Diffractive optical element and curable resin composition

Abstract

The purpose of the present invention is to provide a diffractive optical element having improved shape stability.　This diffractive optical element causes diffraction with respect to incident light, and comprises a substrate that transmits the incident light, a fine structure that is composed of a curable resin composition and forms an unevenness on a first main surface side of the substrate to form a diffraction pattern for diffracting the incident light, and a first protective layer that is transmissive to the incident light and covers the fine structure, the fine structure exhibiting any of a Fresnel zone plate shape, a linear zone plate shape, a fractal zone plate shape, and a photon sieve plate shape when viewed in a direction orthogonal to the first main surface.

Description

Diffractive optical element and curable resin composition

[0001] The present invention relates to a diffractive optical element, particularly to a diffractive optical element applicable to imaging, optical sensors, displays, and optical communications. The present invention also relates to a curable resin composition used in producing the diffractive optical element.

[0002] Optical components are used to appropriately control light in image sensors, optical sensors, displays, and optical communications.

[0003] In recent years, there has been a growing demand for thinner optical components. For example, in camera modules for smartphones and mobile phones, the lens determines the height of the camera module, and the increase in camera module size due to an increase in sensor area has become a problem, leading to a strong demand for thinner optical elements.

[0004] Optical sensors, such as fingerprint authentication sensors, face authentication sensors, proximity sensors, ambient light sensors, and pulse oximeters, are used in smartphones and smartwatches to detect light of multiple wavelengths, but optical sensors are often built into the back of the display, and there is a strong demand for thinner and more compact optical components. These optical sensors also increase the thickness of the device, so there is a strong demand for thinner devices.

[0005] Furthermore, among display devices, holographic optical elements that utilize a grating structure and total internal reflection are used in wearable display elements such as glasses and head-mounted displays in devices for AR (Augmented Reality), VR (Virtual Reality), and MR (Mixed Reality).

[0006] In order to cope with the trend toward thinner optical components, various types of planar diffractive optical elements have been reported in recent years.

[0007] For example, Patent Document 1 reports a metalens, which is a planar diffractive optical element that can focus light with high precision despite a thickness of 1 μm or less by optimizing the arrangement of minute pillars of a high refractive index material. Other known planar optical elements include a diffractive optical element lens that utilizes a shape change due to a photoresponsive resin, as shown in Non-Patent Document 1, and a diffractive optical element lens that has light focusing performance by designing a surface uneven structure using a photoresist resin, as shown in Non-Patent Document 2.

[0008] International Publication No. 2017 / 176921 International Publication No. 2019 / 046827

[0009] Laser Photonics Rev., 2022, 16, 2100514PNAS Vol. 116 Jno. 43 21375-21378 (2019)

[0010] Conventional diffractive optical elements using the above-mentioned microstructures have had the problem of low dimensional stability due to the surface microstructure. The surface microstructure is very fragile, making it difficult to apply it to the outermost surface of optical components. Furthermore, even when the microstructure is mounted inside an optical component, the optical element is prone to defects due to contact during assembly of the optical component.

[0011] Patent Document 2 discloses an example in which planar optical elements can be stacked by filling the gaps between fine pillars formed by etching through a mask with a material having a lower refractive index than the pillars. However, as will be described in detail later, with a fine pillar structure formed by etching through a mask, it is difficult to fill the lower parts of the pillar structure, making it difficult to improve shape stability.

[0012] The present invention addresses the problem of providing a diffractive optical element with shape stability, which has been difficult to achieve with conventional diffractive optical elements. The diffractive optical element makes it possible to prevent defects caused by contact during assembly when the diffractive optical element is mounted inside a structure, and to prevent defects during chemical mechanical polishing, which is required to flatten the surface when stacking diffractive optical elements.

[0013] In view of the above circumstances, an object of the present invention is to provide a diffractive optical element with improved shape stability.

[0014] The present inventors have conducted extensive research to solve the above problems, and as a result, examples of the embodiments of the present invention are shown below.

[0015] [1] A diffractive optical element that diffracts incident light, comprising: a substrate that transmits the incident light; a microstructure made of a curable resin composition, the microstructure forming unevenness on a first main surface side of the substrate to form a diffraction pattern that diffracts the incident light; and a first protective layer that is transparent to the incident light and covers the microstructure, wherein the microstructure exhibits any one of a Fresnel zone plate shape, a linear zone plate shape, a fractal zone plate shape, and a photon sieve plate shape when viewed in a direction perpendicular to the first main surface.

[0016] [2] The diffractive optical element according to the above [1], which has an antireflection structure formed on the first protective layer on the first main surface side.

[0017] [3] The diffractive optical element according to the above [2], wherein the anti-reflection structure is a dielectric multilayer film.

[0018] [4] The diffractive optical element according to any one of [1] to [3] above, characterized in that the microstructure exhibits any one of a phase-type Fresnel zone plate shape, a phase-type linear zone plate shape, a phase-type fractal zone plate shape, and a phase-type photon sieve plate shape.

[0019] [5] The diffractive optical element according to the above [4], wherein the first protective layer is made of a high refractive index material having a refractive index higher than that of the curable resin composition.

[0020] [6] The diffractive optical element according to the above [4] or [5], wherein the curable resin composition has a refractive index of less than 1.85, and the high refractive index material has a refractive index of 1.85 or more.

[0021] [7] The diffractive optical element according to any one of [4] to [6] above, characterized in that the high refractive index material comprises one or more selected from the group consisting of titanium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silicon, germanium, gallium nitride, gallium phosphide, zinc sulfide, zinc telluride, lead zirconate titanate, and barium titanate.

[0022] [8] The diffractive optical element according to any one of [1] to [3] above, characterized in that the microstructure exhibits any one of an amplitude type Fresnel zone plate shape, an amplitude type linear zone plate shape, an amplitude type fractal zone plate shape, and an amplitude type photon sieve plate shape.

[0023] [9] The diffractive optical element according to any one of the above [1] to [3], wherein the microstructure has a shape that tapers with increasing distance from the first main surface of the substrate.

[0024]

[10] The diffractive optical element according to any one of the above [1] to [9], characterized in that the finest line width of the microstructure is 0.2 μm or more and 5 μm or less.

[0025]

[11] The diffractive optical element according to any one of the above [1] to

[10] , characterized in that the surface roughness is 200 nm or less.

[0026]

[12] The diffractive optical element according to any one of the above [1] to

[11] , characterized in that the total thickness is 2 mm or less.

[0027]

[13] The diffractive optical element according to any one of the above [1] to

[12] , characterized in that the F-number obtained by dividing the focal length f of the diffraction pattern by the diameter D of the diffraction pattern is in the range of 0.2 to 4.0.

[0028]

[14] The diffractive optical element according to any one of the above [1] to

[13] , characterized in that the pencil hardness is 5B or more.

[0029]

[15] A curable resin composition that forms the fine structure described in [1] above.

[0030] According to the present invention, a diffractive optical element with improved shape stability is provided.

[0031] 4A is a cross-sectional view schematically showing an example of a structure of a diffractive optical element according to the present invention. FIG. 4B is a drawing showing an example of a Fresnel zone plate shape with a fine structure. FIG. 4C is a cross-sectional view schematically showing another example of a structure of a diffractive optical element according to the present invention. FIG. 4D is a drawing showing a method of counting fine structures. FIG. 4A is a cross-sectional view schematically showing FIG. 4A cut along a plane perpendicular to the main surface of the substrate. FIG. 4E is a drawing showing a state in which parallel light is incident on a diffractive optical element. FIG. 4F is a drawing showing another example of a Fresnel zone plate shape. FIG. 4G is a drawing showing yet another example of a configuration of a diffractive optical element according to the present invention. FIG. 4H is a drawing showing yet another example of a configuration of a diffractive optical element according to the present invention. FIG. 4H is a drawing showing yet another example of a configuration of a diffractive optical element according to the present invention. FIG. 4I is a drawing showing another example of a Fresnel zone plate shape. FIG. 4I is a drawing showing an example of a linear zone plate shape. FIG. 4I is a drawing showing an example of a fractal zone plate shape. FIG. 4I is a drawing showing a schematic diagram of a region division pattern in a fractal zone plate shape. FIG. 4I is a drawing showing an example of a photon sieve plate shape. FIG. 4I is a drawing showing an example of a fine structure formed by etching. 1 is a drawing showing an example of the shape of a fine structure; FIG. 2 is a drawing showing an example of the shape of a fine structure; FIG. 3 is a graph showing the spectra of the refractive index and extinction coefficient in curable resin composition 1; FIG. 4 is an image obtained by observing the cross section of a diffractive optical element according to Example 9; FIG. 5 is an image obtained in the light-gathering evaluation of the diffractive optical element according to Example 4; and FIG. 6 is an image obtained in the lens evaluation of the diffractive optical element according to Example 10.

[0032] Hereinafter, embodiments of the diffractive optical element according to the present invention will be described with reference to the drawings as appropriate. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the description of the embodiments exemplified below. To clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part more schematically than the actual form, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same or similar reference symbols (reference symbols simply having a suffix such as "'" after the number), and detailed descriptions may be omitted as appropriate.

[0033] In this specification, "up" refers to a relative position based on the main surface of the support substrate (for example, the surface on which the solid-state imaging element is disposed), and the direction away from the main surface of the support substrate is "up". In this drawing, "up" refers to the upward direction as viewed from the paper. "Up" also includes the case where the substrate is in contact with the top of an object (i.e., "on") and the case where the substrate is positioned above an object (i.e., "over"). Conversely, "down" refers to a relative position based on the main surface of the support substrate, and the direction approaching the main surface of the support substrate is "down". In this drawing, "down" refers to the downward direction as viewed from the paper.

[0034] Diffractive Optical Element Fig. 1 is a cross-sectional view showing a typical example of the structure of a diffractive optical element according to the present invention. As shown in Fig. 1, the diffractive optical element 1 has a substrate 3, a microstructure 4, and a protective layer 8.

[0035] <Substrate 3> A substrate having a transmittance of 50% or more at any wavelength between 300 nm and 1900 nm is used as the substrate 3. Examples of such transparent substrates include silicate glass substrates, borosilicate glass substrates, phosphate glass substrates, fluorophosphate glass substrates, plastic substrates, and resin film substrates. The substrate 3 is preferably made of a material with a glass transition temperature of 140°C or higher, and the surface roughness Sa of the substrate is preferably less than 200 nm. Here, the surface roughness corresponds to the roughness of the outermost surface measured using a white light interferometer such as a ZYGO.

[0036] The substrate 3 may contain a near-infrared absorbent, and may contain at least one selected from inorganic near-infrared absorbents such as cesium tungsten oxide and copper (II) oxide, near-infrared absorbents that utilize surface plasmons such as gold nanorods, and organic near-infrared absorbents.

[0037] The substrate 3 is preferably made of multiple layers from the viewpoints of crack resistance, ease of addition of a light absorber, and imparting functions and effects, such as electrical conductivity, antistatic effect, foreign matter adhesion prevention effect, scratch prevention effect, anti-fogging property, improved heat resistance, gas barrier properties, high elasticity, scratch erasing effect, flatness, surface roughness, moisture absorption, anti-aging effect, and near-infrared blocking property.

[0038] The diffractive optical element 1 diffracts and focuses incident light incident on the substrate 3 using the microstructures 4 described below. The focused light is incident on, for example, any optical sensor (not shown). As an example, an optical sensor such as a silicon photodiode or an indium gallium arsenide photodiode can be used. From the viewpoint of facilitating the design of the sensitivity characteristics and frequency characteristics of the optical sensor, it is preferable that the substrate 3 have a transmittance of 60% or more at any wavelength between 350 nm and 1600 nm.

[0039] <Fine Structure 4> The fine structure 4 forms a diffraction pattern that diffracts the incident light that is incident on the diffractive optical element 1. The fine structure 4 is made of a curable resin composition.

[0040] An example of the configuration of the microstructure 4 of the diffractive optical element 1 will now be described. Fig. 2 is a diagram schematically showing an example of the microstructure 4 formed on the main surface 3a of the substrate 3 of the diffractive optical element 1. Fig. 2 corresponds to a diagram in which the microstructure 4 is viewed in a direction perpendicular to the main surface 3a of the substrate 3. The main surface 3a corresponds to the "first main surface."

[0041] 2, the microstructure 4 will be described as having a Fresnel zone plate shape when viewed in a direction perpendicular to the main surface 3a of the substrate 3. However, the microstructure 4 may have any of a Fresnel zone plate shape, a linear zone plate shape, a fractal zone plate shape, and a photon sieve plate shape when viewed in a direction perpendicular to the main surface 3a of the substrate 3. Examples of the configuration of the diffraction pattern exhibited by the microstructure 4 will be described later.

[0042] <Fresnel Zone Plate> The Fresnel zone plate has a shape as shown in FIG. 2, and the radius r of the nth zone is n is expressed by the following formula (1): In the following formula (1), λ is the wavelength of light (hereinafter sometimes referred to as the "design wavelength"), and f is the focal length of first-order diffraction. Fresnel zone plates include "amplitude-type Fresnel zone plates" and "phase-type Fresnel zone plates."

[0043] The microstructure 4 may have an absorption characteristic at the design wavelength. When the microstructure 4 has an absorption characteristic at the design wavelength, it is possible to form an amplitude-type Fresnel zone plate that utilizes diffraction caused by interference between the microstructure 4 and a transparent region, which will be described later. The microstructure 4 having an absorption characteristic at the design wavelength means that the extinction coefficient k at the design wavelength of the microstructure 4 has a value greater than 0.01 in an evaluation calculated from spectroscopic ellipsometry or transmittance and reflectance.

[0044] Furthermore, the microstructure 4 does not have to have an absorption characteristic at the design wavelength of the diffractive optical element 1. When the microstructure 4 does not have an absorption characteristic at the design wavelength, it is possible to form a phase-type Fresnel zone plate that refracts and focuses incident light by the phase difference generated between the microstructure 4 and the transparent region. The fact that the microstructure 4 does not have an absorption characteristic at the design wavelength means that the extinction coefficient k at the design wavelength of the microstructure 4 is 0.01 or less in an evaluation calculated from spectroscopic ellipsometry or transmittance and reflectance.

[0045] <Amplitude-type Fresnel Zone Plate> As shown in Figure 2, an amplitude-type Fresnel zone plate is a type of diffractive optical element having a diffractive optical structure with a concentric pattern in which rings (zones) of light-shielding (opaque) regions made up of fine structures 4 and rings (zones) of transparent regions 6 that are transparent to the design wavelength are alternately combined. Designs starting from light-shielding at the center and designs starting from transmission are possible. For example, in the case of a design starting from light-shielding at the center, r n 2 The zones between n=0 and n=1 are light-blocking, the zones between n=1 and n=2 are transparent, and the zones between n=2 and n=3 are light-blocking, with transparent and opaque zones appearing alternately depending on whether n is an odd or even number. The amplitude-type Fresnel zone plate increases the intensity of light at the focal position by blocking (attenuating) incident light that destructively interferes with the incident light that has passed through the transparent region 6 at the focal position.

