JPH07335046A - Manufacture of conductive transparent substrate - Google Patents

Abstract

PURPOSE:To provide a method for manufacturing a conductive transparent substrate having enhanced heat resistance in conductivity, where the conductive transparent substrate is formed by utilizing a transparent conductive film made of amorphous oxide including indium (In) and zinc (Zn) as main cation elements. CONSTITUTION:In a method for manufacturing a conductive transparent substrate, a transparent conductive film composed of amorphous oxide including indium (In) and zinc (Zn) as main cation elements is formed on the transparent substrate by a spattering method using a sintered body target composed of a composition containing indium oxide and zinc oxide. At this time, prior to formation of the transparent conductive film, the target is treated with a plasma at the atmosphere of inert gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a conductive transparent base material, and more particularly to a method for producing a conductive transparent base material of a type in which a transparent conductive film is provided on a predetermined surface of a transparent base material. .

[0002]

2. Description of the Related Art A liquid crystal display device can be made lighter and thinner, and has a lower driving voltage, so that it has been actively introduced to OA equipment such as personal computers and word processors. The liquid crystal display device having the above-mentioned advantages is inevitably in the direction of increasing the area, increasing the number of pixels, and increasing the definition, and a high quality liquid crystal display element without display defects is required. ing. The liquid crystal display element has a sandwich structure in which a liquid crystal is sandwiched by two transparent electrodes arranged so as to face each other, and the transparent electrode is one of the important elements for obtaining a high quality liquid crystal display element. . This transparent electrode is produced, for example, by etching a transparent conductive film formed on a transparent substrate with a predetermined etching solution and patterning it into a desired shape. As a material for such a transparent electrode, a conductive transparent base material of a type in which a transparent conductive film is provided on a predetermined surface of a transparent base material is used.

At present, an ITO (indium tin oxide) film is mainly used as a transparent electrode material.
The ITO film has a relatively low resistance to heat and humidity, and has a drawback that its electric conductivity is likely to decrease due to humidity. As a transparent conductive film capable of solving such a difficulty, indium (In) and zinc (Zn (Zn) are used as main cation elements obtained by sputtering a sintered body target made of a composition containing indium oxide and zinc oxide. The present inventors have already proposed a transparent conductive film made of an amorphous oxide containing (1) (see, for example, Japanese Patent Application No. 5-315075).

[0004]

However, even in the above transparent conductive film, it cannot be said that the heat resistance in the atmosphere is still sufficient, and the deterioration of the conductivity with time in a high temperature environment is relatively large. . For this reason, as a material for a liquid crystal display device for applications where long-term heat resistance stability is required, such as an in-vehicle liquid crystal panel or a liquid crystal projector, the specifications are not always satisfied. An object of the present invention is to provide a conductive transparent substrate using a transparent conductive film made of an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements. It is an object of the present invention to provide a method for producing a conductive transparent substrate, which can obtain a product having further improved heat resistance.

[0005]

Means for Solving the Problems The method for producing a conductive transparent substrate of the present invention that achieves the above object is a sputtering method using a sintered body target made of a composition containing indium oxide and zinc oxide. In forming a transparent conductive film made of an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements on a transparent substrate, an inert gas is used before the formation of the transparent conductive film. The target is plasma-treated in an atmosphere.

The present invention will be described in detail below. First, the target used in the present invention will be described. This target is composed of an oxide sintered body of a composition containing indium oxide and zinc oxide as described above. Here, as specific examples of the above-mentioned sintered body, the following (1) to (2) can be mentioned.

(1) A sintered body target made of a composition of indium oxide and zinc oxide, having an atomic ratio of In / In /
(In + Zn) has a predetermined value. Here, "the atomic ratio In of In / (In + Zn) having a predetermined value" means the atomic ratio In of the finally obtained film In / (In +
Zn) is 0.55 to 0.90, preferably 0.82
It means a desired value within the range of 0.90. Specifically, the atomic ratio In / In / (In + Zn) is 0.55.
˜0.90, preferably 0.82 to 0.90. When the atomic ratio is out of the range of 0.55 to 0.90, In in the film obtained by sputtering this target.
The atomic ratio In / (In + Zn) tends to be less than 0.55 or exceeds 0.90, which makes it difficult to obtain the target transparent conductive film. The atomic ratio is 0.82
When it is set to about 0.90, a transparent conductive film having further excellent heat resistance can be obtained. The sintered body target may be a sintered body made of a mixture of indium oxide and zinc oxide, or a hexagonal layered compound represented by In ₂ O ₃ (ZnO) _m (m = 2 to 20). It may be a sintered body consisting essentially of one or more of the above and In ₂ O ₃ . In addition, the reason why m is limited to 2 to 20 in the above formula representing the hexagonal layered compound is that when m is out of the above range, it does not become a hexagonal layered compound. The preferable range of m is 2 to 8, and more preferably 2 to 6.

(2) A sintered body target made of a composition containing, in addition to indium oxide and zinc oxide, one or more oxides of a third element having a valence of positive trivalence or more, and an In atom. The ratio In / (In + Zn) and the atomic ratio of the total amount of the third element (total third element) / (In + Zn + total third element) are predetermined values. Here, the atomic ratio of In is In / (I
"n + Zn) has a predetermined value" means that the atomic ratio In / In / (In + Zn) of the finally obtained film is 0.5.
It means a desired value within the range of 5 to 0.90, preferably 0.82 to 0.90. Specifically, it is achieved by using a sintered body target having an atomic ratio In / In / (In + Zn) of 0.55 to 0.90, preferably 0.82 to 0.90. Further, “the atomic ratio of the total amount of the third element (total third element) / (In + Zn + total third element) is a predetermined value” means that the atomic ratio of the total amount of the third element in the finally obtained film ( All third element) / (In + Zn + all third)
Element) means that the desired value is 0.2 or less. Specific examples of the third element include Al, Sb, Ga, Ge and the like. The sintered body target may be a sintered body substantially made of a mixture of indium oxide, zinc oxide and at least one oxide of the third element, or In ₂ O
₃ (ZnO) _m (m = 2 to 20), and at least one compound of at least one kind of the third element contained in the hexagonal layered compound, and In ₂ O ₃ It may be a sintered body.

