JPS6290809A - Transparent oxide conductive film and manufacture of the same - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ω-5n (cadmium-tin) based oxide transparent conductive thin film and a method for producing the same.

[Problems to be solved by the conventional technology/invention] Transparent conductive thin films are used in display devices such as liquid crystal displays, electroluminescence devices, electrochromic devices, etc.
The demand for it is increasing as an electrode material for photoelectric conversion devices such as thick ITM or as an infrared reflective film.

The composition of these transparent conductive thin films is tin oxide doped with antimony or fluorine (for example, N
FSAllI) and a composition in which indium oxide is doped with tin (hereinafter referred to as ITO) are known, and each has its own characteristics.

In other words, tin oxide-based transparent conductive films can be manufactured by sputtering, but due to cost and performance reasons, they are manufactured by methods such as spraying and atmospheric CVD. is 1~6X10-3Ω
-1, (Slightly inferior to 1-1 and ITO, there are many pinholes in the film and the surface smoothness is poor, and because it is acid resistant, etching with acid is difficult and precise pattern processing is difficult. There are drawbacks such as.

On the other hand, the conductivity of ITO is 2~5X10-4Ω-!・c
It has a good +e-t and is easy to pattern-etch with acid, but because it is manufactured by a process using a vacuum system such as vacuum evaporation or sputtering, the manufacturing equipment is expensive and the batch method is used for production. There are disadvantages such as poor productivity, difficulty in forming a film over a large area, poor yield of the raw material target, expected depletion of indium resources, and high raw material costs, making the product expensive. Become.

As mentioned above, [TO film is expensive but has good performance, so ITO [! Currently, it is used. Therefore, it is desired to develop a transparent conductive thin film that is inexpensive and has high performance.

Methods for producing ITOll other than the vacuum-based process include a spray method in which a metal salt solution is sprayed onto a heated glass substrate and thermally decomposed, and a coating method in which a metal salt solution is applied onto a substrate and then heated and thermally decomposed. have been proposed and considered. However, the spray method has problems such as the difficulty of forming a thin film with a smooth surface, the thin film becoming cloudy, the need for post-treatment with gases such as thermally decomposed halogens, and increased equipment costs. On the other hand, when using the coating method, compared to ITO II made using a vacuum process, IT
There are problems such as the inability to manufacture O[9.

On the other hand, Nozik has developed a cadmium-tin oxide film with a composition of Cd2sno4 using a sputtering method as a transparent conductive thin film having the same level of conductivity, visible light transmittance, and etching processability as ITOll. (hereinafter referred to as CTO[m) (U.S. Patent No. 3811953@specification). Also, the Cdz
The conductivity is slightly inferior to sno 4, but cdSno
, No. 19 is also known to be used as a transparent conductive i1 film and is attracting attention.

However, the disadvantages of these CTOs [9] are: (1) they must be manufactured by sputtering, so the film formation rate is slow and productivity is low, and the cost is not much lower than that of ITOll; (2) the average visible light Although it has good light transmittance, it is colored yellow due to high absorption in the thermal wavelength region, which may impair its aesthetic appearance.Furthermore, when used in solar cells, high-energy short-wavelength light must be transmitted into the cell. For example, it is difficult to pass through the membrane, reducing efficiency.

The present inventors have already established a method for producing crog by thermally decomposing a composite metal solution containing a cadmium compound on a substrate. It has been found that short wavelength transmittance can be improved by adding a metal selected from alkaline earth metals, boron, and zinc as a third metal component.

Furthermore, the present inventors proceeded to evaluate the practicality of these CTO[9], and found that CTOIII takes in crystal water,
When immersed in water for a long time to form hydrated crystals,
A new drawback was discovered in that the conductivity was significantly reduced, and the conclusion was reached that this property could cause problems in practice.

The present invention has been made to eliminate this new drawback.

