JP2012089437A - Method for forming transparent conductive film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a transparent conductive film on a glass substrate by deposition at or near atmospheric pressure, the transparent conductive film being excellent in conductivity and transparency and mainly composed of titanium oxide.SOLUTION: A method for forming a transparent conductive film, which comprises titanium oxide doped with niobium, on a glass substrate, comprises: a step of forming a film comprising titanium oxide doped with niobium on a glass substrate by spraying an organic niobium compound and an organic titanium compound as gas or minute droplets on the glass substrate at a temperature of 450°C or more at or near atmospheric pressure; and a step of cooling the formed film in an atmosphere, where an oxidizing gas concentration is 10 vol% or less and a reducing gas concentration is 4 vol% or less, until the temperature of the glass substrate decreases to 350°C or less. In the method, the steps are performed in this order.

Description

The present invention relates to a method for forming a transparent conductive film. More specifically, the present invention relates to a method for forming a transparent conductive film made of niobium-doped titanium oxide on a glass substrate.
The transparent conductive film formed by the method of the present invention is excellent in conductivity and transparency, and is used for a member using a transparent conductive film such as a solar cell substrate, a touch panel substrate, and a flat panel display substrate.

Conventionally, a tin oxide (ITO) film doped with indium has been used as the transparent conductive film. However, due to the growing demand for flat panel display substrates and the like, there is a concern about the depletion of indium, which is a rare metal.
On the other hand, titanium oxide doped with niobium (TNO: niobium doped titania) has conductivity close to that of an ITO film and does not use a rare metal. (Patent Document 1).

  In the method described in Patent Document 1, a TNO film is formed using a coating method. For example, Non-Patent Document 1 and Patent Document 2 describe how to form a good conductive niobium-doped titania (TNO) film. As disclosed, it is common to use a vacuum process such as laser ablation or sputtering.

  From the viewpoint of film formation cost, it is desired to form a TNO film by CVD without plasma under atmospheric pressure or a pressure in the vicinity thereof. However, there is a problem that a film formed under atmospheric pressure or a pressure in the vicinity thereof has a high sheet resistance, and a good conductive film cannot be obtained.

Patent Document 3 discloses a method for forming a transparent conductive film having titanium oxide as a main component and excellent in transparency and conductivity. The transparent conductive film mainly composed of titanium oxide in the method described in Patent Document 3 is a thin film mainly composed of titanium oxide having a dopant, and as the dopant, a low-resistance transparent conductive film can be formed. (Nb) is preferred.
In Patent Document 3, in order to form a transparent conductive film mainly composed of titanium oxide on a transparent resin substrate, it is preferable to use an atmospheric pressure plasma CVD method in which plasma is used for reaction of raw materials in a low temperature environment. It is said that.
In the method described in Patent Document 3, a transparent conductive film mainly composed of titanium oxide is formed on a substrate, and then heat treatment is performed as a post-treatment in a plasma gas atmosphere containing hydrogen gas or water vapor. A transparent conductive film excellent in light transmission performance and resistance performance is formed.

Taro Issugi, “Frontier of Titanium Dioxide Transparent Conductive Material” Applied Physics November (2008) 1319.

JP 2009-1335096 A International Publication No. WO2009-119273 International Publication WO2008-044474

As described above, since the method described in Patent Document 3 forms a transparent conductive film on a transparent resin substrate, it is considered preferable to use an atmospheric pressure plasma CVD method capable of forming a film in a low temperature environment. .
However, when a device element is formed on a transparent conductive film, a process of forming a semiconductor element by heating the substrate temperature to about 200 to 300 ° C. may be used, and high heat resistance is required for the substrate. In some cases, it is required to use a glass substrate as a base material for forming the transparent conductive film.
The inventors of the present application have found that when the method described in Patent Document 3 is applied to form a TNO film on a glass substrate, there are the following problems.