When the oxide sintered body of (1) or (2) contains the above-mentioned hexagonal layered compound, the content of the hexagonal layered compound is preferably 5 wt% or more, and 10 wt % Or more is more preferable.
The oxide sintered body in this case contains In ₂ O ₃ as described above, but this In ₂ O ₃ may be amorphous or crystalline.

Further, the atomic ratio of In to Zn in the oxide sintered bodies of (1) and (2) above is In / (In + Zn).
As described above, the atomic ratio In / Zn In / (In + Zn) in the obtained transparent conductive film is 0.55 to 0.9.
The value is a desired value within the range of 0. This is because if the atomic ratio in the transparent conductive film is less than 0.55, the conductivity of the transparent conductive film tends to be low, and if it exceeds 0.90, the wet heat resistance of the transparent conductive film is likely to decrease. . Also, the atomic ratio of the total amount of the third element in the oxide sintered body of (2) above (all third elements) / (In + Zn + all third elements).
Also, as described above, the atomic ratio (total third element) / (In + Zn + total third element) of the total amount of the third element in the obtained transparent conductive film is set to a desired value of 0.2 or less. This is because when the atomic ratio of the total amount of the third element in the transparent conductive film exceeds 0.2, the scattering of ions easily occurs in the transparent conductive film, and the conductivity decreases when the scattering of ions occurs. Is.

The atomic ratio of In and Zn in the oxide sintered body can be controlled by adjusting the mixing ratio of the indium compound and the zinc compound used as starting materials for the sintered body. At this time, when one compound (indium compound or zinc compound) is excessively mixed in an amount exceeding the amount corresponding to the stoichiometric ratio of the hexagonal layered compound described above, the amorphous substance derived from the excessively mixed compound is obtained. Alternatively, it is presumed that crystalline oxide (indium oxide or zinc oxide) will be present in the sintered body as a component other than the hexagonal layered compound. Also, the atomic ratio of the total amount of the third element in the oxide sintered body can be controlled by adjusting the addition amount of the third element compound (compound of the third element) used as the starting material of the sintered body.

On the other hand, the atomic ratio of In and Zn and the total atomic ratio of the third element in the transparent conductive film are the same as the atomic ratio of In and Zn and the third element in the above oxide sintered body used as the target. It roughly agrees with the atomic ratio of quantity. However, when the relative density of the oxide sintered body is less than 70%, the obtained transparent conductive film is easily blackened. In addition, the film forming rate is reduced and the oxide sintered body itself is easily blackened. Therefore, it is preferable that the relative density of the oxide sintered body used as the target is as high as 70% or more. A more preferable relative density of the oxide sintered body is 85% or more, and a further preferable relative density is 90% or more. In order to obtain an oxide sintered body having a high relative density, powder obtained by crushing a starting material or a fired product thereof is molded by CIP (cold isostatic pressure) or the like and then subjected to HIP (hot isostatic pressure) or the like. It is preferable to sinter. Further, the purity of the oxide sintered body is preferably 98% or more. If it is less than 98%, the moisture and heat resistance of the obtained transparent conductive film may be insufficient, the conductivity may be reduced, or the light transmittance may be reduced due to the presence of impurities.

In the method of the present invention, in forming the transparent conductive film on the transparent substrate by the sputtering method using the above-mentioned sintered body target, prior to the formation of the transparent conductive film, the above-mentioned process is performed under an inert gas atmosphere. Is subjected to plasma treatment (hereinafter, this treatment is referred to as pre-sputtering). This pre-sputtering is a treatment for cleaning the target surface, and more specifically, a treatment for removing oxygen, water, carbon dioxide gas and the like adsorbed when exposed to the atmosphere from the target surface.

The pre-sputtering can be carried out by sputtering the target surface in an inert gas atmosphere using a sputtering device such as an RF magnetron sputtering device, a DC magnetron sputtering device, an ion beam sputtering device. It is difficult to unconditionally set the conditions at this time because it varies depending on the sputtering method, the composition of the target, the characteristics of the apparatus used, and the like, but it is preferable to set, for example, as follows.

Degree of vacuum and voltage applied to target during pre-sputtering First, the inside of the vacuum chamber is 1 × 10 ⁻⁵ to 1 × 10 ⁻⁶ Torr.
Sufficiently evacuate to about (1.3 × 10 ^{−3 to} 1.3 × 10 ⁻⁴ Pa). Next, an atmosphere gas is introduced into the chamber for pre-sputtering, and the degree of vacuum at this time is about 1 × 10 ^{−4 to} 5 × 10 ⁻² Torr (1.3 × 10 ⁻² to
6.7 × 10 ⁰ Pa), more preferably 2 × 10 ^{−4
~1 × 10 -2 Torr (2.7 ×} 10 -2 ~1.3 × 10 0 P
a)), more preferably 3 × 10 ^{−4 to} 5 × 10 ⁻³ Torr
(About 4.0 × 10 ^{−2 to} 6.7 × 10 ⁻¹ Pa).
The target applied voltage is preferably 100 to 500V. If the degree of vacuum during pre-sputtering is higher than 1 × 10 ⁻⁴ Torr (pressure lower than 1 × 10 ⁻⁴ Torr), plasma stability is poor and lower than 5 × 10 ⁻² Torr (5 × 10 ⁻² Torr).
^{If the} pressure is higher than ^-2 Torr), the voltage applied to the target cannot be increased. Further, if the target applied voltage is less than 100 V, the time required for pre-sputtering becomes long, which leads to a decrease in throughput.

Atmosphere gas Any atmosphere gas may be used as long as it is an inert gas (He gas, Ne gas, Ar gas, Xe gas, Kr gas), but Ar gas is preferable in terms of pre-sputtering efficiency and cost. The purity of the inert gas does not have to be specified in particular, but when oxygen and water are mixed in, it is preferable to use those which are removed as much as possible. Therefore, it is sufficient to use a dry gas having a purity of 99.99% or more of a commercially available product.

