Metasurface structure and mold

Abstract

To provide a metasurface structure capable of accurately controlling the state of incident light by suppressing defective formation of nanopillars, and to provide a mold for transferring the metasurface structure.SOLUTION: A metasurface structure of a metalens 30 comprises multiple nanopillars 32 arranged on a support surface 31S of a substrate 31. The multiple nanopillars 32 include multiple first nanopillars 33 arranged in a first area 30A and multiple second nanopillars 34 arranged in a ring-like second area 30B surrounding the first area 30A. Each first nanopillar 33 shifts the phase of light having a specific wavelength according to the position of the first nanopillar 33 on the support surface 31S.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present disclosure relates to a metasurface structure and a mold for forming the metasurface structure.

Background Art

[0002] In recent years, there has been an increasing interest in metasurfaces having nanopillars finer than the wavelength of light. An example of a metasurface includes a plurality of nanopillars (see, for example, Patent Document 1). The nanopillars are dielectrics that transmit light of a predetermined wavelength. In a metasurface, by adjusting the material, size, orientation, etc. of the nanopillars, for example, the state of light incident on the metasurface such as the phase and amplitude of the light, or the polarization separated by the metasurface can be controlled.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] From the viewpoint of more accurately controlling the state of light using a metasurface, in the manufacturing process of the metasurface, suppression of defective formation of nanopillars is required. In other words, by suppressing defective formation of nanopillars, it is desired to more accurately control the state of light incident on the metasurface.

Means for Solving the Problems

[0005] The meta-surface structure for solving the above problems is a meta-surface structure including a plurality of nanopillars arranged on a support surface of a substrate, where the plurality of nanopillars include a plurality of first nanopillars arranged in a first region and a plurality of second nanopillars arranged in an annular second region surrounding the first region, and each first nanopillar shifts the phase of light having a specific wavelength according to the position where the first nanopillar is arranged within the support surface.

[0006] When forming the nanopillars on the substrate, if the pattern density indicating the density of the nanopillars around the nanopillars to be formed becomes small, poor formation of the nanopillars is likely to occur. If the second nanopillars in the second region are not formed, the pattern density becomes small near the outer edge of the first region. As a result, poor formation of the first nanopillars is likely to occur near the outer edge of the first region. In this regard, according to the above configuration, the second nanopillars arranged in the second region can suppress the poor formation of the first nanopillars accompanying the abrupt change in the pattern density near the outer edge of the first region. Thereby, the state of the light incident on the plurality of first nanopillars can be controlled more precisely.

[0007] In the above meta-surface structure, when the ratio of the area occupied by the first nanopillars per unit area in the first region is defined as the first pattern density and the ratio of the area occupied by the second nanopillars per unit area in the second region is defined as the second pattern density, it is preferable that the ratio of the second pattern density to the first pattern density is 0.5 or more and 2.0 or less. According to the above configuration, the abrupt change in the pattern density near the outer edge of the first region can be preferably suppressed by the second nanopillars arranged in the second region.

[0008] In the above metasurface structure, in the second nanopillar, it is preferable that the effective refractive index changes in the height direction. According to the above configuration, by changing the effective refractive index of the second nanopillar in the height direction, it functions as a moth-eye structure that minimizes the reflection and refraction of incident light. As a result, it is possible to prevent light that has deviated from the first region from becoming stray light by being reflected or refracted by the second nanopillar.

[0009] In the above metasurface structure, the first nanopillar preferably has a rectangular parallelepiped shape. If there is a distribution in the effective refractive index in the height direction of the first nanopillar, there is a possibility that light incident on the first nanopillar will be less likely to transmit. In this regard, if the first nanopillar has a rectangular parallelepiped shape, since it has a uniform effective refractive index in the height direction, it is possible to prevent the shape of the first nanopillar from affecting the transmittance of incident light.

[0010] In the above metasurface structure, it is preferable that the amount of phase shift of the light in each first nanopillar is defined so that the plurality of first nanopillars function as a lens. According to the above configuration, for example, a structure including a metasurface structure can be made to function as a metalens that condenses light incident on a plurality of nanopillars to a single point.

[0011] In the above metasurface structure, the ratio of the second average volume of the second nanopillars in the second region to the first average volume of the first nanopillars in the first region is preferably 0.5 or more and 2.0 or less. According to the above configuration, when electron beam lithography is used for pattern formation of the nanopillars, the average exposure amount per one first nanopillar in the first region and the average exposure amount per one second nanopillar in the second region can be made equal. As a result, the influence of the proximity effect in electron beam lithography when forming the pattern of the nanopillars can be suitably reduced.

[0012] In the above metasurface structure, the width of the second nanopillar may be larger than the width of the first nanopillar. According to the above configuration, for example, formation defects such as pattern collapse in the second nanopillar can be preferably suppressed.

[0013] The mold for solving the above problems includes a plurality of nanoholes for transferring the plurality of nanopillars in the above metasurface structure to the substrate. The plurality of nanoholes are arranged in a third region, and include a plurality of first nanoholes for transferring the plurality of first nanopillars to the substrate, and a plurality of second nanoholes arranged in an annular fourth region surrounding the third region for transferring the plurality of second nanopillars to the substrate.

[0014] According to the above configuration, in the manufacturing process of the mold, formation defects of the first nanoholes associated with a sharp change in pattern density near the outer edge of the first region can be suppressed. Thereby, formation defects of the first nanopillars caused by formation defects of the first nanoholes can be suppressed, so that a plurality of first nanopillars that can more accurately control the state of the incident light can be formed. Further, in the transfer process of transferring a plurality of nanopillars to the substrate, formation defects such as filling defects and residual film thickness changes caused by a sharp change in pattern density can be suppressed.

Effect of the Invention

[0015] According to the present disclosure, the state of light incident on the metasurface structure can be more accurately controlled.

Brief Description of the Drawings

[0016]

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Embodiments for Carrying Out the Invention

[0017] Hereinafter, with reference to the drawings, the first embodiment and the second embodiment of the metasurface structure and the mold for forming the metasurface structure will be described. In the following first embodiment and second embodiment, a metasurface lens having a metasurface structure will be described. The metasurface lens has light transmissivity for transmitting light of a specific wavelength to be controlled. The light transmissive metasurface lens controls, for example, the state of light such as the phase, amplitude, and polarization of the light transmitted through the metasurface lens. Note that the metasurface lens may have light reflectivity for reflecting light of a specific wavelength. The light reflective metasurface lens controls, for example, the state of light such as the phase, amplitude, and polarization of the light reflected by the metasurface lens.

[0018] [First Embodiment] Referring to FIGS. 1 to 6, the first embodiment will be described. As shown in FIG. 1, the metasurface lens 10 of the first embodiment includes a substrate 11 and a plurality of nanopillars 12. The substrate 11 and the plurality of nanopillars 12 have light transmissibility that transmits light having a wavelength to be controlled. The metasurface lens 10 has, as an example, a function of condensing light having a wavelength to be controlled to a single point.

[0019] The substrate 11 is, for example, made of glass or resin, or may be composed of a plurality of layers combining them. The substrate 11 includes a support surface 11S that supports the plurality of nanopillars 12.

[0020] In the metasurface lens 10, the state of light having a specific wavelength to be controlled is controlled by the nanopillars 12. In other words, the nanosurface structure of the metasurface lens 10 includes a plurality of nanopillars 12. The nanopillars 12 of the first embodiment deflect light having a specific wavelength to be controlled according to the position of each nanopillar 12 within the support surface 11S.

[0021] The nanopillars 12 are made of a dielectric having an arbitrary refractive index greater than 1. The material constituting the nanopillars 12 may be a silicon-based material such as single-crystalline silicon, polycrystalline silicon, amorphous silicon, or an inorganic material such as titanium dioxide, or a resin material such as a polymer material that functions as a dielectric.

[0022] As shown in FIG. 2, in the metasurface lens 10, the plurality of nanopillars 12 are periodically arranged along the respective directions of the first direction D1 and the second direction D2. The first direction D1 and the second direction D2 are directions orthogonal to each other.

