JPH058274B2 - - Google Patents

Description

Detailed Description of the Invention: a. Field of Industrial Application The present invention relates to a method for producing a silicon oxide film, and in particular to a method for producing a silicon oxide film on the surface of the base material by immersing the base material in a saturated silicon oxide aqueous solution of hydrosilicofluoric acid. This invention relates to an improved manufacturing method (hereinafter referred to as precipitation method).

b. Prior Art The present inventors applied a precipitation method as a method for producing a silicon oxide film in an earlier patent application (Japanese Patent Laid-Open No. 1967-44,
It was shown in Japanese Patent Application Laid-Open No. 161944 (1982).

This method for producing a silicon oxide film involves saturating silicon oxide with hydrosilicofluoric acid at a concentration of 0.5 to 3.0 mol/ml, and then adding 2.0 x 10 ^- A method of manufacturing a silicon oxide film on the surface of the substrate by immersing the substrate in a treatment solution containing 2 moles or more (Japanese Patent Application Laid-Open No. 1967-44), and by repeatedly adding boric acid to the treatment solution, silicon oxide maintain the supersaturation state to some extent,
This is a method of repeatedly forming a silicon oxide film.
(Japanese Patent Application Laid-Open No. 161944/1983) Also, by utilizing the above properties, the present inventors developed a silicon oxide saturated aqueous solution of hydrosilicofluoric acid (hereinafter abbreviated as treatment liquid).
A circulating precipitation method was devised in which boric acid is discharged from the treatment tank in which the substrate is immersed, and boric acid is continuously added little by little into the discharged treatment solution to form a supersaturated state of silicon oxide and returned to the treatment tank. (Japanese Patent Application No. 58-137217) According to this method,
-161944) had the advantage of being able to form a silicon oxide film with better productivity (in a shorter time).

However, in order to stably create a silicon oxide film with no irregularities on the surface using the above-mentioned circulating precipitation method, the amount of circulating liquid per minute relative to the total amount of processing liquid must be at least 3%, preferably at least 6%. Something.

Filter the processing liquid that is circulated in the processing tank using a filter with a pore size of 1.5 μm or less.

The following conditions were necessary.

The above conditions are such that if the circulation rate is less than 3%, the flow of the processing liquid will slow down, causing precipitation of silicon oxide in the circulation pipe, clogging of the filter, and the pore size of the filter. This occurs because if the thickness is larger than 1.5 μm, the silicon oxide film formed on the base material tends to become a film with irregularities.

These precipitation methods have the great advantage of being able to create stable, smooth, large-area silicon oxide films on the surfaces of substrates such as glass, ceramics, plastics, metals, and semiconductors without using a firing process or vacuum technology. Even in the method for producing a silicon oxide film by the above-mentioned circulation method, which is considered to be the most practical method, there is a drawback that the filter needs to be replaced frequently.

For example, dissolve industrial silica gel in 2.0 mol/hydrosilicic acid to make a saturated solution of silicon oxide, and add 0.5 mol/l boric acid aqueous solution at a volume ratio of 25:1.
0.5 mol/aqueous boric acid solution was continuously added and mixed at a rate of 0.1 m/min to the total amount of the treatment solution mixed in step ³ .
If the substrate is processed while being filtered using a 1.5 μm filter and returned to the processing solution, the filter becomes clogged approximately 50 hours after starting filtration, making it impossible to depend on the amount of circulating fluid. It was hot.

c Problems to be Solved by the Invention The present invention solves the problem that the conventional method takes a short time to stop circulation due to filter clogging, for example, about 50 hours, and provides silicon oxide that is more stable and more productive. A method of manufacturing a film is provided.

d Means for Solving the Problems In order to solve the above problems, the present invention uses a treatment solution that is made into a supersaturated state of silicon oxide by adding boric acid to an aqueous solution of hydrosilicofluoric acid in which silicon oxide is dissolved, and a base. In the method of producing a silicon oxide film on the surface of a substrate by contacting the silicon oxide with the silicon oxide, (a) as a source of the silicon oxide, silica glass,
silicate glass or silicate mineral is used, (b) the aqueous solution of boric acid is continuously injected and mixed into the processing solution, and (c) 3% or more of the total amount of the processing solution is added every minute to 1.8 to 10 μm. A method is used in which the treated solution is filtered through a filter having a pore size within the range of .

