JP2002088304A - Silica-based coating agent, method for producing thin silica film and thin silica film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a silica-based coating agent capable of giving a strong and thin silica film prepared by a sol-gel method and generating little cracks through drying and heat treating at <=200 deg.C, and to form the thin silica film and to provide a structural body having the silica film. SOLUTION: This silica-based coating agent contains a silica sol obtained by hydrolyzing and condensing at least one species selected from a tetraalkoxysilane having 1-3C alkyls, its hydrolyzed product and its oligomer and having 85,000-500,000 weight average molecular weight. The thin silica film is provided by the sol-gel method and has <=35 deg. contact angle with water on the surface of the film. The structural body has this thin silica film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silica-based coating agent, a method for producing a silica thin film using the same, a silica thin film, and a structure having the silica thin film. More specifically, the present invention provides a strong silica thin film prepared by a sol-gel method and hardly generating cracks by low-temperature heat treatment at 200 ° C. or less and having a small film thickness shrinkage during drying and heat treatment. The present invention relates to a silica-based coating agent, a method for producing a silica thin film using the coating agent, a silica thin film obtained by a sol-gel method having the above performance, and a structure having the silica thin film.

[0002]

2. Description of the Related Art Conventionally, silica-based coatings are excellent in heat resistance, abrasion resistance, corrosion resistance, etc., and therefore, for example, an insulating film between a semiconductor substrate and a metal wiring layer in a semiconductor element, an insulating film between metal wiring layers, and a semiconductor. Coating for flattening unevenness caused by metal wiring layer provided on substrate, between glass substrate and ITO (indium tin oxide) film in liquid crystal display cell, between transparent electrode and alignment film, etc. It is widely used as an insulating film to be provided.

[0003] Various methods are known as a method for forming such a silica-based coating film. In general, a sol-gel method capable of producing a silica film having high purity is often used. This sol-gel method is a method of dissolving alkoxysilane in an organic solvent mainly composed of alcohol, hydrolyzing and condensing to prepare a coating solution, applying the coating solution, and heat-treating to form a silica film. is there. In such a sol-gel method, a heat treatment of at least 600 ° C. or more is required to obtain a dense glassy silica film.

On the other hand, a hard coat film having a good surface hardness and excellent scratch and abrasion resistance is, for example,
It is widely used for attaching surfaces such as window glasses and window plastic boards of vehicles and buildings, or for protecting CRT displays and flat panel displays. In addition, plastic lenses have been rapidly spread in recent years because they are lighter and more excellent in safety, processability, fashionability, and the like than glass lenses. However, this plastic lens has a drawback that it is easily damaged as compared with a glass lens, and therefore, its surface is coated with a hard coat layer.

As a material for such a hard coat film or a hard coat layer provided on a plastic lens, a silica-based coating agent by a sol-gel method is generally used. However, in this case, since it is applied to an organic base material, high-temperature heat treatment of the coating film is impossible, and the heat treatment is usually performed at a temperature of 200 ° C. or less. As a result, it is difficult to form a dense and strong silica film, and the alkoxyl group of the alkoxysilane as a raw material often remains in the film. Often causes.

As a technique for forming a silica film by firing at a low temperature, for example, an alcoholic silica sol prepared by hydrolyzing a lower alkyl silicate in methanol or ethanol is coated and heat-treated at a low temperature of room temperature to 100 ° C. Thus, it is disclosed that a strong film can be formed (JP-A-6-52796). However, in the examples described in this publication, since the concentration of the alkyl silicate is low and the reaction time is as short as 5 hours, the sol growth is insufficient and the film shrinkage after film formation is large. And unevenness may occur during film formation.

[0007]

SUMMARY OF THE INVENTION Under the above circumstances, the present invention has been prepared by a sol-gel method, and
In a low-temperature heat treatment at 0 ° C. or lower, there is almost no occurrence of cracks, and a silica-based coating agent that provides a strong silica thin film having a small film thickness shrinkage during drying and heat treatment, a method for producing a silica thin film using this coating agent, It is an object of the present invention to provide a silica thin film obtained by the sol-gel method having the above performance, and a structure having the silica thin film.

