JPH0467285B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a Cd-Sn (cadmium-tin) based oxide transparent conductive thin film. [Problems to be solved by the conventional technology/invention] Transparent conductive thin films can be used as electrode materials for display devices such as liquid crystal displays, electroluminescence and electrochromic elements, photoelectric conversion devices such as solar cells, or infrared rays. Demand for reflective films is increasing. Known compositions of these transparent conductive thin films include a crude composition in which tin oxide is doped with antimony or fluorine (for example, NESA film), and a composition in which indium oxide is doped with tin (hereinafter abbreviated as ITO). Each has the following characteristics. In other words, tin oxide-based transparent conductive films can be manufactured by sputtering, but for reasons of cost and performance, they are manufactured by methods such as spraying and atmospheric CVD, which can be obtained at low cost.
It has a conductivity of 1 to 6 x 10 ^-3 Ω・cm, which is slightly inferior to ITO film, and has many pinholes in the film, which makes the surface smooth. Also, because it is acid resistant, it is difficult to etch with acid. There are drawbacks such as difficulty in precise pattern processing. On the other hand, ITO film has good conductivity of 2 to 5 × 10 ^-4 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, the batch method is suitable for production, resulting in poor productivity, it is difficult to form a film over a large area, the yield of the raw material target is low, the depletion of indium resources is expected, and the raw material cost is high. There are disadvantages such as high price, making the product expensive. As mentioned above, although ITO films are expensive, they have good performance, and therefore ITO films are currently used for most applications of transparent conductive thin films for electronic devices. Therefore, it is desired to develop a transparent conductive thin film that is inexpensive and has high performance. Methods for producing ITO films other than the vacuum-based process mentioned above 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 being difficult to form a thin film with a smooth surface, easily becoming cloudy, requiring post-treatment of thermally decomposed gases such as halogens, and increasing equipment costs. On the other hand, coating methods have problems such as the inability to produce ITO films with the same level of surface resistance as ITO films made using vacuum processes. On the other hand, Nozik is a transparent conductive thin film that has the same level of conductivity, visible light transmittance, and etching processability as an ITO film, although it is made using a sputtering method, but the rough formation is Cd ₂ SnO ₄ . A cadmium-tin oxide film (hereinafter referred to as a CTO film) has been discovered (US Pat. No. 3,811,953). Although the conductivity is slightly inferior to that of the Cd ₂ SnO ₄ film,
It is known that CdSnO ₃ film can also be used as a transparent conductive thin film and is attracting attention. The disadvantages of these CTO films are that they must be manufactured by sputtering, resulting in slow film formation and low productivity; and, although they have good average visible light transmittance, they have high absorption in the short wavelength range. Therefore, it is colored yellow, which may impair its aesthetic appearance.Furthermore, when used in solar cells, it is difficult for high-energy, short-wavelength light to pass through the cell, reducing efficiency. The present inventors solved the existing drawbacks by establishing a method for producing a CTO film by thermally decomposing a composite metal solution containing a cadmium compound on a substrate, and filed a patent application (Japanese Patent Application No. 58-248342). )
I've come to the point where I can. The present invention has been made to further eliminate the above-mentioned drawbacks. [Means for solving the problem] The present invention has an atomic ratio of Cd/Sn of 0.3 to 2.0,
One or more metal elements selected from the group consisting of Ca, Mg, Ba, Sr, B, Zn, Ni, Fe, Cu and P
The present invention relates to a Cd-Sn-based oxide transparent conductive thin film (hereinafter referred to as a CTO-based thin film) characterized in that it contains Sn (tin) in an atomic ratio of 0.01 to 1.0. [Example] The CTO-based thin film of the present invention has an atomic ratio of Cd/Sn of 0.3.
~2.0, preferably in the range of 0.8 to 1.8, followed by a third
Formed by adding metal components. When the Cd/Sn atomic ratio is less than 0.3, the conductivity of the CTO-based thin film becomes less than about 10Ω ^-1 cm ^-1 , making it impossible to use it as a transparent conductive thin film, and etching with acid tends to become difficult. arise.
