JPH11106934A - Production of metal oxide thin film and metal oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a metal oxide-based transparent conductive film having low resistance and high transmittance for visible rays at a low temp. in a short time by hydrolyzing a coating liquid containing a metal alkoxide and/or metal salt at the low temp., then applying on a transparent substrate, and heating. SOLUTION: A coating liquid containing a metal alkoxide such as metal mothoxide and/or metal salt such as formate is hydrolyzed at a temp. of <=0 deg.C, preferably about -30 to 0 deg.C and then applied on a transparent substrate such as glass and org. polymers. The coating liquid is prepared by using an org. solvent and/or water as a solvent, and if necessary, by adding the fine seed crystal of the objective metal oxide and other additives. The coating film is preferably heated to 20 to 100 deg.C to dry the solvent as well as to carry out hydrolysis and dehydration condensation of the metal alkoxide and metal salt. If necessary, during heating or after heating, the coating film is irradiated with UV rays or visible rays to accelerate the reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a metal oxide thin film and a metal oxide thin film.

[0002]

2. Description of the Related Art Transparent conductive films have good visible light transmittance and good conductivity, and are used for LCDs, touch panels, sensors, electrodes for solar cells, inorganic and organic EL, and selective transmission films for solar heat. It is used for

Among such transparent conductive films, metal oxide-based transparent conductive films (particularly, tin oxide (SnO ₂ ) and indium oxide (In ₂ O ₃ ) -based transparent conductive films) are other materials. It is generally used because of its lower specific resistance, higher visible light transmittance, and better stability than the transparent conductive film. In addition, tin-doped indium oxide (In ₂ O ₃ ), so-called ITO, is widely used in terms of ease of etching.

Incidentally, these metal oxide-based transparent conductive films have conventionally been prepared by depositing a crystalline or amorphous metal oxide on a substrate by vapor deposition, ion plating, sputtering, or the like. Is formed. In these vacuum film forming methods, since the equipment cost and the manufacturing cost are increased, there is great expectation for a wet process such as a sol-gel method.

[0005] German Patent No. 3300589 discloses a film formation method of low specific resistance and high transmittance by a sol-gel method. However, even in a wet process such as the sol-gel method, in order to obtain a film with good performance, that is, a film having low specific resistance and good transmittance of visible light, usually from 300 to 500 ° C.
The substrate needs to be heated to a degree. For this reason, there are restrictions on the substrates that can be used. Therefore, in order to form a film on an organic polymer substrate, a film forming method capable of setting the film forming temperature to 250 ° C. or lower, most preferably 100 ° C. or lower is desired.

Japanese Patent Application Laid-Open No. 3-188938 discloses a technique for low-temperature film formation by light irradiation, and Japanese Patent Application Laid-Open No. 8-253318 discloses a technique for low-temperature film formation using an acid catalyst and an acid amide. However,
Each of these techniques has problems such as the resistance value of the obtained film is not sufficiently low, the required temperature is still high, and the light irradiation time is long. Therefore, a method of forming a low-resistance transparent conductive film at a lower temperature is desired.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a low resistance value and a high visible light transmittance at a lower temperature and in a shorter time than in the case of the conventional vapor deposition method, ion plating method and sputtering method. An object of the present invention is to provide a method capable of forming a metal oxide-based transparent conductive film. Also,
An object of the present invention is to provide a metal oxide-based transparent conductive film which is formed at a low temperature and in a short time as described above and has a low resistance value and a high visible light transmittance.

[0008]