Sputtering output during pre-sputtering When a target having a disc shape of 4 inches in diameter (relative density of 90% or more) is used in an RF magnetron sputtering device and the substrate temperature is 20 ° C., sputtering during pre-sputtering The output is preferably in the range of 0.5 to ⁵ W / cm ² . If it exceeds 5 W / cm ² , the target may be cracked.
If it is less than cm ² , the sputtering efficiency is low and not practical. Also, when using a plate-shaped target (relative density of 90% or more) having a rectangular top surface and a bottom surface of 5 inches × 12 inches in a continuous running DC magnetron sputtering device and a substrate temperature of 20 ° C., pre-sputtering The sputtering output is preferably in the range of 1 to 5 W / cm ² . If it exceeds 5 W / cm ² , the target may be cracked, and if it is less than 1 W / cm ² , the sputtering efficiency is low and it is not practical.

Pre-sputtering time A target having a disc shape with a diameter of 4 inches (relative density 9
0% or more) and the sputtering output is 100W
Then, set the substrate temperature to 20 ℃ and
The pre-sputtering time in the case of performing pre-sputtering with a magnetron sputtering device is 3 to 60.
Minutes, preferably 5 to 30 minutes, more preferably 10 to 20
Minutes. If the pre-sputtering time is less than 3 minutes, the effect of cleaning the target surface by the pre-sputtering is small, and the degree of improvement in heat resistance of the finally obtained transparent conductive film is also small. On the other hand, if the pre-sputtering time is set to 60 minutes or more, the target surface cleaning effect is great, but this leads to a decrease in throughput and is not practical in production.

Further, a plate-like target (relative density 90%) having a rectangular shape of 5 inches × 12 inches on the upper surface and the lower surface is used.
When the sputtering power is set to 1 W and the substrate temperature is set to 20 ° C. and pre-sputtering is performed by the continuous running DC magnetron sputtering apparatus, the pre-sputtering time is 1 to 5 minutes, preferably 1. 5 to 2 minutes. The pre-sputtering time in this case also has an optimum value defined by both the pre-sputtering effect and the throughput for the same reason as above. The optimum pre-sputtering time varies variously depending on the sputtering method, the composition and relative density of the target, the sputtering conditions, the characteristics of the apparatus used, etc., so the present invention is not limited by the above-mentioned time.

By pre-sputtering the target as described above, the target surface can be cleaned, and by sputtering the target whose surface has been cleaned, the heat resistance in terms of conductivity is further improved. An improved transparent conductive film (made of an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements) can be formed on a transparent substrate. As the transparent substrate at this time, various substances or members can be used according to the purpose, but it is preferable to use, for example, a transparent glass or a transparent polymer having an electrically insulating property.

Specific examples of the transparent substrate made of transparent glass include transparent glass films or plates such as soda lime glass, lead glass, borosilicate glass, high silicate glass, and alkali-free glass. Can be mentioned. Among these, those containing no alkali component are preferable from the viewpoint that the diffusion of alkali ions into the transparent conductive film does not occur.

Specific examples of the transparent substrate made of a transparent polymer include polycarbonate resin, polyarylate resin, polyester resin, polyethylene terephthalate resin, polyether sulfone resin, amorphous polyolefin resin, polystyrene resin, acrylic resin and the like. Examples include films or sheets. Among these, those made of polycarbonate resin, polyarylate resin, polyethylene terephthalate resin, or polyether sulfone resin are preferable from the viewpoint of transparency and thermal stability.

The light transmittance of the transparent substrate is preferably 70% or more. When the light transmittance is less than 70%, it is not suitable as a transparent substrate. As the transparent base material, those having a light transmittance of 80% or more are more preferable, and those having a light transmittance of 90% or more are even more preferable. The thickness of the transparent substrate is appropriately selected according to the intended use of the conductive transparent substrate to be obtained, the material of the transparent substrate, etc., but it is preferably in the range of 15 μm to 3 mm, preferably 50 μm to 2 mm. The range is more preferable.

It is difficult to unconditionally define the sputtering conditions for forming the transparent conductive film on the transparent substrate, since it varies depending on the sputtering method, the characteristics of the apparatus used, and the like. For example, a DC magnetron is used. When the sputtering method is used, the following settings are preferable.

Vacuum degree during sputtering and target applied voltage The vacuum degree during sputtering is from 1 × 10 ^{−4 to} 5 × 10 ⁻² To.
rr (about 1.3 × 10 ^{-2 to} 6.7 × 10 ⁰ Pa),
More preferably 2 × 10 ⁻⁴ to 1 × 10 ⁻² Torr (2.7 ×
10 ^{−2 to} 1.3 × 10 ⁰ Pa), more preferably 3
^{× 10 -4 ~5 × 10 -3 Torr} (4.0 × 10 -2 ~6.7 ×
10 ^-1 Pa). The target applied voltage is preferably 100 to 500V. When the degree of vacuum during sputtering is higher than 1 × 10 ^-4 Torr (pressure lower than 1 × 10 ^-4 Torr), plasma stability is poor and 5 × 10 ^-2 Torr
If it is lower (the pressure is higher than 5 × 10 ^-2 Torr), the applied voltage to the target cannot be increased. If the target applied voltage is less than 100 V, it may be difficult to obtain a good quality thin film, or the film forming speed may be limited.

Atmosphere gas As the atmosphere gas, an inert gas such as argon gas or a mixed gas of an inert gas such as argon gas and oxygen gas is preferable. When a mixed gas of argon gas and oxygen gas is used, the volume ratio of the introduced oxygen gas to the argon gas is preferably 50% or less, more preferably 0.001 to 10%. If it is out of this range, a film having low electric resistance and high light transmittance may not be obtained.

Substrate temperature The substrate temperature (temperature of the base material) is appropriately selected within a temperature range in which the base material does not deform or deteriorate due to heat according to the heat resistance of the base material. If the substrate temperature is lower than room temperature, a separate cooling device is required, which increases the manufacturing cost. Also,
The manufacturing cost increases as the substrate temperature is heated to a high temperature. Room temperature to 20 when using a transparent resin substrate
It is preferably in the range of 0 ° C, and when it exceeds 200 ° C, the substrate may be deformed. When a transparent glass substrate is used, it is preferably in the range of room temperature to 400 ° C, and 400 ° C.
If it exceeds, the base material may be deformed or the effect of heating to a high temperature may not be obtained.

