JP2018005136A - Antireflection film and optical element, optical system and optical device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antireflection film having excellent antireflection characteristics to wavelengths from 400 to 700 nm even when a film thickness of a residual film varies, and an optical element, an optical system, and an optical instrument having the antireflection film.SOLUTION: The antireflection film is to be formed on an optical substrate for reducing surface reflection of incident or outgoing rays, and comprises a structural layer having recesses and projections regularly arranged at a pitch of 400 nm or less and an intermediate layer formed between the structural layer and the optical substrate. The intermediate layer has a layered structure of at least one thin film layer. The structural layer comprises a graded part where the refractive index varies in the thickness direction, and a residual film part integrally formed under the graded part, where the refractive index does not vary in the thickness direction. The graded part is configured in such a manner that: a space fill factor on a side closest to the incident of light is 0.05 or more and 0.20 or less; at least one point except for the light incident part is present where the space fill factor discontinuously varies in the thickness direction; and the difference in the space fill factor at the point where the factor discontinuously varies in the thickness direction is 0.05 or more and 0.20 or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an antireflection film provided on an incident / exit surface of an optical element, and particularly relates to an antireflection film having a structure in which a refractive index continuously changes in a depth direction, and an optical element, an optical system, and an optical apparatus having the same. .

  Conventionally, an antireflection structure has been formed on the surface of an optical element in order to reduce the loss of light quantity of incident light. In recent years, an antireflection film using a fine structure arranged at a pitch smaller than the wavelength used is known. ing. Among such antireflection films, like the moth-eye structure that mimics the structure of the eyelet, an antireflection film in which the filling ratio of the structure with respect to the space changes in the film thickness direction is different from the light incident side in the film thickness direction. Therefore, since the refractive index changes substantially continuously, the incident angle characteristic is smaller than that of a conventional antireflection film composed of multilayer films having different refractive indexes.

  As a method of forming an antireflection film using such a fine concavo-convex structure, Patent Document 1 discloses a method of producing a master having a fine concavo-convex structure and transferring the fine structure using the master as a mold. In Patent Document 1, when an optical element is molded using the created mold, a method of directly transferring a fine concavo-convex structure to the surface, or coating the substrate surface with a material such as a resin, and transferring the structure there (nanoimprint) Thus, a method for forming a fine structure is disclosed.

  However, in order to directly create a fine concavo-convex structure on the surface of the optical element by the above method, the material of the optical element is limited to only a part satisfying the conditions required for transfer (glass transition temperature, viscosity, releasability). Will be. In addition, when a structure is transferred using nanoimprint, it is necessary to reduce the difference in refractive index between the substrate and the fine concavo-convex structure as much as possible in order to suppress reflection at the interface between the fine concavo-convex structure and the substrate.

  However, as in the case of direct transfer, the materials that can be used for nanoimprint are practically limited, and the selectable refractive index range is limited. In particular, it is difficult to realize a high refractive index. For example, it is difficult to apply the above method to an optical material having a refractive index of 2.0.

  Therefore, Patent Document 2 proposes a method of providing one layer (intermediate layer) having a refractive index lower than that of the substrate between the microstructure and the substrate. By adding one intermediate layer, the refractive index difference between the substrate and the microstructure is reduced, and by optimizing the thickness of the intermediate layer, the refractive index of the substrate is an average reflectance relative to 1.80. An antireflection performance of 0.1% or less can be obtained.

JP 2006-130841 A International Publication No. 2008/102882

  However, when forming a fine concavo-convex structure by nanoimprinting, it is practically difficult to transfer the structure to the entire structure transfer layer and to the entire element surface, and the part where the structure is not transferred (residual film part) is the structure layer. It will remain at the bottom of.

  Therefore, when using an intermediate layer as in Patent Document 2, it is necessary to use the remaining portion as the intermediate layer or to remove the remaining portion by a process such as dry etching.

  However, when the remaining portion is used as an intermediate layer, it is difficult to uniformly control the film thickness of the remaining portion over the entire device, and the reflectance characteristics are deteriorated due to variations in the film thickness of the remaining portion. Further, when the remaining portion is removed, there is a problem that the manufacturing throughput is lowered and the cost is increased.

  Accordingly, an object of the present invention is to reduce a decrease in reflectance characteristics due to film thickness fluctuations in the remaining film portion, and to provide an antireflection film having excellent antireflection characteristics for wavelengths of 400 to 700 nm, and an optical element having the same It is to provide an optical system and an optical apparatus.

