JP2000111707A - Optical member having antireflection property and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily produce an optical member having antireflection performance at a low cost by forming a thin film of a metal fluoride oxide satisfying a specified relation as a monolayer on an optical substrate having an arbitrary refractive index. SOLUTION: The optical member has a substrate and a thin film of a metal fluoride oxide of the formula MFXOY formed as a monolayer on the substrate and has antireflection property. The refractive index nF of the thin film at a designed central wavelength and the refractive index nS of the substrate at the wavelength satisfy the relation of nF≈nS1/2. For example, the optical member has a BK7 glass substrate 1 whose refractive index nS is 1.51 and a reflecting film 2 comprising aluminum fluoro-oxide formed on the substrate 1 by plasma CVD. In the case of 633 nm central wavelength λ, the optical thickness of the reflecting film 2 is 0.25λ and the refractive index nF is 1.511/2=1.23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical member having antireflection characteristics and a method for manufacturing the same.

[0002]

2. Description of the Related Art It is well known that an antireflection film is formed on an optical substrate. As a conventional antireflection film material, a metal oxide such as aluminum oxide, zirconium oxide, or titanium oxide, or a metal fluoride such as magnesium fluoride or aluminum fluoride has been mainly used.

A refractive index n _F (n _{F) is formed} on an optical substrate having a refractive index n _S.
When a thin film of <n _S ) is formed, the light reflectance at the wavelength λ is minimum when the film thickness d satisfies λ = 4 · n _F · d, and the reflectance R at that time is R = (n _S ² − n _F ) / (n _S
² + n _F ). That is, when the refractive index of the thin film is in a relationship of n _F = n _S ^1/2 with the refractive index of the optical substrate according to the above equation, it is possible to obtain a reflectance = 0 at the wavelength λ.

The metal oxides and metal fluorides used as the anti-reflection coating materials described above have the advantage that the chemical composition is stable and a thin film having a constant refractive index can be stably manufactured. On the other hand, the refractive index n for each substance
_{Since F} is determined, the reflectance by the single-layer anti-reflection film cannot be reduced below the value given by the above equation, even if the film thickness d is adjusted optimally when the combination of the optical substrate and the film material is determined. was there. The characteristics of the anti-reflective coating include
Naturally, the lower the reflectance, the better, but the types of the optical substrate material and the film material are limited, and the antireflection characteristics of the single-layer antireflection film obtained by combining these refractive indices are limited. Conventionally, in order to solve this problem, by stacking a plurality of film materials having different refractive indices sequentially and controlling each film thickness using multilayer film theory, a multilayer having a lower reflectance than a single-layer antireflection film is used. An anti-reflection film was realized.

[0005]

However, in the production of a multilayer anti-reflection film, the structure and steps of the apparatus are complicated, the design man-hours are long, the film formation time is long, and the production error is increased. Was an essential problem. The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide an optical member having antireflection characteristics which can be easily manufactured at low cost and a method of manufacturing the same.

[0006]

As a means for solving the above problems, the present inventors have found that metal fluorides are effective as an antireflection film material. The present invention firstly provides an optical member having an antireflection property comprising a substrate and a single-layer metal fluoride oxide thin film represented by a composition formula MF _X O _Y formed on the substrate. The refractive index n _{F of the} metal fluorinated oxide thin film at the design center wavelength is n _F ≒ n _{S in} relation to the refractive index n _{S of the} substrate at the design center wavelength.
An optical member having anti-reflection characteristics characterized by satisfying a relationship of ^1/2 (claim 1) "is provided.

The metal fluoride is an inorganic compound represented by the composition formula MF _X O _Y. Since the fluoride ion F ^- is an anion having an ionic radius substantially equal to that of the oxide ion O ^2- , the packing state of the crystal becomes substantially the same, and the fluoride oxide is stably present in a wide composition range. Further, a film formation process on an optical substrate such as a lens or a prism is generally performed at a relatively low temperature of about room temperature to about 300 ° C. in order to avoid thermal deformation of a substrate having extremely high mechanical precision. For this reason, the structure of the film is often amorphous, and it is considered that a fluorinated oxide thin film having an intermediate composition between fluoride and oxide is easily formed.

