JPH0447405B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a conductive thin film, and in particular,
The present invention relates to a method for producing a transparent conductive thin film based on a polyethylene terephthalate film having excellent alkali resistance.

Generally, thin films that are transparent in the visible light range and have conductivity are used as transparent electrodes in new display systems such as liquid crystal displays and electroluminescent displays, as well as for preventing static electricity on transparent objects and blocking electrode waves. It is used.

Conventionally, so-called conductive glass, in which an indium oxide film is formed on glass, has been well known as such a transparent conductive thin film, but because the base material is glass, it has poor flexibility and processability. This may be undesirable depending on the application. Therefore, in recent years, transparent conductive thin films based on synthetic resins have been used due to their advantages such as flexibility, processability, excellent impact resistance, and light weight. ,
Polyethylene terephthalate film is preferably used as the base film because it has excellent heat resistance, strength, and the like.

For example, in order to use a transparent conductive thin film as a transparent electrode, it is patterned into a predetermined shape, and in this process, acids and alkalis are often used. On the other hand, polyethylene terephthalate film is generally hydrolyzed by acid or alkali to roughen its surface. Therefore, if the conductive thin film formed on this film has poor adhesion to the film, the film will not lose its transparency during or after the patterning process, or the thin film will peel off, resulting in high quality. It is not possible to obtain a transparent electrode, and the resulting thin film is extremely poor in durability.

The present invention was made to solve the above problems, and is a method for producing a conductive thin film that is particularly stable against alkalis and has excellent adhesion, transparency, conductivity, and durability. The purpose is to provide

The present invention provides a method for forming a conductive thin film on the surface of a polyethylene terephthalate film in vacuum, in which the film is heated with at least 50% argon.
In an atmosphere containing 1×10 ^-3 to 1×10 ^-1 Torr, high-frequency sputter etching was performed at a discharge treatment rate in the range of 0.1 to 30 W·sec/cm ² , and then the degree of vacuum was substantially maintained. It is characterized by forming a conductive thin film as is.

The sputter etching process itself is already well known, but in the present invention, the atmosphere in which the base material, polyethylene terephthalate film, is sputter etched contains at least 50% argon.
%, preferably 80% or more. It is extremely important that the atmospheric gas be mainly composed of argon in order to obtain a conductive thin film with excellent alkali resistance. It is not possible to obtain a conductive thin film with excellent alkali resistance. However, as long as argon accounts for at least 50% of the atmospheric gas, the remaining gas composition may be nitrogen, helium, neon, hydrogen,
It may be a gas commonly used in sputter etching processes, such as air. Further, the atmospheric gas may contain water vapor. The atmospheric pressure is also important and needs to be in the range of 1×10 ⁻³ to 1×10 ⁻¹ Torr. At a vacuum higher than the above range, the glow discharge tends to become unstable, while at a vacuum lower than the above range, the effect of improving the adhesion of the base film to the conductive thin film by the sputter etching treatment is not sufficiently exhibited.

Furthermore, the high frequency output per unit area of the electrode (W/
The amount of discharge treatment, expressed as the product of cm ² ) and discharge treatment time, is in the range of 0.1 to 30 W・sec/cm ² . Below the above range, the treatment effect is insufficient, and above the above range, the film may be deformed. This is not preferable because it may cause staining or coloring. In addition, it is convenient for the high frequency power supply to use 13.56MHz, which is the industrially allocated frequency, for practical purposes.

One important feature of the method of the present invention is that it forms a conductive thin film while substantially maintaining the degree of vacuum in the atmosphere in which the sputter etching process is performed as described above. Here, "substantially maintaining the degree of vacuum in the sputter etching process" means the above-mentioned 1×
This means that a conductive thin film, which is the next step, is formed on the surface of the film without breaking the vacuum in the range of 10 ^-3 to 1×10 ^-1 Torr and within this vacuum range. However, the atmospheric gas composition does not necessarily have to be the same, and may be changed as appropriate depending on the method of forming the conductive thin film employed. On the other hand, even if the film is subjected to sputter etching treatment at the above-mentioned vacuum level, the film is once taken out into the air, and then the conductivity is formed again in a predetermined vacuum atmosphere, although the reason is not necessarily clear. , the resulting conductive thin film has poor alkali resistance.

In the present invention, as long as the degree of vacuum is maintained as described above after sputter etching the base polyethylene terephthalate film, and the conductive thin film is formed in the vacuum atmosphere, the method for forming the conductive thin film is as follows. can be of any value. As a method for forming such a conductive thin film, for example,
As is well known, vacuum evaporation method, sputtering method, ion plating method, etc. can be mentioned. Further, the thin film material is not particularly limited, and for example, indium oxide containing tin oxide, tin oxide containing antimony, etc. are preferably used. Formed several hundred Å thick. However, the method of the present invention is particularly effective when forming an indium oxide-tin oxide conductive thin film by vacuum evaporation, sputtering, etc., and has excellent alkali resistance and low sheet resistance. , a conductive thin film with significantly superior durability can be obtained.

As mentioned above, the atmospheric pressure for forming a conductive thin film is 1 x 10 ^-3 to 1 x 10 ^-1 Torr, but if the vacuum is lower than the above range, the thin film formation efficiency will be poor, and the above If the vacuum is higher than the above range, the transparency of the resulting film in the visible light region will decrease, which is not preferable.

In the present invention, the base film only needs to have a surface made of polyethylene terephthalate, and therefore may of course be a laminated film with another resin film having a surface layer of polyethylene terephthalate.

