JP7410431B2 - Thin film forming materials, optical thin films, and optical members - Google Patents

Description

The present invention relates to a thin film manufacturing method, a thin film forming material, an optical thin film, and an optical member.

The lens surfaces of cameras and telescopes are coated with a thin film to reduce reflected light. When trying to obtain the effect of reducing reflected light with a single layer film, an optical thin film having a refractive index close to the square root of the refractive index of the object to be coated is formed on the outermost surface of the object to be coated. It is effective to do so. In order to obtain an antireflection effect over a wide range of wavelengths, it is necessary to form a multilayer film. Even in such a multilayer film, in order to enhance the antireflection effect against obliquely incident light, a thin film having a refractive index lower than the square root of the object to be coated is required.

In order to obtain a thin film with a refractive index lower than the square root of the material to be deposited, it is useful to include air with a refractive index of 1.0 in the thin film, and air can be incorporated by various methods including the sol-gel method. Optical thin films have been proposed.
For example, Patent Document 1 describes, in order from the glass substrate side, a first layer mainly composed of alumina formed by vacuum evaporation, and a group consisting of MgF ₂ and SiO ₂ formed by vacuum evaporation. An antireflection film is described that includes a second layer made of at least one selected material and a third layer made of an aggregate of mesoporous silica nanoparticles on the second layer.
Furthermore, Patent Document 2 describes that an inorganic base layer made of an inorganic material, a surface modified layer containing an inorganic oxide such as SiO ₂ , and an acrylic resin etc. laminated on the surface modified layer are formed on a base material. An antireflection film is described that includes an adhesive layer containing a binder and a low refractive index layer formed by hollow silica particles bound together by a binder.
Patent Document 3 discloses that a mixture of a sol liquid in which magnesium fluoride (MgF ₂ ) fine particles are dispersed and an amorphous silicon oxide binder solution is applied to a base material and heat-treated. A method for manufacturing an optical thin film in which MgF ₂ fine particles are bound together by an amorphous silicon oxide binder and a large number of voids are formed between the MgF ₂ fine particles is described.

JP2010-38948A JP2015-222450A International Publication No. 2006/030848

However, the optical thin films or antireflection films described in Patent Documents 1 to 3 are formed by gelling a sol containing fine particles and a binder using a sol-gel method. Formation of a thin film using this sol-gel method is performed in the atmosphere, so if the layer below the top layer is formed in a vacuum, foreign matter is likely to be adsorbed when exposed to the atmosphere to perform the sol-gel method, making it difficult to remove foreign matter. There are problems that need to be done. In addition, in order to precisely control the film thickness, it is necessary to strictly control the change in sol viscosity over time, and the viscosity of the sol must be constantly monitored while forming a thin film, which makes manufacturing complicated. It may happen. Furthermore, when applying sol to the object to be coated using the dip coating method, an excessive amount of sol is required, and when applying the sol to the object to be coated using the spin coating method, it is difficult to apply the sol to a curved surface with a uniform thickness. There is also the problem.

Therefore, one embodiment of the present invention aims to solve the above-mentioned problems and provide a method for manufacturing an optical thin film with a low refractive index, a thin film forming material, an optical thin film, and an optical member.

The present invention includes the following forms.
A first embodiment of the present invention includes a step of depositing a thin film-forming material on an object to be film-formed by physical vapor deposition in a non-oxidizing atmosphere to form a vapor-deposited film, and depositing the vapor-deposited film at a pH of 2.5 or more to pH 3. 5 or less to obtain a first thin film having voids, the thin film forming material includes indium oxide and silicon oxide; is 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide.

The second embodiment of the present invention is a mixture containing indium oxide and silicon oxide, in which indium oxide is contained in a range of 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide. This is a characteristic thin film forming material.

A third embodiment of the present invention is an optical thin film containing silicon oxide and having a refractive index of 1.300 or less.

A fourth embodiment of the present invention is an optical thin film containing silicon oxide, coated with silica, and having a refractive index of 1.380 or less.

A fifth embodiment of the present invention is an optical member having the optical thin film and a film-forming object.

According to one embodiment of the present invention, it is possible to provide a method for manufacturing a low refractive index optical thin film, a thin film forming material, an optical thin film, and an optical member.

FIG. 1 is a scanning electron microscope (SEM) photograph of the surface of the optical thin film of Example 1 of the present invention. FIG. 2 is a SEM photograph of a cross section of the optical thin film of Example 1 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical thin film manufacturing method, thin film forming material, optical thin film, and optical member according to the present disclosure will be described below. However, one embodiment shown below is an illustration for embodying the technical idea of the present invention, and the present invention is limited to the following optical thin film manufacturing method, thin film forming material, optical thin film, and optical member. Not done.

Method for manufacturing a thin film One embodiment of the present invention includes a step of depositing a thin film forming material on an object to be deposited by physical vapor deposition in a non-oxidizing atmosphere to form a deposited film, and depositing the deposited film at a pH of 2.5. contact with a first acidic solution containing an acidic substance having a pH of 3.5 or less to obtain a thin film having voids, the thin film forming material containing indium oxide and silicon oxide; This is a method for producing a thin film using a mixture containing indium in a range of 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide.

Thin film forming material A thin film forming material according to an embodiment of the present invention contains indium oxide and silicon oxide, and indium oxide is contained in a range of 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide. It is a mixture.

Indium oxide used as a raw material for the thin film forming material is preferably indium (III) oxide (In ₂ O ₃ ). Indium (III) oxide (In ₂ O ₃ ) may contain inevitable impurities. In the indium (III) oxide (In ₂ O ₃ ) used as a raw material, the content of indium (III) oxide (In ₂ O ₃ ) is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably It is 99% by mass or more.

The silicon oxide used as the raw material for the thin film forming material preferably has silicon monoxide (SiO) as its main component. In this specification, "containing silicon monoxide (SiO) as a main component" means that the content of silicon monoxide (SiO) in the silicon oxide of the raw material is 50% by mass or more. The content of silicon monoxide (SiO) in the raw material silicon oxide is more preferably 80% by mass or more, still more preferably 90% by mass or more, even more preferably 99% by mass or more.

