JP2015084024A - Antireflection film, optical element, and optical equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antireflection film having good antireflection characteristics.SOLUTION: An antireflection film 100 formed on a substrate 1 includes a rugged structure having a pitch smaller than 400 nm and an intermediate layer 2. The rugged structure has a thickness of 165 nm or more and 300 nm or less and has an effective refractive index for light at a center wavelength of 550 nm, varying from a value of 1.35 or more and 1.58 or less on an intermediate layer side toward a light incidence side. The substrate has a refractive index of 1.40 or more and 1.75 or less to the above light. The intermediate layer includes, successively deposited from the substrate side, a first layer having a refractive index n1 to the above light and a physical film thickness d1, a second layer having a refractive index n2 and a physical film thickness d2, a third layer having a refractive index n3 and a physical film thickness d3, and a fourth layer having a refractive index n4 and a physical film thickness d4, satisfying 1.55≤n1≤1.70, 1.35≤n2≤1.52, 1.85≤n3≤2.40, 1.35≤n4≤1.52, 10nm≤n1d1≤260nm, 10nm≤n2d2≤45nm, 5nm≤n3d3≤35nm, and n4d4≤125nm.

Description

  The present invention relates to an antireflection film having a fine concavo-convex structure and having an antireflection function or the like.

  In order to prevent unnecessary reflection, a dielectric multilayer film generally called a multi-coat is often formed on the surface of an optical element such as a lens. As an antireflection film having an antireflection function, a film using a fine uneven structure is also known.

  For example, Patent Document 1 discloses an antireflection film in which a layer having a low refractive index composed of a nanoporous film or a nanoparticulate film is used as the uppermost layer (the layer farthest from the substrate). In Patent Document 1, this antireflection film is composed of only a thin film having a film thickness of 100 nm or more that can be formed with high accuracy, thereby reducing performance deterioration due to film thickness fluctuations during manufacturing, and in particular incident vertically. It is described that high performance can be maintained with respect to light. Patent Document 2 discloses an antireflection film in which a substantial refractive index (effective refractive index) continuously changes from the light incident side to the base material side, and is a plate-shaped material mainly composed of aluminum oxide. A crystal using the uppermost layer is disclosed.

JP 2012-78597 A JP 2008-233880 A

  However, since the antireflection film disclosed in Patent Document 1 suppresses reflection using thin film interference, it has antireflection performance against oblique incidence in which the interference condition is broken, particularly light incidence at an incident angle of 45 degrees or more. There is a possibility of significant deterioration. In addition, when a film is formed on the lens surface of a lens having a large opening angle, it is difficult to form a film with a uniform film thickness at the peripheral part and the central part. It is not optimal and the reflectance characteristics are likely to deteriorate.

  On the other hand, Patent Document 2 does not disclose details of the design value of the film (refractive index structure) and antireflection characteristics.

  The present invention provides an antireflection film which is formed on a base material having a refractive index of 1.75 or less and can provide good antireflection characteristics (wavelength characteristics and incident angle characteristics).

The antireflection film of the present invention has a concavo-convex structure formed on a substrate and having a pitch smaller than 400 nm, and an intermediate layer formed between the concavo-convex structure and the substrate. The thickness of the concavo-convex structure is 165 nm or more and 300 nm or less. The effective refractive index of the concavo-convex structure with respect to light having a central wavelength of 550 nm changes from a value of 1.35 to 1.58 on the intermediate layer side toward the light incident side. The refractive index of the substrate with respect to light having a central wavelength of 550 nm is 1.40 or more and 1.75 or less. The intermediate layer is laminated in order from the substrate side, the first layer having a refractive index n1 and a physical film thickness d1 with respect to light having a central wavelength of 550 nm, and the refractive index having a refractive index n2 with respect to light having a central wavelength of 550 nm. A second layer having a physical film thickness of d2, a third layer having a refractive index of n3 and a physical film thickness of d3 for light having a central wavelength of 550 nm, and a refractive index of n4 having light having a physical wavelength of 550 nm. And a fourth layer having a physical film thickness of d4. And it is characterized by satisfying the following conditions.
1.55 ≦ n1 ≦ 1.70
1.35 ≦ n2 ≦ 1.52
1.85 ≦ n3 ≦ 2.40
1.35 ≦ n4 ≦ 1.52
10 nm ≦ n1d1 ≦ 260 nm
10 nm ≦ n2d2 ≦ 45 nm
5nm ≦ n3d3 ≦ 35nm
n4d4 ≦ 125nm
Note that an optical element having an optical glass and the antireflection film formed on the surface of the optical glass as a base material and an optical system including the optical element also constitute one aspect of the present invention.

  According to the present invention, as a reflective film formed on a substrate having a refractive index with respect to light having a central wavelength of 550 nm of 1.40 or more and 1.75 or less, good antireflection characteristics (wavelength characteristics and incident angle characteristics) are obtained. An antireflection film having the same can be realized. An optical device having excellent optical characteristics can be realized by using the optical element on which the antireflection film is formed for an optical device.

