JP7634381B2 - Thin film transistor manufacturing method and thin film transistor - Google Patents

Description

The present invention relates to a method for manufacturing a thin-film transistor used to drive, for example, an organic electroluminescence (EL) element (organic light emitting diode (OLED)) or a liquid crystal display (LCD), and a thin-film transistor manufactured using the method. More specifically, the present invention relates to a method for manufacturing a thin-film transistor equipped with a coated electrode that can be produced without using a vacuum device, and a thin-film transistor manufactured using the method.

Thin film transistors (TFTs) are used as driving thin film transistors for display devices, and are electronic devices necessary for driving each pixel. As shown in Figure 9, a TFT using metal oxide as the semiconductor material is constructed by stacking a gate electrode 302, a gate insulating film 303, and a semiconductor layer (metal oxide semiconductor layer) 304 on a substrate 301 using a vacuum film formation method such as sputtering (including a photolithography method (see Figure 10)), and then stacking a source electrode 306a and a drain electrode 306b on top of that so that they face each other with a channel gap between them.

That is, in the conventional manufacturing of such TFTs, after evacuating the processing equipment, a film-forming process consisting of a baking process (FIG. 10(A)) is carried out, followed by a pattern-forming process consisting of many processing units such as photosensitive coating, baking process (FIG. 10(B)), exposure process (FIG. 10(C)), development process (FIG. 10(D)), etching process (FIG. 10(E)), and film removal process (FIG. 10(F)), to complete the product.
In particular, IGZO-based metal oxide TFTs using In-Ga-Zn as the metal species are known and used because they generally exhibit relatively high mobility of 5 to 10 cm ² /Vs or more.
However, when a vacuum film-forming method is used, a large-scale vacuum apparatus is required, and it takes time and costs to form a vacuum atmosphere. In addition, the use of a photolithography technique requires many complicated processes as shown in FIG. 10, resulting in problems such as reduced efficiency and increased environmental burden.

For this reason, attention has been focused on a liquid phase coating film formation technique that can easily form a film in an air atmosphere without using a vacuum device.
It has been known to date that a metal oxide (oxide semiconductor) film is formed by a coating method when manufacturing a TFT (see Patent Document 1 below).
In the manufacturing method of an oxide semiconductor by the coating method, a precursor solution of a metal oxide is coated on a substrate (on which a gate electrode and a gate insulating film are provided) to form a precursor thin film, and then the precursor thin film is subjected to an oxidation treatment such as heating and baking to form an oxide thin film.

JP 2019-91740 A

However, in the above-mentioned manufacturing method of TFT, although it is possible to form a metal oxide (oxide semiconductor) by a coating method, it is difficult to form a source electrode and a drain electrode on the metal oxide (oxide semiconductor) by the coating method. That is, the coating solvent used in forming the source electrode and the drain electrode has a characteristic of dissolving and dispersing metal, and when this is applied on the metal oxide (oxide semiconductor), the metal oxide (oxide semiconductor) is dissolved by the solvent and is severely damaged.
In this case, in the manufacture of TFTs, although a metal oxide (oxide semiconductor) can be formed into a film by a coating method, the source electrode and the drain electrode cannot be formed by a coating method. Therefore, the film formation process by the vacuum method cannot be eliminated in the manufacture of TFTs, and a simple manufacturing method has not yet been established.

The present invention has been made to solve the above problems, and aims to provide a method for manufacturing a thin-film transistor, and a thin-film transistor, that can form source and drain electrodes without using a vacuum device and without damaging the semiconductor layer located directly below the laminated structure during the manufacture of the TFT.

In order to achieve the above object, the method for producing a thin film transistor of the present invention comprises the steps of:
A method for manufacturing a thin film transistor comprising: laminating a gate electrode, a gate insulating film, and an oxide semiconductor layer on a substrate; and forming a source electrode and a drain electrode on the oxide semiconductor layer so as to face each other with a channel gap therebetween,
When forming the source electrode and the drain electrode,
applying a solution in which an organic silane compound is dispersed to at least the upper surface and side surfaces of the oxide semiconductor layer to form a hydrophobic electrode patterning film;
a hydrophilic treatment is applied to a region of the electrode patterning film where the source electrode and the drain electrode are to be formed , to form a hydrophilic region between the source electrode and the drain electrode and the oxide semiconductor layer , and a remaining region is not subjected to the hydrophilic treatment to form a hydrophobic region;
Thereafter, an electrode forming solution having a conductive material dispersed therein is applied onto the electrode patterning film, and the source electrode and the drain electrode are formed in the hydrophilic region.
It is characterized by the above.

The electrode patterning film is preferably formed on the upper surface and side surfaces of the oxide semiconductor layer, as well as on the exposed upper surface of the gate insulating film.
The hydrophilization treatment is preferably a treatment in which deep ultraviolet rays are irradiated through a mask having a predetermined shape in an environment containing oxygen.

It is also preferable that the hydrophilization treatment is performed by irradiating the electrode patterning film with energy rays, and that the intensity and duration of the irradiation are configured so that the hydrophilic region of the electrode patterning film can form a monolayer having a thickness of 1 to 2 nm.
Furthermore, the electrode patterning film is preferably formed by applying a solution in which an organosilane compound is dispersed onto at least the upper surface and side surfaces of the oxide semiconductor layer, and then heating the applied solution at a predetermined temperature.