[0046] <Phase-type Fresnel zone plate> The amplitude-type Fresnel zone plate differs in that the fine structure 4 blocks light of wavelength λ, whereas the phase-type Fresnel zone plate transmits light of wavelength λ. The concentric circular pattern of the phase-type Fresnel zone plate has a shape as shown in FIG. 2, for example, and the radius r of the nth zone is n is expressed by the above formula (1), similarly to the amplitude-type Fresnel zone plate. The phase-type Fresnel zone plate increases the intensity of light at the focal position by delaying the phase of incident light passing through the annular zones of the transparent region 6 so that the light passes through the annular zones of the microstructure 4 and the incident light pass through the annular zones of the microstructure 4 constructively.

[0047] Specifically, the transparent region 6 corresponds to a region filled with a protective layer 8, which will be described later. When the height of the fine structure 4 is h1 (see also FIG. 1), the refractive index of the fine structure 4 is nL, the refractive index of the protective layer 8 is nH, and the refractive index difference between nL and nH is Δn, the phase difference between the light transmitted through the region where the fine structure 4 is formed and the light transmitted through the transparent region 6 (protective layer 8) can be calculated by the following formula (2): Phase difference = h1 × Δn / λ × 2π (2)

[0048] The phase difference is preferably 1 / 4×π or more, and more preferably 1 / 2×π or more. The phase difference is preferably between 0.45×π and 2.0×π, and more preferably between 0.8×π and 2.0×π. This design can be achieved, for example, by changing the refractive index nL, the refractive index nH, and the height h1 of the microstructure 4. In light of this, the height h1 of the microstructure 4 is preferably 0.3 μm or more, more preferably 0.4 μm or more, and particularly preferably 0.5 μm or more. Furthermore, from the viewpoint of making it easier to fill the spaces between the microstructures 4 with the protective layer 8 described below, the height of the microstructure 4 is preferably 3 μm or less, and more preferably 2 μm or less.

[0049] Unlike an amplitude type Fresnel zone plate, a phase type Fresnel zone plate does not block light incident on the region where the microstructure 4 is formed. Therefore, a phase type Fresnel zone plate is preferable in that it is easy to increase the intensity of light at the focal position. Typically, the intensity of light at the focal position of a phase type Fresnel zone plate is about four times the intensity of light at the focal position of an amplitude type Fresnel zone plate.

[0050] In this specification, the diffraction pattern formed by the microstructure 4 diffracts incident light includes a case where the pattern of the microstructure 4 blocks a portion of the incident light, thereby changing the direction of travel of the incident light (a so-called "amplitude type" case), and a case where the microstructure 4 is transparent to the incident light, and the direction of travel of the incident light is changed by an optical path difference that occurs depending on the refractive index difference between an area where the pattern of the microstructure 4 is formed and an area where the pattern is not formed (a so-called "phase type" case). The above-mentioned diffraction also includes a case where multiple diffracted beams of light form constructive and destructive points due to interference. Furthermore, "diffraction" in this specification includes both Fresnel diffraction, in which the light source and the observation point are at a finite distance, and Fraunhofer diffraction, in which the diffraction of parallel light rays is observed at an infinite distance.

[0051] The microstructure 4 can be formed on the main surface 3a of the substrate 3, for example, by photolithography, in which light is irradiated in a shape corresponding to the diffraction pattern, or by an imprinting process, in which a master shape having depressions corresponding to the diffraction pattern is transferred.

[0052] 1 and 2 , in the diffractive optical element 1, the transparent regions 6 where the microstructures 4 are not formed are filled with a protective layer 8. In other words, the diffractive optical element 1 has the protective layer 8 that covers the microstructures 4 when viewed in a direction parallel to the main surface 3 a of the substrate 3 (see FIG. 1 ). The protective layer 8 corresponds to a “first protective layer.”

[0053] In the diffractive optical element 1, the transparent region 6 where the microstructure 4 is not formed is filled with the protective layer 8, thereby improving the shape stability of the diffractive optical element 1. This prevents defects in the microstructure 4 due to transfer or the like when the diffractive optical element 1 is mounted on an optical component, for example.

[0054] Furthermore, optical elements often suffer from problems with stray light, such as ghosts and flares, caused by surface reflections. To address this issue, a technique for suppressing these reflections, for example, by providing an anti-reflection structure on the lens surface, is known. However, conventional diffractive optical elements have large surface irregularities resulting from the microstructure. Even if an anti-reflection structure is provided on the microstructure, the optical thickness cannot be controlled, making it difficult to form the anti-reflection structure. In contrast, in the diffractive optical element 1, the microstructure 4 is covered by the protective layer 8, making it easy to form the anti-reflection structure on the protective layer 8. Specific examples of anti-reflection structures will be described later.

[0055] The protective layer 8 is transparent to incident light. Specifically, the protective layer 8 has a transmittance of 50% or more at any wavelength between 300 nm and 1900 nm. As described for the substrate 3, the protective layer 8 may have a transmittance of 60% or more at any wavelength between 350 nm and 1600 nm, or may have a transmittance of 60% or more at any wavelength between 350 nm and 1300 nm.

[0056] Furthermore, when the microstructure 4 is of a phase type, it is preferable that the protective layer 8 has a refractive index larger than that of the microstructure 4. Specifically, it is preferable that the refractive index of the curable resin composition constituting the microstructure 4 is less than 1.85, and that the protective layer 8 is composed of a high refractive index material having a refractive index of 1.85 or more. This allows incident light to be diffracted and focused due to the difference in refractive index between the region where the microstructure 4 is formed and the region where the protective layer 8 is filled.

[0057] The method for forming the protective layer 8 and covering the microstructure 4 with a high refractive index material is not particularly limited, but examples include a method in which a composition having a refractive index of 1.85 or more or a suspension in which high refractive index nanoparticles are dispersed is applied to the substrate 3 on which the microstructure 4 is formed by spin coating, dip coating, spray coating, or die coating, and then the applied film is thermally dried.

[0058] The protective layer 8 may be formed using, for example, sputtering, vacuum vapor deposition, ion-assisted vacuum vapor deposition, ion plating vacuum vapor deposition, ALD, EPD, or CVD. In particular, the protective layer 8 is preferably filled using sputtering, vacuum vapor deposition, ion-assisted vacuum vapor deposition, ion plating, or EPD. The anti-reflection film may require a thickness accuracy of 1 nm, and from the viewpoint of film thickness accuracy, vacuum vapor deposition, ion-assisted vacuum vapor deposition, ion plating vacuum vapor deposition, ALD, or EPD is preferred. From the viewpoint of obtaining an amorphous film with little scattering, ion-assisted vacuum vapor deposition, ion plating vacuum vapor deposition, or EPD is more preferred.

[0059] When increasing the thickness of the protective layer 8 so that the phase difference between the light transmitted through the microstructure 4 and the light transmitted through the protective layer 8 is, for example, 1 / 2 × π or more, from the viewpoint of forming the protective layer 8 in as short a time as possible, it is preferable to use spin coating, dip coating, vacuum deposition, ion-assisted vacuum deposition, ion plating, or EPD.

[0060] Furthermore, it is more preferable to use an ion-assisted vacuum deposition method, an ion plating method, or an EPD method from the viewpoint of reducing the surface roughness Ra of the protective layer 8. In particular, the ion-assisted vacuum deposition method is particularly preferable in that it can form a dense film and easily realize a protective layer 8 with high cut resistance.

[0061] In the diffractive optical element 1, the surface roughness Ra of the protective layer 8 is preferably 200 nm or less. Here, the surface roughness Ra represents the roughness of the outermost surface of the optical element as evaluated by a white light interferometer ZYGO or the like.

[0062] 1, the surface of the protective layer 8 typically has an uneven shape resulting from the microstructure 4. In contrast to this, as shown in FIG. 3, a process may be performed to reduce the uneven shape by polishing the surface of the protective layer 8, for example, by chemical mechanical polishing, ion cleaning, plasma etching, or chemical etching.

[0063] Examples of high-refractive index materials for forming the protective layer 8 include titanium alkoxides (e.g., PC-200 and PC-250 manufactured by Matsumoto Fine Chemical Co., Ltd.), titanium oxide (TiO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), zirconia oxide (ZrO2), hafnium oxide (HfO2), indium tin oxide (ITO), silicon, germanium, gallium nitride, gallium phosphide, zinc telluride, lead zirconate titanate (PZT), barium titanate (BaTiO3), and mixtures thereof. From the viewpoint of easily improving the cut resistance of the diffractive optical element 1, the high-refractive index material preferably includes at least one selected from titanium oxide (TiO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), zirconia oxide (ZrO2), hafnium oxide (HfO2), indium tin oxide (ITO), and barium titanate (BaTiO3). More preferably, the high refractive index material contains at least one selected from titanium oxide, tantalum oxide, niobium oxide, and zirconia oxide.

[0064] When the design wavelength is 900 nm or more, the high refractive index material is preferably selected from silicon, zinc sulfide, and zinc telluride from the viewpoint of increasing the refractive index of the protective layer 8 and facilitating the phase difference of 1 / 2×π or more. When the design wavelength is 1.8 μm or more, the high refractive index material is preferably germanium from the same viewpoint.

[0065] Furthermore, from the viewpoint of facilitating the formation of a phase-type diffraction pattern such as a phase-type Fresnel zone plate, the microstructure 4 is preferably composed of a curable resin composition having a refractive index of less than 1.85. When the refractive index of the curable resin composition constituting the microstructure 4 is 1.85 or higher, the refractive index difference with the protective layer 8 becomes small. As a result, for example, to form a phase-type Fresnel zone plate, it is necessary to increase the height h1 of the microstructure 4. If the height h1 of the microstructure 4 is increased, gaps are more likely to occur between the microstructure 4 and the protective layer 8 when the microstructure 4 is covered with the protective layer 8, making it difficult to improve the shape stability of the diffractive optical element 1. In view of this, the refractive index of the curable resin composition constituting the microstructure 4 is more preferably less than 1.7, and particularly preferably less than 1.65.

[0066] Furthermore, the protective layer 8 is preferably made of a high-refractive index material having a refractive index of 1.85 or higher. If the refractive index of the high-refractive index material constituting the protective layer 8 is less than 1.85, the difference in refractive index with the microstructure 4 becomes small. As a result, for example, to form a phase-type Fresnel zone plate, it becomes necessary to increase the height h1 of the microstructure 4. If the height h1 of the microstructure 4 becomes high, gaps are more likely to occur between the microstructure 4 and the protective layer 8 when the microstructure 4 is covered with the protective layer 8, making it difficult to improve the shape stability of the diffractive optical element 1. In view of this, the refractive index of the high-refractive index material constituting the protective layer 8 is more preferably 1.9 or higher, and particularly preferably 2.0 or higher.

[0067] In the diffractive optical element 1, the total thickness T1 including the substrate 3 is preferably 2 mm or less (see Figure 1, etc.). By focusing incident light using the diffraction pattern formed by the microstructure 4, it is possible to make the total thickness T1 of the diffractive optical element 1 thinner than that of a conventional lens. This makes it possible to reduce the thickness of optical components, etc., that incorporate the diffractive optical element 1. Furthermore, the total thickness T1 of the diffractive optical element 1 is more preferably 1.6 mm or less, even more preferably 1.3 mm or less, and particularly preferably 1 mm or less. Note that the total thickness T1 in Figure 1 is merely shown schematically. The total thickness T1 may be an average value of values ​​measured at multiple locations in a direction parallel to the main surface 3a of the substrate 3.

[0068] Hereinafter, the details of the fine structure 4 will be described using the Fresnel zone plate shape as an example.

[0069] When light having a wavelength λ in the range of 300 nm to 1900 nm is incident as a parallel beam on the main surface 3 a of the substrate 3 from a direction perpendicular to the main surface 3 a of the substrate 3, the focal length f is defined as the distance between the substrate 3 and the focusing position D of the light of the wavelength λ. From the viewpoint of focusing more light from the outer periphery of the optical element and increasing the focusing efficiency at the focusing position D, the lower limit of the focal length f of first-order diffraction is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. From the viewpoint of suppressing a decrease in light utilization efficiency due to light diffusion, the upper limit of the focal length f of first-order diffraction is preferably 80 cm or less, more preferably 50 cm or less, even more preferably 45 cm or less, and particularly preferably 30 cm or less.

[0070] Here, in the diffractive optical element 1, the number of the microstructures 4 in the direction parallel to the main surface 3a of the substrate 3 is preferably more than 15. Fig. 4A is a diagram showing a typical method for counting the microstructures 4, and Fig. 4B is a typical cross-sectional view of Fig. 4A cut along a plane perpendicular to the main surface 3a of the substrate 3. The number of the microstructures 4 refers to the number of microstructures 4 counted by the number of microstructures 4 in the diagonal line (r d1 , r d2 ) on two or more diagonals (r d1 , r d2 ) intersection point C o and the center C o Count the fine structures 4 in any direction from the center of the figure, and determine the boundaries (d1, d2, ..., d n ) is the maximum number of layers. Note that the protective layer 8 is not shown in FIGS. 4A and 4B.

[0071] In FIG. 4A, the diffractive optical element 1 has at least 14 boundaries (d1, d2, . . . , d 14), that is, the diffractive optical element 1 has microstructures 4 formed on 14 concentric circles. The number of microstructures 4 that the diffractive optical element 1 has is preferably more than 59, more preferably more than 150, even more preferably more than 300, and particularly preferably more than 800. If the number of microstructures 4 is within the above-mentioned range, higher light-collecting performance is exhibited, and therefore, a diffractive optical element 1 suitable for a fine imaging element is realized.

[0072] In order to obtain high light-collecting performance, the width of the narrowest structure in the fine structure 4 is preferably 5.0 μm or less. Here, the line width of the narrowest structure in the fine structure 4 is the width of the center C o It is the minimum value of the distance from one transparent region 6 to another transparent region 6 in any circumferential direction.