Sputtering power When a target having a disk shape of 4 inches in diameter (relative density of 90% or more) is used in an RF magnetron sputtering device and the substrate temperature is 20 ° C., the sputtering power is 0.5 to 5 W / It is preferably within the range of cm ² . If it exceeds 5 W / cm ² , the target may be cracked, and if it is less than 0.5 W / cm ² , the sputtering efficiency is small and not practical. In addition, continuous running DC
The magnetron sputtering system has 5 upper and lower surfaces.
When a plate-shaped target (relative density of 90% or more) having a rectangular shape of inches × 12 inches is used and the substrate temperature is 20 ° C., the sputtering output is preferably in the range of 1 to 5 W / cm ² . If it exceeds 5 W / cm ² , the target may be cracked, and 1 W / cm
If it is less than ² , the sputtering efficiency is low and not practical.

The target transparent conductive film can be formed on the transparent substrate by sputtering the target after the above-mentioned pre-sputtering under the above-mentioned conditions. However, as described above, the sputtering conditions vary variously depending on the sputtering method, the characteristics of the apparatus used, and the like, so the present invention is not limited by the above-described conditions.

Atomic ratio I of In and Zn in the transparent conductive film I
n / (In + Zn) is preferably in the range of 0.55 to 0.90, and more preferably 0.82 to 0.90, as already described in the description of the target.
When the transparent conductive film contains one or more kinds of cation elements other than In and Zn and having a valence of positive trivalence or more, the atomic ratio of the total amount of the third elements in all the cation elements. (All third elements) / (In + Zn +
The total third element) is preferably 0.2 or less as already described in the description of the target.

The thickness of the transparent conductive film varies depending on its use, but is preferably 3 to 3000 nm. 3n
If it is less than m, sufficient conductivity cannot be obtained, and if it exceeds 3000 nm, the light transmittance tends to be lowered. The preferred film thickness is 5
1000 nm, more preferably 10-800 nm
Is.

The conductive transparent substrate obtained by the method of the present invention is a conductive transparent substrate using a transparent conductive film made of an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements. It is a material that has further improved heat resistance in terms of conductivity. This conductive transparent substrate has practically sufficient conductivity and light transmittance and is more excellent in moisture resistance than the ITO film. The conductive transparent substrate having such characteristics is useful as a material for transparent electrodes for various purposes such as transparent electrodes for liquid crystal display elements, transparent electrodes for EL (electroluminescence) display elements, transparent electrodes for solar cells, etc. Is.

[0033]

EXAMPLES Examples of the present invention will be described below.

Example 1 A glass substrate (# 705) manufactured by Corning Incorporated was used as a transparent base material.
9; hereinafter abbreviated as CG # 7059), and using a hexagonal layered compound represented by In ₂ O ₃ (ZnO) ₄ as a target and a sintered body (In and In ₂ O ₃ ). Zn atomic ratio In / (In + Zn) = 0.
85, relative density 90%) was used to produce a conductive transparent substrate in the following manner. First, CG # 7059 and the target were attached to an RF magnetron sputtering device, and the pressure inside the vacuum chamber was reduced to 5 × 10 ⁻⁴ Pa or less. Next, Ar gas (purity 99.99%) was used at a vacuum chamber pressure of 1
It was introduced so as to have a pressure of × 10 ^-1 Pa, the sputtering output was set to 1.2 W / cm ² , the substrate temperature was set to 20 ° C, and pre-sputtering was performed for 5 minutes with the shutter closed. After this, Ar gas (purity 99.99
%) And O ₂ gas (purity 99.99%) mixed gas (A
(r gas: O ₂ gas = 1000: 2.8 (volume ratio)) was introduced so that the internal pressure of the vacuum chamber was 1 × 10 ⁻¹ Pa, the sputtering output was 1.2 W / cm ² , and the substrate temperature was 20
The transparent conductive film with a film thickness of 100 nm is C
A film was formed on one side of G # 7059.

In the conductive transparent glass substrate thus obtained, the atomic ratio of In to Zn in the transparent conductive film In
/ (In + Zn) was 0.85, which was the same as the target. Further, as a result of examining the crystallinity of the transparent conductive film by X-ray diffraction, it was found to be amorphous. The measurement result of this X-ray diffraction is shown in FIG. Further, the initial specific resistance (R ₀ ) of this transparent conductive film was measured by the four-terminal method (used model: Mitsubishi Oil Chemical Co., Ltd. Loresta FP), and at 90 ° C. in air.
A heat resistance test was performed under the conditions of, and the specific resistance (R ₁₀₀₀ ) after 1000 hours of test time was measured in the same manner. Then, the specific resistance ratio (R ₁₀₀₀ / R ₀ ) before and after the heat resistance test was defined as the rate of resistance change and used as an index showing the performance of the transparent conductive film. Table 1 shows the values of the initial specific resistance (R ₀ ), the specific resistance after the heat resistance test (R ₁₀₀₀ ), and the resistance change rate (R ₁₀₀₀ / R ₀ ). In addition, the visible light transmittance of the conductive transparent glass substrate after the heat resistance test was measured (used model: Shimadzu UV3100S). Among them, the transmittance of light having a wavelength of 550 nm is also shown in Table 1.

Examples 2 to 5 Pre-sputtering and sputtering were carried out under the same conditions as in Example 1 except that the time for pre-sputtering was changed to the time shown in Table 1 for each example. A transparent conductive film having a film thickness of 100 nm was formed. In each conductive transparent glass substrate thus obtained, the atomic ratio of In to Zn in the transparent conductive film In / (In + Z
n) was 0.85 in all cases. In addition, as a result of examining the crystallinity of each transparent conductive film by X-ray diffraction, it was found that all were amorphous.

Further, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and a heat resistance test under the same conditions as in Example 1 was performed to test for 1000 hours.
The specific resistance (R ₁₀₀₀ ) after the elapse of time was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 1.
Further, the visible light transmittance of each conductive transparent glass substrate after the heat resistance test was measured by the same method as in Example 1. Among them, the transmittance of light having a wavelength of 550 nm is also shown in Table 1.