[0023] For example, the plurality of nanopillars 12 are arranged to have a predetermined orientation and a predetermined pitch L along each of the first direction D1 and the second direction D2. The pitch L refers to the distance between the centers of adjacent nanopillars 12 in each of the first direction D1 and the second direction D2. For example, the plurality of nanopillars 12 are arranged in a square pattern with a constant pitch L. The pitch L is, for example, 100 nm or more and 10 μm or less. Note that the pitch L and the orientation of each nanopillar 12 do not have to be constant, and may be different from each other in each of the first direction D1 and the second direction D2.

[0024] As shown in FIG. 1, the nanopillar 12 has a rectangular parallelepiped shape. The plurality of nanopillars 12 include nanopillars 12 having different heights H and widths W. The nanopillar 12 is configured such that the smaller the width W, the lower the height H. In other words, the plurality of nanopillars 12 include nanopillars 12 having different heights H and volumes. The nanopillar 12 is configured such that the smaller the volume, the lower the height H.

[0025] Note that the width W refers to the width of the nanopillar 12 in the first direction D1. Also, the nanopillar 12 has the same width W as in the first direction D1 in the second direction D2. That is, the nanopillar 12 is configured such that the width in the second direction D2 is equal to the width W in the first direction D1.

[0026] The width W of the nanopillar 12 is, as an example, the average value of the widths between the upper end and the lower end of the nanopillar 12. The width W of the nanopillar 12 is, as an example, the average value of the width at the upper end and the width at the lower end of the nanopillar 12. The width W of the nanopillar 12 may be, as an example, the maximum value of the widths between the upper end and the lower end of the nanopillar 12. The width W of the nanopillar 12 is equal to or smaller than a specific wavelength of the light to be controlled.

[0027] The plurality of nanopillars 12 are arranged such that, for example, in each of the first direction D1 and the second direction D2, the height H and the width W vary periodically according to the position where each nanopillar 12 is disposed within the support surface 11S. Note that the plurality of nanopillars 12 are also periodically arranged in the second direction D2.

[0028] [Method for manufacturing the metasurface 10] An example of the method for manufacturing the metasurface 10 is to form a plurality of nanopillars 12 made of an inorganic material on the support surface 11S of the substrate 11 by combining a plurality of processing processes such as electron beam lithography, dry etching, and ion beam processing. An example of the method for manufacturing the metasurface 10 is to form the nanopillars 12 by depositing or lift-off an inorganic material by physical or chemical vapor deposition or atomic layer deposition (ALD) on the pattern formed on the support surface 11S of the substrate 11 using electron beam lithography. An example of the method for manufacturing the metasurface 10 is to form the nanopillars 12 by transferring a resin that functions as a dielectric onto the support surface 11S of the substrate 11 using a mold in which a nanohole pattern with the nanopillars 12 inverted is formed by dry etching, electroforming, or the like.

[0029] FIG. 3 shows a mold 20 for transferring the nanopillars 12 made of a resin onto the substrate 11. The mold 20 includes a base 21. The material constituting the base 21 is, for example, an inorganic material such as silicon or a metal. The base 21 includes a first surface 21S. A plurality of nanoholes 22 are formed in the first surface 21S of the base 21.

[0030] The mold 20 transfers the resin filled in the nano-holes 22 to the support surface 11S of the substrate 11. Therefore, the nano-holes 22 have a shape obtained by inverting the plurality of nanopillars 12 provided in the metalens 10. That is, the plurality of nano-holes 22 include nano-holes 22 having different widths and depths. Each nano-hole 22 has a shallower depth from the first surface 21S as its width is smaller. In other words, the plurality of nano-holes 22 include nano-holes 22 having different volumes and depths. Each nano-hole 22 has a shallower depth from the first surface 21S as its volume is smaller.

[0031] The nano-holes 22 are formed, for example, by performing dry etching on the first surface 21S of the base 21. When dry etching is used as the manufacturing process of the mold 20, the depth of the nano-holes 22 can be changed according to their width by utilizing the microloading effect. Further, the nano-holes 22 may be formed by performing electroforming (electrocasting) on nanopillar-shaped resist patterns having different heights formed by electron beam lithography. When electron beam lithography is used as the manufacturing process of the mold 20, the height of the resist pattern can be changed according to the width (pillar width) of the resist pattern by utilizing the difference in development speed due to the exposure amount.

[0032] [Light control mode in the metalens 10] With reference to FIGS. 4 to 6, the light control mode in the metalens 10 will be described. The metalens 10 refracts the light incident on each nanopillar 12 to condense the light transmitted through the metalens 10 at one point (focus). That is, each nanopillar 12 shifts the phase of light having a specific wavelength to be controlled according to the position where the nanopillar 12 is arranged within the support surface 11S.

[0033] For example, in the metalens 10, the first phase shift amount φ1 required for each nanopillar 12 is given by the formula (1) shown in FIG. 4. In the formula (1), f represents the designed focal length of the metalens 10. λ dis the wavelength of the light to be controlled. x and y represent the coordinates of each nanopillar 12 when the intersection point of the perpendicular line drawn from the focus to the metalens 10 and the metalens 10 is taken as the origin. For example, x represents the distance in the first direction D1 from the origin to the nanopillar 12. y represents the distance in the second direction D2 from the origin to the nanopillar 12.

[0034] Also, the second phase shift amount φ2 generated in each nanopillar 12 is related to the height H of each nanopillar 12, the effective refractive index n′ in each nanopillar 12, and the wavelength λ which is the wavelength of the light to be controlled d and is given by the formula (2) shown in FIG. 5. The effective refractive index n′ refers to a value obtained by averaging the refractive index of the unit space considering parameters such as the refractive index and thickness in each medium when there are a plurality of media with different refractive indices in a unit space of a predetermined size. In each of the first direction D1 and the second direction D2, the width of the unit space is equal to the pitch L. The height of the unit space is equal to the height H of the nanopillar 12. The unit space encloses one nanopillar 12. Note that the plurality of media in the unit space refer to air and the nanopillar 12.

[0035] The effective refractive index n′ is given by the formula (3) shown in FIG. 6 using the refractive index n of the material constituting the nanopillar 12, the width W of each nanopillar 12, and the pitch L at which the plurality of nanopillars 12 are arranged.

[0036] Therefore, in each nanopillar 12, in order to focus the light transmitted through each nanopillar 12 at the focus, the shape of the nanopillar 12 is determined according to the position and material of the nanopillar 12 so that the second phase shift amount φ2 becomes equal to the first phase shift amount φ1. In other words, the second phase shift amount φ2 in each nanopillar 12 is defined so that the plurality of nanopillars 12 function as a lens.

[0037] Specifically, in a plurality of nanopillars 12 having a predetermined pitch L and refractive index n, in order to focus the light transmitted through the metalens 10 at the focus, it is necessary to adjust the second phase shift amount φ2 in the range of 0 degrees or more and 360 degrees or less according to the position of the nanopillar 12.

[0038] For example, in Formula (3), the value of W / L representing the ratio of the width W of the nanopillar 12 to the pitch L can be adjusted within the range of 0.2 or more and 0.8 or less by changing the width W of the nanopillar 12. In Formula (3), the value of n representing the refractive index of the material is determined according to the material constituting the nanopillar 12. Therefore, in the second phase shift amount φ2 represented by Formula (2), in order to realize an adjustment range of 0 degrees or more and 360 degrees or less, it is preferable to make the height H of the nanopillar 12 as large as possible.

[0039] On the other hand, in each nanopillar 12, when the aspect ratio (H / W) representing the ratio of the height H to the width W becomes excessively large, it becomes difficult to stably pattern the nanopillar 12 in the manufacturing process of the metalens 10. For example, when forming the nanopillar 12 by dry etching or lift-off, an increase in the aspect ratio of the resist pattern causes formation defects such as pattern collapse. In the case of the transfer process, the larger the aspect ratio, the more likely it is to cause insufficient filling of the resin into the mold 20 and insufficient strength of the nanopillar 12.

[0040] Therefore, the nanopillar 12 of the first embodiment is configured such that the height H decreases as the volume and the width W become smaller, and the height H increases as the volume and the width W become larger. Thereby, it is possible to suppress the aspect ratio of each nanopillar 12 from becoming excessively large.

[0041] The aspect ratio (H / W) of each nanopillar 12 is preferably less than 3.5, more preferably 3.1 or less, for example. By setting the aspect ratio within the above range, it is possible to suitably suppress formation defects of the nanopillar 12 while ensuring the adjustment range of the second phase shift amount φ2.

