JP2002043309A - Forming method of silicon dioxide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent SiO2 fine grains on the surface of a silicon dioxide film from being adhered to a glass substrate to obtain the substrate with the silicon dioxide film, which has no clouding, is high in quality and is excellent in a visual appearance, in the method of forming the silicon dioxide film by a supersaturated deposition method. SOLUTION: A glass substrate 1 is brought into contact to a treating liquid consisting of a hexafluorosilicic acid solution with a supersaturated silicon oxide, to form the silicon dioxide film on the surface of the substrate 1. After that, the substrate 1 is dipped into a cleaning tank 20 held with a cleaning liquid, whereby the substrate is cleaned to remove the treating liquid being adhered to the substrate. The silicon concentration of the cleaning liquid in the tank 20 is set in a concentration of 0.3 mol/L or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a silicon dioxide film, and more particularly to a method for depositing a silicon dioxide film on the surface of a substrate by bringing a supersaturated aqueous solution of hydrosilicofluoric acid into contact with the substrate. (Hereinafter sometimes referred to as "supersaturated deposition method"). The present invention relates to a method for obtaining a substrate with a silicon dioxide coating film having high quality and excellent appearance by preventing generation of "cloudiness" due to adhesion of fine particles.

[0002]

2. Description of the Related Art As a method for forming a silicon dioxide film, silicon dioxide is used.
The substrate is brought into contact with a supersaturated aqueous solution of hydrofluoric acid in silicon dioxide.
To deposit a silicon dioxide film on the substrate surface
Method is generally adopted, and this supersaturated precipitation method is
Conventionally, as shown in the following reaction formula,
After saturating the solution with silicon dioxide, dissolve the aluminum
So-called silicon dioxide is precipitated from the liquid phase
There is an aluminum melting method (Japanese Patent Publication No. 62-20876)
Gazette). H₂SiF₆+ 2H₂O → 6HF + SiO₂  Al³⁺+ 6HF → H₃AlF₆+ 3H⁺

The aluminum dissolving method is characterized in that a dense silicon dioxide film can be formed at a low temperature and that a film can be entirely formed on the surface of a substrate having any shape. In substrate applications, a silicon dioxide film is formed on the surface of a glass substrate to prevent the elution of alkali ions from glass, and in plastic substrate applications for liquid crystal displays, a silicon dioxide film is formed on the surface of a plastic substrate to form an interior. To prevent gas diffusion from improving the vacuum film forming processability, or, for example,
In plastic lens applications, it has been applied for various purposes and fields, such as forming a silicon dioxide film on the lens surface to prevent shape change due to moisture absorption and preventing water from entering into plastic.

[0004] As a method of forming a silicon dioxide film, there is a boric acid addition method in addition to the aluminum dissolution method. However, in the aluminum dissolution method, while the film formation rate can be controlled only by the surface area of the aluminum to be immersed,
The boric acid addition method has a disadvantage that the concentration of the solution changes in accordance with the addition of boric acid, so that it is difficult to control the film formation rate. Therefore, the aluminum dissolution method is considered to be suitable.

Conventionally, the formation of a silicon dioxide film by this supersaturated deposition method is shown in FIGS. 1A to 1D, and a supersaturated aqueous solution of hydrosilicofluoric acid (hereinafter referred to as "treatment liquid"). And a cleaning tank 20 for holding a cleaning solution are provided side by side, and are performed in the following procedure. A plurality of glass substrates 1 are set in a processing cassette 2 (FIG. 1A). The processing cassette 2 on which the glass substrate 1 is set is transported to a position above the processing tank 10, pulled down, and immersed in the processing liquid. After depositing a silicon dioxide film on the glass substrate 1 by the supersaturated deposition method, the cassette 2 is pulled up (FIG. 1B). The processing cassette 2 is transported from a position above the processing tank 10 to a position above the cleaning tank 20, and is immersed in a cleaning liquid, washed, and then pulled up (FIG. 1C). The glass substrate 1 from which the processing liquid has been removed by washing is withdrawn from the processing cassette 2 and sent to the next step (FIG. 1).
(D)).

