JP4208051B2 - Method for producing high refractive index metal oxide thin film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a transparent amorphous metal oxide thin film exhibiting a high refractive index.
[0002]
[Prior art]
Thin films of silicon dioxide exhibiting a low refractive index and thin films of metal oxides such as titanium dioxide and aluminum oxide exhibiting a high refractive index are used for various optical products such as multilayer reflective films, antireflective films, and photonic crystals. ing.
[0003]
Transparent metal oxide thin films have heretofore been manufactured using vapor deposition methods typified by vapor deposition or sputtering. However, the method for producing a transparent metal oxide thin film by vapor deposition is because the production apparatus is complicated, and fine adjustment is required for the production operation, and a relatively long operation time is required. However, it is not an industrially advantageous production method.
[0004]
Therefore, a sol-gel method has been developed as a method for producing a thin film as an alternative to the vapor deposition method. The sol-gel method is a method for producing a metal oxide comprising hydrolyzing a metal alkoxide dissolved in a solvent and then subjecting it to condensation polymerization, and in a relatively short production process with a simple production facility. Since a high-quality metal oxide thin film can be obtained, it is frequently used particularly as a method for producing an optical thin film formed on the surface of an optical product.
[0005]
In Non-Patent Document 1, the reflectance is remarkably obtained by laminating a thin film of titanium dioxide (TiO ₂ ) and a thin film of silicon dioxide (SiO ₂ ) using a sol-gel method as an anti-reflective coating film. There is a description that an antireflection film can be obtained.
[0006]
Non-Patent Document 2 describes an antireflection film formed using nanometer-sized fine particles such as antimony-containing tin oxide and tin-containing indium oxide, so-called ultrafine particles, as a thin film.
[0007]
Non-Patent Document 3 describes the use of a silica airgel thin film in order to increase the light extraction efficiency from the organic electroluminescence (EL) to the outside. In this silica airgel thin film, it is described that the refractive index can be adjusted in the range of 1.10 to 1.01 by changing the density of the silica airgel used.
[0008]
Non-Patent Document 4 introduces a technique for producing a photonic crystal using a method in which a mold is immersed in a titanium dioxide gel generated from a high concentration of alkoxide, followed by drying and baking.
[0009]
[Non-Patent Document 1]
"Application of the sol-gel method" by Sakuo Hana, published by Agne Jofusha 1997 [Non-Patent Document 2]
"Antireflection film using ultrafine particles", O plus E, Vol. 24, No. 11, 1231-1235 (November 2002)
[Non-Patent Document 3]
"Improvement of light emission extraction efficiency using airgel", Japan Society of Applied Physics, 9th Workshop on Organic Molecules and Bioelectronics (2001) "Challenge to next generation organic EL: higher efficiency, longer life , "Full color and drive system" text [Non-Patent Document 4]
Jpn. J. et al. Appl. Phys. , Vol. 41 (2002), p. L291-L293.
[0010]
[Problems to be solved by the invention]
Metal oxidation that can be used as a high-quality optical thin film by using a sol-gel method developed as an industrially advantageous thin film manufacturing method instead of the vapor deposition method. A thin film can be obtained. However, in the methods according to the sol-gel method known so far, an optical thin film having a sufficiently low refractive index has not been obtained even with a silicon dioxide thin film. Similarly, in the methods according to the sol-gel method known so far, an optical thin film having a sufficiently high refractive index cannot be obtained even with a titanium dioxide thin film or an aluminum oxide thin film.
[0011]
It has been reported that the silicon dioxide thin film can be produced as an optical thin film exhibiting a desired low refractive index by utilizing the airgel method. However, the method for producing a thin film by the airgel method is industrial. As a production method that can be used in the field, sufficient studies have not yet been made.
[0012]
As described above, the production of the optical thin film by the sol-gel method known so far and the production of the optical thin film by the airgel method have not reached a sufficiently satisfactory level in terms of industrial production. Furthermore, optical thin films produced by these methods have a problem that sufficient physical strength and surface hardness cannot be obtained. That is, an antireflection film formed on the surface of an optical product such as an electroluminescence (EL) element, particularly an organic electroluminescence element, an optical lens, a display such as a CRT, etc., is often in contact with human hands or external equipment. Therefore, high scratch resistance is required. However, the optical thin film obtained by the sol-gel method or the airgel method, which is a method of adjusting the refractive index by allowing a large number of bubbles to exist inside, has a problem that it is difficult to have sufficiently high scratch resistance due to the presence of the bubbles. is there. For the same reason, there is also a problem that the physical strength such as the bending resistance of the thin film and the heat resistance are low.
