JP3010505B2 - Method for producing silicon dioxide coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon dioxide film, and more particularly, to a method for forming a dense silicon dioxide film on the surface of a substrate by contacting the substrate with an aqueous solution of hydrosilicofluoric acid in a supersaturated state of silicon dioxide. It relates to a method of forming.

[0002]

2. Description of the Related Art In recent years, as a silicon dioxide film forming method, there is no need for a vacuum system capable of forming a film at a low temperature. A method of forming silicon dioxide on the surface of a substrate by bringing a substrate into contact with an aqueous solution of hydrosilicofluoric acid in a supersaturated state of silicon (hereinafter, abbreviated as a “precipitation method”) has been attracting attention (for example, see Japanese Patent Application Laid-Open No. HEI 9-163572). 60-33233, JP-A-62-20
876).

[0003]

In the case of forming a silicon dioxide film by a deposition method, the better the film is formed at a higher temperature and the higher the concentration of a hydrosilicofluoric acid aqueous solution, the better the film quality can be obtained. On the other hand, however, under such conditions, harmful gases such as silicon fluoride and hydrogen fluoride are strongly generated, and it is necessary to consider safety. Therefore, in actual film formation, there are limits to the film formation temperature and the concentration of hydrosilicofluoric acid, and naturally, the film quality of silicon dioxide to be obtained is also limited.

In recent years, a method has been proposed in which a silicon dioxide film is formed on a plastic substrate by a deposition method to suppress water absorption of plastics and a method of suppressing permeation of various gases. In order to make this possible, it is necessary to coat the plastic substrate with organic silicon or a hydrolyzate thereof in advance. In order to obtain a silicon dioxide film having a good gas barrier property by a precipitation method, a high-temperature film formation is performed, or the use of a high-concentration hydrosilicofluoric acid aqueous solution causes the above-mentioned organic silicon and a hydrolyzate thereof,
There is a problem in that the film is easily dissolved in an aqueous solution of hydrosilicofluoric acid, and often causes a film formation defect.

Also, when forming a silicon dioxide film as an alkali elution preventing layer on soda lime glass, if a high-temperature and high-concentration aqueous hydrofluoric acid solution is used, when forming a film on a thick glass, There is also a problem that the thickness of the silicon dioxide film formed on the glass surface tends to be non-uniform. For the above reasons, there has been a demand for a method for improving the film quality of the obtained silicon dioxide film when the film formation temperature and the hydrosilicofluoric acid concentration are kept constant.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems and provides a method for forming a dense silicon dioxide film on the surface of a substrate.

According to the present invention, a substrate is brought into contact with a hydrosilicofluoric acid aqueous solution containing sulfuric acid in which silicon dioxide is in a supersaturated state,
It is characterized in that a silicon dioxide coating is obtained on the surface of the substrate. The hydrosilicofluoric acid aqueous solution containing sulfuric acid in which silicon dioxide is in a supersaturated state (hereinafter abbreviated as "treatment liquid") is a mixture of hydrofluoric acid or an aqueous solution of hydrosilicofluoric acid, sulfuric acid, and then mixed. (Silica gel, aerosil, silica glass, other materials containing silicon dioxide, etc.) and dilute with water,
A silicon dioxide supersaturated state can be used by adding an aqueous solution of boric acid or aluminum chloride, adding and dissolving metallic aluminum, or increasing the temperature of the processing solution.

[0008] Further, the treatment liquid contains (a) metallic aluminum dissolved and mixed even at the time of contact with the substrate, so that the treatment liquid is evaporated or removed from the film forming system by taking the substrate in and out. Hydrogen silicofluoride containing sulfuric acid in which silicon dioxide is continuously dissolved and saturated, in which an aqueous solution of hydrosilicofluoric acid saturated with silicon dioxide is continuously or intermittently added to compensate for the decrease caused by carry-out. The acid aqueous solution and water are added separately, or added immediately after mixing,
Excessive processing solution is discarded outside the system.An aqueous solution of hydrosilicofluoric acid containing sulfuric acid saturated with silicon dioxide by temporarily cooling the temperature continuously is added while the temperature is raised or as it is. The supersaturation is maintained at all times by means such as the excess processing solution being discarded outside the system. (C) a processing solution in which the silicon concentration and the sulfur concentration are kept almost constant, and (3) a processing solution of 3% or more of the total processing solution per minute is filtered back through a filter.
Is preferred.

Here, it is preferable to keep the total amount of the processing solution in the film forming system constant by adding and discarding the processing solution in order to always keep the deposition rate of the silicon dioxide film within a certain range. Also, 3
% Or more of the treatment liquid is effective for continuously obtaining a uniform coating, and filtration with a filter is preferable for obtaining a coating having no irregularities.