As described in Patent Document 1, when a TNO film is used as a transparent conductive film, the crystalline phase of the TNO film is an anatase phase, and oxygen defects are present in the crystalline phase from the viewpoint of conductivity. preferable.
In the method described in Patent Document 3, it is preferable to use an atmospheric pressure plasma CVD method capable of forming a film in a low temperature environment in order to form a transparent conductive film mainly composed of titanium oxide on a transparent resin substrate. However, in order to form a TNO film whose crystal phase is an anatase phase, since the raw material molecules are decomposed in plasma, the gas phase reaction of the raw material molecules is inevitable. Not too high. On the other hand, the thermal CVD method in which the source molecules are decomposed by heating the substrate on which the transparent conductive film is formed and spraying the source molecules as gas or fine droplets on the heated substrate. This is preferable because the gas phase reaction is small and the crystallinity of the film is high.

However, when a TNO film is formed on a glass substrate using a thermal CVD method, the glass substrate is heated to a high temperature of 450 ° C. or higher in order to form the TNO film at an industrially feasible film formation rate. It is considered necessary.
In the method described in Patent Document 3, a transparent conductive film mainly composed of titanium oxide is formed on a transparent resin substrate. Therefore, the temperature of the base material in post-processing is preferably 220 ° C. or lower. It is said that. When a TNO film is formed on a glass substrate using a thermal CVD method, the glass substrate is heated to a high temperature of 450 ° C. or higher when the thermal CVD method is performed. It is considered preferable.

However, when a TNO film is formed on a glass substrate using a thermal CVD method and then heat-treated in an atmosphere containing hydrogen gas or water vapor as in the method described in Patent Document 3, the TNO film after the heat treatment is It discovered that it was inferior in electroconductivity and transparency. Specifically, it has been found that when heat treatment is performed in an atmosphere containing a gas having a reducing action such as hydrogen gas, the TNO film after heat treatment is inferior in transparency. On the other hand, when the heat treatment was performed in an atmosphere containing a gas having an oxidizing action such as water vapor, the TNO film after the heat treatment was found to be inferior in conductivity.
In the method described in Patent Document 3, since the temperature of the base material in the post-processing is as low as 220 ° C. or lower, water vapor is used as the reducing gas. However, when a TNO film is formed on a glass substrate using a thermal CVD method, as described above, the temperature of the glass substrate in the post-processing is 350 ° C. or higher, so that water vapor becomes a gas having an oxidizing action.

  In order to solve the above-described problems of the prior art, the present invention provides a transparent conductive film made of TNO and having excellent conductivity and transparency on a glass substrate by film formation under atmospheric pressure or a pressure in the vicinity thereof. An object is to provide a method of forming.

  In order to achieve the above-described object, the present invention sprays an organic niobium compound and an organic titanium compound as a gas or as fine droplets onto a glass substrate having a temperature of 450 ° C. or higher at atmospheric pressure or in the vicinity thereof. And forming the film made of titanium oxide doped with niobium on the glass substrate, and the glass substrate in an atmosphere having an oxidizing gas concentration of 10 vol% or less and a reducing gas concentration of 4 vol% or less. The method of forming a transparent conductive film made of niobium-doped titanium oxide on a glass substrate (hereinafter referred to as “transparent of the present invention”). A conductive film forming method ”).

  In the method for forming a transparent conductive film of the present invention, it is preferable to spray an alcohol having a boiling point of 160 ° C. or lower onto a glass substrate having a temperature of 450 ° C. or higher together with the organic niobium compound and the organic titanium compound.

  In the method for forming a transparent conductive film of the present invention, the organic niobium compound and the organic titanium compound are glass substrates having a temperature of 450 ° C. or higher so that the molar ratio of niobium atoms to titanium atoms is 0.005 to 0.4. It is preferable to be sprayed on. A more preferable range of the molar ratio is 0.05 to 0.3.

  In the transparent conductive film forming method of the present invention, the organic niobium compound is preferably niobium pentaethoxide.