[0006]

However, the glass substrate provided with a silicon dioxide film produced by the above-mentioned conventional method has fine particles adhered to the surface of the silicon dioxide film, and the adhered fine particles scatter light. A cloudy appearance appears that looks white. Further, even in a color filter or the like for a liquid crystal, which is manufactured using a substrate to which fine particles are attached in this way, the appearance of the image becomes “cloudy”, which is a serious defect that impairs the image display quality. Such adhesion of the fine particles to the silicon dioxide film occurs for the following reasons.

That is, of the series of the above-mentioned steps,
In the cleaning step, the processing liquid adhering to the glass substrate surface dissolves into the cleaning liquid stored in the cleaning tank,
At this time, as a result of the equilibrium reaction occurring in the hydrosilicofluoric acid in the treatment liquid, a hydrolysis reaction occurs according to the following reaction formula, and fine particles of silicon dioxide (SiO ₂ ) are generated. H ₂ SiF ₆ + 2H ₂ O → 6HF + SiO ₂

When the glass substrate transferred from the processing tank and having the processing liquid adhered to the surface is repeatedly washed, the above reaction is repeated, and the number of SiO ₂ fine particles in the cleaning tank increases.
This increases the probability that fine particles will adhere to the surface of the glass substrate. For this reason, the fine particles adhere and remain on the surface of the silicon dioxide film of the final product.

The present invention solves the above-mentioned conventional problems, and in a method of forming a silicon dioxide film by a supersaturated deposition method, prevents adhesion of fine particles of SiO _{2 on the} surface of the silicon dioxide film, thereby achieving high quality without “cloudiness”. It is an object of the present invention to obtain a substrate with a silicon dioxide coating excellent in appearance.

[0010]

According to the method of forming a silicon dioxide film of the present invention, a substrate is brought into contact with a processing solution comprising a hydrosilicofluoric acid solution in which silicon dioxide is supersaturated, and the surface of the silicon dioxide is formed on the surface of the substrate. In a method for forming a silicon dioxide film, a film is formed, and then the substrate is washed by immersing the substrate in a cleaning tank holding a cleaning solution to remove a processing solution attached to the substrate. 0.3m silicon concentration
ol / L or less.

In the present invention, since the silicon concentration of the cleaning solution in the cleaning tank is suppressed to 0.3 mol / L or less, the hydrolysis reaction hardly proceeds, and the generation of SiO ₂ fine particles is suppressed. For this reason, adhesion of the SiO ₂ fine particles to the surface of the silicon dioxide coating film that causes “cloudiness” is prevented, and a high-quality substrate with a silicon dioxide coating film excellent in appearance without “cloudiness” can be obtained.

In the present invention, it is preferable that the silicon concentration of the cleaning liquid in the cleaning tank be 0.3 mol / L or less by extracting a part of the cleaning liquid in the cleaning tank and introducing a new cleaning liquid into the cleaning tank. .

[0013]

Embodiments of the present invention will be described below in detail.

According to the method of forming a silicon dioxide film of the present invention, a substrate is brought into contact with a processing solution comprising a hydrosilicofluoric acid solution in which silicon dioxide is supersaturated, and a silicon dioxide film is formed on the surface of the substrate. After that, except that the silicon concentration of the cleaning liquid in the cleaning tank for performing the immersion cleaning for removing the processing liquid attached to the substrate is kept at 0.3 mol / L or less, FIG.
Can be performed in the same manner as in the conventional method shown in FIG.

The silicon concentration of this cleaning liquid is 0.3 mol / L.
When the ratio exceeds the above range, fine particles of SiO ₂ are easily generated in the cleaning liquid, and the fine particles adhere to the product, resulting in a “cloudy” defect.

As described above, as a method for suppressing the silicon concentration of the cleaning liquid in the cleaning tank to 0.3 mol / L or less, a part of the cleaning liquid is withdrawn as a waste liquid from the cleaning tank, and a new amount corresponding to the amount of the extracted liquid is removed. A method of renewing a part of the cleaning liquid by introducing a suitable cleaning liquid (tap water or the like).

That is, since the silicon concentration of the cleaning liquid in the cleaning tank increases as the film forming process is continued, a part of the cleaning liquid in the cleaning tank is removed before the silicon concentration exceeds 0.3 mol / L. Just update and dilute.