Further, since the refractive index of a mixture (compound) (composite) of a metal fluoride and a metal oxide depends on the composition of the metal fluoride, the metal oxide and the metal can be controlled by controlling the composition. An arbitrary refractive index can be obtained with fluoride. Oxygen and fluorine have different values of atomic refraction, and oxides and fluorides of the same metal always have a lower refractive index than fluorides.

The composition of the metal fluorinated oxide thin film can be determined from a composition VS refractive index curve prepared by a method described later. The composition VS refractive index curve can be obtained by preparing an appropriate number of thin film samples having different compositions and experimentally calculating the composition and the refractive index. Preparation of samples having different compositions is performed by controlling appropriate parameters according to the film forming process as described later.

The composition of the prepared thin film is ESCA or X
The refractive index of the thin film is determined by a known analysis method such as RF, and is calculated by a known method such as measurement of reflectance or transmittance or ellipsometry. As described above, since the refractive index of the metal fluoride oxide thin film can be freely adjusted in a wide range at the time of manufacturing, the refractive index n _F ≒ n _S ^1/2 and the thickness d according to the refractive index n _s of the optical substrate. If a thin film of ≒ λ / (4 · n _F ) is formed, it is possible to obtain a reflectance R ≒ 0 at an arbitrary wavelength λ by a single layer film.

Further, the present invention secondly provides "M
Is any one of aluminum, yttrium, gadolinium, calcium, silicon, zirconium, strontium, neodymium, hafnium, barium, magnesium, and lanthanum. In addition, the present invention is a third aspect of the present invention. “After holding an optical substrate in a film formation chamber of a plasma CVD apparatus provided with a plasma generation source, exhausting the film formation chamber to a predetermined vacuum degree, A process for introducing a gas for forming a fluorinated oxide thin film, converting the gas into plasma, and forming a metal fluorinated oxide thin film on the substrate; 3) ”.

Further, the present invention provides a fourth aspect of the present invention, wherein the gas for forming a metal fluoride oxide thin film is an organic metal compound gas, an oxygen gas, and a fluorine-containing compound gas. (Claim 4). " In addition, the present invention is a fifth aspect of the present invention, wherein an optical substrate is held in a film forming chamber of a vacuum evaporation apparatus provided with an evaporation source, and after the film forming chamber is evacuated to a predetermined vacuum degree, a predetermined position in the film forming chamber is determined. Metal fluoride MF _{X '} and metal oxide MO _{Y' provided in}
A method of simultaneously heating and evaporating the metal fluoride by the evaporation source, and depositing a metal fluoride oxide thin film MF _X O _Y on the optical substrate (claim 5). )"I will provide a.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical member according to an embodiment of the present invention and a method for manufacturing the same will be described. FIG.
FIG. 2 is a schematic sectional view of an optical member according to an embodiment of the present invention. The optical member of the embodiment according to the present invention has a refractive index n _S
And an index of refraction n _F formed on the optical substrate
= N metal fluoride oxide thin film which satisfies a relation _S ^1/2 (MF _X
O _Y ) and a single-layer antireflection film.

The optical substrate is made of quartz glass, BK7 glass, or a crystalline material such as fluorite. Prior to forming the anti-reflection film on the substrate, the optical substrate is subjected to a preliminary treatment such as an alkali treatment, a plasma treatment excited by glow discharge, or a treatment with ions to further improve the adhesion with the anti-reflection film. be able to.

