JP2023032281A - Manufacturing method of metal oxide film, metal oxide film manufactured using the same, and electronic device - Google Patents

Abstract

To provide a manufacturing method of a metal oxide film capable of obtaining high carrier mobility capable of responding to driving of a high-definition display without requiring a vacuum deposition method or a complicated process, the metal oxide film, and an electronic device.SOLUTION: A manufacturing method successively implements: a precursor solution coating step (a) of coating a coated body with a generated precursor solution after implementing a precursor solution generating step of generating the precursor solution of a metal oxide with a mol concentration of 0.01 M to 0.20 M by dissolving inorganic acid salt of indium in an aqueous solvent; a soft annealing step (b) of applying smooth annealing to the precursor solution of the metal oxide on the coated body; a metal oxide film generating step (c) of generating a metal oxide film of which the film thickness ranges from 0.5 nm to 5.0 nm and the film density ranges from 6.0 g/cm to 7.1 g/cm3 by radiating and oxidizing energy beams; and an etching step (d) of patterning the metal oxide film.SELECTED DRAWING: Figure 1

Description

The present invention is, for example, the production of metal oxide films for forming thin film transistors used to drive organic EL (Electro-Luminescence) elements (OLED (Organic Light Emitting Diode)) and LCD (Liquid Crystal Display). The present invention relates to a method, a metal oxide film manufactured using the same, and an electronic device equipped with this metal oxide film.

A thin film transistor (hereinafter also referred to as a TFT) is used, for example, as a driving transistor for a display device, and is known as an electronic device for driving each pixel. TFTs using a metal oxide as a semiconductor material have been manufactured and put into practical use by using a vacuum process such as a sputtering method or a vapor deposition method. In particular, IGZO-based metal oxide TFTs using In-Ga-Zn as the metal species are known to exhibit relatively high mobility of about 5-10 cm ² /Vs or more, and are used. ing.

However, when the vacuum film-forming method is used, a large-scale vacuum apparatus is required, resulting in problems such as a decrease in production efficiency and an increase in load on the environment. Another problem is that it is difficult to form a uniform thin film on a large substrate.
Furthermore, with the increasing definition of displays such as 4K and 8K, a high value of 10 cm ² /Vs or more is required for the carrier mobility in semiconductors necessary for driving displays. It is desired to develop a semiconductor material that enhances the

Therefore, research and development has been conducted to achieve high performance of metal oxide semiconductors using a coating-type film forming method that can be easily formed in the atmosphere without requiring a vacuum device and that can be printed. has reached

In general, the manufacturing process of a metal oxide semiconductor using a coating-type film forming method involves coating a metal oxide precursor solution on a substrate to form a precursor thin film, and then heating the precursor thin film. It is formed by performing an oxidation treatment such as firing.

By the way, the denseness of the film in the oxide semiconductor can be analyzed as the film density, and it has been reported that if the film is dense, it has good electrical properties such as mobility (see the following non-patent document 1, 2).

Hong Woo, L. et al. Comprehensive Studies on the Carrier Transporting Property and Photo-Bias Instability of Sputtered Zinc Tin Oxide Thin Film Transistors. IEEE Transactions on Electron Devices 61, 3191-3198, doi:10.1109/ted.2014.2337307 (2014) . Jeong, J. H. et al. Origin of Subthreshold Swing Improvement in Amorphous Indium Gallium Zinc Oxide Transistors. Electrochemical and Solid-State Letters 11, doi:10.1149/1.2903209 (2008).

However, even when the methods described in the above documents are used, it is difficult to say that the film formation process is sufficiently simplified, and the high-performance process that can be used to drive high-definition displays is difficult. However, carrier mobility has not yet been achieved.
Particularly in the coating method, since the film is formed via a precursor solution, it contains many residual impurities derived from metal salts, solvents, additives, etc., making it difficult to form a dense film.

The present invention provides a method for producing a dense metal oxide film that does not require a vacuum film formation method or a complicated process, and can obtain high carrier mobility that can be used to drive a high-definition display. An object of the present invention is to provide a metal oxide film and an electronic device manufactured using the method.