The thin film transistor of the present invention is
On the board,
A gate electrode,
A gate insulating film,
An oxide semiconductor layer ,
an electrode patterning film in which a hydrophilic region is formed between the source electrode and the drain electrode and the oxide semiconductor layer in a region corresponding to a region in which the source electrode and the drain electrode are formed, and a hydrophobic region is formed in a region other than the region in which the source electrode and the drain electrode are formed ;
and coating-type source electrode and drain electrode whose tips face each other via a gap,
It is characterized in that it is laminated in this order.
Moreover, the electrode patterning film is preferably a monolayer having a thickness of 1 to 2 nm.
Furthermore, the electrode patterning film interposed between the source electrode, the drain electrode, and the oxide semiconductor layer preferably contains an organosilane compound having a hydrophilic group.

As described above, according to the method for manufacturing a thin-film transistor of the present invention, a solution containing an organic silane compound is applied to at least the upper and side surfaces of an oxide semiconductor layer to form an electrode patterning film, and the regions of this electrode patterning film where source and drain electrodes are to be formed are subjected to a hydrophilic treatment to make them hydrophilic regions, while the remaining regions are not subjected to a hydrophilic treatment to make them hydrophobic regions. After that, an electrode formation solution in which a conductive material is dispersed is applied onto the electrode patterning film, so that the source and drain electrodes are formed in the hydrophilic regions that are highly wettable to the electrode formation solution, while the electrodes are not formed in the hydrophobic regions that are less wettable to the electrode formation solution, thereby forming and patterning the source and drain electrodes.

According to the method of the present invention, the electrode forming solution is applied onto the oxide semiconductor layer via the electrode patterning film containing an organic silane compound, and the electrode forming solution is not applied directly to the oxide semiconductor layer, so that the method can avoid the unexpected situation where the oxide semiconductor layer is dissolved and damaged by the electrode forming solution. In addition, since the electrode patterning film is subjected to a hydrophilic treatment in the area where the source electrode and the drain electrode are formed, the electrode forming solution adheres only to this hydrophilic area, and is repelled and does not adhere to the remaining area. Therefore, the source electrode and the drain electrode can be easily patterned by the hydrophilic treatment of the electrode patterning film.
Therefore, since it is possible to form source electrodes and drain electrodes of the desired shape without using a vacuum method or a photolithography method, the complexity of TFT manufacturing can be avoided, and further, cost reduction and compactness of manufacturing equipment can be promoted.

In addition, according to the thin-film transistor of the present invention, a gate electrode, a gate insulating film, an oxide semiconductor layer, an electrode patterning film formed in correspondence with the formation regions of the source electrode and the drain electrode, and the source electrode and the drain electrode whose tips face each other via a gap are laminated in this order on a substrate, and the electrode patterning film is configured to be interposed between the oxide semiconductor layer and the source electrode and the drain electrode.

This allows the electrode-forming solution to be applied onto the oxide semiconductor layer through the electrode patterning film during the manufacture of the thin-film transistor, and the electrode-forming solution is not directly applied to the oxide semiconductor layer, thereby avoiding the unexpected situation in which the oxide semiconductor layer is dissolved and damaged by the electrode-forming solution. In addition, since the electrode patterning film is subjected to a hydrophilic treatment in the area where the source electrode and drain electrode are formed, the electrode-forming solution adheres only to this area, and is repelled and does not adhere to the remaining area. Therefore, the hydrophilic treatment of the electrode patterning film allows the film formation and patterning of the source electrode and drain electrode to be performed in a single process.
Therefore, since it is possible to form source electrodes and drain electrodes of the desired shape without using a vacuum method or a photolithography method, the complexity of TFT manufacturing can be avoided, and further, cost reduction and compactness of manufacturing equipment can be promoted.

1A and 1B are conceptual diagrams showing a stacked structure of a thin film transistor according to an embodiment of the present invention (FIG. 1A shows an embodiment in which an electrode patterning film is provided between source and drain electrodes, and FIG. 1B shows an embodiment in which an electrode patterning film is not provided between source and drain electrodes). 1A to 1C are schematic diagrams illustrating a concept of a method for manufacturing a thin film transistor according to an embodiment of the present invention. 2A to 2C are diagrams illustrating steps of a method for manufacturing a thin film transistor according to an embodiment of the present invention. 1A to 1C are schematic diagrams illustrating a concept of a surface modification treatment in a method for manufacturing a thin film transistor according to an embodiment of the present invention. 5A to 5C are diagrams illustrating a state in which water is desorbed by a baking treatment of an electrode in a method for manufacturing a thin film transistor according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing changes in an alkyl chain when irradiated with deep ultraviolet light in the presence of oxygen molecules. 1 is a graph showing the change in the contact angle of water depending on the deep ultraviolet ray irradiation time (◇ is in an N2 atmosphere, and ■ is in an air atmosphere). 1 is a graph showing the change characteristics of drain current (A) versus gate voltage (V) in a transistor according to an example. FIG. 1 is a conceptual diagram showing a laminated structure of a thin film transistor according to a conventional technique. 1A to 1C are process diagrams showing a method for manufacturing a thin film transistor according to a conventional technique.

The following describes a method for manufacturing a thin-film transistor and a thin-film transistor according to an embodiment of the present invention with reference to the drawings.