Schematic which shows the structure of the anti-reflective film which is a typical Example of this invention. The figure which shows the reflectance fluctuation | variation at the time of 0 degree incidence and 45 degree incidence when the refractive index structure of the anti-reflective film which is Example 1 of this invention, a reflectance characteristic, and the film thickness of an intermediate | middle layer change ± 10%. The figure which shows the reflectance characteristic of the anti-reflective film which is Example 2 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 3 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 4 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 5 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 6 of this invention. The figure which shows the reflectance characteristic of the anti-reflective film which is Example 7 and Example 8 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 9 of this invention. The figure which shows the reflectance characteristic of the anti-reflective film which is Example 10 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 11 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 12 of this invention. The figure which shows the refractive index structure and reflectance characteristic of the antireflection film which is Example 13 of this invention. FIG. 18 shows an optical apparatus that is Embodiment 14 of the present invention. The figure which shows the reflectance fluctuation | variation at the time of 0 degree incidence and 45 degree incidence when the film thickness of an intermediate | middle layer fluctuates +/- 10% in the comparative example 1 and the comparative example 2. FIG. FIG. 6 is a graph showing the reflectance characteristics of Comparative Example 2. The figure which shows the refractive index structure and reflectance characteristic of the comparative example 3. The figure which shows the reflectance characteristic of Comparative Examples 4-6. FIG. 10 is a graph showing the reflectance characteristics of Comparative Example 7. The figure which shows the refractive index structure and reflectance characteristic of the comparative example 8.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1A schematically shows the configuration of an antireflection film as a typical embodiment of the present invention. In the following description, the values of the refractive index and the optical film thickness are the refractive index and the optical film thickness for light having a central wavelength of 550 nm incident on the antireflection film.

  The optical substrate 1 as a base material is formed of optical glass or optical plastic having a refractive index of 1.40 or more and 1.75 or less, and the antireflection film 100 of the embodiment is formed on the surface (on the base material). .

  The antireflection film 100 includes a fine concavo-convex structure 3 in which concave portions are formed between convex portions formed with a pitch smaller than 400 nm, and an intermediate layer 2 formed between the concavo-convex structure 3 and the optical substrate 1. It is configured.

  When light is incident on a fine structure having a pitch smaller than the wavelength, the light behaves as if it is incident on a medium having a refractive index according to the volume ratio of the material constituting the fine structure, regardless of the details of the structure. The refractive index according to this volume ratio is called an effective refractive index (neff), and the effective refractive index is expressed by a relational expression (1) between the refractive index nm of the material constituting the structure and the space filling factor ff (Lorentz-Lorenz). ).

Since the concavo-convex structure 3 has a structure in which the space filling factor ff continuously increases from the light incident side toward the intermediate layer side, the effective refractive index neff continuously increases from the light incident side. Reflection of light occurs at the interface between two materials with different refractive indices, and thus a structure in which the refractive index continuously changes is less likely to generate a reflected wave. Compared to an antireflection film using a dielectric multilayer film, the wavelength characteristics And anti-reflection performance with excellent incident angle characteristics.

  In order for the antireflection film 100 to have high antireflection performance, the film thickness of the concavo-convex structure 3 needs to be 165 nm or more and 300 nm or less. When the film thickness is less than 165 nm, the wavelength range where high antireflection performance is obtained becomes narrow, and in particular, the reflectance in the long wavelength side wavelength range (around 650 to 700 nm) in the visible light wavelength range becomes high. Furthermore, when high-performance antireflection performance is required even when the incident angle is 45 degrees or more, the film thickness of the concavo-convex structure 3 is preferably 190 nm or more. On the other hand, when the film thickness of the concavo-convex structure 3 is greater than 300 nm, scattering increases and the transmittance decreases.

  If the uneven structure 3 having the above-described refractive index and film thickness can be realized, the manufacturing method is not particularly limited. However, considering mass productivity, a film containing aluminum oxide (alumina) formed by a vacuum film formation method or a liquid phase method (sol-gel method) is treated as a plate crystal (petal) by steam treatment or hot water immersion treatment. The forming method is preferred. When aluminum oxide is used, the effective refractive index of the concavo-convex structure 3 is continuous from a value of 1.35 to 1.58 on the intermediate layer side (base material side) to 1.0 on the most light incident side. Change (decrease).

  Furthermore, in the concavo-convex structure 3, a homogeneous portion (a portion where the concavo-convex structure is not formed) where the effective refractive index does not change in the thickness direction remains on the intermediate layer side, more specifically, on the portion in contact with the intermediate layer 2. It may be. For example, when the aluminum oxide film is treated with water vapor or warm water as described above, a plate-like crystal of aluminum oxide is deposited on the surface layer to form a concavo-convex structure. A homogeneous part can remain. At this time, the film thickness of the remaining homogeneous portion can be controlled by controlling the treatment time, the treatment temperature, the content of aluminum oxide in the material, and the content of additives such as stabilizers and catalysts.

  However, this is not limited to the case where the aluminum oxide film is treated with water vapor or warm water. For example, a homogeneous portion can be formed even when a fine concavo-convex structure is formed on the surface of the optical element by nanoimprinting. Further, the refractive index of the homogeneous portion may be made substantially coincident with the root portion of the concavo-convex structure.

  On the other hand, the concavo-convex structure 3 has a lower density than a homogeneous film such as a normal vapor deposition film, and therefore moisture from the outside may pass through the concavo-convex structure 3 and affect the optical substrate 1. Therefore, by providing the intermediate layer 2 that is a multilayer film between the concavo-convex structure 3 and the optical substrate 1, the stability as an antireflection film can be improved. Here, in order to further improve the stability, at least one of the thin film layers constituting the intermediate layer 2 is preferably a dense layer having a refractive index higher than that of the optical substrate 1. Further, in order to maintain good reflectance characteristics with respect to the optical substrate 1 whose refractive index is set in a wide range of 1.40 to 1.75, at least one of the thin film layers constituting the intermediate layer 2 is used. Is preferably an H layer having a refractive index higher than that of the optical substrate 1. Furthermore, the refractive index difference between the optical substrate 1 and the H layer is preferably 0.1 or more, and more preferably 0.15 or more.

