JPH11305005A - Anti reflection film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain with good productivity a normal antireflection film of high performance which. SOLUTION: A light-transmitting dielectric film 3 is provided between a circumferential medium 1 and a light-transmitting optical medium 2 which has a reflective index ng . Here, an interface which contacts the circumferential medium 1 is provided and the interface has unevenness in a periodic structure of 2,400 nm in pitch P and 130 nm in mean height and satisfies the phase difference ϕ=4π.n.d.conθ/λ=π of a reflected optical path of the unevenness and λ<P<=30λ, where the center wavelength λ of incident luminous flux made incident on the interface is set to 250 nm and the center incidence angle θis set to 5 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antireflection film for efficiently reducing regular reflection light of an incident light beam incident on an optical element such as a lens.

[0002]

2. Description of the Related Art When light transmitted through a light-transmitting optical element is used, Fresnel reflected light generated at an interface between light-transmitting optical media having different refractive indices is reduced, and the transmittance is improved. Conventionally, an anti-reflection film formed by laminating a light-transmitting dielectric film H having a relatively high refractive index and a light-transmitting dielectric film L having a relatively low refractive index has been used.

[0003] Specifically, if the light-transmitting optical medium having a refractive index n _g is the incident light beam having the central wavelength λ at an incident angle θ at the interface in contact with the surrounding medium of refractive index n (n ≠ n _g) is incident ,
A light-transmitting dielectric film having a refractive index n ₂ intermediate between n and _ng was formed so as to have a film thickness d = λ / (4 · n ₂ · cos θ) to obtain an antireflection effect. .

For example, on an optical glass of _ng = 1.5 placed in air, MgF ₂ of n ₂ = 1.38 is added with d = 100.
The antireflection film obtained by forming a film having a thickness of about nm was able to reduce the Fresnel reflectance from 4.2% to about 1.3% with respect to the vertically incident green wavelength light.

Further, by forming a dielectric multilayer structure in which a light-transmitting dielectric film H having a relatively high refractive index and a light-transmitting dielectric film L having a relatively low refractive index are laminated, 100nm
It was possible to reduce Fresnel reflected light to about 0.5% in a wide wavelength band.

[0006]

However, in the prior art, it has been difficult to produce an antireflection film that stably reduces Fresnel reflected light to about 0.1% or less in a wide wavelength band of several hundreds of nm. In particular, in a reflective optical element utilizing regular reflection light from a surface substantially parallel to the surface on which the antireflection film is formed, the residual regular reflection on the surface of the antireflection film may significantly degrade the performance of the optical element. Was.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and stably reflects regular reflection light generated at the interface of a translucent optical medium having a different refractive index in a wide wavelength band. An object of the present invention is to provide an anti-reflection film that is greatly reduced.

Namely, according to claim 1, light-transmitting optical medium 2 having a refractive index n _g and the surrounding medium 1 having a refractive index n (n
≠ _ng ), an anti-reflection film having at least one light-transmitting dielectric film provided therebetween, an interface S in contact with the surrounding medium 1 is provided, and the interface S has a pitch P and an average height d. Assuming that the center wavelength of the incident light beam incident on the interface S is λ and the phase difference of the optical path between the reflected light from the convex portion and the reflected light from the concave portion is φ, λ <P ≦ 30
Provided is an antireflection film characterized by satisfying λ and φ ≒ (2M + 1) · π (M is 0 or a positive integer). The pitch P average height d and the center wavelength λ use numerical values expressed in the same dimension.

According to a second aspect of the present invention, the light-transmitting dielectric film is formed by laminating a light-transmitting dielectric film H having a relatively high refractive index and a light-transmitting dielectric film L having a relatively low refractive index. An anti-reflection film according to claim 1 is provided.

According to a third aspect of the present invention, the shape of the unevenness is substantially rectangular, and cos θ =
The antireflection film according to claim 1 or 2, which satisfies λ · (2M + 1) / (4n · d).