[Means for solving problems]

The present invention is made of a composite oxide containing cadmium, tin, and phosphorus, and has a Cd/Sn atomic ratio of 08 to 1.8 and a P/Sn
The atomic ratio of 0.01 to 1. It consists of an oxide transparent conductive thin film characterized by the presence of Or, and a composite oxide containing cadmium, tin, and phosphorus, and has a Cd/Sn atomic ratio of 0.8.
~ When producing an oxide transparent conductive thin film with a P/Sn atomic ratio of 001 to 10 in L8, a metal compound having a hydrolyzable or combustible group dissolved in water or an organic solvent is coated on a substrate. The present invention relates to a method for producing oxide transparent conductive Ill, which is characterized in that it is then subjected to heat treatment.

〔Example〕

The CTO system 11111 of the present invention is formed with a Cd/Sn atomic ratio in the range of 0.8 to 1.8 and a phosphorus component added thereto.

When the Cd/Sn atomic ratio is less than 0.8, the CTO thin film thin film conductivity becomes less than about 100-1 (about 1-1), and it cannot be used as an oxide transparent conductive thin film.
Also, etching with acid becomes difficult.

On the other hand, if the Cd/Sn atomic ratio exceeds 1.8, CdO that has not reacted with tin will precipitate, and a single-phase thin film will not be formed.
In addition, the film becomes colored brown, and its translucency is impaired.

In the present invention, phosphorus has an atomic ratio of 0.01 to tin.
-1.01 preferably 0.03-0.5. If the atomic ratio is less than 0.01, the water resistance will hardly be improved by addition.

On the other hand, when the atomic ratio exceeds 10, the long-term water resistance is improved, but the conductivity decreases, making it impractical.

In order to roughly improve conductivity and short wavelength transmittance, a metal component selected from alkaline earth metals, zinc, titanium, indium, boron, nickel, and copper (hereinafter referred to as the fourth metal component) is added as a metal component. One or more types may be added,
For example, the alkaline earth metals H(], Ca, Sr
When , Ba, B, In, etc. are added, the density of the CTO-based am formed increases and the hardness increases, as well as the transparency of short wavelength visible light and near ultraviolet rays improves, compared to when they are not added. , CTO-based thin film is almost bluish and colorless, compared to the yellowish transparent film of additive-free system. Furthermore, the conductivity of the CTO-based t-based film 1 can be improved from the same level as when the fourth metal component is not used, to nearly 50%.

When zl or Ti is used as the fourth metal component, the transparency of the CTO-based thin film in the visible and near ultraviolet wavelengths is significantly improved, and the transparency in aooo is improved by 30 to 50% compared to the unadded system. It also improves conductivity.

On the other hand, when Ni or - is used as the fourth metal component,
Although the light transmittance of the resulting CTO-based 111M is hardly improved, the conductivity is improved.

The above effects can be achieved by using the fourth metal component in an atomic ratio of 0.01 to 0.5, preferably 0.03 to 0.5, relative to tin.

The reason why adding phosphorus to Cd-Sn oxide significantly improves the water resistance of transparent conductive thin films is not fully understood, but X-ray diffraction results show that adding phosphorus promotes amorphization. Therefore, it is expected that the material is vitrified, which makes it difficult to form hydrated crystals and improves water resistance.

Next, the CTO thin film method of the present invention will be explained.

Although it may be manufactured by a CTO-based thin film sputtering method, it may be manufactured by a manufacturing method similar to the manufacturing method described in Japanese Patent Application No. 58-248342 developed by the present inventors, that is, a cadmium compound and a tin compound in an organic solvent. It may be manufactured by thermally decomposing a composite metal solution containing a phosphorus compound and a metal compound as a fourth metal component used as necessary on a substrate, and this method provides high productivity and low manufacturing cost. The target object can be obtained with l~.