  The manufacturing method of each thin film which comprises the intermediate | middle layer 2 is not specifically limited, Arbitrary processes, such as a liquid phase method, a vacuum evaporation method, and a sputtering method, can be selected. However, in order to form a denser film, a dry process is preferable, and a sputtering method is more preferable.

In order to obtain good characteristics for the optical substrate 1 having a wide refractive index range as described above, the intermediate layer 2 has a four-layer structure as shown in FIG. Here, the four layers stacked in the intermediate layer 2 are arranged in order from the optical substrate side, a first layer having a refractive index of n1 and a physical film thickness of d1, and a first layer having a refractive index of n2 and a physical film thickness of d2. There are two layers, a third layer having a refractive index of n3 and a physical film thickness of d3, and a fourth layer having a refractive index of n4 and a physical film thickness of d4. At this time, the first to fourth layers need to satisfy the following conditions.
1.55 ≦ n1 ≦ 1.70 (2)
1.35 ≦ n2 ≦ 1.52 (3)
1.85 ≦ n3 ≦ 2.40 (4)
1.35 ≦ n4 ≦ 1.52 (5)
Moreover, it is more desirable that the numerical range (at least one of the upper limit value and the lower limit value) in any one of the formulas (2) to (5) is as follows.

1.60 ≦ n1 ≦ 1.65 (2a)
1.37 ≦ n2 ≦ 1.47 (3a)
2.00 ≦ n3 ≦ 2.35 (4a)
1.37 ≦ n4 ≦ 1.47 (5a)
If the refractive index range of Formula (2)-(5) (or Formula (2a)-(5a)) is satisfy | filled, the material of a 1st layer-a 4th layer will not be specifically limited. Examples of the material of the first layer to the fourth layer include metal oxides such as SiO ₂ , MgO ₂ , Al ₂ O ₃ , Y ₂ O ₃ , MgO, ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , Ta ₂ O _5. Or a simple substance of a metal fluoride such as LaF ₃ , CeF ₃ , NdF ₃ , MgF ₂ , CaF _2, or a compound thereof can be used. Depending on the material of the optical substrate 1, exposure to the atmosphere may cause components to dissolve on the surface, which may cause a phenomenon called “burning” in which the surface of the optical substrate 1 is cloudy or colored. In order to prevent this, it is preferable to use Al ₂ O ₃ or SiON as the material of the first layer. The fourth layer is preferably a film having low reactivity and stable in the air, and for example, SiO ₂ can be used.

In order to obtain good reflectance characteristics in the intermediate layer 2 having a four-layer structure, the optical film thickness (refractive index n1 to n4 × physical film thickness d1 to d4) of the first to fourth layers is as follows. Need to be satisfied.
10 nm ≦ n1d1 ≦ 260 nm (6)
10 nm ≦ n2d2 ≦ 45 nm (7)
5 nm ≦ n3d3 ≦ 35 nm (8)
n4d4 ≦ 125 nm (9)
In addition, it is preferable that the lower limit of n4d4 in Formula (9) is 10 nm (or more).

When the refractive index of the first layer is higher than the refractive index of the optical substrate 1, the optical film thickness of the first layer is
130 nm ≦ n1d1 ≦ 260 nm (6a)
It is desirable to satisfy When the refractive index of the first layer is lower than the refractive index of the optical substrate 1, the optical film thickness of the first layer is
10 nm ≦ n1d1 ≦ 60 nm (6b)
It is desirable to satisfy This is because the phase of the reflected wave generated at the interface between the optical substrate 1 and the first layer changes due to the refractive index relationship between the optical substrate 1 and the first layer.

Furthermore, it is more desirable to set the numerical value range (at least one of the upper limit value and the lower limit value) of any one of the formulas (6) to (9) as follows.
20 nm ≦ n1d1 ≦ 240 nm (6c)
12 nm ≦ n2d2 ≦ 42 nm (7a)
10 nm ≦ n3d3 ≦ 30 nm (8a)
n4d4 ≦ 120 nm (9a)
When the concavo-convex structure 3 includes a homogeneous portion, when the refractive index of the homogeneous portion is na and the physical film thickness is da, the refractive index na and the optical film thickness (nada) of the homogeneous portion and the fourth layer The sum with the optical film thickness (n4d4) is
1.35 ≦ na ≦ 1.58 (10)
90 nm ≦ n4d4 + nada ≦ 125 nm (11)
Need to be satisfied.

Furthermore, it is more desirable that the numerical range (at least one of the upper limit value and the lower limit value) in any one of the expressions (10) and (11) is as follows.
1.40 ≦ na ≦ 1.54 (10a)
100 nm ≦ n4d4 + nada ≦ 120 nm (11a)
This is because the homogeneous portion and the fourth layer substantially function as one layer. By adopting such a configuration, even when it is difficult to arbitrarily control the film thickness of the homogeneous portion, desired characteristics can be obtained by arbitrarily controlling the film thickness of the fourth layer. In order for the homogeneous portion and the fourth layer to function substantially as one layer, the refractive index difference between the homogeneous portion and the fourth layer is 0.1 or less, that is,
0 ≦ | na−n4 | ≦ 0.1 (12)
It is preferable that Furthermore, it is 0.05 or less, that is,
0 ≦ | na−n4 | ≦ 0.05 (12a)
It is more preferable that

On the other hand, even when the concavo-convex structure 3 does not have a homogeneous layer, the difference between the effective refractive index n _effmax of the concavo-convex structure 3 on the most optical substrate side (intermediate layer side) and the refractive index of the fourth layer is 0.1. That is:
0 ≦ | n _effmax −n4 | ≦ 0.1 (13)
It is preferable that Furthermore, it is 0.05 or less, that is,
0 ≦ | n _effmax −n4 | ≦ 0.05 (13a)
It is more preferable that Thereby, the reflected wave in the interface of the uneven structure 3 and the intermediate | middle layer 2 can be suppressed, and antireflection performance can be improved.