The object of the present invention has been attained by the following means. (A) in a method for producing a metal oxide thin film formed on a transparent substrate, (a) a step of subjecting a liquid containing a metal alkoxide and / or a metal salt to a hydrolysis reaction at a temperature of 0 ° C. or lower; A method for producing a metal oxide-based thin film, comprising a step of coating on a transparent substrate and heating the coating film. (B) The heating of the coating film in the step (b) is from 20 ° C to 10 ° C.
The method for producing a metal oxide-based thin film according to the above (a), wherein the temperature is 0 ° C. (C) The target liquid crystal microparticle seed crystal is added to the coating liquid containing the metal alkoxide and / or metal salt to be hydrolyzed in the step (a), wherein (B) A method for producing a metal oxide thin film. (D) The method for producing a metal oxide-based thin film according to the above (a) to (c), wherein the coating film is irradiated with ultraviolet light and / or visible light simultaneously with or after the step (b). (E) The coating liquid containing the metal alkoxide and / or metal salt used in the step (a) is a coating liquid containing indium alkoxide and / or indium salt and tin alkoxide and / or tin salt. The method for producing a metal oxide thin film according to any one of the above (a) to (d). (F) A metal oxide-based thin film manufactured by the manufacturing method of (a) to (e).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The manufacturing method of the present invention includes the following two processes. (A) a step of subjecting a solution containing a metal alkoxide and / or a metal salt to a hydrolysis reaction at a temperature of 0 ° C. or less; (b) a step of applying the liquid on a transparent substrate and heating the coating film

In the present invention, a metal alkoxide and / or
Alternatively, examples of metal salts include metal methoxide, metal ethoxide, metal propoxide, metal isopropoxide, metal butoxide and the like. Examples of metal salts include formates, acetates, oxalates, nitrates, metal halides and the like and / or hydrates thereof, and compounds thereof, and α
-Or β-diketones, α- or β-keto acids, esters of the above keto acids, chelate compounds with α- or β-amino alcohols, and compounds that form weaker coordination compounds than chelate such as acid amides And a coordination compound with
It also includes metal hydroxide and the like obtained by neutralizing and / or hydrolyzing the compound.

In the present invention, examples of the metal constituting the metal alkoxide and / or the metal salt include Li, Be,
B, Na, Mg, Al, Si, K, Ca, Sc, V, Cr, Mn, Fe, Co, N
i, Cu, Zn, Ga, Rb, Sr, Y, Zr, Ti, Nb, Mo, Cd, In,
Sn, Sb, Cs, Ba, La, Hf, Ta, W, Tl, Pb, Bi, C
e, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
r, Tm, Yb, and Lu. These may be used alone or in combination of two or more. Of these, preferably, B, Mg, Al, Si, C
a, V, Mn, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Cd, In, S
Selected from n, Sb, Ba, La, Ta, W, Pb, Bi, and Ce.

In the present invention, the solvent of the coating solution is
Alcohols such as methanol, ethanol, propanol, isopropyl alcohol and butanol, glycols such as ethylene glycol and trimethylene glycol, acetone, methyl ethyl ketone, diethyl ketone,
Ketones such as acetylacetone and isophorone, esters such as ethyl acetate, butyl acetate and benzyl acetate, ether alcohols such as methoxyethanol and ethoxyethanol, ethers such as dioxane and tetrahydrofuran, N, N-dimethylformamide, N, N Acid amides such as -dimethylacetamide; and aromatic hydrocarbons such as toluene and xylene. In addition, water may be contained in these media. The type and composition of the solvent are selected according to the metal alkoxide and / or metal salt used. For example, if the metal salt used is chloride and the other additives are water-soluble, use water or a mixture of water and an organic solvent as a medium;
If a metal alkoxide is used and the other additives are soluble in an organic solvent, the medium may be an organic solvent or a mixture of an organic solvent and water.

Although a low-boiling compound can be used as a solvent to reduce the drying load described below, care must be taken in handling due to its volatility. One such example is acetone.

The amount of the solvent used varies depending on the type of the metal alkoxide and / or metal salt and other additives to be used, but generally, the weight of the metal alkoxide and / or metal salt and the other additives is changed. Preferably, the content of the component is 1 to 30% by weight. More preferably, it is 2 to 25% by weight, and still more preferably 3 to 20% by weight. When the amount of the solvent is insufficient, the coatability is deteriorated. For example, when the amount of the solvent is too large, the thickness of the obtained metal oxide-based thin film decreases, and problems such as defects are likely to occur.

The coating solution containing a metal alkoxide and / or a metal salt of the present invention may contain other additives. Examples of other additives include resins that function as binders in the resulting coating. In this case, a resin that disintegrates at a low temperature or a resin that disintegrates by acid generation in combination with an acid generator is suitable. If the amount of the resin used is too large, the quality of the resulting metal oxide-based transparent conductive film deteriorates and is insufficient in that a desired resistance value cannot be obtained.