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, have found that cracks and the like are generated in the silica film with the elimination of the residual alkoxyl group over time. In order to suppress the hydrolysis and hydrolysis in the sol-gel reaction, a silica precursor having a small number of alkoxyl groups is produced at the time of condensation, and by adjusting the molecular weight of the precursor to a certain range, only a heat treatment is performed at a temperature of 200 ° C. or less. , A strong silica film free of cracks and the like can be obtained, and by making the water contact angle of the film surface after film formation a certain value or less, the residual alkoxyl group will be reduced, and the alkoxyl group It is possible to suppress the occurrence of cracks due to desorption with the lapse of time, further, after film formation, by reducing the film shrinkage when heat treatment under specific conditions to a certain value or less, after film formation When the change is small, cracks film is also in a heat cycle test was found to not occur.

The present invention has been completed based on such findings. That is, the present invention provides: (1) General formula (I) Si (OR) ₄ ... (I) (wherein, R represents an alkyl group having 1 to 3 carbon atoms, and the four ORs are the same or different. ), At least one selected from oligomers that are partial hydrolysates and condensates thereof, represented by the formula (1), and having a weight average molecular weight of 85,000 to 500. (2) a method for producing a silica thin film, which comprises applying the silica-based coating agent to a substrate surface, followed by drying and heat treatment;
(3) a silica thin film obtained by a sol-gel method, wherein the water contact angle of the film surface is 35 ° or less; (4) a silica-based coating agent of the above (1). It is intended to provide a structure characterized by having a silica thin film formed by using the same, and (5) a structure characterized by having a silica thin film of the above (3).

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the silica-based coating agent of the present invention, a tetraalkoxysilane represented by the general formula (I) Si (OR) ₄ ... (I) is used as a raw material. In the general formula (I), R is an alkyl group having 1 to 3 carbon atoms, specifically, a methyl group, an ethyl group, an n-propyl group and an isopropyl group. The four ORs may be the same or different. When R has 4 or more carbon atoms, the hydrolyzability is poor, and it is difficult to obtain a silica sol having a desired weight average molecular weight, and the water contact angle of the obtained film surface is also hard to be 35 ° or less.

Examples of the tetraalkoxysilane represented by the general formula (I) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, ethoxytrimethoxysilane, propoxytrimethoxysilane, and isopropoxy. Trimethoxysilane, methoxytriethoxysilane, propoxytriethoxysilane, isopropoxytriethoxysilane, methoxytripropoxysilane, ethoxytripropoxysilane, diethoxydimethoxysilane, dimethoxydipropoxysilane, and the like. Methoxysilane and tetraethoxysilane are preferable in terms of hydrolyzability and availability. In the present invention, these tetraalkoxysilanes may be used, a partial hydrolyzate thereof may be used, and an oligomer which is a hydrolytic condensate thereof may be used. Alternatively, a mixture thereof can be used.

The hydrolysis and condensation reactions are carried out in an appropriate polar solvent such as alcohol, ketone or ether using an acid such as hydrochloric acid, sulfuric acid or nitric acid, or a cation exchange resin as a solid acid. C., preferably at a temperature of 20 to 40.degree. C., to form a silica sol having a weight average molecular weight in the range of 85,000 to 500,000. The weight average molecular weight of this silica sol is 85,0
If it is less than 00, the resulting silica film has a water contact angle of less than 35 ° on the film surface, has a large film shrinkage after film formation, and cracks occur with the passage of time. On the other hand, when the weight average molecular weight exceeds 500,000, the solubility in a solvent is reduced, a uniform silica sol is hardly formed, and a desired coating agent cannot be obtained. The weight average molecular weight is a value in terms of polystyrene measured by a gel permeation chromatography (GPC) method.

