JP2003277041A - Method for manufacturing silica thin film on substrate surface having optional surface characteristic and surface form, and composite structural body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a silica thin film having high density and excellent light transmitting property on a substrate having an optional form and surface characteristics, and to provide a method for controlling the surface roughness of the silica thin film. <P>SOLUTION: The method for manufacturing a silica thin film joined to a substrate surface includes processes of: (1) immersing the substrate in a solution comprising a silicon alkoxide, an alcohol, water and an alkali; (2) producing low-density silicate colloid having 1 to 30 nm diameter in the liquid by the hydrolysis of the silicon alkoxide in an alcohol solvent; (3) forming a uniform silica thin film having specified film thickness on the substrate in the liquid by deposition of the colloid on the substrate and by dehydration polycondensation; and (4) keeping the reaction liquid in a dynamic state in the above film deposition process. The invention also discloses a high light- transmitting composite structural body having the silica thin film manufactured by the above method as the surface layer thereof. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a novel silica thin film and a composite structure. More specifically, the present invention relates to a method for forming a thin film on a substrate surface having arbitrary surface characteristics and surface shapes and controlling the film thickness. A new film forming method capable of producing a uniform and high quality silica thin film having a predetermined film thickness on a substrate, and a silica thin film produced by the method as a surface layer. The present invention relates to a composite structure having characteristics such as high translucency, which are included in 1. This silica film is an electrically insulating film, a high-purity protective film that uses high strength, an optical corrugated film that uses high light-transmitting property, a low-reflection coating film that uses low refractive index, and fine defects on the substrate surface. It can be used in various ways as a repair film for repairing and restoring smoothness, an undercoat film for suppressing element diffusion from the substrate, a surface treatment film for modifying the substrate surface to an arbitrary surface roughness, and the like.

[0002]

2. Description of the Related Art Conventionally, for example, a sol-gel method, a sputtering method, an LPD method and the like are well known as chemical methods for forming a silica thin film on the surface of a substrate. Among these, the sol-gel method prepares a partially hydrolyzed stabilized silica sol by adding a reaction catalyst, a stabilizer, etc. to an alcohol solution of silicon alkoxide, and dipping it as a coating solution, spinning, etc. Is applied to the surface of the substrate by the above method, the hydrolysis and the polymerization reaction are carried out on the surface of the substrate, and then the film is formed by heating and baking. The sputtering method is a method of forming a silica thin film on the surface of a substrate by fixing the substrate in a vacuum container and depositing silicon or a silicon compound vaporized by various methods in the container on the surface of the substrate. The LPD method is a method of forming a silica thin film on the surface of a substrate by precipitating silicon fluoride dissolved in the liquid and adhering it to the surface of the substrate by utilizing the change in the degree of supersaturation in an aqueous solution.

However, the following points are pointed out as problems of these conventional techniques. First, the sol-gel method is a method capable of forming a film at a low temperature in a relatively short time.
There is a problem that it is difficult to maintain the uniformity of the film. In addition, organic substances such as stabilizers tend to remain in the silica forming the film, and high temperature firing is required to remove them. Moreover, the acidic gas released during firing has a bad influence on the firing apparatus. In the sputtering method, it is difficult to form a film on a surface having a complicated shape, and the reaction device is complicated and expensive,
There is a problem of high cost. The LPD method has a problem that the process is complicated and water and the like are likely to remain in silica forming a film.

Further, as a method for producing a silica thin film utilizing the hydrolysis of a metal alkoxide, the following can be mentioned. 1) Japanese Unexamined Patent Publication No. 9-295804 "Method for producing silica thin film" However, in the method utilizing hydrolysis of metal alkoxide, 1) no method for strictly controlling the film thickness is proposed, and 2) controlling surface roughness. However, there are problems such as 3) not providing a coating method when the substrate surface is hydrophobic.