In order to achieve the above object, the method for producing a metal oxide film of the present invention comprises:
Water-soluble metal oxidation of a molar concentration of 0.01M or more and 0.20M or less by dissolving an inorganic acid salt composed of a metal salt having indium as the main component in a solvent in which the water solvent accounts for 50% or more by weight. a precursor solution generating step of generating a precursor solution of the substance;
a precursor solution applying step of applying the precursor solution generated in the precursor solution generating step onto a predetermined object to be coated;
Energy rays are applied to a predetermined region of the metal oxide precursor solution applied on a predetermined object to be coated in the precursor solution coating step, and the predetermined region is oxidized so that the film thickness is 0.5 nm or more. a metal oxide film forming step of forming a metal oxide film having a thickness of 5.0 nm or less and a film density of 6.0 g/cm ³ or more and 7.1 g/cm ³ or less;
an etching step of patterning the metal oxide film generated in the metal oxide film generating step;
It is characterized by having

It is preferable that the thickness of the metal oxide film formed in the metal oxide film forming step is 0.5 nm or more and 4.7 nm or less.
In this case, it is preferable that the metal oxide film formed in the metal oxide film forming step has a film density of 6.27 g/cm ³ or more and 7.10 g/cm ³ or less.

Further, it is more preferable that the thickness of the metal oxide film formed in the metal oxide film forming step is 0.5 nm or more and 2.5 nm or less.
In this case, it is more preferable that the metal oxide film formed in the metal oxide film forming step has a film density of 6.81 g/cm ³ or more and 7.10 g/cm ³ or less.

Further, the energy beam irradiation in the metal oxide film forming step is preferably energy beam irradiation in a wavelength range of 185 nm to 255 nm, which is capable of generating active oxygen species in an aqueous solution.
Further, it is preferable that the energy beam irradiation in the metal oxide film forming step is energy beam irradiation in a nitrogen atmosphere.

Further, the metal oxide film of the present invention is
It is characterized by being manufactured by any one of the metal oxide film manufacturing methods described above.

Further, the electronic device of the present invention is
It is characterized by including the metal oxide film described above.
This electronic device can be a thin film transistor in which at least a gate electrode, a gate insulating film, a semiconductor layer made of the metal oxide film, and source/drain electrodes are laminated in this order on a substrate.

According to the method for producing a metal oxide film of the present invention, and the metal oxide film and the electronic device produced by using the method, the method can be carried out without using a vacuum method or a photolithography technique. A metal oxide film can be easily manufactured without requiring a complicated process.

Further, conventionally, in order to increase the mobility of carriers in a semiconductor layer, it is considered effective to increase the film thickness to some extent (for example, about 10 nm to 20 nm or more).
However, the inventors of the present application have doubts about whether such an established theory can be applied to the formation of a metal oxide film by a coating-type film forming method, and as a result of repeated detailed experiments, at least in the above case We obtained the result that the crystallinity of the film structure is greatly improved by thinning the film thickness to near the limit state. Based on this experimental result, the inventors of the present application have found the fact that a high carrier mobility can be obtained by reducing the film thickness to 5 nm or less, and have made the present invention.

Specifically, the metal oxide precursor solution is a solution having a molar concentration of 0.01 M or more and 0.20 M or less, and the film thickness of the generated metal oxide film is set to 0.5 nm or more and 5.0 nm or less. By setting the film density of the material film to 6.0 g/cm ³ or more and 7.10 g/cm ³ or less, for example, it is possible to drive high-definition displays such as 4K and 8K, which is 27 cm ² /Vs or more. A dense and high-performance metal oxide film that can obtain carrier mobility can be produced.