The cadmium compounds used to form the 2-theta thin film include:
Generally, commercially available cadmium compounds can be used, but cadmium compounds produced from cadmium and an organic substance having about 1 to 30 carbon atoms are preferred because they are easy to produce and easy to handle. Typical examples of such cadmium compounds include cadmium carboxylates, cadmium alkoxides, cadmium β-diketone complexes,
Examples include cadmium α-keto acid complexes, cadmium β-keto acid complexes, cadmium α-keto acid ester complexes, and cadmium β-keto acid ester complexes. Specific examples of the cadmium carboxylates include cadmium formate, cadmium acetate, cadmium butyrate, cadmium lactate, cadmium maleate, cadmium oxalate, cadmium octylate, cadmium oleate, cadmium stearate, cadmium linoleate, and cadmium naphthenate. Salts with cadmium monovalent or polyvalent carboxylic acids having 1 to 30 carbon atoms are preferred. As a specific example of cadmium alkoxides, cadmium alkoxide obtained by the reaction of cadmium and 1i[i or polyhydric alcohol having 1 to 20 carbon atoms is used. Cadmium β
- Specific examples of diketone complexes include cadmium acetylacetone and cadmium benzoylacetone; specific examples of cadmium α- or β-keto acid complexes include:
Specific examples of complexes of cadmium with acetylformic acid, acetoacetic acid, propionyl-1so-butyric acid, benzoylacetic acid, etc., and cadmium α- or β-keto acid esters include the above α- or β-1 to 1 to 100% alcohol and methyl alcohol. , complexes of esters with ethyl alcohol, propyl alcohol, butyl alcohol, etc., and cadmium, etc. In addition to these, α- or β-based compounds such as glycolic acid, lactic acid, α-oxybutyric acid, hydroacrylic acid, salicylic acid, etc.
-Complexes of esters of oxyacids with methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, etc. and cadmium, and condensates and polymers of these;
Mixtures can also be used. Among these, those that are soluble in organic solvents and decompose into inorganic cadmium compounds when heated at 400° C. or lower are particularly preferred.

As a tin compound used for forming a CTO-based thin film, a 2i tin compound represented by the general formula (I): sn (OR+)2 (1) (wherein R1 is a hydrocarbon group having 1 to 20 carbon atoms) is used. Tetravalent tin alkoxides represented by general formula (■): Sn (OR+ )4 (1) (in the formula, R1 is the same as above), general formula (I): Sn (OR+ )44 Y
t [) (wherein, R1 is the same as above, Y is a functional group or halogen atom having chelating ability, and X is 1
tin partial alkoxides of 41i1[i or general formula (1), general formula ([)
, a condensation polymer of a compound represented by the general formula fl), and the like. Further, tin carboxylic acid salts of 2+ti represented by the general formula N: Sn (0COR2)2 (Vl (in the formula, R2 is hydrogen or a hydrocarbon group having 1 to 30 carbon atoms), general formula (Vl: Sn (0CORz) a M (in the formula,
Examples include tetravalent tin carboxylic acid salts represented by (R2 is the same as above), and β-diketone complexes which are reaction products of divalent or 411i tin with 7cetylacetone, benzoylacetone, etc., and tinoxyβ - diketone complexes, alkyltins such as tetramethyltin and tetraethyltin, organic tins such as tetraphenyltin, and general formula (vI): J SnX 4-x (wherein, R is a hydrogen atom or carbon@1 -20 hydrocarbon groups, X is a halogen atom such as a chlorine atom or a fluorine atom, an alkoxy group, a carboxylic acid residue, X is the same as above), etc., but are not limited to these. do not have.

Specific examples of the compound represented by the general formula (+1) include:
Jetoxytin, dipropoxytin, di-2-ethylhexoxytin, dipropoxytin, etc., general formula 1ll)
Specific examples of compounds represented by the general formula [111] include tetraethoxytin, te]-rabboxytin, tetrabutoxytin, tetrakis(2-ethylhexoxy)tin, tetrastearoxytin, etc. Examples of compounds represented by the general formula N include stannous acetate, stannous oxalate, stannous tartrate, stannous octylate, and olein. Specific examples of compounds represented by the general formula M, such as stannous acid, stannous linoleate, stannous stearate, etc., include stannous acetate, stannous lactate, stannous butyrate, stannous octylate, etc. Specific examples of compounds represented by the general formula (■) such as tin and stannic linoleate include dioctyltin diacetate, diethyltin oxide, dibutyltin maleate, diphenyltin dichloride, dibenzyltin dihydroxide, tributyltin laurate, and dibutyltin dilaurate. , dibutyltin propoxide, divinyltin dichloride, etc.

