JP2015004919A - Anti-reflection film and optical element having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anti-reflection film having a superior anti-reflection property over a wide wavelength range, and to provide optical elements having the same.SOLUTION: An anti-reflection film 100 is formed on a light transmission surface of a transparent substrate and comprises, in order from a substrate 1 side to an air layer side, an intermediate layer 2 comprising a plurality of laminated layers and a micro concavo-convex structure 3 having a plurality of micro structure sections with a pitch of no more than 400 nm formed thereon. The micro concavo-concave structure 3 has a thickness of no less than 200 nm and no more than 350 nm and has a region where a refractive index continuously increases from 1.0 in a direction from the air layer side toward the substrate 1. The plurality of layers of the intermediate layer 2 are a first layer 21 through a fifth layer 25 in order from the substrate side to the air layer side. Refractive indexes of the plurality of layers are values at a wavelength of 550 nm, and an optical film thickness is defined as (refractive index at a wavelength of 550 nm)×(thickness).

Description

  The present invention relates to an antireflection film provided on a light incident / exit surface of a transparent substrate and an optical element having the same, and in particular, has a structure in which a refractive index continuously changes in a depth direction (film thickness direction) and is wide. It has an antireflection function that is favorable in the wavelength range, and is suitable for optical systems of various optical devices.

  Conventionally, anti-reflection measures have been taken on the surface (light transmission surface) of optical elements such as lenses and filters in order to reduce the light loss of incident light. For example, a dielectric multilayer film called a multi-coat is widely used as an antireflection for visible light, and in recent years, an antireflection film using a fine concavo-convex structure is also known (Patent Documents 1 and 2).

  Patent Document 1 discloses an antireflection film using a plate-like crystal containing aluminum oxide as a main component, whose substantial refractive index continuously changes from the light incident side toward the substrate side. Patent Document 2 discloses an antireflection film in which a plurality of uniform layers made of thin films and a fine concavo-convex structure are laminated on a transparent substrate in order from the substrate side to the air layer side.

  On the other hand, in recent years, in optical instruments that use a wide wavelength band from visible light to near infrared, such as fluorescent microscopes, surveillance cameras, and on-vehicle cameras, light loss, ghosting, and flare are further reduced to obtain high-quality images. It is requested to do. In order to effectively prevent reflection in a wide wavelength range, a multilayer antireflection film is known (Patent Document 3). Patent Document 3 discloses a nine-layer antireflection film composed of a dielectric multilayer film using a low refractive index layer as the uppermost layer (most air layer side). Patent Document 3 discloses an antireflection film having a reflectance of 0.1% or less at an incident angle 5 in a wavelength range of 400 to 900 nm.

JP 2008-233880 A JP 2010-78803 A JP 2008-225210 A

  A light beam having a wide wavelength range is incident on an optical system used in an optical apparatus such as a digital camera or a surveillance camera. For this reason, the antireflection function is required to have a low reflectance over a wide wavelength range. In particular, since many image sensors used in optical devices have sensitivity in the near infrared region, it is required that the reflectance be low in the near infrared region. In order to obtain an optical element having a high antireflection effect from the visible region to the near infrared region, it is important to appropriately set the configuration of the antireflection film formed on the substrate.

  If the structure of the antireflection film is inappropriate, it has high antireflection performance in a wide wavelength range, particularly in the near infrared range of 700 nm or more. For example, in the wavelength range of 450 nm to 1200 nm, good reflectance characteristics are obtained. It becomes difficult.

  An object of the present invention is to provide an antireflection film having excellent antireflection characteristics in a wide wavelength range and an optical element having the antireflection film.

  The antireflection film of the present invention is an antireflection film provided on a light transmission surface of a transparent substrate, and the antireflection film is an intermediate layer having a plurality of layers laminated in order from the substrate side to the air layer side, 400 nm. It has a fine concavo-convex structure in which a plurality of fine structure portions having the following pitches are formed. The fine concavo-convex structure has a film thickness of 200 nm or more and 350 nm or less and a refractive index in the direction from the air layer side toward the substrate. The plurality of layers of the intermediate layer have a first layer, a second layer, a third layer, a fourth layer, and a fifth layer in order from the substrate side to the air layer side. When the refractive index of the plurality of layers is a value at a wavelength of 550 nm and the optical film thickness is (refractive index at a wavelength of 550 nm) × (thickness), the refractive index of the first layer is 1.61. -1.71, optical film thickness is 10-220 nm, refractive index of the second layer is 1.98-2.40, The film thickness is 15 to 65 nm, the refractive index of the third layer is 1.61 to 1.71, the optical film thickness is 60 to 140 nm, the refractive index of the fourth layer is 1.98 to 2.40, the optical film The thickness is 15 to 65 nm, the refractive index of the fifth layer is 1.42 to 1.54, and the optical film thickness is 10 to 140 nm.

  According to the present invention, an antireflection film having excellent antireflection characteristics in a wide wavelength region and an optical element having the antireflection film can be obtained.