[0073] From the viewpoint of imaging applications and sufficient light separation function, the width of the thinnest structure is preferably 3.0 μm or less, more preferably 2.0 μm or less, and particularly preferably 1.0 μm or less. Furthermore, from the viewpoint of realizing a diffraction effect and filling the spaces between the fine structures 4 with the protective layer 8, the lower limit of the width of the thinnest structure is preferably 0.2 μm or more, more preferably 0.25 μm or more, and even more preferably 0.3 μm or more. If the width is below the lower limit, the transparent region 6 and the fine structures 4 exhibit averaged transmission characteristics, particularly for visible light wavelengths, and the light collection efficiency tends to decrease. Furthermore, from the viewpoint of making it easier to fill the spaces between the fine structures 4 with the protective layer described below, the width is preferably 0.35 μm or more, more preferably 0.4 μm or more. Furthermore, from the viewpoint of improving dimensional stability against vibrations, etc., when the diffractive optical element 1 is transferred, the width is preferably 0.4 μm or more, more preferably 0.5 μm or more.

[0074] 4C is a diagram schematically illustrating a state in which parallel light is incident on the diffractive optical element 1. In FIG. 4C, the protective layer 8 is omitted, as in FIGS. 4A and 4B. The F-number is a value obtained by irradiating light of a wavelength λ in the range of 300 nm or more and less than 1900 nm with a parallel light beam T from a direction perpendicular to the main surface 3 a of the substrate 3 (a direction parallel to the optical axis Ax) as shown in FIG.L When the focal length f is the distance between the substrate 3 and the focal position D of light of wavelength λ incident as a diffraction grating, the F-number is the value obtained by dividing the focal length f by the diameter of the circumscribed circle of the diffraction pattern when viewed in a direction perpendicular to the main surface 3a of the substrate 3 (see FIG. 1). In other words, the F-number is expressed by the following equation (3): F-number = f / D (3)

[0075] The F-number is preferably in the range of 0.2 to 4.0. By setting the F-number within this range, it is possible to easily set the light amount, viewing angle, and depth of field suitable for the imaging application, which is preferable. More preferably, the F-number is in the range of 0.2 to 2.5.

[0076] The range of the F-number is not particularly limited, but if it is 0.2 or more, it becomes easy to maintain the line width at which the microstructure 4 exhibits a diffraction effect. The lower limit of the F-number is preferably 0.3 or more, and more preferably 0.4 or more. Furthermore, if the F-number is equal to or less than the above-mentioned upper limit, it becomes easy to ensure the amount of light required for imaging. However, if the F-number is too high, the size of the optical module will be enlarged, limiting its applications, and the influence of aberration will be large, making it difficult to focus light on the entire sensor surface. From these viewpoints, the F-number is preferably 3.5 or less, more preferably 3.2 or less, and particularly preferably 3.0 or less.

[0077] Furthermore, as shown in Fig. 5, the multiple microstructures do not have to be concentric circles, but may be unevenly distributed. An unevenly distributed Fresnel zone plate has high light-collecting performance when collecting obliquely incident light. In the Fresnel zone plate, each microstructure does not have to be a perfect circle, but may be an ellipse. The width of the ellipse may vary depending on the location.

[0078] <Protective Layer 10> Fig. 6 is a diagram showing yet another example of the configuration of the diffractive optical element 1. As shown in Fig. 6, the diffractive optical element 1 may have a protective layer 10 on the protective layer 8 that is different from the protective layer 8. By having the protective layer 10, it is possible to further improve the shape stability of the diffractive optical element 1. The protective layer 10 is preferably made of, for example, silicon oxide or aluminum oxide.

[0079] <Anti-reflection structure 12> Fig. 7A is a diagram showing yet another example configuration of the diffractive optical element 1. As shown in Fig. 7A, the diffractive optical element 1 may have an anti-reflection structure 12 on the protective layer 8. Note that Fig. 7A shows an example in which the protective layer 10 is provided between the protective layer 8 and the anti-reflection structure 12, but the diffractive optical element 1 in Fig. 7A does not necessarily have to have the protective layer 10. The anti-reflection structure 12 also functions as the protective layer 10.

[0080] The antireflection structure 12 has a reflectance of 5% or less at the interface between the protective layer 10 and the antireflection structure 12 or at the interface between the protective layer 8 and the antireflection structure 12 for any wavelength between 300 nm and 1900 nm.

[0081] When the anti-reflection structure 12 is provided on the protective layer 8, the flatness of the optical thickness of the anti-reflection structure 12 is important. Conventional diffractive optical elements have high surface roughness due to the surface structure of the microstructure. In contrast, in the diffractive optical element 1, the microstructure 4 is covered by the protective layer 8, making it easy to form the anti-reflection structure 12 on the protective layer 8.

[0082] From the viewpoint of enhancing the antireflection function of the antireflection structure 12, the surface roughness Ra of the protective layer 8 is preferably 90 nm or less. Furthermore, when the antireflection structure 12 is composed of a dielectric multilayer film, the flatness of the protective layer 8 becomes even more important. In view of this, the surface roughness Ra of the protective layer 8 is more preferably 50 nm or less, and particularly preferably 35 nm or less.

[0083] 7B, the diffractive optical element 1 may have an antireflection structure 12 on the main surface 3b of the substrate 3 opposite the microstructure 4. This makes it possible to set the reflectance at the interface between the substrate 3 and the antireflection structure 12 to 5% or less for any wavelength between 300 nm and 1900 nm.

[0084] For example, when the refractive index of the protective layer 8 or the substrate 3 is n, the antireflection structure 12 may be a film made of a material having a refractive index smaller than n and having a thickness such that the phase at the design wavelength is ¼λ. The refractive index of the antireflection structure 12 is preferably close to the square root of n, and more preferably 1.5 or less.

[0085] A moth-eye structure having a columnar structure or a dielectric multilayer film structure can be used as the anti-reflection structure 12. Commercially available moth-eye structures include G.Moth manufactured by Geomatec Co., Ltd., Mosmite manufactured by Mitsubishi Chemical Group Corporation, and Motheye products manufactured by Dexerials Corporation.

[0086] The diffractive optical element 1 has a protective layer 8 on the microstructure 4, which provides improved dimensional stability compared to conventional diffractive optical elements. Therefore, the diffractive optical element 1 can be transferred when incorporated into an optical component or the like. In light of this, it is preferable that the antireflection structure 12 also has high stability during the transfer process, and the antireflection structure 12 is preferably made of a dielectric multilayer film.

[0087] The dielectric multilayer film according to the present invention is composed of, for example, a multilayer structure in which high-refractive index layers and low-refractive index layers are alternately stacked. The dielectric multilayer film may have a medium-refractive index layer between the high-refractive index layers and the low-refractive index layers.

[0088] The high-refractive index layer preferably has a refractive index of, for example, 1.9 or higher, where n1 is the refractive index at a wavelength of 500 nm. The high-refractive index layer may be, for example, a film containing titanium oxide (TiO2), tantalum oxide (Ta2O5), niobium oxide (Nb2O5), zirconia oxide (ZrO2), hafnium oxide (HfO2), indium tin oxide (ITO), or a mixture thereof. Furthermore, as long as the refractive index is 1.9 or higher, it may contain additives. A higher n1 is preferable because it allows anti-reflection functionality to be achieved with fewer layers.

[0089] The low-refractive index layer preferably has a refractive index of less than 1.6 for light having a wavelength of 500 nm, where n2 is the refractive index of light having a wavelength of 500 nm, and more preferably is lower than the refractive index of the outermost layer of the transparent substrate. The low-refractive index layer may be, for example, a film containing an amorphous resin, silicon oxide (SiO2), magnesium fluoride (MgF2), barium fluoride (BaF2), lithium fluoride (LiF), or a composite thereof. Furthermore, as long as n2 is 1.8 or less or lower than the refractive index of the outermost layer of the transparent substrate, the low-refractive index layer may contain an additive.

[0090] The medium-refractive index layer preferably has a refractive index of 1.6 or more and less than 1.9 for light having a wavelength of 500 nm, where n3 is the refractive index for light having a wavelength of 500 nm, and more preferably has a refractive index lower than that of the outermost layer of the transparent substrate. Examples of the medium-refractive index layer include aluminum oxide (Al2O3), cesium fluoride (CeF3), yttrium oxide (YO3), ytterbium oxide (Yb2O3), and films containing these composite oxides. Furthermore, if n3 is 1.6 or more and less than 1.9, the medium-refractive index layer may contain an additive.

[0091] Dielectric layers such as high-refractive-index layers, medium-refractive-index layers, and low-refractive-index layers are formed using, for example, sputtering, vacuum deposition, ion-assisted vacuum deposition, ion plating vacuum deposition, CVD, and EPD. It is particularly preferable to form the dielectric layers using sputtering, vacuum deposition, ion-assisted vacuum deposition, ion plating, and EPD. For dielectric multilayer films, the accuracy of the thickness of the dielectric layer is important. Sputtering, vacuum deposition, and ion-assisted vacuum deposition are excellent at controlling the thickness when forming the dielectric layer. This allows for increased thickness accuracy for each layer constituting the dielectric multilayer film, which is composed of a stack of dielectric layers, and a dielectric multilayer film with desired optical properties can be obtained. Ion-assisted vacuum deposition is more preferable because it can form a dense film and is easy to realize a dielectric multilayer film with high dimensional stability.

[0092] The antireflection structure 12 made of a dielectric multilayer film may also be preferably provided on both surfaces of the diffractive optical element 1. When provided on both surfaces, an improvement in transmittance can be expected by reducing reflection on both surfaces of the substrate 3, and this is also suitable for reducing warping of the diffractive optical element 1.

[0093] Note that, when the protective layer 10 or the anti-reflection structure 12 is formed on the main surface 3 a of the substrate 3, warping may occur in the diffractive optical element 1. From the viewpoint of preventing warping of the diffractive optical element 1 and deterioration of the light-collecting characteristics of the diffractive optical element 1, the total thickness T1 of the diffractive optical element 1 is preferably 0.05 mm or more, and more preferably 0.1 mm or more.

[0094] 7C is a diagram showing yet another example of the configuration of the diffractive optical element 1. For example, when the microstructure 4 exhibits a phase-type diffraction pattern such as a phase-type Fresnel zone plate, the microstructure 4 may be formed on a layer 4a covering the main surface 3a of the substrate 3, as shown in FIG.

[0095] <Another Configuration Example of Diffraction Pattern> Next, a description will be given of a configuration example of the diffraction pattern formed by the fine structure 4. Fig. 8 is a diagram showing another example of the Fresnel zone plate shape exhibited by the fine structure 4. As shown in Fig. 8, the diffraction pattern exhibited by the fine structure 4 may be divided into a plurality of pattern regions in the circumferential direction with the center C0 as the reference.

[0096] In the example shown in Fig. 8, the diffraction pattern formed by the microstructure 4 is divided into pattern regions A1, A2, and A3. As an example, the pattern region A1 is assumed to have a Fresnel zone plate shape corresponding to red light. The red light may refer to light having a peak wavelength in the range of 600 nm to 780 nm, for example. In this case, "exhibiting a Fresnel zone plate shape corresponding to red light" means that the wavelength λ in the formula (1) shown below is in the range of 600 nm to 780 nm, and the radius r of the nth zone is n This means that the wavelength λ satisfies the formula (1). For example, the wavelength λ is set to 650 nm.

[0097] As an example, pattern region A2 is configured to have a Fresnel zone plate shape corresponding to green light, i.e., light having a peak wavelength in the range of 500 nm or more and less than 600 nm. For example, the wavelength λ is set to 550 nm. Furthermore, pattern region A3 is configured to have a Fresnel zone plate shape corresponding to blue light, i.e., light having a peak wavelength in the range of 380 nm or more and less than 500 nm. For example, the wavelength λ is set to 450 nm.

[0098] "The diffraction pattern is divided into a plurality of pattern regions in the circumferential direction" means that the diffraction pattern exhibited by the fine structure 4 has pattern regions in the circumferential direction that correspond to different wavelengths λ of light. The fine structure 4 constituting the pattern region A1 and the fine structure 4 constituting the pattern region A2 may be continuous in the circumferential direction or may be spaced apart. The same applies to the pattern region A1 and the pattern region A3, and the pattern region A2 and the pattern region A3.

[0099] In the Fresnel zone plate shapes of the pattern areas A1, A2, and A3, the focal lengths f of first-order diffraction in the above formula (1) are equal to each other. Here, "the focal lengths f of first-order diffraction in different pattern areas are equal" means that the difference between the focal lengths f of first-order diffraction in each pattern area is within 1% of the focal length f.

[0100] In Fig. 8, the diffraction pattern exhibited by the microstructure 4 is divided into three equal parts into the pattern regions (A1, A2, A3), i.e., divided at 120° intervals in the circumferential direction with the center C0 of the diffraction pattern as the reference, but the number of divisions of the diffraction pattern is not limited to the example in Fig. 8. Furthermore, the design wavelengths corresponding to each pattern region (A1, A2, A3) are also not limited to those described above.

[0101] <Linear Zone Plate> As shown in Fig. 9, the microstructure 4 may have a linear zone plate shape. n Instead of the line length L from the center to the periphery nThis is a linear diffractive optical structure. Figure 9 shows an example of a linear zone plate observed from above. Linear zone plates have the property of focusing light in any area on the center line, making them ideal for high-definition optical sensors. Linear zone plates also include "amplitude-type linear zone plates" and "phase-type linear zone plates."

[0102] In the case of an amplitude-type linear zone plate, the microstructure 4 has absorption characteristics at the design wavelength and forms a blocking region, and the central portion functions either as a light-blocking or transparent portion, and the same discussion can be made as for a Fresnel zone plate.

[0103] Furthermore, a phase-type linear zone plate differs from an amplitude-type linear zone plate in that the fine structure 4 does not have absorption characteristics for the design wavelength, but transmits light of the design wavelength. As described in the section on phase-type Fresnel zone plates, the phase difference between the light transmitted through the fine structure 4 and the light transmitted through the protective layer 8 is preferably 1 / 4×π or more, and more preferably between 0.45×π and 2.0×π. From the viewpoint of making it easier to fill the protective layer 8, the phase difference is preferably 1.95×π or less, and more preferably 1.9×π or less.

[0104] Similarly to Fresnel zone plates, linear zone plates may be constructed by combining linear zone plates of different designs, some of which have different focal lengths and some of which have different curable resin compositions, or may be decentered or may be stacked together.

[0105] In this specification, a pattern shape having the above-mentioned characteristics is referred to as a "linear zone plate shape."

[0106] <Fractal Zone Plate> As shown in Fig. 10A, the microstructure 4 may have a fractal zone plate shape. Fresnel zone plates include "amplitude type fractal zone plates" and "phase type fractal zone plates."