  The optical element that forms the antireflection film of the embodiment includes various optical elements such as a lens, a prism, and a fly eye integrator. In addition, the optical element provided with the antireflection film is an imaging optical system, a scanning optical system, a projection optical system, etc., of various optical devices used for cameras, video cameras, binoculars, copying machines, printers, projectors, head mounted displays, etc. It can be used as an optical element constituting an optical system.

In the antireflection film of Example 1, an intermediate layer 2 having a four-layer structure is formed on an optical substrate 1 having a refractive index of 1.585, and an uneven structure 3 is formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.459 and a second layer containing SiO ₂ as a main component, and a refractive index of 2. 127, a third layer mainly composed of Ta ₂ O ₅ and a fourth layer made of SiO ₂ having a refractive index of 1.459. The four layers constituting the intermediate layer 2 were each formed by a vacuum deposition method. The optical thicknesses of the four layers are 210 nm for the first layer, 15 nm for the second layer, 16 nm for the third layer, and 109 nm for the fourth layer.

  In addition, the concavo-convex structure 3 was formed by subjecting a film mainly composed of aluminum oxide formed by spin coating by a sol-gel method to a hot water immersion treatment. The refractive index with respect to the thickness direction of the antireflection film formed by this method is shown in FIG. In the concavo-convex structure 3, the refractive index continuously decreases from 1.504 toward 1 from the intermediate layer side toward the light incident side, and the physical film thickness is 224 nm. The change in the refractive index with respect to the film thickness direction is not constant, and the change in the refractive index is smaller in the region closer to the light incident side than in the region closer to the intermediate layer 2. Although such a structure is not necessarily required, it is possible to realize an antireflection characteristic that is more excellent in wavelength characteristics and incident angle characteristics.

  FIG. 2B shows the reflectance characteristics of the antireflection film of this example. In the figure, 0, 15, 30, 45, and 60 indicate the incident angle (unit: degrees) of light to the antireflection film. As can be seen from FIG. 2B, when the incident angle is 0 degree, the antireflection film of this example has a reflectance of 1% or less at 400 nm, a reflectance of 0.2% or less at 450 nm to 650 nm, and 650 nm. It has excellent antireflection performance with a reflectance of 0.4% or less at ˜700 nm. Further, even when the incident angle is 45 degrees, a high-performance antireflection performance with a reflectance of 0.6% or less is realized in a wide wavelength range of the entire visible range (400 to 700 nm).

2 (C) and 2 (D), the film thickness of the intermediate layer 2 formed by the vacuum deposition method of the antireflection film of this example varies up to ± 10% when the incident angles are 0 degree and 45 degrees. In this case, the calculated value of reflectance is shown. Note that the variation in film thickness is uniformly generated between the first layer to the fourth layer by a random number between the central value −10% and the central value + 10%, and the calculated reflectance is the same. The maximum value and the minimum value at each wavelength when the above calculation is repeated 100 times are shown. 2 (C) and 2 (D) 6, the antireflection film of this example has a reflection of 1.0% or less in the visible wavelength region (400 to 700 nm) even when the intermediate layer 2 varies up to 10%. It can be seen that the rate characteristic can be maintained. In other words, it can be seen that it is difficult to be affected by manufacturing variations and variations in the lens surface.
(Comparative Example 1)
Similarly to Example 1 of the present invention, when the incident angles are 0 degree and 45 degrees, the portion corresponding to the intermediate layer of the antireflection film shown in Numerical Example 1 of Patent Document 1 (a layer excluding the low refractive index layer) FIGS. 15A and 15B show the calculated values of the reflectance when the film thickness varies with a film thickness of 10% at maximum as Comparative Example 1. FIG. The reason why the wavelength characteristic of the reflectance is slightly different from the result disclosed in Patent Document 1 is that the refractive index dispersion of each layer is different.

  2 (C), (D) and FIGS. 15 (A), 15 (B), Example 1 of the present invention is more sensitive to variations in the thickness of the intermediate layer than Numerical Example 1 of Patent Document 1. It can be seen that it exhibits good characteristics. In particular, it can be seen that there is a large difference in characteristics at 45 ° incidence. In Patent Document 1, the uppermost layer is a layer composed of nano-particles (a layer having a fine structure smaller than the incident wavelength), but unlike the first embodiment of the present invention, the uppermost layer also has a refractive index in the thickness direction. This is because it is uniform. In other words, since Patent Document 1 is a mechanism for lowering reflectivity by multilayer film interference by four thin films including the uppermost layer, interference conditions such as when the film thickness varies or when the incident angle is large are destroyed. Reflectivity characteristics are degraded. On the other hand, the fine concavo-convex structure of Example 1 of the present invention has a configuration in which it is difficult to generate a reflected wave by the refractive index continuously changing in the thickness direction, and the film thickness is optimized by optimizing the intermediate layer 2. A good anti-reflection film can be realized even when there is variation.

