JPH07257941A - Metal oxide film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a metal oxide film having a controlled film thickness and excellent in optical property by gelating and film forming a metallic alkoxide stuck to the surface of a substrate by dipping into a solution and shrinking the metal oxide film by heating. CONSTITUTION:The substrate is dipped into the metal alkoxide solution and after pulled up, the metal alkoxide on the substrate surface is geleted by hydrolysis. Next, the metal oxide is film formed by removing a solvent and after that, by shrinking the metal oxide film by heating to control the film thickness, the desired metal oxide film is obtained. In this way, the thickness of the metal oxide film is finely adjusted by keeping the concentration of the metal alkoxide coating solution constant through a full period for pulling up the substrate, regulating the pulling-up rate of the substrate and further shrinking the film by heating after drying the coating film of the coating solution. As a result, the film having desired optical property is precisely and efficiently formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide film suitable for a light shielding material, a reflecting mirror, a light wavelength selective transmitting material and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in building glass, reflecting mirrors, lenses, and various optical filters, a thin film made of a metal oxide such as titanium oxide or silicon oxide is formed on a glass substrate to obtain a desired film. Optical properties have been imparted and mechanical strength and thermal strength have been enhanced. The method for forming this metal oxide thin film includes a method of depositing a metal oxide on a glass substrate by vapor deposition such as a vacuum vapor deposition method, a chemical vapor deposition method, and a high frequency sputtering method, or a glass substrate immersed in a metal alkoxide solution. Then, the dip coating method of pulling up the substrate is widely used.

The vapor deposition method is described in, for example, JP-A-51-117.
As described in JP-A-981 and JP-A-54-58717, a glass substrate is placed in a vacuum chamber, and a raw material gas is placed in the chamber while the glass substrate is heated and held at a predetermined temperature. Introducing and exciting the raw material gas by plasma or electron beam, or heating the crucible filled with the vapor deposition material to generate metal vapor, and deposit the metal oxide fine particles generated by this on the substrate. A metal oxide film is formed. Also,
The dip coating method is described in, for example, JP-A-60-7.
As described in JP-A-1547 and JP-A-63-162549, a thin coating film of the metal alkoxide solution is formed on the surface of the glass substrate by immersing the glass substrate in the metal alkoxide solution and pulling it up at a predetermined speed. The metal alkoxide in the coating film is hydrolyzed to gel, and the solvent is removed to form a metal oxide film on the glass substrate.

[0004]

However, in the above vapor deposition method, the substrate must be placed under a vacuum state for film formation, and a large-scale vacuum chamber is required for vapor deposition on a large area substrate. Therefore, the size of the substrate that can be processed is naturally limited because a vacuum device is required. Further, since the film thickness to be formed changes depending on the distance from the vapor deposition source, it is difficult to vapor deposit a uniform thickness over a wide range. Therefore, there is a problem that it cannot be applied to a member having a relatively large area such as a glass for buildings or a light shielding film of a solar cell. Further, there are many restrictions on the adjustment of the degree of vacuum in the vacuum chamber, the control of the introduction amount (gas pressure) of the source gas, and the vapor deposition conditions such as the temperature of the substrate and the vapor deposition source. In particular, in order to form a multi-layered film with different kinds of metal oxides, the vacuum is redrawn to clean the inside of the chamber after each layer is formed,
It is necessary to reset the vapor deposition conditions, which is not preferable because it leads to a decrease in productivity.

On the other hand, according to the dip coating method, although a large area substrate can be processed,
In reality, it is difficult to control the film thickness when it becomes a thin film of about 50 to 100 nm, and even if the atmosphere at the time of pulling up or a slight change in the concentration of the coating solution changes the film thickness significantly, However, the situation is not good enough. Therefore, particularly in applications such as a light-reflecting film and an optical filter that selectively transmit or block incident light, it is difficult to obtain desired optical characteristics, and there is a problem in product quality and yield.

The present invention has been made in view of the above problems, provides a metal oxide film having a controlled film thickness and excellent optical characteristics, and is uniform even on a large-area substrate. An object of the present invention is to provide a method for producing a metal oxide film, which can form a metal oxide film having a film thickness and can accurately and easily control the film thickness.