The composition of the metal fluoride oxide thin film is not limited to a stoichiometric composition and may be non-stoichiometric as long as light absorption due to atomic defects is within a negligible range. The metal fluoride oxide thin film suitable as an antireflection film of the optical member of the embodiment has a suitable refractive index, low light absorption, and has sufficient durability as an industrial product. Aluminum oxide, yttrium fluoride oxide, gadolinium fluoride oxide, calcium fluoride oxide, silicon fluoride oxide, zirconium fluoride oxide, strontium fluoride oxide, neodymium fluoride oxide, hafnium fluoride oxide, barium fluoride oxide, fluoride Magnesium oxide, fluorinated lanthanum oxide and the like are used.

The antireflection film of the optical member according to the embodiment is formed by a plasma CVD method or a vacuum evaporation method. When a film is formed by a plasma CVD method, a metal alkoxide compound corresponding to a target metal fluoride oxide thin film is suitable as a raw material for forming the metal fluoride oxide thin film. For example, as a raw material of the aluminum fluoride oxide thin film, trimethoxyaluminum, triethoxyaluminum, trin-propoxyaluminum, trii-propoxyaluminum, trin-butoxyaluminum,
Tri-i-butoxyaluminum, tri-t-butoxyaluminum, or the like can be used. In these compounds mentioned in the examples, the alkoxy groups coordinated to the central metal are all the same, but are not limited thereto. For example, dimethoxyethoxyaluminum obtained by substituting one methoxy group of trimethoxyaluminum with an ethoxy group can be similarly used.

Further, as a raw material other than the above-mentioned metal alkoxide compound, a metal diketonato complex compound may be mentioned. A chelate complex represented by a metal diketonato complex compound is thermally stable due to an entropy effect, is easily vaporized in a molecular state, and is suitable as a raw material for plasma CVD. Examples of metal diketonato complex compounds include bis (2,
4-pentanedionato) magnesium, tris (2,2,
6,6-tetramethyl-3,5 heptanedionato) aluminum.

Materials other than metal alkoxide compounds and metal diketonato complex compounds include alkyl metal compounds. Alkyl metal compounds are generally very unstable and easily ignited, so there is a high risk. Requires sufficient security measures and extreme caution on the equipment. An example of an alkyl metal compound is trimethylaluminum.

The metal alkoxide compounds, metal diketonato complex compounds, and alkyl metal compounds exemplified as the raw materials for the metal fluorinated oxide thin film have no fluorine atom in the molecule. Therefore, when forming a metal fluorinated oxide thin film using these raw materials, the fluorine-containing compound must be introduced into the reactor simultaneously with these raw materials.

As the fluorine-containing compound, fluorine, hydrogen fluoride, nitrogen trifluoride, carbon tetrafluoride and sulfur hexafluoride are preferred. In addition, oxygen gas can be introduced according to the composition of the target metal fluoride oxide thin film. The composition of the thin film formed by the plasma CVD method is determined by 1) the composition of the source gas, 2) the plasma intensity, and 3) the substrate temperature. Therefore, a method in which the composition is most easily controlled depending on the characteristics of the source gas or the characteristics of the plasma CVD apparatus to be used may be employed.

The discharge method (DC, low frequency, high frequency, microwave, etc.), electrode method (internal, external, electrodeless), input power waveform control (square, triangular wave, etc.) may be used for forming the antireflection film. It is set appropriately and is not particularly limited. When a metal fluorinated oxide thin film is formed by a vacuum evaporation method, it is preferable to use a multi-source evaporation apparatus having two or more evaporation sources. The metal fluoride (evaporation substance) and the metal oxide (evaporation substance) corresponding to the target metal fluoride are simultaneously heated and evaporated by the respective evaporation sources, and a metal fluoride oxide thin film is deposited on the optical substrate. Let it.

Further, the present invention can be implemented in a vacuum evaporation apparatus having only one evaporation source. In this case, the mixture of metal fluoride and metal oxide (evaporation material), which has been adjusted to an appropriate ratio in advance, is evaporated from the evaporation source to deposit the desired metal fluoride oxide thin film. As the evaporation source, a resistance heating type, an electron gun heating type, or the like can be selected according to the melting point or vapor pressure of the deposition material.