When the solid acid is used after the completion of the hydrolysis and condensation reactions, it is removed, and then the concentration in terms of SiO ₂ is preferably 0.5 to 15% by weight, more preferably 1 to 15% by weight.
The silica-based coating agent of the present invention is prepared by diluting with an appropriate polar solvent such as alcohol, ketone, ether or the like so as to be in the range of 10 to 10% by weight.

The silica-based coating agent of the present invention thus obtained is applied to a suitable substrate surface,
The water contact angle of the film surface after the drying treatment for 1 hour is usually 35 ° or less, preferably 30 ° or less, more preferably 2 ° or less.
5 ° or less. When this water contact angle exceeds 35 °,
The amount of alkoxyl groups derived from tetraalkoxysilane as a raw material remaining in the film is large, and cracks and the like are likely to occur as the alkyl groups are eliminated over time. Further, the shrinkage of the film thickness obtained by the method described below also increases.

Further, the silica-based coating agent of the present invention is applied to a silicon wafer surface, dried at 80 ° C. for 1 hour, and then heat-treated at 500 ° C. for 30 minutes. , Preferably 12% or less. If the shrinkage exceeds 15%, cracks occur in a heat cycle test described later. That is, cracks are likely to occur over time.

In the method for producing a silica thin film of the present invention, the above-mentioned silica-based coating agent is applied to the surface of a substrate, followed by drying and heat treatment to form a silica thin film. In this case, as the base material, any of an inorganic base material and an organic base material can be used. However, in the present invention, the organic base material having low heat resistance is dried and heat-treated at a temperature of 200 ° C. or lower. Especially useful for 2
A strong silica thin film free from cracks and the like can be obtained even when dried and heat-treated at a temperature of 00 ° C. or less.

At this time, as a coating method, for example, a known method such as dip coating, spin coating, spray coating, bar coating, knife coating, roll coating, blade coating, die coating, gravure coating, etc. Means can be used. The thickness of the formed silica thin film is usually 1 μm or less, preferably 0.01 to
It is 0.7 μm, more preferably in the range of 0.05 to 0.5 μm.

When an organic substrate is used, it may be subjected to a surface treatment by an oxidation method or a roughening method, if desired, in order to improve the adhesion to the silica thin film. Examples of the oxidation method include corona discharge treatment, chromic acid treatment (wet method), flame treatment, hot air treatment, ozone / ultraviolet irradiation treatment, and examples of the unevenness method include a sand blast method and a solvent treatment method. Is mentioned. These surface treatment methods are appropriately selected according to the type of the base material. In addition, the organic substrate in the present invention has a material other than the organic material, for example, a metal-based material, a glass or ceramic-based material, and a surface of a substrate made of other various inorganic or metal-based materials, having an organic-based coating film. Also encompasses

The present invention also provides a silica thin film obtained by a sol-gel method and having a surface water contact angle of 35 ° or less, preferably 30 ° or less, more preferably 25 ° or less. I do. This silica thin film of the present invention
The shrinkage of the film thickness when the film dried at 1 ° C. for 1 hour is heat-treated at 500 ° C. for 30 minutes is usually 15% or less, preferably 12% or less. The silica thin film of the present invention having the above-mentioned properties has little change with the passage of time, and no crack is observed even when a heat cycle test described later is performed.

The present invention further provides a structure having a silica thin film formed by using the above-mentioned silica-based coating agent and the above-mentioned sol-gel method, wherein the surface has a water contact angle of 35 ° or less, preferably Also provides a structure having a silica thin film of 30 ° or less, more preferably 25 ° or less. In the former structure, the method of the present invention can be applied to the formation of a silica thin film.

[0021]

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 Tetramethoxysilane was added to 2-methoxyethanol so as to have a concentration of 16% by weight in terms of SiO _{2 and an} aqueous solution of 0.1 mol / l nitric acid so that the amount of water was 6 times mol of tetramethoxysilane. This was reacted at 30 ° C. for 24 hours. This solution was diluted with dimethylformamide (DMF) and subjected to gel permeation chromatography (GP).
C, carrier: DMF, calibration curve substance: polystyrene)
When the molecular weight was measured, the weight average molecular weight was 9600.
It was 0. This solution was added in an amount of ₂ % by weight as
It was diluted with 2-methoxyethanol to give a weight%. A 2% by weight solution was applied on a silicon wafer and a 4% by weight solution was applied on an acrylic substrate and a glass substrate at 3000 r.
The substrate was spin-coated at pm for 30 seconds and dried at 80 ° C. for 1 hour.