It is a schematic diagram showing each step (A) of the method for producing a metal oxide film according to the embodiment of the present invention and each step (B) of the method for producing a metal oxide film according to the prior art. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a lamination cross-sectional view ((A) without an etching stop layer, (B) with an etching stop layer) showing the structure of a thin film transistor (electronic device) according to an embodiment of the present invention; 1. It is a figure which conceptually shows the effect|action in the precursor solution application process (A), the energy-beam irradiation process (metal oxide film formation process) (B), and the etching process (C) in embodiment shown in FIG. FIG. 2 is a schematic diagram showing the configuration of a TFT element for evaluation according to an example; 5 is a graph showing the relationship between the film thickness (nm) and the film density (g/cm ³ ) of metal oxide films of TFTs (Samples 1 to 5) according to Examples and Comparative Examples. 7 is a graph (A) showing film density measurement results of a TFT (sample 2) according to Example 2, and a graph (B) showing film density measurement results of a TFT (sample 3) according to Comparative Example 1; 4 is a graph showing the relationship between the film thickness (nm) and the degree of crystallinity (%) of metal oxide films of TFTs (Samples 1 to 3) according to Examples and Comparative Examples. XRD diffraction spectra ((B) is a partially enlarged view of (A)) showing the crystallinity of the metal oxide films of TFTs according to Example 2 (solid line) and Comparative Example 1 (broken line). be. 3 is a graph (A) showing gate voltage-drain current characteristics of a TFT (Sample 1) according to Example 1, and a graph (B) showing gate voltage-drain current characteristics of a TFT (Sample 3) according to Comparative Example 1; .

A method for producing a metal oxide film, and a metal oxide film and an electronic device produced using the method according to embodiments of the present invention will be described below.

≪Embodiment≫
First, a method for manufacturing a metal oxide film according to the present embodiment will be described. As a premise, a cross-sectional structure of a TFT in which this metal oxide film is laminated as a semiconductor layer (channel layer) will be briefly described.
FIG. 2A shows a generally known cross-sectional structure of a TFT (first example: no etching stop layer). A semiconductor layer 104 made of a film and source/drain electrodes 106 are laminated.
FIG. 2B also shows a generally known cross-sectional structure of a TFT (second example: with an etching stop layer). A semiconductor layer 204 made of a film, an etching stop layer 205 for protecting the semiconductor layer 204 from etching, and source/drain electrodes 206 are laminated.

Next, the method for manufacturing the metal oxide film of this embodiment will be described in detail. In addition, the metal oxide film and the thin film transistor (TFT) manufactured by this manufacturing method are also explained.
It is assumed that the TFT layer is configured as shown in FIG.
That is, a gate electrode 102 , a gate insulating film 103 , a semiconductor layer 104 made of a metal oxide film, and source/drain electrodes 106 are sequentially formed on a substrate 101 . The semiconductor layer 104 is coated with a water-soluble metal oxide precursor solution and subsequent processing forms a metal oxide film.

The method for producing a metal oxide film according to the present invention is not limited to the method for producing a metal oxide film for a TFT, but may be applied to the method for producing a metal oxide film for various other electronic devices. can be done. In addition, the present invention can be applied not only to the production of oxides exhibiting semiconductor properties, but also to the production of oxides exhibiting conductive properties used for electrodes and the like, and oxides exhibiting insulating properties.

(1) First, the material for forming the substrate 101 is washed, a barrier layer and a planarization layer (inorganic thin film or organic thin film) are formed on the surface by sputtering or the like, and gate electrodes (eg, gold, titanium, chromium, aluminum, Molybdenum, an alloy thereof, a laminated film, etc.) 102 is formed and patterned into a desired shape. Photolithography (microfabrication technology by ultraviolet exposure) is used for fine pattern formation.

(2) Next, a gate insulating film 103 is formed. The gate insulating film 103 is preferably composed of an inorganic oxide film with a high dielectric constant. Examples of inorganic oxides include silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide. Inorganic nitrides such as silicon nitride and aluminum nitride can also be used.

(3) Next, a water-soluble metal oxide precursor is used to shape the semiconductor layer 104 . In the step of forming the semiconductor layer 104, a precursor solution generating step of generating a precursor solution of a water-soluble metal oxide is performed as a pre-process.
In this metal oxide precursor solution producing step, an inorganic acid salt is used as the precursor solution. Specifically, it is necessary to use a metal nitrate containing indium as the main component, and the molar concentration must be specified to be 0.01M or more and 0.20M or less, but the molar concentration is specified to be 0.05M or more and 0.20M or less. more preferably.

As the metal of the metal oxide, in addition to indium, it is also possible to add a small amount of other metal, and examples of other metals include metal atom-containing compounds that form oxides that can be applied to oxide semiconductors. It can be a metal salt, a metal halide compound, an organometallic compound, etc. containing a metal atom. Specific metal atoms include gallium, zinc, aluminum, strontium, zirconium, tin, and the like.