[0107] Taking an amplitude fractal zone plate as an example, an amplitude fractal zone plate is formed by dividing the light-shielding regions and transparent regions according to the above formula (1), and then connecting the light-shielding regions using a Cantor set, just like a Fresnel zone plate. As shown in FIG. 10B, a Cantor set is expressed by the number of divisions Nc and the number of divisions S. If the central region of the element is number 1 and the outermost light-shielding region is number N, these light-shielding regions are equally divided into (2Nc+1). Then, both ends are made transparent regions and the center is made light-shielding region. In other words, the first to ((N / 3)-1)th regions are transparent regions, the (N / 3) to ((2N / 3)-1)th regions are light-shielding regions, and the (2N / 3) to Nth regions are light-shielding regions. When S is 2 or more (S n = S2, S3, ...), the transparent region is again divided into (2Nc+1) equal parts, and then the process of making both ends transparent and the center a light-shielding region is repeated (n-1) times. In other words, a fractal zone plate is a diffractive optical element in which the alternating divisions of light-shielding and transparent regions in a Fresnel zone plate are converted into light-shielding and transparent regions that form a Cantor set. The shape shown in Figure 10A is an example of the shape of a fractal zone plate when observed from the vertical direction.

[0108] Furthermore, the phase-type fractal zone plate differs from the amplitude-type fractal zone plate in that the fine structure 4 does not have absorption characteristics for the design wavelength, but transmits light of the design wavelength through the fine structure 4. As described in the section on the phase-type Fresnel zone plate, the phase difference between the light transmitted through the fine structure 4 and the light transmitted through the protective layer 8 is preferably 1 / 4×π or more, and more preferably between 0.45×π and 2.0×π.

[0109] In this specification, a pattern shape having the above characteristics is referred to as a "fractal zone plate shape."

[0110] <Photon Sieve Plate> As shown in Fig. 11, the microstructure 4 may have the shape of a photon sieve plate. The photon sieve plate includes an "amplitude type photon sieve plate" and a "phase type photon sieve plate".

[0111] Taking an amplitude type photon sieve plate as an example, the amplitude type photon sieve plate has a structure in which pinholes are arranged in place of the transparent areas of an amplitude type Fresnel zone plate. Since the light-shielding areas are continuous, it is expected that it can be extracted as a free-standing film, which is preferable when using a thin film substrate. The position R from the center of the pinhole n is calculated by the following formula (4).

[0112] nth pinhole radius r pn is r pn = fλ / (4 × R n ) and the number of n-th pinholes N hole is calculated by the following formula (5).

[0113] N ring is the number of rings consisting of pinholes arranged concentrically in the photon sieve plate. ring When reflecting in the actual design, the decimal points are rounded up, down, or rounded down to be used as integer values. hole Even if the number is not 0.5×N, the photon sieve has the effect of concentrating light. hole 1.5N or more hole The following numbers are preferred: The shape shown in Figure 11 is an example of the shape when the photon sieve plate is observed from the vertical direction.

[0114] Furthermore, the phase-type photon sieve plate differs from the amplitude-type photon sieve plate in that the microstructure 4 does not have absorption characteristics for the design wavelength, but transmits light of the design wavelength. As described in the section on the phase-type Fresnel zone plate, the phase difference between the light transmitted through the microstructure 4 and the light transmitted through the protective layer 8 is preferably 1 / 4×π or more, and more preferably between 0.45×π and 2.0×π. From the viewpoint of facilitating filling of the protective layer 8, the phase difference is preferably 1.95×π or less, and more preferably 1.9×π or less.

[0115] In this specification, the shape of the pattern having the above characteristics is referred to as a "photon sieve plate shape."

[0116] In the linear zone plate shape, fractal zone plate shape, and photon sieve plate shape, the F-number is preferably in the range of 0.2 to 4.0, similarly to the case described with reference to the Fresnel zone plate shape.

[0117] The same discussion as that given with reference to the Fresnel zone plate shape can also be applied to the width of the narrowest structure in the diffraction pattern exhibited by the microstructure 4. That is, in the linear zone plate shape, the fractal zone plate shape, and the photon sieve plate shape, the width of the narrowest structure is preferably 0.2 μm or more and 5.0 μm or less.

[0118] In the linear zone plate shape and the fractal zone plate shape, the narrowest line width of the structure is the line width at the center C when the diffractive optical element 1 is observed from a direction perpendicular to the main surface 3 a of the substrate 3. o This corresponds to the minimum value of the distance from one transparent region 6 to another transparent region 6 in any circumferential direction.

[0119] The narrowest line width in the photon sieve plate shape is the line width at the center C o A transparent region 6 that is different from the transparent region 6 and has a center C is formed from a band-shaped region that is formed by virtually connecting transparent regions 6 that are at the same distance from the center C in the circumferential direction. o This corresponds to the minimum value of the distance from the transparent area 6 to the strip area formed by the transparent area 6 at the same distance from the transparent area 6 .

[0120] <Curable Resin Composition> As described above, the microstructure 4 may be composed of a curable resin composition. Using a curable resin composition is preferable because it improves the selectivity of the refractive index of the microstructure 4 and makes it easier to design the refractive index difference between the microstructure 4 and the protective layer 8. Furthermore, the curable resin composition can easily form a diffraction pattern by exposure using a mask having a shape corresponding to the diffraction pattern and eluting the unexposed portions with a resist developing solution. In other words, using a curable resin composition for the microstructure 4 improves the mass productivity of the diffractive optical element 1, which is preferable.

[0121] Furthermore, when fine pillar structures are formed by conventionally known mask-assisted etching, the pillar structures tend to expand as they move away from the substrate on which they are formed. This is because, during the process of etching a preformed layer with a predetermined gas to form the pillar structures, the gas sprayed onto the layer migrates around and removes the layer. FIG. 12 is a diagram showing an example of a fine structure formed by etching. For the pillar structures 104 shown in FIG. 12 , if a protective layer is formed to cover the pillar structures 104 by, for example, ion-assisted vacuum deposition, the protective layer is difficult to fill between the pillar structures 104. In other words, because the pillar structures 104 expand as they move away from the substrate 103, the regions between the pillar structures 104 farther from the substrate 103 are filled first, and the protective layer is difficult to fill in the regions closer to the substrate 103. Therefore, with conventional methods, even if a protective layer is filled between the pillar structures 104, it is difficult to improve morphology stability. This also applies to the case where the protective layer is formed by a method other than the ion-assisted vacuum deposition method, such as a CVD method, a vacuum deposition method, or liquid coating.

[0122] In contrast, when forming a fine columnar structure using a curable resin composition, a coating film made of the curable resin composition is exposed to light in a predetermined pattern, and then one of the exposed and unexposed regions is removed by resist development. Specifically, the exposed regions are photocured, and the unexposed regions that are not photocured are removed by resist development. Therefore, the shape of the fine structure 4 can be adjusted by designing the exposure dose for the exposed regions that are photocured. For example, by increasing the exposure dose to more firmly cure the exposed regions, it is possible to obtain a fine structure 4 that exhibits a rectangular shape when viewed in a direction parallel to the substrate 3, as shown in FIG. 1.

[0123] FIG. 13A is a drawing showing an example of the shape of the microstructure 4. By forming the microstructure 4 from a curable resin composition, it is possible to make the microstructure 4 have a shape that tapers as it moves away from the substrate 3, as shown in FIG. 13A. For example, when exposing the coating film, the focus is set near the substrate 3, so that the photocuring progresses more easily in areas closer to the substrate 3. This makes it possible to obtain a microstructure 4 that, when viewed in a direction parallel to the substrate 3, tapers as it moves away from the substrate 3. In other words, in areas away from the substrate 3, the periphery of the unexposed area is more likely to be removed by resist phenomenon, resulting in a microstructure 4 with a tapered shape, as shown in FIG. 13A, for example.

[0124] When the microstructure 4 has a rectangular shape (FIG. 1) or a shape that tapers away from the substrate 3 (FIG. 13A), when the microstructure 4 is covered with the protective layer 8, the area farther from the substrate 3 is prevented from being filled first. Therefore, in the microstructure 4 made of the curable resin composition, the area close to the substrate 3 can be easily filled with the protective layer 8, and the shape stability can be more suitably improved.

[0125] In addition, in FIG. 13A, from the viewpoint of facilitating filling of the protective layer 8, the angle θ1 formed between the substrate 3 and the microstructure 4 is preferably 20° to 89°, and more preferably 30° to 89°.

[0126] Furthermore, when the microstructure 4 has a shape that tapers as it moves away from the substrate 3, the microstructure 4 may have a trigonometric function shape such as a trapezoid, a triangle, or a sine curve. From the viewpoint of further suppressing higher-order diffraction, a triangular, curved, or sine curve shape is preferred, with a sine curve shape being more preferred. These are preferably formed as straight lines or curves, but may have a shape that is approximated by multiple steps as long as they substantially form the above shape. Note that from the viewpoint of diffraction efficiency, a continuously tapering shape is more preferred than a multi-step shape.

[0127] FIG. 13B is a diagram showing an example of the shape of the microstructure 4. In accordance with the above formula (1), the line width of the microstructure 4 becomes thinner as it moves from the center of the diffractive optical element toward the circumferential direction D1. Therefore, when the curable resin composition exhibits a sine curve shape, as shown in FIG. 13B, the shape may be such that the period of the sine curve becomes shorter as it moves toward the circumferential direction D1. Note that FIG. 13B is merely an example, and the microstructure 4 may have a structure with a substantially constant period in the circumferential direction D1.

[0128] 13A and 13B are merely schematic illustrations. In the case where the microstructure 4 tapers away from the substrate 3, the microstructure 4 may have a tapered shape on only one side, for example. Similarly, the microstructure 4 may have a curved shape on only one side, or may have a shape that tapers in stages.

[0129] The shape of the microstructure 4 can be confirmed, for example, by observing the cross section of the diffractive optical element 1 using an electron microscope. There are no particular limitations on the method for forming the cross section of the diffractive optical element 1, and examples of forming methods include cutting with a sharp blade, cutting with a microtome, irradiation with a focused ion beam (FIB), and cutting by freeze fracturing.

[0130] By varying the composition of the curable resin composition, it is possible to realize an amplitude-type diffraction pattern or a phase-type diffraction pattern. Specifically, in the case of an amplitude-type diffraction pattern such as an amplitude-type Fresnel zone plate, the curable resin composition contains a colorant and a polymerizable compound (colored curable resin composition). This enhances the light-blocking properties of the curable resin composition at a predetermined wavelength. Even when a colorant is contained, if the composition is transparent to a predetermined wavelength, the diffraction effect of a phase-type diffraction pattern can be expected for light of that wavelength. Furthermore, in the case of a phase-type diffraction pattern such as a phase-type Fresnel zone plate, the curable resin composition is preferably a transparent curable resin composition that does not contain a colorant. This makes it easier to enhance the transmittance of the curable resin composition at a predetermined wavelength.

[0131] The curable resin composition of the present invention can be cured by thermal curing or photocuring. Photocuring is preferred, and the curable resin composition is preferably a radiation-sensitive curable resin composition. Examples of the radiation used include ultraviolet light, far ultraviolet light, X-rays, and charged particle beams. Examples of ultraviolet light include g-rays (wavelength 436 nm) and i-rays (wavelength 365 nm). Examples of far ultraviolet light include ArF excimer lasers and KrF excimer lasers. Examples of X-rays include synchrotron radiation. Examples of charged particle beams include electron beams. Of these types of radiation, ultraviolet light is preferred, and among ultraviolet light, radiation including g-rays and / or i-rays is particularly preferred.

[0132] The curable resin composition according to the present invention may contain a colorant (colored curable resin composition). For example, the curable resin composition contains a colorant, a polymerizable compound, a photopolymerization initiator, and a binder resin. For example, the transparent curable resin composition contains a polymerizable compound, a photopolymerization initiator or a photogenerator, and, if necessary, a binder resin and a crosslinking agent. By including a colorant in the curable resin composition, an amplitude-type diffractive optical element can be obtained. Details are described below.

[0133] The colorant has a maximum absorption wavelength in the range of 380 nm to 1,700 nm, and more preferably in the range of 410 nm to 1,100 nm. There are no particular limitations on the colorant as long as it has the above maximum absorption wavelength, but at least one selected from pigments and dyes is preferred.

[0134] The pigment may be either an organic pigment or an inorganic pigment, and preferred specific examples of organic pigments include, in terms of Color Index (C.I.) names, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 224, C.I. Pigment Red 242, C.I. Pigment Red 254, C.I. Pigment Red 264, C.I. Pigment Green 7, C.I. Pigment Green 36, C.I. Pigment Green 58, C.I. Pigment Blue 15:6, C.I. Pigment Blue 80, C.I. Pigment Yellow 83, C.I. Pigment Yellow 129, C.I. Pigment Yellow 138, C.I. Pigment Yellow 139, C.I. Examples of inorganic pigments include C.I. Pigment Yellow 150, C.I. Pigment Yellow 180, C.I. Pigment Yellow 185, C.I. Pigment Yellow 211, C.I. Pigment Orange 38, C.I. Pigment Violet 23, carbon nanotubes, and fullerenes. Furthermore, the colorant may contain a pigment that does not have a maximum absorption wavelength in the wavelength range of 410 to 1100 nm. Examples of colorants that do not have a maximum absorption wavelength in the wavelength range of 410 to 1100 nm include carbon black, titanium black, and graphene. Specific examples of preferred inorganic pigments include titanium oxide, strontium titanate, barium titanate, zinc oxide, magnesium oxide, zirconium oxide, aluminum oxide, barium sulfate, silica, talc, mica, aluminum hydroxide, calcium silicate, aluminum silicate, and zinc sulfide.

[0135] Examples of the dyes include pyrazole azo compounds, anilino azo compounds, triarylmethane compounds, anthraquinone compounds, anthrapyridone compounds, benzylidene compounds, oxonol compounds, pyrazolotriazole azo compounds, pyridone azo compounds, cyanine compounds, phenothiazine compounds, pyrrolopyrazole azomethine compounds, xanthene compounds, phthalocyanine compounds, benzopyran compounds, indigo compounds, pyrromethene compounds, triarylmethane compounds, cyanine compounds, and azo compounds. Quinophthalone compounds and the like can also be used as yellow dyes. Examples of near-infrared absorbing dyes include pyrrolopyrrole compounds, rylene compounds, oxonol compounds, squarylium compounds, cyanine compounds, croconium compounds, phthalocyanine compounds, naphthalocyanine compounds, pyrylium compounds, azulenium compounds, indigo compounds, and pyrromethene compounds. In addition, squarylium compounds, pyrrole ring-containing compounds, squarylium compounds having an aromatic ring at the amide α-position, compounds having a croconium skeleton, dihydrocarbazole bis-type squarylium compounds, etc. can also be used.

[0136] In the present invention, the pigments and dyes may be used either alone or in combination of two or more.