As a method of renewing the cleaning liquid, the silicon concentration of the cleaning liquid in the cleaning tank is measured and monitored, and the renewal amount of the cleaning liquid necessary for the concentration to be 0.3 mol / L or less is calculated. However, in general, the concentration analysis of hydrosilicofluoric acid requires a long time, and is not practical as a concentration control method in industrial production.

It is advantageous from the viewpoint of production control that the renewal operation of the cleaning liquid is performed at a predetermined renewal volume at a predetermined interval set in advance.

In this case, the larger the amount of the cleaning liquid to be renewed, the lower the silicon concentration of the cleaning liquid can be. is not. Therefore, from the viewpoint of waste liquid treatment cost, the amount of the renewal liquid is desirably as small as possible within a range where the silicon concentration of the cleaning liquid in the cleaning tank can be suppressed to 0.3 mol / L or less. At least, the silicon concentration of the cleaning liquid in the cleaning tank gradually increases, and the effect of renewing the cleaning liquid cannot be obtained.

In the formation of the silicon dioxide film, the silicon concentration in the cleaning solution in the cleaning tank may be determined when conditions such as the concentration of the processing solution in the processing apparatus and the total amount of the cleaning solution in the cleaning tank are constant.
Depending on the area and the number of substrates immersed in the cleaning tank in one film forming process, the silicon concentration in the cleaning liquid increases with the number of repetitions of the film forming process. The degree of increase in the silicon concentration is determined in advance, and the amount of the renewal solution is determined so that the silicon concentration of the cleaning solution in the cleaning tank can be suppressed to 0.3 mol / L or less. It is preferable to determine the amount of the renewal liquid according to the above.

For example, in the processing apparatus according to the first embodiment described below, the cleaning tank is updated as in the second embodiment described later. 60 to 110, which corresponds to 5 to 8.5% of the total washing volume of
It has been found that the silicon concentration can be maintained at 0.3 mol / L or less with the renewal liquid amount of L. On the basis of this result, in Example 3 described later, the cleaning liquid is renewed with a renewal liquid amount of 85 L for each film forming process to maintain the silicon concentration.

It is needless to say that the renewal of the cleaning liquid does not necessarily have to be performed for each film forming process, but may be performed for each of a plurality of film forming processes. In this respect, it is desirable to increase the update frequency.

The method of the present invention can be carried out in the same manner as the conventional method for forming a silicon dioxide film except that the silicon concentration of the cleaning solution in the cleaning bath is suppressed. For film formation, for example, a method is used in which aluminum powder or a plate material is added to a hydrosilicofluoric acid solution in which silicon dioxide is saturated to form a supersaturated solution of silicon dioxide, and the substrate is immersed in this solution. be able to.

Here, the concentration of hydrofluoric acid in the hydrosilicic acid solution is preferably about 1.0 to 4.0 mol / L before adding aluminum.

The substrate after the formation of the silicon dioxide film is immersed in a cleaning tank for cleaning.

As the cleaning liquid for the cleaning tank, clean water such as pure water is used, but a surfactant or the like may be added to the cleaning liquid for the purpose of improving the cleaning effect. It is also effective to rock the substrate during immersion or to apply ultrasonic waves.

There is no particular limitation on the immersion time of the cleaning tank,
Generally, 10 to 60 seconds is sufficient.

Since the reaction of generating fine particles in the cleaning tank proceeds as the temperature of the cleaning liquid increases, it is desirable that the temperature of the cleaning liquid is not too high. When the difference is large, the film is disadvantageous in appearance defects such as pinholes, which is not preferable. Therefore, the temperature of the cleaning liquid is generally set to a temperature of about 10 to 40 ° C.

After washing, the product is dried according to a conventional method to obtain a product.

[0031]

The present invention will be described more specifically with reference to the following examples.

Example 1 A silicon dioxide film was formed by the method shown in FIG.