[0005]

Under these circumstances, the inventors of the present invention, in view of the above-mentioned prior art, have a new film forming technique capable of drastically solving the problems of the above-mentioned prior art. As a result of earnest research for the purpose of developing, the low-density silicic acid colloid with a diameter of 1 to 30 nm was produced in the liquid by the hydrolysis of silicon alkoxide, and the adhesion to these substrates and the dehydration polycondensation in the liquid The inventors have found that the intended purpose can be achieved by optimizing the film forming processes in step 1 above and controlling those processes, and further researches have led to the completion of the present invention. That is, the present invention is
In order to solve the above-mentioned problems of the prior art, 1) a method for producing a silica thin film capable of forming an amorphous silica thin film on the surface of a substrate having any shape regardless of hydrophilicity or hydrophobicity, 2) surface roughness of the silica thin film It is an object of the present invention to provide a method for controlling the thickness, and 3) a method for strictly controlling the film thickness of the silica thin film by setting the reaction time. Another object of the present invention is to provide a method for forming a uniform and high quality silica thin film on a substrate by the above method. Further, the present invention provides a composite structure having a high light-transmitting property, wherein the silica thin film obtained by the above method is formed on a surface layer of an arbitrary structure to form a composite, and the silica thin film is formed on the surface layer. It is intended.

[0006]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) A method for producing a silica thin film bonded to the surface of a substrate, comprising: (a) immersing the substrate in a solution consisting of silicon alkoxide, alcohol, water and alkali; (b) hydrolysis of silicon alkoxide in an alcohol solvent. To produce a low-density silicic acid colloid with a diameter of 1 to 30 nm in the liquid by (c) by adhering to these substrates and dehydration polycondensation, a silica thin film having a uniform predetermined thickness is formed on the substrate in the liquid. (D) A method for producing a silica thin film, characterized in that the reaction solution is kept in a dynamic state during the film formation process. (2) The method according to (1) above, wherein the silicon alkoxide is at least one selected from the group consisting of silicon tetramethoxide, silicon tetraethoxide, silicon tetraisopropoxide, and silicon tetrabutoxide. (3) The method according to (1) above, wherein the alcohol that is a solvent is at least one selected from the group consisting of methanol, ethanol, and isopropanol. (4) The method according to (1) above, wherein the silica film has a thickness of 1 nm to 10 μm. (5) The method according to (1) above, wherein the reaction solution is kept in a dynamic state by rocking the reaction solution to promote the adhesion of the low-density silicic acid colloid to the substrate. (6) Circulating a solvent, vibrating the substrate,
Alternatively, the method according to (1) above, wherein the reaction solution is kept in a dynamic state by shaking the reaction tank. (7) The method according to (1) above, wherein the surface roughness of the thin film is controlled by setting the hydrophobicity of the substrate surface. (8) The method according to (1) above, in which a predetermined film thickness is obtained by arbitrarily setting a starting time of dipping the substrate and a holding time thereafter. (9) The method according to (1) above, wherein the substrate is a substrate whose surface is hydrophobized by chemical modification represented by fluorine treatment, silicone rubber, acrylic resin, or cellulose. (10) A method for producing a silica thin film, which comprises drying the silica thin film obtained by the method according to any one of (1) to (9). (11) The method according to (10) above, wherein the density of the film is arbitrarily set by heat treatment after drying. (12) A composite structure having high light transmittance, which has a silica thin film obtained by the method according to any one of (1) to (11) above as a surface layer.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in more detail. As a result of various studies on the solutions to the problems in the above-mentioned prior art, the present inventors have found that 1) the precipitation product of amorphous silica due to the hydrolysis of silicon alkoxide has a diameter of several tens nm or less generated in the hydrolysis reaction process. Is a secondary particle as an aggregation stabilizer of the unstable primary particle of 2)
If any object is immersed in the reaction solution in the process of forming the precipitation product, if the surface of the object is hydrophilic, primary particles will adhere to the surface of the object and form a uniform thin film ( 1), 3) The silica thin film thus obtained is
It is dense and has high adhesion and high strength without requiring heating and baking after drying. 4) If the surface of the substrate is hydrophobic, the primary particles and the primary particles aggregate in the reaction solution. The secondary particles generated by the above process adhere to the surface of the substrate with a low probability due to Brownian motion in the solution and van der Waals coupling, and these form a uniform thin film with large surface roughness (Fig. 2). Was found. FIG. 1 schematically shows a process of forming a silica thin film on a substrate having a hydrophilic surface and a smooth thin film obtained thereby. Also, FIG.
Fig. 1 schematically shows a process of forming a silica film on a substrate having a hydrophobic surface and a thin film having a large surface roughness obtained thereby.