[0137] When a pigment is used as a colorant in the present invention, the pigment may be purified, if desired, by recrystallization, reprecipitation, solvent washing, sublimation, vacuum heating, or a combination thereof before use. Furthermore, the pigment may be used after modifying its particle surface with a resin, if desired. Examples of resins that modify the pigment particle surface include vehicle resins and various commercially available resins for dispersing pigments. Furthermore, the pigment may be used after micronizing primary particles by so-called salt milling.

[0138] When a pigment is used as a colorant in the present invention, it may be used together with a dispersant or a dispersing aid, if desired. Examples of the dispersant include cationic, anionic, and nonionic dispersants, but polymer dispersants are preferred. Specific examples include urethane dispersants, polyethyleneimine dispersants, polyoxyethylene alkyl ether dispersants, polyoxyethylene alkylphenyl ether dispersants, polyethylene glycol diester dispersants, sorbitan fatty acid ester dispersants, polyester dispersants, and acrylic dispersants.

[0139] <Polymerizable Compound> The polymerizable compound of the present invention has a polymerizable functional group, but is not particularly limited thereto. Examples of the polymerizable functional group include an ethylenically unsaturated group, an oxiranyl group, an oxetanyl group, an N-alkoxymethylamino group, a hydrosiloxane group, and a vinylsilyl group. Examples of the ethylenically unsaturated group include a vinyl group, a styryl group, an allyl group, a (meth)acryloyl group, a (meth)acrylamide group, and a maleimide group, with a (meth)acryloyl group being preferred. From the viewpoint of dimensional stability, a hydrosiloxane group and a vinylsilyl group are preferred. The polymerizable compound used in the present invention is preferably selected from the group consisting of compounds having two or more polymerizable functional groups in the molecule.

[0140] Examples of the compound having two or more (meth)acryloyl groups in the molecule include polyfunctional (meth)acrylates obtained by reacting an aliphatic polyhydroxy compound with (meth)acrylic acid, caprolactone-modified polyfunctional (meth)acrylates, alkylene oxide-modified polyfunctional (meth)acrylates, polyfunctional urethane (meth)acrylates obtained by reacting a (meth)acrylate having a hydroxyl group with a polyfunctional isocyanate, and polyfunctional (meth)acrylates having a carboxyl group obtained by reacting a (meth)acrylate having a hydroxyl group with an acid anhydride. Examples of the aliphatic polyhydroxy compounds include divalent aliphatic polyhydroxy compounds such as ethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; and trivalent or higher aliphatic polyhydroxy compounds such as glycerin, trimethylolpropane, pentaerythritol, and dipentaerythritol.

[0141] Examples of the (meth)acrylate having a hydroxyl group include 2-hydroxyethyl (meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol penta(meth)acrylate, and glycerol dimethacrylate; and examples of the polyfunctional isocyanate include tolylene diisocyanate, hexamethylene diisocyanate, diphenylmethylene diisocyanate, and isophorone diisocyanate. Examples of the acid anhydrides include dibasic acid anhydrides and tetrabasic acid dianhydrides. Specific examples of these include the dibasic acid anhydrides such as succinic anhydride, maleic anhydride, glutaric anhydride, itaconic anhydride, phthalic anhydride, and hexahydrophthalic anhydride; and the tetrabasic acid dianhydrides such as pyromellitic anhydride, biphenyltetracarboxylic dianhydride, and benzophenonetetracarboxylic dianhydride.

[0142] Examples of the caprolactone-modified polyfunctional (meth)acrylate include, for example, bisphenol A di(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide, isocyanuric acid tri(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide, trimethylolpropane tri(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide, and ethylene oxide. Examples of the modified acrylate include pentaerythritol tri(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide, pentaerythritol tetra(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide, dipentaerythritol penta(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide, and dipentaerythritol hexa(meth)acrylate modified with at least one selected from ethylene oxide and propylene oxide.

[0143] Examples of compounds having two or more N-alkoxymethylamino groups in the molecule include compounds having a melamine structure, a benzoguanamine structure, or a urea structure. Here, the term "melamine structure" refers to a chemical structure having one or more triazine rings as a basic skeleton, and the term "benzoguanamine structure" refers to a chemical structure having one or more phenyl-substituted triazine rings as a basic skeleton, and these concepts encompass melamine, benzoguanamine, and condensates thereof. Specific examples of compounds having two or more N-alkoxymethylamino groups in the molecule include N,N,N',N',N",N"-hexa(alkoxymethyl)melamine, N,N,N',N'-tetra(alkoxymethyl)benzoguanamine, and N,N,N',N'-tetra(alkoxymethyl)glycoluril.

[0144] Examples of compounds having two or more oxiranyl groups in the molecule include bisphenol A epoxy resins such as Epicoat 1001, 1002, 1003, 1004, 1007, 1009, 1010, and 828 (manufactured by Japan Epoxy Resins Co., Ltd.); bisphenol F epoxy resins such as Epicoat 807 (manufactured by Japan Epoxy Resins Co., Ltd.); phenol novolac epoxy resins such as Epicoat 152, 154, and 157S65 (manufactured by Japan Epoxy Resins Co., Ltd.), EPPN201, and 202 (manufactured by Nippon Kayaku Co., Ltd.); cresol novolac epoxy resins such as EOCN102, 103S, 104S, 1020, 1025, and 1027 (manufactured by Nippon Kayaku Co., Ltd.), and Epicoat 180S75 (manufactured by Japan Epoxy Resins Co., Ltd.); Examples of polyphenol-type epoxy resins include Epicoat 1032H60 and XY-4000 (manufactured by Japan Epoxy Resins); examples of cyclic aliphatic epoxy resins include CY-175, CY-177, CY-179, Araldite CY-182, CY-192, and CY-184 (manufactured by Chiba Specialty Chemicals), ERL-4234, 4299, 4221, and 4206 (manufactured by U.C.C.), Shodyne 509 (manufactured by Showa Denko KK), Epiclon 200 and 400 (manufactured by Dainippon Ink Co., Ltd.), Epicoat 871 and 872 (manufactured by Japan Epoxy Resins), and ED-5661 and 5662 (manufactured by Celanese Coatings); Examples of aliphatic polyglycidyl ethers include Epolite 100MF (manufactured by Kyoeisha Chemical Co., Ltd.) and Epiol TMP (manufactured by NOF Corporation).

[0145] Of the above, preferred polymerizable compounds in the present invention include polyfunctional (meth)acrylates obtained by reacting a trivalent or higher aliphatic polyhydroxy compound with (meth)acrylic acid, caprolactone-modified polyfunctional (meth)acrylates, polyfunctional urethane (meth)acrylates, polyfunctional (meth)acrylates having a carboxyl group, N,N,N',N',N",N"-hexa(alkoxymethyl)melamine, and N,N,N',N'-tetra(alkoxymethyl)benzoguanamine. Among the polyfunctional (meth)acrylates obtained by reacting a trivalent or higher aliphatic polyhydroxy compound with a (meth)acrylic and an acid, trimethylolpropane triacrylate, pentaerythritol triacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate are particularly preferred; and among the polyfunctional (meth)acrylates having a carboxyl group, a compound obtained by reacting pentaerythritol triacrylate with succinic anhydride, a compound obtained by reacting dipentaerythritol pentaacrylate with succinic anhydride, and a compound having two or more oxiranyl groups in the molecule are particularly preferred, since the resulting curable resin composition has high strength and excellent surface smoothness and is less likely to produce background smears, residual film, etc. on the substrate and resin layer in unexposed areas.

[0146] <Binder Resin> The curable resin composition of the present invention may contain a binder resin. The presence of a binder resin can improve the alkali developability and storage stability of the curable resin composition. The binder resin is not particularly limited, but is preferably a resin having an acidic functional group such as a carboxyl group or a phenolic hydroxyl group. Among these, a polymer having a carboxyl group (hereinafter referred to as a "carboxyl group-containing polymer") is preferred, and examples thereof include copolymers of an ethylenically unsaturated monomer having one or more carboxyl groups (hereinafter referred to as an "unsaturated monomer (b1)") and another copolymerizable ethylenically unsaturated monomer (hereinafter referred to as an "unsaturated monomer (b2)").

[0147] Examples of the unsaturated monomer (b1) include (meth)acrylic acid, maleic acid, maleic anhydride, mono[2-(meth)acryloyloxyethyl] succinate, ω-carboxypolycaprolactone mono(meth)acrylate, and p-vinylbenzoic acid.

[0148] These unsaturated monomers (b1) can be used alone or in combination of two or more.

[0149] Examples of the unsaturated monomer (b2) include N-substituted maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide; aromatic vinyl compounds such as styrene, α-methylstyrene, p-hydroxystyrene, p-hydroxy-α-methylstyrene, p-vinylbenzyl glycidyl ether, and acenaphthylene;

[0150] Methyl (meth)acrylate, n-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, allyl (meth)acrylate, benzyl (meth)acrylate, polyethylene glycol (degree of polymerization 2-10) methyl ether (meth)acrylate, polypropylene glycol (degree of polymerization 2-10) methyl ether (meth)acrylate, polyethylene glycol (degree of polymerization 2-10) mono(meth)acrylate, polypropylene glycol (degree of polymerization 2-10) mono(meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclo[5.2.1.0] 2,6 (meth)acrylic acid esters such as ]decan-8-yl (meth)acrylate, dicyclopentenyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyphenyl (meth)acrylate, ethylene oxide-modified (meth)acrylate of para-cumylphenol, glycidyl (meth)acrylate, 3,4-epoxycyclohexylmethyl (meth)acrylate, 3-[(meth)acryloyloxymethyl]oxetane, and 3-[(meth)acryloyloxymethyl]-3-ethyloxetane;

[0151] Cyclohexyl vinyl ether, isobornyl vinyl ether, tricyclo[5.2.1.0 2,6 ] vinyl ethers such as decan-8-yl vinyl ether, pentacyclopentadecanyl vinyl ether, and 3-(vinyloxymethyl)-3-ethyloxetane; and macromonomers having a mono(meth)acryloyl group at the end of the polymer molecular chain, such as polystyrene, polymethyl(meth)acrylate, poly-n-butyl(meth)acrylate, and polysiloxane.

[0152] These unsaturated monomers (b2) can be used alone or in combination of two or more.

[0153] In the copolymer of the unsaturated monomer (b1) and the unsaturated monomer (b2), the copolymerization ratio of the unsaturated monomer (b1) in the copolymer is preferably 5% by mass to 50% by mass, more preferably 10% by mass to 40% by mass. By copolymerizing the unsaturated monomer (b1) in such a range, a colored composition excellent in alkali developability and storage stability can be obtained.

[0154] In the present invention, for example, a carboxyl group-containing polymer having a polymerizable unsaturated bond such as a (meth)acryloyl group in the side chain can also be used as the binder resin.

[0155] Furthermore, in the present invention, a copolymer of an unsaturated monomer containing a (meth)acrylic acid ester having an oxiranyl group, such as glycidyl (meth)acrylate, may be used, and the hydroxyl groups generated by the reaction of the copolymer with the unsaturated monomer (b1) may be further reacted with a polybasic acid anhydride to form a copolymer, which may be used as the binder resin.

[0156] Examples of such polybasic acid anhydrides include anhydrides of dibasic acids such as maleic anhydride, fumaric anhydride, citraconic anhydride, mesaconic anhydride, itaconic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, hexahydrophthalic anhydride, methylhexahydrophthalic anhydride, himic anhydride, phthalic anhydride, and naphthalene-2,3-dicarboxylic anhydride; monoanhydrides of tribasic or higher polybasic acids such as cyclohexane-1,2,4-tricarboxylic anhydride and trimellitic anhydride; and monoanhydrides of cyclohexane-1,2,4-tricarboxylic anhydride and trimellitic anhydride. Examples of suitable dianhydrides include dianhydrides of polybasic acids having tetrabasic or higher acids, such as hexanetetracarboxylic dianhydride, cyclopentanetetracarboxylic dianhydride, cyclohexanetetracarboxylic dianhydride, norbornanetetracarboxylic dianhydride, pyromellitic dianhydride, biphenyltetracarboxylic dianhydride, diphenylethertetracarboxylic dianhydride, benzophenonetetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, and perylene-3,4,9,10-tetracarboxylic dianhydride.

[0157] The binder resin of the present invention can be a resin having a repeating unit formed by cleavage of a polymerizable unsaturated bond of a polymerizable unsaturated compound having a phenolic hydroxyl group (hereinafter referred to as a "phenolic unsaturated compound"). The structure of the phenolic unsaturated compound is not particularly limited, as long as it contains a phenolic hydroxyl group and an unsaturated bond-containing group. Specific examples of the phenolic unsaturated compound include o-vinylphenol, m-vinylphenol, p-vinylphenol, o-isopropenylphenol, m-isopropenylphenol, and p-isopropenylphenol. The phenolic unsaturated compounds may be used alone or in combination. The molecular weight of the resin is not particularly limited, and can be adjusted to various molecular weight ranges as needed. The weight average molecular weight (Mw) measured by GPC in terms of polystyrene standards is typically 2,000 to 20,000, preferably 3,000 to 15,000, and more preferably 3,000 to 10,000.

[0158] The binder resin in the present invention has a weight average molecular weight (Mw) of typically 1,000 to 100,000, and preferably 3,000 to 50,000, in terms of polystyrene, as measured by GPC (elution solvent: tetrahydrofuran). By adopting such an embodiment, it becomes easier to form a coating film that is excellent in film retention, pattern shape, heat resistance, electrical properties, and resolution, and it is also possible to suppress the generation of dried foreign matter during application by a slit nozzle method.

[0159] The ratio (Mw / Mn) of the weight average molecular weight of the binder resin in the present invention to the polystyrene-equivalent number average molecular weight (Mn) measured by GPC (elution solvent: tetrahydrofuran) is preferably 1.0 to 5.0, and more preferably 1.0 to 3.0.

[0160] In the present invention, the binder resins may be used alone or in combination of two or more.

[0161] In the present invention, the content of the binder resin is preferably 10 parts by mass to 1,000 parts by mass, and particularly preferably 20 parts by mass to 500 parts by mass, relative to 100 parts by mass of the colorant (A). By adopting such an embodiment, the alkali developability, the storage stability, and the chromaticity characteristics of the colored composition can be improved.

[0162] The curable resin composition according to the present invention is preferably a radiation-sensitive curable resin composition for forming a diffractive optical element.

[0163] <Photopolymerization initiator> The curable resin composition of the present invention may contain a photopolymerization initiator or a photoacid generator. This makes it possible to impart radiation sensitivity to the curable resin composition, thereby obtaining a radiation-sensitive curable resin composition. The photopolymerization initiator applicable to the present invention is a compound that generates an active species capable of initiating polymerization of a polymerizable compound upon exposure to radiation such as visible light, ultraviolet light, far ultraviolet light, electron beams, or X-rays.