As described above, according to the present invention, a polyethylene terephthalate film as a base material is sputter etched in a vacuum atmosphere consisting of a predetermined gas, and then, while the degree of vacuum in the atmosphere is substantially maintained, It forms a conductive thin film,
The conductive thin film obtained by this method has low resistance and excellent chemical resistance, particularly alkali resistance, and therefore has excellent adhesion to the film and durability.

Examples of the present invention are listed below along with comparative examples, but the present invention is not limited to these Examples in any way. In addition, in the following, the alkali resistance of the obtained polyethylene terephthalate film base conductive thin film was evaluated as follows.

That is, cut the film into strips with a width of 1 cm, and
After being immersed in a heated 1% caustic Zoda aqueous solution in a constant temperature bath at 5 minutes, the sheet resistance of the conductive thin film was measured, and the alkali resistance was evaluated based on the rate of change. This operation was repeated until the conductive thin film was peeled off from the film. Furthermore, a four-terminal method was used to measure the sheet resistance.

Example 1 A polyethylene terephthalate film was sputter etched in an atmosphere of 4×10 ⁻³ Torr consisting of 80% argon and 20% oxygen at a discharge treatment rate of 3 W·sec/cm ² . Thereafter, without breaking the vacuum and in the same atmospheric gas, a 400 Å thick indium oxide-tin oxide conductive thin film (hereinafter referred to as an ITO film) was formed by a reactive sputtering method using an indium-tin alloy. ) was formed.
The sheet resistance of this film was 200Ω/□.

When this film-based conductive thin film was immersed in a caustic soda aqueous solution heated as described above and the sheet resistance was measured over time, the sheet resistance increased only to 1.6 times the initial value even after 50 minutes of immersion. .

Comparative Example 1 The same polyethylene terephthalate film as in Example 1 was used, except that the sputter etching treatment was not performed.
An ITO film was obtained in exactly the same manner as above and Example 1,
When immersed in a caustic soda aqueous solution, the film peeled off after only 10 minutes.

In addition, after the film was subjected to sputter etching treatment, it was taken out into the atmosphere, and then Example 1
An ITO film was formed in the same atmosphere as above, but the sheet resistance of this film reached seven times its initial value 50 minutes after being immersed in a caustic soda aqueous solution.

Example 2 A laminated film in which a polyethylene terephthalate film was laminated on both sides of a polyvinyl alcohol film with an adhesive was used as a base film. This base film is coated with 80% argon and oxygen.
Sputter etching treatment was carried out in an atmosphere of 8×10 ^-2 Torr consisting of 20% and a discharge treatment amount of 10 W·sec/cm ² . Next, while maintaining this vacuum atmosphere and heating the base film to a temperature of 100°C,
By the binary vacuum evaporation method of indium and tin,
An ITO film was formed. This film had a thickness of 400 Å and a sheet resistance of 300 Ω/□.

Even after immersing this membrane in caustic soda aqueous solution for 50 minutes,
The sheet resistance increased only 2.5 times its initial value.

Comparative Example 2 An ITO film was obtained in exactly the same manner as in Example 2, except that the same laminated film as in Example 2 was not subjected to sputter etching treatment, and was immersed in a caustic soda aqueous solution. It was peeled off from.

In addition, after sputter etching the laminated film, it was taken out into the atmosphere and then an ITO film was formed in the same atmosphere as in Example 2, but this film was immersed in a caustic soda aqueous solution for 50 minutes. After minutes, the sheet resistance reached 13 times its initial value.

Example 3 A polyethylene terephthalate film was sputter etched in a vacuum atmosphere of 1×10 ⁻² Torr consisting of 60% argon and 40% oxygen at a discharge treatment rate of 0.5 W·sec/cm ² . Next, while maintaining this vacuum atmosphere, an indium oxide-tin oxide target was used for electron bead evaporation.
An ITO film was obtained. Thereafter, this film was heat-treated at a temperature of 90°C to obtain a transparent conductive ITO film. This film had a thickness of 400 Å and a sheet resistance of 350 Ω/□.

Even after this film was immersed in an aqueous caustic soda solution for 50 minutes, the sheet resistance increased only three times its initial value.

Comparative Example 3 The same polyethylene terephthalate film as in Example 3 was used, except that the sputter etching process was not performed.
When an ITO film was obtained in exactly the same manner as in Example 3 and immersed in an aqueous caustic soda solution, the film was detached from the film after only 10 minutes.

In addition, after sputter etching the polyethylene terephthalate film, it was taken out into the atmosphere and then exposed to the same atmosphere as in Example 3.
An ITO film was formed, but after 50 minutes of being immersed in a caustic soda aqueous solution, the shear resistance reached its initial value.
It reached 15.

Comparative Example 4 In Example 1, the atmosphere gas for sputter etching the film was 80% nitrogen and 20% oxygen.
An ITO film was obtained in exactly the same manner as in Example 1 except for the following. This film has a thickness of 400Å and a sheet resistance of 200Ω/
It was □.

When this film was immersed in a heated aqueous caustic soda solution, the sheet resistance increased to three times its initial value after 10 minutes, and the film peeled off from the film after 20 minutes.

Claims (1)

[Claims] ^1. In a method of forming a conductive thin film on the surface of a polyethylene terephthalate film in vacuum, the film is heated to ^0.1
Production of a conductive thin film characterized by performing high frequency sputter etching treatment at a discharge treatment rate in the range of ~30 W·sec/cm ² and then forming the conductive thin film while substantially maintaining the degree of vacuum. Method.