[0042] Further, it is preferable that the nanopillar 12 is configured such that the aspect ratio becomes smaller as the height H becomes higher. Thereby, the manufacturing of the metalens 10 and the manufacturing of the mold 20 for manufacturing the metalens 10 become easier.

[0043] [Effects of the First Embodiment] (1-1) In the metalens 10, the plurality of nanopillars 12 are configured such that the smaller the width W and volume are, the lower the height H becomes. Thereby, for example, while suppressing an excessive increase in the aspect ratio of the nanopillars 12 compared to a configuration where the height H of the nanopillars 12 is constant, a range in which the second phase shift amount φ2 can be adjusted can be ensured. Therefore, since the formation defect of the plurality of nanopillars 12 can be suppressed, the state of light incident on the plurality of nanopillars 12 can be controlled more accurately. Further, in the configuration of the first embodiment, even when the refractive index n is relatively low, a range in which the second phase shift amount φ2 can be adjusted can be ensured, so that the options for the material constituting the nanopillars 12 can be expanded.

[0044] (1-2) The nanopillars 12 of the first embodiment have a rectangular parallelepiped shape. If there is a distribution in the effective refractive index in the height direction of the nanopillars 12, light incident on the nanopillars 12 may be less likely to transmit. In this regard, if the nanopillars 12 are rectangular parallelepiped-shaped, since they have a uniform effective refractive index in the height direction, it is possible to prevent the shape of the nanopillars 12 from affecting the transmittance of incident light.

[0045] (1-3) By setting the aspect ratio (H / W) of each nanopillar 12 to less than 3.5, preferably 3.1 or less, it is possible to suitably achieve both ensuring the adjustment range of the second phase shift amount φ2 and suppressing the formation defect of the nanopillars 12.

[0046] (1-4) The second phase shift amount φ2 in each nanopillar 12 is defined such that the plurality of nanopillars 12 function as a lens. Thereby, for example, in the case of the metalens 10 of the first embodiment, it is possible to function as a lens that condenses light incident on the plurality of nanopillars 12 to a single point.

[0047] (1-5) The mold 20 includes a plurality of nano-holes 22 having different widths and depths. According to such a mold 20, a plurality of nanopillars 12 having different heights H and widths W can be formed at once. As a manufacturing process of the mold 20, by using dry etching, processing such that the depth becomes deeper according to the width of the nano-hole 22 can be easily performed by the microloading effect.

[0048] [Modification Example of the First Embodiment] Note that the above first embodiment can be implemented with the following modifications. Also, each modification example can be combined within a technically non - conflicting range.

[0049] · In the first embodiment, the metalens 10 having a metasurface structure was described. That is, an example of a configuration in which a plurality of nanopillars 12 included in the metasurface structure function as a lens was shown. However, the present invention is not limited to this. For example, by providing a plurality of nanopillars 12 on a reflector, the plurality of nanopillars 12 may function in a form other than a lens so as to reflect light having a specific wavelength in an arbitrary direction.

[0050] · The aspect ratio of each nanopillar 12 is not limited to a range of less than 3.5. For example, if there is no problem in the manufacturing process of the metalens 10, nanopillars 12 having an aspect ratio of 3.5 or more may be included. Also, if the adjustment range of the second phase shift amount φ2 can be ensured, nanopillars 12 having an aspect ratio of 1 or less may be included.

[0051] ·The shape of the nanopillar 12 is not limited to a rectangular parallelepiped shape and may be, for example, a cylindrical shape. When the nanopillar 12 is cylindrical, the diameter of the cylindrical shape corresponds to the width W. Even in this case, since the nanopillar 12 has a uniform effective refractive index in the height direction, it is possible to prevent the shape of the nanopillar 12 from affecting the transmissivity of incident light. Further, the shape of the nanopillar 12 may be any shape other than a rectangular parallelepiped shape or a cylindrical shape. For example, the shape of the nanopillar 12 may be any quadrangular prism such as a frustum of a square pyramid, or a frustum of a cone. Note that similar changes are possible in the shape of the nanohole 22.

[0052] ·In the above embodiment, in the nanopillar 12, a configuration having the same width W in the first direction D1 and the second direction D2 is illustrated, but the width in the second direction D2 may be different from the width W in the first direction D1. In this case, in each nanopillar 12, at least one of the first aspect ratio representing the ratio of the height H to the width W in the first direction D1 and the second aspect ratio representing the ratio of the height H to the width in the second direction D2 is preferably less than 3.5, more preferably 3.1 or less. Further, it is more preferable that both the first aspect ratio and the second aspect ratio are less than 3.5, more preferably 3.1 or less.

[0053] ·For example, even in a plurality of nanopillars 12 having the same width W, they may be configured to have different heights H. Also, among the two nanopillars 12, the height H of the nanopillar 12 with the larger width W may be made lower than the height H of the nanopillar 12 with the smaller width W. In this case, the smaller the volume of the nanopillar 12, the lower the height H may be configured. Note that similar changes are possible in a plurality of nanoholes 22.

[0054] ·For example, even among a plurality of nanopillars 12 having the same volume, they may be configured to have different heights H. For example, assume a state where a rectangular parallelepiped-shaped nanopillar 12 having a square shape in top view and a cylindrical nanopillar 12 are mixed, and the volume of the rectangular parallelepiped is equal to the volume of the cylinder, or the volume of the cylinder is larger than the volume of the rectangular parallelepiped. In this case, after regarding the radius of the cylindrical shape as the width W, the width W (diameter) and height H of the cylindrical nanopillar 12 can be made larger than the width W and height H of the rectangular parallelepiped-shaped nanopillar 12. Similar changes are possible for the plurality of nanoholes 22.

[0055] ·In the metalens 10, the arrangement of the plurality of nanopillars 12 may be appropriately determined according to the use of the metalens 10. Further, the plurality of nanopillars 12 are not limited to a configuration in which they are arranged in a square pattern in the first direction D1 and the second direction D2, and for example, they may be arranged in a radial direction around an arbitrary point on the substrate 11. Further, the pitch L and the orientation of each nanopillar 12 do not have to be constant.

[0056] [Examples and Comparative Examples of the First Embodiment] Examples 1 and Comparative Example 1 of the first embodiment will be described with reference to FIGS. 7 to 9. Note that the following examples do not limit the configuration of the present disclosure.

[0057] [Example 1: Fabrication of Mold] In Example 1, a metalens 10 including nanopillars 12 having different heights H and widths W was fabricated. First, a mold 20 for transferring to the substrate 11 was fabricated.

[0058] First, an electron beam positive resist material was coated on a silicon wafer with a diameter of 200 mm using a spin coater under the conditions of a rotation speed of 700 rpm and 120 seconds. As a result, an electron beam positive resist layer having a thickness of 500 nm was formed on the silicon wafer. Then, the electron beam positive resist material coated on the silicon wafer was pre-baked using a hot plate under the conditions of 120° C. and 5 minutes to remove the residual solvent contained in the electron beam positive resist material.

[0059] Next, by exposing the electron beam positive resist layer on the silicon wafer, a nanohole pattern was drawn on the electron beam positive resist layer. An electron beam lithography apparatus was used for the exposure. During the exposure, the electron beam was irradiated at an acceleration voltage of 100 keV. The exposure dose was 18 μC / cm 2 The nanohole pattern was arranged in a square array with a pitch L of 800 nm.

[0060] Next, development was performed on the exposed portion (hereinafter referred to as the exposed part) of the electron beam positive resist layer to form a square nanohole pattern. Specifically, the exposed part was developed for 60 seconds using an alkaline developer (product name: SD-1, manufactured by Tokuyama Corporation), and the exposed part was dissolved to form a nanohole pattern. Subsequently, after rinsing with ultrapure water to remove the developer from the electron beam positive resist layer on the silicon wafer, drying was performed with a spin dryer. The width of the opening of the nanohole pattern formed in the electron beam positive resist layer was in the range of 140 nm or more and 700 nm or less.