[0007]

The researchers of the present invention have conducted earnest studies to achieve the above object, and as a result, the metal oxide film formed by the dip coating method has a metal alkoxide The inventors have completed the present invention by finding that it is controlled by heat treatment after pulling up the substrate from the solution, concentration control of the metal alkoxide solution at the time of pulling up, and pulling rate. That is, the above object is a metal oxide film formed by a dip coating method using a metal alkoxide as a raw material, and the film thickness of the metal oxide film is controlled by a heat treatment after film formation. This is achieved with an oxide film. A similar object is a metal oxide film formed by a dip coating method using a metal alkoxide as a raw material, wherein the film thickness of the metal oxide film is controlled by the concentration of the metal alkoxide solution. It is also achieved by a physical film. The metal oxide film may be a multi-layer film in which thin films made of a high refractive index substance and a low refractive index substance are alternately laminated. In addition, the same purpose is to immerse the substrate in a metal alkoxide solution and pull it up, gel the metal alkoxide on the surface of the substrate by hydrolysis, further remove the solvent to form a metal oxide film, It is also achieved by a method for producing a metal oxide film, which is characterized in that the film thickness is controlled by heat-shrinking the film. Similarly, a method of forming a metal oxide film by dipping the substrate in a metal alkoxide solution and pulling it up, gelling the metal alkoxide on the substrate surface by hydrolysis, and further removing the solvent,
It is also achieved by a method for producing a metal oxide film, characterized in that the film thickness of the metal oxide film is controlled by the concentration of the metal alkoxide solution.

The metal oxide film according to the present invention is formed by immersing a substrate such as glass, metal or ceramics in a coating solution containing a metal alkoxide and pulling it up at a predetermined speed to form a coating film of the coating solution on the substrate ( (Dip coating), the coating film is hydrolyzed to gel the metal alkoxide, and then heat treatment is performed to form a film on the substrate. As the metal alkoxide,
It can be appropriately selected depending on the film configuration and the desired optical characteristics, and for example, metal alkoxides such as titanium, silicon, tantalum, zirconium, etc. can be used.

These metal alkoxides are diluted with hydrocarbons such as normal hexane, cyclohexane, benzene, xylene, toluene and acetone, or alcohols such as methanol, ethanol, butanol, propanol, isopropanol and acetyl alcohol. Here, the ratio of the metal alkoxide and the solvent is
Solvent 0.5-200 for 1 mol of metal alkoxide
mol is preferred. Then, in order to carry out hydrolysis, **-** mol of distilled water and a small amount of acid are added to 1 mol of the metal alkoxide to obtain a coating solution. Incidentally, in the metal alkoxide, with respect to an alkoxide of a metal such as titanium that is easily oxidized, it is not necessary to add distilled water and an acid in particular, because the oxidation is performed by air and the hydrolysis proceeds at the same time when the metal is pulled up.
It is also possible to simply dilute the metal alkoxide with a solvent to form a coating solution. Further, in order to stabilize the sol concentration of the coating solution, an appropriate amount of a reaction modifier such as acetic acid, formic acid, nitric acid, hydrochloric acid, ammonia or amine may be added.

By immersing the substrate in this coating solution and pulling it up, a solution of metal alkoxide is coated on the surface of the substrate. Although not shown, the pulling device includes a container filled with the coating solution and a hoist mechanism for pulling up the substrate at a predetermined speed, and the substrate is pulled up from the coating solution in a substantially vertical direction. In the present invention, since the raw material alkoxide concentration in the coating solution is controlled, the pulling rate must be constant in order to obtain the desired film thickness. However, the film thickness can be controlled by the pulling speed as in the conventional technique. In this case, it is necessary to keep the liquid concentration constant, which is not different from the gist of the present invention of controlling the raw material alkoxide concentration in the coating solution of the present invention. When forming an oxide film, if the concentration of the coating solution is kept constant, the film thickness changes with changes in the pulling rate, so the variation in the rate must be kept within 20%, preferably within 10%. The pulling rate is 0.005 to 100 mm / sec, preferably 0.01 to 80 mm / sec in order to keep the optical properties of the film uniform. Here, if it is too fast, the film may become cloudy, and if it is too slow, the film may become uneven.

