. 21, FIG. 22 and FIG. The image display unit of a digital still camera and a camcorder as shown in FIG. 23 and the image display unit of electronic paper as shown in FIG. Furthermore, the flexible semiconductor device obtained by the manufacturing method of the present invention is also applicable to various uses (for example, RF-ID, memory, MPU, solar cell, sensor, etc.) currently being studied for printing electronics. be able to.

10 channel layer 11 channel precursor layer 12 metal oxide film 20 gate electrode 30 gate insulating layer (gate insulating film)
31 Gate insulating precursor layer 40 Source electrode 41, 51 Source electrode / drain electrode precursor layer 50 Drain electrode 60 Substrate 70 Sealing layer 80a, 80b Extraction electrode 90 Metal foil 100 Field effect transistor (for example, thin film transistor)
100 'field effect transistor precursor 200 tubular furnace 210 heater provided in the tubular furnace 300 heating furnace (heating chamber)
1000 Image display device 1100 TFT unit 1200, 1300 Driver unit 1400 EL unit

Claims (17)

A method of manufacturing a field effect transistor comprising a gate electrode, a source electrode, a drain electrode, a channel layer, and a gate insulating layer,
Forming the channel layer with a metal salt-containing composition comprising a metal salt, an organic solvent and water;
In forming the channel layer, the metal salt-containing composition is heat-treated in an atmospheric gas containing an oxygen gas and an inert gas. 2. The method of manufacturing a field effect transistor according to claim 1, wherein the concentration of the oxygen gas in the atmospheric gas is set to 1 to 10,000 ppm. The method for manufacturing a field effect transistor according to claim 1, wherein the heat treatment of the metal salt-containing composition is performed in a state where the atmosphere gas is circulated. 4. The method of manufacturing a field effect transistor according to claim 3, wherein the heat treatment is performed using a tubular furnace, and the atmospheric gas is circulated in the tubular furnace during the heat treatment. 3. The method of manufacturing a field effect transistor according to claim 1, wherein the heat treatment is performed using a heating furnace, and the inside of the heating furnace is set to a positive pressure during the heat treatment. The electric field according to claim 1, wherein the inert gas in the atmospheric gas is one or more gases selected from the group consisting of nitrogen gas, helium, neon and argon. Effect transistor manufacturing method. The method for producing a field effect transistor according to claim 1, wherein the heat treatment of the metal salt-containing composition is performed at a temperature of 200 ° C. to 600 ° C. The metal salt contained in the metal salt-containing composition is at least one selected from the group consisting of nitrates, sulfates, carboxylates, halides, alkoxides, and acetylacetone salts. The manufacturing method of the field effect transistor in any one of -7. The metal salt contained in the metal salt-containing composition is a salt of one or more metals selected from the group consisting of In, Ga and Zn. The manufacturing method of the field effect transistor of description. 10. The field effect transistor according to claim 1, wherein the content of the water contained in the metal salt-containing composition is 0.05 to 50% by weight based on the composition. Manufacturing method. (I) forming a gate electrode on the substrate;
(Ii) forming the gate insulating layer on the substrate so as to cover the gate electrode;
(Iii) providing the metal salt-containing composition on the gate insulating layer to form a channel precursor layer, and heating the channel precursor layer to form a channel layer; and (iv) the channel layer. Forming the source electrode and the drain electrode in contact with each other,
The method of manufacturing a field effect transistor according to claim 1, wherein in the step (iii), the channel precursor layer is heat-treated under the atmospheric gas. (I) 'preparing a metal foil,
(Ii) 'forming the gate insulating layer on the metal foil;
(Iii) ′ providing the metal salt-containing composition on the gate insulating layer to form a channel precursor layer, and heating the channel precursor layer to form a channel layer;
(Iv) ′ forming the source electrode and the drain electrode in contact with the channel layer;
(V) ′ forming a sealing layer so as to cover the channel layer, the source electrode and the drain electrode; and (vi) ′ etching the metal foil to form the gate electrode. ,
The method of manufacturing a field effect transistor according to claim 1, wherein in the step (iii) ′, the channel precursor layer is heat-treated in the atmosphere gas. A field effect transistor obtained by the manufacturing method according to claim 1,
Channel layer,
Gate electrode,
A gate insulating layer positioned at least between the channel layer and the gate electrode; and a source electrode and a drain electrode disposed in contact with the channel layer,
The channel layer includes a metal oxide, and the metal oxide is an oxide formed from the metal salt-containing composition by heating under the atmospheric gas, and the carrier concentration of the channel layer is 10 ¹⁶ / A field-effect transistor having cm ³ to 10 ¹⁸ / cm ³ . 14. The field effect transistor according to claim 13, wherein an arithmetic average roughness Ra of the surface of the channel layer is 10 nm or less. Claim 13 or 14 dependent on claim 9 characterized in that the metal oxide is a metal oxide comprising one or more metals selected from the group consisting of In, Ga and Zn. The field effect transistor as described. The field effect transistor according to claim 13, wherein the metal oxide is an amorphous oxide. The field effect transistor according to claim 13, wherein the field effect transistor is a thin film transistor (TFT).