In addition, the film thickness can be changed by adjusting the solution concentration, and by setting the molar concentration of the solution to 0.20M or less, the film thickness of the metal oxide film formed after the coating process can be reduced to 5.0 nm or less. It becomes possible to According to research by the inventors of the present application, it has been found that TFTs having good semiconductor characteristics can be produced by setting the film thickness of the metal oxide film to 5.0 nm or less. It is important to keep the molarity of the body solution below 0.20M.
In order to function well as a film, the molar concentration of the precursor solution should be 0.01 M or more, preferably 0.05 M or more, and the thickness of the metal oxide film should be 0.5 nm or more. Furthermore, in order to improve the manufacturability of the film, it is essential that the thickness of the metal oxide film is 2 nm or more.

In terms of the solvent ratio, it is preferable that the water solvent is 100%, but an organic solvent can be mixed in order to improve the coatability. In that case, even when the solvent ratio of water is reduced to 50%, the patterning property and the electrical properties as an electronic device can reach predetermined reference values.
As a solvent that can be contained in a small amount in addition to water, solvents such as ethanol, propanol, ethylene glycol, 2-methoxyethanol, and acetonitrile can be mixed together and used in order to improve coating properties. Ph can be acid or basic to further improve solubility.

After completion of the precursor solution generating step shown in (3) above, the semiconductor layer 104 is formed from the generated precursor solution.
That is, as shown in FIG. 1A, a precursor solution application step (a), a soft annealing step (b), an energy beam irradiation step (c), and an etching step (d) are performed in this order to form a semiconductor layer. 104 is generated.
On the other hand, in the formation process of the semiconductor layer 104 according to the conventional technology, as shown in FIG. A photolithography process is employed in which the energy beam irradiation step (d), the development step (e), the etching step (f), and the film removal step (g) are performed in this order. It is clear that the number of steps is less and the processing is simpler than the conventional technology.

Returning to the above description, first, as shown in FIG. A thin film of the precursor solution is formed by coating the upper surface of 101 . The thickness of the semiconductor layer 104 can be adjusted by the concentration of the solution and the number of times the solution is applied.

Note that the thickness of the semiconductor layer 104 is set to 0.5 nm to 5.0 nm. As a coating method, a printing method such as a spray coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, a bar coating method, or a die coating method can be used.

Next, as shown in FIGS. 1A and 1B, a soft annealing (drying treatment such as low-temperature drying) is performed.
The soft annealing process is also referred to as a so-called gentle drying process. Specifically, since the semiconductor layer 104 contains a large amount of water, the soft annealing process is intended to leave water, which is the main component of the solvent. This step is performed in order to ensure the effectiveness of the oxidation treatment of the pattern formed in the energy beam irradiation step which will be performed later.
Low-temperature drying, natural drying, vacuum drying, hot air/cold air/room temperature air drying, infrared light drying, and the like can be used as the soft annealing treatment. It may be dried by reaction with a microwave heating device.

Next, as shown in FIGS. 1A and 1C, an energy beam irradiation step is performed.
In this energy ray irradiation step, by irradiating the moisture remaining in the semiconductor layer 104 with energy rays such as ultraviolet rays, patterning of the metal oxide film can be easily performed. By executing the metal oxide film forming step combining the soft annealing step and the energy beam irradiation step, the state shown in FIG. 3A changes to the state shown in FIG. 3B.
That is, in this energy beam irradiation step, the water molecules remaining in the film are irradiated with energy beams to cause the following photochemical reaction (photooxidation (production of insoluble oxides)).
H ₂ O + hν → HO・+・H
As a result, hydroxyl radicals (OH.), which are active oxygen species, are generated.

The wavelength of the ultraviolet rays to be irradiated here is preferably selected from 180 to 400 nm, more preferably from 185 to 255 nm. Examples thereof include ultraviolet rays from excimer lamps, deuterium lamps, low-pressure mercury lamps, high-pressure mercury lamps, extra-high pressure mercury lamps, metal halide lamps, helium lamps, carbon arc lamps, cadmium lamps, electrodeless discharge lamps, and the like. It is more preferable to use a low-pressure mercury lamp because the precursor film can be easily converted into the oxide film. At this time, by irradiating through a light-shielding mask having a pattern, selective oxidation treatment becomes possible and the pattern can be easily formed.