<Thin Film Transistor>
First, a cross-sectional structure of a thin film transistor (hereinafter, referred to as a TFT) according to this embodiment will be briefly described with reference to FIGS.
FIG. 1A shows a cross-sectional layered structure of a coated TFT 100a according to the first example (with an electrode patterning film between electrodes), which is configured by layering a gate electrode 102, a gate insulating film 103, a semiconductor layer 104 made of a coated oxide semiconductor, an electrode patterning film 105 made of Si and an alkyl chain, and a source electrode 106a and a drain electrode 106b on a substrate 101.
In this TFT 100a, at least the source electrode 106a and the drain electrode 106b are formed by a coating method, and preferably, the other films are also formed by a coating method.

The substrate 101 is made of a plastic film, glass, or the like.
Examples of the plastic film that can be used include films made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polycarbonate (PC), nanocellulose, etc. When a plastic film is used, it is possible to reduce the weight and increase the portability compared to when a glass substrate is used, and it is also possible to realize a flexible electronic device that can be formed into a desired shape.
As the glass, for example, alkali-free glass that does not contain alkali metal oxides, such as that used as substrate glass for display panels, or substrate glass for solar cells that has a function of preventing the diffusion of alkali metal oxides can be used.

The gate electrode 102 may be made of a conductive oxide such as ITO or IZO, a metal such as Au, Al, Ag, Cr, Mo, Ti, or Cu, or an alloy of these.
Examples of the gate insulating film 103 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, barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, yttrium trioxide, etc. Among these, particularly preferred are those formed from silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, etc.
Furthermore, inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.

Next, the semiconductor layer 104 is made of In-Ga-Zn based oxides, In-Zn based oxides, In-Sn-Zn based oxides, Zn-Sn based oxides, etc., which are known as oxide semiconductor materials.
Furthermore, a metal atom-containing compound capable of forming an oxide applicable to an oxide semiconductor can be used, and a metal salt, a metal halide compound, an organometallic compound, etc., containing a metal atom can be used. Specific examples of the metal element that can be used include indium, gallium, zinc, aluminum, strontium, zirconium, tin, cadmium, tantalum, yttrium, gadolinium, etc.

In addition, a precursor solution containing a metal element-containing compound, such as _indium oxide ( _In2O3 ), zinc oxide (ZnO), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO), zinc-tin oxide (ZnSnO), or titanium oxide ( _TiO2 ), may be used.
The solvent is not particularly limited as long as it is a solvent that stably dissolves or disperses the various metal sources, and can be appropriately selected depending on the purpose, and examples of the solvent that can be used include water, methanol, ethanol, propanol, 1-butanol, 1-propanol, 1-pentanol, ethylene glycol, 2-methoxyethanol, acetonitrile, toluene, xylene, mesitylene, etc. Furthermore, the solubility can be improved by making the solution acidic or basic.

The electrode patterning film 105 may be an organic silane compound having a hydrophobic substituent, such as an alkylsilane or alkyldisilazane. Examples of hydrophobic substituents include alkyl groups having an alkyl chain such as a methyl group or an ethyl group, phenyl groups, and fluoroalkyl groups. These have groups that are reactive with hydroxyl groups on the surface of the semiconductor layer 104 and the gate insulating film 103, and chemically bond to form a surface modified film with Si-O-Si bonds.

Examples of alkylsilanes and alkyldisilazanes include alkoxysilane-based materials such as methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, butyltrimethoxysilane, octyltriethoxysilane, octadecyltriethoxysilane, trimethylethoxysilane, methyltrimethosilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, octyltrimethoxysilane, and octadecyltrimethoxysilane, and further examples of alkyldisilazanes include compounds such as hexamethyldisilazane.

The source electrode 106a and drain electrode 106b are made of metals such as In-Sn oxide (ITO), In-Zn oxide (IZO), and Al-Zn oxide (AZO).

As shown in FIG. 1B, instead of the TFT 100a, it is also possible to configure a TFT 100b that does not have an electrode patterning film 105 between the source electrode 106a and the drain electrode 106b. By removing the electrode patterning film 105 made of Si and alkyl chains from between the formation regions of the source electrode 106a and the drain electrode 106b on the semiconductor layer 104 in this way, a clean surface can be formed on the back channel side of the oxide semiconductor without being affected by the carbide of the organic silane compound due to the thermal oxidation treatment.

<Method of Manufacturing Thin Film Transistor>
Next, a method for manufacturing a thin film transistor according to this embodiment will be described with reference to FIGS.
First, the features of the manufacturing method of the thin film transistor according to the present embodiment will be described with reference to the conceptual diagram of FIG. 2. A hydrophobic electrode patterning film 105 is applied onto a substrate 101 (usually provided with a gate electrode 102, a gate insulating film 103, and a semiconductor layer 104), and the electrode patterning film 105 is irradiated with deep ultraviolet light 120 through a metal mask 110 having a predetermined pattern of through holes to form a hydrophilic region on the electrode patterning film 105 (see FIG. 2(A) light irradiation process). At this time, the region of the electrode patterning film 105 that is not irradiated with deep ultraviolet light 120 remains a hydrophobic region. Therefore, the electrode patterning film 105 is divided into a hydrophilic region and the remaining hydrophobic region by irradiating the electrode patterning film 105 with deep ultraviolet light.