The atmosphere temperature during pulling is suitably in the range of 15 to 60 ° C. When the temperature is higher than this, the film becomes cloudy and when it is too low, the film becomes non-uniform. The humidity is preferably 90% or less, more preferably 40% or less. The lower the humidity, the easier the film thickness control described later. It should be noted that various kinds of metal alkoxide are prepared to prepare various kinds of coating solutions, and the steps of alternately dipping the substrate in these coating solutions and pulling up the same are repeatedly carried out to obtain a metal oxide having a multi-layered structure according to the number of repetitions. A film is obtained.

By the way, the metal alkoxide concentration of the coating solution changes with time during the pulling up period due to the evaporation of the solvent, and a concentration gradient occurs in the coating film on the substrate. As a result, the film thickness of the produced metal oxide film is not uniform, and especially on a long substrate or a large-area substrate,
The optical characteristics differ depending on the location on the substrate, which is not preferable. Therefore, the present invention is characterized in that the concentration gradient of the metal alkoxide in the coating solution is monitored during the entire period of pulling up the substrate to prevent the concentration gradient from occurring. As the monitoring method, the concentration of metal alkoxide is instantaneously measured using an analyzer such as an ICP emission spectrometer, and a solvent is added based on the measurement result to constantly maintain a constant concentration range. . As a result, a coating film having a uniform concentration can be formed on the entire surface of the substrate.

The sol particles in the coating film may become huge and the film may become cloudy. To avoid this, the surface of the coating film is observed with an electron microscope to make the sol particles larger. It is necessary to maintain the optical characteristics by observing the degree and exchanging the coating solution when the sol particles are 15 nm or more. In order to suppress the progress of sol particle growth, it is possible to use the coating solution for a long time by using amines such as diethanolamine and triethanolamine as reaction control agents. The addition amount of the amines is preferably 0.01 to 5 mol with respect to 1 mol of the metal alkoxide. As described above, the metal alkoxide concentration and the particle size of the sol particles are controlled to form a coating film of the coating solution on the substrate, which is then dried to remove the solvent contained in the coating film. A metal oxide film is obtained by heat treatment in an active gas atmosphere.

Drying is performed at a temperature of 0 to 300 ° C. for 3 minutes to 8 minutes.
It takes about an hour. If the drying time is too long, moisture in the atmosphere after drying may cause hygroscopic swelling. If the drying time is too short, the film may be insufficiently dried and the film thickness may fluctuate or the film may become non-uniform.

The present invention is characterized in that the metal oxide film is made stronger by heating after drying, and the film thickness of the metal oxide film is controlled. When a transparent dielectric film having a high refractive index and a transparent dielectric film having a low refractive index are alternately laminated on a smooth substrate, the relationship between the film thickness, the refractive index of the dielectric and the target wavelength is as follows (1). It is known that when it satisfies the formula, it becomes a dielectric reflection film that reflects vertically incident light of a target wavelength (Kiuchi, Masazo; “Optical Research on Thin Films”, Iwanami Scientific Literature, 1954, p77). nd = (2m−1) λ / 4 (1) Here, n is the refractive index, d is the film thickness of the dielectric film, λ is the wavelength of the vertically incident light, and m is an integer. The product (nd) of the index and the actual film thickness of the dielectric film is called the optical film thickness, and a reflection peak having this wavelength appears in the spectral curve (wavelength vs. transmittance).