These compounds may be used alone or in combination of two or more, but those that are soluble in organic solvents and decompose into inorganic tin compounds when heated at 400° C. or lower are particularly preferred.

It is important that the phosphorus compound used to form the CTO-based MR be compatible with the solution containing cadmium and tin mentioned above, and that the phosphorus component remains in the film after thermal decomposition. trimethyl acid, triethyl phosphate,
Phosphite esters such as triphenyl phosphate, tributyl phosphate, phosphite esters such as triethyl phosphite, tributyl phosphite, triphenyl phosphite,
Examples include phosphorus pentoxide and phosphoric acid, with phosphorous esters and phosphoric esters being particularly preferred.

Furthermore, a metal compound (hereinafter referred to as the fourth metal compound) that is added as a fourth metal component to improve conductivity and short wavelength transmittance is a metal compound that is compatible with the solution and that is included in the film after thermal decomposition. It is important that the components remain; specific examples include alkaline earth metals such as Ca, Hg, Ba, and Sr, B, In, 2n, Ti, Ni, Cu, and formic acid.
salts with carboxylic acids such as acetic acid, propionic acid, lactic acid, butyric acid, naphthenic acid, octylic acid, acrylic acid, methacrylic acid, or β-diketones such as acetylacetone;
Alternatively, organometallic compounds such as complexes with α- or β-oxyacids or β-ketonic acids, metal alkoxides having an alkoxy group having 1 to 20 carbon atoms, or chlorides and nitrate compounds of the above metals are preferred.

Examples of organic solvents used to form CTO-based thin films include methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol, and pentanol.
1i1 [i Alcohols, polyhydric alcohols such as ethylene glycol, glycerin, 1,4-butanediol, carboxylic acid esters such as ethyl acetate, propyl acetate, isoamyl acetate, propyl formate, acetone, acetylacetone, diethyl ketone , ketones such as methyl ethyl, aromatic solvents such as benzene, 1-toluene, xylene, ethers such as dioxane and tetrahydrofuran, glycol ethers such as methyl cellosolve and ethyl cellosolve, N-methyl-2-pyrrolidone Examples include, but are not limited to, nitrogen-containing organic solvents such as dimethylformamide, dimethylacetamide, and the like. These organic solvents may be used alone or in combination of two or more. Furthermore, water may be used alone or in combination with the organic solvent.

When the organic solvent is 1 (ilIi or ethers such as polyhydric lower alcohols, carboxylic acid esters, dioxane, and tetrahydrofuran, a cadmium compound, a tin compound, a phosphorus compound, and a fourth metal used if necessary) Although it can be used in a wide variety of combinations of compounds, it is preferable to select it appropriately depending on the combination of the cadmium compound, tin compound, phosphorus compound, and fourth metal compound.

The composite metal solution used for forming the CTO-based thin film is prepared by dissolving a cadmium compound, a tin compound, a phosphorus compound, and a fourth metal compound used if necessary in an organic solvent.

The cadmium compound, tin compound, phosphorus compound in the composite gold lil solution and the quaternary compound used if necessary.
The concentration of metal compounds (hereinafter referred to as metal components) is normally used at about 0.01 to 40% (weight %, hereinafter the same) as metal content, but it is set to 3 to 20% from the viewpoint of workability etc. Or preferable.

If necessary, an organic dehydrating agent such as an orthoformate ester may be added to the composite metal solution used for forming the CTO thin film, for example, to prevent hydrolysis of the organometallic compound.

In the present invention, a composite metal solution is applied to the surface of quartz glass, transparent alumina, soda glass, or soda glass to prevent alkali diffusion in a film thickness of 500 to 2000.
21. CTO-based JII is formed by thermal decomposition on the soda glass M base coated with a film made of TiO2, zno2, etc.

The properties of the CTO-based metal that is formed vary greatly depending on the combination of the cadmium compound, tin compound, phosphorus compound, and optionally used fourth metal compound.

