JPH04308616A - Manufacture of transparent conductive film - Google Patents

Abstract

PURPOSE:To manufacture a film of a large surface having a high uniformity, a low resistance, and a high transmission ratio, achieve a high film producing speed, and enable film formation on a plastic substrate by forming a transparent conductive film on the insulation substrate, and applying a plasma process to it. CONSTITUTION:After a transparent conductive film is formed on an insulation substrate, and a plasma process is applied to the film, where at least one of inactive gas, oxygen and hydrogen is included in a plasma atmosphere. For the substrate, glass, quartz, plastic, etc., can be used. For forming the transparent conductive film on the substrate, a composite for forming the translpoarent conductive film in the form of chloride or nitrate is applied on the substrate for applied solution, and it is dried at a low temperature of 70-80 deg.C. In addition, the applied solution on the transparent conductive film can be sorted to ones maily comprising metal chloride of Sn, In, Zn, Cd, Ti, etc., and ones mainly comprising nitrate. A film of a large surface having a high uniformity, a low resistance and a high transmission ratio can thus be provided, a high manufacturing speed can be achieved, and film formation on the plastic film can be enabled.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to a method for forming a transparent conductive film on an insulating substrate.

0002

[Prior Art] In recent years, with the spread of office automation equipment and small portable televisions, etc., cathode ray tubes (CRTs) have been replaced by liquid crystal displays (LCDs), electroluminescence (EL) displays, and plasma displays (
PDP), light emitting diode (LED), fluorescent display tube (V
FD), etc., are being actively researched, and some of them have been put into practical use. Most of these display elements have a transparent electrode film as a basic structure. The physical properties required of a transparent electrode film for display devices are high visible light transmittance and low resistance. In order to obtain such properties, it is said to be important to improve crystallinity, increase grain size (increase in mobility), and deviate from stoichiometry (increase in carrier concentration). In addition, it has become extremely important to increase the area of transparent conductive films having these physical properties and to manufacture them at low temperatures. Currently, transparent electrode materials include ZnO, CdO, ZnS, SnO2, In2O3,
CdSnO4, ITO, etc. are known, and the following methods are known as methods for producing these. (i) Vapor phase synthesis method Vapor phase synthesis methods include vacuum evaporation, sputtering, and ion plating, but in order to obtain a film with high transmittance and low resistance, a substrate temperature of about 350°C is required. Moreover, it is difficult to obtain a film with good uniformity over a large area. The individual methods will be outlined below. (a) Vacuum deposition method (EB deposition method). In2O3-Sn
Pellets such as O2 (5-10 wt%) are heated and evaporated by EB irradiation. Substrate temperature (Ts) is approximately 300~
The temperature is 400° C., and the film forming rate is 18 to 180 Å/min. (b) Ion plating (ionization vapor deposition method). The same pellets as above were evaporated and Ar or O
2 to be ionized by passing through plasma, and accelerated by an electric field applied to the substrate. Ts approx. 300℃, film forming speed approx. 300
Å/min. (c) Sputtering method. In2O3-SnO2 (9-15
Sputtering is performed by mixing Ar or O ions into a target such as (mol%). Ts about 180-300℃, film forming rate 1
The rate is 20 to 300 Å/min. (ii) Chemical synthesis method Chemical synthesis methods include the following methods. (d) Spray method. An aqueous solution of SnCl4, InCl3, etc. is sprayed into a firing furnace heated to 400 to 800°C to cause hydrolysis. (e) Immersion/pyrolysis method. Sn compound similar to the above, In
The substrate is immersed in a solution of a compound or the like and thermally decomposed at Ts of about 500°C. However, these methods have the following problems. However, no matter which method is used, it is impossible to obtain a film with a large area and high uniformity;
It is not possible to satisfy the following conditions: (1) a film with low resistance and high transmittance can be obtained; (2) the film forming rate is high; and (2) the film is formed at the melting point of the plastic substrate, preferably below the glass transition point.

0003

[Object] The object of the present invention is to provide a method for producing a transparent conductive film that satisfies the conditions (1) to (4) above.

0004

[Structure] In the present invention, after forming a transparent conductive film on an insulating substrate,
The present invention relates to a method for producing a transparent conductive film, which is characterized by subjecting the film to plasma treatment. The plasma atmosphere in the plasma treatment includes at least one of an inert gas, oxygen, and hydrogen, and the substrate may be made of glass, quartz, plastic, or the like. In the present invention, the method for forming a transparent conductive film on an insulating substrate is to apply a composition for forming a transparent conductive film in the form of chloride or nitrate onto the substrate as a coating solution, and to apply the composition at a low temperature of 70 to 80°C. It is preferable to use a drying method.