Further, other additives include an acid catalyst or a base catalyst which promotes hydrolysis of a metal alkoxide and / or a metal salt. Examples of acid catalysts include mineral acids such as hydrochloric acid, nitric acid, boric acid, borofluoric acid, and / or
Alternatively, organic acids such as acetic acid, trifluoroacetic acid, p-toluenesulfonic acid, methanesulfonic acid and the like can be mentioned. In addition, a photoacid generator that generates an acid by light irradiation is also used. Examples include diphenyliodonium hexafluorophosphate and the like. Examples of the base catalyst include trietalamine, triethylamine, 1,8-diazabicyclo [5.4.0] -7-undecene, ammonia, and phosphine. However, if the amount of these additives is large, the hydrolysis reaction will accelerate too much
Since there is no point in suppressing the reaction rate in the following, a method using a sufficiently small amount or not using the amount at all is preferable.

Further, as other additives, an inorganic content such as a dye, an organic pigment, and / or carbon black may be added in an amount which does not impair the object of the present invention. By containing such a coloring agent, a colored metal oxide thin film can be obtained.

In the present invention, it is required that the coating solution containing the metal alkoxide and / or the metal salt used in the step (a) is applied after being subjected to a hydrolysis reaction at 0 ° C. or lower.

The hydrolysis at a temperature of 0 ° C. or lower is slow in the reaction and requires a relatively long time. However, when the obtained solution or sol is used for coating, the heating temperature for crystallization decreases. To be observed. Although the cause is unknown, it is thought that the metal-oxygen network structure or the gel network structure in the solution in the low-temperature reaction is amorphous, but may have a structure close to a crystal. It is necessary that the reaction temperature be low, but the lower the temperature, the longer the reaction time. Therefore, it is not practical to make the temperature extremely low. The temperature is preferably from -30 ° C to 0 ° C, and more preferably from -20 ° C to 0 ° C. Although the hydrolysis time is not particularly limited, it is usually appropriately set in the range of 1 minute to 120 hours.

In the present invention, the transparent substrate is glass,
A flat plate, three-dimensional object, or film made of organic polymers, glass fiber reinforced plastics, ceramics, etc. Among them, organic polymer films are preferable, and examples thereof include cellulose triacetate, cellulose diacetate, nitrocellulose, polystyrene, polyethylene terephthalate, polyethylene naphthalate, syndiotactic polystyrene, polyethylene coated paper, polyether sulfone, polyarylate, and polyfluoride. Vinylidene, Teflon, or the like can be used. Further, these supports may be provided with a waterproof layer containing a polyvinylidene chloride-based polymer for the purpose of improving the so-called dimensional stability, whose dimensions change with changes in temperature and humidity. Further, a thin film of an organic and / or inorganic compound may be provided for the purpose of gas barrier. Examples of organic thin films are polyvinyl alcohol and poly (ethylene-co-vinyl alcohol)
And examples of the inorganic compound include silica, alumina, talc, vermiculite, kaolinite, mica, and synthetic mica. In addition, various organic and / or inorganic additives may be added to the substrate for other various functions.

As a coating method in the present invention, any of known methods such as spin coating, dip coating, spray coating, roll coating, and screen printing can be used. For mass production at low cost, roll coating is preferred. Particularly, a method using a bar and a method using a gieser are preferable methods. Also, a screen printing method and an offset printing method are preferable in that the patterning can be performed at the time of coating. The coating amount varies depending on the use of the obtained transparent conductive film, but is generally 0.1 to 10 ml / m ² as the coating amount of the active ingredient other than the solvent. More preferably from 0.2~7ml / m ^2, more preferably 0.4 to 5
ml / m ² .

The heating of the coating film is performed not only for drying the solvent but also for hydrolysis and dehydration condensation of the metal alkoxide and metal salt. The heating conditions after the application are preferably performed at a low temperature so as not to damage the substrate. Preferably, it is carried out at 20 ° C to 100 ° C. More preferably, it is carried out at 30 ° C to 80 ° C. Although the heating time is not particularly limited, it is usually appropriately performed in the range of 1 minute to 120 hours.

