JP2018185394A - Antireflection film and optical element, optical system and optical device having the same - Google Patents

Abstract

An antireflection film that is easy to form and excellent in wavelength band characteristics and incident angle characteristics, and an optical element, an optical system, and an optical device having the same are provided. An antireflection film having a fine concavo-convex structure in which a frustum shape or a substantially frustum shape is arranged at a pitch smaller than the shortest wavelength used, and the fine concavo-convex structure has a substantial refractive index of 180 nm. It has a region that can be considered to change continuously over the above thickness, and a dielectric thin film layer composed of at least three layers having different refractive indexes is provided between the optical substrate and the fine concavo-convex structure. That it is formed. [Selection] Figure 1

Description

  The present invention relates to an antireflection film formed on the surface of an optical element such as a lens, and in particular, an antireflection film using a fine concavo-convex structure having a sub-wavelength size, an optical element having the antireflection film, an optical system, and an optical device Is about

  Conventionally, an antireflection film has been formed on the surface of the optical element in order to reduce the light loss of incident light and suppress the generation of unnecessary light such as flare and ghost. As an antireflection film for a camera lens, a dielectric multilayer film called multi-coat is generally widely used. This is a mechanism to reduce the reflected light by controlling the amplitude and phase of the reflected wave generated on the surface and interface of each film by laminating thin films with different refractive indexes at appropriate thicknesses. It is.

  Therefore, it is possible to exhibit excellent antireflection performance for a light beam having a specific wavelength and incident angle (design light beam) used for optimizing the interference condition. However, interference conditions are lost for light rays having a wavelength or incident angle different from the design light rays. Therefore, it is difficult to maintain high antireflection performance in a wide wavelength band such as the entire visible range (wavelength 400 to 700 nm) and a wide incident angle range such as 0 to 60 °.

  On the other hand, digital cameras that have become widespread in recent years use solid-state image sensors such as CCD and CMOS sensors, which have higher surface reflectance than conventional photographic films. For this reason, unnecessary light called “digital ghost” tends to be generated when the light reflected by the sensor surface is reflected again by the lens surface and reaches the sensor surface again.

  Furthermore, recent digital camera lenses require high specs (zoom magnification and brightness) and portability (small and light) in addition to high image quality, so anomalous dispersion glass, high refractive index glass, and aspherical surfaces are required. There is a tendency to frequently use lenses and lenses with large curvatures. Among these, especially in the case of a lens with a large curvature, a light beam with a large angle is incident on the periphery, etc., so the conventional multi-coat cannot sufficiently reduce the reflection, and the quality of the photographed image such as flare and ghost is lowered. In some cases, unnecessary light was generated.

  Against this background, there is a demand for the realization of high-performance antireflection films that have better wavelength band characteristics and incident angle characteristics than multi-coat. In Patent Document 1, a coating layer made of a transparent material is provided on the outside of the fine concavo-convex structure, so that the antireflection performance is maintained and the reflection is excellent in high temperature / high humidity environment resistance and scratch resistance. A protective film is disclosed.

JP 2012-189846 A

  Patent Document 1 discloses an example in which the average reflectance in the wavelength range of 420 to 680 nm is 0.05% in Example 4. However, although there is no description of the incident angle in Example 4, it is considered that the above value is probably an incident angle of 0 °, but the performance at a large incident angle such as 45 ° or 60 ° is unknown. When the present applicant conducted numerical verification on Example 4, the reflectance characteristic at an incident angle of 45 ° was greatly reduced.