The silicon oxide supply source used in the present invention is a silicate glass such as silica glass, soda lime glass, or borosilicate glass prepared by various manufacturing methods, or a silicate mineral such as pyroxene or feldspar. In other words, as a source of silicon oxide in the present invention, sources other than silica gel can be used.
Raw materials containing SiO ₂ can be used.

The present invention has discovered that the use of silica gel in conventional methods to saturate silicon oxide in a hydrosilicofluoric acid solution is a cause of the tendency for uneven shapes to occur in the silicon oxide film produced. It is based on

In other words, when using silica gel as a saturation source of silicon oxide, substantially more than the saturation amount of silica gel is added to the hydrosilicofluoric acid solution to achieve a saturated state, and a supersaturated amount of silica gel saturates the silicon oxide of the hydrosilicic acid. Very fine undissolved particles remain suspended in the aqueous solution. It is thought that this floating silica gel becomes a nucleus for precipitation of silicon oxide in the processing solution which has become supersaturated due to the addition of the aqueous boric acid solution, so that uneven shapes are likely to occur in the silicon oxide film. Therefore, as in the present invention, the supersaturated raw material remains in the processing liquid as very fine particles and uses a raw material that does not float, thereby removing the suspended SiO ₂ nuclei from the processing liquid. Can be eliminated. Therefore, as will be described later, even if the pore diameter of the circulating fluid filtration filter is increased, unevenness is less likely to occur in the silicon oxide film produced, and the time until the circulation stops due to filter clogging becomes longer. .

The method for manufacturing the silicon oxide film of the present invention is disclosed in Japanese Patent Application Laid-Open No. 57-
196744, JP-A No. 58-161944, it can be applied to the method of manufacturing a silicon oxide film by the usual precipitation method, but in particular, the treatment solution is discharged from the treatment tank in which the substrate is immersed, and the boric acid aqueous solution is discharged. This is particularly effective in a circulating precipitation method in which silicon oxide is added little by little to the solution and circulated to the processing tank to form a supersaturated state of silicon oxide.

The processing liquid used in the present invention is disclosed in Japanese Patent Application Laid-Open No. 57-196744.
Within the concentration range shown in , the concentration of the aqueous solution of hydrosilicofluoric acid is 0.1 to 2.5 mol/, and the amount of boric acid added is 0.01 to 0.025 per mol of hydrosilicic acid.
A range of molar additions is preferred.

By applying the present invention to the circulating precipitation method, the conditions for the circulating precipitation method are such that the amount of circulating liquid per minute relative to the total amount of treated liquid is 3% or more, preferably 6% or more.

The processing liquid circulated in the processing tank is 1.8μm to 10μm
Filter with a filter having a pore size within the range of .

It can be done like this.

If the circulation rate is less than 3%, it will cause the disadvantages mentioned above, and if the circulation rate is too large (for example, a circulation rate of more than 40% of the total treatment liquid volume per minute), the treatment liquid will be severely disturbed on the surface of the substrate to be immersed. This is not preferable because it becomes like a stream and causes unevenness in the silicon oxide film produced by immersion.

In addition, it is preferable that the pore diameter of the filter be as large as possible so that uneven shapes do not appear on the silicon oxide film.
According to the present invention, a filter with a pore diameter larger than 10 μm has an uneven shape (high haze rate).
Since it tends to form a silicon oxide film, use a filter with a diameter of 10 μm or less.

In the present invention, as in Japanese Patent Application No. 58-137217, it is preferable that the treatment liquid flow in a laminar flow parallel to the surface of the substrate to be immersed and treated.

e Examples Example 1 A soda lime glass measuring 100 mm in length, 100 mm in width and 1 mm in thickness was immersed in a 0.5% by weight HF aqueous solution for 10 minutes, then thoroughly washed and dried. Next, a silicon oxide film was formed on the surface of the glass using the immersion tank shown in FIG. 1 in the following manner.