On the other hand, if the Cd/Sn atomic ratio exceeds 2.0, CdO that has not reacted with tin will precipitate, resulting in a failure to form a single-phase thin film, and the film will be colored brown, impairing its translucency. It will be done. The third metal component used in the present invention includes Ca,
Examples include Mg, Ba, Sr, B, Zn, Ni, Cu, Fe, and P, and these may be used alone or in combination of two or more. The third metal component in the present invention has an atomic ratio of 0.01 to 1.0, preferably 0.03 to 0.5, relative to tin.
When the atomic ratio is less than 0.01, the effect of using the third metal component will hardly occur, and the third metal component will be formed.
Translucency and conductivity of CTO-based thin films are not sufficiently improved. On the other hand, when the atomic ratio exceeds 1.0, the light transmittance in the short wavelength range is improved, but the conductivity decreases,
becomes impractical. When an alkaline earth metal such as Mg, Ca, Sr, Ba or B or P is added as a third metal component, the density of the CTO thin film formed increases compared to when it is not added. As the hardness increases, the transparency of short-wavelength visible light and near-ultraviolet light improves, and a nearly colorless CTO-based film with a blue tint can be obtained, compared to a yellowish transparent film without additives. The conductivity of the CTO-based thin film that can be obtained is from the same level to 50% of that when the third metal component is not used.
A near improvement in conductivity can be seen. When Zn is used as the third metal component, CTO
The translucency of short-wavelength visible light and near ultraviolet rays of the system thin film is significantly improved, and the translucency at 4000 Å is improved by 30 to 50% compared to the non-additive system, and the conductivity is also improved. On the other hand, when Fe, Ni, or Cu is used as the third metal component, the light transmittance of the resulting CTO-based thin film is hardly improved, but the conductivity is improved.
The effect of adding Ni and Cu is large. When a CTO-based thin film is manufactured using the third metal component as described above, the transparency of short wavelength visible light and near ultraviolet rays and the conductivity are improved compared to the case where the third metal component is not used. The reason for this has not been elucidated in detail, but since the three metal components are dissolved in the CTO phase, the introduction of the third metal component causes the original
Band gap of CTO compound semiconductor (E _gap )
We believe that the number of free electrons increases due to the doping effect, which causes the fundamental absorption edge to shift to the shorter wavelength side and improves the conductivity. Next, the method for manufacturing the CTO-based thin film of the present invention will be explained. Although the CTO thin film may be manufactured by sputtering method,
Manufactured by the same manufacturing method as described in the specification of No. 248342, that is, by thermally decomposing a composite metal solution containing a cadmium compound, a tin compound, and a third metal compound serving as a third metal component in an organic solvent on a substrate. According to this method, the desired product can be obtained with high productivity and low manufacturing cost. Generally, commercially available cadmium compounds can be used as the cadmium compounds used to form CTO-based thin films, but cadmium compounds manufactured from cadmium and organic substances with about 1 to 30 carbon atoms are easier to manufacture and handle. Therefore, it is suitable.
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 reacting cadmium with a monohydric or polyhydric alcohol having 1 to 20 carbon atoms is used. Specific examples of cadmium β-diketone complexes include cadmium acetylacetone, cadmium benzoylacetone, etc. Specific examples of cadmium α- or β-silicate complexes include acetylformate, acetoacetate, propionyl-
Specific examples of complexes of cadmium with iso-butyric acid, benzoyl acetic acid, etc., and cadmium α- or β-keto acid esters include the above α- or β-keto acids and methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, etc. In addition to these, there are also complexes of esters of and cadmium, and in addition to these, α- or β-oxy acids such as glycolic acid, lactic acid, α-oxybutyric acid, hydroacrylic acid, and salicylic acid and methyl alcohol, ethyl alcohol, and propyl alcohol. Complexes of esters and cadmium with butyl alcohol, etc., and condensates, multimers, and mixtures thereof may also be used. Particularly preferred are those that are soluble in organic solvents and decompose into inorganic cadmium compounds when heated at 400°C or lower. The tin compound used for forming the CTO-based thin film has the general formula (): Sn(OR ₁ ) ₂ () (in the formula, R ₁ is a hydrocarbon group having 1 to 20 carbon atoms).