According to a fourth aspect of the present invention, there is provided the antireflection film according to the first, second or third aspect, wherein the phase difference is φ ≒ π.

Further, in the fifth aspect, the light enters the interface S from the surrounding medium 1 having the refractive index n at the center incident angle θ, and has the center wavelength λ.
In the method for manufacturing an antireflection film for an incident light beam having a refractive index of _ng , a light-transmitting dielectric film is formed on a light-transmitting optical medium 2 having a refractive index of _ng in a thickness d = λ / (4n · cos θ). A linear resist pattern having an irregular shape having a periodic structure of a pitch P is formed on the light-transmitting dielectric film, and the light-transmitting dielectric material which is not masked with a photoresist from the surface side is formed. The body film is etched, the photoresist is removed, a light-transmitting dielectric film is formed in a pattern having a pitch P and an average height d, and the surrounding medium 1 is formed on the light-transmitting dielectric film.
And a method for producing an anti-reflection film, characterized by forming an anti-reflection layer for the light-transmitting optical medium 2.

Incidentally, the incident light beam in the present invention includes a case of a parallel light having a uniform directivity and a case of a single wavelength.
This includes a case of a convergent light beam or a divergent light beam with dispersed incident angles, and an incident light beam with a wide wavelength band. The present invention is effective for any light flux.

In the case of an incident light beam having a dispersed incident angle, the incident angle θ is defined as a central incident angle θ corresponding to an average value of the dispersed angles. Further, for an incident light beam having a wide wavelength band, the wavelength of the incident light beam is defined by a center wavelength λ corresponding to an average value of the wavelength band.

Further, P, P _a , P _b , d, which are parameters indicating the geometrical dimensions of the uneven shape used in the present invention.
The notation in the relational expression for the center wavelength λ of the incident light flux applies the same dimension as the unit of length. The angle and phase are in radians.

The antireflection film of the present invention has an antireflection effect utilizing light interference of a dielectric film in a direction perpendicular to an interface of a translucent optical medium having a different refractive index, and an in-plane direction at the interface of a translucent optical medium. By utilizing the light diffraction of the periodic structure, a highly efficient regular anti-reflection effect can be obtained as a synergistic effect between the two.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The operation of the antireflection film of the present invention will be described below with reference to FIG. FIG. 1 is a schematic sectional view of the antireflection film of the present invention. On the transparent substrate 2 having a refractive index n _g as fine irregularities, it is translucent dielectric film 3 having a refractive index n ₁ in the width P _a height d along the plane perpendicular axis y-direction at an interval P _b It is patterned in parallel lines. further,
The light-transmitting thin film 4 is formed on the uneven surface having such a periodic structure.
Are uniformly formed and are in contact with the surrounding medium 1. The surrounding medium 1 is air under a normal use environment.

With respect to such a periodic structure, there are an x-axis and a y-axis which are orthogonal to each other in a plane on which the uneven structure appears, and an axis in a direction indicating the periodic structure is an x-axis. An axis perpendicular to the axis is defined as a z-axis.

At the interface S having such a periodic structure,
The reflectivity of an incident light beam incident at an incident angle θ is width _Pb and width Pb.
It is calculated in consideration of the optical diffraction caused by the z-axis direction of the periodic structure of the optical interference with the x-axis direction of the optical thin film of _a.

The irregularities shown in the drawings have a periodic structure that can act optically, and in a region where diffraction occurs with respect to the wavelength of the incident light beam, the diffraction angle and the diffraction wavelength are calculated as defined diffraction light intensity. It is known. When the period of the diffractive optical element is sufficiently large compared to the wavelength and can be regarded as a thin periodic structure, the reflectance is calculated by the scalar diffraction theory of Huygens-Fresnel.