<Evaluation of Silicon Wafer Deposition Sample>
The measured water contact angle was 20 °. Next, this film was subjected to an ellipsometer (DVA-36V manufactured by Mizojiri Optical Industrial Co., Ltd.).
It was 75.9 nm when the film thickness was measured using W). After heating this at 500 ° C. for 30 minutes, the film thickness was measured again, and it was 70.0 nm, and the film thickness shrinkage was 7.8%.

<Evaluation of Acrylic Substrate and Glass Substrate Film-Formed Samples>
A 5-cycle endurance test was performed in which one cycle was 2 hours, temperature lowered to -20 ° C / 2 hours, -20 ° C / 2 hours, and temperature raised to 70 ° C / 2 hours. After that, when the surface condition was confirmed, no cracks or the like were found in the silica film on any of the substrates.

Example 2 MS-51 (an oligomer of tetramethoxysilane, manufactured by Colcoat Co., Ltd.) was converted to a SiO ₂ concentration of 16% by weight.
A 0.1 mol / liter nitric acid aqueous solution was added to methyl ethyl ketone so as to be 4 times the mole of water of MS-51. This was reacted at 30 ° C. for 24 hours. Transfer this solution to DM
After dilution with F, the molecular weight was measured by gel permeation chromatography (GPC, carrier: DMF, calibration curve substance: polystyrene). As a result, the weight average molecular weight was 154,800. This solution was diluted with 2-methoxyethanol so as to be 2% by weight and 4% by weight in terms of SiO ₂ . A 2% by weight solution was spin-coated on a silicon wafer and a 4% by weight solution was spin-coated on an acrylic substrate and a glass substrate at 3000 rpm for 30 seconds.
Dried for 1 hour at ° C.

<Evaluation of Silicon Wafer Deposition Sample>
The measured water contact angle was 16 °. Next, this film was subjected to an ellipsometer (DVA-36V manufactured by Mizojiri Optical Industrial Co., Ltd.).
It was 73.3 nm when the film thickness was measured using W). After heating at 500 ° C. for 30 minutes, the film thickness was measured again, and it was 66.1 nm, and the film thickness shrinkage was 9.8%.

<Evaluation of Acrylic Substrate and Glass Substrate Deposition Samples> Using a heat cycle tester, 70 ° C. /
A 5-cycle endurance test was performed in which one cycle was 2 hours, temperature lowered to -20 ° C / 2 hours, -20 ° C / 2 hours, and temperature raised to 70 ° C / 2 hours. After that, when the surface condition was confirmed, no cracks or the like were found in the silica film on any of the substrates.

Example 3 Tetramethoxysilane was added to 2-propanol at a concentration of 16% by weight in terms of SiO ₂ , and a 1 mol / liter nitric acid aqueous solution was added to 2-propanol so that the molar amount of water was 6 times mol of tetramethoxysilane. This was reacted at 30 ° C. for 24 hours. This solution was diluted with DMF, and the molecular weight was measured by gel permeation chromatography (GPC, carrier: DMF, calibration curve substance: polystyrene). As a result, the weight average molecular weight was 340,500. This solution is mixed with SiO ₂
It was diluted with 2-methoxyethanol so as to be 2% by weight and 4% by weight in conversion. A 2 wt% solution was spin-coated on a silicon wafer and a 4 wt% solution on an acrylic substrate and a glass substrate at 3000 rpm for 30 seconds and dried at 80 ° C. for 1 hour.