Schematic of the antireflection film of the present invention (A), (B) Refractive index relationship with respect to substrate thickness of antireflection film of Example 1-1 and reflectance characteristics of antireflection film (A), (B) Refractive index relationship with respect to substrate thickness of antireflection film of Example 1-2 and reflectance characteristics of antireflection film (A), (B) Refractive index relationship with respect to substrate thickness of antireflection film of Example 2-1 and reflectance characteristics of antireflection film (A), (B) Refractive index relationship with respect to substrate thickness of antireflection film of Example 2-2 and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index with respect to substrate thickness of antireflection film of Example 3 and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index to substrate thickness of antireflection film of Example 4 and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index with respect to substrate thickness of antireflection film of Example 5 and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index with respect to substrate thickness of antireflection film of Example 6 and reflectance characteristics of antireflection film (A), (B) Refractive index relationship with respect to substrate thickness of antireflection film of Example 7 and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index with respect to substrate thickness of antireflection film of Example 8-1 and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index with respect to substrate thickness of antireflection film of Example 8-2, and reflectance characteristics of antireflection film (A), (B) Relationship of refractive index with respect to substrate thickness of antireflection film of Example 9 and reflectance characteristics of antireflection film Schematic diagram of the optical instrument of the present invention (A), (B) Relation of refractive index with respect to substrate thickness of antireflection film of Comparative Example 1 and reflectance characteristics of antireflection film Reflectance characteristic diagram of antireflection film of Comparative Example 2 (A), (B) Relation of refractive index with respect to substrate thickness of antireflection film of Comparative Example 3 and reflectance characteristics of antireflection film

  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. The antireflection film of the present invention is provided on the light transmission surface of a transparent substrate. The antireflection film has, in order from the substrate side to the air layer side, an intermediate layer in which a plurality of layers are laminated, and a fine concavo-convex structure body in which a plurality of fine structure portions having a pitch of 400 nm or less are formed on a plane or a curved surface. The fine concavo-convex structure has a film thickness of 200 nm or more and 350 nm or less and a region in which the refractive index continuously increases from 1.0 in the direction from the air layer side to the substrate.

  FIG. 1 is a schematic view (cross-sectional view) of an optical element having an antireflection film of the present invention. In FIG. 1, reference numeral 200 denotes an optical element. Reference numeral 1 denotes a transparent optical substrate. The vicinity of the surface of the optical substrate 1 is shown enlarged. The optical substrate 1 is made of optical glass or optical plastic having a refractive index of 1.40 to 2.30, and the antireflection film 100 of the present invention is formed on at least one of light transmitting surfaces such as a light incident surface and a light emitting surface. Is formed. The antireflection film 100 is provided on the air layer side between the fine concavo-convex structure 3, the optical substrate 1 and the fine concavo-convex structure 3, and an intermediate layer 2 composed of multilayer films (plural layers) having different refractive indexes. Have.

  The fine concavo-convex structure 3 has a plurality of fine structures 3a having a pitch smaller than 400 nm on a plane, and the space filling rate ff is continuous from the light incident side (air layer side) to the optical substrate 1 side. It has a region that becomes higher. Therefore, the effective refractive index neff in this region continuously increases from the light incident side toward the optical substrate 1. In order to prevent diffraction from occurring even if the incident angle is increased with respect to incident light having a wavelength of 400 nm or more and 1300 nm or less, the pitch of the fine structure portions 3a is preferably 200 nm or less, and the pitch is 120 nm. More preferably, it is as follows.

  The fine concavo-convex structure 3 may have a region (hereinafter referred to as a homogeneous region) having a constant space filling rate (that is, a constant refractive index). Further, the fine uneven structure 3 may be a regular structure or an irregular (random) structure. Compared to a regular structure, when a random structure is used, the generation of diffracted light in a specific direction can be suppressed, and thus a random structure is more preferable.

  In order to obtain a high antireflection effect, the film thickness (average value of the height) of the fine uneven structure 3 is preferably 200 nm or more and 350 nm or less. When the film thickness is less than 200 nm, the wavelength band where a high antireflection effect is obtained becomes narrow. On the other hand, when the film thickness is 350 nm or more, the aspect ratio of the fine concavo-convex structure 3 is increased, making it difficult to manufacture, and the transmittance is reduced due to scattering due to the structure and randomness of the fine structure 3a.

  In the present embodiment, the manufacturing method of the fine concavo-convex structure 3 is not particularly limited. For example, a film containing aluminum oxide (alumina) formed by a vacuum film formation method or a liquid phase method (sol-gel method) is treated with water vapor or hot water to make the surface layer boehmite (plate-like crystallization), resulting in fine irregularities The structure 3 can be formed.

  When produced by this method, the effective refractive index of the fine concavo-convex structure 3 is approximately 1 on the light incident side and continuously increases toward the intermediate layer 2 side, and the maximum value of the refractive index is 1.35 to 1. The range is 58. It can also be formed using nanoimprinting or lithography. However, in order to create a large area, it is preferable to form a bottom-up type fine structure such as nanoimprint or microcrystallization or self-organization as described above. Further, when forming on an optical element having a non-flat surface such as a lens having a large opening angle, it is more preferable to form a bottom-up type fine structure.