Silicon dioxide (industrial silica gel) is dissolved in a hydrosilicofluoric acid solution having a concentration of 2.6 mol / L to bring the silicon dioxide into a saturated state.
× 165mm × 3.0mm (thickness) aluminum plate 2
Five pieces were immersed to make the silicon dioxide supersaturated. This treatment liquid was kept at 30 ° C., and was thoroughly washed and dried in advance.
480 sheets of soda lime glass plates of 0 mm × 400 mm × 0.7 mm (thickness) were set in a cassette and immersed.
After holding for 0 minute, a silicon dioxide film having a thickness of 40 nm was formed on the glass plate, then the cassette was pulled up, immersed in a washing tank (water storage capacity of 1300 L) filled with tap water for 30 seconds, washed, and then pulled up. Was. The processing of the 480 glass substrates is defined as one film forming processing unit, and this film forming processing is repeatedly performed. The number of times of processing, the silicon concentration in the cleaning liquid in the cleaning tank after the processing, and the obtained product (silicon dioxide) Glass substrate with coating)
The relationship between the occurrence rates of defects due to “clouding” was examined, and the results are shown in Table 1 and FIG. The presence or absence of the "cloudy" defect was determined by visually observing the substrate under a fluorescent lamp having a dark field of 2000 lx.

[0034]

[Table 1]

As is clear from Table 1 and FIG. 2, the number of film forming processes was 23 and the silicon concentration in the cleaning solution was 0.312 mol.
1 / L, and the occurrence of “cloudy” defects was observed at 0.5%, and thereafter, as the number of times of processing increased, the defect occurrence rate rapidly increased. From this result, the silicon concentration in the cleaning solution was 0.3 m
It can be seen that the “cloudiness” defect can be prevented by suppressing the content to ol / L or less.

Example 2 In Example 1, every time the film forming process was performed 15 times, the entire amount (1300 L) of the cleaning liquid in the cleaning tank was withdrawn as a waste liquid, and the cleaning water was newly introduced into the cleaning tank. And the film forming process was repeated. As a result, even after performing the film forming process 210 times, the occurrence rate of the “cloudy” defect of the product was 0%, and the silicon concentration in the final cleaning solution was 0.221 m.
ol / L could be suppressed to 0.3 mol / L or less.

Embodiment 3 In the embodiment 2, the cleaning liquid of 1300 L is renewed every 15 times of the film forming process, and the renewal amount of the cleaning liquid is about 87 L in one film forming process. Therefore, in this embodiment,
Every time the film forming process was performed, 85 L of the cleaning solution in the cleaning tank was drawn out, and the cleaning solution for introducing fresh water was updated and the film forming process was repeated. As a result, as in the case of the second embodiment, 2
Even after performing the film forming process 10 times, the occurrence rate of the “cloudy” defect of the product is 0%, and the silicon concentration in the final cleaning liquid is 0.235 mol / L, which is 0.3 mol / L or less. Could be suppressed.

[0038]

As described in detail above, the silicon dioxide of the present invention
According to the method of forming the coating, silicon dioxide is
In the method of forming a silicon film, the silicon dioxide film surface
SiO ₂Prevents fine particles from adhering and has no cloudy
Obtain a substrate with a silicon dioxide coating film with excellent quality and appearance
Can be.

Therefore, if the glass substrate provided with the silicon dioxide film manufactured by the method of the present invention is used as a precision base material for a display device such as a liquid crystal display, an abnormal image display may occur. And high quality products can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a processing step of forming a silicon dioxide film by a supersaturated deposition method.

FIG. 2 is a graph showing the relationship between the number of treatments, the concentration of silicon in a cleaning liquid in a cleaning tank after the treatment, and a defect occurrence rate due to “cloudiness” of an obtained product in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Processing cassette 10 Processing tank 20 Cleaning tank

Claims (2)

[Claims] A substrate is brought into contact with a processing solution comprising a hydrosilicofluoric acid solution in which silicon dioxide is supersaturated to form a silicon dioxide film on the surface of the substrate, and thereafter the substrate is maintained in a cleaning liquid. A method for forming a silicon dioxide film, in which a treatment liquid adhered to a substrate is removed by immersion in a cleaning tank, wherein the silicon concentration of the cleaning liquid in the cleaning tank is 0.3 mol / L or less. Method for forming a silicon dioxide film. 2. The method according to claim 1, wherein a part of the cleaning liquid in the cleaning tank is extracted, and a new cleaning liquid is introduced into the cleaning tank to reduce the silicon concentration of the cleaning liquid in the cleaning tank to 0.3 mol / mol.
L or less, a method for forming a silicon dioxide film.