Comparative Examples 1 to 2 In Comparative Example 1, no pre-sputtering was performed, in Comparative Example 2, the pre-sputtering time was set to 2 minutes, and the other conditions were the same as those in Example 1, and one side of CG # 7059 was used. A transparent conductive film having a film thickness of 100 nm was formed. Regarding each conductive transparent glass substrate thus obtained, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and the heat resistance under the same conditions as in Example 1 The test was conducted and the specific resistance (R ₁₀₀₀ ) after 1000 hours of test time was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 1. Further, the visible light transmittance of each conductive transparent glass substrate after the heat resistance test was measured by the same method as in Example 1. Among them, the transmittance of light having a wavelength of 550 nm is also shown in Table 1.

Example 6 PC was subjected to pre-sputtering and sputtering under the same conditions as in Example 1 except that a polycarbonate film (AM3000 manufactured by Teijin Chemicals Ltd., hereinafter abbreviated as PC film) was used as the transparent substrate. A transparent conductive film having a thickness of 100 nm was formed on one surface of the film. In the conductive transparent polymer substrate thus obtained, the atomic ratio In / Zn In / (In + Zn) of the transparent conductive film was 0.85. Further, as a result of examining the crystallinity of the transparent conductive film by X-ray diffraction, it was found to be amorphous.

Further, the initial specific resistance (R ₀ ) of the transparent conductive film
Was measured by the same method as in Example 1, and a heat resistance test was performed under the same conditions as in Example 1 to measure the specific resistance (R ₁₀₀₀ ) after a test time of 1000 hours by the same method as in Example 1. Then, the resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 1. Further, the visible light transmittance of the conductive transparent polymer substrate after the heat resistance test was measured by the same method as in Example 1. Among them, the transmittance of light having a wavelength of 550 nm is also shown in Table 1.

Examples 7 to 10 Presputtering and sputtering were carried out under the same conditions as in Example 6 except that the time of presputtering was changed to the time shown in Table 1 for each example to form a film on one side of the PC film. A transparent conductive film having a thickness of 100 nm was formed. In each conductive transparent polymer substrate thus obtained, the atomic ratio of In to Zn in the transparent conductive film In / (In + Z
n) was 0.85 in all cases. In addition, as a result of examining the crystallinity of each transparent conductive film by X-ray diffraction, it was found that all were amorphous.

Further, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and a heat resistance test under the same conditions as in Example 1 was performed to test for 1000 hours.
The specific resistance (R ₁₀₀₀ ) after the elapse of time was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 1.
Further, the visible light transmittance of each conductive transparent polymer substrate after the heat resistance test was measured by the same method as in Example 1. Among them, the transmittance of light having a wavelength of 550 nm is also shown in Table 1.

Comparative Examples 3 to 4 In Comparative Example 3, pre-sputtering was not performed, in Comparative Example 4, the pre-sputtering time was set to 2 minutes, and the other conditions were the same as in Example 6, and the film was formed on one side of the PC film. A transparent conductive film having a thickness of 100 nm was formed. With respect to each conductive transparent polymer substrate thus obtained, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and the heat resistance under the same conditions as in Example 1 was measured. The specific resistance (R ₁₀₀₀ ) after 1000 hours of the property test was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 1. Further, the visible light transmittance of each conductive transparent polymer substrate after the heat resistance test was measured by the same method as in Example 1. Among them, the transmittance of light having a wavelength of 550 nm is also shown in Table 1.

[0044]

[Table 1]

As is apparent from Table 1, in each of the conductive transparent glass substrates obtained in Examples 1 to 5, the transparent conductive film constituting the substrate has a resistance change rate of 1.03 to 1.13. In contrast, in each of the conductive transparent glass substrates obtained in Comparative Examples 1 and 2, the resistance change rate of the transparent conductive film constituting the conductive transparent glass substrate is as high as 1.28 to 1.31. From this,
It can be seen that the transparent conductive films formed in Examples 1 to 5 have higher heat resistance in terms of conductivity than the transparent conductive films formed in Comparative Examples 1 and 2. And
As can be seen from the comparison of the initial specific resistance and the light transmittance, the transparent conductive films formed in Examples 1 to 5 are transparent in terms of conductivity and light transmittance. It is better than the conductive film.

On the other hand, in each of the conductive transparent polymer substrates obtained in Examples 6 to 10, the rate of change in resistance of the transparent conductive film constituting the substrate is in the range of 1.37 to 1.78. On the other hand, in each conductive transparent polymer substrate obtained in Comparative Examples 3 to 4, the resistance change rate of the transparent conductive film constituting the conductive transparent polymer substrate is 2.3.
It is as high as 0 to 2.90. From this, each of the transparent conductive films formed in Examples 6 to 10 has higher heat resistance in terms of conductivity than the transparent conductive films formed in Comparative Examples 1 and 2. I understand. Then, as can be seen from the comparison of the initial specific resistance and the light transmittance, each transparent conductive film formed in Examples 6 to 10 was formed in Comparative Examples 3 to 4 in terms of conductivity and light transmittance. It is better than each transparent conductive film.

Example 11 As a target, a sintered body (In and In) containing a mixture of In ₂ O ₃ and a Ga (corresponding to the third element) containing a hexagonal layered compound represented by In ₂ O ₃ (ZnO) ₄ was used. Zn atomic ratio I
n / (In + Zn) = 0.84, Ga atomic ratio Ga /
(In + Zn + Ga) = 0.02, relative density 90%) was used, and other conditions were the same as in Example 1 to perform pre-sputtering and sputtering to form a transparent conductive film having a film thickness of 100 nm on one surface of CG # 7059. did. In the conductive transparent glass substrate thus obtained, the atomic ratio In / Zn of the transparent conductive film In / (In + Zn) was 0.87, and the atomic ratio Ga was Ga / (In + Zn + G).
a) was 0.02, which was the same as the target. Also, X
As a result of examining the crystallinity of the transparent conductive film by line diffraction, it was found to be amorphous.