In order to achieve the above object, the antireflection film according to the present invention comprises:
An antireflection film formed on an optical substrate for reducing surface reflection of incident or emitted light,
A structure layer having irregularities regularly arranged at a pitch of 400 nm or less and an intermediate layer formed between the structure layer and the optical substrate;
The intermediate layer has a structure in which one or more thin film layers are laminated,
The structural layer is formed integrally with a graded portion where the refractive index changes in the film thickness direction and a lower film portion where the refractive index does not change in the film thickness direction.
The graded portion has one point other than the light incident portion in which the space filling rate on the most light incident side satisfies 0.05 or more and 0.20 or less and the space filling rate changes discontinuously in the film thickness direction. The difference in the space filling rate at the point where it has the above and changes discontinuously in the film thickness direction is from 0.05 to 0.20.

  According to the present invention, even if the film thickness of the remaining film portion varies, an antireflection film having excellent antireflection characteristics for wavelengths of 400 to 700 nm, and an optical element, an optical system, and an optical device having the antireflection film are provided. can do.

Outline of antireflection film of the present invention Outline of tip shape of graded part 2 Outline shape of graded portion 2 of the present invention Refractive index with respect to the film thickness of the antireflection film of Example 1 Reflectivity of antireflection film of Example 1 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Example 1 Reflectivity when changing the film thickness of the remaining film portion of the antireflection film of Example 1 Refractive index with respect to the film thickness of the antireflection film of Example 2 Reflectivity of antireflection film of Example 2 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Example 2 Refractive index with respect to the film thickness of the antireflection film of Example 3 Reflectivity of antireflection film of Example 3 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Example 3 Refractive index with respect to the film thickness of the antireflection film of Example 4 Reflectivity of antireflection film of Example 4 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Example 4 Refractive index with respect to the film thickness of the antireflection film of Example 5 Reflectivity of antireflection film of Example 5 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Example 5 Refractive index with respect to the film thickness of the antireflection film of Example 6 Reflectance of antireflection film of Example 6 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Example 6 Optical apparatus of the present invention Refractive index with respect to the film thickness of the antireflection film of Comparative Example 1 Reflectivity of antireflection film of Comparative Example 1 Variation in reflectance characteristics due to variation in film thickness of remaining film portion of antireflection film of Comparative Example 1

  Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. The refractive index values in the description are all values at a wavelength of 550 nm.

  FIG. 1 is a schematic view (cross-sectional view) of the antireflection film of the present invention, and shows an enlarged vicinity of the surface of the optical substrate 10.

  The optical substrate 10 is made of optical glass or optical plastic having a refractive index of 1.68 to 2.30, and the antireflection film 100 of the present invention is formed on the surface thereof. The antireflection film 100 is formed by a nanoimprint method, and includes a structural layer 30 having a fine concavo-convex structure and an intermediate layer 20 provided between the optical substrate 10 and the fine concavo-convex structure 30.

  Furthermore, the structural layer 30 includes a graded portion 2 formed of a fine concavo-convex structure in which the space filling rate changes in the film thickness direction (that is, the substantial refractive index changes in the film thickness direction), the graded portion 2, It consists of a remaining film portion 1 that is integrally formed and whose refractive index does not change in the film thickness direction. The remaining portion 1 is a portion where the remaining structure under the structural layer 30 is not transferred when the fine uneven structure is transferred by the nanoimprint method. Further, the intermediate layer 20 has a configuration in which one or two or more thin films having different refractive indexes are laminated.

  The structural layer 30 is formed by a nanoimprint method. The nanoimprint method is roughly classified into thermal nanoimprint, optical nanoimprint, and room temperature nanoimprint depending on the production method, and any method may be used in the present invention. However, it is more preferable to use thermal nanoimprinting in order to form the film uniformly in the film thickness direction. Although the material used for the structural layer 30 is not specifically limited, For example, a thermosetting resin, a thermoplastic resin, a photocurable resin, low melting glass, etc. can be used. In room temperature nanoimprint, a sol-gel material such as spin-on-glass (SOG) or hydrogen silsesquioxane polymer (HSQ) may be used.