When the period of the diffractive optical element is reduced to about the wavelength, it is conventionally calculated that the boundary condition is applied to the boundary surface by applying a vector diffraction theory for performing an electromagnetic field analysis by applying a boundary condition consistent with Maxwell electromagnetic theory. Are known. For example, Sommerfeld Theory Physics Course IV “Optics”
Chapter-6 (author Arnold Sommerfeld Kodansha, published in 1969).

In the present invention, the incident angle θ is applied to the interface of the periodic structure.
An object of the present invention is to reduce a regular reflected light beam component reflected at an angle θ of the incident light beam incident at the point (a) and reflected as a reflected light beam. Hereinafter, the 0th-order diffracted light that is a regular reflection component will be described.

In the periodic structure shown in FIG. 1, the convex portion having _a width Pa is based on the refractive index and the film thickness of the light transmitting dielectric film 3 and the light transmitting thin film 4 with respect to the incident light beam having the wavelength λ according to the light interference theory. The amplitude reflectance r _a (λ, θ) is defined. Amplitude reflectance by light interference theory with respect to the incident light beam of wavelength lambda by the recess is the refractive index and film thickness of the translucent film 4 in the same manner that the width P _b r _b (λ,
θ) is defined.

The width P _a recess periodically arranged periodic structure of mesas and width P _b of, i.e. unevenness of the pitch P = P _a + P
In the grating structure of _b, the zero-order reflected diffracted light intensity I ₀ is r _a and r _b of the intensity _{| r a |, | r b} | if is sufficiently small compared to 1, described by approximately (1) Is done. Further, when the phase between r _a and r _b are substantially equal,
It becomes minimum in the case of the expression (1A).

[0025]

[Number 1] _{I 0 = 2 | (P a} · r a + P b · r b · exp (i · 4π · n · d · cosθ / λ)) / P | ··· (1) 4π · n · d · cos θ / λ = π · (2L + 1): L is 0 or a positive integer (1A)

That is, the regular reflection is minimized when d _X, which is the amplitude of the concavo-convex, is given by equation (2). Here, n indicates the refractive index of the surrounding medium 1 corresponding to the concave portion in FIG.

[0027]

D _x = (2L + 1) · λ / (4 · n · cos θ): L is 0 or a positive integer (2)

This is due to the phase difference φ of the optical path length between the convex portion and the concave portion.
= 4π · nd · cos θ / λ is a condition that is almost an odd multiple of π. At this time, the regular reflectance (0th-order reflected diffracted light intensity I ₀ ) is represented by Expression (3).

[0029]

(3) I _O = 2 · | (P _a · r _a −P _b · r _b ) / (P _a + P _b ) |

Therefore, λ and θ of r _a and r _b
Although it depends on the dependence, the regular reflectance = 0 under the condition of P _a · r _a = P _b · r _b . That is, the main wavelength λ of the incident light beam (2) having a refractive index n in the width P _a to meet if defining the thickness d of the translucent dielectric film 3, at the wavelength range around the central wavelength λ Regular reflectance can be maintained at a low value.

In order to reduce the wavelength dependency and the incident angle dependency of the zero-order diffracted light and obtain the regular reflection preventing effect in a wide wavelength range, the phase difference φ = 4π · n ·
d · cos θ / λ is π, that is, d = λ / (4 · n · c
osθ).

A combination of the light-transmitting dielectric film 3 and the light-transmitting thin film 4 or the light-transmitting thin film 4 is alternately laminated with a dielectric film having a relatively high refractive index and a dielectric film having a relatively low refractive index. with the dielectric multilayer antireflection film, amplitude reflectance r _a in a wide wavelength band, it becomes possible to maintain the r _b to a low value, the antireflection effect by the diffraction described in (3) Synergistically, a high regular antireflection effect can be obtained in a wide wavelength band.

When such an antireflection film is applied to an optical element, it is effective in an angle region using only the 0th-order diffracted light. The antireflection effect is reduced.
Then, the diffraction angle of the high-order diffracted light will be described below. The diffraction angle θ _k of the _{k-th order} diffracted light is described by Expression (4), and the first-order diffraction angle θ ₁ is the smallest angle diffracted light.