The processing solution has a silicon concentration of about 1 to 4 mol /
l, preferably 1.5 to 3.5 mol / l. If the silicon concentration of the treatment liquid is less than 1 mol / l, silicon dioxide is apt to be generated as particles in the treatment liquid, and the film formation rate on the substrate is undesirably reduced.

Further, the silicon concentration of the processing solution is 4 mol / l
When the temperature exceeds the above range, the amount of silicon fluoride chemical species evaporating from the processing solution tends to increase drastically. The silicon fluoride chemical species is easily hydrolyzed by moisture in the atmosphere or moisture evaporating from the processing liquid, and is covered by a liquid (processing liquid) and a solid (inner wall of the apparatus) in the silicon dioxide film manufacturing apparatus. On the gas-solid interface of the gaseous part, such as the inner wall of the piping of the circulation system or the part of the filter where air did not escape, the inner wall of the filter housing, the wall or lid covering the space above the treatment liquid in the immersion tank, etc. It becomes frosty silicon dioxide and adheres. Care should be taken in some cases, as this can lead to pipe clogging.

The concentration of sulfuric acid contained in the treatment liquid is represented by the concentration of sulfur component, and the molar ratio of S / Si = 10 ^-4 to 10, more preferably 10 to 10 with respect to the concentration of silicon component.
^-2 to 1.

When S / Si <10 ^-4 , the effect of adding sulfuric acid disappears. Conversely, when S / Si> 10, the effect of sulfuric acid addition is saturated, which is not only uneconomical, but also hinders the precipitation of silicon dioxide.

When the film forming temperature and the silicon concentration of the treatment liquid are constant, the silicon dioxide film obtained from the treatment liquid to which sulfuric acid is added is a treatment liquid which does not contain a sulfur component in the film but does not contain sulfuric acid. The fluorine concentration in the film is higher and the refractive index is lower than those obtained from

The deposition of silicon dioxide by the deposition method is represented by the hydrolysis of hydrosilicofluoric acid as shown in the following formula. H ₂ SiF ₆ + 2H ₂ O = SiO ₂ + 6HF

In the present invention, since a part of H ₂ O to be consumed in the hydrolysis is restrained by the addition of sulfuric acid, the sulfuric acid addition system uses a high concentration of hydrosilicofluoric acid. Dense, like silicon dioxide coating obtained
It is presumed to indicate the refractive index and the F concentration in the film.

Further, it is presumed that sulfuric acid gives a dense film in order to promote dehydration-condensation of hydroxysilane species in the treatment liquid and dehydration crosslinking of a silicon dioxide film already deposited in the treatment liquid.

FIG. 1 is a system diagram of a silicon dioxide film manufacturing apparatus used in the present invention. In FIG. 1, the immersion tank comprises an outer tank 1 and an inner tank 2, and the space between the inner tank 1 and the outer tank 2 is filled with water 3. The water is heated by a heater 4 so as to have a constant temperature, and is stirred by a stirrer 5 to make the temperature distribution uniform.

The inner tank 2 comprises a front part 6, a middle part 7, and a rear part 8. Each part has an aqueous solution of hydrosilicofluoric acid of a predetermined concentration obtained by dissolving and saturating silicon dioxide using industrial silica gel powder as a source of silicon dioxide. Or 6.5 liters of sulfuric acid added thereto. Here, the three-way cock 13
The a, 13a ', 13b, 13b' were adjusted, and the circulation pump 12a was operated to draw out a certain amount of the reaction solution in the rear portion 8 of the inner tank, and the circulation of the processing liquid which was filtered by the filter 11a and returned to the inner tank 6 was started.

Here, the mesh of the filter 11a is 1.5 μm, and the circulation flow rate of the reaction solution is set to 520 ml / min (the circulation flow rate is about 8% / min because the total volume of the reaction solution is 6.5 liters). did.

Thereafter, the height is 50 mm, the width is 50 mm, and the thickness is 3
Five aluminum plates 15 of 5 mm were immersed in the rear part 8 of the inner tank, and the stirrer 16 was operated to accelerate the dissolution of the aluminum plates.

By keeping this state for 12 to 50 hours, the reaction liquid became a processing liquid having an appropriate degree of saturation of silicon dioxide (a silicon dioxide film can be formed). When the reaction liquid has a silicon dioxide film forming ability, silicon dioxide is generated as particles in the reaction liquid, grows, and is eventually filtered by the filter 11a, which causes clogging of the filter. This tendency was observed 30 to 70 hours after the addition of the aluminum, resulting in a decrease in the circulation flow rate. Therefore,
After returning the reaction solution in the pipe and the filter 11a to the inner tank 2, the three-way cock 1 is circulated so that the reaction solution is circulated in the inner tank rear part 8 → the filter 11b → the circulation pump 12a → the inner tank front part 6.
3a, 13a ', 13b, and 13b' were set, and the circulation of the reaction solution was started again.
It recovered to 20 ml / min. Here, the mesh of the filter 11b is 1.5 μm like the filter 11a.