  In the transparent conductive film forming method of the present invention, the organic titanium compound is preferably titanium tetraisoporopoxide.

  In the method for forming a transparent conductive film of the present invention, the oxygen concentration and the water vapor concentration in the atmosphere in which the step of forming a film made of niobium-doped titanium oxide on the glass substrate is substantially 0 vol%. preferable.

  Moreover, this invention provides the glass substrate with a transparent conductive film obtained by the transparent conductive film formation method of this invention.

According to the method of the present invention, a transparent conductive film composed of TNO having excellent conductivity and transparency can be formed on a glass substrate.
In the method of the present invention, the transparent conductive film is formed by film formation under atmospheric pressure or a pressure in the vicinity thereof. Therefore, the method is simpler than film formation by a vacuum process or film formation using plasma, and The cost for film formation can be greatly reduced.
The glass substrate with a transparent conductive film obtained by the method of the present invention is preferably used as a member using a transparent conductive film such as a solar cell substrate, a touch panel substrate, and a flat panel display substrate.

FIG. 1 is a schematic diagram of a film forming apparatus used in Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 2 is a schematic diagram of a film forming apparatus used in Examples 4 to 8.

Hereinafter, the transparent conductive film forming method of the present invention will be described.
In the method for forming a transparent conductive film of the present invention, an organic niobium compound and an organic titanium compound are sprayed on a glass substrate having a temperature of 450 ° C. or higher as a gas or as a fine droplet at atmospheric pressure or a pressure in the vicinity thereof. , A step of forming a TNO film on a glass substrate (TNO film forming step), and an atmosphere having an oxidizing gas concentration of 10 vol% or less and a reducing gas concentration of 4 vol% or less, the temperature of the glass substrate is 350 ° C. or less. A transparent conductive film made of TNO is formed on the glass substrate by performing the cooling process (cooling process) in this order in this order.
The atmospheric pressure or the pressure in the vicinity thereof in the present invention is about 20 kPa to 110 kPa, preferably about 93 to 104 kPa.

When the organic niobium compound and the organic titanium compound, which are raw materials of the TNO film, are sprayed on the glass substrate as gases, the gas obtained by vaporizing these organic metal compound raw materials (organic niobium compound, organic titanium compound) is heated to a temperature of 450 ° C. or higher. What is necessary is just to spray on the surface which forms the transparent conductive film of the heated glass substrate.
There is no particular limitation on the method for vaporizing these organometallic compound raw materials, but the organometallic compound is vaporized by blowing a nitrogen gas or a rare gas such as argon into the container containing the organometallic compound raw material as a carrier gas. There are a so-called bubbling method and a method of directly vaporizing the organometallic compound by sending the organometallic compound to a heated vaporizing chamber.
In any of the above methods, the organic niobium compound and the organic titanium compound used as the raw material of the TNO film may be vaporized in advance, or may be mixed with gas obtained by vaporizing the respective organic metal compounds.
Further, in the above-described method for directly vaporizing the organometallic compound, an organometallic compound raw material dissolved in an organic solvent such as ethanol, acetone, isopropyl alcohol, or the like may be used.

  When the organic niobium compound and the organic titanium compound, which are the raw materials of the TNO film, are sprayed on the glass substrate as fine droplets, these organic metal compound raw materials (organic niobium compound, organic titanium compound) are minutely dispersed using a spray nozzle or the like What is necessary is just to spray on the surface which forms the transparent conductive film of the glass substrate heated to the temperature of 450 degreeC or more as a droplet.

  When the organometallic compound raw material is sprayed on the glass substrate as a gas or as fine droplets, these gases or the fine droplets are diluted with nitrogen gas or a rare gas such as argon on the glass substrate. You may spray.