The thin film forming material is a mixture containing indium (III) oxide (In ₂ O ₃ ) and silicon oxide as raw materials, and silicon monoxide (SiO) as the main component of the silicon oxide. The content of indium (III) (In ₂ O ₃ ) is in the range of 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide. Using this thin film forming material, a vapor deposited film containing silicon dioxide (SiO ₂ ) and indium (I) oxide (In ₂ O) is formed on an object by physical vapor deposition in a non-oxidizing atmosphere. I can do it. The deposited film may contain trace amounts of indium (III) oxide (In ₂ O ₃ ) and/or indium (In). Indium (III) oxide (In ₂ O ₃ ) contained in the thin film forming material is dissociated into indium (I) oxide (In ₂ O), indium (In), and oxygen (O) by heating. Silicon monoxide (SiO) contained in the thin film forming material has a standard free energy of formation for oxidation of silicon monoxide (SiO) which is lower than that of indium (I) oxide (In ₂ O). It preferentially reacts with oxygen (O) to produce silicon dioxide (SiO ₂ ). Even when a deposited film is formed using a thin film forming material in a non-oxidizing atmosphere, oxygen (O) dissociated from indium (III) oxide (In ₂ O ₃ ) preferentially converts to silicon monoxide (SiO ) to produce silicon dioxide (SiO ₂ ). Therefore, almost no silicon monoxide (SiO) remains in the deposited film. The first thin film (optical thin film) obtained by contacting the deposited film with the first acidic solution does not absorb visible light derived from silicon monoxide (SiO), which has a black body color. In addition, oxygen (O) dissociated from indium (III) oxide (In ₂ O ₃ ) contained in the thin film forming material is absorbed by silicon monoxide (SiO) to generate silicon dioxide (SiO ₂ ), so it is dissociated. The formation of indium (III) oxide (In ₂ O ₃ ) due to further oxidation of the indium (I) oxide (In ₂ O) can be suppressed. Indium (I) oxide (In ₂ O) has very high solubility in acidic substances, so indium (I) oxide (In ₂ O) can be dissolved by bringing the deposited film into contact with a first acidic solution containing an acidic substance. ) can be preferentially eluted to obtain a first thin film (optical thin film) having voids satisfying a desired refractive index and having a skeleton composed of silicon dioxide (SiO ₂ ).

Indium (In) produced by dissociation of indium (III) oxide (In ₂ O ₃ ) is the amount of indium (In) gas contained in the atmosphere dissociated from indium (III) oxide (In ₂ O ₃ ). is about 3 to 5% by volume (``Thermodynamics of Oxides'' by I. S. Kulikov, Nisso Tsushinsha, p. 146, 1987), and when it is contained in an extremely small amount in the atmosphere during the formation of a deposited film. There is.

When indium (In) is present in the vapor dissociated from indium (III) oxide (In ₂ O ₃ ), there is a standard formation freedom in which indium (In) oxidizes to indium (III) oxide (In ₂ O ₃ ). Since the energy is even lower than the standard free energy of formation of silicon monoxide (SiO) to oxidize to silicon dioxide (SiO ₂ ), indium (III) oxide (In ₂ O ₃ ) may be included in the deposited film.

However, using a thin film forming material containing indium oxide (In ₂ O ₃ ) and silicon oxide (SiO), in which indium oxide is contained in a range of 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide. The formed vapor deposited film contains only a trace amount of indium (III) oxide (In ₂ O ₃ ) and/or indium (In), as will be described later.
If indium (III) oxide (In ₂ O ₃ ) is present in the deposited film, even if a transparent first thin film is obtained by contacting the deposited film with the first acidic solution, this When the first thin film is further immersed in a strongly acidic solution with a pH of 2.0 or less, the refractive index of the first thin film decreases. When the refractive index of the first thin film brought into contact with the strong acid solution decreases, it can be confirmed that indium (III) oxide (In ₂ O ₃ ) remains in the first thin film. When the deposited film contains indium (In), when the deposited film is brought into contact with the first acidic solution, the color of the thin film changes from black to gray and then becomes transparent, indicating that it remains. This can be confirmed.

When the molar ratio of indium (III) oxide (In ₂ O ₃ ) contained in the thin film forming material is less than 0.230 to 1 mole of silicon oxide, the indium (III) oxide (In 2 O ₃ ) in the thin film forming material is less than 0.230 per mole of silicon oxide. O ₃ ) is too small, and unoxidized silicon monoxide (SiO) remains in the deposited film. If silicon monoxide (SiO) remains in the deposited film, the silicon monoxide (SiO) will not be eluted even if the deposited film is brought into contact with the first acidic solution, and the silicon monoxide (SiO) will not be eluted in the resulting first thin film (optical thin film). Silicon monoxide (SiO), which has a black body color, remains. If silicon monoxide (SiO) remains in the first thin film (optical thin film), the first thin film (optical thin film) will cause high absorption of visible light derived from silicon monoxide (SiO). Furthermore, if unoxidized silicon monoxide (SiO) remains in the deposited film, silicon monoxide (SiO) will not be eluted from the deposited film even if the deposited film is brought into contact with the first acidic solution, so that desired voids will be formed. This makes it difficult to form a first thin film (optical thin film) having voids that satisfy a desired refractive index.

When the molar ratio of indium (III) oxide (In ₂ O ₃ ) contained in the thin film forming material exceeds 0.270 to 1 mole of silicon oxide, the amount of indium (III) oxide (In ₂ O ₃ ) So much indium (I) oxide (In ₂ O) and/or indium (In) is generated in the deposited film that the oxidation eluted when the deposited film is brought into contact with the first acidic solution. If the amount of indium (I) (In ₂ O) and/or indium (In) is too large, there will be too many voids, and the first thin film (optical thin film) composed of silicon dioxide (SiO ₂ ) as a skeleton. The strength of the first thin film decreases, and the first thin film easily peels off from the object to be coated. In addition, excess oxygen generated by dissociation from excess indium (III) oxide (In ₂ O ₃ ) causes indium (I) oxide (In ₂ O) and/or indium (In) to become indium (III) oxide ( There is a possibility that the refractive index of the first thin film may increase due to oxidation to In ₂ O ₃ ).

The molar ratio of indium (III) oxide (In ₂ O ₃ ) contained in the thin film forming material is in the range of 0.230 mol to 0.270 mol, preferably 0.240 mol to 1 mol of silicon oxide. 0.270 mol or less, more preferably 0.240 or more and 0.265 or less, still more preferably 0.250 or more and 0.260 or less, even more preferably 0.252 The range is from 0.258 to 0.258.

The thin film forming material contains indium (III) oxide (In ₂ O ₃ ) and silicon oxide (SiO, SiO ₂ ), with indium oxide being 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide. It is preferable that the raw material mixture be mixed to obtain a raw material mixture, press-molded to form a molded product, and then fired to obtain a sintered mixture (sintered body). By using a sintered mixture (sintered body) as a thin film forming material, the thin film forming material is almost uniformly vaporized by the physical vapor deposition method, and the thin film forming material is vaporized almost uniformly by the thermal decomposition of indium (III) oxide (In ₂ O ₃ ). A vapor deposition film containing a substantially uniform mixture of indium (I) oxide (In ₂ O) and silicon dioxide (SiO ₂ ) can be deposited substantially uniformly on the surface of the object.