In this state, the circulating pump 12b is operated,
5% hydrofluoric acid aqueous solution 10 is used for washing liquid tank 9 → filter 1
The clogged filter 11a was washed and regenerated by circulating in the order of 1a → circulation pump 12a → washing liquid tank 9. According to the above procedures, the three-way cocks 13a, 13a ', 13b,
By immersing the base material 14 in the inner tank 7 for a predetermined time while adjusting the filter 13b 'to switch the filter, a silicon dioxide film could be continuously obtained on the base material surface.

[0024]

The present invention will be described in detail below with reference to examples, comparative examples and reference examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention. Example 1, Comparative Example 1, Reference Example 1 10 parts by weight of γ-aminopropyltriethoxysilane was added to 100 parts of isopropyl alcohol.
100 mm vertical, which was previously washed with a solution diluted to 0 parts by weight,
It was applied to a polycarbonate flat plate having a width of 100 mm and a thickness of 1 mm and a polycarbonate film having a length of 100 mm and a width of 100 mm and a thickness of 100 μm by an immersion method and heat-treated in a hot-air drying oven at 80 ° C. for 30 minutes. The film thickness of the primary film thus obtained was 15 nm.

CSGL-0803P (manufactured by Chisso Corporation)
Hydrolysis solution containing tetraethoxysilane as one component) 2
The polycarbonate flat plate and the polycarbonate film on which the layer of γ-aminopropyltriethoxysilane was formed were immersed in a solution obtained by diluting 0 parts by weight to 1000 parts by weight of isopropyl alcohol. For 100 minutes. The thickness of the secondary coating film thus obtained was 30 nm.

The above-mentioned primary coating and secondary coating are necessary to obtain a transparent silicon dioxide coating having excellent adhesion with excellent uniformity of film thickness on a polycarbonate by a deposition method. After the polycarbonate flat plate and the film were immersed in the interior middle part 7 of the silicon dioxide film manufacturing apparatus shown in FIG. 1, they were held for a predetermined time to form a silicon dioxide film having a predetermined thickness.

The temperature of the processing solution circulating in the silicon dioxide film manufacturing apparatus is determined whether the sulfuric acid is added (Example 1) or not (Comparative Example 1).
The heater 4 was set to be 0 ° C. The treatment solution to which the sulfuric acid was added was prepared by diluting 3.8 l of hydrosilicofluoric acid having a silicon concentration of 4.3 mol / l in which silica gel was dissolved and saturated with 3.8 l of tap water and then adding 0.5 l of concentrated sulfuric acid. It was created by adding liters.

The processing solution to which sulfuric acid is not added is as follows:
It is prepared by diluting 3.8 liters of hydrosilicofluoric acid having a silicon concentration of 4.3 mol / l and dissolving and saturating silica gel with 3.8 liters of tap water. The deposition rate of each silicon dioxide film was about 50 nm / hr for both.

Each of the processing liquids during the silicon dioxide film formation is collected and
The results of examining the concentration of each element contained in each of the processing solutions are shown in the first section.
It is shown in the table. The water absorption of the polycarbonate flat plate formed with each silicon dioxide was determined based on the JISK-6911 method, and the water vapor transmission rate of the polycarbonate film was determined according to JISZ-0.
It was measured based on the 208 method (40 ° C., 90% RH).
The results are shown in Table 2.

Table 2 also shows, as a reference example, the results of measurement of the water absorption of an untreated polycarbonate flat plate and the moisture permeability of a polycarbonate film (Reference Example 1).

[0031]

From Tables 1 and 2, it can be seen that the concentration of silicon in the processing solution is higher even though the processing solution to which sulfuric acid is added is lower than the processing solution to which sulfuric acid is not added. It turns out that it shows gas barrier properties. That is, it is apparent that the gas barrier property of the obtained silicon dioxide film is improved by adding sulfuric acid to the hydrosilicofluoric acid aqueous solution.

The silicon dioxide film obtained from the processing solution containing sulfuric acid was subjected to X-ray photoelectron spectroscopy (ESCA; Electro
n Spectroscopy for Analysis
As a result of analysis using is), it was confirmed that most of the gas was composed of SiO ₂ and that no sulfur component was contained.