The organic niobium compound and the organic titanium compound which are the raw materials for the TNO film are not particularly limited, but niobium pentaethoxide is preferable as the organic niobium compound, and titanium tetraisoporopoxide is preferable as the organic titanium compound.
In the transparent conductive film forming method of the present invention, an organometallic compound material is used as a material for the TNO film. Therefore, unlike the case of using an inorganic metal compound raw material such as a metal halide such as titanium tetrachloride or niobium pentachloride, a TNO film can be formed without using an oxidizing agent. It is easy to control the gas conditions in the atmosphere during execution and during the cooling process.

  The organic niobium compound and the organic titanium compound that are the raw materials of the TNO film are preferably sprayed onto the glass substrate so that the molar ratio of niobium atoms to titanium atoms is 0.005 to 0.4. When the molar ratio of niobium atoms to titanium atoms is less than 0.005, the conductivity of the formed TNO film may be inferior. On the other hand, when the molar ratio of niobium atoms to titanium atoms exceeds 0.4, the transparency of the formed TNO film may deteriorate. A more preferable range of the molar ratio is 0.05 to 0.3.

In addition to the organic metal compound raw material, alcohols having a boiling point of 160 ° C. or less (carbon number of 6 or less) such as ethanol, methanol, isopropyl alcohol, etc. were heated to a temperature of 450 ° C. or more as gas or as fine droplets. When sprayed on a glass substrate, it is preferable because it tends to suppress powder generation due to vapor phase decomposition of the organometallic compound raw material.
When these alcohols are sprayed on the glass substrate together with the organometallic compound raw material, the amount of the alcohol is preferably 1.0 or more and more preferably 5.0 or more in a molar ratio with respect to the organometallic compound raw material. preferable. This is because as the molar ratio with respect to the organometallic compound raw material is increased, the generation of powder due to vapor phase decomposition of the organometallic compound raw material is suppressed.
The alcohol used for the above purpose is preferably ethanol from the viewpoint of safety.

When these alcohols are sprayed on a glass substrate as a gas, in the method for directly vaporizing the organometallic compound described above, an organometallic compound raw material dissolved in an alcohol may be used. Alternatively, vaporized alcohol may be mixed before introduction into the film formation chamber or in the film formation chamber.
When these alcohols are sprayed on the glass substrate as fine droplets, an organic metal compound raw material dissolved in the alcohol may be sprayed onto the glass substrate using a spray nozzle or the like.

  The higher the oxygen concentration and the water vapor concentration in the atmosphere in which the TNO film forming step is performed, the greater the degree of powder generation due to the vapor phase decomposition of the organometallic compound raw material, so the oxygen concentration and water vapor concentration in the atmosphere are preferably low. Specifically, the oxygen concentration and the water vapor concentration in the atmosphere are each preferably 10 vol% or less, more preferably 4 vol% or less, and still more preferably 0 vol%.

In the transparent conductive film formation method of this invention, it is calculated | required that the temperature of the glass substrate at the time of spraying an organometallic compound is 450 degreeC or more. This is because if the temperature of the glass substrate is lower than 450 ° C., the decomposition rate of the organometallic compound that is the raw material of the TNO film is slow, and a sufficient film formation rate cannot be obtained. The film formation rate of the TNO film is preferably 5 nm / min or more, because it is an industrially feasible film formation rate, more preferably 10 nm / min or more, and more preferably 25 nm / min or more. More preferably it is.
For the above reasons, the temperature of the glass substrate when spraying the organometallic compound is preferably 500 ° C. or higher, and more preferably 530 ° C. or higher.
On the other hand, there is no particular upper limit on the temperature of the glass substrate when spraying the organometallic compound, but if the temperature of the glass substrate is too high, vapor phase decomposition of the organometallic compound raw material may occur and the deposition rate of the TNO film may be reduced. Therefore, the temperature of the glass substrate when the organometallic compound is sprayed is preferably 700 ° C. or lower.
The conductivity of the TNO film is expressed by oxygen vacancies generated in the crystal phase. As the number of oxygen defects present in the crystal phase increases, the conductivity of the TNO film tends to increase. Oxygen defects are formed in the TNO film by the above formation method.