[0164] Examples of such photopolymerization initiators include thioxanthone-based compounds, acetophenone-based compounds, biimidazole-based compounds, triazine-based compounds, O-acyloxime-based compounds, onium salt-based compounds, benzoin-based compounds, benzophenone-based compounds, α-diketone-based compounds, polynuclear quinone-based compounds, diazo-based compounds, imidosulfonate-based compounds, and onium salt-based compounds.

[0165] In the present invention, the photopolymerization initiator may be used alone or in combination of two or more. The photopolymerization initiator is preferably at least one selected from the group consisting of thioxanthone compounds, acetophenone compounds, biimidazole compounds, triazine compounds, and O-acyloxime compounds.

[0166] Among the preferable photopolymerization initiators in the present invention, specific examples of the thioxanthone-based compounds include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone.

[0167] Specific examples of the acetophenone-based compound include 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butan-1-one, and 2-(4-methylbenzyl)-2-(dimethylamino)-1-(4-morpholinophenyl)butan-1-one.

[0168] Specific examples of the biimidazole-based compound include 2,2'-bis(2-chlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis(2,4-dichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole, and 2,2'-bis(2,4,6-trichlorophenyl)-4,4',5,5'-tetraphenyl-1,2'-biimidazole.

[0169] When a biimidazole compound is used as a photopolymerization initiator, it is preferable to use a hydrogen donor in combination, as this can improve sensitivity. The term "hydrogen donor" as used herein refers to a compound capable of donating a hydrogen atom to a radical generated from the biimidazole compound upon exposure. Examples of hydrogen donors include mercaptan hydrogen donors such as 2-mercaptobenzothiazole and 2-mercaptobenzoxazole, and amine hydrogen donors such as 4,4'-bis(dimethylamino)benzophenone and 4,4'-bis(diethylamino)benzophenone. In the present invention, the hydrogen donors can be used alone or in combination of two or more. However, it is preferable to use a combination of one or more mercaptan hydrogen donors and one or more amine hydrogen donors, as this can further improve sensitivity.

[0170] Specific examples of the triazine compounds include 2,4,6-tris(trichloromethyl)-s-triazine, 2-methyl-4,6-bis(trichloromethyl)-s-triazine, 2-[2-(5-methylfuran-2-yl)ethenyl]-4,6-bis(trichloromethyl)-s-triazine, 2-[2-(furan-2-yl)ethenyl]-4,6-bis(trichloromethyl)-s-triazine, 2-[2-(furan-2-yl)ethenyl]-4,6-bis(trichloromethyl)-s-triazine, and 2-[2-(4-diethylamino-2-methylphenyl)ethenyl]-4,6-bis(trichloromethyl)-s-triazine.

[0033] Examples of triazine compounds having a halomethyl group include 2-[2-(3,4-dimethoxyphenyl)ethenyl]-4,6-bis(trichloromethyl)-s-triazine, 2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine, 2-(4-ethoxystyryl)-4,6-bis(trichloromethyl)-s-triazine, and 2-(4-n-butoxyphenyl)-4,6-bis(trichloromethyl)-s-triazine.

[0171] Specific examples of the O-acyloxime compound include 1,2-octanedione, 1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime), ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), ethanone, 1-[9-ethyl-6-(2-methyl-4-tetrahydrofuranylmethoxybenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), ethanone, 1-[9-ethyl-6-{2-methyl-4-(2,2-dimethyl-1,3-dioxolanyl)methoxybenzoyl}-9H-carbazol-3-yl]-, 1-(O-acetyloxime), and the like.

[0172] In the present invention, when a photopolymerization initiator other than a biimidazole compound, such as an acetophenone compound, is used, a sensitizer can also be used in combination. Examples of such sensitizers include 4,4'-bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 4-diethylaminoacetophenone, 4-dimethylaminopropiophenone, ethyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,5-bis(4-diethylaminobenzal)cyclohexanone, 7-diethylamino-3-(4-diethylaminobenzoyl)coumarin, and 4-(diethylamino)chalcone.

[0173] In the present invention, the photoacid generator is not particularly limited as long as it is a compound that generates an acid (e.g., p-toluenesulfonic acid, camphorsulfonic acid, etc.) upon irradiation with radiation. Examples of such photoacid generators include 1-(4-hydroxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate, 1-(4-n-butoxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate, 1-(4,7-diethoxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate, 1-(4,7-dibutoxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate, and the like. thiophenium trifluoromethanesulfonate, 1-(4,7-dipropylhydroxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate, 1-(4,7-dihydroxy-1-naphthalenyl)tetrahydrothiophenium hexafluorophosphate, 1-(4,7-dihydroxy-1-naphthalenyl)tetrahydrothiophenium hexafluorophosphate, etc. Of these, 1-(4,7-dibutoxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate and 1-(4,7-dihydroxy-1-naphthalenyl)tetrahydrothiophenium trifluoromethanesulfonate are preferred. Other examples include diphenyl(4-(phenylthio)phenyl)sulfonium trifluoromethanesulfonate, diphenyl(4-(phenylthio)phenyl)sulfonium hexafluorophosphate, diphenyl(4-(phenylthio)phenyl)sulfonium hexafluoroantimonate, diphenyl(4-(phenylthio)phenyl)sulfonium trifluorotrispentafluoroethylphosphate, diphenyl(4-(phenyl)phenyl)sulfonium trifluorotrispentafluoroethylphosphate, diphenyl(4-(naphthyl)phenyl)sulfonium trifluorotrispentafluoroethylphosphate, diphenyl(4-(anthranyl)phenyl)sulfonium trifluorotrispentafluoroethylphosphate, and the like.Of these, diphenyl(4-(phenylthio)phenyl)sulfonium trifluorotrispentafluoroethyl phosphate and diphenyl(4-(phenyl)phenyl)sulfonium trifluorotrispentafluoroethyl phosphate are preferred. Further examples include bis(t-butylsulfonyl)diazomethane, bis(cyclohexylsulfonyl)diazomethane, bis(benzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(4-t-butylbenzenesulfonyl)diazomethane, bis(naphthalenesulfonyl)diazomethane, and bis(anthracenesulfonyl)diazomethane. Of these, bis(cyclohexylsulfonyl)diazomethane and bis(p-toluenesulfonyl)diazomethane are preferred. Furthermore, compounds that are generated within carboxylic acid molecules upon irradiation with light, such as naphthoquinone diazide, can also be used.

[0174] The crosslinking agent in the present invention is not particularly limited, and examples of the crosslinking agent include N-(alkoxymethyl)amino compounds such as N-(alkoxymethyl)glycoluril compounds, N-(alkoxymethyl)urea compounds, N-(alkoxymethyl)melamine compounds, and N-(alkoxymethyl)ethyleneurea compounds.

[0175] Specific examples of the N-(alkoxymethyl)glycoluril compound include N,N,N,N-tetra(methoxymethyl)glycoluril, N,N,N,N-tetra(ethoxymethyl)glycoluril, N,N,N,N-tetra(n-propoxymethyl)glycoluril, N,N,N,N-tetra(i-propoxymethyl)glycoluril, N,N,N,N-tetra(n-butoxymethyl)glycoluril, and N,N,N,N-tetra(t-butoxymethyl)glycoluril. Specific examples of the N-(alkoxymethyl)urea compound include N,N'-di(methoxymethyl)urea, N,N'-di(ethoxymethyl)urea, N,N'-di(n-propoxymethyl)urea, N,N'-di(i-propoxymethyl)urea, N,N'-di(n-butoxymethyl)urea, and N,N'-di(t-butoxymethyl)urea. Specific examples of the N-(alkoxymethyl)melamine compound include N,N,N,N,N,N,N-hexa(methoxymethyl)melamine, N,N,N,N,N,N-hexa(ethoxymethyl)melamine, N,N,N,N,N,N-hexa(n-propoxymethyl)melamine, N,N,N,N,N,N-hexa(i-propoxymethyl)melamine, N,N,N,N,N,N-hexa(n-butoxymethyl)melamine, and N,N,N,N,N,N,N-hexa(t-butoxymethyl)melamine. Specific examples of the N-(alkoxymethyl)ethyleneurea compound include N,N-di(methoxymethyl)-4,5-di(methoxymethyl)ethyleneurea, N,N-di(ethoxymethyl)-4,5-di(ethoxymethyl)ethyleneurea, N,N-di(n-propoxymethyl)-4,5-di(n-propoxymethyl)ethyleneurea, N,N-di(i-propoxymethyl)-4,5-di(i-propoxymethyl)ethyleneurea, N,N-di(n-butoxymethyl)-4,5-di(n-butoxymethyl)ethyleneurea, and N,N-di(t-butoxymethyl)-4,5-di(t-butoxymethyl)ethyleneurea.

[0176] Among these other crosslinking agents, N-(alkoxymethyl)glycoluril compounds are preferred, and N,N,N,N-tetra(methoxymethyl)glycoluril is particularly preferred. The other crosslinking agents can be used alone or in combination of two or more.

[0177] In the present invention, the colored curable resin composition preferably contains the photopolymerization initiator in an amount of 0.01 to 120 parts by mass, and particularly preferably 1 to 100 parts by mass, relative to 100 parts by mass of the polymerizable compound (C). By adopting such an embodiment, the curability and film properties become good.

[0178] In the present invention, the transparent curable resin composition preferably contains the photoacid generator in an amount of 0.01 to 20 parts by mass, and more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the polymerizable compound. By adopting such an embodiment, the curability and film properties become good.

[0179] In the present invention, the curable resin composition may contain inorganic particles from the viewpoint of adjusting the refractive index. Examples of inorganic particles include silicon oxide, aluminum oxide, lanthanum oxide, tungsten oxide, magnesium fluoride, yttrium fluoride, titanium oxide, tantalum oxide, niobium oxide, and hafnium oxide. The inorganic particles contained in the curable resin composition may be made of a single material or multiple types of materials. In addition, from the viewpoint of suppressing the generation of scattered light, the inorganic particles preferably have a diameter of 200 nm or less, more preferably a diameter of 50 nm or less, and particularly preferably a diameter of 30 nm or less.

[0180] The effect of forming a microstructure in a diffractive optical element and then covering the microstructure with a protective layer was examined and will be described below. Details of the materials used in each example are as follows.

[0181] [Curable resin composition 1: JSSG-9135 manufactured by JSR Corporation] The refractive index and extinction coefficient of the microstructure formed by curable resin composition 1 were evaluated, and the results are shown in Figure 14. As shown in Figure 14, curable resin composition 1 had maximum absorptance for light with wavelengths of 483 nm, 659 nm, and 738 nm, with a maximum transmittance of 86% and a minimum transmittance of 0.5%.

[0182] [Constituent Materials of Protective Layer] Details of the constituent materials of the protective layer used in each example and their refractive indices are as follows. These were used as the dielectric multilayer film forming the protective layer 8 or the anti-reflection layer. Niobium oxide: Nb manufactured by Canon Optron Co., Ltd. ２ O ５ , refractive index 2.3 Zirconium oxide: ZrO manufactured by Canon Optron Co., Ltd. ２ , refractive index 2.0 Tantalum oxide: OA-100 manufactured by Canon Optron Inc., refractive index 2.1 Titanium oxide: OS-50 manufactured by Canon Optron Inc., refractive index 2.4 Hafnium oxide: Rare Metals Co., Ltd., refractive index 1.9 Titanium alkoxide: PC-200 manufactured by Matsumoto Fine Chemical Co., Ltd., refractive index 1.8 Silicone resin: A mixture of equal amounts of KE-109A and KE-109B manufactured by Shin-Etsu Chemical Co., Ltd., refractive index 1.4

[0183] <Refractive Index and Extinction Coefficient> The refractive index n and extinction coefficient k of the curable resin were measured by applying a sample to a thickness of 1 μm to a silicon wafer (111 orientation, undoped, diameter 10 mm, thickness 280 μm, manufactured by Universalwafer Inc.) using a spinner, and measuring the refractive index n and extinction coefficient k using a spectroscopic ellipsometry (M-2000D manufactured by J.A. Woollam).

[0184] The refractive index nH of the protective layer 8 was measured using a sample coated or vapor-deposited to a thickness of 1 μm on a silicon wafer (111 orientation, undoped, diameter 10 mm, thickness 280 μm, manufactured by Universalwafer Inc.) using a spectroscopic ellipsometry (M-2000D manufactured by J.A. Woollam) at a wavelength of 500 nm.

[0185] Example 1 An adhesion promoter (AP3000 manufactured by The Dow Chemical Company) was applied to a glass substrate (Corning Incorporated, Eagle XG, diameter 8 inches, thickness 0.7 mm, surface roughness 20 nm) using a spinner, and then heated on a hot plate at 190°C for 300 seconds to form an adhesion promoter layer. Onto the quartz glass substrate with this adhesion promoter layer, curable resin composition 1 (JSSG-9135 manufactured by JSR Corporation, refractive index 1.7 at 500 nm) was applied using a spinner, and then prebaked on a hot plate at 100°C for 180 seconds to form a substrate with a coating film. The substrate with this coating film was exposed using an i-line stepper (Canon Inc., FPA-3030i5+) via the following reticle: The conditions for the pattern formed on the reticle were a Fresnel zone plate shape with a focal length f of 500 μm in the above formula (1), a wavelength λ of 850 nm, and the number of diffraction structures of 253. The diameter was 1023 μm, and the narrowest line width was 0.6 μm.

[0186] After the exposure, the substrate was immersed in a resist developer (S-170809 manufactured by Kanto Chemical Co., Ltd.) to dissolve the unexposed portions. After rinsing the resist developer with pure water, the substrate was air-dried with an air gun and then post-baked on a hot plate at 200°C for 300 seconds to form a fine structure made of the curable resin composition and exhibiting a Fresnel zone plate shape on the main surface of the substrate.

[0187] Next, an ion-assisted deposition process in which oxygen ions and argon ions were irradiated onto the substrate on which the microstructure had been formed using an ion-assisted deposition apparatus (Sapio 1300, manufactured by Showa Vacuum Co., Ltd.) while heating the hafnium oxide with an electron gun heating device, and an etching process in which oxygen ions and argon ions were irradiated were repeated to form a protective layer made of hafnium oxide that covered the microstructure, thereby obtaining a diffractive optical element.

[0188] 14, the curable resin composition 1 has an extinction coefficient of less than 0.01 at a design wavelength of 850 nm, and does not have absorption characteristics at the design wavelength. That is, in Example 1, the microstructure has a phase-type Fresnel zone plate shape.

