JPS6144950B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a metal oxide thin film on a substrate.

Conventionally, there are the following methods for forming a metal oxide thin film on a substrate such as glass.

(a) Vacuum evaporation method (b) Sputtering method (c) CVD method (d) Hot spray method However, among these methods, methods (a) and (b) use a vacuum system, which increases the manufacturing cost. ,Also
In methods (c) and (d), the formed film becomes cloudy, and both have drawbacks.

On the other hand, a method in which a metal alcoholate solution is applied to a substrate to form a coating film and then fired allows the formation of a metal oxide thin film at low cost.
This would be a promising method if it could be put into practical use. However, in this method, metal alcoholates are generally susceptible to hydrolysis by water, and even a small amount of water causes the solution to become cloudy, so even if such a solution is applied to the substrate, it is difficult to achieve a homogeneous coating. Membranes are difficult to obtain.

That is, metal alcoholates are generally hydrolyzed by moisture and converted into hydroxides or oxides, resulting in precipitation. For example, titanium tetraisopropoxide and tantalum pentaethoxide are alcoholates that are liquid at room temperature and easily dissolve in common organic solvents. However, when the solution is left in the air, a white precipitate forms within a few minutes and becomes a suspension. Even if such a suspension is applied onto a substrate, a homogeneous transparent coating film cannot be obtained, and when it is fired, it turns into powder, making it impossible to obtain a homogeneous film.

The object of the present invention is to provide a novel method for preparing a metal alcoholate solution that is stable against moisture, etc., which eliminates the drawbacks or solves the problems in the prior art as described above, and a method for preparing such a stable metal alcoholate solution. An object of the present invention is to provide a method for forming a metal oxide thin film using a metal alcoholate solution.

The method of the present invention for the above purpose includes adding at least one type of organic acid such as carboxylic acid, phenol, or a phenol derivative as a stabilizer to a solution of a metal alcoholate in an organic solvent. After the solution is stabilized against moisture and the metal alcoholate solution thus stabilized is applied onto a substrate to form a coating, it is heated, preferably to a temperature of 350 to 700°C. hand,
The purpose is to obtain a metal oxide thin film on a substrate.

According to the present invention, the metal alcoholate solution is stabilized against moisture etc. by adding an organic acid such as carboxylic acid, phenol, or a phenol derivative to the metal alcoholate solution.
Metal alcohol solutions can be prepared that do not cause precipitation. When such a metal alcoholate solution is applied onto a substrate, a coating film that is stable against moisture and the like can be obtained. In this case, the application method may be any method such as spinner application, dipping application, spray application, or printing method.
There are no particular restrictions. Metal alcoholates to which the present invention can be applied include titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide, tantalum pentaethoxide, aluminum triethoxide, aluminum triisopropoxide, aluminum tributoxide, and aene diethoxide. antimony trithoxide, antimony trithoxide, tin tetramethoxide,
Examples include tin tetraethoxide, tin tetraisopropoxide, tin tetrabutoxide, zirconium tetraethoxide, zirconium tetraisopropoxide, vanadyl methoxide, vanadyl ethoxide, panadyl butoxide, and the like.

There are no particular limitations on the carboxylic acid, phenol, or phenol derivative used as a stabilizer for the metal alcoholate solution used in the present invention, but preferred monobasic carboxylic acids include:
Those represented by the general formula RCOOH (R is 1 to 15 carbon atoms), as dibasic carboxylic acids, maleic acid, fumaric acid, citraconic acid, mesaconic acid, malonic acid, succinic acid, glutaric acid, ajihinic acid, pimelic acid , suberic acid, azelaic acid, sebacic acid, itaconic acid, methylmalonic acid, methylsuccinic acid, phthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid, etc., as tribasic or higher polybasic carboxylic acids, acrylic acid and methacrylic acid. ,
Examples of copolymers with acrylic esters and methacrylic acid and phenol derivatives include salicylic acid, catechol, cresol, hydroquinone, and resorcinol.