<Evaluation of Silicon Wafer Deposition Sample>
The measured water contact angle was 22 °. Next, this film was subjected to an ellipsometer (DVA-36V manufactured by Mizojiri Optical Industrial Co., Ltd.).
When the film thickness was measured using W), it was 99.6 nm. After heating at 500 ° C. for 30 minutes, the film thickness was measured again. As a result, it was 89.8 nm and the film thickness shrinkage was 9.8%.

<Evaluation of Acrylic Substrate and Glass Substrate Film-Formed Samples>
A 5-cycle endurance test was performed in which one cycle was 2 hours, temperature lowered to -20 ° C / 2 hours, -20 ° C / 2 hours, and temperature raised to 70 ° C / 2 hours. After that, when the surface condition was confirmed, no cracks or the like were found in the silica film on any of the substrates.

COMPARATIVE EXAMPLE 1 Tetraethoxysilane was added to 2-propanol so as to have a concentration of 16% by weight in terms of SiO _{2 and an} aqueous solution of 0.1 mol / liter nitric acid which was 4 times the molar amount of tetraethoxysilane. This was reacted at 30 ° C. for 24 hours. This solution was diluted with DMF, and the molecular weight was measured by gel permeation chromatography (GPC, carrier: DMF, calibration curve substance: polystyrene) to find that the weight average molecular weight was 72,200. This solution is mixed with SiO ₂
It was diluted with 2-methoxyethanol so as to be 2% by weight and 4% by weight in conversion. A 2 wt% solution was spin-coated on a silicon wafer and a 4 wt% solution on an acrylic substrate and a glass substrate at 3000 rpm for 30 seconds and dried at 80 ° C. for 1 hour.

<Evaluation of Silicon Wafer Deposition Sample>
The measured water contact angle was 38 °. Next, this film was subjected to an ellipsometer (DVA-36V manufactured by Mizojiri Optical Industrial Co., Ltd.).
The film thickness was measured using W) and found to be 234.6 nm. After heating this at 500 ° C. for 30 minutes, the film thickness was measured again and found to be 185.2 nm and the film thickness shrinkage was 21.1%.

<Evaluation of Acrylic Substrate and Glass Substrate Film-Formed Samples>
A 5-cycle endurance test was performed in which one cycle was 2 hours, temperature lowered to -20 ° C / 2 hours, -20 ° C / 2 hours, and temperature raised to 70 ° C / 2 hours. After that, when the surface state was confirmed, cracks and the like were confirmed in the silica film in each of the substrates.

Comparative Example 2 Tetraethoxysilane was added to methyl ethyl ketone such that the concentration of SiO ₂ was 16% by weight and an aqueous solution of 0.1 mol / liter nitric acid was water having a molar concentration of 4 times the amount of tetraethoxysilane. This was reacted at 30 ° C. for 24 hours.
This solution was diluted with DMF, and the molecular weight was measured by gel permeation chromatography (GPC, carrier: DMF, calibration curve substance: polystyrene).
The weight average molecular weight was 82,900. This solution is converted to SiO
_It was diluted with 2-methoxyethanol so as to be 2% by weight and 4% by weight in terms of 2. A 2 wt% solution was spin-coated on a silicon wafer and a 4 wt% solution on an acrylic substrate and a glass substrate at 3000 rpm for 30 seconds and dried at 80 ° C. for 1 hour.

<Evaluation of Silicon Wafer Deposition Sample>
The measured water contact angle was 37 °. Next, this film was subjected to an ellipsometer (DVA-36V manufactured by Mizojiri Optical Industrial Co., Ltd.).
The film thickness was measured using W) and found to be 184.6 nm. After heating this at 500 ° C. for 30 minutes, the film thickness was measured again and found to be 153.6 nm, with a film thickness shrinkage of 16.8%.

<Evaluation of Acrylic Substrate and Glass Substrate Deposition Samples>
A 5-cycle endurance test was performed in which one cycle was 2 hours, temperature lowered to -20 ° C / 2 hours, -20 ° C / 2 hours, and temperature raised to 70 ° C / 2 hours. After that, when the surface state was confirmed, cracks and the like were confirmed in the silica film in each of the substrates.