[0189] Example 2 An adhesion promoter (AP3000 manufactured by The Dow Chemical Company) was applied to a glass substrate (Corning Incorporated, Eagle XG, diameter 8 inches, thickness 0.7 mm, surface roughness 20 nm) using a spinner, and then heated on a hot plate at 190°C for 300 seconds to form an adhesion promoter layer. Onto the quartz glass substrate with this adhesion promoter layer, curable resin composition 1 (JSSG-9135 manufactured by JSR Corporation, refractive index 1.7 at 500 nm) was applied using a spinner, and then prebaked on a hot plate at 100°C for 180 seconds to form a substrate with a coating film. The substrate with this coating film was exposed using an i-line stepper (Canon Inc., FPA-3030i5+) via the following reticle. The conditions for the pattern formed on the reticle were a fractal zone plate shape with a focal length f of 500 μm in the above formula (1), a wavelength λ of 650 nm, and the number of diffraction structures of 15. The number of divisions Nc of the fractal zone plate was 2, and the number of divisions S was 4. The diameter was 466 μm, and the narrowest line width was 0.8 μm.

[0190] After the exposure, the substrate was immersed in a resist developer (S-170809 manufactured by Kanto Chemical Co., Ltd.) to dissolve the unexposed portions. After rinsing the resist developer with pure water, the substrate was air-dried with an air gun and then post-baked on a hot plate at 200°C for 300 seconds to form a microstructure consisting of the curable resin composition and exhibiting a fractal zone plate shape on the main surface of the substrate.

[0191] Next, an ion-assisted deposition process was performed on the substrate on which the microstructure was formed, using an ion-assisted deposition apparatus (Sapio 1300, manufactured by Showa Shinku Co., Ltd.) in which niobium oxide was irradiated with oxygen ions while being heated by an electron gun heating device, and an etching process in which oxygen ions and argon ions were irradiated, thereby forming a protective layer made of niobium oxide that covered the microstructure. This resulted in a diffractive optical element.

[0192] 14, the curable resin composition 1 has an extinction coefficient of more than 0.01 at a design wavelength of 650 nm, and has absorption characteristics at the design wavelength. That is, in Example 2, the microstructure has an amplitude-type fractal zone plate shape.

[0193] [Example 3] This example was carried out under the same conditions as Example 2, except that the conditions of the pattern formed on the reticle were changed. In Example 3, the pattern was set to the following in equation (4): focal length f = 1000 μm, wavelength λ = 650 nm, the number of structures in the diffraction structure was 34, and N in equation (5) was set to hole The number of is 0.8 × N hole The photon sieve plate shape was set to 1.0 μm. The diameter of the photon sieve plate shape was set to 272 μm, and the narrowest line width was set to 1.0 μm. In Example 3, the microstructure was an amplitude-type photon sieve plate shape. In Example 3, the high refractive index material constituting the protective layer covering the microstructure was changed from niobium oxide to zirconia oxide. The other implementation procedures were the same as in Example 2.

[0194] [Example 4] In Example 2, the conditions for the pattern formed on the reticle were changed. In Example 4, the pattern was a Fresnel zone plate shape in which, in the above formula (1), the focal length f was 30 mm, the wavelength λ was 550 nm, and the number of structures in the diffraction structure was 3600. The diameter of the Fresnel zone plate shape was 22.1 mm, and the narrowest line width was 0.8 μm. In Example 4, the high refractive index material constituting the protective layer covering the microstructure was changed from niobium oxide to tantalum oxide. The other implementation procedures were the same as in Example 2.

[0195] 14, the curable resin composition 1 has an extinction coefficient of more than 0.01 at a design wavelength of 550 nm, and has absorption characteristics at the design wavelength. That is, in Example 4, the microstructure has an amplitude-type Fresnel zone plate shape.

[0196] [Example 5] In Example 2, the substrate was a cycloolefin resin ARTON (manufactured by JSR Corporation, thickness 0.2 mm). In Example 5, the pattern formed on the reticle was a linear zone plate shape in which, in the above formula (1), the focal length f was 1 mm, the wavelength λ was 940 nm, and the number of diffraction structures was 1038. The diameter of the linear zone plate shape was 3.4 mm, and the narrowest line width was 0.5 μm. In Example 5, the high refractive index material constituting the protective layer covering the microstructure was changed from niobium oxide to titanium oxide. The remaining implementation procedures were the same as in Example 2.

[0197] 14, the curable resin composition 1 has an extinction coefficient of 0.01 or less at a design wavelength of 940 nm, and does not have absorption characteristics at the design wavelength. That is, in Example 5, the microstructure is a phase-type linear zone plate shape.

[0198] Example 6 was carried out under the same conditions as Example 5, except that the conditions for the pattern formed on the reticle were changed. In Example 6, the pattern was a linear zone plate shape in which, in the above formula (1), the focal length f was 0.5 mm, the wavelength λ was 450 nm, and the number of structures in the diffraction structure was 242. The diameter of the linear zone plate shape was 0.3 mm, and the narrowest line width was 0.4 μm.

[0199] 14, the curable resin composition 1 has an extinction coefficient of more than 0.01 at a design wavelength of 450 nm, and has absorption characteristics at the design wavelength. That is, in Example 6, the microstructure has an amplitude-type linear zone plate shape.

[0200] Example 7 This example was carried out under the same conditions as Example 5, except that a dielectric multilayer film was formed as an anti-reflection structure on the upper layer of the protective layer made of titanium oxide and on the surface of the substrate opposite the microstructure (hereinafter, for convenience, sometimes referred to as the "back surface"). The structure of the dielectric multilayer film is shown in Table 1 below. In Table 1, Design 1A corresponds to the dielectric multilayer film on the upper layer of the protective layer, and Design 1B corresponds to the dielectric multilayer film on the back surface side of the substrate. In Table 1, the layer located on the substrate side is listed at the top. The dielectric multilayer film was formed by ion-assisted deposition using an ion-assisted deposition apparatus (Sapio 1300, manufactured by Showa Vacuum Co., Ltd.) in which titanium oxide or silicon oxide was heated with an electron gun heating device and irradiated with oxygen ions.

[0201] Example 8 This example was carried out under the same conditions as Example 5, except that a dielectric multilayer film was formed as an anti-reflection structure on the upper layer of the protective layer made of niobium oxide and on the surface of the substrate opposite the microstructure (back surface). The structure of the dielectric multilayer film is shown in Table 2 below. In Table 2, Design 2A corresponds to the dielectric multilayer film on the upper layer of the protective layer, and Design 2B corresponds to the dielectric multilayer film on the back surface of the substrate. In Table 2, the layer located on the substrate side is listed at the top. The dielectric multilayer film was formed by ion-assisted deposition using an ion-assisted deposition apparatus (Sapio 1300, manufactured by Showa Vacuum Co., Ltd.) based on the design shown in Table 1 above.

[0202] Example 9 After producing a diffractive optical element under the same conditions as in Example 5, a dielectric multilayer film and a titanium oxide layer having a thickness of 1,187 nm were formed by ion-assisted deposition based on Design 3A shown in Table 3 below. The surface of the titanium oxide layer was then polished using a polishing device (POLI-400 manufactured by G&P Technology), washed with ultrapure water, and then dried. Details of the polishing conditions are shown below. Slurry: Slurry for acidic chemical mechanical polisher containing 3% by weight of colloidal silica and having a pH of 3.0 Slurry flow rate: 50 ml / min Pad / head rotation speed: 90 / 91 rpm Pressing pressure: 172 hPa

[0203] Thereafter, an antireflection structure was formed by ion-assisted deposition on the top layer of the titanium oxide layer and on the surface of the substrate opposite the microstructure, based on the design shown in Table 3 above. In Table 3, Design 3B corresponds to the dielectric multilayer film on the top layer of the titanium oxide layer, and Design 3C corresponds to the dielectric multilayer film on the back side of the substrate. In Table 3, the layer located on the substrate side is listed at the top. In this way, a diffractive optical element was obtained.

[0204] [Example 10] A silicone resin having a refractive index of 1.4 (a mixture of equal amounts of KE-109A and KE-109B manufactured by Shin-Etsu Chemical Co., Ltd.) was spin-coated onto a substrate on which a fine structure had been formed, and then heated in an oven at 100°C for 1 hour. This was carried out under the same conditions as in Example 5, except that a protective layer was formed on the upper layer of the fine structure using the silicone resin instead of a high refractive index material.

[0205] [Reference Example 1] In Reference Example 1, the microstructure 4 was made of quartz (silicon oxide) and was a phase-type Fresnel zone plate. The detailed execution procedure is as follows.

[0206] A 100 nm thick chromium layer was deposited on a quartz glass substrate (manufactured by Electronics and Materials Corporation, diameter 100 mm, thickness 0.525 mm, surface roughness 10 nm) using a vacuum deposition apparatus (Sapio 1300, manufactured by Showa Shinku Co., Ltd.). A resist material (NFR107, manufactured by JSR Corporation) was applied to the quartz glass substrate with this chromium layer using a spinner, and then pre-baked on a hot plate at 100°C for 180 seconds to form a substrate with a coating film. The substrate with this coating film was exposed using an i-line stepper (FPA-3030i5+, manufactured by Canon Inc.) through the following reticle. The conditions for the pattern formed on the reticle were a Fresnel zone plate shape with a focal length f = 3 mm, wavelength λ = 530 nm, and the number of diffraction structures in the above formula (1) = 3636. The diameter of the Fresnel zone plate was 7.0 mm, and the narrowest line width was 0.3 μm.

[0207] After exposure, the substrate was immersed in a resist developer (TMAH 2.38%, manufactured by Tama Chemicals Co., Ltd.) to dissolve the unexposed portions. Cl gas was sprayed onto the substrate using an etching device (CE-S, manufactured by ULVAC, Inc.) to partially etch the chromium layer, forming a chromium mask on the substrate. CHF gas was then sprayed onto the substrate to partially etch the substrate. After cleaning, Cl gas was sprayed again to remove the chromium layer, forming a quartz Fresnel zone plate-shaped microstructure on the main surface of the substrate. Because quartz does not exhibit absorption characteristics at the design wavelength, the microstructure takes the shape of a phase-type Fresnel zone plate.

[0208] Next, titanium alkoxide (PC-200, refractive index 1.8, manufactured by Matsumoto Fine Chemical Co., Ltd.) was diluted with 1-butanol to prepare a titanium alkoxide solution, and a coating film made from the titanium alkoxide solution was spin-coated onto the substrate on which the microstructure had been formed. The coating film was dried in an atmosphere at 140°C for 30 minutes, and then heated on a hot plate at 230°C for 30 minutes to harden it. This process of applying, drying, and hardening the titanium alkoxide solution was repeated multiple times to form a protective layer made of titanium alkoxide on the main surface of the substrate, covering the microstructure. This resulted in a diffractive optical element.

[0209] Comparative Example 1 This was carried out under the same conditions as in Example 1, except that no protective layer was formed on the upper layer of the microstructure.

[0210] Comparative Example 2 was carried out under the same conditions as in Example 5, except that no protective layer was formed on the upper layer of the microstructure.

[0211] Comparative Example 3 was carried out under the same conditions as in Example 4, except that a dielectric multilayer film was formed as an anti-reflection structure on the main surface of a substrate on which a microstructure was formed, without forming a protective layer on top of the microstructure. The dielectric multilayer film was formed by ion-assisted deposition using an ion-assisted deposition apparatus (Sapio 1300, manufactured by Showa Vacuum Co., Ltd.). The design of the dielectric multilayer film was the same as Design 1A on the high refractive index material side in Example 7.

[0212] In each of the above examples, the cross section of the diffractive optical element was observed using an SEM to evaluate the morphology stability of the microstructure. Figure 15 shows, as an example, a cross-sectional image of the diffractive optical element according to Example 9, observed using a scanning electron microscope (Hitachi Corporation, S-4800). The cross section of the diffractive optical element was formed using an FIB (Hitachi Corporation, FB2200), and the cross-sectional observation was performed with the diffractive optical element tilted at 20°. As shown in Figure 15, the protective layer covering the microstructure was smoothly filled up to the substrate portion, confirming that the morphology stability of the microstructure had been improved.

[0213] Furthermore, in Examples 1 to 8 and 10, it was confirmed that the protective layer covering the microstructure was smoothly filled up to the substrate portion, improving the shape stability of the microstructure, as in Example 9. That is, the diffractive optical elements according to Examples 1 to 10 were evaluated as having shape stability of "good."

[0214] On the other hand, in Comparative Examples 1 to 3, the microstructure is not covered with a protective layer. Therefore, the shape stability of the microstructure is low in all of Comparative Examples 1 to 3. In other words, the shape stability of the diffractive optical elements according to Comparative Examples 1 to 3 was evaluated as "X." Furthermore, according to Comparative Example 3, it can be seen that the shape stability is not improved even if an anti-reflection structure is formed without forming a protective layer.

[0215] Furthermore, in Reference Example 1, a protective layer was formed on the upper layer of the microstructure, which improved the morphology stability compared to Comparative Examples 1 to 3. However, in the diffractive optical element according to Reference Example 1, many areas close to the substrate were found to be unfilled with the protective layer. This is thought to be because in Reference Example 1, the microstructure made of silica was formed by etching through a mask, as described above with reference to FIG. 12 .

[0216] That is, it is considered that the shape stability of Reference Example 1 was improved compared to Comparative Examples 1 to 3, but it was found that the shape stability was clearly inferior compared to Examples 1 to 10. Therefore, the shape stability of Reference Example 1 was evaluated as "△".

[0217] The experimental results for each example are shown in Table 4 below.

[0218] As described above, it has been confirmed that a diffractive optical element with improved shape stability can be obtained by forming a microstructure from a curable resin composition and covering the microstructure with a protective layer.

[0219] Furthermore, according to Examples 7 to 9, it was confirmed that after the fine structure is covered with a protective layer, an anti-reflection structure can be formed on the protective layer.

[0220] Next, in order to examine the diffractive optical elements according to the examples in more detail, the following evaluations were carried out.

[0221] <Light-Concentration Evaluation> The light-focusing performance of the diffractive optical element according to the present invention was evaluated by placing the diffractive optical element between the subject and the camera with the DAYLIGHT light source turned on in a standard light source device (Macbeth Judge II) manufactured by Sakata Inx Corporation. A "good" was given if the subject was imaged according to the lens formula, and an "unclear" was given if it was not. A ColorChecker Classic manufactured by Calibrite LCC was used as the subject. When the design wavelength λ of the diffractive optical element was less than 675 nm, a smartphone (iPhone 15 Pro Max manufactured by Apple Inc.) was used as the camera. When the design wavelength λ of the diffractive optical element was 675 nm or greater, a visible-near-infrared camera (ABA-013VIR-GE manufactured by Aval Data) equipped with a C-series fixed-focus lens (focal length 35 mm, #23-223) manufactured by Edmund Optics was used.