EXAMPLE 2, COMPARATIVE EXAMPLE 2, REFERENCE EXAMPLE 2 A 30 mm square, 1.1 mm thick soda lime glass was first prepared.
After being immersed in the interior middle part 7 of the silicon dioxide film manufacturing apparatus shown in the figure, each was held for 60 minutes to form a silicon dioxide film of 50 nm. The treatment solution containing sulfuric acid used was the same treatment solution as in Example 1 (Example 2), and the treatment solution containing no sulfuric acid used the same treatment solution as Comparative Example 1 ( Comparative Example 2). The film forming temperature is also 30 ° C. as in Example 1 and Comparative Example 1.

The soda lime glass formed with each silicon dioxide was immersed in 100 ml of boiling water at 100 ° C. for 24 hours, and the results of analysis of the Na concentration in the immersion water are shown in Table 3.

[0036]

Table 3 also shows the measurement results of untreated soda lime glass (Reference Example 2) as Reference Examples. From Table 3, it is apparent that the addition of sulfuric acid to the hydrosilicofluoric acid aqueous solution improves the ability of the resulting silicon dioxide film to prevent Na ion elution.

Examples 3 and 4 A silicon wafer having a diameter of 4 inches was immersed in the interior middle part 7 of the apparatus for producing a silicon dioxide film shown in FIG. 1 and held for about 2 hours to form a silicon dioxide film having a thickness of 100 nm. . In addition, the processing solution used contains sulfuric acid,
The same processing liquid as in Example 1 was used (Example 3), and the same processing liquid as Comparative Example 1 was used without sulfuric acid (Example 4). In addition, the film formation temperature was set to the values in Example 1 and Comparative Example
30 ° C. as in the above. Table 4 shows the results of measuring the refractive index of the silicon dioxide film formed on each silicon wafer using an automatic ellipsometer.

[0039]

Examples 5 and 6 A silicon wafer having a diameter of 4 inches was immersed in the interior middle part 7 of the apparatus for manufacturing a silicon dioxide film shown in FIG. 1 and held for about 4 hours to form a silicon dioxide film having a thickness of 200 nm. . In addition, the processing solution used contains sulfuric acid,
The same processing solution as in Example 1 was used (Example 5), and the same processing solution as in Comparative Example 1 was used without sulfuric acid (Example 6). In addition, the film formation temperature was set to the values in Example 1 and Comparative Example 1.
30 ° C. as in the above. Table 5 shows the results of measuring the concentration of the fluorine component contained in the silicon dioxide film formed on each silicon wafer by X-ray fluorescence analysis.

[0041]

As can be seen from Tables 4 and 5, by adding sulfuric acid to the hydrosilicofluoric acid aqueous solution, it is possible to increase the fluorine concentration in the resulting silicon dioxide film and lower the refractive index. It is clear that there is.

[0043]

As described in detail above, the method for producing a silicon dioxide film according to the present invention is characterized in that the substrate is brought into contact with an aqueous solution of hydrosilicofluoric acid containing sulfuric acid in which silicon dioxide is in a supersaturated state, so that According to the method of the present invention, a silicon film is formed, and the film quality of the silicon dioxide film can be improved and the refractive index can be improved without changing the conditions of the deposition method (film formation temperature, hydrofluoric acid concentration). Can be reduced, and the resulting silicon dioxide coating is
When applied to plastics, various drawbacks of the plastics (for example, water absorption, gas permeability, gas release) can be improved. When applied to soda lime glass, it provides excellent alkali barrier properties. And other excellent effects.

[Brief description of the drawings]

FIG. 1 is a system explanatory diagram of a silicon dioxide film manufacturing apparatus used for carrying out the present invention.

[Explanation of symbols]

 1-Outer tank, 2-Inner tank, 3-Water 4-Heater 5-Agitator 6-Inner tank front 7-Inner tank middle 8-Inner tank rear 9-Cleaning liquid tank 10-5% HF aqueous solution 11- Filter 12-Circulation pump 13-Three-way cock 14-Base material 15-Aluminum plate 16-Stirrer

Continuation of the front page (56) References JP-A-61-281047 (JP, A) JP-A-62-20876 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C01B 33 / 12-33/193 C08J 7/04 C03C 17/25

Claims (2)

(57) [Claims] 1. A method of manufacturing a silicon dioxide film of silicon dioxide to form a silicon dioxide coating on the hydrosilicofluoric acid solution and the substrate is contacted with by the substrate surface in a supersaturated state, the silicofluoride
A method for producing a silicon dioxide film, characterized by including sulfuric acid in an aqueous hydrofluoric acid solution. 2. Sulfuric acid in said hydrosilicofluoric acid aqueous solution is represented by a concentration S of a sulfur component in a molar ratio of S / Si = 10 ^-4 to 10 with respect to a concentration Si of a silicon component. The method for producing a silicon dioxide film according to claim 1, which is included.