  Furthermore, considering the transmittance and moldability for light with a wavelength of 400 to 700 nm, the refractive index na of the material of the structural layer 30 is preferably 1.38 or more and 1.60 or less. Furthermore, in order to prevent diffraction with respect to incident light having a wavelength of 400 nm or more and 700 nm or less, the pitch of the fine concavo-convex structure in the graded portion is preferably 400 nm or less, and in order to obtain the effect over a wide incident angle. More preferably, the pitch is 200 nm or less.

  The fine uneven structure of the graded portion 2 has a structure in which the space filling rate continuously increases from the light incident side to the substrate side. The substantial refractive index ne of the graded portion 2 is obtained by the following equation (1) using the space filling factor (FF).

In the graded portion 2, the space filling factor continuously increases in the film thickness direction, so that the substantial refractive index ne also continuously increases from the light incident side. For this reason, it is difficult to generate a reflected wave that normally occurs at an interface having a refractive index difference, and a high antireflection effect can be obtained with respect to light incident on the remaining portion from the air.

  Here, considering the moldability and the strength of the structure, it is preferable that the tip of the graded portion 2 is not a sharp shape (FIG. 2 (a)), and has a flat shape (FIG. 2 (b)) or rounded without corners. It is preferable that the shape has a shape (FIGS. 2 (c) and 2 (d)). In consideration of moldability and strength, the space filling factor (FF) at the tip is preferably 5% or more, and more preferably 10% or more. Note that the filling rate of the tip here is calculated by assuming that the structure is not round (approximate round structure in FIG. 2-3) even when it is rounded.

  In addition, when the shape of the graded part 2 is a truncated cone or a polygonal truncated cone, the filling rate at the height distance d (nm) from the lower end of the structure (that is, the boundary between the graded part 2 and the remaining film part) is 2 is required.

Here, D (nm) is the physical film thickness of the graded portion 2, and FF (MAX) and FF (min) are the maximum value and the minimum value of the filling rate, respectively.

  On the other hand, in the case of the structure where the tip is not sharp as described above, a difference in refractive index occurs at the portion where the light is incident on the structure from the air, and a reflected wave is generated. Therefore, a structure that cancels this reflected wave is required. This can be realized, for example, by forming a discontinuous portion in the structure of the graded portion 2 (FIG. 3). In other words, by providing a portion having a refractive index difference in the structure of the graded portion, a reflected wave having an opposite phase and the same amplitude as that of the reflected wave generated at the interface between the air and the light incident portion is generated. The reflected wave generated from the can be canceled out. In order to exhibit this effect more, it is preferable to satisfy the following formulas (3) and (4).

Here, ne1, ne2, and ne3 are substantial refractive indexes of the portion shown in FIG. The portion where the filling rate is discontinuous may be formed in any portion of the graded portion 2, and may be provided, for example, at the most substrate side, that is, at the interface between the graded portion 2 and the remaining portion 1. However, in order to have higher performance antireflection performance, the physical film thickness ratio D2 / D1 preferably satisfies 0.5 or more, and more preferably 1.0 or more. Here, D1 and D2 are the physical film thickness from the discontinuous part to the light incident part and the physical film thickness from the interface with the remaining film part 1 to the discontinuous part, respectively.

  Further, the physical film thickness (D1 + D2) of the entire graded portion 2 is preferably 150 nm or more and 500 nm or less, and more preferably 250 nm or more and 350 nm or less. When the physical film thickness is less than 150 nm, the wavelength band in which a high antireflection effect is obtained becomes narrow, and the performance for an incident angle of 30 degrees or more is particularly deteriorated. On the other hand, when the optical film thickness is increased, the aspect ratio of the structure is increased, making it difficult to manufacture, and unnecessary light is generated due to scattering due to the defective structure.

  On the other hand, the intermediate layer 20 has a single layer structure formed on the optical substrate 1 or a structure in which two or more different thin film layers are stacked, and serves to suppress reflected waves generated at the interface between the remaining film portion 1 and the substrate. Take on. Therefore, the number of layers and the film configuration may be selected according to the refractive index na of the remaining film portion 1 and the refractive index ns of the substrate. For example, when 30 is made of a material of 1.48 or more and 1.70 or less and the refractive index of the optical substrate 1 is 1.68 or more and 2.30 or less, the M layer, the H layer, and the M layer are formed from the optical substrate side. A three-layer configuration or a four-layer configuration of H layer, M layer, H layer, and M layer can be selected.