There are cases in which the CTO-based thin film has a simple mixed composition of metal components, and cases in which the added metal compounds co-react to form a coordination compound or a composite metal complex.
The latter shows better performance and is preferable for making the desired CTO-based thin film.In order to make such a compound (ff compound or composite metal complex), a highly reactive metal alkoxide or metal β is added as a metal compound. - It is preferable to use a diketone complex or the like to azeotropically and reflux the solution in order to produce the CTO system.

In addition, in order to promote co-reaction between these compounds,
7 also applied such a composite metal solution onto a substrate by dipping.
By drying in a oven at 0 to 150°C for about 5 to 60 minutes, and then heat-treating at about 400 to 700°C for about 15 minutes to 2 hours in air or in an oxidizing atmosphere with adjusted oxygen partial pressure. - A subsequent firing is carried out. Of course, the temperature may be higher than 700°C, but 100°C
Even if the temperature exceeds C, there are no special advantages. Note that if the secondary firing is performed at about 600°C or lower,
It has been found from the results of X-ray diffraction of thin films that they are generally amorphous, and that when carried out at temperatures below about 500°C, the entire thin film becomes almost amorphous, and above about 600°C, it becomes crystallized. .

Particularly when using soda glass, which is an inexpensive glass substrate material, it is important to perform the heat treatment at a temperature of 550° C. or lower from the viewpoint of the softening temperature of the glass.

The Ill thickness of such a CTO type sheet can be controlled by the concentration of the composite metal solution to be applied, and, for example, in the case of dip coating, the pulling rate during dip coating. The concentration of the composite metal solution is as described above,
The pulling speed can be arbitrarily adjusted and is not particularly limited, but for example, when using a carboxylic acid metal compound, the pulling speed is 5 to 30 cm, minute Pi! You can use the degree as a guide. The concentration of the composite metal solution and the pulling rate during dip coating depend on the combination of cadmium compound, tin compound, phosphoric acid compound, fourth metal compound used if necessary, organic solvent, thermal decomposition method, desired film thickness, etc. It may be determined as appropriate. The number of films formed in this way can be selected as appropriate depending on the application, but usually 200
~20,000 people are preferable, and 500~
More preferably, the number of participants is about 10,000.

The CTO thin film obtained through the primary firing process usually has a conductivity of 10-1 to 102 Ω-1 (1-1, which is quite low, but
By irradiating the film with ultraviolet rays or subjecting it to the following annealing, the conductivity can be improved by about one to two orders of magnitude.

Annealing is the process of heat-treating a thin film that has undergone primary firing for the purpose of decomposing the composite metal solution under a reducing atmosphere, an inert gas atmosphere, or under reduced pressure, usually about 50 aa+Hg or less.

Heat treatment in a reducing atmosphere means, for example, in a reducing gas such as hydrogen or carbon monoxide at a temperature of about 50 to 400°C for about 1 to 90 minutes, and heat treatment in an inert gas atmosphere means, for example, argon , nitrogen, helium, or other inert gas for about 5 to 180 minutes at about 200 to 700 °C.
This method is performed at approximately 700°C for 5 minutes (1 to 3 hours).These annealing steps may also be performed consecutively with the primary firing process.These annealings improve the conductivity of the CTO thin film. In addition to the transparent #
4 region is shifted to the ultraviolet region side.

- The same effect as annealing can be obtained by irradiating the thin film after the next firing with ultraviolet rays. The UV light to be irradiated is UV light with a wavelength of about 2,000 to 4,000 lux, and the illuminance of the M root soil is 500,000 to 1,000,000 lux.
By irradiating for minutes to 10 hours, the effect of improving conductivity and visible light transmittance can be obtained.

Although the method for manufacturing the CTO-based thin film of the present invention has been explained based on the dip WA coating method, coating methods other than the dip coating method, such as spin coating, roll coater, and doctor blade methods, can also be employed. Further, a CTO-based thin film can also be produced by spraying a composite metal solution used for forming a CTO-based thin film onto a heated substrate and thermally decomposing the solution.

The CTO-based vJm produced in this manner can be suitably used as an electrode material for liquid crystal displays, electroluminescence, solar cells, and the like.