Further, the initial specific resistance (R ₀ ) of the transparent conductive film
Was measured by the same method as in Example 1, and a heat resistance test was performed under the same conditions as in Example 1 to measure the specific resistance (R ₁₀₀₀ ) after a test time of 1000 hours by the same method as in Example 1. Then, the resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 2. Further, the visible light transmittance of the conductive transparent glass substrate after the heat resistance test was measured by the same method as in Example 1. Of these, the transmittance of light having a wavelength of 550 nm is also shown in Table 2.

Example 12 to Example 15 Presputtering and sputtering were performed under the same conditions as in Example 11 except that the time of presputtering was changed to the time shown in Table 2 for each example, and CG # 7059 was coated on one side. A transparent conductive film having a film thickness of 100 nm was formed.
In each conductive transparent glass substrate thus obtained,
In / Zn atomic ratio In / (In + in the transparent conductive film
Zn) is 0.87 in all cases, and the atomic ratio of Ga is Ga /
(In + Zn + Ga) was 0.02 in all cases. In addition, as a result of examining the crystallinity of each transparent conductive film by X-ray diffraction, it was found that all were amorphous.

Further, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and a heat resistance test under the same conditions as in Example 1 was performed to test for 1000 hours.
The specific resistance (R ₁₀₀₀ ) after the elapse of time was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 2.
Further, the visible light transmittance of each conductive transparent glass substrate after the heat resistance test was measured by the same method as in Example 1. Of these, the transmittance of light having a wavelength of 550 nm is also shown in Table 2.

Comparative Examples 5 to 6 In Comparative Example 5, pre-sputtering was not performed, in Comparative Example 6, the pre-sputtering time was set to 2 minutes, and the other conditions were the same as those in Example 11, and one side of CG # 7059 was used. A transparent conductive film having a film thickness of 100 nm was formed. Regarding each conductive transparent glass substrate thus obtained, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and the heat resistance under the same conditions as in Example 1 The test was conducted and the specific resistance (R ₁₀₀₀ ) after 1000 hours of test time was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1.
These values are shown in Table 2. Further, the visible light transmittance of each conductive transparent glass substrate after the heat resistance test was measured by the same method as in Example 1. Of these, the transmittance of light having a wavelength of 550 nm is also shown in Table 2.

Example 16 PC was subjected to pre-sputtering and sputtering under the same conditions as in Example 11 except that a polycarbonate film (AM3000 manufactured by Teijin Chemicals Ltd .; hereinafter abbreviated as PC film) was used as the transparent substrate. A transparent conductive film having a thickness of 100 nm was formed on one surface of the film. In the conductive transparent polymer base material thus obtained, the atomic ratio In / (In + Zn) of In and Zn in the transparent conductive film was 0.87, and the atomic ratio Ga was Ga / (In + Zn + G).
a) was 0.02. Further, as a result of examining the crystallinity of the transparent conductive film by X-ray diffraction, it was found to be amorphous. Further, the initial specific resistance (R ₀ ) of the transparent conductive film was measured by the same method as in Example 1, and a heat resistance test was conducted under the same conditions as in Example 1 to obtain a specific resistance (R ₁₀₀₀ ) after a test time of 1000 hours. Was measured by the same method as in Example 1. And
The resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 2. Further, the visible light transmittance of the conductive transparent polymer substrate after the heat resistance test was measured by the same method as in Example 1. Of these, the transmittance of light having a wavelength of 550 nm is also shown in Table 2.

Examples 17 to 20 Presputtering and sputtering were carried out under the same conditions as in Example 16 except that the time for presputtering was changed to the time shown in Table 2 for each example to form a film on one surface of the PC film. A transparent conductive film having a thickness of 100 nm was formed. In each conductive transparent polymer substrate thus obtained, the atomic ratio of In to Zn in the transparent conductive film In / (In + Z
n) is 0.87 in each case, and the atomic ratio of Ga is Ga /
(In + Zn + Ga) was 0.02 in all cases. In addition, as a result of examining the crystallinity of each transparent conductive film by X-ray diffraction, it was found that all were amorphous.

Furthermore, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and a heat resistance test was conducted under the same conditions as in Example 1 to test for 1000 hours.
The specific resistance (R ₁₀₀₀ ) after the elapse of time was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 2.
Further, the visible light transmittance of each conductive transparent polymer substrate after the heat resistance test was measured by the same method as in Example 1. Of these, the transmittance of light having a wavelength of 550 nm is also shown in Table 2.

Comparative Examples 7 to 8 In Comparative Example 7, no pre-sputtering was performed, in Comparative Example 8, the pre-sputtering time was set to 2 minutes, and the other conditions were the same as those in Example 16, and the film was formed on one side of the PC film. A transparent conductive film having a thickness of 100 nm was formed. With respect to each conductive transparent polymer substrate thus obtained, the initial specific resistance (R ₀ ) of each transparent conductive film was measured by the same method as in Example 1, and the heat resistance under the same conditions as in Example 1 was measured. The specific resistance (R ₁₀₀₀ ) after 1000 hours of the property test was measured by the same method as in Example 1. Then, each resistance change rate (resistivity ratio) was obtained by the same method as in Example 1. These values are shown in Table 2. Further, the visible light transmittance of each conductive transparent polymer substrate after the heat resistance test was measured by the same method as in Example 1. Of these, the transmittance of light having a wavelength of 550 nm is also shown in Table 2.

[0056]

[Table 2]

As is clear from Table 2, in each of the conductive transparent glass substrates obtained in Examples 11 to 15, the transparent conductive film constituting them has a resistance change rate of 1.08 to 1.19. In contrast, in each of the conductive transparent glass substrates obtained in Comparative Examples 5 to 6, the resistance change rate of the transparent conductive film constituting the conductive transparent glass substrate is as high as 1.34 to 1.36. From this, each of the transparent conductive films formed in Examples 11 to 15 has higher heat resistance in terms of conductivity than the transparent conductive films formed in Comparative Examples 5 to 6. I understand. Then, as can be seen from the comparison of the initial specific resistance and the light transmittance, the respective transparent conductive films formed in Examples 11 to 15 were formed in Comparative Examples 5 to 6 in terms of conductivity and light transmittance. It is better than each transparent conductive film.