[0034]

Sin θ _k = sin θ + k · λ / P (k is 0 or a positive integer) (4)

Therefore, in order to prevent higher-order diffracted light from being mixed into the regular reflected light beam, the pitch P of the unevenness is set small, and the first-order diffracted light diffraction angle θ ₁ is increased with respect to the incident light beam having the center wavelength λ. Just set it.

When the pitch P is smaller than the wavelength λ, the diffraction efficiency is not approximated by the equation (1), and its value is reduced.
> Λ is preferred. The first-order diffraction angle is 2 °
The above is practical for securing the directivity of the incident light beam, and it is preferable that P ≦ 30λ. Therefore,
The pitch P preferably satisfies Expression (5) with respect to the wavelength λ of the incident light beam.

[0037]

Λ <P ≦ 30λ (5)

As an example of the operation of the present invention, a groove type having a rectangular laminar cross section shown in FIG. 1 has been described, but other cross sectional shapes may be used. For example, even in the case of a blazed diffraction grating shape having a sawtooth cross section or a sine wave cross section, the expression (1) for the 0th-order light diffraction intensity and the expression (4) for the diffraction angle are used.
However, similar effects can be obtained.

In the present invention, the regular reflected light flux is reduced as compared with the case where only the anti-reflection film is provided at the interface having no unevenness. However, the light corresponding to the reduced amount is the component that transmits straight through the interface and the diffracted light. And becomes a component that is reflected or transmitted.
Therefore, when the antireflection film of the present invention is used, most of the incident light flux passes straight and the regular reflection light flux has an extremely low value. Therefore, mixing of the regular reflection light flux is prevented, and only the 0th-order diffraction transmitted light is used as the signal light. It is suitable for use as an optical element that does not use diffracted light of the next order or higher. Hereinafter, the present invention will be specifically described with reference to examples.

[0040]

(Embodiment 1) FIG. 1 is a sectional view of an antireflection film of this embodiment. The manufacturing method is shown in FIG. 2 (Configuration Example 1). An SiO ₂ film having a refractive index of about n ₂ = 1.45 is coated on a surface of a translucent glass substrate having a refractive index of about _ng = 1.5 with respect to a normal incident light having a center wavelength λ = 520 nm of the incident light used. Then, a film is formed so that the film thickness d is 130 nm corresponding to λ / 4 (FIG. 2A).

Next, a photoresist is applied on the SiO ₂ film, baked and hardened, and then the line width P _a =
A linear resist pattern 5 is formed by exposing and developing using a photomask in which fine lines of 1.2 μm, space width P _b = 1.2 μm, and pitch P of irregularities P = 2.4 μm are formed (FIG. 2 (b)).

Next, by uniformly irradiating the substrate surface with ions, the non-masked S
The iO ₂ film is patterned by reactive ion etching (RIE). Here, the etching amount of the SiO ₂ film can be controlled by the ion etching time. Usually, the etching at the time when the direction of the SiO ₂ film is no longer SiO ₂ film has high etch rate compared to glass used as a substrate is complete. Therefore, the height d of the projections can be accurately controlled by previously forming a SiO ₂ film having a thickness corresponding to the height d of the projections required in advance (FIG. 2C).

Next, the photoresist used as the masking is removed by a solvent. Then, the line width P _a = 1.2 [mu] m shown in FIG. 2 (d), space - scan width P _b = 1.2 microns
m, pitch P of unevenness = 2.4 μm, average height = 130 n
A periodic pattern 3 of fine lines made of m ₂ SiO ₂ is formed. Since the surrounding medium is air (n = 1.0), the amplitude d of the unevenness of the periodic pattern 3 is n · d = d.