Accordingly, an object of the present invention is to provide an antireflection film satisfying << reflectance standard 1 >> shown below, which has both wavelength band characteristics and incident angle characteristics, and an optical element, optical system, and optical apparatus having the same. It is. However, in this reflectance standard 1, for the wavelength range from 400 to 430 nm, the standard value at the wavelength of 400 nm and the standard value at the wavelength of 430 nm are connected by a straight line, and between the wavelength range of 670 to 700 nm, the standard at the wavelength of 670 nm. The value obtained by connecting the value and the standard value at a wavelength of 700 nm with a straight line is defined as the standard.
≪Reflectance standard 1≫
For light rays with an incident angle of 0 to 45 °,
(1) Reflectance of 0.05% or less in the wavelength range of 430 to 670 nm
(2) Reflectance of 0.10% or less at wavelengths of 400 nm and 700 nm
For rays with an incident angle of 60 °,
(3) Reflectance of 1.0% or less in the wavelength range of 430 to 670 nm
(4) Reflectance less than 1.5% at wavelengths of 400nm and 700nm

The antireflection film of the present invention, and the optical system and optical apparatus having the antireflection film are antireflection films formed on an optical substrate having a refractive index at a wavelength of 550 nm of 1.65 or more and 2.20 or less,
A frustum shape or a substantially frustum shape having a fine concavo-convex structure layer regularly arranged at a pitch of 250 nm or less,
The fine concavo-convex structure layer has a region where the substantial refractive index can be regarded as continuously changing over a range of 180 nm or more and 300 nm or less,
A four-layer dielectric thin film having at least three kinds of refractive indexes is formed between the optical substrate and the fine concavo-convex structure layer.

  According to the present invention, it is possible to provide an antireflection film having both excellent wavelength band characteristics and incident angle characteristics, and an optical system and an optical apparatus having the antireflection film.

Schematic of refractive index structure of antireflection film of the present invention Schematic sectional view of the antireflection film of the present invention Refractive index structure and reflectance characteristics of antireflection film of Example 1 Refractive index structure and reflectance characteristics of antireflection film of Example 2 Refractive index structure and reflectance characteristics of antireflection film of Example 3 Refractive index structure and reflectance characteristics of antireflection film of Example 4 Refractive index structure and reflectance characteristics of antireflection film of Example 5 Refractive index structure and reflectance characteristics of antireflection film of Example 6 Refractive index structure and reflectance characteristics of antireflection film of Example 7 Optical sectional view of the optical system of Example 8 Schematic diagram of the optical apparatus of Example 9 Schematic sectional view of the antireflection film of the present invention (when the shape of the fine relief structure is dull) Schematic diagram showing how to replace a dull shaped microstructure with a frustum

  Embodiments of the present invention will be described with reference to the accompanying drawings. All the refractive indexes in the description are values at a wavelength of 550 nm.

FIG. 1 schematically and schematically shows the refractive index structure of the antireflection film of the present invention. FIG. 2 schematically shows a cross section of the antireflection film of the present invention, and shows an enlarged surface portion of an optical element to which the antireflection film of the present invention is applied on an optical substrate such as a lens. It is. The optical substrate 11 is a member having a refractive index N _sub of 1.65 to 2.20, on which the antireflection film 12 of the present invention is formed. The antireflection film 12 includes a dielectric thin film layer 13 and a fine concavo-convex structure layer 14, and in order from the optical substrate 11 side, a first layer 101, a second layer 102, a third layer 103, a fourth layer 104, a fifth layer 105 and the sixth layer 106.

  Here, the fine concavo-convex structure layer 14 is a layer formed by a nanoimprint method or a photolithography method, and the sixth layer 106 is a portion where a fine concavo-convex shape is formed (transferred or etched), and the fifth layer 105 Is an underlying layer that remains without being uneven. That is, the fine concavo-convex structure layer 106 and the base layer 105 are made of the same material.