In the present invention, when a mechanical strength of the formed thin film is required, a protective film may be formed on the thin film. When this protective film is formed, a normal coating liquid for forming a protective film, for example, a coating liquid for forming a silica-based film containing an alkoxysilane hydrolyzate is used.

In the present invention, the metal alkoxide and / or
Alternatively, it is preferable that the metal oxide fine particle seed crystal is added to the coating solution containing the metal salt. The addition ratio of the metal oxide fine particle seed crystal is preferably 10 wt% to 90 wt% of the sol weight when the sol was formed from the metal alkoxide and / or the metal salt, and particularly preferably 10 wt%.
~ 80 wt%. As described below, in the present invention, the metal oxide may be crystallized by light irradiation. In this case, since the seed crystal is added,
Crystallization of the metal oxide is further promoted. Addition of 10 wt% to 90 wt% of metal oxide fine particle seed crystals of metal alkoxide and / or metal salt is effective in promoting crystallization. It seems that homoepitaxial growth is involved.

Although the size of the seed crystal is arbitrary, it is preferably 0.1 μm or less in terms of sphere from the viewpoint of transmittance.

The seed crystal to be added may not be the target metal oxide itself, but may be any one that is suitable for heteroepitaxial growth, such as one having the same crystal form and / or having a value close to the lattice constant. . For example, when forming an ITO thin film, indium oxide can be used as a seed crystal.

As the above seed crystal, a commercially available product or a synthesized product may be used. When the metal oxide thin film is ITO, commercially available products such as those manufactured by Mitsubishi Materials and Sumitomo Metal Mining can be used. Examples of the synthesis method include a sol-gel method, hydrothermal synthesis, and ordinary sintering.
For details on the sol-gel method, see "Sol-gel Method Science, Saio Sakubana, Agne Shofusha, 1988", "Sol-gel Method for Thin Film Coating, Technical Information Association, 1994" and "Sol-Gel Method". The current status and future prospects of the law, supervised by Masayuki Yamane, Technical Information Services Conference [ATIS] Sol-Gel Method Report Publishing Association, 1992 ”, etc. are described in detail.

In the present invention, when the coating film is heated and / or
Alternatively, light irradiation may be performed after heating. As a light source for irradiating the coating film with ultraviolet light or visible light, any light source may be used as long as light having a wavelength of 150 nm to 700 nm is generated. For example, there are an ultra-high pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, a xenon lamp, a halogen lamp, a sodium lamp, and the like. Preferred are an ultra-high pressure mercury lamp, a high pressure mercury lamp, a low pressure mercury lamp, and a xenon lamp. In addition, a transparent conductive pattern can be formed by using a photomask together. Further, a laser oscillation device can be used. Examples of the laser oscillation device include an excimer laser, an argon laser, a helium neon laser, a semiconductor laser, a YAG laser, a carbon dioxide laser, and a dye laser. When a laser beam is used, a portion other than the irradiated portion does not become a metal oxide, so that a pattern can be formed without using screen printing or the like at the time of application. Synchrotron radiation can also be used. These devices can be selected in consideration of the wavelength to be irradiated. When a coating solution containing a metal alkoxide and / or a metal salt is reacted, a metal hydroxide is left along with the formation of the metal oxide, but taking into account the absorption of the metal-OH bond, an ultraviolet light of 400 nm or less is considered. It is preferable to use a device that generates light including the light. Furthermore, the dehydration reaction proceeds,
When a metalloxane network is formed, the absorption of the metal-O-metal bond is shorter than that of the metal-OH bond, but the metal oxide is exposed to light of a wavelength that can activate the metal-O-metal bond. The crystallization of the product is accelerated. The irradiation time is not particularly limited, but is usually 1 minute to 120 minutes.
It is done as appropriate during the time.