Since the energy irradiation by the ultraviolet light at this time is in a wavelength range in which the ultraviolet light reacts with oxygen in the air, it is desirable that the irradiation treatment be performed in a so-called nitrogen atmosphere in which at least oxygen is reduced. If the oxygen is not decompressed, the desired pattern cannot be obtained even if the mask is irradiated with light.

An oxide thin film formed using this water-soluble metal oxide precursor can be efficiently subjected to an oxidation process by light when the film thickness is as thin as 0.5 nm to 5.0 nm. As shown in FIG. 3B, when the thickness of the film is thin, photo-oxidation can be sufficiently performed to the inside of the film. In other words, the photo-oxidation treatment generated from the irradiated surface side can be sufficiently applied to the inside of the film, and the thickness at which a dense and substantially uniform film can be formed in the vertical direction is 5.0 nm or less. is set in this range.

On the other hand, when the film is thick (for example, 10 nm to 20 nm) as in the past, gradation occurs during photooxidation between the film regions on the irradiation surface side and the substrate surface side. In this case, problems such as the reliability of device characteristics arise. As a result, it becomes difficult to obtain good switching characteristics in the TFT.
Further, in this embodiment, the thickness of the metal oxide film is set to 0.5 nm or more. This is because when the thickness of the metal oxide film is less than 0.5 nm, it becomes difficult to function as the oxide semiconductor layer 104 containing indium as a main component, and the productivity deteriorates. This is done in consideration of the difficulty of realization.

After the energy beam irradiation step is completed as described above, as shown in FIGS. An etching process is performed to remove the preformed precursor film.
In the etching step, it is preferable to use an etching solution that causes little damage to the metal oxide film. Generally known organic acids such as acid, tartaric acid, oxalic acid, formic acid, glycolic acid and maleic acid may be used.

By thoroughly performing a rinse treatment with pure water or the like after etching, the oxide thin film can be patterned only in the regions selectively irradiated in the energy beam irradiation step.

After that, the patterned metal oxide film is further subjected to a baking treatment to accelerate the oxidation treatment, and the semiconductor layer 104 of the TFT having further excellent characteristics can be obtained. The baking treatment in this case is performed at, for example, 150° C. to 400° C. for a period of 30 minutes to 6 hours.
In the baking treatment at this time, natural drying, hot air/cold air/room temperature air drying, infrared light drying, reduced pressure drying, or the like can be used. Drying by a heating device using microwaves may also be used. Each firing process can be performed not only in the atmosphere but also in a gas atmosphere such as oxygen, nitrogen, argon or the like.

(4) After completing the formation of the semiconductor layer 104 made of metal oxide as described above, a step of forming source/drain electrodes 106 as shown in FIG. will be

As a material for the source/drain electrodes 106, transparent electrodes such as ITO and IZO, metal electrodes such as Al, Ag, Cr, Mo and Ti, and alloys thereof can be used. By using a laminated film of two or more layers, the contact resistance can be reduced and the adhesion can be improved.

As the etching solution, various etching solutions such as a mixed acid of phosphoric acid, acetic acid and nitric acid (PAN etchant) and oxalic acid can be used. When patterning the source/drain electrodes 106 by wet etching, an etching stop layer (corresponding to the etching stop layer 205 in FIG. 2B) may be formed in order to mitigate damage to the semiconductor layer 104. By doing so, deterioration of semiconductor characteristics can be suppressed. A material similar to that of the gate insulating film 103 can be used as the etching stop layer.

In the source/drain electrode 106 and the gate electrode 102 described above, the composition of the oxide is a highly conductive material, so that a water-soluble metal oxide precursor is used to form a conductive film related to the oxide. is also possible. An inorganic acid salt is used as the precursor solution for forming the conductive film here. More specifically, it is composed of at least one metal salt selected from nitrates, chlorides, sulfates, acetates, carbonates and fluorides.