  The fine concavo-convex structure 3 may have a uniform layer (homogeneous region) in which the refractive index formed from the same material is adjacent to the intermediate layer 2 in the film thickness direction. For example, when an aluminum oxide film is treated with water vapor or warm water, a plate-like crystal of aluminum oxide is deposited on the surface layer to form the fine concavo-convex structure 3 in which the space filling rate changes in the thickness direction. Then, an amorphous aluminum oxide layer (homogeneous region) having a constant space filling rate may remain below (on the intermediate layer 2 side).

  The film thickness in the homogeneous region can be adjusted by controlling the treatment temperature and treatment time, the content of aluminum oxide in the material, and the content of additives such as stabilizers and catalysts. Moreover, even when formed by nanoimprinting or lithography, a homogeneous region can be formed. In addition, the refractive index of a homogeneous area | region may be made to correspond with the part nearest to a homogeneous part among the fine concavo-convex structures 3, and may differ. That is, the refractive index is preferably 1.35 to 1.58.

  The intermediate layer 2 is formed on the optical substrate 1, and five thin films of a first layer to a fifth layer having a predetermined refractive index and an optical film thickness (refractive index × thickness) are stacked in order from the optical substrate 1 side. With structure. That is, the first layer 21 has a refractive index of 1.61 to 1.71 and an optical film thickness of 10 to 220 nm. The second layer 22 has a refractive index of 1.98 to 2.40 and an optical film thickness of 15 to 65 nm. The third layer 23 has a refractive index of 1.61 to 1.71 and an optical film thickness of 60 to 140 nm. The fourth layer 24 has a refractive index of 1.98 to 2.40 and an optical film thickness of 15 to 65 nm. The fifth layer 25 has a refractive index of 1.42 to 1.54 and an optical film thickness of 10 to 140 nm.

  In the present embodiment, the manufacturing method of each layer of the intermediate layer 2 is not particularly limited, and any process such as a liquid phase method, a vacuum deposition 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. Further, when the refractive index of the first layer 21 is lower than the refractive index of the optical substrate 1, the optical film thickness of the first layer 21 is preferably 10 to 35 nm, and the refractive index of the first layer 21 is higher. In that case, the optical film thickness is preferably 180 to 220 nm.

  This is because the phase of the reflected wave generated at the interface between the optical substrate 1 and the first layer 21 changes depending on the magnitude relationship between the refractive indexes of the optical substrate 1 and the first layer 21. Further, in the case where a homogeneous region (uniform layer) is provided in a portion adjacent to the fine relief structure 3 and the intermediate layer 2, the sum of the optical film thickness of the homogeneous region and the optical film thickness of the fifth layer 25 is 10 nm. It is preferable that it is 140 nm or less.

  This is because the homogeneous region and the fifth layer 25 may be combined to serve as the fifth layer 25. In addition, in order for the homogeneous region and the fifth layer 25 to behave as one layer in appearance, the refractive index difference is preferably 0.1 or less, and more preferably 0.05 or less. .

Here, the material of each layer of the intermediate layer 2 is, for example, a metal oxide compound such as SiO ₂ , MgO ₂ , Al ₂ O ₃ , MgO, SiON, ZrO ₂ , HfO ₂ , Ta ₂ O ₅ , or TiO _2. it can. Furthermore, a simple substance of a metal fluoride such as LaF ₃ , CeF ₃ , MgF ₂ , NdF ₃ , 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 elute on the surface and cause clouding or coloring (called “burning”). To prevent this, the first layer 21 is It is preferable to use Al ₂ O ₃ or SiON. The fifth layer 25 is preferably a film that has low reactivity and is stable in the air. For example, SiO ₂ is preferably used.

  Further, the refractive index difference at the interface between the fine uneven structure 3 and the intermediate layer 2 (that is, the refractive index difference of the fifth layer 25 and the refractive index closest to the optical substrate 1 of the fine uneven structure 3) is 0.1 or less. Preferably, it is 0.05 or less. By reducing the difference in refractive index, the reflected wave generated at the interface can be suppressed, and the antireflection performance is improved.

  When an optical element having an antireflection film is used in an optical system, it has the following antireflection effect, and in order to obtain sufficient transmittance, ghost and flare suppression effects, the following settings are made. good. That is, it is preferable that the reflectance can be reduced to 0.2% or less at a wavelength of 450 to 1000 nm and 1.0% or less at a wavelength of 1000 to 1200 nm. Moreover, it is preferable that it can be reduced to 1.0% or less at a wavelength of 450 to 1000 nm with respect to an incident angle of 45 degrees. Furthermore, it is more preferable that the reflectance can be reduced to 0.1% or less at a wavelength of 450 to 1000 nm and 0.6% or less at a wavelength of 1000 to 1200 nm.

  The optical substrate 1 preferably has a refractive index of 1.40 to 2.30, more preferably 1.40 to 1.60 or 1.8 to 2.20. When the refractive index of the optical substrate 1 satisfies the above range, high antireflection performance can be easily obtained by forming the antireflection film of the present invention.