The present invention is characterized in that the metal oxide film is heated and shrunk to change the film thickness to obtain desired optical characteristics. Then, the control of the film thickness at that time is performed by obtaining a spectral curve of the metal oxide film after heating and measuring the wavelength of the reflection peak thereof. For example,
When the metal oxide film heat-treated at a certain temperature has a reflection peak on the longer wavelength side than the target wavelength, the film is shrunk so as to have the target reflection peak by heat treatment again. The temperature of this heat treatment is 300 ° C to 1300 ° C,
The temperature is preferably 400 ° C. to 1200 ° C. If it is too low, the carbide remains and becomes brown and the light transmittance is lowered. On the contrary, if it is too high, the composition reacts with the substrate and the composition of the film changes. In either case, the optical characteristics are deteriorated, which is not preferable. Further, the heating time is preferably 10 minutes to 24 hours. When the heating time is short, the film thickness does not shrink, the film thickness cannot be controlled, and carbides remain to reduce the light transmittance. On the other hand, even if heating is performed for 24 hours or more, the change rate of the film thickness with respect to the heating time is small, and the effect of controlling the film thickness due to heat shrinkage cannot be seen. Furthermore, in the case of a metal oxide film having a multi-layer structure, this heat treatment may be performed every time each layer is formed, or may be performed after stacking the multi-layers. Alternatively, it may be performed every plural layers.

As described above, the present invention is characterized in that the film thickness of the metal oxide film is controlled by controlling the concentration of the coating solution, the pulling rate of the substrate and the heat treatment after the film formation. By combining these comprehensively, more precise film thickness control becomes possible.

[0018]

【Example】

Example 1 Two 2 cm × 4 cm quartz glass plates are put together, held by a clip so that one side is coated, and the ends are bonded so that the liquid does not enter inside. This glass substrate was prepared by first preparing a titania coating solution 1 (30 g of titanium isopropoxide: 50 g of normal hexane) prepared in advance.
Immerse in. Then, it is pulled up at a pulling rate of 59 mm / min, dried for 30 minutes, placed in an electric furnace maintained at 500 ° C., held for 10 minutes, and then taken out of the furnace and discharged.
This is designated as Sample 1-1. Next, the sample 1-1 was dipped in a silica coating solution (tetraethyl silicate 20 g: distilled water 12 g: ethanol 37.5 g) prepared in advance, pulled up at a speed of 0.98 mm / sec, and kept at 500 ° C. It is put in the electric furnace and held for 10 minutes. After holding, take out from the furnace and cool. The obtained sample is referred to as sample 1-2. This sample 1-2 is a titania thin film on quartz glass,
Further, it has a two-layer structure thin film having a silica thin film formed thereon.

Further, a titania coat is applied to the sample 1-2 under the conditions of obtaining the sample 1-1 to obtain a sample 1-3. This sample 1-3 has a (titania-silica-titania) three-layer structure. Further, a silica coat is applied to the sample 1-3 under the same conditions as the sample 1-2 to obtain a sample 1-4. The samples 1-4 are (titania-silica-titania-silica).
It has a four-layer structure. Subsequently, the sample 1-1 is added to the sample 1-1.
A titania coat is applied under the conditions obtained above to obtain Sample 1-5.
This sample 1-5 has a (titania-silica-titania-silica-titania) five-layer structure. Further, a sample obtained by repeating the operations of the samples 1-1 and 1-2 once more is referred to as a sample 1-7. This sample 1-7 is (titania-
(Silica-titania-silica-titania-silica-titania) 7-layer structure. Sample 1 obtained in this way
The reflectances of 1, 1-3 and 1-7 were as shown in Table 1.

[0020]

[Table 1]

The results of measuring the spectroscopic curves of Samples 1-1, 1-3, 1-5 and 1-7 with a spectrophotometer manufactured by Hitachi Ltd. are shown in FIGS. 1 (a) to 1 (d). As shown in the figure, a reflection peak starts to appear in Sample 1-3, and Sample 1-
In 5 and 1-7, a large reflection peak was confirmed around 540 nm. The multi-layer film thus obtained is He
It is suitable as a reflective film having a wavelength of 543 nm of the -Ne laser. In this way, a multilayer film that selectively reflects a desired wavelength can be obtained by performing the heat treatment each time each layer is formed and controlling the film thickness to form it.