Examples of the highly conductive material include metal atom-containing compounds that form oxides (oxide conductor materials) that exhibit conductive properties when oxidized. compound etc. can be mentioned. Specific metal elements include indium, gallium, zinc, and tin.
Specific oxide conductor materials include In--Sn oxides, Ga--Zn-based oxides, In--Zn-based oxides, and Zn-based oxides, but are not limited to these.
The metal oxide film can be easily patterned by irradiating the moisture remaining in the film with energy rays such as ultraviolet rays using a method similar to that used for the semiconductor layer 104 .

In addition, by using a similar method, by changing the composition of the metal elements in the oxide to, for example, Zr, Hf, Al, etc., it is possible to form a functional oxide that can be applied to an insulating film having high dielectric properties. can.
As described above, a TFT can be formed by a simple method.

By the way, in this embodiment, by making the thickness of the semiconductor layer 104 as thin as 0.5 nm to 5.0 nm, a TFT with excellent characteristics can be produced.
Especially in the case of a film containing indium oxide as a main component (hereinafter simply referred to as an indium oxide film), it is possible to form a dense film by making the film thin as described above. This is because

The fact that it is possible to form a dense film when the indium oxide film is made as thin as 0.5 nm to 5.0 nm is due to the fact that the density of the indium oxide film (X-ray reflectance obtained by measurement).

As a result of X-ray reflectance measurement, it was clarified that the density of the indium oxide film can be increased to 6.0 g/cm ³ or more when the thickness of the indium oxide film is 5.0 nm or less (described later). see the description of the embodiment for Since the theoretical maximum value of the film density of indium oxide is 7.1 g/cm ³ , the uniformity (crystallinity) of the film can be improved by setting the film density to 6.0 g/cm ³ or more. It is clear that it is possible to Therefore, by making the indium oxide film as thin as 5.0 nm or less, the uniformity (degree of crystallinity) of the film can be improved. It is possible to enhance semiconductor characteristics such as degree of hardness.

The evaluation of crystallinity by X-ray diffraction described above is known as a technique for evaluating film quality.
It is generally known that the peak intensity in X-ray diffraction is proportional to the amount of substance, and the ratio of the crystalline scattering intensity to the total scattering intensity that is the sum of the crystalline diffraction peak and the amorphous diffraction peak The degree of crystallinity of the formed thin film can be evaluated by (represented by the following formula (1)).

本実施形態により作成したインジウム酸化物（In₂O₃）膜について、上式（１）を用いて算出すると、結晶化度が90％以上の良質な薄い膜が得られることが明らかである。すなわち、本実施形態により半導体の物性的な特性を向上することができ、薄膜トランジスタとして適用する際にはキャリアの高移動度化を実現できる。

As for the indium oxide (In ₂ O ₃ ) film produced according to the present embodiment, calculation using the above formula (1) reveals that a good thin film with a degree of crystallinity of 90% or more can be obtained. That is, according to this embodiment, the physical properties of the semiconductor can be improved, and when the semiconductor is applied as a thin film transistor, it is possible to realize high mobility of carriers.

As a TFT for evaluation according to this example, a TFT element as shown in FIG. 4 was produced using a low resistance silicon wafer with a thermally oxidized film having a thickness of 100 nm.
That is, in this embodiment, a low resistance silicon wafer with a thermal oxide film is used as the substrate 1, the gate electrode 2 and the gate insulating film 3. FIG. Next, in order to form the semiconductor layer 4, the metal oxide precursor solution was applied onto the silicon wafer by spin coating.

その後、室温にて、6時間撹拌することで完全に溶解した状態の前駆体溶液を作成した。 As a water-soluble metal oxide precursor for forming a metal oxide film, indium nitrate hydrate (In(NO ₃ ) ₃ xH ₂ O manufactured by Aldrich) was weighed and dissolved in pure water. A coating type semiconductor precursor solution shown in No. 1 was prepared. At this time, the sample concentration was varied as shown in Table 1 below. Here, Samples 1 and 2 are for Examples 1 and 2, and Samples 3, 4 and 5 are Comparative Examples 1, 2 and 3 prepared for comparison with Examples 1 and 2. It is for

Then, the mixture was stirred at room temperature for 6 hours to prepare a completely dissolved precursor solution.

Subsequently, the precursor solution prepared in this manner was applied onto a silicon wafer using a spin coating method (spin rotation speed: 4000 rpm), and the temperature was low enough that water, which is the main component of the solvent, remained in the film. 70 degrees) for 1 minute on a hot plate.