The present invention is based on the discovery of such a new fact. The present invention is based on the fact that a substrate is immersed in a solution consisting of silicon alkoxide, alcohol, ammonia and water and kept at a temperature below room temperature. The present invention relates to a novel method for producing a silica thin film, characterized in that silica produced by hydrolysis of silicon alkoxide is attached to the surface of a substrate. Broadly speaking, the present invention provides a method for forming a silica thin film on the surface of a substrate, further a method for controlling the surface roughness by controlling the surface condition of the substrate, and a silica thin film obtained by the method as a surface layer. To provide the composite structure.

In the present invention, the solution consisting of silicon alkoxide, alcohol, water and alkali used for forming a thin film means 1) silicon alkoxide, preferably silicon methoxide, silicon ethoxide, silicon isopropoxide, silicon Butoxide, 2) as a solvent alcohol, preferably methanol, ethanol, isopropanol, butanol, and 3) water required for hydrolysis and an alkali as a catalyst for promoting hydrolysis, preferably , Ammonia. It is preferable that these are mixed in the following concentration ranges. 1) Silicon alkoxide: 0.05 to 0.5 mol /
12) Alkali (ammonia): 0.5 to 5.0 mol /
13) Water: 1-10 mol / l

Next, an outline of the method of the present invention is shown in FIG.
The silica film of the present invention preferably uses silicon alkoxide, alcohol, ammonia and water, and after mixing and stirring a predetermined amount of these, the substrate is immersed therein, and several minutes to several tens of minutes are set at a predetermined temperature. It is made by holding for a time. Whether or not a film is formed on the surface of the substrate is governed by the production rate and polymerization state of silicon acid produced by hydrolysis of silicon alkoxide, and the amount ratio of silicon alkoxide to water in the prepared solution composition. Is important. The formation of the film on the surface of the substrate is due to the transient adhesion of primary particles having a diameter of 1 to 30 nm generated in the hydrolysis reaction process. Therefore, if the surface of the substrate is hydrophilic, the primary particles will adhere to the surface of the object and the film will be uniform, and if the surface of the substrate is hydrophobic, the probability of adhesion of the primary particles will decrease, and the aggregates Because the secondary particles that are
Unevenness occurs on the surface of the film. Therefore, the surface characteristics of the substrate are important for the desired shape of the film surface.

In the present invention, as the substrate, for example, a metal,
Glass such as soda lime glass and silica glass, plastics such as polyethylene and polystyrene, and silicone rubber are used. However, it is not limited to these, and any one may be used. The surface of the substrate may be hydrophilic or hydrophobic. For example, the surface of the substrate may be hydrophobized by subjecting the surface of the substrate to a chemical modification represented by fluorine treatment. The surface condition of the substrate may be smooth or uneven. The optimum mixing ratio of the above components for forming a film on the hydrophobic substrate surface is the mixing ratio for forming monodispersed spherical silica particles as secondary particles in the solvent.

The optimum mixing ratio of the above components for forming a film on the surface of a hydrophilic substrate is 1) the mixing ratio for forming monodispersed silica particles as secondary particles in a solvent, and 2) compared with 1) above. Then, the mixing ratio has a slightly slower hydrolysis rate, that is, the mixing ratio in which the water concentration or the ammonia concentration is lower than the condition under which the monodisperse silica particles as the secondary particles are formed in the solvent. When a uniform film is not formed due to rapid progress of hydrolysis, the hydrolysis can be suppressed by setting the treatment temperature low, and a uniform film can be obtained. Therefore, in the present invention, the silicon alkoxide concentration is not important, and when the silicon alkoxide concentration is lowered, the water concentration or ammonia concentration is increased and a long reaction time is set to form a uniform silica film. be able to.