[0023]

EXAMPLES Example 1 As means for producing a single-layer antireflection film made of metal fluoride having an arbitrary refractive index,
In this embodiment, a film formation method by plasma CVD will be exemplified. The optical member of the first embodiment includes a BK7 glass substrate 1 having a refractive index n _s = 1.51 and a plasma CVD on the substrate.
When the center wavelength λ formed by the method is 633 nm, the optical film thickness is 0.25λ, and the refractive index n _F = 1.
And an antireflection film 2 made of aluminum fluorinated oxide in which 51 ^1/2 = 1.23.

Hereinafter, a method of forming the antireflection film of the optical member according to the first embodiment will be described. First, BK7 glass serving as a substrate is prepared, and the surface is subjected to precision cleaning. Surface cleanliness is important. Wet ultrasonic cleaning using a neutral detergent or the like generally used for optical components may be used. More preferably, the cleaning is performed by a light cleaning method. Next, the substrate 1 is set on the substrate holding electrode 13 provided in the vacuum chamber 11 of the parallel plate type CVD apparatus shown in FIG. 2, and the vacuum chamber 11 is evacuated to 1 × 10 ⁻⁵ Torr by the vacuum pump 17. Then, the substrate 1 is heated by a heating wire (substrate heater) 14 provided inside the substrate holding electrode 13.
To about 300 ° C.

A tri-isopropoxy aluminum (raw material) is charged into a stainless steel cylinder container 202 under an inert gas atmosphere, and the whole is heated in an oil bath 201 to generate a tri-isopropoxy aluminum gas (raw material gas). . Next, an argon gas whose flow rate is precisely controlled through the mass flow meter 205 is introduced into the triisopropoxyaluminum melt as a carrier gas, and the vacuum chamber connected to the outlet side together with the triisopropoxyaluminum gas (raw material gas) is introduced into the vacuum chamber. Lead to. The supply pipe of the source gas introduction system is provided with a heating and keeping mechanism 209 so that the source gas is not condensed in the supply pipe 208.

The flow rates of SF6 gas as a fluorine source and oxygen gas as an oxygen source reacting with triisopropoxyaluminum gas (raw material gas) are adjusted by mass flow meters 206 and 207 provided in respective supply pipes. , And similarly introduced into a vacuum chamber. At this time, the relationship between the flow rates of the two and the refractive index of the film to be formed is examined in advance, and the flow rate is set so that a film having a desired refractive index is obtained.

After introducing triisopropoxyaluminum gas (raw material gas), SF ₆ gas, and oxygen gas into the vacuum chamber, the exhaust speed is adjusted by the throttle valve 16 to adjust the pressure in the container from 1 Torr to 1 × 10 ^-2. High frequency (13.56 MHz) between electrodes while maintaining a constant value between Torr
Plasma is generated by applying power. The source gas decomposed by the energy of the plasma generates aluminum fluoride oxide and deposits on the substrate.

Measure the relationship between discharge time and film thickness in advance
Stop discharge when the specified film thickness is obtained
And triisopropoxy aluminum gas (raw material gas)
S), SF ₆The supply of gas and oxygen gas was stopped. On board
Has a refractive index of 1.23 at 633 nm and an optical film thickness
0.25λ aluminum fluorinated oxide was formed.

FIG. 3 shows a spectral reflectance curve of the antireflection film manufactured in Example 1. FIG. 3 shows that the reflectance at 633 nm is almost 0%. Embodiment 2 In this embodiment, a method of forming a single-layer antireflection film made of a metal fluoride having an arbitrary refractive index by a vacuum evaporation method will be exemplified.