Example 2 Instead of the titanium coating solution 1 of Example 1, a titanium coating solution 2 composed of (titanium isopropoxide 27 g: normal hexane 50 g) and a silica coating solution 1 (tetraethyl silicate 25 g: distilled water) were used. A silica coating solution 2 consisting of 12 g: ethanol 37.5 g) was used, and the same pulling method and heat treatment as in Example 1 were performed to form a multilayer film. Reflectance of titania single layer (Sample 2-1), (titania-silica-titania) 3-layer film (Sample 2-3) and (titania-silica-titania-silica-titania) 5-layer film (Sample 2-5) Was as shown in Table 2.

[0023]

[Table 2]

The spectral curves of Samples 2-1, 2-3, 3-5 and 2-7 are shown in FIGS. 2 (a)-(d). As in Example 1, a reflection peak began to appear in Sample 2-3,
In Samples 1-5 and 1-7, a large reflection peak was confirmed near 600 nm. As a result, it was found that the film thickness changes depending on the difference in the concentration of each coating solution.

Example 3 A sample prepared under the same conditions as in Example 2 was further heat-treated in an electric furnace at 800 ° C. for 1 hour and allowed to cool outside the furnace. Due to the shrinkage of the thin film due to this heat treatment, the reflection peak could be changed up to 540 nm as shown in Table 3 and FIG.

[0026]

[Table 3]

Example 4 When forming a titanium oxide thin film on a quartz glass substrate,
The concentration of the coating solution was changed as shown in Table 4 to form a film, and the change in optical film thickness was examined. In the table, TPT is the amount of tetraisopropoxy titanate in the coating solution and nHx is the amount of normal hexane.

[0028]

[Table 4]

The target optical film thickness is set to a quarter wavelength of 600 nm.
The substrate is immersed in each solution, pulled up at a constant rate of 1.33 mm / sec, and heat-treated at 500 ° C. for 10 minutes,
After cooling, the reflection peak was obtained from the spectral curve. No reflection peak was observed up to Sample 4-5, a reflection peak began to appear at 440 nm in Sample 4-6, and a reflection peak appeared at 600 nm which is the target reflection peak in Sample 4-7. From this, it is understood that the optical film thickness can be adjusted depending on the concentration of the coating solution.

[0030]

As described above, according to the present invention,
By keeping the concentration of the metal alkoxide coating solution constant over the entire period of pulling up the substrate, adjusting the substrate pulling rate, and further shrinking the film by heat treatment after drying the coating film of the coating solution. The film thickness of the film can be finely adjusted, and the film having the desired optical characteristics can be formed accurately and efficiently. Further, by using the dip coating method, it is possible to cope with a large-area substrate without increasing the size of the device, and it is possible to easily produce a large-area light-shielding plate particularly suitable for glass for buildings, solar cells, and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a spectral curve of a metal oxide film prepared in Example 1.

FIG. 2 is a diagram showing a spectral curve of a metal oxide film prepared in Example 2.

FIG. 3 is a diagram showing a spectral curve after heat treatment of Sample 2-7 prepared in Example 2.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Shinko 8-10-16 Shimorenjaku, Mitaka City, Tokyo Nittetsu Mining Co., Ltd. −202

Claims (5)

[Claims] 1. A metal oxide film formed by a dip coating method using a metal alkoxide as a raw material, wherein the film thickness of the metal oxide film is controlled by heat treatment after film formation. Physical film. 2. A metal oxide film formed by a dip coating method using a metal alkoxide as a raw material, wherein the film thickness of the metal oxide film is controlled by the concentration of the metal alkoxide solution. Physical film. 3. The metal oxide film according to claim 1, wherein the metal oxide film is a multilayer film in which thin films made of a high refractive index substance and a low refractive index substance are alternately laminated. . 4. The substrate is immersed in a metal alkoxide solution and pulled up, the metal alkoxide on the surface of the substrate is hydrolyzed to gel, and the solvent is removed to form a metal oxide film. A method for producing a metal oxide film, comprising controlling the film thickness by heating and shrinking the film. 5. A method for forming a metal oxide film by immersing a substrate in a metal alkoxide solution and pulling it up to hydrolyze the metal alkoxide on the surface of the substrate and further removing the solvent to form a metal oxide film. A method for producing a metal oxide film, wherein the film thickness of the oxide film is controlled by the concentration of the metal alkoxide solution.