[0061] Next, dry etching was performed on the silicon wafer with the electron beam positive resist layer having the nanohole pattern formed thereon to transfer the nanohole pattern onto the silicon wafer. A mixed gas such as SF6 or C4F8 was used as the etching gas. The etching time was 300 seconds. In dry etching, by adjusting the amount of the etching gas and the like, the depth can be changed according to the width of the silicon hole due to the microloading effect. Here, the etching conditions were adjusted so that the width of the silicon hole was in the range of 180 nm or more and 740 nm or less, and the depth of the silicon hole was in the range of 580 nm or more and 1060 nm or less.

[0062] Finally, the electron beam positive resist layer was removed by a cleaning process. Specifically, the silicon wafer with the electron beam positive resist layer was immersed in a mixed solution of sulfuric acid and hydrogen peroxide (80 °C) for 10 minutes, rinsed with ultrapure water, immersed in a mixed solution of ammonia and hydrogen peroxide (room temperature) for 10 minutes, and rinsed with ultrapure water in this order. Through the above procedure, a silicon mold, which is an example of the mold 20, was obtained.

[0063] [Example 1: Fabrication of a metalens] Next, the metalens 10 was fabricated by transferring the nanopillars 12 onto the substrate 11 using the above silicon mold. As the substrate 11, a 125 mm square glass substrate was used. First, an ultraviolet curable resin was coated on the support surface 11S of the substrate 11, and then, with the silicon mold pressed against the ultraviolet curable resin, light with a wavelength of 365 nm was irradiated from the substrate 11 side to cure the ultraviolet curable resin. Thereafter, by releasing the ultraviolet curable resin from the silicon mold, the nanopillars 12 made of the cured ultraviolet curable resin were formed on the support surface 11S of the substrate 11. In Example 1, 12 patterns of nanopillars 12 (nanopillars A1 to A12) with different widths W and heights H were formed. Note that, as the ultraviolet curable resin, a resin having a refractive index of 1.99 with respect to the wavelength 850 nm to be controlled was used.

[0064] [Comparative Example 1: Fabrication of a metalens] In Comparative Example 1, the metalens 10 was fabricated in the same procedure as in Example 1, except that the depth of the silicon hole was made constant, that is, the height H of the nanopillars 12 was made constant. Note that, in Comparative Example 1, 13 patterns of nanopillars 12 (nanopillars B1 to B13) with the same height H and different widths W were formed. In Comparative Example 1, the height H of the nanopillars 12 was set to 1051.3 nm, which is the maximum value of the height H in Example 1.

[0065] [Evaluation: Dimension measurement, appearance inspection] The metalens 10 of Example 1 and Comparative Example 1 was cleaved, and an image of the nanopillars 12 was acquired using FE-SEM. For each nanopillar 12, the width W and height H were measured from the acquired image. The measurement results of Example 1 are shown in FIG. 7. Also, the measurement results of Comparative Example 1 are shown in FIG. 8. Additionally, the results of the visual inspection regarding the presence or absence of collapse of each nanopillar 12 are shown in FIGS. 7 and 8.

[0066] As shown in FIG. 7, in Example 1, the width W of the nanopillars 12 was in the range of 185.7 nm or more and 740 nm or less. The height H of the nanopillars 12 was in the range of 584.9 nm or more and 1051.3 nm or less. The aspect ratio (H / W) of the nanopillars 12 was in the range of 1.4 or more and 3.1 or less. Also, the smaller the width W of the nanopillars 12, the lower the height H of the nanopillars 12 was configured to be. The higher the height H of the nanopillars 12, the smaller the aspect ratio of the nanopillars 12 was configured to be. In Example 1, collapse of the nanopillars 12 was not confirmed.

[0067] As shown in FIG. 8, in Comparative Example 1, the width W of the nanopillars 12 was in the range of 185.7 nm or more and 740 nm or less. The height H of the nanopillars 12 was constant at 1051.3 nm. The aspect ratio of the nanopillars 12 was in the range of 1.4 or more and 5.7 or less. In Comparative Example 1, collapse was confirmed in the nanopillars 12 having an aspect ratio of 3.5 or more.

[0068] [Evaluation: Phase shift amount] For each nanopillar 12 of the metalens 10 in Example 1 and Comparative Example 1, the phase of the transmitted light at a predetermined position was calculated by performing Rigorous Coupled-Wave Analysis (RCWA). Then, for each of Example 1 and Comparative Example 1, based on the phase in the nanopillar 12 having the minimum width W, the phase difference from the reference was calculated as the phase shift amount in each nanopillar 12. In Example 1, nanopillar A1 with a width W of 185.7 nm was used as the reference (phase shift amount = 0 degrees). In Comparative Example 1, nanopillar B5 with a width W of 320 nm, which is the smallest among the non-collapsed nanopillars 12, was used as the reference (phase shift amount = 0 degrees).

[0069] In the graph 100 shown in FIG. 9, the horizontal axis represents the width W of the nanopillar 12, and the vertical axis represents the phase shift amount of the light transmitted through the nanopillar 12. The curve 101 in the graph 100 represents the phase shift amount of the light transmitted through the nanopillar 12 with respect to the width W of the nanopillar 12 in Example 1. The curve 102 in the graph 100 represents the phase shift amount of the light transmitted through the nanopillar 12 with respect to the width W of the nanopillar 12 in Comparative Example 1.

[0070] As shown in FIG. 9, in Example 1 where the width W and height H were changed, it was confirmed that the phase shift amount could be adjusted in the range from 0 degrees to 381.9 degrees based on nanopillar A1 with a width W of 185.7 nm. On the other hand, in Comparative Example 1 where only the width W was changed while the height H was kept constant, it was confirmed that the adjustable range of the phase shift amount was limited to the range from 0 degrees to 196.6 degrees based on nanopillar B5 with a width W of 320 nm. From the above, it was confirmed that in the metalens 10, by configuring the nanopillars 12 such that the smaller the width W and volume, the lower the height H, the adjustable range of the phase shift amount can be expanded compared to the case where the height H is kept constant.

[0071] [Second Embodiment] Hereinafter, the second embodiment will be described with reference to FIGS. 10 to 12. As shown in FIG. 10, the metasurface lens 30 of the second embodiment includes a substrate 31 and a plurality of nanopillars 32. The plurality of nanopillars 32 are arranged on a support surface 31S provided by the substrate 31. The substrate 31 and the plurality of nanopillars 32 have light transmissibility for transmitting light having a wavelength to be controlled. The metasurface lens 30 has, as an example, a function of condensing light having a wavelength to be controlled at a single point.

[0072] In the metasurface lens 30, the state of light having a specific wavelength to be controlled is controlled by the nanopillars 32. In other words, the nanostructure of the metasurface lens 30 includes a plurality of nanopillars 32. Note that the substrate 31 can be made of the same material as the substrate 11 of the first embodiment. The nanopillars 32 can be made of the same material as the nanopillars 12 of the first embodiment.

[0073] The plurality of nanopillars 32 include a plurality of first nanopillars 33 and a plurality of second nanopillars 34. The plurality of first nanopillars 33 are arranged in a first region 30A. The plurality of second nanopillars 34 are arranged in a second region 30B. The first nanopillars 33 and the second nanopillars 34 are arranged in a square array at a constant pitch L.

[0074] The first nanopillars 33 shift the phase of light having a specific wavelength according to the position where the first nanopillars 33 are arranged within the support surface 31S. The first nanopillars 33 have, as an example, a rectangular parallelepiped shape. The first nanopillars 33 have, for example, a constant height H1. The metasurface lens 30 of each second embodiment condenses the light transmitted through each first nanopillar 33 at a focal point by changing the width W1 of the first nanopillar 33.

[0075] Therefore, in each first nanopillar 33, in order to condense the light transmitted through each first nanopillar 33 at a focal point, the shape of the first nanopillar 33 is determined according to the position and material of the first nanopillar 33 so that the second phase shift amount φ2 is equal to the first phase shift amount φ1. In other words, the second phase shift amount φ2 in each first nanopillar 33 is defined so that the plurality of first nanopillars 33 function as a lens.