In FIG. 1, the dipping tank consists of an outer tank 1 and an inner tank 2, and water 3 is filled between the inner tank and the outer tank. This water is heated with a heater 4 to a temperature of 35° C., and is stirred with a stirrer 5 to make the temperature distribution uniform. The inner tank consists of a front part 6, a middle part 7, and a rear part 8, and each part is filled with ordinary plate glass powder with a particle size of 0.5 to 2 mm, which is used as a source of silicon oxide to melt and melt silicon oxide.
It is filled with the reaction solution No. 3, which is obtained by diluting a saturated and fractionated aqueous solution of hydrosilicic fluoride acid at a concentration of 2.0 mol/fold with water. First, the circulation pump 10 was activated to pump out a certain amount of the reaction liquid from the rear part 8 of the inner tank, filter it with the filter 11, and start circulating the treated liquid back to the front part 6 of the inner tank.

Thereafter, a 0.5 mol/aqueous boric acid solution 12 was continuously dropped into the rear part 8 of the inner tank and maintained for 10 hours. In this state, the reaction solution became a treatment solution with an appropriate degree of SiO ₂ supersaturation.

Here, the mesh of filter 11 is set to 2.5 μm, and the processing liquid circulation rate is set to 240 ml/min (the total processing liquid volume is approximately 3 μm).
Therefore, the circulation rate was set at 8%/min. Then, the HF-treated glass 9 was immersed vertically into the middle part 7 of the inner tank under the conditions described above (0.5 mol/boric acid aqueous solution was added at 0.2 ml/min, circulated at 8%/min, and filtered through a 2.5 μm filter). (filter) for 4 hours.

The silicon oxide film on the sample glass plate obtained by the above treatment has a thickness of about 1000 Å, and has a haze rate (JlS, K-
6714 (1977) method for measuring the haze value of methacrylic resin plates for aircraft), it was 0.18%.

Comparative Example 1 A silicon oxide film was created under the same conditions as in Example 1, except that industrial silica gel was used as a source of silicon oxide to saturate hydrofluorosilicic acid with silicon oxide.

The obtained silicon oxide film had a molecular weight of about 1000 as in Example 1.
The haze rate was 0.36%.

Comparing the above examples and comparative examples, it can be seen that the deposition rate of the silicon oxide film is the same, and the haze rate of the film obtained in the comparative example is higher than that of the example.

Here, under the example conditions, a silicon oxide film with a lower haze rate was obtained compared to the comparative example conditions, but in the comparative example (conventional method), the example (present invention)
In order to obtain a coating with the same haze ratio as , the filter pore diameter must be made smaller in practical terms. In general, a filter with a smaller diameter is more likely to become clogged under the same filtration conditions; therefore, in the conventional method, the filter becomes clogged more quickly than in the present invention.

f Effects of the Invention According to the present invention, it is possible to produce a good silicon oxide film without unevenness using a filter having a larger pore diameter than conventional filters. Therefore, the time for clogging to occur can be extended, and a more stable silicon oxide film can be produced.

The main purpose of the present invention is to prevent the formation of floating silica gel in a saturated silicon oxide aqueous solution of hydrosilicofluoric acid. 1/2 of the amount of silica gel is first dissolved and then saturated using silicate glass) and embodiments thereof.

[Brief explanation of the drawing]

FIG. 1 is a system explanatory diagram of a circulation type processing apparatus used in Examples and Comparative Examples of the present invention. 1... Outer tank, 2... Inner tank, 3... Water, 4... Heater, 5... Stirrer, 6... Inner tank front, 7...
Center part of inner tank, 8...Rear part of inner tank, 9...Glass, 1
0...Circulation pump, 11...Filter, 12...
...boric acid aqueous solution.

Claims (1)

[Claims] 1. A treatment solution in which boric acid is added to a hydrosilicofluoric acid aqueous solution in which silicon oxide is dissolved to make it supersaturated with silicon oxide is brought into contact with a substrate to form a silicon oxide film on the surface of the substrate. In the manufacturing method, (a) silica glass, as a source of the silicon oxide;
silicate glass or silicate mineral is used, (b) the aqueous solution of boric acid is continuously injected and mixed into the processing solution, and (c) at least 3% of the total amount of the processing solution is mixed with 1.8 to 10 μm per minute. A method for producing a silicon oxide film, characterized in that the treatment solution is filtered through a filter having a pore size within the range of .