On the other hand, in each of the conductive transparent polymer substrates obtained in Examples 16 to 20, the rate of change in resistance of the transparent conductive film constituting the substrate is in the range of 1.63 to 1.85. On the other hand, in each of the conductive transparent polymer base materials obtained in Comparative Examples 7 to 8, the resistance change ratio of the transparent conductive film constituting the conductive transparent polymer base material is 2.
It is as high as 93-3.35. From this, each of the transparent conductive films formed in Examples 16 to 20 has higher heat resistance in terms of conductivity than the transparent conductive films formed in Comparative Examples 7 to 8. I understand. Then, as can be seen from the comparison of the initial specific resistance and the light transmittance, Examples 16 to
Each of the transparent conductive films formed in Example 20 is also improved in terms of conductivity and light transmittance as compared with each of the transparent conductive films formed in Comparative Examples 7 to 8.

Example 21 A long biaxially stretched polyethylene terephthalate film (size: 300 mm × 10 m, thickness 0.1 mm; hereinafter referred to as PET roll) was used as a transparent substrate, and In ₂ O ₃ (sputtering target was used. ZnO) ₄ hexagonal layered compound and indium oxide (In ₂ O
₃ ) Sintered body (In / Zn atomic ratio In / (I
n + Zn) = 0.85, relative density 90%) was used to manufacture a transparent conductive film in the following manner. First, the PET roll and the target were mounted on a continuous running DC magnetron sputtering device, and the inside of the vacuum chamber was depressurized to 5 × 10 ⁻³ Pa or less. Next, Ar gas (purity 99.99%) was introduced so that the pressure in the vacuum chamber was 1 × 10 ⁻¹ Pa, the sputtering output was 2.6 W / cm ² , and the substrate temperature was 2
Each was set to 0 ° C., and pre-sputtering was performed for 1.0 minute with the shutter closed. After this, Ar
Gas (purity 99.99%) and O ₂ gas (purity 99.99%)
%) Mixed gas (Ar gas: O ₂ gas = 1000:
2.8 (volume ratio) was introduced so that the pressure in the vacuum chamber was 1 × 10 ⁻¹ Pa, and the sputtering output was 2.6 W / c.
m ² and the substrate temperature set to 20 ° C., 5 min / min
Sputtering was performed while the PET roll was wound on another roll at a running speed of 0 cm and the shutter was opened to form a transparent conductive film on one surface of the PE roll.

Regarding the conductive transparent polymer substrate thus obtained, a point 0.1 m from the end on the film formation start side,
0.2m point, 0.5m point, 1.0m point,
When the thickness of the transparent conductive film was measured at a point of 2.0 m and a point of 5.0 m, 160 nm ± 16 nm
It was constant within the range. In addition, I in the transparent conductive film
The atomic ratio In / (In + Zn) of n and Zn was 0.85, which was the same as that of the target at each of the above-mentioned points. As a result of investigating the crystallinity of the transparent conductive film by X-ray diffraction, it was found to be amorphous at each of the above-mentioned points. Further, the electric resistance of the transparent conductive film at each of the above-mentioned points was measured by the four-terminal method (used model: Loresta FP manufactured by Mitsubishi Petrochemical Co., Ltd.), and variations in electric resistance value were evaluated by standard deviation. The results are shown in Table 3.

Example 22 to Example 23 Presputtering and sputtering were performed under the same conditions as in Example 21 except that the time of presputtering was changed to the time shown in Table 3 for each example, and each side of the PET roll was subjected. A transparent conductive film was formed. For each conductive transparent polymer substrate thus obtained, the film thickness of the transparent conductive film was measured at the same points as the measurement points in Example 21 (total 6 points), and the range was 160 nm ± 16 nm. It was constant within. In addition, the atomic ratio In / (In + Zn) of In and Zn in each transparent conductive film was 0.85, which was the same as that of the target at each of the above-mentioned points. As a result of examining the crystallinity of each transparent conductive film by X-ray diffraction, it was found to be amorphous at each of the above-mentioned points.

Furthermore, the electric resistance of the transparent conductive film at each of the above-mentioned points was measured by the same method as in Example 21, and the variation in the electric resistance value was evaluated by the standard deviation. The results are shown in Table 3.

Comparative Examples 9 to 10 In Comparative Example 9, pre-sputtering was not performed, and Comparative Example 10
Then, the pre-sputtering time was set to 0.5 minutes, and the other conditions were the same as in Example 21, and a transparent conductive film was formed on one surface of the PET roll. For each conductive transparent polymer substrate thus obtained, the electrical resistance of the transparent conductive film was measured at the same points as the measurement points (total 6 points) in Example 21 by the same method as in Example 21, The variation of the electric resistance value was evaluated by the standard deviation. These results are shown in Table 3.
Shown in.

[0064]

[Table 3]

As is clear from Table 3, in each of the conductive transparent polymer base materials obtained in Examples 21 to 23, the standard deviation of the electric resistance values of the transparent conductive films measured at six points was 0.
11 to 1.26, while Comparative Example 9 to
In each conductive transparent polymer substrate obtained in Comparative Example 10, the standard deviation of the electric resistance value of the transparent conductive film measured at six points is as high as 2.10 to 2.28. From this fact, Example 21
-Each conductive transparent polymer substrate obtained in Example 23 has a smaller variation in electric resistance value in the longitudinal direction than each conductive transparent polymer substrate obtained in Comparative Examples 9 to 10. . Further, as can be seen from the comparison of the electric resistance values at each point, the conductivity of each transparent conductive film formed in Examples 21 to 23 is higher than that of each transparent conductive film formed in Comparative Examples 9 to 10. Has improved.