COMPARATIVE EXAMPLE 3 Tetramethoxysilane was added to 2-propanol at a concentration of 16% by weight in terms of SiO ₂ , and a 1 mol / liter aqueous solution of nitric acid was converted to water having a molar ratio of 20 times that of tetramethoxysilane. This was reacted at 30 ° C. for 48 hours. This solution was diluted with DMF, and the molecular weight was measured by gel permeation chromatography (GPC, carrier: DMF, calibration curve substance: polystyrene). As a result, the weight average molecular weight was 550,000. This solution is converted to SiO
_An attempt was made to prepare a coating solution by diluting with 2-methoxyethanol so as to be 2% by weight and 4% by weight in terms of 2.
A precipitate was formed, and a coating solution composed of a uniform silica sol was not obtained, and film formation was impossible.

[0038]

The silica-based coating agent of the present invention is prepared by a sol-gel method and has almost no cracks when subjected to a low-temperature heat treatment at 200 ° C. or lower.
A strong silica thin film having a small film thickness shrinkage during drying and heat treatment is applied to both organic and inorganic substrates. Especially, it can be suitably applied to an organic substrate having low heat resistance.

The silica-based coating agent of the present invention can be used, for example, as a material for a hard coat layer provided on a hard coat film or a plastic lens, as well as a material for an insulating film or a flattening film in a semiconductor element, or an insulating film in a liquid crystal display cell. Are preferably used.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01L 21/768 H01L 21/90 K (72) Inventor Norihiro Nakayama 2-1-1 Yabuta Nishi, Gifu City, Gifu Prefecture No. Ube Nitto Kasei Co., Ltd. F term (reference) 4D075 BB24Y BB24Z BB28Z BB93Y BB93Z BB95Y BB95Z CA02 CA03 CA18 CA23 CA33 CA37 CA50 DA06 DA23 DB01 DB13 DB14 DB43 DC01 DC11 DC22 DC24 EA07 EB43 EB47 EB52 H07 EB47 EB52 EB47 EB52 EB47 LL11 MM31 MM36 NN21 PP17 RR05 UU01 4J038 AA011 DL021 HA441 LA02 MA14 NA11 PA19 PB09 5F033 GG03 GG04 QQ00 QQ74 RR09 RR25 SS00 SS03 SS22 WW00 WW03 XX01 XX12 XX17

Claims (9)

[Claims] 1. General formula (I) Si (OR) ₄ ... (I) wherein R represents an alkyl group having 1 to 3 carbon atoms, and four ORs may be the same or different. ), A silica sol having a weight average molecular weight of 85,000 to 500,000, obtained by hydrolyzing and condensing at least one selected from tetraalkoxysilanes, partial hydrolysates thereof and oligomers which are condensates thereof. A silica-based coating agent comprising: 2. The silica-based coating agent according to claim 1, wherein the silica-based coating agent has a water contact angle of 35 ° or less on a film surface obtained by applying the composition to a substrate surface and drying at 80 ° C. for 1 hour. 3. Applying to a silicon wafer surface at 80 ° C.
3. The silica-based coating agent according to claim 1, wherein a shrinkage ratio of the film thickness when heat-treated at 500 ° C. for 30 minutes after drying for 1 hour is 15% or less. 4. A method for producing a silica thin film, comprising applying a silica-based coating agent according to claim 1, 2 or 3 to a surface of a substrate, followed by drying and heat treatment. 5. A silica thin film obtained by a sol-gel method, wherein the water contact angle of the film surface is 35 ° or less. 6. A membrane dried at 80 ° C. for 1 hour is treated with 50
The silica thin film according to claim 5, wherein a shrinkage ratio of the film thickness when heat-treated at 0 ° C for 30 minutes is 15% or less. 7. A structure comprising a silica thin film formed by using the silica-based coating agent according to claim 1, 2, or 3. 8. The structure according to claim 7, wherein the silica thin film is formed by the method according to claim 4. 9. A structure comprising the silica thin film according to claim 5 or 6.