Thereafter, the mask 110 is removed from the electrode patterning film 105, and a water-soluble electrode forming coating material 130 is applied onto the electrode patterning film 105 using a coating means such as a blade coater 140. On the electrode patterning film 105, the coating material 130 wets the hydrophilic regions, allowing the necessary electrodes (source electrode 106a, drain electrode 106b) to be formed, but the coating material 130 does not wet the hydrophobic regions, and no electrodes are formed (see the coating material printing process in Figure 2 (B)).
After that, a baking process is performed to dry the source electrode 106a and the drain electrode 106b (see the baking process in FIG. 2C), thereby completing the TFT.
In this manner, in this embodiment, only predetermined areas of the hydrophobic electrode patterning film 105 are hydrophilized (surface modified) to form areas that are wettable with a water-soluble electrode coating material, and then the electrode coating material is applied onto the electrode patterning film 105 to form electrodes only in the above-mentioned predetermined areas. This allows the film formation process and pattern formation process in the conventional photoresist method to be carried out simultaneously, and enables the construction of a simple printing method.

Next, specific steps of the method for manufacturing the thin film transistor according to this embodiment will be described with reference to FIGS.
First, as shown in FIG. 3A, a semiconductor layer formation process (semiconductor layer formation step) is performed to form a coating type semiconductor layer (also referred to as a metal oxide semiconductor layer) 104′ on a silicon substrate 101′ (formed by laminating a gate electrode 102 and a gate insulating film 103).
Specifically, a material for forming the substrate 101' is cleaned, a barrier layer or a planarization layer (an inorganic thin film or an organic thin film) is formed on the surface, a gate electrode (e.g., gold, titanium, chromium, aluminum, molybdenum, or an alloy or laminated film thereof) 102 (see FIG. 1A) is formed, and patterning is performed to obtain a desired shape.
Next, a gate insulating film 103 (see FIG. 1A) is formed. The gate insulating film 103 is preferably made of an inorganic oxide film having a high relative dielectric constant.

Thereafter, the semiconductor layer 104' is formed.
The precursor solution is an inorganic acid salt. More specifically, the precursor solution is composed of at least one metal salt selected from the group consisting of nitrates, chlorides, sulfates, acetates, carbonates, and fluorides. The metal components include, but are not limited to, In-Ga-Zn oxides, In-Zn oxides, In-Sn-Zn oxides, and Zn-Sn oxides, which are known as oxide semiconductor materials.

More specifically, examples of the metal-atom-containing compounds include those that form oxides that can be applied to oxide semiconductors, such as metal salts, metal halide compounds, and organometallic compounds that contain metal atoms. Specific examples of the metal elements include indium, gallium, zinc, aluminum, strontium, zirconium, tin, cadmium, tantalum, yttrium, and gadolinium.
The metal element-containing compound may be a precursor solution containing dispersed fine particles _of metal oxide such as indium oxide ( _In2O3 ), zinc oxide (ZnO), indium-zinc oxide (IZO), indium-gallium-zinc oxide (IGZO), zinc-tin oxide (ZnSnO), or titanium oxide ( _TiO2 ).

These metal salts are dissolved in a solvent to prepare a precursor solution. The solvent to be used is not particularly limited as long as it is capable of stably dissolving or dispersing the various metal sources, and can be appropriately selected depending on the purpose. Examples of the solvent include water, methanol, ethanol, propanol, 1-butanol, 1-propanol, 1-pentanol, ethylene glycol, 2-methoxyethanol, acetonitrile, toluene, xylene, and mesitylene. Furthermore, the solubility can be improved by making the solution acidic or basic.
The obtained precursor solution is applied onto the substrate 101' to form a thin film of the precursor solution. The thickness of the semiconductor layer 104' can be adjusted by the concentration of the solution and also by the number of times the solution is applied.
The coating method may be a film-forming method such as spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, or die coating.

Subsequently, a baking process is carried out to promote the oxidation process, and the semiconductor layer 104' can be obtained. The baking process in this case is carried out, for example, at a temperature of 150° C. to 600° C. for a period of 30 minutes to 6 hours.
In this firing process, natural drying, hot air/cold air/room temperature air drying, infrared light drying, reduced pressure drying, etc. may be used. Drying using a microwave heating device may also be used. Each firing process may be carried out not only in air, but also in a gas atmosphere such as oxygen, nitrogen, argon, etc. In terms of promoting oxidation, it is also possible to irradiate the thin film with energy rays such as ultraviolet rays before or after firing.

Examples of energy rays include excimer lamps, deuterium lamps, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, helium lamps, carbon arc lamps, cadmium lamps, and electrodeless discharge lamps. In particular, the use of a low-pressure mercury lamp can easily promote the conversion of the precursor film to an oxide film.
In this manner, the semiconductor layer 104' is formed, and a process is performed to form a thin film of an organic compound composed of silicon and alkyl chains on the semiconductor layer 104'.
In this manner, the semiconductor layer forming process (semiconductor layer forming step) shown in FIG.

Next, the process of forming the source electrode 106a and the drain electrode 106b, which is a characteristic feature of this embodiment, will be described in detail with reference to FIGS.
First, the process of forming an electrode patterning film (monomolecular film) will be described with reference to FIG.
That is, first, the surface of the film made of silicon and alkyl chains is modified.
For the surface modification process, an organic silane compound having a hydrophobic substituent can be used, for example, a material made of alkylsilane or alkyldisilazane. Examples of hydrophobic substituents include alkyl groups having an alkyl chain such as a methyl group or an ethyl group, phenyl groups, and fluoroalkyl groups. These have groups that are reactive with hydroxyl groups and the like on the surface of the semiconductor layer 104' and the gate insulating film 103, and chemically bond to form a surface modified film with Si-O-Si bonds.