In the present invention, the atmosphere in the light irradiation process is free, but it is preferable to carry out in a certain reducing atmosphere. It is considered that under a certain reducing atmosphere, an increase in carrier density due to an increase in oxygen vacancies and / or an adsorption of oxygen molecules to grain boundaries was suppressed.

On the other hand, a high boiling point low molecular weight solvent which decomposes by light irradiation may be used. Such examples include isophorone and benzyl acetate.

When light irradiation is performed as a material that can be added to a liquid containing a metal alkoxide and / or a metal salt, a resin made by photolysis can be used. For example, diazonium salts such as polymethyl vinyl ketone, polyvinyl phenyl ketone, polysulfone, p-diazodiphenylamine / paraformaldehyde polycondensate, 1,2
Quinonediazides such as -naphthoquinone-2-diazide-5-sulfonic acid isobutyl ester; polymethyl methacrylate; polyphenylmethylsilane; polymethylisopropenyl ketone; In the case of the above resin, 0 to 100 parts by weight of total metal alkoxide or metal salt
It is desirable to use 1000 parts by weight. If the amount of the resin used is too large, the quality of the resulting metal oxide-based transparent conductive film deteriorates and is insufficient in that a desired resistance value cannot be obtained.

Further, when the light irradiation is performed, when the wavelength of the irradiated light is different from the absorption wavelength of the metal alkoxide, the metal salt and / or the chelate compound thereof, another liquid containing the metal alkoxide and / or the metal salt is added to the liquid. It is preferable to add a photosensitizer as an additive.

In the present invention, the coating solution containing a metal alkoxide and / or a metal salt is preferably a coating solution containing an indium alkoxide and / or an indium salt and / or a tin alkoxide and a tin salt. Examples of indium alkoxide include indium methoxide, indium ethoxide, indium propoxide, indium isopropoxide, indium butoxide and the like. Examples of indium salts include indium formate, indium acetate, indium oxalate, indium nitrate, indium chloride, and / or hydrates thereof, and compounds thereof, and α- or β-
Coordination compounds with diketones, α- or β-keto acids, esters of the keto acids, chelate compounds with α- or β-aminoalcohols, and compounds such as acid amides that perform coordination weaker than chelate And indium hydroxide obtained by neutralizing and / or hydrolyzing the compound. Examples of the tin alkoxide include tin methoxide, tin ethoxide, tin propoxide, tin isopropoxide, tin butoxide and the like. Examples of tin salts include tin formate, tin acetate, tin oxalate, tin nitrate, tin chloride, and / or hydrates thereof, and compounds thereof, and α- or β-diketones, α- or β. −
Keto acids, esters of the keto acids, chelate compounds with α- or β-aminoalcohols, coordination compounds with compounds that perform weaker coordination than chelate such as acid amides, Also includes tin hydroxide obtained by summing and / or hydrolyzing.

When the indium compound and the tin compound are used, the ratio is preferably indium / tin = 99/1 to 80/20 in atomic ratio of indium to tin. More preferably, indium / tin = 97/3 to 85
/ 15. When the amount of tin decreases, the carrier density decreases and the conductivity deteriorates, which is insufficient.
When the amount of tin increases, carrier scattering occurs, which is insufficient in that the carrier mobility decreases and the conductivity deteriorates.

The metal oxide thin film of the present invention can be used for, for example, liquid crystal panels, touch panels, solar cells, and inorganic and organic
It can be used as EL material.

Next, specific examples of the method for producing a metal oxide thin film of the present invention will be specifically described, but the present invention is not limited to these.

(Measurement of Surface Resistance and Specific Resistance) The surface resistance was measured by a four-probe method using LORESTA-FP manufactured by Mitsubishi Chemical Corporation. (Measurement of film thickness) The film thickness is obtained by measuring with a surface profile microscope (Keyence Corporation) using a sample that has been etched with aqua regia, or by measuring the cross section of an SEM [JEOL JSM-5400; accelerating voltage: 20 kV]. Was. (Measurement of transmittance) Measure the transmittance at 550 nm with a self-recording spectrophotometer UV2.
It measured using 400-PC (made by Shimadzu). (X-ray diffraction measurement) Powder X-ray diffractometer (Rigaku Denki Co., Ltd.)
(With wide angle goniometer, CuKα)
Line, 2θ / θ scan).

