Method for manufacturing metal oxide film, metal oxide film manufactured using the same, and electronic device

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

Technical Field

[0001] The present invention relates to a method for manufacturing a metal oxide film for forming a thin film transistor used for driving, for example, an organic EL (Electro-Luminescence) element ((OLED (Organic Light Emitting Diode)) or an LCD (Liquid Crystal Display)), a metal oxide film manufactured using the same, and an electronic device equipped with this metal oxide film.

Background Art

[0002] A thin film transistor (hereinafter also referred to as TFT) is used, for example, as a driving transistor for a display device and is known as an electronic device that performs driving and the like in each pixel. TFTs using a metal oxide as a semiconductor material have been manufactured and put into practical use using vacuum processes such as sputtering and evaporation. In particular, in the case of an IGZO-based metal oxide TFT having In-Ga-Zn as metal species, it is generally known and utilized that it exhibits a relatively high mobility of about 5-10 cm 2 / Vs or more.

[0003] However, when using a vacuum film forming method, a large-scale vacuum apparatus is required, and there are problems such as a decrease in production efficiency and an increase in the environmental load. Also, it has been a problem that it is difficult to form a uniform thin film on a large-area substrate. Furthermore, with the high definition of displays such as 4K and 8K, a high value of 10 cm 2 / Vs or more is required as the carrier mobility in the semiconductor required for driving the display, and the development of a semiconductor material that further increases the mobility described above is desired.

[0004] Therefore, research and development have been carried out to achieve high performance of a metal oxide semiconductor using a coating type film forming method that does not require a vacuum apparatus and can be easily formed in the atmosphere and enables printing.

[0005] Generally, in the manufacturing process of a metal oxide semiconductor using a coating-type film-forming method, a precursor solution of a metal oxide is applied onto a substrate to form a precursor thin film, and then this precursor thin film is formed by subjecting it to an oxidation treatment such as heat baking.

[0006] By the way, the denseness of the film in an oxide semiconductor can be analyzed as film density, and it has been reported that a dense film also has good electrical characteristics such as mobility (see Non-Patent Documents 1 and 2 below).

Prior Art Documents

Non-Patent Documents

[0007]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, even when the methods described in each of the above documents are used, it is difficult to say that a sufficiently simplified film formation process has been achieved, and a high carrier mobility that can also support the driving of high-definition displays has not been realized. Particularly in the case of the coating method, since it is prepared via a precursor solution, it contains a large number of residual impurities derived from metal salts, solvents, additives, etc., and it is difficult to form a dense film.

[0009] An object of the present invention is to provide a method for manufacturing a dense metal oxide film that does not require a vacuum film formation method or a complicated process and can obtain a high carrier mobility that can also support the driving of high-definition displays, a metal oxide film manufactured using the same, and an electronic device.

Means for Solving the Problems

[0010] In order to achieve the above object, the method for manufacturing a metal oxide film of the present invention includes: a precursor solution generation step of dissolving an inorganic acid salt composed of a metal salt having indium as a main component of a metal component in a solvent in which an aqueous solvent occupies 50% or more by weight to generate a water-soluble precursor solution of a metal oxide having a molar concentration of 0.01 M or more and 0.20 M or less; a precursor solution coating step of coating the precursor solution generated in the precursor solution generation step on a predetermined object to be coated; irradiating an energy ray on a predetermined region of the precursor solution of the metal oxide coated on a predetermined object to be coated in the precursor solution coating step to oxidize the predetermined region, and having a film thickness of 0.5 nm or more and 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 to generate a metal oxide film; a metal oxide film generation step; an etching step of patterning the metal oxide film generated in the metal oxide film generation step; and is characterized by having the above.

[0011] In the metal oxide film formation step, it is preferable that the thickness of the metal oxide film formed is 0.5 nm or more and 4.7 nm or less. In this case, the film density of the metal oxide film formed in the metal oxide film formation step is 6.27 g / cm 3 or more and 7.10 g / cm 3 or less.

[0012] Furthermore, it is more preferable that the thickness of the metal oxide film formed in the metal oxide film formation step is 0.5 nm or more and 2.5 nm or less. In this case, it is more preferable that the film density of the metal oxide film formed in the metal oxide film formation step is 6.81 g / cm 3 or more and 7.10 g / cm 3 or less.