  In the transparent conductive film forming method of the present invention, after performing the TNO film forming step, the temperature of the glass substrate becomes 350 ° C. or lower in an atmosphere having an oxidizing gas concentration of 10 vol% or less and a reducing gas concentration of 4 vol% or less. Allow to cool. By performing this procedure, oxygen defects formed at the time of film formation are maintained even at the time of taking out, and good conductivity can be obtained.

When carrying out the cooling step, the oxidizing gas concentration in the atmosphere is required to be 10 vol% or less. The oxidizing gas mentioned here includes a wide range of gases having an oxidizing action, and corresponds to oxygen, water vapor, carbon dioxide, nitric acid, hydrogen peroxide, ozone, dinitrogen monoxide, and the like.
If the oxidizing gas concentration in the atmosphere exceeds 10 vol% during the cooling step, oxygen defects in the TNO film formed during film formation are oxidized by the permeation action of the oxidizing gas into the film. The increase in specific resistance of the TNO film is remarkable, and a good conductive film cannot be obtained.
The specific resistance of the TNO film after the cooling process is preferably 100 Ωcm or less. This is because if the specific resistance of the TNO film exceeds 100 Ωcm, it is necessary to increase the film thickness of the TNO film in order to obtain a TNO film having sufficient conductivity, thereby increasing the film formation cost. There is no particular lower limit value of the specific resistance of the TNO film, more preferably 10 Ωcm or less, still more preferably 1 Ωcm or less.
For the above reasons, the oxidizing gas concentration in the atmosphere during the cooling step is preferably 5 vol% or less.

When carrying out the cooling step, the reducing gas concentration in the atmosphere is required to be 4 vol% or less. The reducing gas referred to here includes a wide variety of gases having a reducing action, and corresponds to hydrogen, carbon monoxide, or organic gases such as methane and ethane.
Further, in the TNO film forming step, when an alcohol having a boiling point of 160 ° C. or less (carbon number of 6 or less) is sprayed on the glass substrate together with the organic metal compound raw material, the gas obtained by vaporizing these alcohols also becomes a reducing gas. Since the concentration of the gas in which these alcohols are vaporized is extremely low in the atmosphere, there is no problem.

  The reason why the reducing gas concentration in the atmosphere is required to be 4 vol% or less during the cooling step is as follows.

As described above, the conductivity of the TNO film is improved by carrying out the cooling process because oxygen deficiency generated in the crystal phase is prevented from being reduced by oxidation. As the number of oxygen defects present in the crystal phase increases, the conductivity of the TNO film tends to increase.
According to the prior art, in order to generate more oxygen defects in the crystal phase, it is considered preferable to perform the cooling step in a reducing atmosphere.
In the method described in Patent Document 1, the TNO film undergoes a crystal transition from the amorphous phase to the anatase phase by performing an annealing process by heating in a reducing atmosphere, and oxygen vacancies are generated in the crystal phase. Even in the method described in Patent Document 3, an appropriate amount of oxygen deficiency is generated in the transparent conductive film by performing heat treatment in a reducing gas atmosphere in a plasma state as post-processing.

However, the inventors of the present application, when the reducing gas concentration in the atmosphere is high at the time of performing the cooling step, specifically, if the reducing gas concentration in the atmosphere is more than 4 vol%, It has been found that in the TNO film, the absorption of light in the visible wavelength range increases, and the transparency of the TNO film decreases.
When the reducing gas concentration in the atmosphere is 4 vol% or less at the time of the cooling process, the TNO film after the cooling process does not increase the light absorption in the visible wavelength range, and the TNO film is transparent. Excellent in properties.
For the above reasons, the reducing gas concentration in the atmosphere during the cooling step is preferably 4 vol% or less, and preferably 1 vol% or less.

