JPH0523637A - Thin film forming method by sol-gel processing - Google Patents

Abstract

PURPOSE:To form a thin film by exposing at reduced pressure a hydrolysate solution formed by adding water, alcohol and acid to a metallic alkoxide for concentrating the solution to stick on a substrate to form a thin film. CONSTITUTION:As a metallic alkoxide, alkoxide of silicon, boron, titanium, germanium or aluminum is used. By this method, viscosity is increased without using a thickener, etc., so a thick film can be obtained.

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film by the sol-gel method.

[0001]

2. Description of the Related Art The sol-gel method uses metal alkoxides in water,
This is a method of obtaining a glass body by allowing a hydrolysis / polycondensation reaction to proceed in a solution to which alcohol or the like is added (hereinafter referred to as a hydrolysis solution) to solidify as a porous body and heating this. Since this sol-gel method goes through a solution state, uniform coating can be relatively easily performed over a wide substrate using a solution, and a film having new functions such as mechanical, chemical protection, and optical properties can be formed. It is useful as a coating method.

As a general method of the sol-gel method, for example, “Journal of Ceramic Industry”, 90 , (6), p. 328-332
(1982), ethyl silicate, titanium isopropoxide and ethanol, and water-HCl as a catalyst are added and stirred to prepare a hydrolysis solution (coating solution). The substrate to be coated is dipped in this solution and pulled up at a constant rate to form a film on the surface of the substrate, and a glass film is produced through drying and heating steps.

[0003]

Conventionally, a transparent and uniform coating film having a film thickness of 0.1 to 0.3 .mu.m has been obtained by this type of sol-gel method, but if the film thickness is further increased, it is attempted. Defects such as crack generation, white clouding, and peeling from the substrate occur. Even in the method of adding glycerin or ethyl ether as a thickener to increase the film thickness, the limit is at most 0.5 μm. The present invention has been made with the object of proposing a novel manufacturing method capable of forming a film thicker than before by the sol-gel method.

[0004]

As a result of various studies on the method for obtaining a thicker and more uniform coating film than the conventional one, the present inventors have concentrated the solution by depressurizing the hydrolysis solution to remove volatile components. Then, they found that coating the substrate was very effective, and arrived at the present invention. That is, the present invention is a method of depositing a hydrolysis solution obtained by adding water, alcohol, and acid to a metal alkoxide to form a thin film on a substrate, after concentrating the hydrolysis solution by keeping it under reduced pressure. It is characterized in that it is attached to the substrate. In a particularly preferred embodiment of the present invention, the metal alkoxide is silicon,
It may be an alkoxide of boron, titanium, germanium or aluminum.

[0005]

The present inventors considered the reason why the film cannot be thickened by the conventional method as follows. That is, as a method for attaching a film to a substrate, there are a spin coating method in which a hydrolysis solution is dropped on a rotating substrate and a dipping method in which the substrate is immersed in the hydrolysis solution and pulled up at a constant speed. Also, the thicker the hydrolysis solution, the thicker the film can be coated. For that purpose, a method of adding a thickener such as an organic polymer to the hydrolysis solution has been used, but in this method, the organic polymer decomposes and evaporates from the inside of the film when heated after coating, so Shrinkage increases and the film is likely to crack. Another method of increasing the viscosity is to reduce the amount of alcohol added to the metal alkoxide, but this method has its limitations. When the amount of alcohol is reduced, the metal alkoxide and water are separated and the hydrolysis reaction does not proceed. On the other hand, according to the present invention, without reducing the amount of alkoxide added to the metal alkoxide,
By holding the solution under reduced pressure after hydrolysis, components such as alcohol that are likely to volatilize are removed, the hydrolysis solution can be concentrated, and as a result, the viscosity can be increased. Also, since the amount of alcohol in the hydrolyzed solution can be reduced in this way before coating, the amount of alcohol that must be removed from the membrane after coating is also small. The cracks in the film and the peeling from the substrate are considered to be due to the evaporation of the solvent (alcohol) inside the film, and as a result, the method of the present invention in which the hydrolysis solution is depressurized and concentrated. However, it is also effective in preventing cracks and peeling.