[0013] Moreover, it is preferable that the energy ray irradiation in the metal oxide film formation step is energy ray irradiation in the wavelength range of 185 nm - 255 nm that can generate active oxygen species in an aqueous solution. Also, it is preferable that the energy ray irradiation in the metal oxide film formation step is energy ray irradiation in a nitrogen atmosphere.

[0014] In addition, the metal oxide film of the present invention is characterized by being manufactured by the manufacturing method of any of the above-described metal oxide films.

[0015] In addition, the electronic device of the present invention is characterized by including the above-described metal oxide film. This electronic device can be a thin film transistor in which at least a gate electrode, a gate insulating film, a semiconductor layer composed of the above-described metal oxide film, and source and drain electrodes are laminated in this order on a substrate.

Advantages of the Invention

[0016] According to the method for manufacturing a metal oxide film, the metal oxide film manufactured using the same, and an electronic device of the present invention, since it can be carried out without using a vacuum method or photolithography techniques, it is possible to easily manufacture a metal oxide film without requiring large-scale equipment or a complicated process.

[0017] Also, conventionally, in order to increase the carrier mobility in a semiconductor layer, it has been considered effective to increase the film thickness to a certain extent (for example, to 10 nm - 20 nm or more). However, the inventors of the present application have doubts about whether such a conventional theory can be applied even when forming a metal oxide film by a coating-type film formation method. As a result of repeated detailed experiments, at least in the above case, it was found that by reducing the film thickness to near the limit state, the crystallinity of the film structure was significantly improved. 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 thus have made the present invention.

[0018] Specifically, a precursor solution of a metal oxide is made into a solution having a molar concentration of 0.01 M or more and 0.20 M or less, the film thickness of the formed metal oxide film is set to 0.5 nm or more and 5.0 nm or less, and the film density of the metal oxide film is 6.0 g / cm 3 or more and 7.10 g / cm 3 or less. By doing so, for example, it is possible to generate a dense and high-performance metal oxide film that can also support the driving of high-definition displays such as 4K and 8K, and can obtain a carrier mobility of 27 cm 2 / Vs or more.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0020] Hereinafter, a method for manufacturing a metal oxide film according to an embodiment of the present invention, the metal oxide film and the electronic device manufactured using the same will be described.

[0021] ≪Embodiment≫ First, the method for manufacturing a metal oxide film according to this embodiment will be described. As a prerequisite, the 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. 2(A) shows a cross-sectional structure of a generally known TFT (first example: without an etching stop layer). On a substrate 101, 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 laminated. FIG. 2(B) also shows a cross-sectional structure of a generally known TFT (second example: with an etching stop layer). On a substrate 201, a gate electrode 202, a gate insulating film 203, a semiconductor layer 204 made of a metal oxide film, an etching stop layer 205 for protecting the semiconductor layer 204 from etching, and source / drain electrodes 206 are laminated.

[0022] Next, the method for manufacturing the metal oxide film of this embodiment will be described in detail. Also, the metal oxide film and thin film transistor (TFT) manufactured by this manufacturing method will be described. As the layer of the TFT, assume the one configured as shown in FIG. 2(A). That is, on the substrate 101, 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. The semiconductor layer 104 is coated with a water-soluble metal oxide precursor solution, and a metal oxide film is formed by subsequent processing.

[0023] Note that the method for manufacturing a metal oxide film according to the present invention is not limited to the method for manufacturing a metal oxide film of a TFT, and can be applied to the method for manufacturing a metal oxide film of various other electronic devices. Also, it can be applied not only to the manufacture of oxides exhibiting semiconductor characteristics, but also to the manufacture of oxides exhibiting conductive characteristics used for electrodes and the like, and oxides exhibiting insulating characteristics.

[0024] (1) First, clean the forming material of the substrate 101, form a barrier layer and a planarization layer (inorganic thin film or organic thin film) on the surface by sputtering or the like, form a gate electrode (for example, gold, titanium, chromium, aluminum, molybdenum or their alloys, laminated films, etc.) 102, and perform patterning to obtain a desired shape. For fine pattern formation, photolithography (a fine processing technology by ultraviolet exposure) is used.

[0025] (2) Next, form a gate insulating film 103. The gate insulating film 103 is preferably composed of an inorganic oxide film with a high relative dielectric constant. Examples of the inorganic oxide include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, etc. Inorganic nitrides such as silicon nitride and aluminum nitride can also be used.