  The optical element 200 that forms the antireflection film 100 on any one of the light incident surface and the light emitting surface includes, for example, a lens, a prism, a fly eye integrator, and the like. The optical system having the optical element 200 includes, for example, an imaging optical system, a scanning optical system, and a projection optical system, and includes a camera, a video camera, binoculars, a copier, a printer, a projector, a head-mounted display, an astronomical telescope, and a microscope. It can be used for optical instruments such as.

  As described above, according to the present invention, an antireflection film having excellent antireflection characteristics in a visible to near-infrared broadband and an optical element having the antireflection film can be obtained. Next, the antireflection film of each example will be described.

[Example 1]
Table 1 shows numerical values of the film configuration of Example 1-1. In Table 1, the physical film thickness is the actual thickness. The same applies hereinafter. The antireflection film of Example 1-1 has the configuration shown in FIG. In the antireflection film 100, an intermediate layer 2 having a five-layer structure is formed on an optical substrate 1 having a refractive index of 2.162, and a fine uneven structure 3 is formed thereon.

The intermediate layer 2 has a refractive index of 1.694 and SiON as a main component (here, the main component is that the specified component contains 85 wt% or more in the formed layer), A second layer 22 having a refractive index of 2.323 and TiO ₂ as a main component, a refractive index of 1.694 and a third layer 23 having a main component of SiON, a refractive index of 2.323, and TiO ₂ as a main component. This is the fourth layer 24. Furthermore, the refractive index is 1.458, and the fifth layer 25 is composed mainly of SiO _2. Each layer is formed by sputtering. The optical thickness of each layer is 24 nm for the first layer 21, 51 nm for the second layer 22, 81 nm for the third layer 23, 30 nm for the fourth layer 24, and 55 nm for the fifth layer 25.

The fine concavo-convex structure 3 is prepared by preparing a sol solution containing aluminum, forming a film by spin coating, baking it in an oven at 200 ° C. for 30 minutes, coating a transparent amorphous Al ₂ O _3, and It was formed by immersing in warm water for 30 minutes and then drying. FIG. 2A shows the refractive index with respect to the thickness direction of the antireflection film 100 formed by this method.

  The horizontal axis of FIG. 2A represents the thickness from the optical substrate (substrate) 1, the surface of the substrate 1 on the side where the antireflection film is formed is 0 nm, and the light incident side of the fine concavo-convex structure 3 is 474 nm. It is. The vertical axis represents the refractive index in the film thickness direction of each member constituting the antireflection film 100.

  Hereinafter, the explanatory views of the refractive index with respect to the thickness direction of the antireflection film are the same. The fine concavo-convex structure 3 has a refractive index continuously increasing from 1 to 1.504 from the air layer side to the intermediate layer 2 side, and its physical film thickness is 242 nm. The change in the refractive index with respect to the film thickness direction is not constant, and the region closer to the air layer has a structure in which the refractive index change with respect to the thickness direction is smaller than the region closer to the intermediate layer.

Such a structure is not necessarily required, but can exhibit antireflection characteristics that are more excellent in wavelength band and incident angle characteristics. In addition, a homogeneous region (residual film of amorphous Al ₂ O ₃ ) (uniform layer) having a refractive index of 1.504 is formed at an optical film thickness of 57 nm below the fine uneven structure 3 (substrate side).

  FIG. 2B shows the reflectance characteristics of the antireflection film 100 of this example. In the figure, 0, 30, 45, and 60 represent incident angles (unit: degrees). 2B, when the incident angle is 0 degree, the antireflection film 100 of Example 1-1 is 0.1% or less at a wavelength of 400 to 1000 nm and 0.5% at a wavelength of 1000 nm to 1200 nm. The following excellent antireflection performance is shown. In addition, it can be seen that even when the incident angle is 45 degrees, high-performance antireflection performance with a reflectance of 1.0% or less is realized in a wide wavelength band of wavelength 400 to 1000 nm.

  The average reflectance in the wavelength region of 400 to 1000 nm was 0.03% at 0 degree incidence and 0.26% at 45 degree incidence. Moreover, although the antireflection film 100 of Example 1-1 and the board | substrate 1 and film | membrane structure are the same, the case where the film thickness of the fine concavo-convex structure 3 is thinner is shown as Example 1-2.

  Table 2 shows the numerical values of the film configuration of Example 1-2. In Example 1-2, the intermediate layer 2 is formed by sputtering, and the constituent material and refractive index are the same as those in Example 1-1. The optical thickness of each layer is 22 nm for the first layer 21, 58 nm for the second layer 22, 75 nm for the third layer 23, 35 nm for the fourth layer 24, and 66 nm for the fifth layer 25. Moreover, although the fine concavo-convex structure 3 was formed by the same method as in Example 1-1, the physical film thickness of the fine concavo-convex structure 3 was greater than that in Example 1-1 by controlling the film thickness during spin coating. The thickness was about 223 nm, which was about 10% thinner.

  Further, the homogeneous region at the lower part (substrate 1 side) of the fine concavo-convex structure 3 is also formed with an optical film thickness of 51 nm, which is thinner than that of Example 1-1. The refractive index with respect to the thickness direction of the antireflection film prepared by this method is shown in FIG.