Example 24 As a target, a sintered body (In and In) containing a mixture of In ₂ O ₃ containing a hexagonal layered compound represented by In ₂ O ₃ (ZnO) ₄ and Ga (corresponding to the third element) was used. Zn atomic ratio I
n / (In + Zn) = 0.87, Ga atomic ratio Ga /
(In + Zn + Ga) = 0.02, relative density 90%) was used, and other conditions were the same as in Example 21, pre-sputtering and sputtering were performed to form a transparent conductive film on one surface of the PET roll. Regarding the conductive transparent polymer substrate thus obtained, a point 0.1 m, a point 0.2 m, and a point 0.5 m from the end on the film formation start side,
When the film thickness of the transparent conductive film was measured at a point of 1.0 m, a point of 2.0 m, and a point of 5.0 m, respectively, 16
It was constant within the range of 0 nm ± 16 nm. In addition, the atomic ratio of In to Zn in the transparent conductive film In / (In + Z
n) is 0.87, which is the same as the target at each of the above-mentioned points, and the atomic ratio of Ga is Ga / (In + Zn).
+ Ga) was 0.02, which was the same as the target at any of the above points. As a result of investigating the crystallinity of the transparent conductive film by X-ray diffraction, it was found to be amorphous at each of the above-mentioned points. Further, the electric resistance of the transparent conductive film at each of the above-mentioned points was measured by the four-terminal method (used model: Loresta FP manufactured by Mitsubishi Petrochemical Co., Ltd.), and the variation of the electric resistance value was evaluated by the standard deviation. The results are shown in Table 4.

Example 25 to Example 26 Presputtering and sputtering were carried out under the same conditions as in Example 24 except that the time of presputtering was changed to the time shown in Table 4 for each example, and one side of each PET roll was subjected. A transparent conductive film was formed. For each conductive transparent polymer substrate thus obtained, the film thickness of the transparent conductive film was measured at the same points as the measurement points (total 6 points) in Example 24, and found to be in the range of 160 nm ± 16 nm. It was constant within. Further, the atomic ratio In / (In + Zn) of In and Zn in each transparent conductive film is 0.87, which is the same as the target at each of the above-mentioned points,
The Ga atomic ratio Ga / (In + Zn + Ga) was 0.02, which was the same as that of the target at each of the above-mentioned points. As a result of examining the crystallinity of each transparent conductive film by X-ray diffraction, it was found to be amorphous at each of the above-mentioned points. Furthermore, the electric resistance of the transparent conductive film at each of the above-mentioned points was measured by the same method as in Example 24, and the variation in the electric resistance value was evaluated by the standard deviation. The results are shown in Table 4.

Comparative Examples 11 to 12 In Comparative Example 11, pre-sputtering was not performed, and Comparative Example 1
In No. 2, the pre-sputtering time was 0.5 minutes, and the other conditions were the same as in Example 24, and a transparent conductive film was formed on one surface of the PET roll. For each conductive transparent polymer substrate thus obtained, the electrical resistance of the transparent conductive film was measured at the same points as the measurement points (total 6 points) in Example 24 by the same method as in Example 24, The variation of the electric resistance value was evaluated by the standard deviation. The results are shown in Table 4.

[0069]

[Table 4]

As is clear from Table 4, in each of the conductive transparent polymer base materials obtained in Examples 24 to 26, the standard deviation of the electric resistance values of the transparent conductive films measured at six points was 0.
11 to 1.06, while Comparative Example 11
-In each conductive transparent polymer base material obtained in Comparative Example 12, the standard deviation of the electric resistance value of the transparent conductive film measured at six points is as high as 2.03 to 2.40. From this fact, Example 24
-Each conductive transparent polymer substrate obtained in Example 26 has smaller variation in electric resistance value in the longitudinal direction than each conductive transparent polymer substrate obtained in Comparative Examples 11 to 12. . Further, as can be seen from the comparison of the electric resistance values at each point, the conductivity of each transparent conductive film formed in Examples 24 to 26 is higher than that of each transparent conductive film formed in Comparative Examples 11 to 12. Has improved.

[0071]

As described above, the conductive transparent base material obtained by the method of the present invention is a transparent conductive material composed of an amorphous oxide containing indium (In) and zinc (Zn) as main cation elements. It is a conductive transparent substrate using a film, and has further improved heat resistance in terms of conductivity. The conductive transparent substrate has practically sufficient conductivity and light transmittance. Therefore, according to the present invention, it is possible to provide a transparent conductive material whose conductivity does not deteriorate with time even in a high temperature environment.

[Brief description of drawings]

FIG. 1 is a graph showing the measurement results of X-ray diffraction on the transparent conductive film formed in Example 1.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C23C 14/34 N 8939-4K G02F 1/1343

Claims (9)

[Claims] 1. A sputtering method using a sintered body target made of a composition containing indium oxide and zinc oxide, wherein indium (I
n) and a transparent conductive film made of an amorphous oxide containing zinc (Zn) are formed on a transparent substrate, prior to the formation of the transparent conductive film, the target is plasma-treated in an inert gas atmosphere. A method for producing a conductive transparent substrate, which comprises treating. 2. The method according to claim 1, wherein the target is an oxide sintered body containing an In—Zn-based hexagonal layered compound. 3. The target contains one or more kinds of third elements having a valence of positive trivalence or more as cation elements other than In and Zn, and the atomic ratio of the total amount of the third elements in all the cation elements. (All third elements) / (In + Zn
The method according to claim 1 or 2, wherein + all third elements are 0.2 or less. 4. The relative density of the target is 70% or more, and the atomic ratio In / (In + Zn) of In and Zn in this target is in the range of 0.55 to 0.90. The method according to claim 3. 5. The target has a relative density of 70% or more, and the atomic ratio In / (In + Zn) of In and Zn in the target is in the range of 0.82 to 0.90. The method according to claim 3. 6. The method according to claim 1, wherein the atomic ratio In / (In + Zn) of In and Zn in the transparent conductive film is in the range of 0.55 to 0.90. . 7. The transparent conductive film contains one or more kinds of a third element having a valence of positive trivalence or more as a cation element other than In and Zn, and a total amount of the third element in all the cation elements is contained. Atomic ratio (all third elements) / (In + Zn
The method according to any one of claims 1 to 6, wherein + total third element) is 0.2 or less. 8. The method according to claim 1, wherein the transparent substrate is made of transparent glass. 9. The method according to claim 1, wherein the transparent substrate is made of a transparent polymer.