  Further, when the refractive index difference between the material forming the structural layer 30 and the substrate is about 0.1, the M layer or the L layer can be used as a single layer. Here, the L layer is a thin film layer satisfying a refractive index of 1.35 to 1.50, the M layer is a thin film layer satisfying a refractive index of 1.60 to 1.72, and the H layer has a refractive index of 1.95. It is a thin film layer that satisfies 2.20 or less.

  The manufacturing method of the intermediate layer 20 is not particularly limited, and any process such as a liquid phase method, a vacuum deposition method, or 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.

The material of each layer of the intermediate layer 20 is, for example, a metal oxide such as SiO ₂ , MgO, Al ₂ O ₃ , SiON, ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , TiO ₂ , LaF ₃ , CeF ₃ , MgF _2. , NdF ₃ , CaF ₂ or other metal fluorides or their compounds can be used. However, depending on the material of the optical substrate 10, components may elute on the surface when exposed to the atmosphere, resulting in fogging or coloring (called “burning”). The layer to be used is preferably Al ₂ O ₃ or SiON.

  As described above, in the antireflection film 100, the graded portion 2 suppresses the reflected wave generated at the interface between the air and the remaining film portion 1, and the intermediate layer 20 suppresses the reflected wave generated at the interface between the remaining film portion 1 and the substrate. It becomes the composition to do. Therefore, the film thickness sensitivity to the reflectance characteristics of the remaining film portion 1 can be reduced. In addition, the film thickness of the remaining film part 1 is not specifically limited. However, if the thickness is too large, the moldability deteriorates or the scattering increases and the transmittance of the element decreases, so the film thickness of the remaining film portion 1 is preferably 10 μm or less.

  The refractive index of the optical substrate 10 is not particularly limited. However, when the refractive index difference between the optical substrate 10 and the structural layer 30 is sufficiently small, the reflected wave generated at the interface between the structural layer 30 and the optical substrate 10 becomes small, and performance can be obtained without the intermediate layer 20. . Therefore, in order to exhibit the effect of the intermediate layer 20 more, the refractive index difference between the structural layer 30 and the optical substrate 10 is preferably 0.1 or more, and more preferably 0.2 or more.

  The optical element forming the antireflection film 100 includes, for example, a lens, a prism, a fly eye integrator, and the like. The optical system having this optical element includes, for example, an imaging optical system, a scanning optical system, and a projection optical system, such as a camera, a video camera, a binocular, a copying machine, a printer, a projector, a head-mounted display, an astronomical telescope, a microscope, and the like. It can be used for optical instruments. In such an optical apparatus, in order for the optical system on which the antireflection film of the present invention is formed to obtain sufficient transmittance and a ghost / flare suppression effect, even when the film thickness of the remaining film portion 1 varies. The reflectance at 0 degree incidence is preferably 0.3% or less, and the reflectance at 45 degree incidence is preferably 1.0% or less.

  The antireflection film of the present invention will be described below based on specific calculation examples. In the following calculation example, the refractive index of the structure portion is treated as a film having the refractive index obtained from the above (1).

[Example 1]
In the antireflection film of Example 1, an intermediate layer 20 formed of a multilayer film of three layers is formed on an optical substrate 10 having a refractive index of 1.808, and a structural layer 30 in which frustoconical shapes are regularly arranged thereon. Have. In the structural layer 30, the graded portion 2 and the remaining film portion 1 are integrally formed using PMMA, and the refractive index of the remaining film portion 1 is 1.493. There is a portion where the filling rate changes discontinuously, and the light incident side from that portion is defined as a graded portion 2a and the substrate side is defined as a graded portion 2b. The refractive index of the graded portion 2b continuously changes from 1.493 to 1.164 on the substrate side according to the change in the filling rate.

  Similarly, the graded portion 2a continuously changes from 1.097 to 1.045. At this time, the space filling factor FF changes from 1.00 on the most substrate side to 0.10 at the light incident part, and the filling factors at the discontinuous part are 0.35 and 0.21, respectively. . The physical film thicknesses D1 and D2 of the graded portion are 124 nm and 165 nm, respectively. The intermediate layer 20 has a refractive index of 1.621 from the substrate side, a first layer having an optical film thickness of 41 nm, a refractive index of 2.127, a second layer having an optical film thickness of 20 nm, a refractive index of 1.621, It is formed from a third layer having an optical film thickness of 157 nm. Table 1 shows the configuration of the antireflection film of Example 1.

FIG. 4 shows the refractive index with respect to the film thickness direction (physical film thickness / nm) of the antireflection film of Example 1. Further, FIG. 5 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm. Note that 0 deg, 30 deg,... In FIG.