The first layer 101 is a thin film layer having a refractive index N ₁ of 1.55 to 1.95 and a film thickness D ₁ of 5.0 to 40.0 nm. The second layer 102 is a thin film layer having a refractive index N ₂ of 1.70 to 2.40 and a film thickness D ₂ of 5.0 to 40.0 nm. The third layer 103 is a thin film layer having a refractive index N ₃ of 1.55 to 1.95 and a film thickness D ₃ of 30.0 to 110.0 nm. The fourth layer 104 is a thin film layer having a refractive index N ₄ of 1.35 to 1.55 and a film thickness D ₄ of 90.0 nm or less. The fifth layer 105 is a thin film layer having a refractive index N ₅ of 1.35 to 1.55 and a film thickness D ₅ of 90.0 nm or less. The sixth layer 106 has a thickness D ₆ of 180 to 300 nm, and a refractive index at the bottom (substrate side) portion from a value N _{6b in} the range of 1.20 to 1.50, being refracted at the top (vertex side) portion. The rate has a region that changes substantially continuously up to a value N _{6t in} the range of 1.015 to 1.05. Moreover, it is preferable that each refractive index and film thickness satisfy | fill the following formula | equation.

0.14 ≦ N ₂ −N ₁ ≦ 0.55
0.14 ≦ N ₂ −N ₃ ≦ 0.55
0.14 ≦ N ₃ −N ₄ ≦ 0.50
50 nm ≤ D ₄ + D ₅ ≤ 90 nm
0.22 ≦ N _6b −N _6t ≦ 0.38

Here, the expression “substantially changes” means that the refractive index of the material forming the sixth layer 106 does not change continuously, but the space of the concavo-convex structure having a period smaller than the wavelength. This means that the “effective refractive index” changes continuously as the filling rate changes continuously in the thickness direction. This is due to the property that light recognizes a fine concavo-convex structure having a size smaller than its own wavelength as a medium having an “effective refractive index” corresponding to the space occupancy. The effective refractive index N _eff is the Bruggeman equation, where N _m is the refractive index of the material that forms a concavo-convex structure finer than the wavelength, and ff is the space occupancy of the material.

Can be used to calculate. That is, a structure in which the space occupancy continuously changes at a pitch smaller than the wavelength can be regarded as a film in which the substantial refractive index (effective refractive index) changes continuously.

In the present invention, the production method is not particularly limited as long as it is an antireflection film satisfying the above-described refractive index and film thickness. In consideration of environmental durability, at least one of the dielectric thin film layers 13, preferably the first layer 101 is a SiON (silicon oxynitride) film formed by dry film formation such as sputtering or Al ₂ O ₃ ( A film containing an (aluminum oxide) film is preferred. In addition, if the fine uneven structure layer 14 uses a transfer method such as nanoimprint, it is preferable that the fifth layer 106 and the sixth layer 106 can be formed simultaneously.

  By adopting the refractive index structure as described above, the antireflection film of the present invention realizes high performance that satisfies both the wavelength band characteristics and the incident angle characteristics that satisfy the << reflectance standard 1 >> shown below. Can do.

≪Reflectance standard 1≫
For light rays with an incident angle of 0 to 45 °,
(1) Reflectance of 0.05% or less in the wavelength range of 430 to 670 nm
(2) Reflectance of 0.10% or less at wavelengths of 400 nm and 700 nm
For rays with an incident angle of 60 °,
(3) Reflectance of 1.0% or less in the wavelength range of 430 to 670 nm
(4) Reflectance less than 1.5% at wavelengths of 400nm and 700nm

  Here, the reflectance standard on which the present invention is based on high performance will be described. The antireflection film of the present invention places importance on the reflectance characteristics at wavelengths of 430 to 670 nm, and the characteristics at wavelengths of 400 to 430 nm and wavelengths of 670 to 700 nm are relaxed.

  This takes into account the spectral sensitivity characteristics of image sensors such as CCD and CMOS used in digital cameras. In other words, image sensors for cameras have high sensitivity in the wavelength range of 430 to 670 nm in order to faithfully reproduce images viewed by humans, but low sensitivity at wavelengths of 400 to 430 nm and wavelengths of 670 to 700 nm. It is set to be. Therefore, even if the reflectance characteristics at wavelengths of 400 to 430 nm and wavelengths of 670 to 700 nm are somewhat high, unnecessary light such as flare and ghost hardly affects the captured image, so the reflectance standard for the same wavelength band is relaxed. Is possible.