  FIG. 3B shows the reflectance characteristics of the antireflection film of Example 1-2. As shown in FIG. 3B, the antireflection film 100 of Example 1-2 has a wavelength of 400 to 1000 nm and a wavelength of 0.1% or less, and a wavelength of 1000 nm to a wavelength of 1200 nm of 0.7% when the incident angle is 0 degree. The following excellent antireflection performance is shown. Further, it can be seen that even when the incident angle is 45 degrees, high-performance antireflection performance with a reflectance of 1.0% or less is realized in a wide wavelength band of 400 to 1000 nm. The average reflectance in the wavelength region of 400 to 1000 nm was 0.04% at 0 degree incidence and 0.35% at 45 degree incidence.

[Comparative Example 1]
Although the antireflection film of Example 1-1 and Example 1-2 have the same substrate and film configuration, a case where the film thickness of the fine concavo-convex structure 3 is still thinner is shown as Comparative Example 1. Table 13 shows the numerical values of the film configuration of Comparative Example 1. The method for forming the film is the same as in Examples 1-1 and 1-2. The optical thickness of each layer of the intermediate layer 2 is 15 nm for the first layer 21, 56 nm for the second layer 22, 69 nm for the third layer 23, 35 nm for the fourth layer 24, and 67 nm for the fifth layer 25. Further, the physical thickness of the fine concavo-convex structure 3 is 182 nm, which is thinner than that of Example 1-2, and the homogeneous region is also an optical thickness of 47 nm.

  The refractive index with respect to the thickness direction of the antireflection film 100 of Comparative Example 1 is shown in FIG. FIG. 15B shows the reflectance characteristics of the antireflection film of Comparative Example 1.

  From FIG. 15B, the antireflection film of Comparative Example 1 has a reflectance on the long wavelength side of about 0.5% at a wavelength of 1000 nm and about 1.5% at a wavelength of 1200 nm when the incident angle is 0 degree. It will go up. It can also be seen that when the incident angle is 45 degrees, the incident angle characteristic is reduced to about 1.5% at a wavelength of 1000 nm. The average reflectance in the wavelength region of 400 to 1000 nm was 0.14% at 0 degree incidence and 0.78% at 45 degree incidence, which was more than double that of Example 1.

  When the film thickness of the fine concavo-convex structure 3 is too low, the reflectance characteristics and the angle characteristics at a wavelength of 700 nm or more are deteriorated. In order for the average reflectance in the wavelength region of 400 to 1000 nm to satisfy 0.10% or less at 0 degree incidence, the film thickness of the fine concavo-convex structure 3 (excluding the homogeneous region) is desirably 190 nm or more. .

  Furthermore, in order for the reflectance at a wavelength of 400 to 1000 nm to be 0.1% or less, the film thickness of the fine concavo-convex structure 3 is more preferably 200 nm or more. Furthermore, in order to realize a reflectance characteristic of 1% or less at a wavelength of 400 to 1000 nm even at 45 ° incidence, it is more preferable that the thickness of the fine concavo-convex structure 3 (excluding the homogeneous region) is 215 nm or more.

  On the other hand, when the film thickness of the fine concavo-convex structure 3 becomes too thick, the randomness of the structure and the scattering derived from the structure increase and the transmittance decreases, so the film thickness is preferably 400 nm or less. In addition, if the height is too large with respect to the pitch of the fine structure portions 3a of the fine concavo-convex structure 3, the strength of the fine concavo-convex structure 3 is reduced and it becomes difficult to form the structure. More preferably, the thickness is 350 nm or less.

[Example 2]
The antireflection film of Example 2-1 has the configuration shown in FIG. Table 3 shows the numerical values of the film configuration of Example 2-1. The antireflection film 100 is formed on the optical substrate 1 having a refractive index of 2.011. The intermediate layer 2 includes a first layer 21 having a refractive index of 1.621 and Al ₂ O ₃ as a main component, a second layer 22 having a refractive index of 2.127 and Ta ₂ O ₅ as a main component, and a refractive index of 1.621, having a third layer 23 mainly composed of Al ₂ O ₃ . Further, the fourth layer 24 has a refractive index of 2.127 and Ta ₂ O ₅ as a main component, and the fifth layer 25 has a refractive index of 1.458 and a main component of SiO ₂ .

  Each layer was formed by a vacuum deposition method. The optical thickness of each layer is 13 nm for the first layer 21, 62 nm for the second layer 22, 63 nm for the third layer 23, 43 nm for the fourth layer 24, and 60 nm for the fifth layer 25. The fine concavo-convex structure 3 was produced by the same method as in Example 1-1. The refractive index with respect to the thickness direction of the antireflection film 100 of Example 2-1 is shown in FIG.

  FIG. 4B shows the reflectance characteristics of the antireflection film 100 of this example. From FIG. 4B, the antireflection film of Example 2-1 has a wavelength of 400 to 1000 nm and a wavelength of 0.1% or less, and a wavelength of 1000 nm to a wavelength of 1200 nm and a wavelength of 0.6% or less when the incident angle is 0 degree. Excellent anti-reflection performance. In addition, it can be seen that even when the incident angle is 45 degrees, high-performance antireflection performance with a reflectance of 1.0% or less is realized in a wide wavelength band of wavelength 400 to 1000 nm. The average reflectance in the wavelength region of 400 to 1000 nm was 0.04% at 0 degree incidence and 0.29% at 45 degree incidence.