After that, a mask having a pattern shape of the semiconductor layer 4 formed on the low-resistance silicon wafer (including the substrate 1, the gate electrode 2, and the gate insulating film 3) with a thermal oxide film is applied to the applied metal oxide precursor. It was set on the body film, and through this mask, the metal oxide precursor film was irradiated with ultraviolet rays from a low-pressure mercury lamp for 10 minutes. The predominant UV wavelengths were 185 nm and 254 nm. Thus, the oxidation treatment process of the metal oxide precursor film was performed. At this time, by irradiating the water remaining in the precursor film with ultraviolet rays, a partial oxidation treatment was performed by radicalized hydroxyl radicals, thereby forming a metal oxide film.

After that, an etching treatment is performed with a 0.1% solution of citric acid, which is a hydroxycarbonate-based organic acid, to remove the metal oxide precursor film in the non-irradiated region of the ultraviolet rays, which is not subjected to the oxidation treatment. become.
As described above, a semiconductor layer 4 made of a metal oxide film having a desired pattern was formed.

After that, the metal oxide film was subjected to baking treatment in an air atmosphere oven at 350° C. for 1 hour to form a semiconductor layer 4 .
The film thickness of the semiconductor layer 4 at this time was 15 nm.
Subsequently, the substrate was masked with a metal mask having a predetermined shape, and source/drain electrodes 6a and 6b were formed by DC sputtering using molybdenum.
Thus, a TFT for evaluation was produced.
The film thicknesses at this time were the values shown in Table 2 below. That is, in Example 1, the film thickness was 2.5 nm, in Example 2, the film thickness was 4.7 nm, in Comparative Example 1, the film thickness was 12.5 nm, in Comparative Example 2, the film thickness was 15.0 nm, and in Comparative Example 3, the film thickness was 20.5 nm.

Table 3 below shows the evaluation of the semiconductor characteristics of the obtained TFTs of Examples and Comparative Examples. In addition, film density and crystallinity were evaluated for each example and each comparative example using X-ray reflectance measurement and X-ray diffraction method.

When the concentration of the solution is sufficiently low (Examples 1 and 2), a thin film of 5 nm or less can be formed, and then a good thin film with no compositional unevenness in the depth direction can be formed by the subsequent photo-oxidation process. be able to. On the other hand, when the concentration of the solution is high (Comparative Examples 1, 2, and 3), the photo-oxidation in the depth direction is not sufficiently performed, resulting in deterioration of the film quality, and the resulting semiconductor characteristics do not meet the desired characteristics. hard to get.
That is, in Examples 1 and 2, the carrier mobilities (cm ² /Vs) are 30.6 and 27.6, respectively, but in Comparative Examples 1, 2, and 3, the carrier mobilities (cm ² /Vs) are cannot be detected.

In addition, the film densities (g/cm ³ ) of Examples 1 and 2 are 6.81 and 6.27, respectively, which are both good values of 6.0 or more. The densities (g/cm ³ ) are less than 5.81, 5.51, 5.32 and 6.00 respectively, which is not good. This is also shown in the graph of FIG. 5, and it is clear that when the film thickness is 5 nm or less, the film density greatly exceeds 6.00 g/cm ³ and the semiconductor characteristics are improved.

6A and 6B are graphs showing the relationship of the reflectance to the X-ray incident angle (deg.) in Example 2 and Comparative Example 1. FIG. From the shapes of the graphs shown in FIGS. 6A and 6B, it is clear that Example 2 has a higher film density than Comparative Example 1. FIG.
Furthermore, FIG. 7 shows the relationship between the film thickness (nm) and the degree of crystallinity (%).

In addition, as a method for evaluating the film quality of the above Examples and Comparative Examples, crystallinity (crystallinity) was evaluated using an X-ray diffraction method. The evaluation of the crystallinity was performed using the crystallinity derived from the above formula (1). Rigaku SmartLab (XRD) was used as an XRD measurement device.
As shown in FIG. 8, the diffraction intensity of the In ₂ O ₃ crystal uses the area of the 222 peak (crystalline diffraction peak) at a diffraction angle of 30 degrees. The area of the amorphous diffraction peak around 30 degrees was used.