The molded product obtained by press-molding the raw material mixture is preferably fired in an inert atmosphere. The inert atmosphere means an atmosphere containing argon (Ar) and helium (He) as main components. An inert atmosphere may necessarily contain oxygen as an impurity, but in this specification, an atmosphere is defined as an inert atmosphere if the concentration of oxygen contained in the atmosphere is 15% by volume or less. The concentration of oxygen in the inert atmosphere is preferably 10% by volume or less, more preferably 5% by volume or less, even more preferably 1% by volume or less. The concentration of oxygen in the inert atmosphere is preferably as low as possible, even more preferably 0.1% by volume or less, particularly preferably 0.01% by volume or less, and most preferably 0.001% by volume or less (10% by volume or less). ). By firing the solid material obtained by press-molding the raw material mixture in an inert atmosphere, the thin film forming material can be made to contain as little excess oxide as possible.

The temperature at which the raw material mixture is fired to form a sintered body is preferably 500°C or more and 900°C or less, more preferably 600°C or more and 880°C or less, and still more preferably 700°C or more and 850°C or less. When the temperature at which the raw material mixture is fired exceeds the upper limit, metallic indium (In) reduced from indium (III) oxide (In ₂ O ₃ ) is dissolved and evaporated to obtain a thin film forming material with the desired composition. I can't. If the temperature at which the raw material mixture is fired is below the lower limit, the strength of the sintered body obtained by firing will be insufficient, and the sintered mixture (sintered body), which is the thin film forming material, will crack due to thermal stress during vapor deposition. There are concerns. If the sintered body, which is the thin film forming material, cracks during vapor deposition, the amount of evaporation will change significantly, making it impossible to form a stable vapor deposited film.

Step of Forming a Vapor Deposited Film In a manufacturing method according to an embodiment of the present invention, a thin film forming material is deposited on an object to be film-formed by physical vapor deposition in a non-oxidizing atmosphere to form a vapor deposited film.

Examples of the physical vapor deposition method include electron beam evaporation, resistance heating evaporation, ion plating, and sputtering. Among these, it is preferable to use an electron beam evaporation method or a resistance heating evaporation method, and it is more preferable to use an electron beam evaporation method. The electron beam evaporation method or the resistance heating evaporation method can uniformly form a deposited film even on a large area or a curved surface with a small radius of curvature. Furthermore, the electron beam evaporation method has high thermal efficiency because the thin film forming material is directly irradiated with an electron beam to heat it, and even thin film forming materials such as oxides with a high melting point and low thermal conductivity can be vaporized efficiently. A deposited film having a stable composition based on the composition of the thin film forming material can be formed on the object in a relatively short time. Further, the deposited film may be formed using ion assist. When using ion assist, an ion source is provided to assist during the formation of a vapor deposited film, and an ion gun (ion beam) is used to accelerate and irradiate gas ions onto the object to be deposited while forming the vapor deposited film. Ion-beam assisted deposition (IAD) may also be used. Preferably, the ion source for ion beam assist is an inert gas ion source. Inert gas ions for ion beam assist include Ar ions and He ions, preferably Ar ions.

Silicon monoxide (SiO) contained in the thin film forming material is a black oxide, so when a vapor-deposited film is formed in a non-oxidizing atmosphere, silicon monoxide (SiO), which has a black body color, is mixed into the vapor-deposited film. In some cases, a thin film using this vapor-deposited film cannot be used as an optical thin film. Despite this, we decided to form a vapor deposited film in a non-oxidizing atmosphere because silicon monoxide (SiO) is preferentially reacted with oxygen to generate silicon dioxide (SiO ₂ ), and it also reacts with acidic solution. This is because the formation of indium (III) oxide (In ₂ O ₃ ), which has low solubility, can be suppressed. Silicon monoxide (SiO) is more easily oxidized than indium (I) oxide (In ₂ O), so it is oxidized by oxygen dissociated from indium (III) oxide (In ₂ O ₃ ) contained in the thin film forming material. Silicon (SiO) is preferentially oxidized to silicon dioxide (SiO ₂ ). On the other hand, indium (I) oxide (In ₂ O) is difficult to oxidize, and indium (III) oxide (In ₂ O ₃ ), which is obtained by oxidizing indium (I) oxide (In ₂ O), is difficult to generate.

The non-oxidizing atmosphere during the formation of the deposited film may be any one or more of an inert atmosphere, a reducing atmosphere, and a vacuum. The inert atmosphere refers to an inert atmosphere if the concentration of oxygen contained in the atmosphere is 15% by volume or less, similar to the inert atmosphere in which a molded product obtained by press-molding the raw material mixture is fired. The reducing atmosphere refers to an atmosphere whose main component is a mixed gas containing hydrogen, carbon monoxide, and the like. Vacuum refers to an atmosphere with a pressure of 1.0×10 ⁻⁵ Pa or more and 1.0×10 ⁻² Pa or less. In this specification, vacuum refers to an inert gas such as argon (Ar) gas or helium (He) gas, which is the main component of an inert atmosphere, or a mixed gas containing hydrogen, carbon monoxide, etc. An atmosphere in which the pressure is 1.0×10 ⁻⁵ Pa or more and 1.0×10 ⁻² Pa or less, and the oxygen concentration is 15% by volume or less, without introducing oxygen. When the non-oxidizing atmosphere is a vacuum, the majority of the gaseous components in the atmosphere are water vapor.
When the non-oxidizing atmosphere during the formation of the deposited film is a reducing atmosphere containing a mixed gas containing hydrogen and carbon monoxide or a vacuum, the molar ratio of indium oxide (In ₂ O ₃ /SiO) to silicon oxide is relatively low. Even if the amount of oxygen in the vapor generated from the thin film forming material increases, the amount of oxygen in the atmosphere increases faster than the indium (I) oxide (In ₂ O) generated from the thin film forming material oxidizes. Hydrogen or carbon monoxide contained in the mixed gas, or hydrogen contained in vacuum, oxidizes preferentially, suppressing the formation of indium (III) oxide (In ₂ O ₃ ) in the deposited film. I can do it.

The oxygen concentration in the non-oxidizing atmosphere at the time of forming the deposited film may be 15% by volume or less, preferably 10% by volume or less, more preferably 5% by volume or less, still more preferably 1% by volume or less. In order to obtain the first thin film having the desired refractive index, the concentration of oxygen in the non-oxidizing atmosphere when forming the vapor deposition film is preferably as low as possible, even more preferably 0.1% by volume or less, particularly preferably It is 0.01 volume % or less, most preferably 0.001 volume % or less (10 volume ppm or less). If the oxygen concentration in the non-oxidizing atmosphere during the formation of the deposited film is high, the generated indium (I) oxide (In ₂ O) and/or indium (In) will be oxidized again by the oxygen in the atmosphere, and the deposited film will be Indium (III) oxide (In ₂ O ₃ ) is generated in the deposited film, and even if the deposited film is brought into contact with the first acidic solution, indium (III) oxide (In ₂ O ₃ ) is not eluted and remains in the deposited film. may remain, making it impossible to obtain a thin film with a desired low refractive index. Indium (III) oxide (In ₂ O ₃ ) has a relatively high refractive index of about 2.0, and if indium (III) oxide (In ₂ O ₃ ) remains in the deposited film, the desired low refractive index will be reduced. It is not possible to obtain a thin film having . On the other hand, if the oxygen concentration in the non-oxidizing atmosphere at the time of vapor deposition film formation is low, the indium (I) oxide (In ₂ O) generated from the thin film forming material will be regenerated by the oxygen in the atmosphere because there is less oxygen in the atmosphere. Oxidation can be suppressed, and generation of indium (III) oxide in the deposited film can be suppressed.