  Moreover, although the antireflection film 100 of Example 2-1 and the board | substrate 1 and film | membrane structure are the same, the case where there is no homogeneous area | region of the lower part of the fine concavo-convex structure 3 is shown as Example 2-2. Table 4 shows the numerical values of the film configuration of Example 2-2.

  The intermediate layer 2 is formed by a vacuum vapor deposition method as in Example 2-1, and the constituent material and refractive index are also the same. The optical thickness of each layer is 19 nm for the first layer 21, 53 nm for the second layer 22, 71 nm for the third layer 23, 32 nm for the fourth layer 24, and 109 nm for the fifth layer 25. The fine concavo-convex structure 3 was formed by the same method as in Example 2-1, but it was homogeneous in the lower part of the fine concavo-convex structure 3 by adjusting the film forming conditions during spin coating and the conditions during hot water immersion treatment. The structure has no area. The refractive index with respect to the thickness direction of the antireflection film of Example 2-2 is shown in FIG.

  FIG. 5B shows the reflectance characteristics of the antireflection film of Example 2-2. As shown in FIG. 5B, when the incident angle is 0 degree, the antireflection film 100 of Example 2-2 is 0.1% or less at a wavelength of 400 to 1000 nm and 0.5% at a wavelength of 1000 nm to 1200 nm. The following excellent antireflection performance is shown. In addition, it can be seen that even when the incident angle is 45 degrees, high-performance antireflection performance with a reflectance of 0.8% or less is realized in a wide wavelength band of wavelength 400 to 1000 nm. The average reflectance in the wavelength region of 400 to 1000 nm was 0.03% at 0 degree incidence and 0.26% at 45 degree incidence.

  Since the layer including the homogeneous region and the fifth layer 25 of the intermediate layer 2 behaves substantially as one layer, the thickness of the fifth layer 25 is adjusted when there is no homogeneous region as in Example 2-2. By doing so, the reflectance characteristics can be exhibited. However, the presence of the homogeneous region is easier to manufacture, and the thickness of the homogeneous region and the thickness of the fifth layer 25 can be controlled, which may be advantageous in terms of antireflection performance.

[Comparative Example 2]
As Comparative Example 2, an antireflection film (Table 1-7) described in Patent Document 3 is shown. The refractive index of the optical substrate used for the calculation is 2.00, which is almost the same as in Example 2-1 and Example 2-2. Table 14 shows the refractive indexes and film thicknesses of the first to ninth layers.

  FIG. 16 shows the reflectance characteristics (calculated values) of the antireflection film of Comparative Example 2. From the comparison between FIG. 16 and FIG. 2-7 of Patent Document 3, it can be seen that almost the same calculated value is obtained. The antireflection film of Comparative Example 2 has excellent reflectance characteristics such that when the incident angle is 5 degrees, the reflectance is 0.1% or less at a wavelength of 400 to 1000 nm, and the reflectance is 0.1% or less at a wavelength of 1000 nm to 900 nm. Show. However, the reflectivity suddenly increases from a wavelength of about 950 nm and is reflected by about 1.8% at a wavelength of 1200 nm. In addition, in the case of 45 degree incidence, the reflectance characteristic starts to deteriorate at a wavelength of 850 nm or more, and the reflection is about 1.6% at a wavelength of 1000 nm.

  Therefore, in the configuration using the low refractive index film as the uppermost layer as in Comparative Example 2, in a wide wavelength band (wavelength 450 to 1200 nm) from the visible region to the near infrared region as in the antireflection film of the present invention. It is difficult to obtain good reflectance characteristics.

[Example 3]
The antireflection film of Example 3 will be described. In Example 3, the intermediate layer 2 is composed of five layers. Table 5 shows the numerical values of the film configuration of Example 3. The antireflection film 100 of Example 3 is formed on the optical substrate 1 having a refractive index of 1.808.

The intermediate layer 2 has a refractive index of 1.621, a first layer 21 having Al ₂ O ₃ as a main component, a refractive index of 2.038, a second layer 22 having ZrO ₂ as a main component, and a refractive index of 1.2. 621 and a third layer 23 mainly composed of Al ₂ O ₃ . The fourth layer 24 has a refractive index of 2.038 and ZrO ₂ as a main component, and the fifth layer 25 has a refractive index of 1.458 and a main component of SiO ₂ , each formed by a vacuum deposition method. .

  The fine concavo-convex structure 3 was produced by the same method as in Example 1-1. However, the film thickness of the fine concavo-convex structure 3 is larger than that of Example 1-1 by adjusting the film forming conditions during spin coating and the physical properties of the sol solution. The refractive index with respect to the thickness direction of the antireflection film 100 of Example 3 is shown in FIG.