Example 2 has the same configuration as Example 1 except that the optical thickness of the fourth layer is 120 nm. FIG. 3 shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 3, the antireflection film of this example also has a reflectance of 1.0% or less at 400 nm when the incident angle is 0 degree, a reflectance of 0.2% or less at 450 nm to 650 nm, and 650 nm to 700 nm. And has an excellent antireflection performance with a reflectance of 0.4% or less. Furthermore, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.5% or less at 400 to 700 nm is realized.
(Comparative Example 2)
Comparative Example 2 has the same configuration as Example 1 except that the optical thickness of the fourth layer is 131 nm. FIG. 16 shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 16, in this comparative example, the reflectance is 1.0% at 400 nm when incident at 0 degree, and exceeds 0.2% at 450 nm. From this comparative example, when the incident angle is 0 degree, the reflectance is 1% or less at 400 nm, the reflectance is 0.2% or less at 450 nm to 650 nm, and the reflectance is 0.4% or less at 650 nm to 700 nm. In order to obtain the prevention characteristic, the optical film thickness of the fourth layer needs to be 125 nm or less.

The antireflection film of Example 3 is composed of an intermediate layer 2 having a four-layer structure formed on the optical substrate 1 having a refractive index of 1.440, and a concavo-convex structure 3 formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.459 and a second layer containing SiO ₂ as a main component, and a refractive index of 2. The third layer 127 is composed of a third layer mainly composed of Ta ₂ O ₅ and the fourth layer is composed of SiO ₂ having a refractive index of 1.459. These first to fourth layers were all formed by vacuum deposition. The optical thicknesses of the first layer are 138 nm, the second layer is 22 nm, the third layer is 26 nm, and the fourth layer is 51 nm.

  The concavo-convex structure 3 continuously decreases from 1.534 on the intermediate layer side to 1.0 on the light incident side, and has a physical film thickness of 187 nm. In addition, a homogeneous layer having a refractive index of 1.534 is formed with an optical film thickness of 37 nm on the intermediate layer side portion of the concavo-convex structure 3. The concavo-convex structure 3 in this example was formed by the same method as in Example 1, but by adjusting the film forming conditions during spin coating and the conditions of the hot water immersion treatment, A homogeneous layer is formed, and the refractive index of the root and the homogeneous part of the concavo-convex structure 3 is higher than that of the first embodiment. FIG. 4A shows the refractive index in the thickness direction of the antireflection film of this example.

  FIG. 4B shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 4B, the antireflection film of this example has a reflectance of 1.0% or less at 400 nm and an reflectance of 0.2% or less at 450 nm to 650 nm when the incident angle is 0 degree. Excellent antireflection performance with a reflectance of 0.4% or less at 650 nm to 700 nm. Further, since the thickness of the concavo-convex structure 3 is smaller than that of Example 1 or Example 2, the reflection characteristics are slightly deteriorated at a high incident angle of 45 degrees or more, but it is still 400 when the incident angle is 45 degrees. A high antireflection performance with a reflectance of 1.6% or less at ˜700 nm is realized.

  The antireflection film of Example 4 has the same configuration as that of Example 3 except that the concavo-convex structure 3 has a physical film thickness of 170 nm. The refractive index with respect to the thickness direction of the antireflection film of this example is shown in FIG.

FIG. 5B shows the reflectance characteristics of the antireflection film of this example. Compared with FIG. 4B, the reflectance at 450 nm or less is reduced and the reflectance at 650 nm or more is increased due to the thin film thickness of the uneven structure 3. However, the antireflection film of this example also has a reflectance of 1.0% or less at 400 nm when the incident angle is 0 degree, a reflectance of 0.2% or less at 450 nm to 650 nm, and a reflectance at 650 nm to 700 nm. Excellent antireflection performance of 0.4% or less is obtained. Also. Even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 2.0% or less at 400 to 700 nm is realized.
(Comparative Example 3)
The antireflection film of Comparative Example 3 has the same configuration as that of Example 3 except that the physical thickness of the concavo-convex structure is 160 nm. The refractive index with respect to the thickness direction of the antireflection film of this comparative example is shown in FIG.

  FIG. 17B shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 17B, in this comparative example, the reflectivity exceeds 0.4% at 700 nm when incident at 0 degree. Thus, when the physical film thickness of the concavo-convex structure is less than 165 nm, the reflectance characteristics are deteriorated on the long wavelength side. For this reason, in order to obtain good antireflection performance in the examples, the physical film thickness of the concavo-convex structure 3 needs to be 165 nm or more. On the other hand, if the physical film thickness of the concavo-convex structure 3 is thicker than 300 nm, scattering due to the structure becomes remarkable, which is not preferable. For this reason, the physical film thickness of the uneven structure 3 needs to be 165 nm or more and 300 nm or less.

The antireflection film of Example 5 is constituted by an intermediate layer 2 having a four-layer structure formed on the optical substrate 1 having a refractive index of 1.585, and a concavo-convex structure 3 formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.459 and a second layer containing SiO ₂ as a main component, and a refractive index of 2. The third layer 127 is composed of a third layer mainly composed of Ta ₂ O ₅ and the fourth layer is composed of SiO ₂ having a refractive index of 1.459. These first to fourth layers were all formed by vacuum deposition. The optical thicknesses of the first layer are 165 nm, the second layer is 15 nm, the third layer is 11 nm, and the fourth layer is 107 nm.

  The uneven structure 3 continuously decreases from 1.504 on the intermediate layer side to 1.0 on the light incident side, and the physical film thickness is 224 nm. The uneven structure 3 was formed by the same method as in Example 1. The refractive index with respect to the thickness direction of the antireflection film of this example is shown in FIG.