[0076] The plurality of second nanopillars 34 have the same shape as each other. As an example, the second nanopillars 34 have a shape such that the width W2 decreases as it goes from the base end on the substrate 31 side toward the tip. For example, the second nanopillars 34 have a needle-like structure or a conical shape that tapers toward the tip. In other words, the cross-sectional area of the second nanopillars 34 in a cross-section orthogonal to the height direction changes stepwise or continuously in the height direction. Thereby, in the second nanopillars 34, the effective refractive index thereof is configured to change stepwise or continuously in the height direction. Therefore, the second nanopillars 34 function as a moth-eye structure that minimizes the reflection and refraction of incident light. Incidentally, as an example, the second nanopillars 34 have a constant height H2. The height H2 of the second nanopillars 34 may be the same as or different from the height H1 of the first nanopillars 33.

[0077] As shown in FIG. 11, the metalens 30 has, as an example, a circular shape in a top view. The metalens 30 includes a first region 30A having a circular shape in a top view and a second region 30B surrounding the first region 30A. The second region 30B has an annular shape in a top view. A plurality of first nanopillars 33 are arranged in the first region 30A. A plurality of second nanopillars 34 are arranged in the second region 30B. In FIG. 11, the first region 30A and the second region 30B are shown with different dot densities.

[0078] For example, the plurality of nanopillars 32 are arranged in a square array so as to have a predetermined pitch L along each of the first direction D1 and the second direction D2. The plurality of first nanopillars 33 are arranged such that, for example, the width W periodically changes in each of the first direction D1 and the second direction D2. Incidentally, the pitch L and the orientation of each nanopillar 32 do not have to be constant.

[0079] For example, the plurality of first nanopillars 33 have, in the first direction D1, an array pattern in which the first nanopillars 33 having a smaller width W are arranged from the center P side to the outer peripheral side of the metalens 30 as one repeating unit. In the first region 30A, the first nanopillars 33 are arranged such that a large number of repeating units are arranged from the center P side to the outer peripheral side of the metalens 30. For example, the length of one repeating unit in the first direction D1 is 0.1 μm or more and 10 μm or less. In the first region 30A, the same array pattern is also formed in the second direction D2.

[0080] The second region 30B has a width W3 in the outer peripheral direction. The lower limit value of the width W3 is, for example, at least 10 μm or more, preferably 100 μm or more. The upper limit value of the width W3 is not particularly limited, but is, for example, 1 mm or less, preferably 500 μm or less.

[0081] Note that the metalens 30 is not limited to a circular shape in a top view, and may have any shape. Similarly, the shape of the first region 30A is not limited to a circular shape in a top view, and may have any shape. The shape of the second region 30B is not limited to an annular shape in a top view, and may be an annular shape surrounding the first region 30A.

[0082] [Method for manufacturing the metalens 30] The metalens 30 of the second embodiment can be manufactured by the same manufacturing method as the metalens 10 of the first embodiment.

[0083] FIG. 12 shows a mold 40 for transferring nanopillars 32 made of resin onto a substrate 31. The mold 40 includes a base 41. The base 41 can be made of, for example, the same material as the base 21 of the first embodiment.

[0084] The base 41 includes a first surface 41S. A plurality of nanoholes 42 are formed in the first surface 41S of the base 41. The nanoholes 42 are formed by performing dry etching, electroforming, or the like on the first surface 41S of the base 41.

[0085] The plurality of nano-holes 42 includes a plurality of first nano-holes 43 for transferring the plurality of first nanopillars 33 to the substrate 31 and a plurality of second nano-holes 44 for transferring the plurality of second nanopillars 34 to the substrate 31.

[0086] The nano-holes 42 have a shape obtained by inverting the plurality of nanopillars 32 provided in the metalens 30. That is, the first nano-holes 43 have a shape obtained by inverting the first nanopillars 33. The second nano-holes 44 have a shape obtained by inverting the second nanopillars 34.

[0087] The mold 40 includes a third region 40A and a fourth region 40B. The plurality of first nano-holes 43 are arranged in the third region 40A. The plurality of second nano-holes 44 are arranged in the fourth region 40B. The third region 40A is configured in a circular shape corresponding to the first region 30A. The fourth region 40B is configured in an annular shape corresponding to the second region 30B.

[0088] [Operation of the Second Embodiment] In the manufacturing process of the metalens 30, when forming the nanopillars 32 on the substrate 31, if the pattern density indicating the density of the nanopillars 32 around each nanopillar 32 to be formed becomes small, defective formation of the nanopillars 32 is likely to occur.

[0089] The pattern density refers to the ratio of the occupied area of the nanopillars 32 in a virtual region centered on an arbitrary position within the metalens 30 in a top view seen from a viewpoint facing the support surface 31S. The virtual region for calculating the pattern density may be rectangular or circular. The virtual region encloses a plurality of nanopillars 32. For example, the virtual region encloses one or more repeating units constituted by the plurality of first nanopillars 33. As an example, the virtual region is configured in a circular shape having a radius of 10 μm or more and 100 μm or less.

[0090] For example, the pattern density is calculated from a SEM image captured from a position facing the support surface 31S. For example, from a SEM image of a virtual region including a plurality of nanopillars 32, the ratio of the area of the nanopillars 32 included in the virtual region to the total area of the virtual region is calculated. Note that when calculating the pattern density, image processing such as binarization may be performed on the SEM image to distinguish between the portion where the nanopillars 32 are arranged and the other portions.

[0091] In the first region 30A of the metalens 30, a plurality of first nanopillars 33 having different widths W1 are periodically arranged. Therefore, in most of the first region 30A, it has a substantially constant pattern density.

[0092] On the other hand, if the second nanopillars 34 in the second region 30B are not formed, in the vicinity of the outer edge of the first region 30A, the region where the first nanopillars 33 are not formed is included in the virtual region for calculating the pattern density. Therefore, if the second nanopillars 34 are not formed in the second region 30B, the pattern density rapidly decreases as approaching the vicinity of the outer edge of the first region 30A in the metalens 30.

[0093] The rapid change in the pattern density in the vicinity of the outer edge of the first region 30A may cause processing defects in the manufacturing process of the metalens 30. For example, in electron beam lithography, due to the influence of the proximity effect, the actual exposure amount decreases more in the region where the pattern density is small. Therefore, as the exposure amount is more likely to be insufficient in the region where the pattern density is small, pattern formation defects occur. The proximity effect refers to the phenomenon in which the electron beam scatters or reflects on the resist surface or the substrate 31 and the energy diffuses. Note that such a phenomenon can occur not only during the manufacture of the metalens 30 using electron beam lithography but also during the manufacture of the mold 40 using electron beam lithography.

[0094] For example, in dry etching, due to the influence of the microloading effect, the etching rate increases in regions with a lower pattern density. Therefore, in regions with a lower pattern density, the etching amount (etching depth) is more likely to become excessive, leading to poor pattern formation. Also, for example, in the transfer process using the mold 40, formation defects such as filling defects and residual film thickness changes due to a sharp change in pattern density are likely to occur.

[0095] In this regard, in the metalens 30 of the second embodiment, a second region 30B in which the second nanopillars 34 are arranged is provided so as to surround a first region 30A in which the first nanopillars 33 for shifting the phase of light having a specific wavelength are arranged. Therefore, the sharp change in pattern density near the outer edge of the first region 30A is suppressed by the second nanopillars 34 arranged in the second region 30B.

[0096] For example, let the pattern density of a first virtual region that encloses the first nanopillars 33 in the first region 30A and does not enclose the second nanopillars 34 in the second region 30B be a first pattern density ρ1. Let the pattern density of a second virtual region that encloses the second nanopillars 34 in the second region 30B and does not enclose the first nanopillars 33 in the first region 30A be a second pattern density ρ2.

[0097] Note that both the first virtual region and the second virtual region have a circular shape with the same radius. This radius has a size such that in the first virtual region, it encloses at least one repeating unit of the first nanopillars 33. Also, this radius has a size such that the second virtual region does not protrude outward from the second region 30B. As described above, this radius is preferably 10 μm or more and 100 μm or less.

[0098] In this case, the first pattern density ρ1 refers to the ratio of the area occupied by the first nanopillars 33 per unit area in the first region 30A. Also, the second pattern density ρ2 refers to the ratio of the area occupied by the second nanopillars 34 per unit area in the second region 30B.