  From FIG. 5, the antireflection film of this example has an excellent reflectivity of 0.1% or less over the entire range of 400 to 700 nm when the incident angle is 0 degree, and 0.3% or less when the incident angle is 45 degrees. It can be seen that it exhibits characteristics. The average reflectance at 400 to 700 nm was 0.01% at 0 °, 0.06% at 45 °, and 0.72% at 60 °.

  Next, FIG. 6 shows the fluctuation range (calculated value) of the reflectance characteristic when the film thickness of the remaining film portion 1 varies. FIG. 6 shows the result when the calculation for changing the film thickness randomly within the range of ± 200 nm with respect to the design value is repeated 100 times, and FIG. 6A shows the case where the incident angle is 0 degree. FIG. 6B shows a case where the incident angle is 45 degrees.

  From FIG. 6, even if the film thickness of the remaining film part 1 varies in the order of several hundreds of nm, the reflection is as follows: 0.2% or less at 450 to 700 nm at 0 degree incidence and 0.8% or less at 45 degree incidence. It can be seen that the impact on the rate is very small.

  FIG. 7 shows reflectance characteristics when the film thickness of the remaining film portion 1 is changed. FIG. 7A shows a case where the incident angle is 0 degree, and FIG. 7B shows a case where the incident angle is 45 degrees.

  From FIG. 7, it can be seen that even if the film thickness of the remaining film portion 1 is changed from 0 to 10000 nm, the variation of the reflectance characteristic is within the range shown in FIG.

[Comparative Example 1]
As Comparative Example 1, an antireflection film described in Numerical Example 2 of Patent Document 2 will be described. In this comparative example, only the configuration that provides the highest antireflection performance among the film configurations disclosed in Numerical Example 2 of Patent Document 2 is shown.

  In this comparative example, the structural layer 30 referred to in the present invention is formed on an optical substrate having a refractive index of 1.800. The structural layer 30 is made of a material having a refractive index of 1.620, the refractive index of the remaining film portion 1 is 1.620, and the refractive index of the graded portion 2 is the most light incident side from 1.620 on the most substrate side. Continuously changing according to the filling rate up to 1.113. In Numerical Example 2, there is no disclosure of a specific refractive index regarding the graded portion 2, but the filling rate is 1.0 on the most substrate side and between 0.22 and 0.50 on the most light incident side. Since there is a description of a truncated cone having a value, it was calculated based on the formula (1) based on this.

  For the most light incident side, the value with the best reflectance characteristics was used in this calculation. Table 2 shows the configuration of the antireflection film of Comparative Example 1.

FIG. 24 shows the refractive index in the film thickness direction of the antireflection film of Comparative Example 1. Further, FIG. 25 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm.

  From FIG. 25, in the antireflection film of this comparative example, the reflectance exceeds 1.0% in the vicinity of 450 nm even at 0 degree reflection. Further, the average reflectance at 400 to 700 nm was 0.47% at 0 degree, 0.74 at 45 degree, and 2.4% at 60 degree.

  Next, FIG. 26 shows the reflectance fluctuation when the film thickness of the remaining film portion is varied by a maximum of ± 20 nm.

  Comparing FIG. 6 and FIG. 26, in the comparative example, the film thickness variation is about 1/10 of that of Example 1, but the reflectance variation is about 1.0% at the maximum, which is more than twice that of Example 1. I understand that This shows that the antireflection film of the present invention can provide an excellent antireflection effect even if the film thickness of the remaining film varies.

[Example 2]
In the antireflection film of Example 2, the material forming the structural layer 30 and the intermediate layer 20 are the same as those of Example 1, and the structure of the graded portion 2 is different. In Example 1, the portion where the filling rate is discontinuous (the portion where there is a difference in refractive index) is arranged in the middle of the graded portion 2, but in Example 2, the refractive index difference is present at the interface with the remaining film portion 1. Is provided. The space filling factor FF of the graded portion 2 changes from 0.89 on the most substrate side to 0.10 of the light incident portion. The physical film thickness D of the graded portion is 464 nm. Table 3 shows the configuration of the antireflection film of Example 2.

FIG. 8 shows the refractive index in the film thickness direction of the antireflection film of Example 2. Further, FIG. 9 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm.