The solvent used in the present invention may be any solvent as long as it dissolves the metal alcoholate, and is not particularly limited, but alcohols, esters, and ketones are preferable.

The firing temperature in the present invention is 350°C to 700°C.
Temperatures in the range of .degree. C. are preferred. If the firing temperature is lower than 350°C, the combustion of organic components will be insufficient, making it difficult to completely form metal oxides, and if the firing temperature is higher than 700°C, the glass substrate may be deformed or melted. This is not desirable because it causes

The present invention will be explained in more detail below using comparative examples and examples of the present invention.

Comparative Example 4.5 g of titanium tetraisopropoxide was dissolved in 15 ml of ethanol. This solution gradually underwent hydrolysis and became a suspension. When this suspension was applied onto a glass substrate using a spinner at 4000 rpm, the coating became cloudy. this thing
When baked at 500°C for 1 hour, titanium oxide particles were precipitated, resulting in a cloudy film with no adhesive strength to the glass substrate.

In this way, a thin film of metal oxide could not be obtained in a method using a metal alcoholate solution to which the present invention was not applied.

Next, an example in which the present invention is applied will be described.

Example 1 4.5 g of titanium tetraisopropoxide and 2.5 g of octylic acid were dissolved in 15 ml of ethanol. When this solution was applied onto a glass substrate using a spinner at 4000 rpm, a homogeneous coating film was obtained. This coating did not become cloudy even when left in the air. this
After firing at 500°C for 1 hour, a colorless and transparent titanium oxide thin film was obtained. This thin film had strong adhesion to the glass substrate. Membrane thickness is 1300
The dielectric constant was 68 (frequency 1 kHz).

Example 2 3.5 g of tin tetraethoxide, 0.3 g of antimony triethoxide, and 1.5 g of propionic acid were dissolved in 10 ml of isopropyl alcohol. When the same operation as in Example 1 was performed using this solution, a tin oxide thin film containing antimony was obtained. This thin film is a colorless and transparent thin film similar to that in Example 1,
The adhesion to the substrate was strong. The thickness of the membrane is
At 800 Å, the sheet resistance value was 13.5 kΩ/□.

Example 3 3 g of zirconium tetraisopropoxide and 1.2 g of salicylic acid were dissolved in 15 ml of methyl ethyl ketone, and the same operation as in Example 1 was carried out,
A colorless and transparent zirconium oxide thin film with strong adhesion to the substrate was obtained.

As is clear from the above description, according to the present invention, it is possible to stabilize metal alcoholate solutions that are unstable against moisture, etc., and to form various metal oxide thin films on various substrates including glass substrates. It can be formed stably. This makes it economical and easy to operate.
Metal alcoholates, which were difficult to use industrially as materials for forming metal oxide thin films due to their instability, can now be used for conductive thin films, resistive thin films, insulating thin films, high dielectric constant thin films, etc. It has become possible to form a wide range of metal oxide thin films easily and at extremely low cost. That is, for example, the formation of metal oxide thin films in liquid crystal display elements, EL
It can be applied to the formation of high dielectric constant insulating layers and high dielectric constant light emitting layers in display devices, thin film resistors in thin film hybrid circuits, thin film capacitors, and insulating thin films, and can significantly reduce manufacturing costs. Therefore, the industrial value of the present invention is extremely large.

Claims (1)

[Claims] 1. At least one compound selected from the group consisting of carboxylic acids, phenols, and phenol derivatives is added as a stabilizer for the metal alcoholate into an organic solvent solution of the metal alcoholate, and Apply the added solution to the substrate to form a coating film,
A method for forming a metal oxide thin film, which comprises heating the substrate on which the coating film is formed to a high temperature to form a thin oxide film of the metal on the substrate. 2. The metal oxide thin film forming method according to claim 1, wherein the substrate on which the coating film is formed is heated at a temperature in the range of 350 to 700°C.