[0099] The ratio (ρ2 / ρ1) of the second pattern density ρ2 to the first pattern density ρ1 is preferably 0.5 or more and 2.0 or less, more preferably 0.6 or more and 1.5 or less, and even more preferably 0.8 or more and 1.2 or less. If ρ2 / ρ1 is within the above range, a rapid change in the pattern density near the outer edge of the first region 30A is preferably suppressed.

[0100] When electron beam lithography is used for forming the pattern of the nanopillars 32 of the metalens 30, from the viewpoint of preferably reducing the influence of the proximity effect, it is preferable that the average exposure amount per one nanopillar 32 is equivalent between the first region 30A and the second region 30B. In other words, it is preferable that the first average exposure amount E1 per one first nanopillar 33 in the first region 30A is equivalent to the second average exposure amount E2 per one second nanopillar 34 in the second region 30B. According to such a configuration, when forming the pattern of the first nanopillars 33 located near the outer edge of the first region 30A, the influence of the proximity effect in electron beam lithography can be further reduced. For example, the ratio (E2 / E1) of the second average exposure amount E2 to the first average exposure amount E1 is preferably 0.5 or more and 2.0 or less, more preferably 0.6 or more and 1.5 or less, and even more preferably 0.8 or more and 1.2 or less.

[0101] Also, when electron beam lithography is used for forming the pattern of the nanopillars 32, the exposure amount for forming each nanopillar 32 has a correlation with the volume of each nanopillar 32. For example, in forming the pattern of the nanopillars 32, when exposing the pattern portion of the nanopillars 32, the exposure amount for forming each nanopillar 32 has a positive correlation with the volume of each nanopillar 32. For example, in forming the pattern of the nanopillars 32, when exposing the portion other than the pattern of the nanopillars 32, the exposure amount for forming each nanopillar 32 has a negative correlation with the volume of each nanopillar 32.

[0102] Therefore, it is preferable that the first average volume V1 per one first nanopillar 33 in the first region 30A is equal to the second average volume V2 per one second nanopillar 34 in the second region 30B. Thereby, when electron beam lithography is used for patterning the nanopillars 32, the first average exposure amount E1 in the first region 30A and the second average exposure amount E2 in the second region 30B can be made equal. The ratio (V2 / V1) of the second average volume V2 to the first average volume V1 is preferably 0.5 or more and 2.0 or less, more preferably 0.6 or more and 1.5 or less, and even more preferably 0.8 or more and 1.2 or less.

[0103] Note that the first average volume V1 of the first nanopillars 33 in the first region 30A can be the value obtained by dividing the sum of the volumes of the plurality of first nanopillars 33 in the first region 30A by the total number of the plurality of first nanopillars 33 in the first region 30A. Also, the second average volume V2 of the second nanopillars 34 in the second region 30B can be the value obtained by dividing the sum of the volumes of the plurality of second nanopillars 34 in the second region 30B by the total number of the plurality of second nanopillars 34 in the second region 30B.

[0104] Similarly, when electron beam lithography is used for patterning the nanoholes 42 of the mold 40, from the viewpoint of suitably reducing the influence of the proximity effect, it is preferable that the average exposure amount per one nanohole 42 is equal between the third region 40A and the fourth region 40B. In other words, it is preferable that the third average exposure amount E3 per one first nanohole 43 in the third region 40A is equal to the fourth average exposure amount E4 per one second nanohole 44 in the fourth region 40B. According to such a configuration, when patterning the first nanohole 43 at a position corresponding to the first nanopillar 33 located near the outer edge of the first region 30A, the influence of the proximity effect in electron beam lithography can be further reduced. For example, the ratio (E4 / E3) of the fourth average exposure amount E4 to the third average exposure amount E3 is preferably 0.5 or more and 2.0 or less, more preferably 0.6 or more and 1.5 or less, and even more preferably 0.8 or more and 1.2 or less.

[0105] In addition, when electron beam lithography is used for the pattern formation of the nano-holes 42, the exposure dose for forming each nano-hole 42 has a correlation with the volume of each nano-hole 42. For example, in the pattern formation of the nano-holes 42, when the pattern portion of the nano-holes 42 is exposed, the exposure dose for forming each nano-hole 42 has a positive correlation with the volume of each nano-hole 42. For example, in the pattern formation of the nano-holes 42, when the portion other than the pattern of the nano-holes 42 is exposed, the exposure dose for forming each nano-hole 42 has a negative correlation with the volume of each nano-hole 42.

[0106] Therefore, it is preferable that the first average volume C1 per first nano-hole 43 in the third region 40A is equal to the second average volume C2 per second nano-hole 44 in the fourth region 40B. Thereby, when electron beam lithography is used for the pattern formation of the nano-holes 42, the third average exposure dose E3 in the third region 40A and the fourth average exposure dose E4 in the fourth region 40B can be made equal. For example, the ratio (C2 / C1) of the second average volume C2 to the first average volume C1 is preferably 0.5 or more and 2.0 or less, more preferably 0.6 or more and 1.5 or less, and even more preferably 0.8 or more and 1.2 or less.

[0107] Note that the first average volume C1 of the first nano-hole 43 in the third region 40A can be the value obtained by dividing the sum of the volumes of the plurality of first nano-holes 43 in the third region 40A by the total number of the plurality of first nano-holes 43 in the third region 40A. Also, the second average volume C2 of the second nano-hole 44 in the fourth region 40B can be the value obtained by dividing the sum of the volumes of the plurality of second nano-holes 44 in the fourth region 40B by the total number of the plurality of second nano-holes 44 in the fourth region 40B.

[0108] [Effects of the Second Embodiment] (2-1) The metalens 30 of the second embodiment includes a plurality of first nanopillars 33 for shifting the phase of light having a specific wavelength. Further, the metalens 30 includes a plurality of second nanopillars 34 disposed in a second region 30B surrounding a first region 30A where the plurality of first nanopillars 33 are disposed. According to such a configuration, the second nanopillars 34 disposed in the second region 30B can suppress the formation defect of the first nanopillars 33 accompanying the abrupt change in the pattern density near the outer edge of the first region 30A. Thereby, the state of the light incident on the plurality of first nanopillars 33 can be controlled more accurately. In the example of the present embodiment, the condensing efficiency when condensing the light incident on the plurality of first nanopillars 33 to a single point can be increased.

[0109] (2-2) The ratio (ρ2 / ρ1) of the second pattern density ρ2 in the second region 30B to the first pattern density ρ1 in the first region 30A is configured to be 0.5 or more and 2.0 or less, preferably 0.6 or more and 1.5 or less, and more preferably 0.8 or more and 1.2 or less. Thereby, the abrupt change in the pattern density near the outer edge of the first region 30A can be preferably suppressed by the second nanopillars 34 disposed in the second region 30B.

[0110] (2-3) By changing the effective refractive index of the second nanopillars 34 in the height direction, the second nanopillars 34 function as a moth-eye structure that minimizes the reflection and refraction of the incident light. Thereby, it is possible to prevent the light deviated from the first region 30A from becoming stray light by being reflected or refracted by the second nanopillars 34. Further, in the case of the metalens 30 of the second embodiment, it also contributes to reducing the focusing diameter when condensing the light incident on the plurality of first nanopillars 33 to a single point.

[0111] (2-4) The first nanopillars 33 have a rectangular parallelepiped shape similar to the nanopillars 12 of the first embodiment. Therefore, the same effects as those in the above (1-2) can be obtained. (2-5) The second phase shift amount φ2 in each of the first nanopillars 33 is defined such that the plurality of first nanopillars 33 function as a lens. Thereby, for example, in the case of the metalens 30 of the second embodiment, it can function as a lens that condenses the light incident on the plurality of first nanopillars 33 to a single point.

[0112] (2-6) The ratio (V2 / V1) of the second average volume V2 of the second nanopillars 34 to the first average volume V1 of the first nanopillars 33 is configured to be 0.5 or more and 2.0 or less, preferably 0.6 or more and 1.5 or less, and more preferably 0.8 or more and 1.2 or less. Thereby, when electron beam lithography is used for pattern formation of the nanopillars 32, the first average exposure amount E1 in the first region 30A and the second average exposure amount E2 in the second region 30B can be made equal. As a result, the influence of the proximity effect in electron beam lithography when forming the pattern of the nanopillars 32 can be suitably reduced.