  As shown in FIG. 9, the antireflection film of this example has an excellent reflectivity of 0.2% or less over the entire range of 400 to 700 nm when the incident angle is 0 degree, and 0.4% or less when the incident angle is 45 degrees. It can be seen that it exhibits characteristics. The average reflectance at 400 to 700 nm was 0.07% at 0 degree, 0.13% at 45 degree, and 0.67% at 60 degree.

  Next, FIG. 10 shows the reflectance variation when the remaining film portion is dispersed as in the first embodiment.

  From FIG. 10, even if the film thickness of the remaining film portion varies as described above, the influence on the reflectance is small, that is, 0.4% or less at 400 to 700 nm at 0 degree incidence and 0.7% or less at 45 degree incidence. I understand that. As shown in Examples 1 and 2, the portion where the filling rate becomes discontinuous is set at an arbitrary position such as in the middle of the graded portion 2 or the interface with the remaining film portion, and the effect of reducing the film thickness sensitivity is obtained. be able to. When installed at the interface with the remaining film portion 1 as in the second embodiment, there is an advantage that the structure becomes simple. On the other hand, when provided in the middle of the graded portion 2, the film thicknesses D1 and D2 of the graded portion 2 can be used as parameters, respectively, and the reflectance can be further reduced.

[Example 3]
The antireflection film of Example 3 is the same as that of Example 1 in the material forming the structural layer 30, and the substrate is different. The refractive index of the optical substrate is 1.888, and the intermediate layer 20 is formed of a multilayer film of three layers. Table 4 shows the configuration of the antireflection film of Example 3.

Moreover, the refractive index with respect to the film thickness direction of the antireflection film of Example 3 is shown in FIG. Further, FIG. 12 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm.

  As shown in FIG. 12, the antireflection film of this example has an excellent reflectivity of 0.1% or less over the entire range of 400 to 700 nm when the incident angle is 0 degree, and 0.2% or less when the incident angle is 45 degrees. It can be seen that it exhibits characteristics. The average reflectance at 400 to 700 nm was 0.01% at 0 °, 0.04% at 45 °, and 0.58% at 60 °.

  Next, FIG. 13 shows the reflectance variation when the remaining film portion is dispersed as in the first embodiment. From FIG. 13, even if the film thickness of the remaining film portion varies in this way, the influence on the reflectance is extremely low at 0 to incidence of 0.2% or less at 450 to 700 nm, and at 45 ° incidence of 0.6% or less. I understand that it is small.

[Example 4]
The antireflection film of Example 4 is the same as that of Example 1 in the material forming the structural layer 30, and the substrate is different. The refractive index of the optical substrate is 2.116, and the intermediate layer 20 is formed of a multilayer film of three layers. Table 5 shows the configuration of the antireflection film of Example 4.

FIG. 14 shows the refractive index in the film thickness direction of the antireflection film of Example 4. Further, FIG. 15 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm.

  From FIG. 15, the antireflection film of this example has an excellent reflectivity of 0.2% or less in the entire region of 450 to 700 nm when the incident angle is 0 degree, and 0.3% or less when the incident angle is 45 degrees. It can be seen that it exhibits characteristics. The average reflectance at 400 to 700 nm was 0.07% at 0 degree, 0.08% at 45 degree, and 0.66% at 60 degree.

  Next, FIG. 16 shows the reflectance variation when the remaining film portion is dispersed as in the first embodiment.

  FIG. 16 shows that even if the film thickness of the remaining film portion varies, the influence on the reflectance is extremely small, with 0.2% or less at 450 to 700 nm at 0 degree incidence and 0.5% or less at 45 degree incidence. I understand. Thus, when the configuration of the present invention is used, the film thickness sensitivity of the remaining film portion 1 can be lowered even when the refractive index difference between the optical substrate and the structural layer 30 (residual film portion 1) is large.

[Example 5]
In the antireflection film of Example 5, the optical substrate is the same as that of Example 4, and the material constituting the structural layer 30 and the structure of the intermediate layer 20 are different. The intermediate layer 20 of the present embodiment is formed of four multilayer films, and the structural layer 30 is formed of PC. Table 6 shows the configuration of the antireflection film of Example 5.

  FIG. 17 shows the refractive index in the film thickness direction of the antireflection film of Example 5. Further, FIG. 18 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm.

  As shown in FIG. 18, the antireflection film of this example has an excellent reflectance of 0.2% or less over the entire range of 400 to 700 nm when the incident angle is 0 degree, and 0.3% or less when the incident angle is 45 degrees. It can be seen that it exhibits characteristics. The average reflectance at 400 to 700 nm was 0.03% at 0 °, 0.07% at 45 °, and 0.74% at 60 °.