When the silicon alkoxide concentration is increased, a uniform silica thin film can be formed by lowering the water concentration or the ammonia concentration and lowering the reaction temperature. In the present invention, as described above, as the silicon alkoxide, one or more of silicon methoxide, silicon ethoxide, silicon isopropoxide, and silicon butoxide can be used. As the solvent, one or more of methanol, ethanol, isopropanol and butanol can be used. Among these, silicon tetraethoxide is preferable as the silicon alkoxide, and ethanol or isopropanol is preferable as the solvent. Its concentration is 0.
05-0.5 mol / l, preferably 0.1-0.2 m
ol / l. Water is necessary to cause the hydrolysis of silicon alkoxides and produce silicon acids.
The amount is 1 in a molar ratio with respect to the silicon alkoxide.
The range is from -100.

In the present invention, alkali is necessary as a catalyst for causing hydrolysis of silicon alkoxide to produce silicic acid colloid. In the present invention, ammonia is preferably used as the alkali. The amount is
The molar ratio to the silicon alkoxide is in the range of 1 to 100. The holding temperature of the reaction solution during the film formation process is
It may be below freezing or at room temperature or higher, but is preferably 0 ° C. or higher and 30 ° C. or lower. In this case, the reaction may be carried out in a closed container for the purpose of preventing the solvent from volatilizing. It is necessary to keep the reaction liquid in a dynamic state in order to promote the adhesion of the low-density silicic acid colloid to the substrate. in this case,
As a method for keeping the reaction solution in a dynamic state, shaking the reaction solution, preferably, shaking the reaction tank,
Examples include, but are not limited to, circulating a solvent and vibrating the substrate. Also,
These operating means are not particularly limited, and any means can be used. In the present invention, keeping the reaction solution in a dynamic state is extremely important.
When the reaction solution is allowed to stand, it becomes difficult to optimize the reaction conditions, and it becomes difficult to achieve the intended purpose. In addition, in the present invention, "to be kept in a dynamic state" means
This means keeping the reaction solution in a non-stationary state without leaving it in a stationary state.

In the present invention, by properly setting the reaction conditions, the film formation rate can be expressed as a logarithmic function of the retention time. Further, since the film formation is due to the transient adhesion of the primary particles, the initiation time of the immersion of the substrate in the reaction solution may be any time while the reaction is continued. Therefore, a desired film thickness can be obtained by appropriately setting the start time of immersion and the holding time thereafter. The rate of film formation is proportional to the concentration of silicon alkoxide in the solvent. Therefore, the film thickness can be controlled by adjusting the silicon alkoxide concentration even during the same processing time. By hydrophobizing the surface of the substrate, it is possible to reduce the probability that transient primary particles adhere to the substrate surface, and at the same time increase the probability that secondary particles, which are aggregates of primary particles, adhere to the substrate surface. Therefore, the surface shape of the thin film can be controlled by increasing the hydrophobicity of the substrate surface.
As described above, at this time, as a film forming condition, it is extremely important to keep the reaction solution in a dynamic state. Therefore, in the present invention, shaking of the reaction tank, circulation of the solvent, or vibration of the substrate is required. Is positioned as an important component.

The amorphous silica film obtained by the method of the present invention has a high density in the deposited state, and the drying process can be omitted. Furthermore, by drying at room temperature, sufficient hardness is exhibited. The amorphous silica film obtained by the method of the present invention becomes insoluble in alcohol by drying, and a thicker film can be obtained by repeating this treatment. Further, when this is heated and fired, O remaining inside the structure of the amorphous silica film obtained by the method of the present invention.
The H and alkyl groups can be removed, whereby a thin film made of high-purity amorphous silica can be formed.

The silica film of the present invention has excellent properties such as high translucency, high insulation, high density, and superhydrophobicity (due to hydrophobicity). Therefore, this silica film can be formed on the surface of any structure to form a composite. As a result, a composite structure having the above characteristics can be manufactured. The silica film of the present invention can be used as, for example, an insulating film, a low reflection coating film, an optical corrugated film formation, a light transmission material, an undercoat film, a surface treatment film, or the like, and the silica film is a surface layer thereof. Can be applied to all kinds of composite structures such as films, optical glasses, liquid crystal panels, cathode ray tubes, glass windows, protective covers, materials, electronic parts, and structures.