FIG. 6B shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 6B, the antireflection film of this example has a reflectance of 1.0% or less at 400 nm and an reflectance of 0.2% or less at 450 nm to 650 nm when the incident angle is 0 degree. Excellent antireflection performance with a reflectance of 0.4% or less at 650 nm to 700 nm. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.6% or less at 400 to 700 nm is realized.
(Comparative Example 4)
The antireflection film of Comparative Example 4 has the same configuration as that of Example 5 except that the optical thickness of the third layer is 4 nm. FIG. 18A shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 18A, in this comparative example, the reflectivity exceeds 0.2% at 450 nm when incident at 0 degree. From this, it can be seen that when the optical film thickness of the third layer is less than 5 nm, the reflectance characteristic decreases on the short wavelength side. Further, as a result of the same examination, it was found that when the optical film thickness exceeds 42 nm, the reflectance characteristic on the long wavelength side is deteriorated. Therefore, in order to obtain good reflectance characteristics in the examples, the optical thickness of the third layer needs to be 5 nm or more and 35 nm or less, which is thinner than 42 nm. Furthermore, it was found that when the refractive index of the third layer is less than 1.85, the wavelength range is narrowed even when the optical film thickness condition is satisfied. For this reason, the refractive index of the third layer needs to be 1.85 or more, and more preferably 1.98 or more.

The antireflection film of Example 6 is composed of an intermediate layer 2 having a four-layer structure formed on the optical substrate 1 having a refractive index of 1.699, and a concavo-convex structure 3 formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.459 and a second layer containing SiO ₂ as a main component, and a refractive index of 2. The third layer 127 is composed of a third layer mainly composed of Ta ₂ O ₅ and the fourth layer is composed of SiO ₂ having a refractive index of 1.459. These first to fourth layers were all formed by vacuum deposition. The optical thickness is 23 nm for the first layer, 29 nm for the second layer, 25 nm for the third layer, and 58 nm for the fourth layer.

  The uneven structure 3 continuously decreases from 1.504 on the intermediate layer side to 1.0 on the light incident side, and the physical film thickness is 242 nm. In addition, a uniform layer having a refractive index of 1.504 is formed at an optical film thickness of 58 nm on the intermediate layer side portion of the concavo-convex structure 3. The uneven structure 3 of this example was formed by the same method as in Example 1. However, by adjusting the film forming conditions during spin coating and the conditions of the hot water immersion treatment, the uneven structure 3 was formed on the intermediate layer side portion of the uneven structure. A homogeneous layer is formed, and the refractive index of the root and the homogeneous part of the concavo-convex structure 3 is higher than that of the first embodiment. FIG. 7A shows the refractive index with respect to the thickness direction of the antireflection film of this example.

  FIG. 7B shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 7B, the antireflection film of this example has a reflectance of 1.0% or less at 400 nm and an reflectance of 0.2% or less at 450 nm to 650 nm when the incident angle is 0 degree. Excellent antireflection performance with a reflectance of 0.4% or less at 650 nm to 700 nm. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.5% or less at 400 to 700 nm is realized.

  The antireflection film of Example 7 has the same configuration as that of Example 6 except that the optical film thickness of the second layer is 15 nm. FIG. 8A shows the reflectance characteristics of the antireflection film of this example. Compared with FIG. 7B, the reflectance at 450 nm or less is slightly increased as compared with Example 6 because the optical film thickness of the second layer is reduced. However, the antireflection film of this example also has a reflectance of 1.0% or less at 400 nm when the incident angle is 0 degree, a reflectance of 0.2% or less at 450 nm to 650 nm, and a reflectance at 650 nm to 700 nm. Excellent antireflection performance of 0.4% or less. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.4% or less at 400 to 700 nm is realized.

The antireflection film of Example 8 has the same configuration as that of Example 6 except that the optical film thickness of the second layer is 32 nm. FIG. 8B shows the reflectance characteristics of the antireflection film of this example. Compared with FIG. 7B, the reflectance in the vicinity of 500 nm is slightly increased as compared with Example 6 due to the decrease in the optical film thickness of the second layer. However, the antireflection film of this example also has a reflectance of 1.0% or less at 400 nm when the incident angle is 0 degree, a reflectance of 0.2% or less at 450 nm to 650 nm, and a reflectance at 650 nm to 700 nm. Excellent antireflection performance of 0.4% or less. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.5% or less at 400 to 700 nm is realized.
(Comparative Example 5)
The antireflection film of Comparative Example 5 has the same configuration as that of Example 6 except that the optical film thickness of the second layer is 8 nm. FIG. 18B shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 18 (B), in this comparative example, the reflectance characteristic of 450 nm or less is reduced when incident at 0 degree, and the reflectance is particularly 1.0% at 400 nm and 0.2% at 450 nm. Over.
(Comparative Example 6)
The antireflection film of Comparative Example 6 has the same configuration as that of Example 6 except that the optical thickness of the second layer is 44 nm. FIG. 18C shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 18C, in this comparative example, the reflectivity characteristic of 450 nm or more is lowered when the incident angle is 0 degree, and the reflectivity exceeds 0.2% particularly at 500 nm.

  As can be seen from Comparative Examples 5 and 6, the optical thickness of the second layer is desirably 10 nm or more and 42 nm or less in order to obtain good reflectance characteristics in the examples.

The antireflection film of Example 9 is composed of an intermediate layer 2 having a four-layer structure formed on the optical substrate 1 having a refractive index of 1.585, and a concavo-convex structure 3 formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.459 and a second layer containing SiO ₂ as a main component, and a refractive index of 2. The third layer 127 is composed of a third layer mainly composed of Ta ₂ O ₅ and the fourth layer is composed of SiO ₂ having a refractive index of 1.459. These first to fourth layers were all formed by vacuum deposition. The optical thickness is 210 nm for the first layer, 15 nm for the second layer, 16 nm for the third layer, and 69 nm for the fourth layer.