  And, by using the optical element on which the antireflection film of the present invention is formed in an optical system such as a camera lens, a high-quality optical system and optical device that suppress the generation of unnecessary light and harmful light such as flare and ghost are suppressed. Can be realized.

  Examples of the present invention will be specifically described below. The refractive index and film thickness of each example are shown in Table 1.

[Example 1]
FIG. 3 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 1 of the present invention. (a) is a refractive index structure, (b) and (c) are diagrams showing reflectance characteristics, and (b) is 1.5% full scale and (c) 0.1% full scale.

  The optical substrate 11 in the present embodiment is K-PSFn173 made by Sumita Optical Glass Co., Ltd. The refractive index and film thickness of each layer are as shown in Table 1. The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm), and satisfies the above-described << Reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.036% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.85% or less is achieved for light rays with an incident angle of 60 °.

In the present embodiment, the first layer 101 and the third layer 103 are made of SiON (silicon oxynitride). The material of the first layer and the third layer is not limited to SiON as long as the refractive index shown in Table 1 can be realized, but SiON can be arbitrarily adjusted within the range of 1.4 to 2.0 by adjusting the mixing ratio of oxygen and nitrogen. It is preferable because it can be set. SiON is also a preferable material because it has a high ability to suppress moisture permeation from the outside and elution of alkali components from the inside of the glass material (optical substrate). For the same reason, Al ₂ O ₃ (aluminum oxide) may be used. In the present embodiment, the first layer and the third layer have the same refractive index, but the present invention is not limited to this and can be arbitrarily set in the range of 1.55 to 1.95.

TiO ₂ (titanium oxide) is used for the second layer 102, but this can also be substituted for a dielectric thin film having a refractive index in the range of 1.70 to 2.40. For example, ZrO ₂ (zirconium oxide), SiN (silicon nitride), SiON, etc. can be used alone or as a mixed material thereof. However, the refractive index N ₂ of the second layer is preferably larger than the refractive index N ₁ of the _first layer and the refractive index N ₃ of the third layer, and more preferably set to a value greater than 0.14. . When SiON is used for the second layer in addition to the first layer and the third layer, the above refractive index range may be satisfied by controlling the mixing ratio of oxygen and nitrogen.

The fourth layer 104 is made of SiO ₂ (silicon oxide), which can be substituted for a dielectric thin film having a refractive index in the range of 1.35 to 1.55. For example, MgF ₂ (magnesium fluoride) or SiON can be used. However, the refractive index N ₄ of the fourth layer is preferably a value smaller than the refractive index N ₃ of the third layer, and more preferably set to a value smaller than 0.15.

  In the present invention, the method for forming the dielectric thin film layer 13 is not limited, but any method such as a vacuum deposition method, a sputtering method, a molecular beam epitaxy (MBE) method, or a plasma CVD method can be used. In forming a dielectric thin film, even if the material is the same, the refractive index and the refractive index dispersion slightly vary depending on the film forming conditions (substrate temperature, ultimate vacuum, etc.). In such a case, substantially the same high performance can be obtained by correcting the film thickness so that the optical film thickness (refractive index × physical film thickness) value of the above film matches.

The fine concavo-convex structure layer 14 is a film formed by transferring a fine concavo-convex shape to a resin (refractive index: 1.493) mainly composed of acrylic by a nanoimprint method. The sixth layer 106 is a portion to which the fine concavo-convex shape has been transferred, and the fifth layer 105 is a base layer that remains under the structure without being transferred. The uneven shape of the sixth layer 106 is a regular arrangement of frustum shapes (conical shapes, quadrangular pyramids, and hexagonal pyramidal apexes cut off) with a pitch of 250 nm or less. The refractive index is 1.288 by setting the height (film thickness) D ₆ to 229.0 nm, the space occupancy at the bottom (FF _b ) to 59.7%, and the space occupancy at the top (FF _t ) to 4%. It is a layer that changes continuously from 1.018 to 1.018.