Next, the CTO thin film of the present invention and its manufacturing method will be explained based on Examples, but the present invention is not limited thereto.

Example 1 and Comparative Example 1 Cadmium acetate anhydride 10. Dissolve OQ and 9.9 g of tin tetrabutoxide in 80 g of ethyl alcohol.

Furthermore, 0.8 g of triethyl phosphite is added and reflux treatment is performed for about 4 hours to form a CTO-based thin film.
ll wave cloth was prepared (Cd/Sn-1,8, P/5
n-0,2).

A coating solution containing no triethyl phosphite was prepared in the same manner.

Each of these solutions was used as an alkali diffusion prevention treatment for approximately 1,500 3i0. on a soda glass substrate (thickness 1.1 mm) coated with ill at a pulling speed of 1.
After coating with 0CI/Win dip coating method, 150″
CX was dried for 30 minutes, and further baked at 540° C. for 30 minutes in an air atmosphere in a Matsufuru furnace to obtain a transparent CTO-based thin film.

Both of the obtained thin films had a thickness of 1200 mm and a surface resistance value of 5.5 Ω/mm for the film with P added, and 4.5 Ω/mm for the film without P.

The two types of rough substrates were mixed into 12: H2-1:1 (
When annealing was performed at 300°C for 30 minutes in a mixed gas with a molar ratio of They exhibited good conductivity, and X-ray diffraction revealed that they were all amorphous.

As a water resistance acceleration test, the above two types of substrates were immersed in distilled water kept at 70°C and the change in surface resistance value over time was measured.The surface resistance value of the substrate without P added was 1.0% after 6 hours. The conductivity has begun to deteriorate, and the 2
It was found that after 4 hours, the surface resistance became completely infinite and the conductivity disappeared. On the other hand, the surface resistance value of the material to which P was added hardly changed even after immersion for 120 hours, and it was found that the water resistance was extremely high.

Furthermore, when the surfaces of the two types of CTO-based thin films were observed using a scanning electron microscope after the water resistance test, it was found that in the case of the one without phosphorus added, countless dice-shaped particles of about 0.5 μm, which are considered to be hydrated crystals, were precipitated. However, with the addition of phosphorus, the film was as smooth and uniform as before the test, indicating a clear difference in water resistance.

Example 2 and Comparative Example 2 Two types of solutions were prepared in the same manner as in Example 1: a solution containing cadmium acetate, tin tetrabutoxide, and a solution containing triethyl phosphite, and a solution containing no triethyl phosphite. A coating solution was prepared by adding the metal components listed in Table 1 and refluxing for about 4 hours. These solutions were coated on a silica-coated soda glass substrate in the same manner as in Example 1, baked, and annealed, and the conductivity and water resistance were evaluated and the surface was observed using a scanning electron microscope. It was found that water resistance was improved.

[Margin below]

[Effects of the Invention] The thin film of the present invention is a transparent conductive film with extremely excellent water resistance, and the manufacturing method of the present invention allows the thin film having these characteristics to be formed at high speed and at low cost. I can do it.

Claims (1)

[Claims] 1. Comprised of a composite oxide containing cadmium, tin, and phosphorus, with a Cd/Sn atomic ratio of 0.8 to 1.8 and a P/Sn atomic ratio of 0.01 to 1.0. An oxide transparent conductive thin film characterized by the following. 2 In addition to cadmium, tin, and phosphorus, one or more metals selected from alkaline earth metals, zinc, titanium, indium, boron, nickel, and copper with an atomic ratio of 0.01 to 0.5 to tin. 2. The thin film of claim 1, further comprising: . 3. Oxide transparent conductive material consisting of a composite oxide containing cadmium, tin, and phosphorus, with a Cd/Sn atomic ratio of 0.8 to 1.8 and a P/Sn atomic ratio of 0.01 to 1.0. A method for producing an oxide transparent conductive thin film, which comprises applying a metal compound having a hydrolyzable or combustible group dissolved in water or an organic solvent onto a substrate, and then subjecting the film to heat treatment. .