[0026] (3) Next, use a water-soluble metal oxide precursor to form the shape of the semiconductor layer 104. In the formation process of the semiconductor layer 104, a precursor solution generation process for generating a precursor solution of the water-soluble metal oxide is performed as a previous process. In this precursor solution generation process of the metal oxide, an inorganic acid salt is used as the precursor solution. Specifically, a metal nitrate mainly composed of indium is used, and it is necessary to define the molar concentration to be 0.01M or more and 0.20M or less, but it is more preferable to define the molar concentration to be 0.05M or more and 0.20M or less.

[0027] In addition to indium, other metals can be added in a small amount as the metal of the metal oxide. Examples of other metals include metal atom-containing compounds that form oxides applicable to oxide semiconductors, and can be metal salts, metal halide compounds, organometallic compounds, etc. containing metal atoms. Specific metal atoms include gallium, zinc, aluminum, strontium, zirconium, tin, etc.

[0028] In addition, the film thickness can be changed by adjusting the solution concentration. By setting the molar concentration of the solution to 0.20 M or less, it becomes possible to make the film thickness of the metal oxide film formed after the coating process 5.0 nm or less. According to the research of the inventors of the present application, it has been found that by making the film thickness of the metal oxide film 5.0 nm or less, it is possible to fabricate a TFT having good semiconductor characteristics. Therefore, it is important to set the molar concentration of the precursor solution to 0.20 M or less as a condition therefor. In addition, in order for the film to function well, the molar concentration of the precursor solution is set to 0.01 M or more, preferably 0.05 M or more, and a film thickness of the metal oxide film of 0.5 nm or more is ensured. Furthermore, in order to improve the manufacturability of the film, it is important to make the film thickness of the metal oxide film 2 nm or more.

[0029] In terms of the solvent ratio, it is preferable to set the water solvent to 100%. However, in order to improve the coatability, an organic solvent can be mixed. In that case, even when the solvent ratio of water is reduced to a ratio of 50% or less, the patterning property and the electrical characteristics as an electronic device can reach a predetermined reference value. As a solvent that can contain a small amount in addition to water, solvents such as ethanol, propanol, ethylene glycol, 2-methoxyethanol, and acetonitrile can be mixed and used together in order to improve the coatability. Furthermore, in order to improve the solubility, it is also possible to make the pH acidic or basic.

[0030] When the precursor solution generation step shown in (3) above is completed, the semiconductor layer 104 is formed by the generated precursor solution. That is, as shown in Fig. 1(A), the semiconductor layer 104 is generated by performing the precursor solution coating step (a), the soft annealing step (b), the energy beam irradiation step (c), and the etching step (d) in this order. On the other hand, in the formation process of the semiconductor layer 104 according to the prior art, as shown in FIG. 1(B), a photolithography process is adopted, which is performed in the order of a precursor solution coating process (a), an annealing process (b), a photoresist coating process (c), an energy beam irradiation process (d), a development process (e), an etching process (f), and a film removal process (g). In the manufacturing method of this embodiment, it is clear that the number of processes is smaller and the processing is simpler compared with such prior art.

[0031] Returning to the above description, first, as shown in FIG. 1(A)(a), a precursor solution composed of a metal nitrate mainly containing indium, which is generated in the above-described precursor solution generation process, is applied to the upper surface of the substrate 101 to form a thin film of the precursor solution. The thickness of the semiconductor layer 104 can be adjusted by the solution concentration and the number of times the solution is applied.

[0032] Note that the thickness of the semiconductor layer 104 is set to be from 0.5 nm to 5.0 nm. As the coating method, printing methods 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, and a die coating method can be used.

[0033] Next, as shown in FIG. 1(A)(b), a soft annealing (performing a drying process such as low-temperature drying) process is performed. The soft annealing process is also referred to as a gentle drying process. Specifically, since the semiconductor layer 104 contains a large amount of moisture, it is performed for the purpose of leaving water, which is the main component of the solvent, and is a process performed to ensure the effectiveness of the oxidation treatment of the pattern formed in the energy beam irradiation process performed later. As the soft annealing treatment, low-temperature drying, natural drying, reduced-pressure drying, hot air / cold air / room-temperature air drying, infrared light drying, etc. can be used. Drying may be performed by a reaction using a heating device with microwaves.