In order to obtain good reflectance characteristics, FF _t is preferably a small value. This is because if the top portion is conical, the refractive index is 1.0, the same as air, and the reflection there can be zero. However, in molding such as nanoimprint, it is practically difficult to achieve FF _t close to 0% considering the mold manufacturing method, durability, and mold release after molding. Therefore, in this embodiment, it is 4%. However, the FFt of the present invention is not limited to 4.0%, and if it is set in the range of 1 to 9%, it is possible to achieve both the durability of the mold, the formation of profit after molding, and the antireflection performance.

Yet a six-layer height (thickness) D ₆ can be increased higher antireflection performance (especially performance at a large incident angle). However, if the height of the irregularities is increased, in the present invention, in the nanoimprint method and the sol-gel method, the releasability at the time of molding is lowered.
180nm ≤ D ₆ ≤ 300nm
It is set to become. More preferably,
210nm ≤ D ₆ ≤ 270nm
It is good to set it in the range.

  From the viewpoint of releasability, not only the height but also the aspect ratio (height / pitch) is important. As the aspect ratio increases, the releasability decreases, so the pitch is preferably set in the range of 100 to 250 nm.

  Similarly, considering the mold manufacturing method in nanoimprint, it is difficult to realize a strict frustum shape. In fact, as shown in FIG. 12, the bottom part and the top part are dull and rounded. turn into. In such a case, as shown in FIG. 13, a frustum 202 having the same volume that can be formed by extending the inclination of the cone as it is is formed above the point 201 where the deviation starts from the shape of the frustum. By substituting with a middle broken line), it can be converted into an almost equivalent frustum shape. The same idea can be applied to the bottom part. That is, when the shape of the microstructure layer is rounded, the effect of the present invention can be obtained by setting the frustum shape replaced by the above method to be in the numerical range as described above. be able to.

  As for the arrangement of the fine structure, any arrangement such as a hexagonal arrangement and a square arrangement may be used as long as the above refractive index range is satisfied. The frustum shape may be any shape such as a frustum, an elliptic frustum, or a polygonal frustum as long as the refractive index range is satisfied.

 In this embodiment, a resin mainly composed of acrylic is used as the material of the fine concavo-convex structure layer 13, but the present invention is not limited to this. Any material other than acrylic, such as polycarbonate, polystyrene, cycloolefin polymer, etc., that satisfies the above-mentioned refractive index conditions and film thickness conditions and can transfer and form a microstructure can be used. Can be expressed. The curing method may be any method such as an ultraviolet curable resin, a thermosetting resin, or a thermoplastic resin. A sol-gel material such as spin-on-glass (SOG) may be used.

[Example 2]
FIG. 4 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 2 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 is K-PSFn173 made by Sumita Optical Glass, as in Example 1. The first layer 101 and the third layer 103 use SiON (silicon oxynitride), the second layer 102 uses TiO ₂ (titanium oxide), and the fourth layer 104 uses SiO ₂ (silicon oxide). Further, as the material of the fine concavo-convex structure layer 14, a resin (refractive index: 1.588) mainly composed of polycarbonate is used. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 228.1 nm, a space occupancy rate (FF _b ) of 52.9% at the bottom part, and a space occupancy ratio (FF _t ) of 4% at the top part. As a result, the refractive index continuously changes from 1.300 to 1.020.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.036% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.86% or less is achieved for light rays with an incident angle of 60 °.

[Example 3]
FIG. 5 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 3 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 in this embodiment is S-LAH79 manufactured by OHARA INC. The first layer 101 and the third layer 103 use SiON (silicon oxynitride), the second layer 102 uses TiO ₂ (titanium oxide), and the fourth layer 104 uses SiO ₂ (silicon oxide). As the material of the fine concavo-convex structure layer 14, a resin (refractive index: 1.493) containing acrylic as a main component is used. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 231.0 nm, a space occupancy (FF _b ) of 61.9% at the bottom, and a space occupancy (FF _t ) of 4% at the top. Thus, the layer has a refractive index continuously changing from 1.299 to 1.018.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.040% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.90% or less is achieved for light rays with an incident angle of 60 °.