  FIG. 6B shows the reflectance characteristics of the antireflection film 100 of this example. 6B, when the incident angle is 0 degree, the antireflection film 100 of Example 3 has a wavelength of 450 to 950 nm of 0.1% or less and a wavelength of 1000 nm to 1200 nm of 0.6% or less. Excellent antireflection performance. In addition, it can be seen that even when the incident angle is 45 degrees, high-performance antireflection performance with a reflectance of 1.0% or less is realized in a wide wavelength band of wavelength 400 to 1000 nm. The average reflectance in the wavelength range of 400 to 1000 nm was 0.06% at 0 degree incidence and 0.29% at 45 degree incidence.

[Comparative Example 3]
As Comparative Example 3, reflection using an intermediate layer composed of a single layer that satisfies the conditions described in Patent Document 1 (refractive index of substrate ≧ refractive index of intermediate layer ≧ refractive index of the fine uneven structure (the intermediate layer side)) The prevention film is shown. Table 15 shows the numerical values of the film configuration of Comparative Example 3. The substrate 1 and the fine concavo-convex structure 3 are the same as those in Example 3. The intermediate layer 2 is a film mainly composed of polyimide based on the description in Patent Document 1, and a film having a refractive index of 1.647 is formed with an optical film thickness of 72 nm. The refractive index with respect to the thickness direction of the antireflection film 100 at this time is shown in FIG.

  FIG. 17B shows the reflectance characteristics of the antireflection film of this example. From FIG. 17B, the antireflection film of Comparative Example 3 has a wavelength of 400 to a wavelength even when the incident angle is 0 degree and the wavelength 400 to a wavelength of 700 nm is 0.1% or less and the incident angle is 45 degrees. It can be seen that good characteristics are exhibited in the visible wavelength region of 700 nm 0.2% or less. However, in the case of 0-degree incidence, the reflectance is high in the near infrared region of about 0.6% at a wavelength of 1000 nm and at a wavelength of 1,400 nm at a wavelength of 1200 nm.

  Also, in the case of 45 degree incidence, the reflectance is as high as about 1.8% at a wavelength of 1000 nm. From this, it can be seen that it is difficult to obtain a high-performance antireflection performance in a wide wavelength band as in the present invention by combining the fine concavo-convex structure 3 with a single intermediate layer.

[Example 4]
The antireflection film of Example 4 will be described. In Example 4, the intermediate layer 2 is composed of five layers. Table 6 shows the numerical values of the film configuration of Example 4. The antireflection film of Example 4 is formed on an optical substrate having a refractive index of 1.743. The refractive index with respect to the thickness direction of the antireflection film 100 of Example 4 is shown in FIG. FIG. 7B shows the reflectance characteristics of the antireflection film of this example. The average reflectance in the wavelength region of 400 to 1000 nm was 0.07% at 0 ° incidence and 0.25% at 45 ° incidence.

[Example 5]
The antireflection film of Example 5 will be described. In Example 5, the intermediate layer 2 is composed of five layers. Table 7 shows the numerical values of the film configuration of Example 5. The antireflection film of Example 5 is formed on the optical substrate 1 having a refractive index of 1.658. The refractive index with respect to the thickness direction of the antireflection film of Example 5 is shown in FIG.

  FIG. 8B shows the reflectance characteristics of the antireflection film of this example. In Examples 1 to 4, the film configuration is such that the refractive index of the first layer 21 of the intermediate layer 2 is smaller than the refractive index of the material of the substrate 1, but in Example 5, as shown in FIG. In addition, the refractive index of the first layer 21 is larger. The average reflectance in the wavelength region of 400 to 1000 nm was 0.07% at 0 ° incidence and 0.16% at 45 ° incidence.

[Example 6]
The antireflection film of Example 6 will be described. In Example 6, the intermediate layer 2 is composed of five layers. Table 8 shows the numerical values of the film configuration of Example 6. The antireflection film of Example 6 is formed on the optical substrate 1 having a refractive index of 1.585. The refractive index with respect to the thickness direction of the antireflection film 100 of Example 6 is shown in FIG. FIG. 9B shows the reflectance characteristics of the antireflection film of this example. The average reflectance in the wavelength region of 400 to 1000 nm was 0.04% at 0 degree incidence and 0.22% at 45 degree incidence.

[Example 7]
The antireflection film of Example 7 will be described. In Example 7, the intermediate layer 2 is composed of five layers. Table 9 shows the numerical values of the film configuration of Example 7. The antireflection film of Example 7 is formed on the optical substrate 1 having a refractive index of 1.518. The refractive index with respect to the thickness direction of the antireflection film 100 of Example 7 is shown in FIG.

  FIG. 10B shows reflectance characteristics of the antireflection film of this example. The average reflectance in the wavelength region of 400 to 1000 nm was 0.04% at 0 degree incidence and 0.11% at 45 degree incidence.

[Example 8]
The antireflection film of Example 8-1 will be described. In Example 8-1, the intermediate layer 2 is composed of five layers. Table 10 shows the numerical values of the film configuration of Example 8-1.