FIG. 9 is a graph (A) showing the gate voltage-drain current characteristics of the TFT according to the example (Example 1), and the gate voltage-drain current characteristics of the TFT according to the comparative example (Comparative Example 1). Graph (B). From these figures, it is clear that Example 1 has good switching characteristics, and Comparative Example 1 cannot have good switching characteristics.

The method for producing a metal oxide film of the present invention, and the metal oxide film and electronic device produced by using the method are not limited to those described in the above embodiments, and other various modifications can be made. It is possible. For example, in the embodiments of the present invention, the metal oxide film is of the coating type, and the other layers are not necessarily of the coating type, but the other layers may also be of the coating type. If all the layers are of the coated type, no system for processing in a vacuum can be required.

Further, even when the electronic device of the present invention constitutes a TFT, it is not limited to those described in the above embodiments, and it is also possible to adopt a structure in which other layers are interposed between the layers shown in the embodiments. be.
Further, in the above-described embodiments, a bottom-gate type TFT is described as an electronic device, but a top-gate type TFT is also applicable to the electronic device of the present invention. However, in the case of a top-gate type TFT, a metal oxide film precursor solution is usually applied onto the source/drain electrodes and the substrate to form the metal oxide film.

Further, the method for producing a metal oxide film of the present invention is not limited to the method used as a method for producing a semiconductor layer (channel layer) of a TFT. It can also be suitably used for manufacturing methods of various electrodes and the like.

1, 101, 201 substrate 2, 102, 202 gate electrode 3, 103, 203 gate insulating film 4, 104, 204 semiconductor layer (metal oxide film)
205 etching stop layer 106, 206 source/drain electrode 6a source electrode 6b drain electrode

Claims (10)

Water-soluble metal oxidation of a molar concentration of 0.01M or more and 0.20M or less by dissolving an inorganic acid salt composed of a metal salt having indium as the main component in a solvent in which the water solvent accounts for 50% or more by weight. a precursor solution generating step of generating a precursor solution of the substance;
a precursor solution applying step of applying the precursor solution generated in the precursor solution generating step onto a predetermined object to be coated;
Energy rays are applied to a predetermined region of the metal oxide precursor solution applied on a predetermined object to be coated in the precursor solution coating step, and the predetermined region is oxidized so that the film thickness is 0.5 nm or more. a metal oxide film forming step of forming a metal oxide film having a thickness of 5.0 nm or less and a film density of 6.0 g/cm ³ or more and 7.1 g/cm ³ or less;
an etching step of patterning the metal oxide film generated in the metal oxide film generating step;
A method for producing a metal oxide film, comprising: 2. The method for producing a metal oxide film according to claim 1, wherein the thickness of the metal oxide film produced in the metal oxide film producing step is 0.5 nm or more and 4.7 nm or less. 3. The metal oxide film according to claim 2, wherein the metal oxide film formed in the metal oxide film forming step has a film density of 6.27 g/cm ³ or more and 7.10 g/cm ³ or less. Production method. 2. The method for producing a metal oxide film according to claim 1, wherein the thickness of the metal oxide film produced in the metal oxide film producing step is 0.5 nm or more and 2.5 nm or less. 5. The metal oxide film according to claim 4, wherein the metal oxide film formed in the metal oxide film forming step has a film density of 6.81 g/cm ³ or more and 7.10 g/cm ³ or less. Production method. 2. The energy ray irradiation in the metal oxide film forming step is energy ray irradiation in a range of wavelengths of 185 nm or more and 255 nm or less capable of generating active oxygen species in an aqueous solution. 6. A method for producing a metal oxide film according to any one of items 1 to 5. 7. The method for producing a metal oxide film according to claim 1, wherein the energy beam irradiation in the metal oxide film forming step is energy beam irradiation in a nitrogen atmosphere. A metal oxide film produced by the method for producing a metal oxide film according to any one of claims 1 to 7. An electronic device comprising the metal oxide film according to claim 8 . 10. The thin film transistor according to claim 9, wherein the thin film transistor is formed by laminating at least a gate electrode, a gate insulating film, a semiconductor layer made of the metal oxide film, and a source/drain electrode on a substrate in this order. electronic device.

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