[0034] Next, as shown in FIG. 1(A)(c), an energy beam irradiation process is performed. In this energy ray irradiation step, by irradiating energy rays such as ultraviolet rays onto the moisture remaining in the semiconductor layer 104, patterning of the metal oxide film can be easily performed. By executing the metal oxide film formation step combining the above soft annealing step and this energy ray irradiation step, the state shown in Fig. 3(A) changes to the state shown in Fig. 3(B). That is, in this energy ray irradiation step, energy rays are irradiated onto the water molecules remaining in the film to cause the following photochemical reaction (photooxidation (formation of insoluble oxide)). H2O + hν → HO·+·H As a result, hydroxyl radicals (OH·), which are active oxygen species, are generated.

[0035] The wavelength of the ultraviolet rays irradiated here is preferably selected from 180 to 400 nm, and more preferably 185 to 255 nm. Examples include ultraviolet rays from an excimer lamp, a deuterium lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a metal halide lamp, a helium lamp, a carbon arc lamp, a cadmium lamp, an electrodeless discharge lamp, etc. In addition, using a low-pressure mercury lamp is more preferable because the conversion from the precursor film to the oxide film can be easily performed. At this time, by irradiating through a light-shielding mask having a pattern, selective oxidation treatment becomes possible and a pattern can be easily formed.

[0036] Since the energy irradiation by ultraviolet light at this time is in a wavelength band where ultraviolet rays react 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 decompressed. If oxygen is not decompressed, a desired pattern cannot be obtained even when light is irradiated onto the mask.

[0037] When the oxide thin film formed using the precursor of this water-soluble metal oxide has a thickness as thin as 0.5 nm - 5.0 nm, the oxidation process by light can be efficiently carried out. As shown in FIG. 3(B), when the film thickness is thin, photooxidation can be sufficiently carried out to the inside of the film. That is, the photooxidation treatment generated from the irradiation surface side can sufficiently reach the inside of the film, and the thickness is 5.0 nm or less, enabling dense and substantially uniform film formation in the vertical direction. In this embodiment, the film thickness is set within this range.

[0038] On the other hand, as in the conventional case, when the film is thick (for example, 10 nm - 20 nm), a gradation during photooxidation occurs between the film regions on the irradiation surface side and the substrate surface side. When applied to a TFT as the semiconductor layer 104, problems occur in the reliability of device characteristics and the like. As a result, it becomes difficult to obtain good switching characteristics in the TFT. Also, in this embodiment, the thickness of the metal oxide film is set to 0.5 nm or more. This is considered in view of the fact that 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 mainly composed of indium, and the productivity deteriorates, making it difficult to achieve.

[0039] After the energy beam irradiation step is completed as described above, as shown in FIG. 1(A)(d), an etching step is performed to remove the precursor film applied to the unoxidized region (for example, the region not irradiated with the energy beam by the mask). In the etching step, it is preferable to use an etching solution that causes little damage to the metal oxide film. Specifically, acetic acid, propionic acid, oxalic acid, succinic acid, citric acid, malonic acid, malic acid, tartaric acid, oxalic acid, formic acid, glycolic acid, maleic acid, etc. with appropriately adjusted concentrations, which are generally known organic acids, can be used.

[0040] By sufficiently performing a rinsing process with pure water or the like after etching, the oxide thin film can be patterned only in the region selectively irradiated in the energy beam irradiation step.

[0041] Thereafter, by further performing a firing process on the patterned metal oxide film, the oxidation process can be promoted, and a semiconductor layer 104 of a TFT having more excellent characteristics can be obtained. The firing process in this case is, for example, in the range of 150°C to 400°C for a time ranging from 30 minutes to 6 hours. In the firing process at this time, natural drying, hot air, cold air, room temperature air drying, infrared light drying, vacuum drying, etc. can be used. Drying by a heating device using microwaves may also be possible. Each firing process can be performed not only in the atmosphere but also in a gas atmosphere such as oxygen, nitrogen, argon, etc.

[0042] (4) After the formation of the semiconductor layer 104 made of metal oxide is completed as described above, a step of forming source / drain electrodes 106 as shown in Fig. 2(A) is performed on this semiconductor layer 104.

[0043] As materials for the source / drain electrodes 106, transparent electrodes such as ITO and IZO, metal electrodes such as Al, Ag, Cr, Mo, Ti, and alloys thereof can be used. By making it a laminated film of two or more layers, the contact resistance can be reduced and the adhesion can be improved.