  The antireflection film of Example 8-1 is formed on the optical substrate 1 having a refractive index of 1.498. The refractive index with respect to the thickness direction of the antireflection film 100 of Example 8-1 is shown in FIG. FIG. 11B shows reflectance characteristics of the antireflection film of this example. The average reflectance in the wavelength region of 400 to 1000 nm was 0.05% at 0 degree incidence and 0.28% at 45 degree incidence.

  The antireflection film of Example 8-2 will be described. In Example 8-2, the intermediate layer 2 is composed of five layers. Table 11 shows the numerical values of the film configuration of Example 8-2. In Example 8-2, the optical substrate 1 is the same as that in Example 8-1, but the refractive index of the fine concavo-convex structure 3 is different. This can be adjusted according to the type and concentration of the solvent and stabilizer added to the sol, the conditions of the hot water treatment, and the conditions during spin coating. The refractive index with respect to the thickness direction of the antireflection film of Example 8-2 is shown in FIG.

  FIG. 12B shows the reflectance characteristics of the antireflection film of this example. The average reflectance in the wavelength region of 400 to 1000 nm was 0.06% at 0 degree incidence and 0.14% at 45 degree incidence.

[Example 9]
The antireflection film of Example 9 will be described. In Example 9, the intermediate layer 2 is composed of five layers. Table 12 shows the numerical values of the film configuration of Example 9.

  The antireflection film of Example 7 is formed on the optical substrate 1 having a refractive index of 1.440. The refractive index with respect to the thickness direction of the antireflection film of Example 9 is shown in FIG.

  FIG. 13B shows the reflectance characteristics of the antireflection film of this example. The average reflectance in the wavelength region of 400 to 1000 nm was 0.05% at 0 ° incidence and 0.31% at 45 ° incidence.

FIG. 14 is a schematic diagram of a main part of an imaging apparatus using an optical element provided with the antireflection film 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) having an antireflection film of the present invention formed on a light transmission surface. The imaging optical system 102 is composed of a plurality of optical elements, and the antireflection film of the present invention is formed on at least one of the lens surfaces of these optical elements. Therefore, the digital camera of the present embodiment can obtain an image in which generation of harmful light such as flare and ghost is suppressed, and can realize a high-quality optical device.

  In this embodiment, a digital camera is taken as an example of an optical device, but the optical element according to the present invention is not limited to this, and is used for other optical devices such as binoculars, an image projection apparatus, and a fluorescence microscope. .

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

1: Optical substrate 2: Intermediate layer 3: Fine uneven structure 21: First layer of intermediate layer 22: Second layer of intermediate layer 23: Third layer of intermediate layer 24: Fourth layer of intermediate layer 25: Intermediate layer 100: Antireflection film 101 of the present invention: Optical apparatus of the present invention 102: Optical system of the present invention 200: Optical element

Claims (9)

An antireflection film provided on a light transmission surface of a transparent substrate, wherein the antireflection film comprises an intermediate layer in which a plurality of layers are laminated in order from the substrate side to the air layer side, and a fine structure portion having a pitch of 400 nm or less. It has a plurality of fine concavo-convex structures formed,
The fine concavo-convex structure has a region where the film thickness is 200 nm or more and 350 nm or less and the refractive index continuously increases from 1.0 in the direction from the air layer side toward the substrate,
The plurality of layers of the intermediate layer include a first layer, a second layer, a third layer, a fourth layer, and a fifth layer in order from the substrate side to the air layer side, and the refractive index of the plurality of layers is When the value at a wavelength of 550 nm and the optical film thickness are (refractive index at a wavelength of 550 nm) × (thickness),
The refractive index of the first layer is 1.61-1.71, the optical film thickness is 10-220 nm,
The refractive index of the second layer is 1.98 to 2.40, the optical film thickness is 15 to 65 nm,
The refractive index of the third layer is 1.61-1.71, the optical film thickness is 60-140 nm,
The refractive index of the fourth layer is 1.98 to 2.40, the optical film thickness is 15 to 65 nm,
The fifth layer has a refractive index of 1.42 to 1.54 and an optical thickness of 10 to 140 nm.
An antireflective film characterized by being.   Between the fine concavo-convex structure and the intermediate layer, there is a uniform layer having a uniform refractive index in the film thickness direction, and the refractive index of the uniform layer is 1.35 to 1.58. The antireflection film according to claim 1, wherein the sum of the thickness and the optical film thickness of the fifth layer is 10 nm to 140 nm.   When the refractive index of the first layer is lower than the refractive index of the substrate, the optical film thickness of the first layer is 10 nm to 35 nm, and when the refractive index of the first layer is higher than the refractive index of the substrate, 3. The antireflection film according to claim 1, wherein the optical thickness of the first layer is 180 nm to 220 nm. 4. The antireflection film according to claim 1, wherein the first layer contains Al ₂ O ₃ or SiON as a main component. 5. The antireflection film according to claim 1, wherein the fifth layer contains SiO ₂ as a main component.   The antireflection film according to claim 1, wherein the fine structure portion is a layer formed of a plate crystal mainly composed of alumina.   An optical element, wherein the antireflection film according to claim 1 is formed on a light transmission surface of a substrate.   An optical system comprising one or more optical elements according to claim 7.   An optical apparatus comprising the optical system according to claim 8.