[0013]
An object of the present invention is to provide an amorphous metal oxide thin film exhibiting a high refractive index and high scratch resistance.
[0014]
[Means for Solving the Problems]
The present invention provides a metal alkoxide in an alcohol solvent comprising at least one compound selected from the group consisting of a salt of a weak acid and a weak base, a salt of a hydrazine derivative, a salt of a hydroxylamine derivative, and a salt of an acetamidine derivative and water. Non-transparent and containing fine voids inside, comprising hydrolysis in the presence and condensation polymerization to obtain a sol, forming a thin film of the sol, and heating and baking the sol thin film A non-crystalline metal oxide thin film having a refractive index (refractive index of light having a wavelength of λ = 500 nm) of 1.8 or more and a fine void diameter that accounts for 80 vol% or more of the entire fine void is 5 nm or less. A method for producing a crystalline metal oxide thin film.
[0015]
A preferred embodiment of the amorphous metal oxide thin film produced by the method of the present invention is described below.
(1) The diameter of the fine voids occupying 80% by volume or more of the entire fine voids is 2 nm or less.
(2) The diameter of the fine voids occupying 90% by volume or more of the entire fine voids is 2 nm or less.
(3) The metal oxide is an oxide of titanium, an oxide of zirconium, an oxide of aluminum,
It is at least one metal oxide selected from the group consisting of tantalum oxide, hafnium oxide, niobium oxide, and rare earth metal oxide.
[0016]
(4 ) The thickness of the thin film is in the range of 10 nm to 20 μm.
[0017]
In the high refractive index metal oxide thin film produced by the method of the present invention, the volume of the entire fine voids and the ratio (volume%) of the fine voids having a specific diameter mean values measured by the following method.
First, the pore volume per mass per specific diameter is determined by a nitrogen adsorption device. When this is multiplied by the density obtained by the density measuring device, the pore volume per volume per specific diameter is obtained. This is expressed as a percentage, which is the ratio of fine voids per specific diameter.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Next, described the preparation of amorphous high refractive index metal oxide thin film of the present invention, an optical thin film for further use of the thin film, multilayer reflective film, an antireflection film, and the photonic crystal will be described.
[0019]
[Amorphous high refractive index metal oxide thin film]
The high refractive index metal oxide thin film is typically represented by, for example, titanium oxide, zirconium oxide, aluminum oxide, tantalum oxide, hafnium oxide, niobium oxide, and rare earth metal oxide. Formed from a metal oxide or a mixture thereof. A stable metal alkoxide can be obtained, and the metal oxide is not limited to the above metal oxide as long as the metal oxide itself has a high refractive index.
[0020]
Next , the high- refractive-index metal oxide thin film will be described in detail by taking a typical example of titanium oxide (titanium dioxide).
The high refractive index titanium dioxide thin film produced by the method of the present invention has a nanometer level of voids (bubbles) contained therein compared to a titanium dioxide thin film obtained by a conventionally known sol-gel method. The main feature is the size and the remarkably small gap. That is, the titanium dioxide thin film to be produced by the method of the present invention, since a large number of voids in the thin film is present as a very fine voids, titanium dioxide thin film of this, not only shows high transparency The desired high refractive index and high mechanical strength (especially high scratch resistance and high bending resistance) and heat resistance (heat deformation resistance) are exhibited.
[0021]
Such a titanium dioxide thin film is obtained by hydrolyzing titanium alkoxide in an alcohol solvent in the presence of at least one compound selected from the group consisting of a hydrazine hydrochloride derivative, a hydroxylamine derivative, and an acetamidine derivative, and water. can be prepared by utilizing the step of obtaining by condensation polymerization sol, the step of forming the sol into a thin film, and the industrially readily actual 施出 comes method comprising the step of heating and firing the sol film .
[0022]
Titanium alkoxide is hydrolyzed in an alcohol solvent and subjected to condensation polymerization to obtain a sol. The sol is then formed into a thin film, and then the sol thin film is heated and fired. Already known and practically used as a method for producing a titanium dioxide thin film by the gel method.