Examples of alkylsilanes and alkyldisilazanes include alkoxysilane-based materials such as methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, dimethyldimethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, butyltrimethoxysilane, octyltriethoxysilane, octadecyltriethoxysilane, trimethylethoxysilane, methyltrimethosilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, octyltrimethoxysilane, and octadecyltrimethoxysilane, and further examples of alkyldisilazanes include compounds such as hexamethyldisilazane.

Further, the surface modification step in this embodiment will be described below as an example of a process in which the substrate 101' coated with the above-mentioned organosilane compound is placed in a sealed container and the organosilane compound is exposed to steam in the atmosphere of the sealed container; however, the surface modification process is not limited to these methods.
That is, the surface modification treatment of the exposed surfaces of the semiconductor layer 104' and the gate insulating film 103 is performed by putting an organosilane compound into a sealed container with a nitrogen atmosphere, exposing the exposed surfaces of the semiconductor layer 104' and the gate insulating film 103 to steam, removing the substrate 101' from the container, cleaning it with an alcohol-based organic solvent, and then heating the substrate 101' to perform a hydrophobization treatment.
The container may be any container that is not corroded, decomposed, or adsorbed by the vapor, and specific examples include fluororesin, stainless steel containers, etc. The vaporization temperature can be raised from room temperature to 150° C., which is sufficient for the surface modification treatment.

More preferably, the temperature is 100° C. or higher and 150° C. or lower, in terms of being able to eliminate the influence of water. The time of exposure to steam can be adjusted to a predetermined time between 1 minute and 3 hours, and in particular, in the case of a trimethoxy-based organic silane compound, from the viewpoint of reactivity, sufficient surface modification can be performed by heating at 110° C. for 2 hours, filling the container with the steam, and exposing the exposed surfaces of the semiconductor layer 104' and the gate insulating film 103. As the heating means, a hot plate or an oven can be used.
When the surface modification treatment of the electrode patterning film 105' made of an organic silane compound is performed using OTS (octadecyl-trimethoxy-silane) under the conditions described above, the electrode patterning film 105' can be made hydrophobic so that the contact angle of water on the electrode patterning film 105' is 100 degrees or more.
Alternatively, a method can be used in which a liquid of an organosilane compound is diluted with an alcohol-based organic solvent, and the diluted liquid containing the organosilane compound is directly applied by a spin coating method or the like to form a film, or a method can be used in which a substrate is immersed in the diluted liquid to form a film.

Next, the process of hydrophilizing a predetermined region (light irradiation process) will be described with reference to FIG.
The hydrophilization treatment can be performed by irradiation with energy rays such as ultraviolet rays or lasers, or by a dry process such as RIE.
An excimer lamp or an excimer laser can be used as a light source of an energy ray such as a laser. Here, irradiation with deep ultraviolet rays having an output light wavelength of 172 nm using an _Xe2 excimer lamp as a light source of the energy ray will be described as an example of the hydrophilization treatment.

The organosilane compound formed on the substrate 101' has hydrophobic substituents formed on the outside. When deep ultraviolet light (ultraviolet light with a wavelength of 300 nm or less), especially vacuum ultraviolet light (ultraviolet light with a wavelength of 200 nm or less) is irradiated in an oxygen-containing environment, oxygen is excited into a highly reactive state such as active oxygen and ozone. These active oxygen react with the terminal alkyl groups ( _-CH3 ) of the surface modification film, for example, as shown in Figure 4, to oxidize the surface and make it hydrophilic, and hydroxyl groups (-OH), aldehyde groups (-CHO), carboxyl groups (-COOH), etc. are bonded to the outermost surface (the state of Figure 4(a) is converted to the state of Figure 4(b)).

Depending on the amount of deep ultraviolet light irradiated, the hydrophobic group in the organosilane compound undergoes an intermittent reaction, and the length of the alkyl chain changes.
However, if the exposure is continued for a long time, the hydrophobic groups are eventually etched away by oxidation, and the hydrophobic groups in the organosilane compound disappear, so that in the subsequent printing process using a coating solution, the coating solution comes into contact with the semiconductor layer 104' located below the organosilane compound.
That is, the solvent contained in the coating solution comes into direct contact with the semiconductor layer 104', and therefore a good interface is not formed, and in some cases, the semiconductor layer 104' may dissolve. To prevent such a situation from occurring, it is essential to take care that the organic silane compound is distributed over the entire interface.

The time for UV irradiation should be such that the hydrophobicity of the surface modified by the organic silane compound is lost and hydrophilization is promoted, and the time should be such that the water contact angle can be reduced by 30 degrees or more. More preferably, the water contact angle is reduced to 10 degrees or less, and in this case, the electrode patterning can be made sufficiently good by using a printing method that utilizes the difference in the surface state between the hydrophobic and hydrophilic regions (see FIG. 6).
On the other hand, excessive irradiation with ultraviolet light is undesirable because it etches the hydrophobic substituents contained in the organosilane compound.

Next, the steps of the printing process for the coated electrodes will be described with reference to FIG.
The printing process may be a printing method using a general-purpose printer, such as a coating method including spray coating, spin coating, blade coating, dip coating, casting, roll coating, bar coating, and die coating, or an inkjet method.
In the method of this embodiment, the wettability of the surface can be controlled down to a minute area, so that a film is formed in a self-aligning manner only in the required area without using a conventional patterning process such as photolithography, and a pattern shape required for device application can be created. That is, the source electrode and drain electrode required for a transistor can be easily and satisfactorily formed. Note that FIG. 3(D) shows an example in which an ITO solution 160 is applied.