Example 1 Synthesis of ITO Thin Film Indium isopropoxide (In (OC ₃ H ₇ ) ₃ ) and tin isopropoxide (Sn (OC ₃ H ₇ ) ₄ ) were converted to In / tin at an atomic ratio of In / tin. Mix so that Sn = 0.93 / 0.07,
Add acetic acid to isopropyl alcohol, and add 0 ℃
For 30 hours. This solution was mixed with borosilicate glass (1 mm thick) and polyethylene terephthalate (PET;
(5 μm thickness) with a wire bar and heated to 80 ° C. for 30 minutes.

Example 2 Example 1 was repeated except that ITO fine particles (manufactured by Sumitomo Metal) were added to the coating solution in an amount of 10 wt% of the sol weight when a sol was formed from indium and tin isopropoxide. A similar operation was performed.

Example 3 Example 3 was repeated except that light was irradiated with low-pressure mercury during heating.
Operation similar to 1 was performed.

Comparative Example 1 The same operation as in Example 1 was performed except that the hydrolysis before coating was performed at 40 ° C.

Comparative Example 2 Hydrolysis before coating was performed at 40 ° C., and heating after coating was performed at 500 ° C.
The same operation as in Example 1 was performed except that the above operation was performed.

The results are summarized in Table 1. The X of sample 11
The line diffraction pattern is shown in FIG.

[0044]

[Table 1]

As is clear from Table 1, the sample of the present invention is formed at a low temperature and in a short time, and has a low resistance value and a high transmittance.

[0046]

By using the manufacturing method of the present invention,
It was found that a metal oxide-based transparent conductive film could be formed at a low temperature in a short time, and the obtained transparent conductive film had a low specific resistance and a high visible light transmittance.

[Brief description of the drawings]

FIG. 1 shows an X-ray diffraction diagram of Sample 11.

[Procedure amendment]

[Submission date] November 6, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

Further, other additives include an acid catalyst or a base catalyst which promotes hydrolysis of a metal alkoxide and / or a metal salt. Examples of acid catalysts include mineral acids such as hydrochloric acid, nitric acid, boric acid, borofluoric acid, and / or
Alternatively, organic acids such as acetic acid, trifluoroacetic acid, p-toluenesulfonic acid, methanesulfonic acid and the like can be mentioned. In addition, a photoacid generator that generates an acid by light irradiation is also used. Examples include diphenyliodonium hexafluorophosphate and the like. Examples of the base catalyst include trietalamine, triethylamine, 1,8-diazabicyclo [5.4.0] -7-undecene, ammonia, and phosphine. However, if the amount of these additives is large, the hydrolysis reaction will accelerate too much
Since it is meaningless to suppress the reaction rate below, it is preferable to use a sufficiently small amount or not to use it at all.

Claims (6)

[Claims] 1. A method for producing a metal oxide thin film formed on a transparent substrate, comprising: (a) hydrolyzing a solution containing a metal alkoxide and / or a metal salt at a temperature of 0 ° C. or lower; (B) A method for producing a metal oxide-based thin film, comprising a step of applying the composition on a transparent substrate and heating the applied film. 2. The method according to claim 2, wherein the heating of the coating film in step (b)
The method for producing a metal oxide-based thin film according to claim 1, wherein the temperature is from 100C to 100C. 3. The method according to claim 1, wherein a seed crystal of the desired metal oxide fine particles is added to a coating solution containing a metal alkoxide and / or a metal salt to be hydrolyzed in the step (a). 3. The method for producing a metal oxide-based thin film according to any one of claims 1 to 2. 4. The method for producing a metal oxide thin film according to claim 1, wherein the coating film is irradiated with ultraviolet light and / or visible light simultaneously with or after the step (b). 5. The coating solution containing a metal alkoxide and / or metal salt used in the step (a) is a coating solution containing indium alkoxide and / or indium salt and tin alkoxide and / or tin salt. 5. The method for producing a metal oxide-based thin film according to claim 1, wherein: 6. A metal oxide-based thin film produced by the production method according to claim 1.