  Since the atmosphere in which the cooling step is performed is an oxidizing gas concentration of 10 vol% or less and a reducing gas concentration of 4 vol% or less, the main gas in the atmosphere is nitrogen gas or a rare gas such as helium, neon, argon, etc. It is an inert gas. The atmosphere in which the cooling step is performed preferably has an inert gas concentration of 90 vol% or more, more preferably 95 vol% or more, and further preferably 100 vol%.

  In the transparent conductive film forming method of the present invention, an inert gas with a high concentration may be used in order to set the oxidizing gas concentration and the reducing gas concentration in the atmosphere in which the cooling step is performed to a predetermined condition. It is preferable from the viewpoint of cost that nitrogen gas or a rare gas such as helium, neon, or argon is mixed to set the oxidizing gas concentration and reducing gas concentration in the atmosphere to predetermined conditions. It is particularly preferable to set the oxidizing gas concentration and reducing gas concentration in the atmosphere to predetermined conditions by mixing gases.

  In the method for forming a transparent conductive film of the present invention, the oxidizing gas concentration and the reducing gas concentration in the atmosphere must be maintained at the predetermined conditions described above until the temperature of the glass substrate becomes 350 ° C. or lower. Thereafter, the oxidizing gas concentration and the reducing gas concentration in the atmosphere may not satisfy the above-described predetermined conditions. However, maintaining the oxidizing gas concentration and the reducing gas concentration in the atmosphere at the above-described predetermined conditions until the temperature of the glass substrate becomes 300 ° C. or lower improves the conductivity and transparency of the TNO film. Therefore, it is more preferable to maintain the oxidizing gas concentration and the reducing gas concentration in the atmosphere under the predetermined conditions described above until the temperature of the glass substrate becomes 250 ° C. or lower.

  In the transparent conductive film forming method of the present invention, the glass substrate on which the TNO film is formed is not particularly limited. Therefore, the transparent conductive film forming method of the present invention can be applied to various glass substrates having different materials and manufacturing methods. However, when the transparent conductive film forming method of the present invention is applied to a glass substrate obtained by float forming, the TNO film forming step and the cooling step are performed in this order on the high-temperature glass substrate after float forming. Thus, energy required for forming the transparent conductive film made of the TNO film on the glass substrate can be reduced, and the yield can be improved.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these Examples.

Example 1
In this example, a transparent conductive film made of TNO was formed on a glass substrate by the procedure described below.
In this example, the film forming apparatus shown in FIG. 1 was used. Regarding the raw material of the TNO film, titanium tetraisooxide (TTIP) was used as the organic titanium compound, and niobium pentaethoxide (PEN) was used as the organic niobium compound.
Titanium tetraisopoxide and niobium pentaethoxide are each dissolved in a predetermined amount of ethanol (EtOH), this solution 4 is vaporized using a vaporizer 3, and the vaporized gas is diluted with a diluted nitrogen gas 5 into a nozzle in the CVD chamber 1. 6 was fed. A glass substrate 2 heated to 500 ° C. by an electric heater 7 is installed immediately below the nozzle 6, and a gas supplied from the nozzle 6 is sprayed on the glass substrate 2 for 5 minutes to form a TNO film on the glass substrate 2. Filmed. The conditions during film formation are shown in Table 1 below.
After the film formation, the electric heater 7 was turned off, the glass substrate 2 was cooled in a nitrogen stream, and when the temperature of the glass substrate 2 reached 300 ° C., the glass substrate 2 was taken out from the CVD chamber 1. In order to confirm the oxidizing gas concentration in the atmosphere at the time of carrying out the cooling step, the oxygen concentration in the exhaust gas 9 discharged from the exhaust pipe 8 was measured with an oxygen concentration meter, and the oxygen concentration was 5%. Further, in order to measure the reducing gas concentration in the atmosphere at the time of the cooling process, the hydrogen concentration in the exhaust gas 9 discharged from the exhaust pipe 8 was measured with a hydrogen concentration meter. The hydrogen concentration was less than 1 ppm. .
When a part of the TNO film formed on the glass substrate 2 was peeled off and the film thickness was measured with a stylus type step gauge (DEKTAK), it was 80 nm. Further, when the sheet resistance of the TNO film was measured and the specific resistance was calculated, it was 7 Ωcm, and it was found that a good conductive film was formed. In addition, almost no powder was observed in the exhaust pipe trap (not shown) through the TNO film forming process and the cooling process.