[0044] Note that various etching solutions such as a mixed acid of phosphoric acid, acetic acid, and nitric acid (PAN etchant) and oxalic acid can be used as the etching solution. When patterning the source / drain electrodes 106 by wet etching, an etching stop layer (corresponding to the etching stop layer 205 in Fig. 2(B)) may be formed to mitigate damage to the semiconductor layer 104, and by doing so, deterioration of semiconductor characteristics can be suppressed. As the etching stop layer, the same material as the gate insulating film 103 can be applied.

[0045] In addition, in the source-drain electrodes 106 and the gate electrode 102 described above, by using a material with a high oxide conductivity as the oxide composition, it is also possible to form a conductive film related to the oxide using a water-soluble metal oxide precursor. When forming the conductive film here, the precursor solution is an inorganic acid salt. More specifically, it is composed of at least one metal salt of nitrate, chloride salt, sulfate salt, acetate salt, carbonate salt, and fluoride salt.

[0046] Examples of the material with high conductivity include metal atom-containing compounds that form oxides (oxide conductor materials) showing conductor characteristics upon oxidation, such as metal salts, metal halide compounds, and organometallic compounds containing metal atoms. Specific metal elements include indium, gallium, zinc, tin, etc. Specific examples of the oxide conductor material include, but are not limited to, In-Sn-based oxides, Ga-Zn-based oxides, In-Zn-based oxides, Zn-based oxides, etc. Using a method similar to the method used to create the semiconductor layer 104, by irradiating energy rays such as ultraviolet rays to the moisture remaining in the film, patterning of the metal oxide film can be easily performed.

[0047] Also, by using a similar method and setting the composition of the metal element in the oxide to, for example, Zr, Hf, Al, etc., a functional oxide applicable to an insulating film having high dielectric characteristics can be formed. As described above, a TFT can be formed by a simple method.

[0048] By the way, in this embodiment, by making the thickness of the semiconductor layer 104 a thin film of 0.5 nm to 5.0 nm, a TFT with excellent characteristics can be created. This is because, particularly in the case of a film mainly composed of indium oxide (hereinafter simply referred to as an indium oxide film), by making it a thin film as described above, it becomes possible to form a dense film.

[0049] When the indium oxide film is made into a thin film with a thickness of 0.5 nm to 5.0 nm, it becomes clear that a dense film can be formed by obtaining the characteristics of the density of the indium oxide film (obtained by X-ray reflectivity measurement) with respect to the thickness of the indium oxide film.

[0050] As a result of X-ray reflectivity measurement, when the indium oxide film is made into a thin film with a thickness of 5.0 nm or less, it became clear that the density of the indium oxide film can be made 6.0 g / cm 3 or more (see the description of the examples described later). The maximum value of the theoretical density of the indium oxide film is 7.1 g / cm 3 . Therefore, it is clear that by making the film density 6.0 g / cm 3 or more, the uniformity (crystallinity) of the film can be made good. Therefore, by making the indium oxide film into a thin film with a thickness of 5.0 nm or less, the uniformity (crystallinity) of the film can be made good, and when used for TFTs etc., semiconductor characteristics such as the carrier mobility of the semiconductor layer 104 can be enhanced.

[0051] The above-described evaluation of crystallinity by X-ray diffraction is known as a method for evaluating film quality. Generally, it is known that the peak intensity in X-ray diffraction is proportional to the amount of substance, and the crystallinity of the produced thin film can be evaluated by the ratio of the scattering intensity of crystallinity to the total scattering intensity obtained by adding the diffraction peak of crystallinity and the diffraction peak of amorphousness (represented by the following formula (1)).

[0052] [Number] When calculating the indium oxide (In2O3) film produced according to this embodiment using the above formula (1), it is clear that a high-quality thin film with a 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 applied as a thin film transistor, high carrier mobility can be realized. [Examples]

[0053] As the TFT for evaluation according to this embodiment, a low-resistance silicon wafer with a thermal oxide film having a thickness of 100 nm was used to fabricate a TFT element as shown in FIG. 4. That is, in this embodiment, a low-resistance silicon wafer with a thermal oxide film was used as the substrate 1, the gate electrode 2, and the gate insulating film 3. Next, in order to form the semiconductor layer 4, a metal oxide precursor solution was applied onto the silicon wafer by the spin coating method.