The pressure of the non-oxidizing atmosphere during the formation of the deposited film varies depending on the type of physical vapor deposition method used. When electron beam evaporation is used as the physical vapor deposition method, the atmospheric pressure when forming the vapor deposited film on the object is preferably 1.0×10 ⁻⁵ Pa or more and 5.0×10 ⁻² Pa or less, more preferably 1.0×10 ⁻⁵ Pa or more and 1.0×10 ⁻² Pa or less, and even more preferably 5.0×10 ⁻⁵ Pa or more and 1.0×10 ⁻² Pa or less. If the non-oxidizing atmosphere is a vacuum, the pressure of the vacuum atmosphere without introducing an inert gas or mixed gas into the atmosphere may be 1.0 × 10 ^-5 Pa or more and 1.0 × 10 ^-2 Pa or less. Bye. When the atmospheric pressure during vapor deposition film formation is within the above range, it is possible to suppress the indium (I) oxide (In ₂ O) generated from the thin film forming material from being oxidized again by oxygen in the atmosphere, and the vapor deposition Generation of indium (III) oxide (In ₂ O ₃ ) in the film can be suppressed. The pressure of the non-oxidizing atmosphere during the formation of the deposited film can be controlled, for example, by introducing an inert gas such as argon or a mixed gas into the deposition apparatus.

In the manufacturing method of one embodiment of the present invention, the object to be film-formed may be made of glass or plastic. Examples of the glass include optical glass. Examples of plastics include polyester-based, acrylic-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, and polyolefin-based resins. The form of the object to be film-formed may be, for example, a flat plate-like or lens-like substrate having a curved surface, or a flexible sheet. Since the manufacturing method of one embodiment of the present invention enables the formation of a deposited film even at a relatively low temperature, it is possible to form an optical thin film with a low refractive index even on a deposition target made of a material with low heat resistance. can do.

A step of bringing the deposited film into contact with a first acidic solution A manufacturing method according to an embodiment of the present invention includes: bringing the deposited film into contact with a first acidic solution containing an acidic substance having a pH of 2.5 or more and a pH of 3.5 or less; The method includes a step of obtaining a first thin film having voids.

As a thin film forming material, a mixture containing indium oxide and silicon oxide, in which indium oxide is present in an amount of 0.230 mol or more and 0.270 mol or less per 1 mol of silicon oxide, is used to form a film on the object by physical vapor deposition. The formed deposited film contains silicon dioxide (SiO ₂ ) and indium (I) oxide (In ₂ O). Among the substances constituting these deposited films, indium (I) oxide (In ₂ O) and/or indium (In) have very high solubility in acidic substances, so they are Even if the substance is a weakly acidic substance, indium (I) oxide (In ₂ O) and/or indium ( By preferentially eluting In), it is possible to obtain a first thin film (optical thin film) having voids satisfying a desired refractive index and having a skeleton composed of silicon dioxide (SiO ₂ ).

Even if the deposited film is laminated with a film having a composition different from that of the deposited film in order to form a multilayer film, the acidic substance contained in the first acidic solution is a weakly acidic substance. Therefore, indium (I) oxide (In ₂ O) and/or indium (In) in the deposited film can be eluted to form a silicon dioxide (SiO ₂ ) skeleton without affecting films of other compositions. A first thin film (optical thin film) having a desired porosity can be obtained. The composition of the film laminated on the vapor-deposited film includes, for example, a composition containing alumina.

The first thin film (optical thin film) obtained by the manufacturing method of one embodiment of the present invention is made of indium (I) oxide (In ₂ O) that is easily eluted by contacting the deposited film with a first acidic solution. And/or almost all indium (In) can be eluted from within the deposited film, and by eluting indium (I) oxide (In ₂ O) and/or indium (In), silicon dioxide (SiO ₂ ), which becomes the skeleton, can be eluted. It is possible to form an optical thin film having a first thin film having a high porosity and a low refractive index by creating voids therebetween.

The deposited film may contain indium (III) oxide (In ₂ O ₃ ) and/or indium (In), but even in that case, the indium (III) oxide (In ₂ O ₃ ) and/or the amount of indium (In) is such that the refractive index of the first thin film decreases by approximately 0.01 after the first thin film is brought into contact with a strongly acidic solution having a pH of 2.0 or less. It is a trace amount. The extremely small amount that causes the refractive index of the first thin film to decrease by about 0.01 means that a very small amount of indium (III) oxide (In ₂ O ₃ ) and a very small amount of dioxide (SiO ₂ ) are desorbed and This is an amount that increases the porosity of the thin film No. 1 by about 3%.
A part of silicon dioxide (SiO ₂ ) in the deposited film is surrounded by indium (I) oxide (In ₂ O) and/or indium (In), and silicon dioxide surrounded by this indium (I) oxide A part of (SiO ₂ ) may also come off from the deposited film at the same time as indium (I) oxide (In ₂ O) and/or indium (In) is eluted from the deposited film. When the first thin film _is brought into contact with a strong acidic solution having a pH of 2.0 or less, indium ( _I ) oxide (In ₂ O ) and/or a very small amount of silicon dioxide (SiO ₂ ) surrounded by indium (In) is desorbed, the refractive index of the first thin film decreases by about 0.01, and the porosity increases by about 3%. .

Indium (I) oxide (In ₂ O) has a black body color, and if indium (I) oxide (In ₂ O) remains in the first thin film (optical thin film), it absorbs visible light. . For example, by measuring the absorption rate {100 - (transmittance + reflectance)} of a thin film with a spectrophotometer, it can be seen that when a thin film absorbs visible light, the absorption rate of the thin film increases; If so, it can be confirmed that indium (I) oxide (In ₂ O) and/or indium (In) remains in the thin film.

Examples of the acidic substance contained in the first acidic solution include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid, citric acid, and oxalic acid. The acidic substance is preferably an acid that has a buffering effect and has a plurality of acid dissociation constants, and weakly acidic substances such as citric acid and oxalic acid are more preferable. An acid without a buffering effect tends to increase the pH and therefore tends to require a long acid treatment time.