Examples 2 and 3
Example except that the molar ratio of niobium atoms to the titanium atoms in the gas supplied onto the glass substrate 2 (Nb / Ti molar ratio) and the oxygen concentration in the atmosphere during the cooling step were set as shown in Table 1 below. The same procedure as 1 was performed.
As a result, in Example 2 where the Nb / Ti molar ratio in the gas supplied onto the glass substrate 2 is 0.15 and the oxygen concentration in the atmosphere during the cooling process is 7%, the specific resistance of the TNO film is 10 Ωcm. In Example 3 where the Nb / Ti molar ratio in the gas supplied onto the glass substrate 2 is 0.02 and the oxygen concentration in the atmosphere during the cooling step is 7%, the specific resistance of the TNO film is 50 Ωcm It can be seen that both exhibit good conductivity.
When the transparency of the formed film is visually compared, it can be seen that the transparency increases in the order of Examples 1, 2, and 3. When the Nb / Ti molar ratio in the gas supplied onto the glass substrate 2 is increased, the TNO film It was confirmed that the transparency was lowered. However, the TNO films of Examples 1 to 3 have sufficient transparency as a transparent conductive film.

Comparative Examples 1-4
The same procedure as in Example 1 was performed except that the Nb / Ti molar ratio in the gas supplied onto the glass substrate 2 was set to the conditions shown in Table 3 below, and the oxygen concentration in the atmosphere at the time of the cooling step was changed to 15%. Carried out. As a result, in any case, the specific resistance of the TNO film was increased by three orders of magnitude or more compared to the examples, and it was confirmed that a good conductive film could not be obtained.

Examples 4-8
In this example, the film forming apparatus shown in FIG. 2 was used. As in Example 1, titanium tetraisopoxide and niobium pentaethoxide, which are TNO film raw materials, are dissolved in ethanol in a predetermined amount, and this solution 11 is sprayed with a dilute nitrogen gas 12 using a two-fluid nozzle 13 to obtain a fine liquid. Created a drop. The fine droplets were sprayed on the glass substrate 16 heated by the electric heater 15 through the CVD nozzle 14 to form a TNO film on the glass substrate 2. The conditions at the time of film formation are shown in Table 2 below.
After film formation, the electric heater 15 is turned off, the glass substrate 16 is cooled in a nitrogen stream, and the temperature of the glass substrate 16 is 250 ° C. (Examples 4, 6, 7, 8) or 300 ° C. (Example 5). At that time, the glass substrate 16 was taken out. In order to confirm the oxidizing gas concentration in the atmosphere at the time of the cooling process, the oxygen concentration in the exhaust gas 17 was measured with an oxygen concentration meter, and the oxygen concentration was 1% in all cases. Further, in order to measure the reducing gas concentration in the atmosphere during the cooling process, the hydrogen concentration in the exhaust gas 17 was measured with a hydrogen concentration meter, and the hydrogen concentration was less than 1 ppm.
Similar to Example 1, the thickness of the TNO film and the sheet resistance were measured. It can be seen that any of Examples 4 to 8 has a low specific resistance of the TNO film and exhibits good conductivity. In particular, in Example 8 where the Nb / Ti ratio of the raw material was increased to 0.29, the specific resistance of the obtained film was 0.07 Ωcm, indicating that an excellent conductive film was obtained.