[0018]

In the present invention, the substrate is immersed in a solution containing silicon alkoxide, alcohol, water and alkali, and the silicon alkoxide is hydrolyzed in an alcohol solvent to produce a low-density silicic acid colloid having a diameter of 1 to 30 nm. Let By holding the reaction liquid in a dynamic state by an arbitrary means in the process of forming the silica thin film, the film formation in the liquid by adhesion to these substrates and dehydration polycondensation can be promoted. As a result, a silica film having a uniform predetermined thickness can be formed on the substrate in the liquid. in this case,
The thickness of the silica film can be controlled by the silicon alkoxide concentration, water concentration, catalyst concentration, treatment temperature, treatment time, number of treatments, and the like. In addition, the surface shape of the thin film can be controlled by increasing the hydrophobicity of the substrate surface. The amorphous silica film produced by the above method has a uniform and high density, and high hardness can be added by drying the amorphous silica film at room temperature. Further, by heating and baking this, a high-purity and high-density amorphous silica film can be obtained. The silica film of the present invention has a property of improving the light transmittance of a glass substrate, for example, as shown in Examples described later.

The deposition of the low-density silicic acid colloid on the substrate and dehydration polycondensation in the present invention will be described. The transient silicon acid generated by the hydrolysis of the silicon alkoxide is repeatedly condensed and redissolved in the liquid. However, among the transient silicic acid colloids formed by condensation, only those colliding with each other and having a small surface area / volume ratio are escaped from re-dissolution and become a solid phase. This transient silicic acid colloid constantly repeats formation and dissolution during the progress of the reaction, and its size is proportional to the supersaturation degree of the dissolved silicic acid. In the present invention, this allows the silica film to be formed on the surface of the substrate by arbitrarily setting the start and duration of immersion of the substrate while the above reaction is in progress. Further, by keeping the reaction solution in a dynamic state by, for example, moving the solution and the substrate relatively,
Even if the surface of the substrate is hydrophobic, it is possible to make the transient silicic acid colloid adhere to the surface of the substrate.

[0020]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to the following examples. Example 1 As a substrate, a silicon substrate having a hydrophilic surface and 1H, 1H, 2H, 2H-perfl having a strongly hydrophobic surface are used.
uorodecyl trimethysilan
A silicon substrate whose surface was chemically modified (fluorine treated) with a monomolecular film was used. A solution of silicon tetraethoxide dissolved in ethanol at a reaction time of 0.11 mol / l and water at a reaction time of 3.0 mol / l
1 and ammonia 1.0 mol / l to prepare a solution in which these were dissolved in ethanol, and the substrate was immersed in the former. While holding the reaction solution in a dynamic state by shaking the former container, after adding the latter to this, the container is sealed with a film and further shaken to keep the reaction solution in a dynamic state. Hold at 20 ° C.

After a lapse of a predetermined time, the substrate was taken out, and 120 ml of ethanol was added to 0.648 of water.
It was washed with the addition of ml and dried at 70 ° C. The thickness of the obtained silica film was examined by an atomic force microscope (AFM). The film thickness was expressed by the following equation as a function of time t (minute) from the reaction time of 60 minutes to 240 minutes (FIG. 4). On untreated silicon plate: d (nm) = 30 log
(T) -8.8 On hydrophobically treated silicon plate: d (nm) = 33 log
(T) -36 Further, the surface roughness of the silica film on the silicon single crystal substrate is R.
The MS roughness was 1 nm. The surface roughness of the fluorine-treated silicon single crystal substrate was RMS roughness of 10 to 14 nm.

Example 2 In Example 1, the substrate was soda lime glass, and both surfaces of the glass plate were covered with an amorphous silica film having a film thickness of 137 nm. The transmittance of this sample was measured with an ultraviolet-visible light spectrophotometer. When compared with the untreated substrate, it was found that the coating of the amorphous silica film improved the light transmittance (FIG. 5).