[0023]
In the manufacturing method of the titanium dioxide thin film by the sol-gel method, tetramethoxy titanium, tetraethoxy titanium, tetra-n-propoxy titanium, tetraisopropoxy titanium, tetra-n-butoxy titanium, tetraisobutoxy titanium, tetra-t-butoxy Tetraalkoxytitanium such as titanium or a derivative thereof is dissolved in a lower aliphatic alcohol solvent such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, etc., and water is added thereto at room temperature. By stirring and mixing with heating as desired, at least a part of tetraalkoxytitanium or a derivative thereof is hydrolyzed, and then a condensation polymerization reaction occurs between the hydrolysates to form a condensation polymer. . Then, it is formed into a thin film in a low-viscosity sol in which the progress of the condensation polymerization is not sufficient.
[0024]
In the production of the amorphous titanium dioxide films according to the present invention, upon hydrolysis and condensation polymerization of titanium alkoxides, salts of weak acids and bases, salts of hydrazine derivatives, salts of hydroxylamine derivatives, and the salts of acetamidine derivatives At least one compound selected from the group (salt catalyst, condensation polymerization accelerator) is present. Examples of the salt of a weak acid and a weak base include ammonium carboxylate (eg, ammonium acetate, ammonium formate), ammonium carbonate, and ammonium bicarbonate. Further, as described above, the hydrazine hydrochloride derivative, the hydroxylamine derivative salt and the acetamidine derivative salt are described in JP-A No. 2000-26849, and in the present invention, the compounds described in the publication are also described. Can be used.
[0025]
In the manufacture of the amorphous titanium dioxide films according to the present invention, by the presence of a condensation polymerization reaction accelerator upon hydrolysis and condensation polymerization of a titanium alkoxide, condensation polymerization of the hydrolyzate of a titanium alkoxide is promoted, in a one-dimensional direction It is considered that a matrix structure in which a polymer chain extends in a three-dimensional direction is preferentially generated rather than a polymer chain extending to generate a long-chain polymer. And it is estimated that the void | hole formed in the condensation polymer to produce | generate becomes a fine void | hole of a molecular order by formation of the matrix structure in which a polymer chain preferentially extends in this three-dimensional direction.
[0026]
The sol obtained by hydrolysis and condensation polymerization of titanium alkoxide is then formed into a thin film. For forming the sol thin film, for example, the sol is uniformly coated on the substrate by a method such as spin coating, or a known method such as a dip coating method in which the substrate is immersed in the sol and then lifted is used. Can be done. The substrate to be used is preferably subjected to surface treatment such as plasma treatment in the presence of oxygen gas.
[0027]
The sol thin film is then heated and fired to obtain an amorphous titanium dioxide thin film which is the object of the present invention. The heating and firing is usually performed at a temperature in the range of 100 to 1100 ° C. In addition, the porosity of the amorphous titanium dioxide thin film to be generated can be adjusted by changing the conditions such as the stirring and mixing temperature and the stirring time at the time of the previous sol formation, or by selecting the temperature of this heating and firing. At the same time, the refractive index can be adjusted.
[0028]
[Antireflection film]
The antireflective film is a light wavelength (λ) for reflecting a high refractive index amorphous metal oxide thin film (eg, titanium dioxide thin film) produced by the above-described method of the present invention on a substrate. (Λ / 4) × n (n is an integer of 1 or more), or a thickness in the vicinity thereof. Incidentally, the amorphous metal oxide film having a high refractive index of this, by laminating a low refractive index metal oxide thin film such as silicon dioxide thin film, it is possible to effectively prevent the reflection of light in a wide wavelength region, Such a configuration is also preferable.
[0029]
An antireflection film made of a high refractive index amorphous metal oxide thin film, and a low refractive index amorphous metal oxide thin film laminated on a thin film made of a high refractive index amorphous metal oxide thin film. forming techniques are well known, also in the formation of the antireflection film according to the present invention, it is possible to use those known in the art.
[0030]
[Multilayer reflective film]
The multilayer reflective film is a multilayer reflective film having a structure in which an amorphous silicon dioxide thin film having a low refractive index and an amorphous metal oxide thin film having a high refractive index are alternately laminated on a substrate. The basic structure of the multilayer reflective film is already known.