In the present invention, the degree of pressure reduction of the hydrolysis solution is 10 to 500 Torr, and the time is 10 minutes to 1
It only takes about a time, resulting in a viscosity of about 0.1-10 poise. If it is less than 0.1 poise, a film can be obtained, but it is as thick as a thin film prepared by a conventional method, and if it exceeds 10 poise, the polycondensation reaction after hydrolysis proceeds, so that the particles in the solution are Formed and the film is not uniform after coating. Examples of the metal alkoxide used as the raw material of the hydrolysis solution of the present invention include silicon, titanium, germanium, aluminum or boron methoxide, ethoxide, propoxide, and the like, and one or more metal alkoxides can be used. . As the alcohol used in the hydrolysis solution of the present invention, for example, alcohols such as methanol, ethanol, isopropyl alcohol and butanol can be used, but the alcohol is not limited to these. Further, in the hydrolysis solution of the present invention,
An acid such as hydrochloric acid, nitric acid, sulfuric acid or phosphoric acid can be used as a catalyst for promoting hydrolysis. The molar ratio of alcohol and water is about 0.5 to 5 times, and the metal alkoxide added to the hydrolysis solution is 2 to 5 in molar ratio to water.
The amount of the acid used as the catalyst is 5 times, and the pH is generally about 1 to 5. The material of the substrate used in the present invention is not particularly limited, and metal, plastic, or the like can be used in addition to glass. The means for depositing the hydrolyzed solution on the substrate may be any of the methods commonly used in this type of technical field, and examples thereof include a spin coating method and a dipping method. By controlling the viscosity by adjusting the degree of pressure reduction and the time period, the amount of adhesion can be increased or decreased and the film thickness can be controlled. After being attached on the substrate, it is dried and solidified by a known technique to obtain a film. Examples of specific conditions are shown in the examples below.

[0007]

EXAMPLES The present invention will be described below with reference to examples.
The present invention is not limited to this. Example 1 Silicon ethoxide 50 ml, ethanol 40 ml, 1
20 ml of N hydrochloric acid was placed in a beaker and stirred for about 30 minutes to obtain a hydrolysis solution. The hydrolyzed solution was kept under a pressure of 10 Torr for 15 minutes to be concentrated. The viscosity of the concentrated hydrolyzed solution was 4 poise. Next, this concentrated hydrolyzed solution was spin-coated on a quartz substrate to form a film. This film was dried by keeping it at 100 ° C. for 48 hours and then gradually heated to 1000 ° C. to be vitrified. It was confirmed that the obtained glass film had a thickness of 1.5 μm and was transparent and homogeneous.

Comparative Example 1 When the hydrolyzed solution of Example 1 was spin-coated as it was without concentrating and vitrified similarly, the film thickness was 0.3 μm. At this time, the viscosity of the hydrolyzed solution was 0.05 poise. Example 2 50 ml of silicon ethoxide, 1 ml of titanium isopropoxide and 20 ml of 1N hydrochloric acid were placed in a beaker and stirred for about 30 minutes to obtain a hydrolysis solution. 1 hydrolyzed hydrolysis solution
It was kept under a pressure of 00 Torr for 20 minutes to be concentrated. At that time, the viscosity of the concentrated hydrolyzed solution was 3 poise. Next, immerse the quartz substrate in this concentrated hydrolysis solution and
The solution was coated (dipping) by pulling up at a rate of / min. After that, when heat treatment was performed in the same manner as in Example 1, a homogeneous transparent film having a thickness of 1.3 μm was obtained. A functional film can be formed by adding various functional elements, compounds (compounds having a non-linear optical effect, etc.), semiconductors, etc. to the hydrolysis solution of the present invention.

[0009]

As described above, according to the present invention, it is possible to easily form a thick film, which has been difficult by the conventional sol-gel method, and thus it has mechanical, chemical and electromagnetic functions. It is very effective when used for forming a coating film.

Claims (2)

[Claims] 1. A method for producing a thin film by adhering a hydrolysis solution obtained by adding water, alcohol, and acid to a metal alkoxide to form a thin film, after the hydrolysis solution is concentrated under reduced pressure. A method for producing a thin film, which comprises depositing on a substrate. 2. The method for producing a thin film according to claim 1, wherein the metal alkoxide is an alkoxide of silicon, boron, titanium, germanium or aluminum. [0001]