Reference examples 1 and 2
In order to confirm the influence of the reducing atmosphere on the transparency of the TNO film, in Reference Examples 1 and 2, the TNO film formed by the Cat-CVD (catalytic CVD) method and the thermal CVD method was used in the visible light wavelength range (550 nm). The light absorption of was compared.
The Cat-CVD method is a method in which a metal wire heated to about 1000 ° C. is installed between a raw material blowing nozzle and a substrate as a catalyst, and the TNO film raw material is activated using the catalyst. When an organic metal compound such as TTIP is used as a raw material for the TNO film, an organic component in the raw material is decomposed in advance and easily reacts with oxygen, so that a strongly reducing atmosphere is created.
In Reference Example 1, the pressure at the time of film formation is 50 Pa, the substrate temperature is 500 ° C., and the metal wire (tungsten wire) is heated to 1100 ° C., and Nb is doped by 2.8% using the Cat-CVD method. The TNO film having a thickness of 210 nm was formed on a glass substrate. The light absorption at a wavelength of 550 nm of the formed TNO film was calculated by {100% − (transmittance + reflectance)} by measuring the transmittance and reflectance at a wavelength of 550 nm using a spectrophotometer UV3100 manufactured by Shimadzu Corporation. The light absorption was 7.2%.
On the other hand, in Reference Example 2, the film forming pressure was 100 Pa, the substrate temperature was 500 ° C., and the film was doped with 2.6% Nb using the thermal CVD method without heating the metal wire. A 200 nm TNO film was deposited on a glass substrate. When light absorption at a wavelength of 550 nm was measured in the same manner as in Reference Example 1, the light absorption was 4.4%. From this result, it is confirmed that when the TNO film is placed in a strongly reducing atmosphere, the light absorption in the visible light wavelength region (550 nm) increases and the transparency of the TNO film decreases. Although this result relates to the TNO film formed by the vacuum film formation process, in the transparent conductive film forming method of the present invention, the TNO film formed by the TNO film forming step has a reducing gas concentration exceeding 4 vol%. Similarly, when the glass substrate temperature is cooled to 350 ° C. or lower in a strongly reducing atmosphere, the light absorption in the visible wavelength region (550 nm) increases and the transparency of the TNO film decreases. It is predicted.

1: CVD chamber 2, 16: Glass substrate 3: Vaporizer 4, 11: Raw material solution 5, 12: Diluted nitrogen gas 6: Nozzle 7: Electric heater 8: Exhaust pipe 9, 17: Exhaust gas 13: Two-fluid nozzle 14 : CVD nozzle

Claims (7)

  It consists of titanium oxide doped with niobium by spraying an organic niobium compound and an organic titanium compound as a gas or as fine droplets onto a glass substrate at a temperature of 450 ° C. or higher at atmospheric pressure or a pressure in the vicinity thereof. A step of forming a film on the glass substrate, and a step of cooling until the temperature of the glass substrate becomes 350 ° C. or lower in an atmosphere having an oxidizing gas concentration of 10 vol% or less and a reducing gas concentration of 4 vol% or less. A method of forming a transparent conductive film made of niobium-doped titanium oxide on a glass substrate.   The method according to claim 1, wherein an alcohol having a boiling point of 160 ° C. or lower is sprayed on a glass substrate having a temperature of 450 ° C. or higher together with the organic niobium compound and the organic titanium compound.   The organic niobium compound and the organic titanium compound are sprayed onto the glass substrate at a temperature of 450 ° C or higher so that a molar ratio of niobium atoms to titanium atoms is 0.005 to 0.4. Item 3. The method according to Item 1 or 2.   The method according to claim 1, wherein the organic niobium compound is niobium pentaethoxide.   The method according to claim 1, wherein the organic titanium compound is titanium tetraisoporopoxide.   6. The oxygen concentration and water vapor concentration in an atmosphere for carrying out the step of forming a film made of titanium oxide doped with niobium on a glass substrate is substantially 0 vol%. The method of crab.   A glass substrate with a transparent conductive film obtained by the method according to claim 1.