The optical member of the second embodiment is an optical glass substrate 1 having a refractive index n _S = 1.89 at a wavelength of 515 nm.
The optical film thickness is 0.25λ when the center wavelength λ formed on the substrate by the vacuum evaporation method is 515 nm, and the refractive index n _F = 1.89 ^1/2 = 1.37. And an antireflection film 2 made of a certain magnesium fluoride oxide thin film.

Hereinafter, a method for forming a film of an optical member according to the second embodiment will be described. First, an optical glass serving as a substrate is prepared, and the surface is subjected to precision cleaning. Surface cleanliness is important. Wet ultrasonic cleaning using a neutral detergent or the like generally used for optical components may be used. More preferably, the cleaning is performed by a light cleaning method. A refractive index ns = at a wavelength of 515 nm in a cylindrical vacuum chamber having a diameter of 800 mm and a height of 850 mm.
An optical glass substrate of 1.89 and magnesium fluoride and magnesium oxide were set as evaporation sources,
After evacuation to × 10 ⁻⁶ Torr, oxygen was introduced to 1 × 10 ⁻⁴ Torr, vapor deposition was performed by electron beam heating, and a refractive index n _F = 1.37 at a wavelength of 515 nm and an optical film thickness of 0 were used. A .25λ magnesium fluoride oxide thin film was formed.

This thin film had a reflectance of almost 0% at 515 nm.

[0033]

As described above, according to the optical member of the present invention, n _F ≒ n _S ^1/2 on an optical substrate having an arbitrary refractive index.
The reflectance can be set to O% only by forming a single layer of the metal fluorinated oxide thin film satisfying the relationship, and the problem that occurs in the multilayer antireflection film does not occur.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical member according to the present invention.

FIG. 2 shows plasma CVD for producing an antireflection film according to the present invention.
It is the schematic of an apparatus.

FIG. 3 is a diagram illustrating a spectral reflectance characteristic of the antireflection film manufactured in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass substrate 2 ... Antireflection film 11 ... Vacuum tank 12 ... High frequency electrode 13 ... Substrate holding electrode 14 ... Heating wire 15 ... High frequency power supply 16 ... Throttle valve 201: Oil bath 202: Cylinder container 205, 206, 207: Mass flow meter 208: Supply pipe 209: Heat insulation mechanism

Claims (5)

[Claims] 1. An optical member having antireflection properties, comprising: a substrate; and a single-layer metal fluoride oxide thin film represented by a composition formula MF _X O _Y formed on the substrate. The refractive index n _{F of the} metal fluorinated oxide thin film at a center wavelength, in relation to the refractive index n _{S of the} substrate at a design center wavelength, satisfies the relationship of n _F ≒ n _S ^1/2. An optical member having antireflection properties. 2. In the above formula, M is aluminum, yttrium, gadolinium, calcium, silicon, zirconium, strontium, neodymium, hafnium,
The optical member according to claim 1, wherein the optical member is one of barium, magnesium, and lanthanum. 3. A plasma CV provided with a plasma generation source.
After holding the optical substrate in the film forming chamber of the D apparatus and evacuating the film forming chamber to a predetermined degree of vacuum, a gas for forming a metal fluoride oxide thin film is introduced into the film forming chamber, and the substrate is turned into plasma. A method for producing an optical member having antireflection film characteristics, comprising a step of forming a metal fluoride oxide thin film thereon. 4. The gas for forming a metal fluoride oxide thin film,
4. The method for producing an optical member according to claim 3, wherein the gas is an organic metal compound gas, an oxygen gas, and a fluorine-containing compound gas. 5. An optical substrate is held in a film forming chamber of a vacuum evaporation apparatus provided with an evaporation source, and after the film forming chamber is evacuated to a predetermined degree of vacuum, the optical substrate is provided at a predetermined position in the film forming chamber. Reflection comprising a step of simultaneously heating and evaporating the metal fluoride MF _{X ′} and the metal oxide MO _{Y ′} by the evaporation source to deposit a metal fluoride oxide thin film MF _X O _Y on the optical substrate. A method for producing an optical member having prevention properties.