[0222] <Pencil Hardness> A detailed evaluation of the cut resistance of the protective layer according to the present invention was performed in accordance with JIS K5600, except that a load of 300 g was used instead of 750 g. After the evaluation, the pencil hardness at which no scratches, plastic deformation, or cohesive failure were observed by visual inspection was taken as the pencil hardness of the sample.

[0223] <Surface Roughness Evaluation> The surface roughness was evaluated using a white light interferometer (ZYGO Corporation, ZYGO NewView NX2). The surface roughness Ra was determined by measuring the surface of the diffractive optical element using a 5.5x lens, and the arithmetic mean roughness obtained from the measured values ​​after removing the cylindrical deflection of the observation surface.

[0224] <Reflectance Measurement> For evaluation according to the present invention, for diffractive optical elements with a diameter of 1.5 mm or more, the 5° reflectance at the design wavelength λ of the diffractive optical element was measured using an absolute reflectance measurement unit VAR-7030 connected to a spectrophotometer V7300 manufactured by JASCO Corporation. For diffractive optical elements with a diameter of 1.5 mm or less, the reflectance was measured using a microscopic ultraviolet-visible-near-infrared spectrophotometer (MSV-370) manufactured by JASCO Corporation.

[0225] <Thickness Measurement> To evaluate the thickness of the diffractive optical element, the thickness was measured using a digital length measuring machine (Litematic VL-50) manufactured by Mitutoyo Corporation.

[0226] The diffractive optical element according to Example 1 had a surface roughness Ra of 75 nm and a pencil hardness of H. Furthermore, when the light-gathering ability was evaluated, it was rated as "good," confirming that it functioned as a lens. Furthermore, when the reflectance was measured, the reflectance at a wavelength λ=850 nm was 10%. The thickness was evaluated and found to be 0.71 mm.

[0227] The diffractive optical element according to Example 2 had a surface roughness Ra of 95 nm and a pencil hardness of 3B. Furthermore, when the light-gathering ability was evaluated, it was rated as "good," confirming that it functioned as a lens. Furthermore, when the reflectance was measured, the reflectance at a wavelength λ=650 nm was 12%. The thickness was evaluated and found to be 0.71 mm.

[0228] The surface roughness Ra of the diffractive optical element according to Example 3 was 38 nm, and the pencil hardness was 5B. Furthermore, when the light-gathering ability was evaluated, it was rated as "Good," and it was confirmed that it functioned as a lens. Furthermore, when the reflectance was measured, the reflectance at a wavelength λ=650 nm was 8%. The thickness was evaluated and found to be 0.71 mm.

[0229] The diffractive optical element according to Example 4 had a surface roughness Ra of 33 nm and a pencil hardness of H. As an example, an image obtained in the light-gathering evaluation of Example 4 is shown in FIG. 16. In FIG. 16, the position 20 of the diffractive optical element relative to the object 21 is indicated by a dashed line. As shown in FIG. 16, the light-gathering evaluation was performed, resulting in an evaluation of "good," confirming that the element functions as a lens. Furthermore, when the reflectance was measured, the reflectance at a wavelength λ=550 nm was 10%. The thickness was evaluated and found to be 0.71 mm.

[0230] The diffractive optical element according to Example 5 had a surface roughness Ra of 50 nm and a pencil hardness of 2B. Furthermore, a light-gathering evaluation was performed, resulting in a rating of "Good," confirming that the element functions as a lens. Furthermore, a reflectance measurement was performed, resulting in a reflectance of 7% at a wavelength λ of 940 nm. A thickness evaluation was performed, resulting in a thickness of 0.21 mm.

[0231] The diffractive optical element according to Example 6 had a surface roughness Ra of 50 nm and a pencil hardness of B. A light-gathering evaluation was performed, resulting in a rating of "Good," confirming that the element functioned as a lens. Furthermore, a reflectance measurement was performed, resulting in a reflectance of 7% at a wavelength λ of 450 nm. A thickness evaluation was performed, resulting in a thickness of 0.71 mm.

[0232] The diffractive optical element according to Example 7 had a surface roughness Ra of 30 nm and a pencil hardness of H. Furthermore, when the light-gathering ability was evaluated, it was rated as "good," confirming that it functioned as a lens. Furthermore, when the reflectance was measured, the reflectance at a wavelength λ of 940 nm was 4%. The thickness was evaluated and found to be 0.71 mm.

[0233] The surface roughness Ra of the diffractive optical element according to Example 8 was 35 nm, and the pencil hardness was 4B. Furthermore, when the light-gathering ability was evaluated, it was rated as "Good," confirming that it functioned as a lens. Furthermore, when the reflectance was measured, the reflectance at a wavelength λ=940 nm was 3%. The thickness was evaluated and found to be 0.71 mm.

[0234] The diffractive optical element according to Example 9 had a surface roughness of 10 nm and a pencil hardness of H. Furthermore, a light-gathering evaluation was performed, resulting in a rating of "Good," confirming that the element functioned as a lens. Furthermore, a reflectance measurement was performed, resulting in a reflectance of 2% at a wavelength λ=940 nm. A thickness evaluation was performed, resulting in a thickness of 0.71 mm.

[0235] The surface roughness Ra of the diffractive optical element according to Example 10 was 50 nm. An image obtained in the light-gathering evaluation of Example 10 is shown in FIG. 17 . In FIG. 17 , as in FIG. 16 , the position 20 of the diffractive optical element relative to the subject 21 is indicated by a dashed line. As shown in FIG. 17 , the diffractive optical element was positioned and a light-gathering evaluation was performed, but the lens function could not be confirmed, resulting in an evaluation of "x." Reflectance measurement revealed a reflectance of 6% at a wavelength λ=940 nm. Thickness evaluation revealed a value of 0.81 mm. The pencil hardness was found to be less than 6B.

[0236] The diffractive optical element according to Reference Example 1 had a surface roughness Ra of 225 nm and a pencil hardness of less than 6B. Furthermore, a light-gathering evaluation was performed, resulting in a rating of "Good," confirming that the element functioned as a lens. Furthermore, a reflectance measurement was performed, resulting in a reflectance of 18% at a wavelength λ=530 nm. A thickness evaluation was performed, resulting in a thickness of 0.52 mm.

[0237] The surface roughness of the diffractive optical element according to Comparative Example 1 was 450 nm. The light-gathering ability was evaluated as "good," confirming that it functioned as a lens. Furthermore, the reflectance was measured, and the reflectance at a wavelength λ of 850 nm was 8%. The thickness was evaluated and found to be 0.71 mm.

[0238] The surface roughness of the diffractive optical element according to Comparative Example 2 was 250 nm. The light-gathering ability was evaluated as "Good," confirming that it functioned as a lens. Furthermore, the reflectance was measured, and the reflectance at a wavelength λ of 940 nm was 8%. The thickness was evaluated and found to be 0.71 mm.

[0239] The surface roughness of the diffractive optical element according to Comparative Example 3 was 230 nm. The light-gathering ability was evaluated as "good," confirming that it functioned as a lens. Furthermore, the reflectance was measured, and the reflectance at a wavelength λ of 530 nm was 5%. The thickness was evaluated and found to be 0.71 mm.

[0240] The evaluation results for each example are shown in Table 5 below.

[0241] As shown in Tables 4 and 5, in Examples 1 to 9, the shape stability of the microstructure was improved, and the pencil hardness of the diffractive optical element was 5B or higher. If the pencil hardness of the diffractive optical element is higher than 6B, it becomes easier to avoid cuts during the transfer process, which is a more preferable result. On the other hand, in Example 10, the pencil hardness was less than 6B. This is thought to be due to the result depending on the pencil hardness of the material constituting the protective layer. In view of this, it is preferable that the constituent material of the protective layer is selected from the group consisting of niobium oxide, zirconium oxide, tantalum oxide, titanium oxide, and hafnium oxide.

[0242] Since the pencil hardness of the protective layer is considered to depend on the material constituting the protective layer, it is considered that the pencil hardness of the protective layer can be improved by selecting a material with high pencil hardness. As a specific example, it is more preferable that the material constituting the protective layer is a material with a pencil hardness of 4H or more. Furthermore, the pencil hardness of the material constituting the protective layer is more preferably 5H or more, particularly preferably 8H or more, and most preferably 9H or more.

[0243] In Reference Example 1, even though the microstructure was covered with a protective layer, the pencil hardness was less than 6 B. This is presumably because, when the microstructure was formed, etching caused the microstructure to expand as it moved away from the substrate (see FIG. 12 ), resulting in insufficient filling of the protective layer in the region close to the substrate.

[0244] According to Table 5, the evaluation result of the light-collecting ability of Example 10 was "X". This is thought to be because the difference in refractive index between the microstructure and the protective layer was small, resulting in a phase difference of less than 1 / 4π. In other words, in a diffractive optical element exhibiting a phase type, it is preferable that the protective layer be made of a high-refractive index material having a refractive index higher than that of the curable resin composition. More specifically, considering the refractive index (1.8) of the titanium alkoxide used in Reference Example 1, the refractive index of the high-refractive index material is preferably 1.85 or higher.

[0245] In Examples 1 to 6 and Example 10, the surface roughness Ra corresponds to the surface roughness of the protective layer. Comparing these with Comparative Examples 1 and 2, it can be seen that the surface roughness Ra of the diffractive optical element can be reduced by forming a protective layer. Specifically, while the surface roughness of the protective layer in Comparative Examples 1 and 2 is greater than 200 nm, the surface roughness Ra of the protective layer in Examples 1 to 6 and Example 10 is 200 nm or less, even below 100 nm. In other words, it can be seen that forming a protective layer makes it easier to form an anti-reflection structure. This is consistent with the fact that the surface roughness of the diffractive optical element, i.e., the surface roughness of the anti-reflection structure, is low in Examples 7 to 9.

[0246] Furthermore, in view of Examples 7 to 9, it can be seen that the reflectance is further reduced when the diffractive optical element has an anti-reflection structure. Therefore, it is preferable for the diffractive optical element to have an anti-reflection structure on the upper layer of the protective layer or on the surface of the substrate opposite the microstructure. Furthermore, Comparative Example 3 shows that when an anti-reflection structure is formed directly on the microstructure, the surface roughness Ra of the diffractive optical element becomes greater than 200 nm. In other words, by forming a protective layer, it is possible to easily form an anti-reflection structure on the surface of the substrate facing the microstructure.

[0247] Furthermore, cut resistance, as exemplified by pencil hardness evaluation, is caused by stress concentration originating from the surface unevenness structure catching, resulting in chipping. Particles contained in pencils are often 1 μm or larger, and by setting the surface roughness Ra, which is less than one-fourth of that, to 200 nm or less, pencil catching is suppressed, enabling high pencil hardness to be achieved. The surface roughness Ra is more preferably 150 nm or less, and particularly preferably 100 nm or less.

[0248] In the above examples, the microstructure was made of the curable resin composition 1. However, considering that the protective layer covering the microstructure can improve the morphological stability of the microstructure in the diffractive optical element, it can be said that the material constituting the microstructure is not limited to the above. In other words, even when the microstructure is made of another curable resin composition, it can be understood that the morphological stability of the diffractive optical element can be improved by forming a protective layer covering the microstructure.

[0249] The diffractive optical element of the present invention is a thin diffractive optical element that combines high light-collecting performance and dimensional stability, and more preferably, high cut resistance and is highly suitable for mass production, and can be suitably used as a diffractive optical lens for imaging, an optical lens for an optical sensor, an optical lens for a display, or an optical lens for optical communication.

[0250] 1: Diffractive optical element 3: Substrate 3a, 3b: Main surface 4: Microstructure 6: Transparent region 8: Protective layer 10: Protective layer 12: Anti-reflection structure 20: Position of diffractive optical element 21, 22: Subject

Claims

1. A diffractive optical element that diffracts incident light, comprising: a substrate that transmits the incident light; a microstructure made of a curable resin composition that forms irregularities on a first main surface side of the substrate to form a diffraction pattern that diffracts the incident light; and a first protective layer that is transparent to the incident light and covers the microstructure, wherein the microstructure exhibits any one of a Fresnel zone plate shape, a linear zone plate shape, a fractal zone plate shape, and a photon sieve plate shape when viewed in a direction perpendicular to the first main surface.

2. The diffractive optical element according to claim 1, further comprising an anti-reflection structure formed on the first protective layer on the first main surface side of the substrate.

3. The diffractive optical element according to claim 2, wherein the anti-reflection structure is a dielectric multilayer film.

4. The diffractive optical element according to any one of claims 1 to 3, wherein the microstructure exhibits one of a phase-type Fresnel zone plate shape, a phase-type linear zone plate shape, a phase-type fractal zone plate shape, and a phase-type photon sieve plate shape.

5. The diffractive optical element according to claim 4, wherein the first protective layer is made of a high refractive index material having a refractive index higher than that of the curable resin composition.

6. The diffractive optical element according to claim 5, wherein the curable resin composition has a refractive index of less than 1.85, and the high refractive index material has a refractive index of 1.85 or more.

7. The diffractive optical element according to claim 5, wherein the high refractive index material comprises one or more materials selected from the group consisting of titanium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silicon, germanium, gallium nitride, gallium phosphide, zinc sulfide, zinc telluride, lead zirconate titanate, and barium titanate.

8. The diffractive optical element according to any one of claims 1 to 3, wherein the microstructure exhibits any one of an amplitude type Fresnel zone plate shape, an amplitude type linear zone plate shape, an amplitude type fractal zone plate shape, and an amplitude type photon sieve plate shape.

9. A diffractive optical element according to any one of claims 1 to 3, wherein the microstructure has a shape that tapers with increasing distance from the first main surface of the substrate.

10. A diffractive optical element according to any one of claims 1 to 3, characterized in that the finest line width of the microstructure is 0.2 µm or more and 5 µm or less.

11. A diffractive optical element according to any one of claims 1 to 3, characterized in that the surface roughness is 200 nm or less.

12. A diffractive optical element according to any one of claims 1 to 3, characterized in that the total thickness is 2 mm or less.

13. A diffractive optical element according to any one of claims 1 to 3, characterized in that the F-number, obtained by dividing the focal length f of the diffraction pattern by the diameter D of the diffraction pattern, is within the range of 0.2 to 4.

0.

14. A diffractive optical element according to any one of claims 1 to 3, characterized in that the pencil hardness is 5B or more.

15. A curable resin composition for forming the microstructure of claim 1.

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