  The uneven structure 3 continuously decreases from 1.504 on the intermediate layer side to 1.0 on the light incident side, and the physical film thickness is 224 nm. In addition, a homogeneous layer having a refractive index of 1.504 is formed at an optical film thickness of 51 nm on the intermediate layer side portion of the concavo-convex structure 3. In addition, although the uneven | corrugated structure 3 of a present Example was formed by the method similar to Example 1, the homogeneous layer is formed in the part by the side of the intermediate | middle layer of a concavo-convex structure by adjusting the conditions of a warm water immersion process. The refractive index with respect to the thickness direction of the antireflection film of this example is shown in FIG.

  FIG. 9B shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 9B, the antireflection film of this example has a reflectance of 1.0% or less at 400 nm when the incident angle is 0 degree, and a reflectance of 0.2% or less at 450 nm to 650 nm. Excellent antireflection performance with a reflectance of 0.4% or less at 650 nm to 700 nm. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.6% or less at 400 to 700 nm is realized.

The antireflection film of Example 10 has the same configuration as that of Example 9 except that the optical film thickness of the first layer is 235 nm. FIG. 10 shows the reflectance characteristics of the antireflection film of this example. Compared with FIG. 9B, the reflectance at 450 nm or less is slightly increased compared to Example 9 due to the increase in the optical film thickness of the first layer. However, the antireflection film of this example also has a reflectance of 1.0% or less at 400 nm when the incident angle is 0 degree, a reflectance of 0.2% or less at 450 nm to 650 nm, and a reflectance at 650 nm to 700 nm. Excellent antireflection performance of 0.4% or less. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.7% or less at 400 to 700 nm is realized.
(Comparative Example 7)
The antireflection film of Comparative Example 7 has the same configuration as that of Example 9 except that the optical thickness of the first layer is 279 nm. FIG. 19 shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 19, in this comparative example, the reflectance characteristic at 450 nm or less is reduced when incident at 0 degree, and the reflectance is particularly 1.0% at 400 nm and the reflectance is 0.2% at 450 nm. Over. Similarly, when the optical film thickness of the first layer is less than 165 nm, the reflectance characteristic at 450 nm or less decreases at 0 degree incidence, and the reflectance at 400 nm is 1.0%, and the reflectance at 450 nm is 450 nm. The reflectivity exceeds 0.2%. For this reason, when the refractive index of the optical substrate is lower than the refractive index of the first layer, the film thickness of the first layer is desirably 165 nm or more and 260 nm or less in order to obtain good reflectance characteristics in the examples. . From the same examination, when the refractive index of the optical substrate 1 is higher than the refractive index of the first layer, the film thickness of the first layer is desirably 10 nm or more and 60 nm or less.

The antireflection film of Example 11 is composed of an intermediate layer 2 having a four-layer structure formed on the optical substrate 1 having a refractive index of 1.404, and a concavo-convex structure 3 formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.382 and a second layer containing MgF ₂ as a main component, and a refractive index of 2. 323 includes a third layer mainly composed of TiO ₂ and a fourth layer mainly composed of MgF ₂ having a refractive index of 1.382. These first to fourth layers were all formed by vacuum deposition. The optical film thickness is 105 nm for the first layer, 41 nm for the second layer, 30 nm for the third layer, and 55 nm for the fourth layer.

  The uneven structure 3 continuously decreases from 1.504 on the intermediate layer side to 1.0 on the light incident side, and the physical film thickness is 216 nm. In addition, a homogeneous layer having a refractive index of 1.504 is formed at an optical film thickness of 62 nm on the intermediate layer side portion of the concavo-convex structure 3. The uneven structure 3 of this example was formed by the same method as in Example 1, but the film thickness of the uneven structure was made thinner than that of Example 1 by adjusting the film forming conditions during spin coating. FIG. 11A shows the refractive index with respect to the thickness direction of the antireflection film of this example.

  FIG. 11B shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 11B, the antireflection film of this example has a reflectance of 1.0% or less at 400 nm and an reflectance of 0.2% or less at 450 nm to 650 nm when the incident angle is 0 degree. Excellent antireflection performance with a reflectance of 0.4% or less at 650 nm to 700 nm. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.8% or less at 400 to 700 nm is realized.

The antireflection film of Example 12 is composed of an intermediate layer 2 having a four-layer structure formed on the optical substrate 1 having a refractive index of 1.644, and a concavo-convex structure 3 formed thereon. The intermediate layer 2 has a refractive index of 1.621 and a first layer containing Al ₂ O ₃ as a main component, a refractive index of 1.459 and a second layer containing SiO ₂ as a main component, and a refractive index of 2. 323 includes a third layer mainly composed of TiO ₂ and a fourth layer whose refractive index is 1.459 and mainly composed of SiO ₂ . These first to fourth layers were all formed by vacuum deposition. The optical film thickness is 40 nm for the first layer, 13 nm for the second layer, 30 nm for the third layer, and 51 nm for the fourth layer.

  The uneven structure 3 continuously decreases from 1.504 on the intermediate layer 2 side to 1.0 on the light incident side, and the physical film thickness is 282 nm. In addition, a homogeneous layer having a refractive index of 1.504 is formed at an optical film thickness of 56 nm on the intermediate layer side portion of the concavo-convex structure 3. The uneven structure 3 of this example was formed by the same method as in Example 1, but the film thickness of the uneven structure 3 was thicker than that of Example 1 by adjusting the film formation conditions during spin coating. . The refractive index with respect to the thickness direction of the antireflection film of this example is shown in FIG.