[0054] As the water-soluble metal oxide precursor for forming the metal oxide film, indium nitrate hydrate (In(NO3)3·xH2O, manufactured by Aldrich) was weighed and dissolved in pure water to prepare a coating-type semiconductor precursor solution shown in Table 1 below. At this time, the concentration of the sample 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 for Comparative Examples 1, 2, and 3 prepared for comparison with Examples 1 and 2.

Table 1

[0055] Subsequently, the precursor solution thus prepared was applied onto the silicon wafer using the spin coating method (spin rotation speed: 4000 rpm) and dried on a hot plate at a low temperature (70 degrees) for 1 minute so that water, which is the main component of the solvent, remained in the film.

[0056] Subsequently, a mask having a pattern shape of a semiconductor layer 4 formed on a low-resistance silicon wafer with a thermal oxide film (including a substrate 1, a gate electrode 2, and a gate insulating film 3) was set on the applied metal oxide precursor film, and ultraviolet irradiation with a low-pressure mercury lamp was performed on the metal oxide precursor film through this mask for 10 minutes. The main wavelengths of the ultraviolet rays were 185 nm and 254 nm. Thereby, an oxidation treatment process of the metal oxide precursor film was performed. At this time, the water remaining in the precursor film was irradiated with ultraviolet rays, and partial oxidation treatment was performed with radicalized hydroxyl radicals to create a metal oxide film.

[0057] Subsequently, an etching treatment was performed with a 0.1% solution of citric acid, which is a hydroxycarbonate-based organic acid, and the metal oxide precursor film in the non-irradiation region of the ultraviolet rays where no oxidation treatment was performed was removed. As described above, a semiconductor layer 4 made of a metal oxide film having a desired pattern was formed.

[0058] Subsequently, the metal oxide film was baked in an air atmosphere oven at 350 °C for 1 hour to form the semiconductor layer 4. The film thickness of the semiconductor layer 4 at this time was 15 nm. Subsequently, masking was performed with a metal mask having a predetermined shape, and source and drain electrodes 6a and 6b were formed by a DC sputtering method using molybdenum. Thereby, a TFT for evaluation was fabricated. 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.

[0059]

Table 2

[0060] The semiconductor characteristics of the obtained examples and comparative examples of TFTs are shown in Table 3 below. Also, using X-ray reflectivity measurement and X-ray diffraction method, the film density and crystallinity of each example and each comparative example were evaluated.

Table 3

[0061] When the solution concentration is sufficiently low (Examples 1 and 2), a thin film with a thickness of 5 nm or less can be formed, and then, by continuously performing a photo-oxidation process, a good thin film with no compositional unevenness in the depth direction can be formed. On the other hand, when the solution concentration is high (Comparative Examples 1, 2, and 3), photo-oxidation in the depth direction is not sufficient, resulting in deterioration of the film quality, and it is difficult to obtain the desired semiconductor characteristics. 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) cannot be detected.

[0062] Also, in Examples 1 and 2, the film densities (g / cm 3 ) are 6.81 and 6.27 respectively, both of which are good at 6.0 or more. However, in Comparative Examples 1, 2, and 3, the film densities (g / cm 3 ) are 5.81, 5.51, and 5.32 respectively, which are less than 6.00 and cannot be said to be good. This is also shown by the graph in Fig. 5. When the film thickness is 5 nm or less, the film density is much higher than 6.00 g / cm 3 , and it is clear that the semiconductor characteristics are improved.

[0063] Also, graphs showing the relationship between the reflectivity and the X-ray incident angle (deg.) in Example 2 and Comparative Example 1 are shown in Figs. 6(A) and 6(B). From the shapes of the graphs shown in Figs. 6(A) and 6(B), it is clear that the film density of Example 2 is higher than that of Comparative Example 1. Furthermore, FIG. 7 shows the relationship between the crystallinity (%) and the film thickness (nm). When the film thickness is 5 nm or less, the crystallinity shows a high value of 95% or more.

[0064] Also, as a method for evaluating the film quality of the above Examples and Comparative Examples, the crystallinity (crystallization degree) was evaluated using the X-ray diffraction method. In the evaluation of the crystallinity, the crystallinity derived from the above-described formula (1) was used. As the XRD measuring apparatus, SmartLab (XRD) manufactured by Rigaku Corporation was used. As shown in FIG. 8, for the diffraction intensity of the In2O3 crystal, the area of the peak 222 at a diffraction angle of 30 degrees (the diffraction peak of crystallinity) was used, and for the amorphous scattering intensity, the area of the amorphous diffraction peak in the vicinity of a diffraction angle of 30 degrees was used.