The pH of the first acidic solution is in the range of pH 2.5 or more and pH 3.5 or less, preferably in the range of pH 2.7 or more and pH 3.2 or less. If the pH of the solution containing an acidic substance is less than 2.5, the adhesion between the obtained first thin film and the object to be coated will be low, and the first thin film will not be formed after contacting with the solution containing an acidic substance. It may peel off from the film. When the pH of the first acidic solution exceeds 3.5, the dissolution rate of indium (I) oxide (In ₂ O) and/or indium (In) contained in the deposited film becomes slow, and indium oxide (In ₂ This is not preferable because it takes time to completely elute O) and/or indium (In), which reduces production efficiency.

Room temperature is sufficient for the temperature at which the deposited film is brought into contact with the first acidic solution, and the room temperature is in the range of 15°C to 28°C, preferably in the range of 15°C to 25°C. The higher the temperature at which the deposited film is brought into contact with the first acidic solution, the more the elution of indium (I) oxide (In ₂ O) and/or indium (In) in the deposited film can be promoted, and the contact time can be shortened. This is preferable in terms of manufacturing. If the temperature is too high, the solvent of the first acidic solution will evaporate and the pH will drop, so a closed container or equipment to constantly monitor and adjust the pH is required, which reduces manufacturing costs. There is a risk that the price will rise. If it is too low, a cooling device may be required, which may increase manufacturing costs.
The time for which the vapor deposited film is brought into contact with the first acidic solution may be any time that the entire thin film becomes transparent.

The method of bringing the vapor deposited film into contact with the first acidic solution is generally a method of immersing the object on which the vapor deposited film has been formed in the first acidic solution, or a method of bringing the vapor deposited film formed on the object into the film into contact with the first acidic solution. One example is a method of immersing only the first acidic solution in the first acidic solution. In the method of immersing the deposited film in the first acidic solution, indium (I) oxide (In ₂ O) and/or indium (In) in the deposited film is eluted after a predetermined period of time. Indium (I) oxide (In ₂ O) and/or indium (In) in the deposited film is eluted, and in some cases, indium dioxide covered with indium (I) oxide (In ₂ O) and/or indium (In) is dissolved. A thin film having voids is obtained by eluting silicon (SiO ₂ ) together with indium (I) oxide (In ₂ O) and/or indium (In).

First Thin Film: Optical Thin Film The first thin film manufactured by the method of one embodiment of the present invention is an optical thin film containing silicon oxide and having a refractive index of 1.300 or less. The first thin film (optical thin film) is made of indium (I) oxide (In 2 O) from a deposited film containing silicon dioxide (SiO ₂ ) and indium (I) oxide (In ₂ O) and/or indium (In) _. It is an optical thin film having a refractive index of 1.300 or less, having voids formed by elution of indium (In), and having a silicon dioxide (SiO ₂ ) skeleton. The first thin film (optical thin film) preferably has a refractive index of 1.250 or less, more preferably 1.200 or less, and even more preferably 1.170 or less. In the first thin film (optical thin film), indium (I) oxide (In ₂ O) and/or indium (In) constituting the deposited film are eluted to form a large number of voids, and the silicon dioxide remaining without being eluted is formed. (SiO ₂ ) serves as a skeleton. The first thin film may contain an extremely small amount of indium (III) oxide (In ₂ O ₃ ) in addition to silicon dioxide (SiO ₂ ) that constitutes the skeleton, and the content is equal to or less than the first thin film. This is the amount by which the refractive index of the first thin film after being treated with the acidic solution is brought into contact with a strong acidic solution having a pH of 2.0 or less by about 0.01.

Since the first thin film, which is an optical thin film, has a refractive index of 1.300 or less, the antireflection effect can be enhanced over the entire visible region.
The refractive index of an optical thin film is determined by measuring the reflection spectrum with a spectrophotometer, measuring the minimum value of the reflected light intensity when the incident light intensity is 100, and calculating the Fresnel coefficient from the minimum value of the measured reflectance. It can be calculated using

The first thin film having voids, which is an optical thin film, preferably has a porosity in a range of 30% or more and 90% or less. If the porosity of the first thin film is 30% or more, the refractive index of the thin film can be lowered, and if it is 90% or less, it has the strength to maintain the thin film formed on the object to be film-formed. The refractive index of the thin film can be lowered. The first thin film, which is an optical thin film, has a porosity that is more preferably 40% or more and 90% or less, still more preferably 50% or more and 90% or less, and even more preferably 60% or more and 85% or more. % or less. The porosity (total porosity Vp) of the optical thin film can be determined using the Lorenz-Lorenz formula based on the examples described later.

Step of obtaining a second thin film in which the first thin film is coated with silica A manufacturing method according to an embodiment of the present invention includes coating the surface of the first thin film with a silica coat forming material and then heat-treating the surface of the first thin film. The method includes the step of obtaining a thin film of No. 2. The second thin film is formed by coating the first thin film formed on the object to be coated with silica, and includes the first thin film and silica coating the first thin film. In the manufacturing method according to an embodiment of the present invention, heat treatment is performed after coating the surface of the first thin film with a silica coat forming material so that a silica coat is formed on the entire first thin film having voids. is preferred.

The silica coat forming material preferably contains silicon alkoxide. The silica coat is preferably formed by a sol-gel method. The silicon alkoxide is preferably a silane compound having two or more alkoxyl groups, specifically dimethyldiethoxysilane, diethyldiethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, phenyltriethoxysilane, 3- It is preferable to use at least one selected from the group consisting of glycidoxypropyltrimethoxysilane (GPTMS), tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), tetraisopropoxysilane, and tetrabutoxysilane.

In order to improve film formation, the silica coat forming material preferably contains a solvent. Examples of solvents include alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and isophorone. Examples include: One type of solvent may be used alone, or two or more types may be used in combination. The silica coat forming material preferably contains a silicon alkoxide and a solvent, and further preferably includes a second acidic solution.

The manufacturing method according to an embodiment of the present invention includes, when the silica coat forming material contains silicon alkoxide, adding a second acidic solution to the silica coat forming material in order to hydrolyze the silicon alkoxide, The pH of the second acidic solution is preferably in the range of pH 0.8 or more and pH 1.8 or less, more preferably pH 1.0 or more and pH 1.5 or less.

The second acidic solution added to the silica coat forming material can hydrolyze silicon alkoxide if the silica coat forming material contains silicon alkoxide, as long as the pH is in the range of pH 0.8 or more and pH 1.8 or less. , followed by dehydration condensation. By coating the surface of the first thin film with a silica coat forming material, a second thin film in which the surface of the first thin film is coated with silica can be obtained. The second thin film includes the first thin film and silica coated thereon, and can have sufficient film strength. If the pH of the second acidic solution added to the silica coat forming material is less than pH 0.8 or greater than pH 1.8, the particle growth of particles generated by hydrolysis of silicon alkoxide during hydrolysis will be excessively promoted. Therefore, it becomes difficult to coat the surface of the first thin film with silica. The acidic substance contained in the second acidic solution added to the silica coat forming material is preferably at least one selected from hydrochloric acid, sulfuric acid, nitric acid, oxalic acid, and acetic acid.