[0005] The coating solution for the transparent conductive coating film is Sn, In
, Zn, Cd, Ti and other metal chlorides and nitrate-based systems. The transparent conductive film to be obtained is Sn.
In the case of O2, the coating solution consists only of Sn chloride or nitrate, and in the case of In2O3, it consists only of In chloride or nitrate, but in the case of ITO film, it consists of Sn and In.
using a mixture of chlorides or nitrates. When carrying out the present invention using the coating method, the steps include (a) formation of a coating film, (b) preliminary drying, (c) heating to reaction temperature, and (d) plasma treatment, and (c) and ( It is preferable to carry out the step (d) at the same time. At the same time, elimination of -OH, -R, etc., metal-oxygen bond formation, and rearrangement are more likely to occur.

(Example using a chloride system) FIG. 1 shows a flowchart. First, indium chloride was mixed with a solvent such as acetylacetone, and after refluxing, glycerin was added to adjust the viscosity to prepare solution A. Next, tin chloride was mixed with a solvent such as acetylacetone to prepare solution B, and an appropriate amount of solution B was mixed with solution A to obtain a coating solution. At this stage, it may be further diluted with acetone or the like to adjust the viscosity depending on the application method. In addition, the solvent is not limited to acetylacetone, but also CH3OH, C2H5O
Organic solvents such as alcohols such as H and ketones such as acetone may also be used. Next, spin on, roll coat,
A coating film was formed on the substrate by a method such as dipping (the thickness of the coating film depends on the coating method and viscosity, but it is about several hundred Å to several microns).
It can be controlled within a range of m. In most cases 600Å~
The usable range is 1 μm. ). Prior to plasma treatment, pre-drying (about 70 to 80° C.) is performed in air for several minutes, mainly to prevent rapid volatilization of the solvent in vacuum. There are many -OH groups, -R groups (alkyl groups), and -OR groups (alkoxy groups) bonded to metals in the coating film at this stage.
Denseness is extremely low. As a result of dehydration condensation or condensation with removal of -OR and -R groups from these states, high quality ITO is produced.
However, plasma treatment has the effect of activating these functional groups in the coating film and promoting elimination and condensation reactions even at relatively low temperatures. Although the nature of the effect is not necessarily clear, there are two possibilities. (1) Physical effect: Bombardment of ions in the plasma activates the stretching movement of functional groups, promoting desorption. (2) Chemical effect: Oxygen, hydrogen, radicals, or ions in the plasma chemically bond with functional groups to form a gas (H
2O, as a hydrocarbon). When the plasma gas is a rare gas (N2, Ar, He, Ne, etc.), (1) mainly acts, and when it is oxygen, hydrogen, etc., mainly (2) [(1) is also included] acts. The plasma gas is not limited to oxygen or hydrogen gas, but any gas containing these elements may be used. For example, O2, CO, CO2, H2, H2O, H2O2, CH
4, Hydrocarbons such as C2H6, CH3OH, C2H5O
Alcohols such as H, ketones, ethers, etc. As shown in FIGS. 3 and 4, a capacitively coupled plasma device or an inductively coupled plasma device is used as a plasma processing device. In order to promote the effect of ion irradiation, negative self- - It is better to set the substrate 3 on the RF power supply side where a bias is applied. Furthermore, it is more effective to actively apply a bias of several tens to several hundreds of volts using the DC bias power supply 5. Typical processing conditions are shown in Table 1.

[Table 1] The effects of plasma treatment can be summarized as follows based on the results of the IR spectrum of the film. As shown in Figure 5, when plasma treatment is not performed, as the firing temperature (solid line) increases, the absorption peak due to the metal complex or solvent becomes smaller and disappears at approximately 450°C. Accordingly, the absorption peaks due to In-O and Sn-O bonds have almost perfect shapes. On the other hand, when plasma treatment was performed, the IR spectrum corresponded to the solid line of 450°C, even if the temperature was approximately 150°C (dotted line), and it can be said that there was a temperature reduction effect of approximately -300°C. . The results shown in Figure 5 are based on plasma treatment (
Gas flow rate: O2/Ar=10/5SCCM, pressure: 0.
15 torr, RF power: 0.3 W/cm 2 , and substrate temperature: room temperature to 200° C.).