Finally, an anti-reflection film 4 for reducing the interfacial reflection between a glass substrate having a refractive index of 1.45 to 1.5 and air (n = 1) as a surrounding medium is formed. Specifically, Al ₂ O ₃ (n = 1.63) / ZrO ₂ (n = 2.
0) / MgF ₂ (n = 1.38) so that the optical film thickness ( _nd ) is (λ / 4) / (λ / 2) / (λ / 4). Note that the center wavelength λ of the incident light beam is
520 nm.

FIG. 3 (a) shows the spectral reflectance of the antireflection film thus manufactured in the visible wavelength range at normal incidence. An antireflection effect with a regular reflectance of 0.1% or less can be obtained in a wide visible wavelength range of 420 to 700 nm.

As Comparative Example 1, the same antireflection film Al ₂ O ₃ (n = 1.63, _nd = λ /
4) / ZrO ₂ (n = 2.0, _nd = λ / 4) / Mg
FIG. 3B shows the spectral reflectance at the interface of the substrate on which F ₂ (n = 1.38, _nd = λ / 4) is deposited. 430-
Although the reflectance is 0.4% or less in the visible wavelength region of 670 nm, the residual reflectance is higher at any wavelength as compared with the present invention.

As Comparative Example 2, the spectral reflectance at the glass substrate interface shown in FIG.
It is shown in (c). Although the residual reflection is 0.1% or less in a wavelength range narrower than 520 nm, the residual reflection increases in a short wavelength range and a long wavelength range, and the antireflection effect in a visible range is inferior to that of Comparative Example 1.

According to the present invention, an excellent effect which cannot be realized by the conventional antireflection film or diffraction grating is achieved.

FIG. 4 shows the wavelength dependence of the diffraction angle θ ₁ of the _first-order diffracted light according to the structure of the present invention with reference to the 0-order diffracted light angle of 0 °. Accordingly, since the first-order diffracted reflected light of the visible wavelength light of 420 nm or more is scattered at an angle of 10 ° or more with respect to the normal incident light, the visible wavelength region is used in an optical element using only the dispersion angle light of 10 ° or less. It can be used as an anti-reflection film.

[0050] Although the light-transmitting dielectric layer 3 of the convex portion of the width P _a in the present embodiment has described the case of the SiO ₂ film, it may be in other media. Preferably, the refractive index _ng of the translucent substrate 2
A translucent dielectric film 3 having the same refractive index as that described above is suitable. It is preferable to use an optical material having a refractive index of 1.4 to 1.8. As the film medium corresponding to this refractive index, SiO ₂
And a mixture of _{Si 3 N 4 SiO x N y} (x + y =
By forming a film by a sputtering method using 1) as a target, it is possible to prepare a thin film having a refractive index in the middle range of 1.45 to 1.8.

Embodiment 2 FIG. 5 is a sectional view of a convex lens 6 having an anti-reflection film formed thereon. FIG. 6 shows a partially enlarged view of a cross section at the interface (configuration example 2). The convex lens is made of a translucent plastic material having a refractive index of about _ng = 1.5, and is formed by using a metal mold.
It is molded as As shown in FIG. 6, on the surface of the lens, a line width P _a = 1.2 μm and a space width P _b
= 1.2 μm and the pitch P of the irregularities = 2.4 μm and height 13
A groove is formed in a molding die in advance so that a fine line shape 3 of 0 nm is transferred. In this case, since the material of the convex portion in FIG. 1 is the same as that of the substrate 2, the refractive index n ₂ = _ng =
1.5. The surrounding medium 1 is air.

A three-layer antireflection film 4 is formed on the surface of the aspherical convex plastic lens 6 thus formed in the same manner as in the first embodiment.

By such a manufacturing method and configuration, an aspherical convex plastic lens in which the regular reflection light flux on the lens surface is reduced is manufactured. Particularly, when the plastic lens is used as a condensing element of a reflection type optical element, the regular reflection prevention at the lens interface is prevented. A useful effect is obtained when is a problem.