FIG. 12B shows the reflectance characteristics of the antireflection film of this example. As can be seen from FIG. 12B, the antireflection film of this example has a reflectance of 1.0% or less at 400 nm and an reflectance of 0.2% or less at 450 nm to 650 nm when the incident angle is 0 degree. Excellent antireflection performance with a reflectance of 0.4% or less at 650 nm to 700 nm. Further, even when the incident angle is 45 degrees, a high antireflection performance of a reflectance of 0.5% or less at 400 to 700 nm is realized.
(Comparative Example 8)
The structure of the anti-reflective film of the comparative example 8 produced according to the anti-reflective film shown by Example 13 of patent document 2 is shown. In this comparative example, as shown in Example 13 of Patent Document 2, the optical substrate is S-TIH1 (refractive index is 1.722), and the intermediate layer is an organic resin layer having a refractive index of 1.59. It consists only of layers. The refractive index with respect to the thickness direction of the antireflection film of this comparative example is shown in FIG.

  FIG. 20B shows the reflectance characteristics of the antireflection film of this comparative example. As can be seen from FIG. 20B, in this comparative example, when the incident angle is 0 degree, the reflectance exceeds 0.2% at 600 nm or less, and particularly at 550 nm or less, the reflectance becomes 0.3% or more. The reflectance characteristic is lower than that of the example of the invention (for example, Example 6 in which the refractive index of the optical substrate 1 is close to this comparative example).

  This is because the intermediate layer of Patent Document 2 is composed of only one organic resin layer, whereas the intermediate layer of the embodiment of the present invention is composed of four layers having different refractive indexes, so a wider wavelength range. This is because the reflectance characteristics can be improved in the region. Further, in Patent Document 2, an organic intermediate layer is used. In the embodiment of the present invention, since an inorganic material is formed by using a vacuum deposition method or a sputtering method, a reflective layer having a denser and more stable intermediate layer is used. Preventive film can be realized.

  FIG. 14 shows an imaging apparatus as an optical apparatus that is Embodiment 13 of the present invention. In FIG. 14, reference numeral 101 denotes a digital camera as an image pickup apparatus, and reference numeral 102 denotes an image pickup optical system configured using an optical element (lens) on which any one of the antireflection films of Examples 1 to 12 is formed. . The imaging optical system 102 includes a plurality of lenses, and any one of the antireflection films of Examples 1 to 12 is formed on at least one of these lens surfaces.

  For this reason, the digital camera 101 of the present embodiment can suppress generation of harmful reflected light such as flare and ghost, and an image with good image quality can be obtained.

  In this embodiment, a digital camera has been described as an example of an optical device. However, the digital camera may be used in an optical system of various optical devices such as an interchangeable lens, binoculars, and an image projection apparatus.

  In Table 1, the structure of the anti-reflective film of the said Examples 1-12 and Comparative Examples 1-8 is shown collectively.

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  An antireflection film having excellent optical characteristics can be provided and can be used in various optical devices.

DESCRIPTION OF SYMBOLS 1 Optical substrate 2 Intermediate | middle layer 3 Uneven structure 21-24 The 1st-4th layer of an intermediate | middle layer 100 Antireflection film

Claims (5)

An antireflection film formed on a substrate,
A concavo-convex structure formed with a pitch smaller than 400 nm;
An intermediate layer formed between the uneven structure and the substrate,
The uneven structure has a thickness of 165 nm or more and 300 nm or less,
The effective refractive index of the concavo-convex structure for light having a central wavelength of 550 nm changes from a value of 1.35 to 1.58 on the intermediate layer side toward the light incident side,
The refractive index of the base material with respect to light having a central wavelength of 550 nm is 1.40 or more and 1.75 or less,
The intermediate layer was laminated in order from the base material side,
A first layer having a refractive index n1 and a physical film thickness d1 for light having a central wavelength of 550 nm;
A second layer having a refractive index of n2 and a physical thickness of d2 for light having a central wavelength of 550 nm;
A third layer having a refractive index n3 and a physical film thickness d3 for light having a central wavelength of 550 nm;
A fourth layer having a refractive index of n4 and a physical film thickness of d4 with respect to light having a center wavelength of 550 nm,
An antireflection film characterized by satisfying the following conditions.
1.55 ≦ n1 ≦ 1.70
1.35 ≦ n2 ≦ 1.52
1.85 ≦ n3 ≦ 2.40
1.35 ≦ n4 ≦ 1.52
10 nm ≦ n1d1 ≦ 260 nm
10 nm ≦ n2d2 ≦ 45 nm
5nm ≦ n3d3 ≦ 35nm
n4d4 ≦ 125nm The concavo-convex structure includes a homogeneous portion where the effective refractive index does not change in the thickness direction on the intermediate layer side,
2. The antireflection film according to claim 1, wherein the following condition is satisfied when the refractive index of the homogeneous portion is na and the physical film thickness is da for the light having the central wavelength of 550 nm.
1.35 ≦ na ≦ 1.58
90 nm ≦ n4d4 + nada ≦ 125 nm   3. The antireflection film according to claim 1, wherein the uneven structure is formed of a plate-like crystal of a material containing aluminum oxide. Optical glass,
An optical element comprising the optical glass as the base material and the antireflection film according to any one of claims 1 to 3 formed on a surface thereof.   An optical apparatus comprising an optical system including the optical element according to claim 4.