As the coating solution for forming the source electrode 106a and the drain electrode 106b, a solution in which nanoparticles of a metal conductive material such as Ag or Au are dispersed, a solution in which nanoparticles of a conductive oxide such as ITO, IZO, AZO, or ZnO are dispersed, or an oxide precursor solution obtained by mixing metal salts such as ITO, IZO, AZO, or ZnO in a composition that provides conductivity and dissolving them in water or an organic solvent, as in the case of the semiconductor layer 104', can be used. In addition, PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)), which is known as a conductive polymer material, can also be used. Furthermore, a solution in which materials such as carbon nanotubes and graphene that exhibit conductivity are dispersed can also be used.

As a coating method for coating these coating solutions, a blade coating method or the like is used, but the method is not limited to this.
Here, an example using an ITO precursor solution will be described.
That is, in the process of generating a precursor solution of a metal oxide, which is an electrode material, an inorganic acid salt is used as the precursor solution. More specifically, the precursor solution is composed of at least one metal salt selected from the group consisting of nitrates, chlorides, sulfates, acetates, carbonates, and fluorides. Examples of the metal component include, but are not limited to, In-Sn oxides (ITO), In-Zn oxides (IZO), and Al-Zn oxides (AZO).

More specifically, these metal salts are dissolved in a solvent to prepare a precursor solution.
The solvent may be any solvent capable of stably dissolving or dispersing the various metal salts described above, and may be appropriately selected depending on the purpose, and examples thereof include water, methanol, ethanol, propanol, 1-butanol, 1-propanol, 1-pentanol, ethylene glycol, 2-methoxyethanol, acetonitrile, toluene, xylene, mesitylene, etc. Since the pattern shape of the electrode changes depending on the type of solution, an appropriate pattern shape depending on the lyophilic region and the lyophobic region can be obtained by appropriately changing the ratio of these solvents used.

Next, the step of baking in air after printing of the coated electrode will be described with reference to FIG.
In this air baking process, a pre-annealing process is performed to remove the solvent, and then a baking process is performed to promote the oxidation process of the source electrode 106a' and the drain electrode 106b', thereby forming these electrodes 106a', b'. The baking process in this case is performed, for example, at 150°C to 600°C for 30 minutes to 6 hours.

In this firing process, natural drying, hot air/cold air/room temperature air drying, infrared drying, reduced pressure drying, etc. can be used. Drying using a microwave heating device may also be used. Each firing process can be carried out not only in air, but also in a gas atmosphere such as oxygen, nitrogen, or argon.

In order to further promote oxidation, it is also possible to irradiate the thin film of electrodes 106a', b' with energy rays such as ultraviolet rays before or after firing. Examples of energy rays include excimer lamps, deuterium lamps, low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, metal halide lamps, helium lamps, carbon arc lamps, cadmium lamps, and electrodeless discharge lamps. In particular, the use of a low-pressure mercury lamp can easily promote the conversion of the precursor film to an oxide film.

Figure 5 shows how water is released by the baking process of electrodes 106a' and 106b'. That is, as shown in Figure 5(a), the oligomer forms hydrogen bonds with the OH groups of the substrate, and as drying progresses through the baking process, water is released and covalent bonds are formed, as shown in Figure 5(b).

In addition, when the baking temperature is high, such as 250°C or higher, a process of removing the organic alkyl chains on the surface of the semiconductor layer 104' can also be performed after pre-annealing using a UV ozone device or oxygen plasma device. By performing this process of removing the organic alkyl chains, it is possible to prevent deterioration of device characteristics due to carbonization of the organic material on the surface of the semiconductor layer 104' caused by high-temperature treatment. In this way, as shown in Figure 3 (E), the organic silane compound can be removed from the back channel side of the semiconductor layer 104', improving the transistor characteristics.

By subjecting the patterned oxide thin film to a baking process for further oxidation, a coated electrode layer of a metal oxide conductive film having the necessary functions as a TFT can be obtained. As mentioned above, this baking process is preferably carried out at 150°C to 600°C for 30 minutes to 6 hours.

For example, heat treatment is performed for 30 to 60 minutes in air or an oxygen atmosphere at 250 to 450°C, followed by another heat treatment for 30 to 60 minutes in a hydrogen-containing atmosphere at 200 to 450°C. This type of heat treatment promotes the removal of organic components, and allows the formation of a high-quality conductive film with a thickness of approximately 30 to 200 nm.

By forming a coating electrode using the process described above, a fine pattern can be formed on the semiconductor layer 104' using a simple printer. This eliminates the need for a large-scale film-forming device equipped with a vacuum system for sputtering or the like, and allows thin-film transistors required for displays and the like to be easily and quickly produced using inexpensive film-forming equipment.

The following describes in more detail the thin-film transistor manufacturing method and the thin-film transistor of the present invention by comparing an embodiment of the present invention with comparative examples 1 and 2.

(Example)
A low-resistance silicon wafer with a thermally oxidized film having a thickness of 100 nm was used to fabricate an evaluation TFT according to the embodiment, as shown in FIG. 1(A).
That is, in this embodiment, a low-resistance silicon wafer with a thermal oxide film was used, in which a gate electrode 102 and a gate insulating film 103 were laminated on a substrate 101. Next, in order to form a coating-type semiconductor layer 104, a metal oxide precursor solution was applied onto the silicon wafer by a spin coating method.