[0031]
The high refractive index amorphous metal oxide thin film produced by the method of the present invention can be advantageously used as the high refractive index thin film constituting the multilayer reflective film.
The amorphous silicon dioxide thin film exhibiting a low refractive index is an amorphous silicon dioxide thin film that is transparent and contains a large number of fine voids inside, and has a refractive index (λ = 500 nm light refractive index) of 1. It is preferable to use an amorphous silicon dioxide thin film having a diameter of 5 nm or less in the range of 01 to 1.40 and occupying 80% by volume or more of the entire fine gap.
[0032]
[Photonic crystal ]
A photonic crystal is an optical material used as a waveguide of a laser oscillation element, etc., and a photonic crystal exhibiting desired characteristics by using the method for producing a high refractive index metal oxide amorphous thin film of the present invention. Nick crystals can be manufactured.
[0033]
Specifically, said photonic crystals using an amorphous metal oxide film having a high refractive index, a metal alkoxide such as titanium alkoxide in an alcohol solvent, a salt of a hydrazine derivative, a salt of hydroxylamine derivatives and acetamidine Hydrolysis in the presence of at least one compound selected from the group consisting of derivative salts and water, condensation polymerization to obtain a sol, and coating the sol on the surface of the substrate. obtaining a thin film, the step of superimposing the uneven pattern of the mold into a gel film on the substrate having a predetermined uneven pattern and symmetrical patterned surface, overlapping with a gel-like thin film and the mold heated It can be produced by a method comprising a step of firing and then a step of releasing the fired product from the mold.
[0034]
This manufacturing method will now be described with reference to FIG. 1 of the accompanying drawings.
First, a metal alkoxide is hydrolyzed in an alcohol solvent in the presence of at least one compound selected from the group consisting of a salt of a hydrazine derivative, a salt of a hydroxylamine derivative, and a salt of an acetamidine derivative, and condensation polymerization. To obtain a sol. This sol can be prepared according to the method described above.
Next, this sol is applied to the surface of the substrate 11 using a spin coating method or the like to obtain a sol coating layer. The sol coating layer 12 changes to a highly viscous gel layer 13 over time. Next, the gel layer 13 and a separately prepared mold 14 having a pattern opposite to the waveguide pattern are superposed on the surface. Next, when this laminate is heated and fired, a metal oxide thin film 15 having a predetermined waveguide pattern is formed on the substrate 11. After that, the target photonic crystal is obtained by removing the mold.
[0035]
Alternatively, said photonic crystals using an amorphous metal oxide film having a high refractive index, a metal alkoxide in an alcohol solvent, a salt of a hydrazine derivative, from the group consisting of a salt of a salt of hydroxylamine derivatives and acetamidine derivatives Hydrolysis in the presence of at least one selected compound and water, condensation polymerization to obtain a sol, and the concavo-convex pattern of a mold having a predetermined concavo-convex pattern and a symmetrical concavo-convex pattern on the surface of the sol It can also be produced by a production method comprising a step of applying a film on the surface and heating and baking, and a step of removing the fired product from the mold.
[0036]
【Example】
[Reference Example 1]-Production of amorphous silicon dioxide thin film having a low refractive index Under a nitrogen stream, tetramethoxy silicon (12.5 mmol) and hydroxyacetone (hydrolysis accelerator, 12.5 mmol) were mixed with a solvent ( Methanol containing 62.5 mmol of ion exchange water, 16.15 mL) and mixed. In parallel, ammonium acetate (1.25 mmol) was added to the solvent (methanol, 5 mL) and mixed. Next, these two kinds of mixed solutions were combined and mixed at 25 ° C. for 24 hours to obtain a mixture sol.
[0037]
This mixture sol was applied onto a silicon substrate using a spin coater to form a uniform coating film. Next, this mixed sol coating film was heated and fired at 300 ° C. for 2 hours to obtain a silicon dioxide amorphous thin film having a thickness of 130 nm. The refractive index (500 nm) of this silicon dioxide thin film was 1.16. Moreover, this silicon dioxide thin film contained many fine voids, the porosity was 80%, and the diameter of the fine voids that accounted for 90% by volume or more of the entire fine voids was 2 nm or less. The surface of this silicon dioxide thin film showed high scratch resistance.