  Next, FIG. 19 shows the reflectance variation when the remaining film portion is dispersed as in the first embodiment. From FIG. 19, even if the film thickness of the remaining film portion varies in this way, the influence on the reflectivity is extremely high at 0.2 to less than 450% at 700 to 700 nm at 0 degree incidence and less than 0.6% at 45 degree incidence. I understand that it is small.

[Example 6]
The antireflection film of Example 6 has the intermediate layer 20 formed of one thin film layer on the optical substrate 10 having a refractive index of 1.699. The structural layer 30 is made of PS. Table 7 shows the configuration of the antireflection film of Example 6.

  FIG. 20 shows the refractive index in the film thickness direction of the antireflection film of Example 6. Further, FIG. 21 shows reflectance characteristics with respect to wavelengths of 400 to 700 nm.

  From FIG. 21, the antireflection film of this example has an excellent reflectivity of 0.2% or less over the entire range of 400 to 700 nm when the incident angle is 0 degree, and 0.3% or less when the incident angle is 45 degrees. It can be seen that it exhibits characteristics. The average reflectance at 400 to 700 nm was 0.06% at 0 degree, 0.13% at 45 degree, and 0.94% at 60 degree. Next, FIG. 22 shows the reflectance variation when the remaining film portion is dispersed, as in the first embodiment.

  From FIG. 22, even if the film thickness of the remaining film portion varies as described above, the influence on the reflectivity is extremely high at 0.3 to less than 0.3% at 450 to 700 nm at 0 degree incidence and less than 0.6% at 45 degree incidence. I understand that it is small.

[Example 7]
FIG. 23 is a schematic diagram of an optical apparatus according to the seventh embodiment.

  In FIG. 23, reference numeral 101 denotes a digital camera, and 102 denotes an imaging optical system configured using an optical element on which an antireflection film of the present invention is formed. The imaging optical system 102 includes a plurality of lenses, and the antireflection film of the present invention is formed on at least one of these lens surfaces. In this embodiment, a digital camera is taken as an example of an optical apparatus, but the present invention is not limited to this, and may be used for other optical apparatuses such as binoculars and an image projection apparatus.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist.

1 remaining film part, 2 graded part, 10 optical substrate, 20 intermediate layer, 30 structure layer,
100 Antireflection film of the present invention, 101 Optical apparatus (digital camera) of the present invention,
102 Optical system of the present invention

Claims (9)

An antireflection film formed on an optical substrate for reducing surface reflection of incident or emitted light,
A structure layer having irregularities regularly arranged at a pitch of 400 nm or less and an intermediate layer formed between the structure layer and the optical substrate;
The intermediate layer has a structure in which one or more thin film layers are laminated,
The structural layer is formed integrally with a graded portion in which the refractive index changes in the film thickness direction and a remaining film portion in which the refractive index does not change in the film thickness direction. A space filling factor on the light incident side satisfies 0.05 or more and 0.20 or less, and the space filling factor has one or more points other than the light incident part in the film thickness direction. An antireflection film characterized in that a difference in space filling rate at a point of discontinuous change is 0.05 or more and 0.20 or less. The effective refractive index on the most light incident side of the graded portion is ne1,
If the effective refractive index of the discontinuously changing points is ne2, ne3 (ne2 <ne3),
2. The antireflection film according to claim 1, wherein ne1, ne2, and ne3 satisfy the following relational expression.
However, the effective refractive index ne in the above relational expression is obtained from the following relational expression using the space filling factor FF and the refractive index na of the material constituting the graded portion.
The antireflection film according to claim 1 or 2, wherein a difference between the effective refractive indexes ne2 and ne3 is 0.03 or more and 0.1 or less. 4. The antireflection film according to claim 1, wherein the graded portion is formed of a truncated cone or a polygonal truncated cone. 5. 5. The antireflection film according to claim 1, wherein, of the thin film layers constituting the intermediate layer, the most substrate side layer is made of Al ₂ O ₃ or SiON. 6. The antireflection film according to any one of claims 1 to 5, wherein the graded portion and the remaining portion are made of an energy curable resin. An optical element comprising the antireflection film according to any one of claims 1 to 6. An optical system comprising at least one optical element according to claim 7. An optical apparatus using the optical system according to claim 8.