Examples of methods for coating with the silica coat forming material include spin coating, dip coating, spray coating, flow coating, bar coating, reverse coating, gravure coating, and printing.

After coating the surface of the first thin film with the silica coat-forming material, the heat treatment temperature may be any temperature that can form a silica coat, preferably 250°C or more and 350°C or less, more preferably 280°C or more and 320°C or less. preferable. Further, the heat treatment time may be any time as long as it is possible to form a silica coat, and is preferably 0.5 hours or more and 3 hours or less, and more preferably 0.5 hours or more and 2 hours or less.

A second thin film formed by coating the first thin film with silica: an optical thin film The second thin film formed by coating the first thin film with silica contains silicon oxide and has a refractive index of 1.380 or less. preferable.

The second thin film, which is an optical thin film, is coated with silica so as to cover the surface of silicon oxide (SiO ₂ ), which is the skeleton of the first thin film. Since silicon oxide (SiO ₂ ), which forms the skeleton of the first thin film, has voids, it is assumed that the surface is mesh-like, and that silica is coated along this surface. The second thin film, which is an optical thin film, has sufficient film strength because the surface of the first thin film is coated with silica.

In addition, the second thin film, which is an optical thin film, has a low refractive index of 1.380 or less, which is equal to or lower than 1.380, which is the refractive index of magnesium fluoride (MgF ₂ ), which is known as a conventional low refractive material. The refractive index is . Since the second thin film has a low refractive index of 1.380 or less, for example, when optical glass or plastic is the object to be coated, the second thin film has a refractive index of about 1.200 to about 1.300 ), and the antireflection effect can be enhanced. The refractive index of the second thin film obtained by coating the first thin film with silica is preferably 1.380 or less, more preferably 1.300 or less, still more preferably 1.250 or less, even more preferably 1.200 or less. It is.

Optical member An optical member including an optical thin film and a film-forming object according to an embodiment of the present invention is a disk drive device equipped with optical pickup parts such as an astronomical telescope, an eyeglass lens, a camera, a bandpass filter, and a beam splitter. , it can be used as an optical member for display devices and the like equipped with high-definition liquid crystal panels. In addition, by applying an optical thin film to the part of the light emitting device that extracts light to the outside, it is possible to promote the emission of light from the light emitting device to the outside, and to improve the light extraction efficiency and reduce heat generation.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example 1
Production of thin film forming material 160 g of indium (III) oxide powder (In ₂ O ₃ ) (purity: 99.99 mass %) and 100 g of silicon monoxide powder (SiO) (purity: 99.9 mass %) were added to 1 L of A nylon ball with a diameter of 20 mm (φ20) was added together with these powders, and the mixture was mixed for 30 minutes while loosening aggregates to obtain a raw material mixture. The molar ratio of indium oxide to 1 mole of silicon oxide (In ₂ O ₃ /SiO molar ratio) was 0.254. The raw material mixture was taken out from the pot and press-molded into a molded body. This molded body was fired at 800° C. for 2 hours in an inert atmosphere (argon (Ar): 99.99% by volume) to obtain a thin film forming material (sintered body) 1.

Manufacture of the first vapor deposited film A disc-shaped double-sided polished plate glass (manufactured by SCHOTT AG, BK-7) was used as the object to be deposited. The object to be deposited and the thin film forming material 1 were placed in a vapor deposition apparatus, and while the pressure inside the vapor deposition apparatus was reduced to 1.0×10 ^-4 Pa, an electron beam (JEOL Ltd.) was applied to the thin film forming material 1. A vapor deposited film containing indium (I) oxide (In ₂ O) and silicon dioxide (SiO ₂ ) was formed on one side of a substrate-shaped object to be film-formed by irradiating the substrate with a JEBG-102UH0 (manufactured by JEBG-102UH0) at 140 mA. The temperature of the film to be deposited during film formation was 100°C, and ion-beam assisted deposition (IAD) (accelerated Voltage value-acceleration current value=900V-900mA) was used. In order to prevent charge-up of the film to be deposited, a neutralizer (RFN-2, manufactured by Synchron Co., Ltd., bias current value = 1000 mA) was used.

Manufacturing a first thin film with voids An oxalic acid solution with a pH of 3.2 is used as the first acidic solution, and the object on which a vapor deposited film has been formed is immersed in this oxalic acid solution at room temperature to remove oxidation from the vapor deposited film. Indium (I) (In ₂ O) was preferentially eluted to produce a first thin film having voids. The contact time (immersion time) between the deposited film and the acidic solution was 90 minutes to obtain a first thin film that did not absorb visible light. The refractive index of the obtained first thin film having voids was measured by the method described below. A first thin film with voids having a refractive index of 1.091 was obtained. The amount of indium (III) oxide (In ₂ O ₃ ) and/or indium (In) contained in the first thin film is determined by contacting the first thin film with a strong acidic solution having a pH of 2.0 or less. This amount decreased the refractive index of the thin film by 0.011, and increased the porosity by approximately 3% (including silicon dioxide (SiO ₂ ) which was dropped).

Production of second thin film 0.5 g of tetraethoxysilane (TEOS, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silica coat forming material was added to 12.85 g of dehydrated ethanol, and then a second acidic solution with a pH of 1.0 was added to 12.85 g of dehydrated ethanol. A silica coat forming material was manufactured by adding 0.47 g of hydrochloric acid and mixing the prepared liquid for 24 hours. After dropping the silica coat forming material onto the surface of the first thin film having voids and impregnating it, removing the excess silica coat forming material from the surface of the first thin film by rotating the first thin film, The surface of the first thin film was coated with a silica coat forming material and held at 300° C. for 1 hour to produce a second thin film in which the first thin film was coated with silica. The refractive index of the second thin film obtained was 1.139.

Example 2
155 g of In ₂ O ₃ powder and 100 g of SiO powder (In ₂ O ₃ /SiO molar ratio is 0.246) were mixed and sintered in the same manner as in Example 1 to obtain a thin film forming material 2. Using this thin film forming material 2, a first thin film having voids was produced in the same manner as in Example 1 except that it was not coated with silica. The refractive index of the obtained thin film was 1.140.

Example 3
A first thin film having voids was produced in the same manner as in Example 1, except that an oxalic acid solution with a pH of 2.5 was used as the first acidic solution, and the film was not coated with silica. The refractive index of the obtained thin film was 1.094.

Example 4
A first thin film having voids was produced in the same manner as in Example 1 except that an oxalic acid solution with a pH of 2.7 was used as the first acidic solution and that it was not coated with silica. The refractive index of the obtained thin film was 1.093.

Example 5
A first thin film having voids was produced in the same manner as in Example 1, except that an oxalic acid solution with a pH of 3.5 was used as the first acidic solution, and the film was not coated with silica. The refractive index of the obtained thin film was 1.092.