[0113] (2-7) According to the mold 40 of the second embodiment, in the manufacturing process of the mold 40, it is possible to suppress the formation defect of the first nanohole 43 accompanying the rapid change in the pattern density in the vicinity of the outer edge of the third region 40A. As a result, since it is possible to suppress the formation defect of the first nanopillar 33 caused by the formation defect of the first nanohole 43, it is possible to form a plurality of first nanopillars 33 that can control the state of the incident light with higher accuracy. Further, according to the mold 40, in the transfer process of transferring the plurality of nanopillars 32 to the substrate 31, it is possible to suppress formation defects such as filling defects and residual film thickness changes caused by the rapid change in the pattern density.

[0114] (2-8) The ratio (C2 / C1) of the second average volume C2 of the second nanohole 44 to the first average volume C1 of the first nanohole 43 is configured to be 0.5 or more and 2.0 or less, preferably 0.6 or more and 1.5 or less, more preferably 0.8 or more and 1.2 or less. Thereby, when electron beam lithography is used for pattern formation of the nanoholes 42, the third average exposure amount E3 in the third region 40A and the fourth average exposure amount E4 in the fourth region 40B can be made equal. As a result, the influence of the proximity effect in electron beam lithography when forming the pattern of the nanoholes 42 can be suitably reduced.

[0115] [Modification Example of the Second Embodiment] Note that the above second embodiment can be implemented with the following modifications. Also, each modification example can be combined within a technically non - conflicting range.

[0116] · In the second embodiment, the metalens 30 having a metasurface structure was described. That is, an example of a configuration in which a plurality of first nanopillars 33 included in the metasurface structure function as a lens was illustrated. However, the present invention is not limited to this. For example, by providing a plurality of first nanopillars 33 on a reflector, the plurality of first nanopillars 33 may function in a form other than a lens so as to reflect light having a specific wavelength in an arbitrary direction.

[0117] · The shape of the first nanopillar 33 is not limited to a rectangular parallelepiped shape, and for example, it may be a cylindrical shape. Even in this case, since the first nanopillar 33 has a uniform effective refractive index in the height direction, it is possible to prevent the shape of the first nanopillar 33 from affecting the transmissivity of incident light. Further, the shape of the first nanopillar 33 may be any shape other than a rectangular parallelepiped shape or a cylindrical shape. For example, the shape of the first nanopillar 33 may be any quadrangular prism such as a frustum of a quadrangular pyramid, or a frustum of a cone.

[0118] · For example, the second nanopillar 34 may refract incident light in a direction away from the focal point by a blazed structure. · The effective refractive index of the second nanopillar 34 may be constant in the height direction. In this case, for example, while the first nanopillar 33 focuses incident light at a single point (focus), the shape and arrangement of the second nanopillar 34 may be determined so that the incident light is refracted in a direction away from the focus. For example, the second nanopillar 34 may be arranged in an inverted phase state in which the shape and arrangement of the first nanopillar 33 are inverted. According to such a configuration, light deviating from the first region 30A can be suppressed from passing near the focus as stray light. It also contributes to reducing the focusing diameter.

[0119] · The second nanopillar 34 is not limited to a needle-like structure and may be configured in any shape such as a rectangular parallelepiped shape having a width W2 larger than the width W1 of the first nanopillar 33, or a cylindrical shape (in this case, the diameter corresponds to the width W2). Thereby, for example, formation defects such as pattern collapse in the second nanopillar 34 can be preferably suppressed. Also, light incident on the second nanopillar 34 can be preferably suppressed from becoming stray light. Since the W2 of the second nanopillar 34 is configured to be larger than the W1 of the first nanopillar 33, the ratio (ρ2 / ρ1) of the second pattern density ρ2 to the first pattern density ρ1 is greater than 1.0. That is, ρ2 / ρ1 is preferably greater than 1.0 and less than 2.0, and more preferably greater than 1.0 and less than or equal to 1.5.

[0120] · The shape and arrangement of the second nanopillar 34 in the second region 30B are not limited to the above examples and may be in any shape and arrangement. For example, the shape and arrangement of the second nanopillar 34 may be configured to function as an identifier such as a two-dimensional code. In this case, for example, the manufacturing lot can be traced and the authenticity of a counterfeit can also be determined based on the shape and arrangement of the second nanopillar 34 arranged in the second region 30B.

[0121] · In the metalens 30, the arrangement of the plurality of first nanopillars 33 may be appropriately determined according to the use of the metalens 30. Further, the plurality of first nanopillars 33 are not limited to the configuration of being arranged in a square pattern in the first direction D1 and the second direction D2. For example, they may be arranged radially around an arbitrary point on the substrate 31.

[0122] · The shape and arrangement of the first nanopillars 33 in the first region 30A are not limited to the above example and may be of any shape and arrangement. For example, the first embodiment and the second embodiment may be combined. That is, in the metalens 30 of the second embodiment, the plurality of first nanopillars 33 arranged in the first region 30A may be configured such that the height H1 becomes lower as the width W1 and the volume are smaller, similar to the nanopillars 12 of the first embodiment. In other words, in the metalens 10 of the first embodiment, a second region 30B in which the second nanopillars 34 are arranged may be provided so as to surround the region where the nanopillars 12 of the first embodiment are arranged. In the above case, the modification example of the first embodiment and the modification example of the second embodiment can be combined within a technically non - conflicting range.

[0123] · Even when electron beam lithography is used for the pattern formation of the nanopillars 32 of the metalens 30, the first average exposure amount E1 per one first nanopillar 33 and the second average exposure amount E2 per one second nanopillar 34 may be set to be different. Further, even when electron beam lithography is used for the pattern formation of the nanoholes 42 of the mold 40, the third average exposure amount E3 per one first nanohole 43 and the fourth average exposure amount E4 per one second nanohole 44 may be set to be different.

[0124] ·If it is possible to suppress the formation defect of the first nanopillar 33 due to the abrupt change in the pattern density near the outer edge of the first region 30A, the ratio (ρ2 / ρ1) of the second pattern density ρ2 to the first pattern density ρ1 may be less than 0.5 or may be greater than 2.0. Also, the first pattern density ρ1 was defined as the ratio of the occupied area of the first nanopillars 33 within a circular first virtual region, but the first virtual region may be any region within the first region 30A. For example, the first pattern density ρ1 may be calculated with the entire first region 30A as the first virtual region. Similarly, the second pattern density ρ2 was defined as the ratio of the occupied area of the second nanopillars 34 within a circular second virtual region, but the second virtual region may be any region within the second region 30B. For example, the second pattern density ρ2 may be calculated with the entire second region 30B as the second virtual region.

[0125] [Examples and Comparative Examples of the Second Embodiment] Examples 2 and Comparative Example 2 of the second embodiment will be described with reference to FIGS. 13 to 16. Note that the following examples do not limit the configuration of the present disclosure.

[0126] [Example 2: Fabrication of a Metalens] As shown in FIG. 13, in Example 2, first, an SOQ wafer 50 was prepared by forming a silicon layer 52 having a thickness of 150 nm on a quartz glass wafer 51 with a diameter of 200 mm. Then, an electron beam positive resist layer 53 having a thickness of 400 nm was formed on the silicon layer 52 of the SOQ wafer 50. A spin coater was used to form the electron beam positive resist layer 53. The conditions of the spin coater were a rotation speed of 700 rpm and 120 seconds. Thereafter, the electron beam positive resist layer 53 coated on the SOQ wafer 50 was pre-baked under the conditions of 180° C. and 5 minutes using a hot plate to remove the residual solvent contained in the electron beam positive resist layer 53.

[0127] Next, by exposing the electron beam positive resist layer 53, a pattern of a plurality of nano-pillars 32 corresponding to the plurality of first nano-pillars 33 in the first region 30A and the plurality of second nano-pillars 34 in the second region 30B was drawn. An electron beam lithography apparatus was used for the exposure. During the exposure, the electron beam was irradiated at an acceleration voltage of 100 keV.

[0128] The first region 30A was circular with a diameter of 2 mm. Inside the first region 30A, square dots corresponding to unexposed portions were spread in a square array with a pitch L of 600 nm. Note that the width of each square dot was adjusted in the range from 120 nm to 480 nm according to the position of the first region 30A so as to realize a phase profile that condenses near-infrared light with a wavelength of 940 nm at a single point in space. The exposure dose of the exposed portion corresponding to the portion other than the square dots in the first region 30A was 150 μC / cm 2 was set.