Divalent tin alkoxides represented by the general formula (): Sn(OR ₁ ) ₄ () (in the formula, R ₁ is the same as above), tetravalent tin alkoxides represented by the general formula () : Sn(OR ₁ ) _4-x Y _x () (wherein R ₁ is the same as above, Y is a functional group having chelating ability or a halogen atom, and x is an integer from 1 to 3) 4 Examples thereof include partial tin alkoxides of the same valence, or condensation polymers of compounds represented by the general formula (), the general formula (), and the general formula (). In addition, divalent tin carboxylates represented by the general formula (): Sn(OCOR ₂ ) ₂ () (in the formula, R ₂ is hydrogen or a hydrocarbon group having 1 to 30 carbon atoms), general formula ( ): Sn(OCOR ₂ ) ₄ () (In the formula, R ₂ is the same as above). β-diketone complexes, tinoxyβ-diketone complexes, alkyltins such as tetramethyltin and tetraethyltin, organic tins such as tetraphenyltin, and general formula (): R _x SnX _{4 -x} () (In the formula, R is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms, X is a halogen atom such as a chlorine atom or a fluorine atom, an alkoxy group, or a carboxylic acid residue, and x is the same as above) Examples include, but are not limited to, compounds represented by the following. Specific examples of the compound represented by the general formula () include diethoxytin, dipropoxytin, di-2-ethylhexoxytin, distearoxytin, etc. Specific examples of the compound represented by the general formula () include: Tetraethoxytin, tetrapropoxytin, tetrabutoxytin, tetraxy(2-
Specific examples of compounds represented by the general formula (), such as ethylhexoxy)tin and tetrastearoxytin, include the general formula (), such as tin butoxydichloride and tristearoxytin monochloride.
Specific examples of compounds represented by include stannous acetate, stannous oxalate, stannous tartrate, stannous octylate, stannous oleate, stannous linoleate, stannous stearate, etc. , Specific examples of compounds represented by the general formula () include stannous acetate, stannous lactate, stannous butyrate, stannous octylate, stannous linoleate, etc. Specific examples of the compound include dioctyltin diacetate, diethyltin oxide, dibutyltin maleate, diphenyltin dichloride, dibenzyltin dihydroxide, tributyltin laurate, dibutyltin dilaurate, dibutyltin propoxide, divinyltin dichloride, and the like. These compounds may be used alone or in combination of two or more, but they are soluble in organic solvents and can be heated at 400°C or less.
Particularly preferred are those that decompose into inorganic tin compounds. It is important that the third metal compound used to form the CTO-based thin film be compatible with the solution containing the aforementioned cadmium and tin, and that the metal component should remain in the film after thermal decomposition. Mg, Ba, B,
Salts of Zn, Ni, Cu, Fe, P and carboxylic acids such as formic acid, acetic acid, propionic acid, lactic acid, butyric acid, naphthenic acid, octylic acid, acrylic acid, and methacrylic acid, or β-diketone complexes such as acetylacetone, or α Alternatively, organometallic compounds such as complexes with β-oxyacids and β-ketonic acids, or chlorides and nitric acid compounds of the above metals are preferable. Organic solvents used for forming CTO-based thin films include:
For example, methyl alcohol, ethyl alcohol,
Monohydric alcohols such as isopropyl alcohol, butyl alcohol, and pentanol, polyhydric alcohols such as ethylene glycol, glycerin, and 1,4-butanediol, and carboxylic acid esters such as ethyl acetate, propyl acetate, isoamyl acetate, and propyl formate. , ketones such as acetone, acetylacetone, diethyl ketone, and methyl ethyl ketone, aromatic solvents such as benzene, toluene, and xylene, ethers such as dioxane and tetrahydrofuran, glycol ethers such as methyl cellosolve and ethyl cellosolve, N-methyl-2 Examples include, but are not limited to, nitrogen-containing organic solvents such as -pyrrolidone, dimethylformamide, and dimethylacetamide. These organic solvents may be used alone or in combination of two or more. When the organic solvent is monovalent or polyvalent lower alcohols, carboxylic acid esters, dioxane, ethers such as tetrahydrofuran, it can be widely used for various combinations of cadmium compounds, tin compounds, and third metal compounds. However, it is preferable to select it appropriately depending on the combination of the cadmium compound, the tin compound, and the third metal compound. The composite metal solution used to form CTO-based thin films is
It is prepared by understanding cadmium compounds, tin compounds and tertiary metal compounds in organic solvents. a cadmium compound in the composite metal solution;
The concentration of tin compounds and third metal compounds (hereinafter referred to as metal components) is usually 0.01 to 40% as metal content.