Example 6
A first thin film having voids was produced in the same manner as in Example 1 except that it was not coated with silica using a hydrochloric acid solution with a pH of 3.0 as the first acidic solution. The refractive index of the obtained thin film was 1.095.

Example 7
A first thin film having voids was produced in the same manner as in Example 2 except that ion beam assisted vapor deposition using Ar ions was not used and silica coating was not used. The refractive index of the obtained thin film was 1.266.

Comparative example 1
140 g of In ₂ O ₃ powder and 100 g of SiO powder (In ₂ O ₃ /SiO molar ratio is 0.222) were mixed and sintered in the same manner as in Example 7 to obtain a thin film forming material 3. Using this thin film forming material 3, a thin film having voids was produced in the same manner as in Example 7 except that it was not coated with silica. The refractive index of the obtained thin film was 1.321.

Comparative example 2
180 g of In ₂ O ₃ powder and 100 g of SiO powder (In ₂ O ₃ /SiO molar ratio is 0.286) were mixed and sintered in the same manner as in Example 1 to obtain a thin film forming material 4. A vapor deposited film was produced in the same manner as in Example 1 except that this thin film forming material 4 was used, and the vapor deposited film was brought into contact with the same first acidic solution as in Example 1, but after the acid treatment, the vapor deposited film peeled off from the object to be film-formed, making it impossible to obtain a thin film with voids.

Comparative example 3
A deposited film was produced in the same manner as in Example 1 except that an oxalic acid solution with a pH of 2.0 was used as the first acidic solution, and the deposited film was brought into contact with the same first acidic solution as in Example 1. However, the deposited film peeled off from the object to be deposited after the acid treatment, and a thin film with voids could not be obtained.

Comparative example 4
A thin film having voids was produced in the same manner as in Example 1 except that it was not coated with silica, using an oxalic acid solution adjusted to pH 4.0 as the first acidic solution. The resulting thin film did not become transparent.

Evaluation of Thin Film (Optical Thin Film) The first thin film, which is the optical thin film of Examples and Comparative Examples, was evaluated as follows. The results are shown in Table 1.

Refractive index Using a spectrophotometer (Hitachi High-Technologies Corporation, product name: U-4100, incident angle 5°), the reflection spectrum of the thin film (optical thin film) having voids of Example was measured. The minimum value of the reflected light intensity when the incident light intensity is 100 was measured as the reflectance, and the refractive index was calculated from the measured reflectance using the Fresnel coefficient.
In the examples, since double-sided polished glass is used as the substrate-like film-forming object on which the thin film is formed, the reflectance R' obtained from the measurement includes multiple repeated reflections including backside reflection. Since the measured reflectance R' includes multiple repeated reflections, the reflectance R of the thin film can be expressed by the following equation (1).

In the above formula (1), R _o is the reflectance of the substrate (film-forming object). The reflectance R of the thin film was calculated based on equation (1) from the actually measured reflectance R' of the thin film. The reflectance R of the thin film is a reflectance that does not take into account reflection from the back surface.
The reflectance R of the thin film can be expressed using the following equation (2) using the Fresnel coefficient, the refractive index _nm of the substrate (film-forming object), and the refractive index n of the thin film.

Here, if the refractive index of the atmosphere is approximated as 1 and the refractive index n of the thin film is larger than the square root of the refractive index n _m of the substrate, then the refractive index n of the thin film can be expressed by the following equation (3). can.

Further, when the refractive index n of the thin film is smaller than the square root of the refractive index _nm of the substrate, the refractive index n of the thin film can be expressed by the following equation (4).

The refractive index n of the first thin film and the second thin film, which are optical thin films, was calculated based on the above formulas (1) to (4). Regarding the refractive index n of optical thin films, please refer to "Mitsunobu Kohiyama, "Basic Theory of Optical Thin Films - Fresnel Coefficients, Characteristic Matrix", published by Optronics Co., Ltd., February 25, 2011, expanded and revised edition 1st printing. ” was used as a reference.

Porosity (%)
The porosity (total porosity Vp) of the first thin film and the second thin film, which are optical thin films, was determined using the Lorenz-Lorenz equation shown in equation (5) below. In the following equation (5), n _f is the observed refractive index of the thin film, and n _b is the refractive index of the skeleton of the thin film. The refractive index n _f of the thin film is the refractive index of a thin film (optical thin film) having voids determined based on the above formulas (1) to (4). The refractive index n _b of the thin film skeleton is mainly composed of silicon dioxide (SiO ₂ ), and therefore was determined using the refractive index of silicon dioxide (SiO ₂ ) (1.460).

Absorption rate (%)
Using a spectrophotometer (Hitachi High-Technologies Corporation, product name: U-4100, incident angle 5°), the absorption rate of the thin film (optical thin film) having voids of the example was measured. The reflected light intensity and the transmitted light intensity were measured when the incident light intensity was set to 100, and the value obtained by subtracting them from the incident light intensity of 100 was measured as the absorption rate. Since the absorption rate is higher on the shorter wavelength side, it was taken as an average value from 390 nm to 410 nm.

As shown in Table 1, the first thin films of Examples 1 to 7 were able to have a low refractive index of 1.300 or less. The first thin films of Examples 1 to 6 using ion beam assisted deposition (IAD) using Ar ions were able to lower the refractive index to 1.170 or less. The absorption rate of the first thin film of Example 1 was measured using a spectrophotometer based on the transmittance and reflectance, and the absorption rate was found to be sufficiently _low . It was confirmed that no indium (I) (O) and/or indium (In) was present, and all indium (I) oxide (In ₂ O) and/or indium (In) in the thin film was eluted by contact with the acidic substance. Ta. Furthermore, it was confirmed that silicon monoxide (SiO), which has a black body color, was not present in the first thin film of Example 1.

As shown in Comparative Example 1, when the In ₂ O ₃ /SiO molar ratio of the thin film forming material is 0.222 and the In ₂ O ₃ /SiO molar ratio of the thin film forming material is less than 0.230, the first The refractive index of the thin film was 1.321, and the refractive index did not become lower than 1.300. As shown in Comparative Example 2, the In ₂ O ₃ /SiO molar ratio of the thin film forming material is 0.286, and when the In ₂ O ₃ /SiO molar ratio of the thin film forming material exceeds 0.270 mol, the first The vapor deposited film peeled off due to contact with the acidic solution, and it was not possible to form the first thin film having voids in the desired portion of the object to be film-formed.

As shown in Comparative Example 3, if the pH of the first acidic solution is too low, the deposited film will peel off after contact, making it impossible to form the first thin film with voids in the desired portion of the film-forming object. There wasn't. Furthermore, as shown in Comparative Example 4, when the pH of the first acidic solution is too high, a black substance is observed in the first thin film, and the black substance indium (I) oxide (In ₂ O) and/or Indium (In) could not be eluted.

Next, Examples 1 and 8 to 14 of the second thin film in which the first thin film is coated with silica will be described.