[0129] The ratio of the area of the exposed portion in the first region 30A was 71%. Note that the ratio of the area of the exposed portion refers to the ratio of the area of the exposed portion to the sum of the area of the exposed portion and the area of the unexposed portion in the first region 30A. Therefore, the average exposure dose per unit cell, which is a square with a side length of the pitch L, was 106.5 μC / cm 2 was.

[0130] The second region 30B was annular with a width W3 (see FIG. 11) of 400 μm. The second region 30B was arranged so as to surround the first region 30A. In the second region 30B, tone drawing patterns for forming a needle-like structure were spread in a square array. The tone exposure pattern had a shape in which squares with different side lengths were overlapped so that their centers of gravity coincided. The side length of the square in the tone exposure pattern was 60 nm, 120 nm, 180 nm, 240 nm, 300 nm, 360 nm, 420 nm, 480 nm, 540 nm, 600 nm in order from the inside.

[0131] In the gradation drawing pattern, different exposure amounts were assigned to the ten areas divided by the above ten squares. The exposure amounts of the respective areas were 15, 30, 45, 60, 75, 90, 105, 120, 135, and 150 μC / cm from the inside 2 respectively. The average exposure amount per gradation drawing pattern calculated from the area ratio and the exposure amount of each area was 107.25 μC / cm 2 .

[0132] Next, as shown in FIG. 14, by developing the exposed electron beam positive resist layer 53, a rectangular parallelepiped-shaped first transfer nanopillar 53A was formed in the first region 30A, and a needle-shaped second transfer nanopillar 53B was formed in the second region 30B. The first transfer nanopillar 53A and the second transfer nanopillar 53B are composed of the electron beam positive resist layer 53.

[0133] Specifically, the exposed portion was dissolved by developing the electron beam positive resist layer 53 with methyl isobutyl ketone for 75 seconds. At this time, since the development rate increases as the exposure amount increases, in the portion of the gradation exposure pattern, the electron beam positive resist layer 53 remains as the needle-shaped second transfer nanopillar 53B. Subsequently, after removing the developer from the electron beam positive resist layer 53 on the SOQ wafer 50 by rinsing with ultrapure water, drying was performed with a spin dryer. The height of the first transfer nanopillar 53A produced in the above process was about 320 nm, and the height of the second transfer nanopillar 53B was about 250 nm.

[0134] Next, as shown in FIG. 15, by performing dry etching on the SOQ wafer 50 with the electron beam positive resist layer 53, the shapes of the first transfer nanopillar 53A and the second transfer nanopillar 53B were transferred to the silicon layer 52 of the SOQ wafer 50. As a result, in the first region 30A, a rectangular parallelepiped-shaped first nanopillar 52A composed of the silicon layer 52 was formed, and in the second region 30B, a needle-shaped second nanopillar 52B composed of the silicon layer 52 was formed.

[0135] As the etching gas, a mixed gas such as SF6 or C4F8 was used. The etching time was set to 63 seconds. Here, by adjusting the etching conditions such as the etching gas, the etching rate of the silicon layer 52 and the etching rate of the electron beam positive resist layer 53 can be made 1:1. Thereby, the shape of the electron beam positive resist layer 53 can be faithfully transferred to the silicon layer 52. The etching time was set so that the silicon layer 52 and the electron beam positive resist layer 53 were etched by 150 nm based on the etching rate of the silicon layer 52.

[0136] Finally, the electron beam positive resist layer 53 was removed by a cleaning process. Specifically, the silicon wafer with the electron beam positive resist layer was immersed in a mixed solution of sulfuric acid and hydrogen peroxide water (80 °C) for 10 minutes, rinsed with ultrapure water, immersed in a mixed solution of ammonia and hydrogen peroxide water (room temperature) for 10 minutes, and rinsed with ultrapure water, in this order. Through the above procedure, a metasurface including the first nanopillar 52A and the second nanopillar 52B was obtained.

[0137] The first pattern density ρ1 of the first nanopillar 52A in the first region 30A was 0.28. The second pattern density ρ2 of the second nanopillar 52B in the second region 30B was 0.27. The ratio of the second pattern density ρ2 to the first pattern density ρ1 was 1.04 (= ρ2 / ρ1).

[0138] [Comparative Example 2: Fabrication of Metasurface] In Comparative Example 2, when exposing the electron beam positive resist layer 53, while drawing the same square dots as in Example 2 in the first region 30A, no pattern was drawn in the second region 30B. Otherwise, a metasurface shown in FIG. 16 was obtained by the same procedure as in Example 2.

[0139] As shown in FIG. 16, the metasurface of Comparative Example 2 includes the first nanopillar 52A composed of the silicon layer 52 in the first region 30A. Also, in the second region 30B, the silicon layer 52 was left as it was after film formation.

[0140] [Evaluation: Light Collection Performance Evaluation] An infrared laser with a wavelength of 940 nm and a beam diameter of φ2 mm was incident perpendicularly on the first region 30A of each of the metalenses fabricated in Example 2 and Comparative Example 2. The light that passed through the metalens was captured by a CCD camera installed at the focal position and then converted into the light intensity distribution on a plane parallel to the metalens and including the focal point. Here, the value obtained by dividing the sum of the light intensity distribution in a region with a radius of 20 μm centered on the focal point by the sum of the light intensity distribution in a region of φ2 mm in the infrared laser is defined as the light collection rate. Also, the full width at half maximum of the light intensity distribution in a region with a radius of 20 μm centered on the focal point is defined as the focusing diameter.

[0141] In the metalens of Example 2, the light collection rate was 52% and the focusing diameter was 4.1 μm. In the metalens of Comparative Example 2, the light collection rate was 46% and the focusing diameter was 4.9 μm. Therefore, it was confirmed that by forming the second nanopillars 52B in the second region 30B surrounding the periphery of the first region 30A where the first nanopillars 52A were arranged, the light collection rate can be increased and the focusing diameter can be made thinner.

Explanation of Reference Signs

[0142] H, H1, H2... Height L... Pitch W, W1, W2... Width 10, 30... Metalens 11, 31... Substrate 11S, 31S... Support Surface 12, 32... Nanopillar 20, 40... Mold 22, 42... Nanohole 30A... First Region 30B... Second Region 33... First Nanopillar 34... Second Nanopillar 40A... Third Region 40B... Fourth Region 43... First Nanohole 44... Second Nanohole

Claims

1. A metasurface structure comprising a plurality of nanopillars disposed on a support surface of a substrate, wherein the plurality of nanopillars includes a plurality of first nanopillars disposed in a first region and a plurality of second nanopillars disposed in an annular second region surrounding the first region, each first nanopillar shifts the phase of light having a specific wavelength according to the position where the first nanopillar is disposed within the support surface metasurface structure.

2. In the first region, when the ratio of the area occupied by the first nanopillars per unit area is defined as the first pattern density, and in the second region, when the ratio of the area occupied by the second nanopillars per unit area is defined as the second pattern density, the ratio of the second pattern density to the first pattern density is 0.5 or more and 2.0 or less The metasurface structure according to claim 1.

3. In the second nanopillars, the effective refractive index changes in the height direction The metasurface structure according to claim 1 or 2.

4. The first nanopillars have a cuboid shape The metasurface structure according to claim 3.

5. The amount of phase shift of the light in each first nanopillar is defined such that the plurality of first nanopillars function as a lens The metasurface structure according to claim 1 or 2.

6. The ratio of the second average volume of the second nanopillars in the second region to the first average volume of the first nanopillars in the first region is 0.5 or more and 2.0 or less The metasurface structure according to claim 1 or 2.

7. The width of the second nanopillars is larger than the width of the first nanopillars The metasurface structure according to claim 1.

8. A mold comprising a plurality of nanoholes for transferring the plurality of nanopillars in the metasurface structure according to claim 1 to the substrate, wherein the plurality of nanoholes are disposed in a third region and include a plurality of first nanoholes for transferring the plurality of first nanopillars to the substrate, and are disposed in an annular fourth region surrounding the third region and include a plurality of second nanoholes for transferring the plurality of second nanopillars to the substrate mold.

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