[Example 4]
FIG. 6 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 4 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 in this embodiment is S-LAH58 manufactured by OHARA INC. The first layer 101 and the third layer 103 use SiON (silicon oxynitride), the second layer 102 uses Ta ₂ O ₅ (tantalum pentoxide), and the fourth layer 104 uses SiO ₂ (silicon oxide). As the material of the fine concavo-convex structure layer 14, a resin (refractive index: 1.493) containing acrylic as a main component is used. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 247.7 nm, a space occupancy ratio (FF _b ) of 68.9% at the bottom part, and a space occupancy ratio (FF _t ) of 4.0% at the top part. As a result, the refractive index continuously changes from 1.335 to 1.018.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.042% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.86% or less is achieved for light rays with an incident angle of 60 °.

[Example 5]
FIG. 7 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 5 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 in this example is S-LAH58 manufactured by OHARA INC. As in Example 4. The first layer 101 and the third layer 103 are made of SiON (silicon oxynitride), and the second layer 102 is made of Ta ₂ O ₅ (tantalum pentoxide). As the material of the fine concavo-convex structure layer 14, a resin (refractive index: 1.493) containing acrylic as a main component is used.

In this embodiment, since the film thickness D ₅ of the fifth layer 105 and 72.3Nm, that has a thickness of the fourth layer 104 to zero is characterized. When the fine concavo-convex structure layer 14 is formed by the nanoimprint method or the like, the fourth layer 104 can be omitted if the film thickness of the underlayer (fifth layer) 105 can be controlled with high accuracy. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 251.1 nm, a space occupancy rate (FF _b ) of 71.0% at the bottom, and a space occupancy rate (FF _t ) of 4.0% at the top. As a result, the refractive index continuously changes from 1.346 to 1.018.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.044% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.86% or less is achieved for light rays with an incident angle of 60 °.

[Example 6]
FIG. 8 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 6 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 in this embodiment is S-LAH65V manufactured by OHARA INC. The first layer 101 and the third layer 103 are made of Al ₂ O ₃ (aluminum oxide), the second layer 102 is made of ZrO ₂ (zirconium oxide), and the fourth layer 104 is made of SiO ₂ (silicon oxide). As the material of the fine concavo-convex structure layer 14, a resin (refractive index: 1.493) containing acrylic as a main component is used. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 251.0 nm, a space occupancy rate (FF _b ) at the bottom portion of 72.6%, and a space occupancy rate at the top portion (FF _t ) of 4%. Thus, the layer has a refractive index that continuously changes from 1.354 to 1.018.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.045% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.91% or less is achieved for light rays with an incident angle of 60 °.

[Example 7]
FIG. 9 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 7 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 in this embodiment is S-LAL14 manufactured by OHARA INC. The first layer 101 and the third layer 103 use SiON (silicon oxynitride), the second layer 102 uses SiON (silicon oxynitride), and the fourth layer 104 uses SiO ₂ (silicon oxide). However, the first layer 101, the third layer 103, and the second layer 102 are films having different refractive indexes because the mixing ratio of oxygen and nitrogen is different. As the material of the fine concavo-convex structure layer 14, a resin (refractive index: 1.493) containing acrylic as a main component is used. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 258.1 nm, a space occupancy ratio (FF _b ) of 65.5% at the bottom part, and a space occupancy ratio (FF _t ) of 4.0% at the top part. Thus, the layer has a refractive index continuously changing from 1.317 to 1.018.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.033% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.76% or less is achieved for light rays with an incident angle of 60 °.

[Example 8]
FIG. 10 shows the refractive index structure and reflectance characteristics of the antireflection film of Example 8 of the present invention. The substrate refractive index, the refractive index of each layer, and the film thickness in this example are as shown in Table 1.