Specifically, indium nitrate hydrate (In(NO3)3.xH2O, manufactured by Aldrich) and zinc nitrate hydrate (Zn(NO3)2.xH2O, manufactured by Aldrich) were weighed out in a molar ratio of 8:2 as water-soluble metal oxide precursors for forming the semiconductor layer 104, and dissolved in pure water at a concentration of 0.3 mol/L to prepare a coating type semiconductor precursor solution. The precursor solution was then completely dissolved by stirring at room temperature for 6 hours.

The precursor solution thus prepared was then applied onto a silicon wafer by spin coating (spin speed: 4000 rpm) and dried for 1 minute on a hot plate at 150° C. Then, the semiconductor layer 104 was formed by baking for 1 hour in an oven in an air atmosphere at 350° C. The thickness of the semiconductor layer 104 at this time was 15 nm.
As the patterning treatment, patterning was performed using a photolithography method to form a semiconductor layer 104 having a predetermined pattern.

Next, a surface modification treatment was performed using OTS (octadecyl-trimethoxy-silane). For the treatment, 1 ml of OTS solution and the substrate 101 having the semiconductor layer 104 were placed in a fluorine-based container, and the substrate 101 was heated in an oven at 105°C for 1 hour. After that, the substrate 101 was washed with ethanol and isopropanol, and dried again at 80°C to perform surface modification.
The surface side of the substrate 101 thus modified was made into a hydrophobic region showing a contact angle _θ1 with water of 105° or more on both the semiconductor layer 104 and the gate insulating film 103. Specifically, as shown in Fig. 6, the contact angle _θ1 with water in the hydrophobic region according to this embodiment is 109°, and a non-wetted region is formed on the electrode patterning film 105.

Next, deep ultraviolet irradiation was performed using an excimer lamp with an output wavelength of 172 nm. The substrate 101 was set so that the deep ultraviolet irradiation was performed in an air atmosphere. In addition, a mask (110' in FIG. 3C) having a pattern of electrodes 106a and 106b was set on the substrate 101 so that the deep ultraviolet of 172 nm wavelength was irradiated only to the desired area during irradiation, and ultraviolet irradiation was performed for 1 minute through this mask (110). The area irradiated with deep ultraviolet became hydrophilic with a water contact angle θ ₂ of 10 degrees or less. Specifically, as shown in FIG. 6, the water contact angle θ ₂ in the hydrophilic area according to this embodiment is 6°, and a patterned wet area is formed on the electrode patterning film 105.

FIG. 7 shows the experimental results showing the change in the contact angle of water versus the irradiation time of deep ultraviolet light.
As shown in Fig. 7, it is possible to convert a hydrophilic region into a hydrophobic region by irradiation with deep ultraviolet light in an air atmosphere for about 1 minute. Note that Fig. 7 shows the change in contact angle when similar deep ultraviolet light irradiation is performed in a _N2 atmosphere.
Thereafter, a printing process was carried out using an ITO precursor solution by a printing machine with a blade coater 140 (see FIG. 2B).
The gap between the blade of the blade coater 140 and the substrate surface was set to about 10 to 20 μm, and the ITO precursor solution was applied to the substrate surface (actually, onto the semiconductor layer 104 and onto the gate insulating film 103) with this blade, thereby applying the ITO precursor solution in a pattern shape irradiated with deep ultraviolet light through a mask.

Next, the substrate 101 coated with the ITO precursor solution was baked at 400° C. in an air atmosphere to oxidize the ITO precursor solution, thereby reducing the resistance of the electrodes 106 a and 106 b.
At that time, the sheet resistance of the electrodes 106a and 106b was 5 kΩ/□.

The semiconductor characteristics (gate voltage-drain current characteristics) of the obtained TFT of the above embodiment were measured. The results are shown in Figure 8. According to the characteristics shown in Figure 8, the gate voltage rises from a state of approximately 0, and it is possible to achieve a state in which almost no hysteresis occurs, clearly demonstrating good performance.
Although not shown in FIG. 8, when similar measurements were repeated, the variation was extremely small and good characteristics were obtained in all cases, confirming reproducibility.
The TFT of this example showed good results, with a mobility of 6.0 (cm ² /Vs) and an I _on /I _off ratio of 10 ⁶ or more.

(Comparative Example 1)
On the other hand, a TFT according to Comparative Example 1 was fabricated in the same manner as in the above-mentioned Example, except that a film made of an organosilane compound was not formed.
In the TFT according to Comparative Example 1, deep ultraviolet irradiation was performed using a mask in accordance with the pattern shape of the electrode in the same manner as in the Example, but an electrode having a pattern shape like that of the Example was not obtained. Furthermore, dissolution occurred in a part of the semiconductor layer.

The TFT of Comparative Example 1 had a mobility of 6.0 (cm ² /Vs) and an I _on /I _off ratio of 10 ⁶ or more, and thus obtained good results in these respects.
Next, the substrate coated with the ITO precursor solution was baked at 400°C in an air atmosphere to oxidize the ITO precursor solution, thereby lowering the resistance of the electrode. At that time, the sheet resistance of the electrode was 5 kΩ/□.
However, it was not possible to obtain the structure (pattern shape) of the source and drain electrodes required for the TFT, and the TFT that was created did not have its intended function and could not function as a TFT.

(Comparative Example 2)
In addition, a TFT according to Comparative Example 2 was fabricated in the same manner as in the above-mentioned Example, except that an electrode patterning film was formed using an organic silane compound and then the electrode patterning film was sufficiently removed. At that time, the sheet resistance of the electrode was 5 kΩ/□.