[0038]
[Example 1] - under a nitrogen stream of high refractive index titanium dioxide amorphous thin film, tetra -n- butoxy titanium (12.5 mmol) and diethylene glycol (hydrolysis inhibitor, 25 mmol) and the solvent (N-butanol, 7.36 mL) was added and mixed. In parallel with this, ion-exchanged water (reaction initiator, 25 mmol) and hydrazine monohydrochloride (salt catalyst, 0.125 mmol) were added to the solvent (n-butanol, 10 mL) and mixed. Next, these two kinds of mixed solutions were combined and stirred and mixed in an incubator adjusted to 25 ° C. for 2 hours to obtain a mixture sol.
[0039]
This mixture sol was applied onto a silicon substrate using a spin coater to form a uniform coating film. Then, 1 hour at this mixed sol coating 200 ° C., and heating and firing, the thickness was obtained titanium dioxide amorphous thin film of 125 nm. The refractive index (500 nm) of this titanium dioxide thin film was 2.1. Further, this titanium dioxide thin film contained fine voids, and the diameter of the fine voids accounting for 90% by volume or more of the entire fine voids was 2 nm or less. And the surface of this titanium dioxide thin film showed high scratch resistance.
[0040]
Reference Example 2 Production of Multilayer Reflective Film A silicon dioxide amorphous thin film having a thickness of 125 nm was formed on a glass substrate by the method described in Reference Example 1 (however, the firing temperature was changed to 200 ° C.). Formed. Next, a titanium dioxide amorphous thin film having a film thickness of 70 nm was formed on the amorphous thin film by the method described in Example 1 (however, the firing temperature was changed to 700 ° C.). By repeating these operations, a multilayer in which four pairs of laminates (total of 8 layers) composed of a titanium dioxide amorphous thin film (upper layer) and a silicon dioxide amorphous thin film (lower layer) are laminated on a glass substrate. A membrane was obtained. The reflectance (wavelength 700 nm) of this multilayer film was as high as 94.36%.
[0041]
Reference Example 3 Production of Photonic Crystal From a mixture sol obtained from tetra-n-butoxytitanium by the method described in Example 1, a photonic crystal having a waveguide pattern was produced using the method shown in FIG. Obtained. That is, the mixture sol was applied to the surface of the substrate (made of silicon) 11 by a spin coating method to obtain a sol coating layer. This sol coating layer 12 was left for 2 hours to change to a highly viscous gel layer 13. Next, this gel layer 13 and an elastomer mold prepared separately using an elastomer mold having a reverse pattern to the waveguide pattern on the surface (an elastomer mold created using Sylpot 184W / C manufactured by Dow Corning Asia Co., Ltd.) The laminate is heated and fired to form a titanium dioxide thin film 15 having a predetermined waveguide pattern on the substrate 11 by superimposing a mold 14 having a diffraction grating region of 1 mm × 1 mm and a line / space with a period of 600 nm. After that, by removing the mold, a photonic crystal composed of the target titanium dioxide thin film was obtained.
[0042]
【The invention's effect】
According to the present invention, an amorphous metal oxide (eg, titanium dioxide, aluminum oxide) thin film exhibiting a high refractive index, high mechanical strength, and high heat resistance can be provided. This amorphous thin film can be effectively used as a material for forming a multilayer reflective film. In addition, an amorphous metal oxide thin film exhibiting a high refractive index, high mechanical strength, and high heat resistance is useful as an antireflection film material or a photonic crystal material.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining each step of a photonic crystal manufacturing method using a high refractive index thin film of the present invention.
[Explanation of symbols]
11 Substrate 12 Sol coating layer 13 Gel layer 14 Mold 15 Photonic crystal

Claims (1)

A metal alkoxide in an alcohol solvent in the presence of at least one compound selected from the group consisting of a salt of a weak acid and a weak base, a salt of a hydrazine derivative, a salt of a hydroxylamine derivative and a salt of an acetamidine derivative and water. Amorphous metal oxidation comprising a step of hydrolyzing and condensation-polymerizing to obtain a sol, a step of forming a thin film of the sol, and a step of heating and firing the sol thin film and containing fine voids therein An amorphous metal oxide having a refractive index (refractive index of light having a wavelength of λ = 500 nm) of 1.8 or more and a diameter of a fine void that accounts for 80 volume% or more of the entire fine void is 5 nm or less. Method of manufacturing a thin film.

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