The optical substrate 11 in this example is S-LAL14 manufactured by OHARA INC. As in Example 7. The first layer 101 and the third layer 103 are made of SiON (silicon oxynitride), the second layer 102 is made of SiON (silicon oxynitride), and the fourth layer 104 is made of MgF ₂ (magnesium fluoride). However, the first layer 101, the third layer 103, and the second layer 102 are films having different refractive indexes because the mixing ratio of oxygen and nitrogen is different.

In this embodiment, since the film thickness D ₄ of the fourth layer 104 and 73.2Nm, that has a thickness of the fifth layer 105 (base layer of the fine unevenness layer) to zero is characterized. When the film thickness of the underlying layer (fifth layer) 105 of the fine concavo-convex structure layer 14 can be made zero by nanoimprinting or the like, high antireflection performance can be realized by controlling the fourth layer 104 to be thick. As a material for the fine concavo-convex structure layer 14 (the fifth layer 105 does not exist in this embodiment), a resin (refractive index: 1.493) containing acrylic as a main component is used. The uneven shape of the sixth layer 106 has a height (film thickness) D ₆ of 249.3 nm, a space occupancy rate (FF _b ) of 72.9% at the bottom, and a space occupancy rate (FF _t ) of 4.0% at the top. Thus, the layer has a refractive index continuously changing from 1.275 to 1.018.

  The antireflection film of this example exhibits high antireflection performance over the entire visible wavelength band (wavelength 400 to 700 nm) and satisfies << reflectance standard 1 >>.

Especially in the wavelength range of 430 to 670 nm
0.031% or less for rays with an incident angle of 0 to 45 °,
Excellent performance of 0.68% or less is achieved for light rays with an incident angle of 60 °.

In Examples 1 to 8 of the present invention, the space occupancy ratio (FF _t ) in the top portion of the uneven shape of the sixth layer 106 was set to 4.0%, but the present invention is not limited to this, and 1.0 What is necessary is just to set in the range of -9.0%. Further, although the fifth layer 105 and the sixth layer 106 show the case where a resin mainly composed of acrylic or polycarbonate is formed by a nanoimprint method or the like, the present invention is not limited to this, and the sol-gel is not limited thereto. An inorganic material formed by a method or the like may be used. Further, the method of forming the uneven shape may be a method combining photolithography and etching.

[Example 9]
FIG. 11 is a schematic view when the optical element (lens) on which the reflection mask of the present invention is formed is applied to an optical device (camera). In FIG. 9, since the digital camera 2001 uses the lens 1001 having the antireflection film of the present invention to reduce the generation of harmful light such as flare and ghost, a high-quality image can be obtained. it can.

11 Optical substrate (lens)
12 Anti-reflective coating
13 Dielectric thin film layer
14 Fine relief structure layer
101 1st layer
102 2nd layer
103 3rd layer
104 4th layer
105 5th layer (underlayer)
106 6th layer (fine structure layer)
1001 optical system
2001 Optical device (camera)

Claims (12)