(Example using a nitrate system) FIG. 2 shows a flowchart for a nitrate system, which is generally the same as the chloride system shown in FIG. 1 except that the starting material is a nitrate. It is also possible to mix nitrates and chlorides. Next, a case will be described in which a plastic film or a plastic plate is used as the substrate material. In general, the Tg of transparent polymers is approximately 150° C. or less, and it has been difficult to produce a high-quality transparent conductive film on plastic with good flatness and uniformity using conventionally known methods. Therefore, the present invention
It can be said to be optimal for producing transparent conductive films on plastic substrates. Furthermore, compared to conventional methods (mainly vapor phase synthesis), the present invention has the following advantages when the combination with a plastic substrate is considered. ■The surface flatness of plastics is generally inferior to glass surfaces. When a transparent conductive film is produced by vapor phase synthesis, its surface almost reproduces the unevenness of the plastic surface. However, according to the present invention, since the coating film is in a semi-solution state, it is reflowed to cover the irregularities on the substrate surface and the film surface becomes smooth. ■It has superior adhesion to the polymer compared to gas phase synthesis (this is thought to be because the coating film has organic functional groups, so it has excellent wettability with the organic (polymer) surface. Therefore, the gas phase synthesis method becomes an inorganic-organic junction field.) From the above points as well, a transparent conductive film formed using this method on a polymer substrate is highly useful.

[0008]

[Examples] Example 1 Acetylacetone was mixed with anhydrous indium chloride, and after refluxing, glycerin was added to prepare an indium solution. Next, nitric acid was added to Sn metal to form Sn(NO3)4, and acetylacetone was dissolved in this to form a tin solution. This indium solution (A) and tin solution (B) [(B)
]/[(A)+(B)]=2 to 10 mol%, preferably 4 to 8 mol% to prepare a coating solution. Next, this was diluted with acetone, adjusted to a viscosity of about 30 cps, and coated with 4000 cps on Pyrex glass using a roll coater.
It was applied at a thickness of about . After pre-drying this coating film at 70°C for about 1 minute, O2/Ar=5/5, pressure 0.1 torr
Plasma treatment was performed for 60 minutes under the following conditions: r, RF power of 0.5 W/cm 2 , and substrate temperature of 200° C. The properties of the obtained ITO are as follows: specific resistance: 7×1/105Ω・cm
, the transmittance was as good as 90%. Furthermore, the evaluation results of flatness and uniformity were superior to the conventional method as shown in Table 2.

[Table 2] Example 2 The method of Example 1 was applied, except for the following points.・Tin solution Starting material: SnCl4
Solvent: C2H
5OH・Viscosity: 10cps・Coating: Performed with a spinner・Substrate: Polyethylene terephthalate, polyarylate film or polyethersulfone・Film thickness: 2000Å・Plasma conditions: Substrate temperature 140℃・Characteristics: Specific resistance 2×1/104Ω・cm , transmittance 88%
・Flatness and uniformity: As shown in Table 3

[Table 3]

[0008]

[Effect] ■ A film with a large area and good uniformity can be obtained. (2) Since modification is carried out in a plasma atmosphere, it is possible to produce a transparent conductive film even at relatively low temperatures (room temperature to 200°C, with good quality films even at 140°C). Therefore, a film with low resistance and high transmittance can be obtained. ■With the coating method, relatively thick films can be formed in a short time (compared to the gas phase). ■It is possible to form a film on a plastic substrate.

[Brief explanation of the drawing]

FIG. 1 is a flow chart when a chloride-based coating solution is used.

FIG. 2 is a flowchart when a nitrate-based coating solution is used.

FIG. 3 is a schematic diagram of a capacitively coupled plasma device that can be used in the present invention.

FIG. 4 is a schematic diagram of an inductively coupled plasma device that can be used in the present invention.

FIG. 5 is a comparison diagram of IR spectra when the plasma treatment of the present invention is performed (dotted line) and when it is not performed (solid line).

[Explanation of symbols]

1 Earth electrode 2 RF electrode 3 Board 4 RF power supply 5 Bias power supply 6 Matching circuit 7 Induction coil

Claims (2)

[Claims] 1. A method for producing a transparent conductive film, which comprises forming a transparent conductive film on an insulating substrate and then subjecting the film to plasma treatment. 2. The method for producing a transparent conductive film according to claim 1, wherein the plasma atmosphere in the plasma treatment contains at least one selected from the group consisting of an inert gas, oxygen, and hydrogen.