[0023]

As described in detail above, the present invention relates to a method for producing a novel silica thin film and a composite structure,
According to the present invention, the following special operational effects are exhibited. (1) According to the method for producing a silica thin film of the present invention, an amorphous silica thin film is formed on a substrate having an arbitrary surface characteristic and an arbitrary surface shape by controlling the film thickness to obtain a substrate. A uniform and high-quality silica film having a predetermined film thickness can be formed on the upper surface. (2) If the temperature is equal to or lower than the heat resistant temperature of the substrate, the impurities remaining inside the film can be removed by heating and baking to achieve high purification. (3) This silica thin film uses an electrical insulating film that utilizes electrical insulation, a high-purity protective film that utilizes high strength, an optical corrugated film that utilizes high translucency, and fine irregularities on the surface. It can be used for various purposes such as a low-reflection film and a repair film for repairing fine defects on the surface of a substrate. (4) It is possible to provide a composite structure having a silica thin film obtained by the above method as a surface layer and having high light transmittance.

[Brief description of drawings]

FIG. 1 is a schematic view of a process of forming a smooth film on a substrate according to the present invention.

FIG. 2 is a schematic view of a process of forming a film having a large surface roughness on a substrate according to the present invention.

FIG. 3 shows an overview of the method of the invention.

FIG. 4 shows the relationship between the thickness of the silica film and the reaction time.

FIG. 5 shows the results of measuring the light transmittance of glass with an ultraviolet-visible light spectrophotometer.

Continued front page    F-term (reference) 4F205 AA33 GA08 GB11 GE24 GF01                       GF02 GF05                 4G059 AA08 AC04 AC16 AC20 AC24                       EA05 EB07                 4G072 AA26 AA28 BB09 FF07 GG03                       HH30 JJ11 JJ21 JJ38 MM01                       MM31 MM35 UU30                 5F058 BA20 BC02 BF46 BG10 BH01                       BJ01

Claims (12)

[Claims] 1. A method for producing a silica thin film bonded to a surface of a substrate, which comprises (1) immersing the substrate in a solution consisting of silicon alkoxide, alcohol, water and alkali.
(2) Hydrolysis of silicon alkoxide in an alcohol solvent produces a low-density silicic acid colloid with a diameter of 1 to 30 nm in the liquid. (3) Adhesion to these substrates and dehydration polycondensation on the substrate in the liquid. A silica thin film having a uniform predetermined thickness is formed on (4), and (4) the reaction liquid is kept in a dynamic state during the film formation process. 2. The method according to claim 1, wherein the silicon alkoxide is at least one selected from the group consisting of silicon tetramethoxide, silicon tetraethoxide, silicon tetraisopropoxide, and silicon tetrabutoxide. 3. An alcohol as a solvent is methanol,
The method according to claim 1, wherein the method is at least one selected from the group consisting of ethanol and isopropanol. 4. The method according to claim 1, wherein the thickness of the silica film is 1 nm to 10 μm. 5. The method according to claim 1, wherein the reaction liquid is kept in a dynamic state by rocking the reaction liquid to promote the adhesion of the low-density silicic acid colloid to the substrate. 6. The method according to claim 1, wherein the reaction solution is kept in a dynamic state by circulating a solvent, vibrating the substrate, or shaking the reaction tank. 7. The method according to claim 1, wherein the surface roughness of the thin film is controlled by setting the hydrophobicity of the substrate surface. 8. The method according to claim 1, wherein a predetermined film thickness is obtained by arbitrarily setting a start time of dipping the substrate and a holding time thereafter. 9. A substrate whose surface is hydrophobized by chemical modification represented by fluorine treatment, silicone rubber,
The method according to claim 1, which is an acrylic resin or cellulose. 10. A method for producing a silica thin film, which comprises drying the silica thin film obtained by the method according to any one of claims 1 to 9. 11. The method according to claim 10, wherein the density of the film is arbitrarily set by heat treatment after drying. 12. A composite structure having a high light transmittance, comprising a silica thin film obtained by the method according to claim 1 as a surface layer.