An antireflection film having a fine concavo-convex structure in which a frustum shape or a frustum shape is arranged at a pitch smaller than the shortest wavelength used,
The fine concavo-convex structure has a region where the refractive index can be regarded as continuously changing over a thickness of 180 nm or more,
An antireflection film, wherein a dielectric thin film layer comprising four layers having at least three different refractive indexes is formed between an optical substrate and the fine concavo-convex structure. The antireflection film according to claim 1,
The refractive index of the optical substrate (lens) on which the antireflection film is formed is N _sub, and in order from the optical substrate,
A first layer having a refractive index of N ₁ and a thickness of D ₁ ;
A second layer having a refractive index of N ₂ and a thickness of D ₂ ;
A third layer having a refractive index of N ₃ and a film thickness of D ₃ ;
A fourth layer having a refractive index of N ₄ and a thickness of D ₄ ;
A fifth layer (underlayer) having a refractive index of N ₅ and a film thickness of D ₅ ;
Period at 300nm or less, are formed to a thickness of the sixth layer (the height of the fine unevenness) is D ₆ (fine unevenness layer) are integrally (same material),
In the sixth layer, when the space filling factor at the bottom of the microstructure layer is FF _b , the effective refractive index is N _6b , the space filling factor at the top is FF _t , and the effective refractive index is N _6t ,
An antireflection film characterized in that the refractive index and film thickness of each layer satisfy the following conditions.
1.65 ≤ N _sub ≤ 2.20,
1.50 ≤ N ₁ ≤ 2.00,
1.65 ≤ N ₂ ≤ 2.40,
1.50 ≤ N ₃ ≤ 2.00,
1.30 ≤ N ₄ ≤ 1.60,
1.30 ≤ N ₅ ≤ 1.60,
1.20 ≤ N _6b ≤ 1.60, 1.015 ≤ N _6t ≤ 1.050, 180nm ≤ D ₇
N ₄ <N ₁ <N ₂
N ₄ <N ₃ <N ₂
0.22 ≦ N _6b −N _6t ≦ 0.50 The antireflection film according to claim 2,
An antireflection film characterized in that the refractive index and film thickness of each layer satisfy the following conditions.
1.65 ≤ N _sub ≤ 2.20,
1.55 ≤ N ₁ ≤ 1.95, 5.0 nm ≤ D ₁ ≤ 40.0 nm,
1.70 ≤ N ₂ ≤ 2.40, 5.0 nm ≤ D ₂ ≤ 40.0 nm,
1.55 ≤ N ₃ ≤ 1.95, 30.0 nm ≤ D ₃ ≤ 110.0 nm,
1.35 ≤ N ₄ ≤ 1.55, D ₄ ≤ 90.0nm,
1.35 ≤ N ₅ ≤ 1.55, D ₅ ≤ 90.0nm,
1.20 ≤ N _6b ≤ 1.50, 1.015 ≤ N _6t ≤ 1.050, 180 nm ≤ D ₇ ≤ 300.0 nm
0.14 ≦ N ₂ −N ₁ ≦ 0.55
0.14 ≦ N ₂ −N ₃ ≦ 0.55
0.14 ≦ N ₃ −N ₄ ≦ 0.50
50nm ≤ D ₄ + D ₅ ≤ 90nm
0.22 ≦ N _6b −N _6t ≦ 0.38 The antireflection film is
For light rays with an incident angle of 0 to 45 °,
In the wavelength range of 430 to 670 nm, the reflectance is 0.05% or less, and
At a wavelength of 400 nm and 700 nm, for a light beam with a reflectance of 0.10% and an incident angle of 60 °,
In the wavelength range of 430 to 670 nm, the reflectance is 1.0% or less, and
The antireflection film according to claim 2, wherein the antireflection film satisfies a performance of a reflectance of 1.5% or less at wavelengths of 400 nm and 700 nm. The first layer and the third layer are:
5. The antireflection film according to claim 1, wherein the antireflection film is any one of SiON (silicon oxynitride) or Al ₂ O ₃ (aluminum oxide). The third layer is
It is a film containing any one of TiO ₂ (titanium oxide), Ta ₂ O ₅ (tantalum pentoxide), ZrO ₂ (zirconium oxide), SiN (silicon nitride), and SiON (silicon oxynitride). The antireflection film according to any one of claims 1 to 4. The fourth layer is
The antireflection film according to any one of claims 1 to 4, wherein the antireflection film is any one of SiO ₂ (silicon oxide), MgF ₂ (magnesium fluoride), and SiON (silicon oxynitride). The fifth and sixth layers are:
The antireflection film according to claim 1, wherein the antireflection film is a layer made of an energy curable resin material and formed by a nanoimprint method or a photolithography method. The fifth and sixth layers are:
The antireflection film according to claim 1, wherein the antireflection film is a layer made of an inorganic material and formed by a sol-gel method. An optical element, wherein the antireflection film according to any one of claims 1 to 9 is formed. An optical system comprising the optical element according to claim 10. An optical apparatus comprising the optical system according to claim 8.