JPS6365621B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for forming a silicon oxide film on the surface of a substrate. More specifically, the present invention relates to an improvement in a method of forming a silicon oxide film on the surface of a substrate by immersing the substrate in a treatment solution prepared by adding boric acid to a saturated silicon oxide aqueous solution of hydrofluorosilicic acid. Nowadays, coating the surfaces of various materials with silicon oxide films is widely practiced. For example, it has long been practiced to reduce the reflection effect of the surface by forming alternating multilayer films of titanium oxide and silicon oxide on the glass surface. Alternatively, it is widely practiced to form a silicon oxide film on the surface of metal/alloy materials as a protective film. Furthermore, when alkali-containing glasses such as soda lime glass or borosilicate glass are used for substrate glass for liquid crystal display panels and solar cells, the surfaces of these glasses are coated with a silicon oxide film in order to prevent the elution of alkaline components from the glass. Coating is performed. In particular, preventing the elution of alkaline components from glass has become an indispensable technology for maintaining the lifespan of liquid crystal displays or solar cells. To form a silicon oxide film on the surface of glass, many methods such as vacuum evaporation, sputtering, CVD, and dip coating have been used. However, these methods have the disadvantage that the equipment or ancillary equipment is expensive, which increases the cost required for coating with silicon oxide, and that only small pieces of glass can be processed. In view of these shortcomings of conventional silicon oxide film forming methods, a new method for forming silicon oxide films has been proposed using a treatment solution in which boric acid is added to a silicon oxide saturated aqueous solution of hydrosilicofluoric acid (JP-A-57 −196744). However, although this method requires simple equipment and is capable of forming a silicon oxide film on large pieces of glass, increasing the amount of boric acid added to the processing solution to increase the rate of formation of the film causes oxidation. The drawback was that the haze rate of the silicon coating was high. Furthermore, if the amount of boric acid added is large, a precipitate of silicon oxide is formed in the treatment solution, which causes a rapid decrease in the rate of film formation, resulting in a loss of effectiveness of the treatment solution. In view of these problems, the present inventors conducted intensive research and found that by circulating the treatment liquid and introducing a filtration step during this period, even if the amount of boric acid was increased, that is, the rate of silicon oxide film formation could be increased. It has also been found that the haze rate of the coating does not increase, and furthermore, it is possible to prevent precipitation from occurring in the processing solution. That is, the present invention provides a method for forming a silicon oxide film on the surface of a substrate by immersing the substrate in a treatment solution in which boric acid is added to a saturated silicon oxide aqueous solution of hydrosilicofluoric acid, including (a) treatment step. This is a continuous processing process that consists of continuously pumping out a certain amount of the processing liquid from the immersion tank, filtering it continuously with a filter, and returning it to the immersion tank. The ratio of the amount of processing solution circulated per minute to the amount of solution is 3% or more, and (c) and the necessary amount of boric acid is made into an aqueous solution and continuously injected into the processing solution.
It is characterized by mixing. In this case, the filter mesh preferably has a diameter of 1.5 microns or less; if the diameter is larger than this, it is difficult to obtain the desired haze rate. In addition, in the continuous circulation treatment process, it is effective to set the ratio of the amount of circulating processing liquid per minute to the total amount of processing liquid in a range of 3% or more. If this rate of circulation is too small, the time it takes for the treatment liquid to circulate through one cycle becomes longer, and as a result, silicon oxide precipitates in the treatment liquid during this time, easily clogging the filter. In other words, continuous processing becomes impossible. Thus, by adding boric acid to a saturated silicon oxide aqueous solution of hydrosilicofluoric acid, the solution becomes supersaturated with silicon oxide, and therefore, when left for a long time, silicon oxide precipitates in the treatment solution. For this reason, appropriate filtration intervals are required for the processing liquid. The amount of boric acid is 1.2×10 ^-2 to 2 per mol of hydrosilicofluoric acid.
It is desirable that the amount is ×10 ^-2 mol. In addition, the flow of the treatment liquid in the immersion tank must be a laminar flow parallel to the surface of the substrate, and turbulent flow is not preferable because it will cause unevenness and uneven thickness of the silicon oxide coating. Furthermore, in this case, the relative speed of the flow of the treatment liquid to the substrate surface is
If the speed is too high, the film formation rate decreases, which is not preferable. In addition, in the present invention, the base material is not only glass but also ceramics, metals (iron plate, silicon base material, etc.),
Alternatively, it may be an organic material (plastic material). Examples of the present invention will be described below. Example 1 A soda lime glass with a size of 100 (mm) x 100 (mm) and a thickness of 1 (mm) was immersed in a 0.5% concentration (wt%) HF aqueous solution for 10 minutes, then thoroughly washed and dried. did. Next, the glass was immersed in the immersion bath shown in FIG. The immersion 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. In the experiment, the water was heated with a heater 4 so that the temperature of this water was 35° C., and was 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 2.0mol/silicon oxide.
It is filled with a treatment solution prepared by mixing a concentrated aqueous solution of hydrosilicic fluoric acid and an aqueous solution of boric acid with a concentration of 0.5 mol/concentration in a volume ratio of 25:1. The aforementioned HF-treated glass 9 is vertically immersed and held in the center portion 7 of the inner tank.
The processing liquid in the rear part 8 of the inner tank is pumped out in fixed amounts by a circulation pump 10, passed through a filter 11, and returned to the front part 6 of the inner tank. In this circulation system, the total amount of processing liquid is 3, and at the rear of the inner tank is pumped at a rate of 0.1ml/min.
A boric acid aqueous solution 12 with a concentration of 0.5 mol/min is continuously added dropwise. Under these conditions, the filter mesh
The silicon oxide obtained by using 0.6μ, 1.2μ, 1.5μ, 2.5μ and no filter (i.e. conventional method) and changing the circulation rate of the treatment liquid to 60, 90, 120, 240ml/min for each filter. The film formation speed and haze rate (%) were compared. The haze ratio was measured and compared with the thickness of the silicon oxide film being set to 1400 Å. The results are shown in Tables 1 and 2, and the size of the filter mesh is 1.5 microns or less.
Regarding the rate of circulation flow rate, when the circulation rate is 90 ml/min, that is, the circulation rate per minute is 3% or more of the total amount of treated liquid, the haze rate (%) can be reduced to 0.5% or less.
That is, the effects of the present invention can be seen in Tables 1 and 2.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a circulation system showing an embodiment 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)

[Scope of Claims] 1. A method for producing a silicon oxide film on the surface of a substrate by immersing the substrate in a treatment solution in which boric acid is added to a saturated silicon oxide aqueous solution of hydrosilicofluoric acid. ) A boric acid aqueous solution is continuously injected and mixed into the processing liquid, and (b) 3% or more of the total amount of processing liquid is continuously filtered through a filter every minute and returned to the processing liquid. A method for producing a silicon oxide film. 2. Production of a silicon oxide film according to claim 1, wherein the treatment liquid in the immersion tank in which the substrate is immersed in the treatment liquid flows in a laminar flow parallel to the surface of the immersed substrate. Method.