% (weight %, the same applies hereinafter), but from the viewpoint of workability, it is preferable to keep the temperature at 3 to 20°C. 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, the composite metal solution includes quartz glass,
A CTO-based thin film is formed by thermal decomposition on a substrate made of transparent alumina, soda glass, or soda glass coated with silica to prevent alkali diffusion. The properties of the CTO-based thin film formed vary greatly depending on the combination of the cadmium compound, tin compound, and third metal compound. Among these combinations, combinations of cadmium carboxylate, tin carboxylate, and carboxylate of the third metal component or acetylacetonate complex of the third metal component, cadmium carboxylate, tin alkoxide, and third metal component combination with a carboxylate or acetylacetonate complex of a third metal component,
A combination of a cadmium β-diketone complex, a tin alkoxide, and a carboxylate salt of a third metal component or an acetylacetonate complex of a third metal component is preferred for the following reasons. That is,
Cadmium carboxylic acid, tin carboxylate and tertiary
The combination of a carboxylate salt of a metal component or an acetylacetonate complex of a third metal component is the cheapest raw material and is therefore useful. Moreover, oleic acid,
Adding an unsaturated carboxylic acid that causes an oxidative hardening reaction, such as linoleic acid or linolenic acid, or using a curable group such as using a cadmium salt, a third metal component salt, or a tin salt of these unsaturated carboxylic acids, is present in the liquid. By doing so, a thin film with even better surface condition can be obtained. It is preferable that the compound having the curable group is contained in the composite metal solution in an amount of 0.1% or more,
It is more preferable that the content is 5 to 100% based on the carboxylate compound, and a remarkable effect is produced in such a case. A combination of a cadmium carboxylate, a tin alkoxide and a carboxylate of a third metal component or an acetylacetonate complex of a third metal component, or a combination of a cadmium β-diketone complex, a tin alkoxide and a carboxylate of a third metal component or In the case of a combination with an acetylacetonate complex of three metal components, the hydrolyzability of the added tin alkoxide is extremely weak compared to the case of tin alkoxide alone, and it is not just a mixed composition but a co-reaction. It is thought that it becomes a coordination compound by causing a reaction, and because of this hydrolyzability, it has particularly excellent film forming properties on substrates. Particularly favorable effects can be expected when azeotropically treating a solution to produce a target compound film. In addition, in order to promote the co-reaction between these compounds, such a composite metal solution is coated by dip coating on a substrate, dried in an oven at 70 to 150°C for about 5 to 60 minutes, and then exposed to air or oxygen. Temporary firing is performed by heat treatment at about 400 to 700° C. for about 15 minutes to two hours in an oxidizing atmosphere with adjusted pressure. Of course, the temperature may be set to a high temperature exceeding 700°C, but even if the temperature is set to a high temperature exceeding 700°C, no special advantage is obtained. It has been found from the results of thin film and X-ray diffraction that if the primary firing is performed at a temperature below about 600°C, the thin film will generally become amorphous, and if the primary firing is performed at a temperature below about 500°C, the entire thin film will become almost amorphous and the film will become amorphous. It has been found that it crystallizes at temperatures above about ℃. The thickness of such a CTO-based thin film can be controlled by the concentration of the composite metal solution 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, but the pulling speed can be adjusted arbitrarily and is not particularly limited, but for example, when using a carboxylic acid metal compound, the pulling speed may be 5 to 30 cm/3. You can aim for about a minute.
The concentration of the composite metal solution, the pulling rate during dip coating, etc. may be appropriately determined depending on the combination of cadmium compound, tin compound, third metal compound, organic solvent, thermal decomposition method, desired film thickness, etc. The thickness of the film formed in this manner may be appropriately selected depending on the application, but it is usually preferably about 200 to 20,000 Å, more preferably about 500 to 10,000 Å. The CTO-based thin film obtained through the temporary firing process is
Although the conductivity is usually quite low at 10 ^-1 to ^{10 2} Ω ^-1 cm ^-1 ,
By irradiating the thin film with ultraviolet rays or subjecting it to the following annealing process, the conductivity can be increased to approximately 1~1.