In the TFT of Comparative Example 2, deep ultraviolet light was irradiated using a mask in accordance with the pattern shape of the electrodes in the same manner as in the Example, but an electrode having a pattern shape like that of the Example could not be obtained.
As a result, it was not possible to obtain the structure (pattern shape) of the source and drain electrodes required for the TFT, and the TFT thus produced did not have its intended function and was unable to operate as a TFT.
Furthermore, a part of the semiconductor layer was dissolved.

In addition, in a transistor having a coating electrode formed according to this embodiment, an electrode patterning film made of an organic silane compound is interposed at the interface between the coating electrode and the semiconductor layer, which prevents the solvent contained in the coating solution from directly contacting the semiconductor layer and dissolving it.
That is, the electrode patterning film is an extremely useful component in that it can prevent the applied electrode solution from coming into direct contact with the semiconductor layer and suppress solubility.
In addition, the thickness of the organosilane compound constituting the electrode patterning film is preferably a thin film (5 nm or less), and ideally, a monolayer film, from the viewpoint of reducing the contact resistance between the electrode and the semiconductor layer in a thin-film transistor.

The method for producing a thin film transistor and the thin film transistor of the present invention are not limited to those described in the above embodiment, and various other modifications are possible.
For example, in the method for manufacturing a thin film transistor according to the embodiment described above, the regions of the electrode patterning film where the source and drain electrodes are to be formed are irradiated with deep ultraviolet light to perform a hydrophilic treatment and modify the film, but the method for hydrophilization is not limited to this, and the film may be hydrophilized by irradiating other energy rays or by using a dry process such as RIE.

In the above embodiment, a coating method is used to form the electrode patterning film and the source/drain electrodes, as well as the oxide semiconductor layer. It is preferable to use a coating method for forming each of the other layers as well. However, if necessary, they may be formed appropriately using a vacuum method (including a photolithography method).
Furthermore, the electronic device of the present invention is not limited to the above-described embodiment, and other layers may be interposed between the layers shown in the embodiment.

100a, b, 300 TFT
101, 101', 301 Substrate 101a' Substrate heating unit 102, 302 Gate electrode 103, 303 Gate insulating film 104, 104', 304 Semiconductor layer (metal oxide semiconductor layer)
105, 105', 105a to d Electrode patterning film 106a, 106a', 306a Source electrode 106b, 106b', 306b Drain electrode 110, 110' Mask 120 Deep ultraviolet light 130, 330 Coating material 140 Blade coater 160 ITO solution

Claims (8)

A method for manufacturing a thin film transistor comprising: laminating a gate electrode, a gate insulating film, and an oxide semiconductor layer on a substrate; and forming a source electrode and a drain electrode on the oxide semiconductor layer so as to face each other with a channel gap therebetween,
When forming the source electrode and the drain electrode,
applying a solution in which an organic silane compound is dispersed to at least the upper surface and side surfaces of the oxide semiconductor layer to form a hydrophobic electrode patterning film;
a hydrophilic treatment is applied to a region of the electrode patterning film where the source electrode and the drain electrode are to be formed , to form a hydrophilic region between the source electrode and the drain electrode and the oxide semiconductor layer , and a remaining region is not subjected to the hydrophilic treatment to form a hydrophobic region;
Thereafter, an electrode forming solution having a conductive material dispersed therein is applied onto the electrode patterning film, and the source electrode and the drain electrode are formed in the hydrophilic region.
A method for manufacturing a thin film transistor comprising the steps of: The method for manufacturing a thin-film transistor according to claim 1, characterized in that the electrode patterning film is formed on the upper surface and side surfaces of the oxide semiconductor layer as well as on the exposed upper surface of the gate insulating film. The method for manufacturing a thin-film transistor according to claim 1 or 2, characterized in that the hydrophilization treatment is a treatment in which deep ultraviolet light is irradiated through a mask of a predetermined shape in an oxygen-containing environment. The method for manufacturing a thin-film transistor according to any one of claims 1 to 3, characterized in that the hydrophilization treatment is performed by irradiating the electrode patterning film with energy rays, and the intensity and duration of the irradiation are configured so that the hydrophilic region of the electrode patterning film can form a monolayer having a thickness of 1 to 2 nm. The method for manufacturing a thin-film transistor according to any one of claims 1 to 4, characterized in that the electrode patterning film is formed by applying a solution in which an organic silane compound is dispersed to at least the upper surface and side surfaces of the oxide semiconductor layer, and then heating the applied solution at a predetermined temperature. On the board,
A gate electrode,
A gate insulating film,
An oxide semiconductor layer ,
an electrode patterning film in which a hydrophilic region is formed between the source electrode and the drain electrode and the oxide semiconductor layer in a region corresponding to a region in which the source electrode and the drain electrode are formed, and a hydrophobic region is formed in a region other than the region in which the source electrode and the drain electrode are formed ;
and coating-type source electrode and drain electrode whose tips face each other via a gap,
A thin film transistor characterized by being laminated in this order. The thin-film transistor according to claim 6, characterized in that the electrode patterning film is a monolayer having a thickness of 1 to 2 nm. The thin-film transistor according to claim 6 or 7, characterized in that the electrode patterning film interposed between the source electrode, the drain electrode, and the oxide semiconductor layer contains an organic silane compound having a hydrophilic group.

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