Example 8
A second thin film obtained by coating the first thin film with silica in the same manner as in Example 1 except that a hydrochloric acid solution with a pH of 1.5 was used as the second acidic solution added to the silica coat forming material. was created. The refractive index of the second thin film obtained was 1.171.

Example 9
A second thin film in which the first thin film was coated with silica was prepared in the same manner as in Example 1 except that 3-glycidoxypropyltrimethoxysilane (GPTMS) was used as the silicon alkoxide as the silica coat forming material. did. The refractive index of the second thin film obtained was 1.178.

Example 10
The first thin film was coated with silica in the same manner as in Example 1, except that a hydrochloric acid solution with a pH of 0.5 was used as the second acidic solution added to the silica coat forming material. A thin film was prepared. The refractive index of the second thin film obtained was 1.159.

Example 11
A second thin film was prepared in which the first thin film was coated with silica in the same manner as in Example 1 except that a hydrochloric acid solution with a pH of 2.0 was used as the second acidic solution added to the silica coat forming material. A thin film was prepared. The refractive index of the second thin film obtained was 1.151.

Example 12
A second thin film was prepared in which the first thin film was coated with silica in the same manner as in Example 1 except that a hydrochloric acid solution with a pH of 3.0 was used as the second acidic solution added to the silica coat forming material. A thin film was prepared. The refractive index of the second thin film obtained was 1.100.

Example 13
A second thin film was prepared in which the first thin film was coated with silica in the same manner as in Example 1 except that a hydrochloric acid solution with a pH of 4.0 was used as the second acidic solution added to the silica coat forming material. A thin film was prepared. The refractive index of the second thin film obtained was 1.120.

Example 14
A second thin film was prepared in which the first thin film was coated with silica in the same manner as in Example 1 except that a hydrochloric acid solution with a pH of 5.0 was used as the second acidic solution added to the silica coat forming material. A thin film was prepared. The refractive index of the second thin film obtained was 1.107.

Evaluation of thin film (optical thin film) As the evaluation of the second thin film of Examples 1 and 8 to 14, the refractive index and porosity were evaluated in the same manner as the evaluation of the first thin film of Example 1. The results are shown in Table 2.

Film strength test A sheet of Silbon paper was placed on top of the second thin film (optical thin film) in which the first thin film was coated with silica, and a pencil hardness tester (JIS K5600 scratch hardness (pencil method) compliant with the Silbon paper was used). .), 20 reciprocations were carried out in a dry manner while applying a load of 500 g/cm ² . Remove the silbon paper and visually check the surface of the second thin film (optical thin film). If there are scratches or color changes in the reflected light, it is evaluated as bad (B: Bad) and the surface of the second thin film (optical thin film) is evaluated as bad. Those with no change on the surface were evaluated as good (G: good). The results are shown in Table 2. In addition, the examples evaluated as (B: Bad) also had good film strength when compared with the examples without silica coating.

SEM Image A SEM image of the second thin film obtained by coating the first thin film with silica was obtained using a scanning electron microscope (SEM). FIG. 1 is a SEM photograph of the surface of the second thin film (optical thin film) of Example 1, and FIG. 2 is a SEM photograph of a cross section of the second thin film (optical thin film) of Example 1.

As shown in Table 2, the first thin films of Examples 1 and 8 to 14 had a refractive index of 1.300 or less, and more specifically, the refractive index could be as low as 1.098 or less. . Further, the second thin film obtained by coating the first thin film of Examples 1, 8 to 14 with silica has a refractive index of 1.380 or less, more specifically, a refractive index of 1.178 or less. The refractive index (1.380) of magnesium fluoride (MgF ₂ ), which is known as a conventional low refractive material, could be lowered.

As shown in Example 1, when a silica coat forming material to which a second acidic solution with a pH of 1.0 was added was used, and as shown in Example 8, a second acidic solution with a pH of 1.5 was used. In the case of using a silica coat forming material to which is added, or as shown in Example 9, when using a silica coat forming material containing 3-glycidoxypropyltrimethoxysilane (GPTMS), the obtained Thin film No. 2 showed sufficient film strength.

As shown in Examples 11 to 14, a silica coat-forming material to which a second acidic solution with a high pH of more than 1.8 was added was used, and as shown in Example 10, a silica coat-forming material with a high pH of more than 1.8 was used. When a silica coat forming material to which a second acidic solution with a low pH of less than 8 was added was used, the second thin film could not obtain sufficient film strength.

As shown in FIG. 1, the first thin film of Example 1 was formed by elution of indium (I) oxide (In ₂ O) between a skeleton composed of silicon dioxide (SiO ₂ ). A void exists. As shown in FIG. 2, when observing the cross section of the second thin film obtained by coating the first thin film of Example 1 with silica, the skeleton formed of silicon dioxide (SiO ₂ ) is removed from the thin film from the object to be filmed. It can be confirmed that the film continues all the way to the surface, and has a shape different from that of, for example, a thin film composed of an aggregate of silica particles.

According to the method for manufacturing a thin film in an embodiment of the present invention, it is possible to relatively easily manufacture an optical thin film with a low refractive index, and the optical film can be used not only for camera lenses but also for high-definition liquid crystal panels, etc. A thin film can be provided. The optical thin film in one embodiment of the present invention is suitable for use in optical devices such as astronomical telescopes, spectacle lenses, cameras, disk drive devices equipped with optical pickup parts such as bandpass filters and beam splitters, and display devices equipped with high-definition liquid crystal panels. It can be used as a member.

Claims (7)

a step of depositing a thin film-forming material on an object to be film-formed by physical vapor deposition in a non-oxidizing atmosphere to form a vapor-deposited film containing silicon dioxide and indium (I) oxide;
By bringing the deposited film into contact with a first acidic solution containing an acidic substance and having a pH of 2.5 to 3.5, indium (I) oxide is preferentially eluted, and the indium dioxide Obtaining a first thin film having a silicon skeleton;
A method for producing an optical thin film, comprising a step of coating the surface of the first thin film with a silica coat forming material and then heat-treating the surface to obtain a second thin film. The method for manufacturing an optical thin film according to claim 1, wherein the first thin film has a refractive index of 1.30 or less. The method for producing an optical thin film according to claim 1 or 2, wherein the porosity is in the range of 30% or more and 90% or less. the first thin film has a refractive index of 1.300 or less,
The second thin film has a refractive index of 1.100 or more and 1.178 or less, and a porosity of 58.2% or more and 76.1% or less, according to any one of claims 1 to 3. Method for manufacturing optical thin films. 5. The method for manufacturing an optical thin film according to claim 1, wherein the skeleton of the first thin film is continuous from the object to be formed to the surface of the first thin film. 6. The method for producing an optical thin film according to claim 1, wherein the object to be film-formed is made of glass or plastic. 7. The method of manufacturing an optical thin film according to claim 1, wherein the optical thin film is applied to a portion of a light emitting device from which light is extracted to the outside.