Improve by 2 digits. Annealing refers to heat-treating the composite metal solution and the thin film that has undergone primary firing for the purpose of decomposition in a reducing atmosphere, an inert gas atmosphere, or under reduced pressure, usually about 50 mmHg 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 50 to 400°C for about 1 to 90 minutes, and heat treatment in an inert gas atmosphere means, for example, argon Heat treatment at 200 to 700°C for 5 to 180 minutes in an inert gas such as nitrogen, helium, etc., and heat treatment under reduced pressure as described above at 200 to 700°C for 5 to 3 minutes. This is a method that takes about an hour. Further, these annealing steps may be performed continuously with the primary firing step. These annealing methods not only improve the conductivity of the CTOT-based thin film but also shift the light-transmitting region toward the ultraviolet region. Even if the thin film after primary firing is irradiated with ultraviolet rays,
The same effect as annealing can be obtained. Conductivity and visible light transmittance can be improved by irradiating ultraviolet rays with a wavelength of about 2000 to 4000 Å for 1 minute to 10 hours under conditions such that the illuminance on the substrate is 500,000 to 1 million lux. The effect of improvement can be obtained. Although the CTO thin film and manufacturing method of the present invention have been explained based on the dip coating method, coating methods other than the dip coating method,
For example, a spin coating method, a doctor plate method, etc. 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 thin film produced in this way can be used for liquid crystal displays, electroluminescence, etc.
It can be suitably used as an electrode material for solar cells and the like. Next, the CTO-based thin film of the present invention will be explained based on examples, but the present invention is not limited thereto. Examples 1 to 10 and Comparative Examples 1 to 4 15.0 g of cadmium octylate ethyl cellosolve solution with a metal cadmium content of 14.5%, 8.2 g of tin octylate with a metal tin content of 28.0%, and further the first
Add the third metal component listed in the table in the form of metal octylate to 10 mol% based on the metal tin, then add 15.0 g of linoleic acid and 21.8 g of isoamyl acetate, apply azeotropically for 4 hours, and apply. A solution was prepared (metal content approximately 8%, Cd/Sn atomic ratio 1.5). A quartz glass plate with a thickness of 0.8 mm was immersed in this solution, pulled up at a pulling speed of 10 cm/min, and then dried in a dryer at 150°C for 30 minutes to form a transparent cured film on the quartz glass plate. Formed. Next, this sample was baked at 600° C. for 1 hour in the air to obtain a transparent inorganic compound, and its surface resistance, X-ray diffraction, and visible light transmittance were measured using the DC four-terminal method. Subsequently, these substrates were mixed with H ₂ :N ₂ in a ratio of 1:1.
Annealing treatment was performed at 300° C. for 30 minutes in a mixed gas of (molar ratio), and the same measurements as above were performed. In addition, these thin films were analyzed using fluorescent X-ray analysis.
The composition ratios of Cd, Sn, and the third metal were determined, and it was confirmed that the composition ratios were almost unchanged from the composition before annealing and the starting composition. Further, steps were created in the film by etching with acid, and the thickness of each thin film was measured using a step-type film thickness meter to determine the volume resistivity of each film. The results of these Examples are summarized in Table 1.

【table】

〔Effect of the invention〕

By adding a specific metal as a component of a cadmium-tin oxide transparent conductive thin film, a cadmium-tin oxide transparent conductive thin film with improved conductivity and transparency can be obtained.

[Brief explanation of drawings]

Figure 1 is a graph showing the volume resistivity of the film obtained in Example 11 as a function of the amount of Zn added to Sn, and Figure 2 is the relationship between wavelength and transmittance of the film obtained in Example 12. This is a graph showing.

Claims (1)

[Claims] 1 Cd/Sn has an atomic ratio of 0.3 to 2.0, Ca,
One or more metal elements selected from the group consisting of Mg, Ba, Sr, B, Zn, Ni, Fe, Cu and P are Sn
A Cd-Sn based oxide transparent conductive thin film characterized by containing 0.01 to 1.0 in atomic ratio of Cd-Sn based oxide.