The present invention provides, in addition to the above embodiments,
The present invention can be applied to a liquid crystal lens, a liquid crystal shutter, a liquid crystal optical element, or a liquid crystal display element. Particularly, in an apparatus using a reflection type optical configuration, excellent optical characteristics are exhibited. S /
As for the N ratio and the contrast ratio, good numerical values that cannot be achieved by the conventional example are obtained. The present invention is also applicable to various applications within a range that does not impair the effects of the present invention.

[0055]

According to the present invention, the generation of regular reflected light is suppressed,
Excellent optical characteristics can be obtained. Further, the manufacturing method is easy, the structure can be controlled with high accuracy, and a high-performance product can be manufactured stably.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating the present invention (Configuration Example 1).

FIG. 2 is a sectional view showing a manufacturing method of the present invention (Configuration Example 1).

3A is a graph showing spectral reflectance data in a first configuration example of an antireflection film of the present invention, and FIG. 3B is a graph showing spectral reflectance data in Comparative Example 1 when only a conventional antireflection film is used. Graph, (c) Graph showing spectral reflectance data in Comparative Example 2 when only a conventional diffraction grating is used.

FIG. 4 is a graph showing data showing the wavelength dependence of the diffraction angle of the first-order diffracted light in the present invention (Structural Example 1).

FIG. 5 is a sectional view of a convex lens according to the present invention (Configuration Example 2).

FIG. 6 is an enlarged cross-sectional view near the interface of a convex lens according to the present invention (Structural Example 2).

[Explanation of symbols]

 1: Surrounding medium 2: Translucent optical medium 3: Fine irregularities 4: Transparent dielectric (antireflection film) 5: Photoresist mask pattern for forming minute irregularities 6: Convex lens

Claims (5)

[Claims] 1. A surrounding medium 1 having a refractive index n and a refractive index n _g
In the anti-reflection film in which at least one layer of the light-transmitting dielectric film is provided between the light-transmitting optical medium 2 (n ≠ _ng ) and the light-transmitting optical medium 2 (n ≠ _ng ), the interface S in contact with the surrounding medium 1 is provided. Has irregularities with a periodic structure having a pitch P and an average height d, and the central wavelength of the incident light beam incident on the interface S is λ,
Assuming that the phase difference of the optical path between the reflected light from the convex portion and the reflected light from the concave portion is φ, λ <P ≦ 30λ, and φ ≒ (2M +
1) An anti-reflection film characterized by satisfying π (M is 0 or a positive integer). 2. The light-transmitting dielectric film according to claim 1, wherein a light-transmitting dielectric film having a relatively high refractive index and a light-transmitting dielectric film having a relatively low refractive index are laminated. Anti-reflective coating. 3. The shape of the unevenness is substantially rectangular, and cos θ = λ · (2M + 1) / with respect to the incident angle θ of the central incident light beam.
The antireflection film according to claim 1 or 2, wherein (4nd) is satisfied. 4. The method according to claim 1, wherein the phase difference is φ ≒ π.
The antireflection film as described in the above. 5. incident at the central incident angle θ from the surrounding medium 1 having a refractive index n at the interface S, a manufacturing method of the antireflection film of the incident light beam having a center wavelength lambda, Toru having a refractive index n _g A transparent dielectric film is formed on the optical optical medium 2 with a thickness d = λ /
(4n · cos θ), a linear resist pattern having a concave-convex shape having a periodic structure with a pitch P is formed on the transparent dielectric film, and masking is performed with a photoresist from the surface side. The light-transmitting dielectric film that has not been etched is etched, the photoresist is removed, the light-transmitting dielectric film is formed in a pattern having a pitch P and an average height d, and the light-transmitting dielectric film is formed on the light-transmitting dielectric film. A method for manufacturing an anti-reflection film, comprising forming an anti-reflection layer for the surrounding medium 1 and the translucent optical medium 2.