[0065] Further, FIG. 9 is a graph (A) showing the gate voltage-drain current characteristics of the TFT according to the Example (Example 1) and a graph (B) showing the gate voltage-drain current characteristics of the TFT according to the Comparative Example (Comparative Example 1). From these figures, it is clear that good switching characteristics can be obtained for the one in Example 1, while good switching characteristics cannot be obtained for the one in Comparative Example 1.

[0066] The manufacturing method of the metal oxide film of the present invention, the metal oxide film and the electronic device manufactured using the same are not limited to those described in the above embodiments, and various other modifications are possible. For example, in the embodiment of the present invention, the metal oxide film is of the coating type, and not all of the other layers are necessarily of the coating type, but the other layers may also be made of the coating type. When all the layers are of the coating type, all the systems for processing in a vacuum can be made unnecessary.

[0067] Also, 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 configuration in which other layers are interposed between the layers shown in the embodiment. In addition, in the above-described embodiment, a bottom-gate type TFT as an electronic device has been described. However, as the electronic device of the present invention, a top-gate type TFT can be similarly applied. However, in the case of a top-gate type TFT, the precursor solution of the metal oxide film is usually applied on the source / drain electrodes and the substrate to form the metal oxide film.

[0068] Further, the method for manufacturing the metal oxide film of the present invention is not limited to being used as a method for manufacturing the semiconductor layer (channel layer) of a TFT, and can also be suitably used for manufacturing methods of display elements such as liquid crystal, plasma, and EL, solar cells, and further touch panels and various electrodes.

Explanation of Reference Numerals

[0069] 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

1. A precursor solution generation step of dissolving an inorganic acid salt composed of a metal salt having indium as a main component of a metal component in a solvent in which an aqueous solvent occupies 50% or more by weight to produce a precursor solution of a water-soluble metal oxide having a molar concentration of 0.01M or more and 0.20M or less; A precursor solution coating step of coating the precursor solution produced in the precursor solution generation step on a predetermined object to be coated; Irradiate an energy beam onto a predetermined region of the precursor solution of the metal oxide applied onto a predetermined object to be coated in the precursor solution coating step, oxidize the predetermined region, and form a metal oxide film having a film thickness of 0.5 nm or more and 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, and a metal oxide film forming step of forming a metal oxide film; An etching step of patterning the metal oxide film produced in the metal oxide film formation step; A method for producing a metal oxide film, characterized by comprising the above steps.

2. The method for producing a metal oxide film according to claim 1, wherein the film thickness of the metal oxide film produced in the metal oxide film formation step is 0.5 nm or more and 4.7 nm or less.

3. The film density of the metal oxide film formed in the metal oxide film forming step is 6.27 g / cm 3 or more and 7.10 g / cm 3 or less. The method for producing a metal oxide film according to claim 2, characterized in that.

4. The method for producing a metal oxide film according to claim 1, wherein the film thickness of the metal oxide film produced in the metal oxide film formation step is 0.5 nm or more and 2.5 nm or less.

5. The film density of the metal oxide film formed in the metal oxide film formation step is 6.81 g / cm 3 or more and 7.10 g / cm 3 or less, and the method for producing a metal oxide film according to claim 4, characterized in that.

6. The method for producing a metal oxide film according to any one of claims 1 to 5, wherein the energy ray irradiation in the metal oxide film formation step is energy ray irradiation in a region having a wavelength of 185 nm or more and 255 nm or less, which can generate active oxygen species in an aqueous solution.

7. The method for producing a metal oxide film according to any one of claims 1 to 6, wherein the energy ray irradiation in the metal oxide film formation step is energy ray irradiation in a nitrogen atmosphere.

8. A metal oxide film, characterized by being produced by the method for producing a metal oxide film according to any one of claims 1 to 7.

9. An electronic device, characterized by comprising the metal oxide film according to claim 8.

10. The electronic device according to claim 9, comprising a thin film transistor in which at least a gate electrode, a gate insulating film, a semiconductor layer composed of the metal oxide film, and a source / drain electrode are laminated in this order on a substrate.

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